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Sample records for memory polymer therapeutic

  1. Shape memory polymer therapeutic devices for stroke

    NASA Astrophysics Data System (ADS)

    Wilson, Thomas S.; Small, Ward, IV; Benett, William J.; Bearinger, Jane P.; Maitland, Duncan J.

    2005-11-01

    Shape memory polymers (SMPs) are attracting a great deal of interest in the scientific community for their use in applications ranging from light weight structures in space to micro-actuators in MEMS devices. These relatively new materials can be formed into a primary shape, reformed into a stable secondary shape, and then controllably actuated to recover their primary shape. The first part of this presentation will be a brief review of the types of polymeric structures which give rise to shape memory behavior in the context of new shape memory polymers with highly regular network structures recently developed at LLNL for biomedical devices. These new urethane SMPs have improved optical and physical properties relative to commercial SMPs, including improved clarity, high actuation force, and sharper actuation transition. In the second part of the presentation we discuss the development of SMP based devices for mechanically removing neurovascular occlusions which result in ischemic stroke. These devices are delivered to the site of the occlusion in compressed form, are pushed through the occlusion, actuated (usually optically) to take on an expanded conformation, and then used to dislodge and grip the thrombus while it is withdrawn through the catheter.

  2. Shape Memory Polymer Therapeutic Devices for Stroke

    SciTech Connect

    Wilson, T S; Small IV, W; Benett, W J; Bearinger, J P; Maitland, D J

    2005-10-11

    Shape memory polymers (SMPs) are attracting a great deal of interest in the scientific community for their use in applications ranging from light weight structures in space to micro-actuators in MEMS devices. These relatively new materials can be formed into a primary shape, reformed into a stable secondary shape, and then controllably actuated to recover their primary shape. The first part of this presentation will be a brief review of the types of polymeric structures which give rise to shape memory behavior in the context of new shape memory polymers with highly regular network structures recently developed at LLNL for biomedical devices. These new urethane SMPs have improved optical and physical properties relative to commercial SMPs, including improved clarity, high actuation force, and sharper actuation transition. In the second part of the presentation we discuss the development of SMP based devices for mechanically removing neurovascular occlusions which result in ischemic stroke. These devices are delivered to the site of the occlusion in compressed form, are pushed through the occlusion, actuated (usually optically) to take on an expanded conformation, and then used to dislodge and grip the thrombus while it is withdrawn through the catheter.

  3. Shape memory polymers

    DOEpatents

    Wilson, Thomas S.; Bearinger, Jane P.

    2015-06-09

    New shape memory polymer compositions, methods for synthesizing new shape memory polymers, and apparatus comprising an actuator and a shape memory polymer wherein the shape memory polymer comprises at least a portion of the actuator. A shape memory polymer comprising a polymer composition which physically forms a network structure wherein the polymer composition has shape-memory behavior and can be formed into a permanent primary shape, re-formed into a stable secondary shape, and controllably actuated to recover the permanent primary shape. Polymers have optimal aliphatic network structures due to minimization of dangling chains by using monomers that are symmetrical and that have matching amine and hydroxyl groups providing polymers and polymer foams with clarity, tight (narrow temperature range) single transitions, and high shape recovery and recovery force that are especially useful for implanting in the human body.

  4. Shape memory polymer medical device

    DOEpatents

    Maitland, Duncan; Benett, William J.; Bearinger, Jane P.; Wilson, Thomas S.; Small, IV, Ward; Schumann, Daniel L.; Jensen, Wayne A.; Ortega, Jason M.; Marion, III, John E.; Loge, Jeffrey M.

    2010-06-29

    A system for removing matter from a conduit. The system includes the steps of passing a transport vehicle and a shape memory polymer material through the conduit, transmitting energy to the shape memory polymer material for moving the shape memory polymer material from a first shape to a second and different shape, and withdrawing the transport vehicle and the shape memory polymer material through the conduit carrying the matter.

  5. Porous Shape Memory Polymers

    PubMed Central

    Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C.; Wilson, Thomas S.; Maitland, Duncan J.

    2013-01-01

    Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use. PMID:23646038

  6. Surface shape memory in polymers

    NASA Astrophysics Data System (ADS)

    Mather, Patrick

    2012-02-01

    Many crosslinked polymers exhibit a shape memory effect wherein a permanent shape can be prescribed during crosslinking and arbitrary temporary shapes may be set through network chain immobilization. Researchers have extensively investigated such shape memory polymers in bulk form (bars, films, foams), revealing a multitude of approaches. Applications abound for such materials and a significant fraction of the studies in this area concern application-specific characterization. Recently, we have turned our attention to surface shape memory in polymers as a means to miniaturization of the effect, largely motivated to study the interaction of biological cells with shape memory polymers. In this presentation, attention will be given to several approaches we have taken to prepare and study surface shape memory phenomenon. First, a reversible embossing study involving a glassy, crosslinked shape memory material will be presented. Here, the permanent shape was flat while the temporary state consisted of embossed parallel groves. Further the fixing mechanism was vitrification, with Tg adjusted to accommodate experiments with cells. We observed that the orientation and spreading of adherent cells could be triggered to change by the topographical switch from grooved to flat. Second, a functionally graded shape memory polymer will be presented, the grading being a variation in glass transition temperature in one direction along the length of films. Characterization of the shape fixing and recovery of such films utilized an indentation technique that, along with polarizing microscopy, allowed visualization of stress distribution in proximity to the indentations. Finally, very recent research concerning shape memory induced wrinkle formation on polymer surfaces will be presented. A transformation from smooth to wrinkled surfaces at physiological temperatures has been observed to have a dramatic effect on the behavior of adherent cells. A look to the future in research and applications for surface shape memory in polymers will round out the talk.

  7. TARGETING POLYMER THERAPEUTICS TO BONE

    PubMed Central

    Low, Stewart; Kope?ek, Jind?ich

    2012-01-01

    An aging population in the developing world has led to an increase in musculoskeletal diseases such as osteoporosis and bone metastases. Left untreated many bone diseases cause debilitating pain and in the case of cancer, death. Many potential drugs are effective in treating diseases but result in side effects preventing their efficacy in the clinic. Bone, however, provides an unique environment of inorganic solids, which can be exploited in order to effectively target drugs to diseased tissue. By integration of bone targeting moieties to drug-carrying water-soluble polymers, the payload to diseased area can be increased while side effects decreased. The realization of clinically relevant bone targeted polymer therapeutics depends on (1) understanding bone targeting moiety interactions, (2) development of controlled drug delivery systems, as well as (3) understanding drug interactions. The latter makes it possible to develop bone targeted synergistic drug delivery systems. PMID:22316530

  8. Multifunctional shape-memory polymers.

    PubMed

    Behl, Marc; Razzaq, Muhammad Yasar; Lendlein, Andreas

    2010-08-17

    The thermally-induced shape-memory effect (SME) is the capability of a material to change its shape in a predefined way in response to heat. In shape-memory polymers (SMP) this shape change is the entropy-driven recovery of a mechanical deformation, which was obtained before by application of external stress and was temporarily fixed by formation of physical crosslinks. The high technological significance of SMP becomes apparent in many established products (e.g., packaging materials, assembling devices, textiles, and membranes) and the broad SMP development activities in the field of biomedical as well as aerospace applications (e.g., medical devices or morphing structures for aerospace vehicles). Inspired by the complex and diverse requirements of these applications fundamental research is aiming at multifunctional SMP, in which SME is combined with additional functions and is proceeding rapidly. In this review different concepts for the creation of multifunctionality are derived from the various polymer network architectures of thermally-induced SMP. Multimaterial systems, such as nanocomposites, are described as well as one-component polymer systems, in which independent functions are integrated. Future challenges will be to transfer the concept of multifunctionality to other emerging shape-memory technologies like light-sensitive SMP, reversible shape changing effects or triple-shape polymers. PMID:20574951

  9. Shape-Memory Polymer Composites

    NASA Astrophysics Data System (ADS)

    Madbouly, Samy A.; Lendlein, Andreas

    The development of shape-memory polymer composites (SMPCs) enables high recovery stress levels as well as novel functions such as electrical conductivity, magnetism, and biofunctionality. In this review chapter the substantial enhancement in mechanical properties of shape-memory polymers (SMPs) by incorporating small amounts of stiff fillers will be highlighted exemplarily for clay and polyhedral oligomeric silsesquioxanes (POSS). Three different functions resulting from adding functional fillers to SMP-matrices will be introduced and discussed: magnetic SMPCs with different types of magnetic nanoparticles, conductive SMPCs based on carbon nanotubes (CNTs), carbon black (CB), short carbon fiber (SCF), and biofunctional SMPCs containing hydroxyapatite (HA). Indirect induction of the shape-memory effect (SME) was realized for magnetic and conductive SMPCs either by exposure to an alternating magnetic field or by application of electrical current. Major challenges in design and fundamental understanding of polymer composites are the complexity of the composite structure, and the relationship between structural parameters and properties/functions, which is essential for tailoring SMPCs for specific applications. Therefore the novel functions and enhanced properties of SMPCs will be described considering the micro-/nanostructural parameters, such as dimension, shape, distribution, volume fraction, and alignment of fillers as well as interfacial interaction between the polymer matrix and dispersed fillers. Finally, an outlook is given describing the future challenges of this exciting research field as well as potential applications including automotive, aerospace, sensors, and biomedical applications.

  10. Shape-Memory Polymers for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Yakacki, Christopher M.; Gall, Ken

    Shape-memory polymers (SMPs) are a class of mechanically functional "smart" materials that have generated substantial interest for biomedical applications. SMPs offer the ability to promote minimally invasive surgery, provide structural support, exert stabilizing forces, elute therapeutic agents, and biodegrade. This review focuses on several areas of biomedicine including vascular, orthopedic, and neuronal applications with respect to the progress and potential for SMPs to improve the standard of treatment in these areas. Fundamental studies on proposed biomedical SMP systems are discussed with regards to biodegradability, tailorability, sterilization, and biocompatibility. Lastly, a proposed research and development pathway for SMP-based biomedical devices is proposed based on trends in the recent literature.

  11. Shape memory alloy/shape memory polymer tools

    SciTech Connect

    Seward, Kirk P.; Krulevitch, Peter A.

    2005-03-29

    Micro-electromechanical tools for minimally invasive techniques including microsurgery. These tools utilize composite shape memory alloy (SMA), shape memory polymer (SMP) and combinations of SMA and SMP to produce catheter distal tips, actuators, etc., which are bistable. Applications for these structures include: 1) a method for reversible fine positioning of a catheter tip, 2) a method for reversible fine positioning of tools or therapeutic catheters by a guide catheter, 3) a method for bending articulation through the body's vasculature, 4) methods for controlled stent delivery, deployment, and repositioning, and 5) catheters with variable modulus, with vibration mode, with inchworm capability, and with articulated tips. These actuators and catheter tips are bistable and are opportune for in vivo usage because the materials are biocompatible and convenient for intravascular use as well as other minimal by invasive techniques.

  12. Therapeutic gene delivery using bioreducible polymers.

    PubMed

    Ryu, Kitae; Kim, Tae-Il

    2014-01-01

    Bioreducible polymers, which can be degraded in reducing environment due to the cleavage of internal disulfide bonds, have been developed for gene delivery systems. They show high stability in extracellular physiological condition and cytoplasm-specific release of genetic materials, as well as decreased cytotoxicity because cytoplasm is a reducing environment containing high level of reducing molecules such as glutathione. Based on these advantages, recently, many bioreducible polymers have been further investigated with therapeutic genes for the treatment of diseases and demonstrated promising results. This review will focus on the therapeutic gene delivery using bioreducible polymers and the evaluation of therapeutic efficacy for cancer, myocardial infarction, diabetes and miscellaneous diseases. PMID:24178745

  13. Post polymerization cure shape memory polymers

    DOEpatents

    Wilson, Thomas S; Hearon, Michael Keith; Bearinger, Jane P

    2014-11-11

    This invention relates to chemical polymer compositions, methods of synthesis, and fabrication methods for devices regarding polymers capable of displaying shape memory behavior (SMPs) and which can first be polymerized to a linear or branched polymeric structure, having thermoplastic properties, subsequently processed into a device through processes typical of polymer melts, solutions, and dispersions and then crossed linked to a shape memory thermoset polymer retaining the processed shape.

  14. Memory as a new therapeutic target

    PubMed Central

    Nader, Karim; Hardt, Oliver; Lanius, Ruth

    2013-01-01

    This review aims to demonstrate how an understanding of the brain mechanisms involved in memory provides a basis for; (i) reconceptualizing some mental disorders; (ii) refining existing therapeutic tools; and (iii) designing new ones for targeting processes that maintain these disorders. First, some of the stages which a memory undergoes are defined, and the clinical relevance of an understanding of memory processing by the brain is discussed. This is followed by a brief review of some of the clinical studies that have targeted memory processes. Finally, some new insights provided by the field of neuroscience with implications for conceptualizing mental disorders are presented. PMID:24459414

  15. Shape memory polymer actuator and catheter

    DOEpatents

    Maitland, Duncan J. (Pleasant Hill, CA); Lee, Abraham P. (Walnut Creek, CA); Schumann, Daniel L. (Concord, CA); Matthews, Dennis L. (Moss Beach, CA); Decker, Derek E. (Byron, CA); Jungreis, Charles A. (Pittsburgh, PA)

    2007-11-06

    An actuator system is provided for acting upon a material in a vessel. The system includes an optical fiber and a shape memory polymer material operatively connected to the optical fiber. The shape memory polymer material is adapted to move from a first shape for moving through said vessel to a second shape where it can act upon said material.

  16. Shape memory polymer actuator and catheter

    DOEpatents

    Maitland, Duncan J.; Lee, Abraham P.; Schumann, Daniel L.; Matthews, Dennis L.; Decker, Derek E.; Jungreis, Charles A.

    2004-05-25

    An actuator system is provided for acting upon a material in a vessel. The system includes an optical fiber and a shape memory polymer material operatively connected to the optical fiber. The shape memory polymer material is adapted to move from a first shape for moving through said vessel to a second shape where it can act upon said material.

  17. Release mechanism utilizing shape memory polymer material

    DOEpatents

    Lee, Abraham P. (Walnut Creek, CA); Northrup, M. Allen (Berkeley, CA); Ciarlo, Dino R. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA); Benett, William J. (Livermore, CA)

    2000-01-01

    Microfabricated therapeutic actuators are fabricated using a shape memory polymer (SMP), a polyurethane-based material that undergoes a phase transformation at a specified temperature (Tg). At a temperature above temperature Tg material is soft and can be easily reshaped into another configuration. As the temperature is lowered below temperature Tg the new shape is fixed and locked in as long as the material stays below temperature Tg. Upon reheating the material to a temperature above Tg, the material will return to its original shape. By the use of such SMP material, SMP microtubing can be used as a release actuator for the delivery of embolic coils through catheters into aneurysms, for example. The microtubing can be manufactured in various sizes and the phase change temperature Tg is determinate for an intended temperature target and intended use.

  18. Medical applications of shape memory polymers

    NASA Technical Reports Server (NTRS)

    Sokolowski, Witold M.

    2005-01-01

    Shape memory polymers are described here and major advantages in some applications are identified over other medical materials such as shape memory alloys (SMA). A number of medical applications are anticipated for shape memory polymers. Some simple applications are already utilized in medical world, others are in examination process. Lately, several important applications are being considered for CHEM foams for self-deployable vascular and coronary devices. One of these potential applications, the endovascular treatment of aneurysm was experimentally investigated with encouraging results and is described in this paper as well.

  19. Guide wire extension for shape memory polymer occlusion removal devices

    DOEpatents

    Maitland, Duncan J.; Small, IV, Ward; Hartman, Jonathan

    2009-11-03

    A flexible extension for a shape memory polymer occlusion removal device. A shape memory polymer instrument is transported through a vessel via a catheter. A flexible elongated unit is operatively connected to the distal end of the shape memory polymer instrument to enhance maneuverability through tortuous paths en route to the occlusion.

  20. Optically transparent high temperature shape memory polymers.

    PubMed

    Xiao, Xinli; Qiu, Xueying; Kong, Deyan; Zhang, Wenbo; Liu, Yanju; Leng, Jinsong

    2016-03-01

    Optically transparent shape memory polymers (SMPs) have potential in advanced optoelectronic and other common shape memory applications, and here optically transparent shape memory polyimide is reported for the first time. The polyimide possesses a glass transition temperature (Tg) of 171 C, higher than the Tg of other transparent SMPs reported, and the influence of molecular structure on Tg is discussed. The 120 ?m thick polyimide film exhibits transmittance higher than 81% in 450-800 nm, and the possible mechanism of its high transparency is analyzed, which will benefit further research on other transparent high temperature SMPs. The transparent polyimide showed excellent thermomechanical properties and shape memory performances, and retained high optical transparency after many shape memory cycles. PMID:26686222

  1. Temperature and electrical memory of polymer fibers

    SciTech Connect

    Yuan, Jinkai; Zakri, Cécile; Grillard, Fabienne; Neri, Wilfrid; Poulin, Philippe

    2014-05-15

    We report in this work studies of the shape memory behavior of polymer fibers loaded with carbon nanotubes or graphene flakes. These materials exhibit enhanced shape memory properties with the generation of a giant stress upon shape recovery. In addition, they exhibit a surprising temperature memory with a peak of generated stress at a temperature nearly equal to the temperature of programming. This temperature memory is ascribed to the presence of dynamical heterogeneities and to the intrinsic broadness of the glass transition. We present recent experiments related to observables other than mechanical properties. In particular nanocomposite fibers exhibit variations of electrical conductivity with an accurate memory. Indeed, the rate of conductivity variations during temperature changes reaches a well defined maximum at a temperature equal to the temperature of programming. Such materials are promising for future actuators that couple dimensional changes with sensing electronic functionalities.

  2. Temperature and electrical memory of polymer fibers

    NASA Astrophysics Data System (ADS)

    Yuan, Jinkai; Zakri, Ccile; Grillard, Fabienne; Neri, Wilfrid; Poulin, Philippe

    2014-05-01

    We report in this work studies of the shape memory behavior of polymer fibers loaded with carbon nanotubes or graphene flakes. These materials exhibit enhanced shape memory properties with the generation of a giant stress upon shape recovery. In addition, they exhibit a surprising temperature memory with a peak of generated stress at a temperature nearly equal to the temperature of programming. This temperature memory is ascribed to the presence of dynamical heterogeneities and to the intrinsic broadness of the glass transition. We present recent experiments related to observables other than mechanical properties. In particular nanocomposite fibers exhibit variations of electrical conductivity with an accurate memory. Indeed, the rate of conductivity variations during temperature changes reaches a well defined maximum at a temperature equal to the temperature of programming. Such materials are promising for future actuators that couple dimensional changes with sensing electronic functionalities.

  3. Memory operation mechanism of fullerene-containing polymer memory

    SciTech Connect

    Nakajima, Anri Fujii, Daiki

    2015-03-09

    The memory operation mechanism in fullerene-containing nanocomposite gate insulators was investigated while varying the kind of fullerene in a polymer gate insulator. It was cleared what kind of traps and which positions in the nanocomposite the injected electrons or holes are stored in. The reason for the difference in the easiness of programming was clarified taking the role of the charging energy of an injected electron into account. The dependence of the carrier dynamics on the kind of fullerene molecule was investigated. A nonuniform distribution of injected carriers occurred after application of a large magnitude programming voltage due to the width distribution of the polystyrene barrier between adjacent fullerene molecules. Through the investigations, we demonstrated a nanocomposite gate with fullerene molecules having excellent retention characteristics and a programming capability. This will lead to the realization of practical organic memories with fullerene-containing polymer nanocomposites.

  4. Laser-activated shape memory polymer intravascular thrombectomy device.

    PubMed

    Small Iv, Ward; Wilson, Thomas; Benett, William; Loge, Jeffrey; Maitland, Duncan

    2005-10-01

    A blood clot (thrombus) that becomes lodged in the arterial network supplying the brain can cause an ischemic stroke, depriving the brain of oxygen and often resulting in permanent disability. As an alternative to conventional clot-dissolving drug treatment, we are developing an intravascular laser-activated therapeutic device using shape memory polymer (SMP) to mechanically retrieve the thrombus and restore blood flow to the brain. Thermal imaging and computer simulation were used to characterize the optical and photothermal behavior of the SMP microactuator. Deployment of the SMP device in an in vitro thrombotic vascular occlusion model demonstrated the clinical treatment concept. PMID:19498850

  5. Development of multifunctional shape memory polymer foams

    NASA Astrophysics Data System (ADS)

    Song, Janice J.; Srivastava, Ijya; Naguib, Hani E.

    2015-05-01

    Shape memory polymers (SMP) are a class of stimuli-responsive materials which are able to respond to external stimulus such as temperature and deformation by changing their shape, and return to their original shape upon reversal or removal of the external stimulus. Although SMP materials have been studied extensively and have been used in a wide range of applications such as medicine, aerospace, and robotics, only few studies have looked at the potential of designing multifunctional SMP foams and blends. In this study, we investigate the feasibility of a design of SMP foam materials and blends. The actuator construct will contain a core SMP epoxy and blend of polylactic acid and polyurethane. The effects of the processing parameters of shape memory polymer (SMP) foams on the shape memory effect (SME) were investigated. The solid state foaming technique was employed to obtain the desired foamed cellular structure. One particular point of interest is to understand how the processing parameters affect the SMP and its glass transition temperature (Tg). By correctly tailoring these parameters it is possible to modify the SMP to have an improved shape memory effect SME.

  6. Thermoviscoelastic shape memory behavior for epoxy-shape memory polymer

    NASA Astrophysics Data System (ADS)

    Chen, Jianguo; Liu, Liwu; Liu, Yanju; Leng, Jinsong

    2014-05-01

    There are various applications for shape memory polymer (SMP) in the smart materials and structures field due to its large recoverable strain and controllable driving method. The mechanical shape memory deformation mechanism is so obscure that many samples and test schemes have to be tried in order to verify a final design proposal for a smart structure system. This paper proposes a simple and very useful method to unambiguously analyze the thermoviscoelastic shape memory behavior of SMP smart structures. First, experiments under different temperature and loading conditions are performed to characterize the large deformation and thermoviscoelastic behavior of epoxy-SMP. Then, a rheological constitutive model, which is composed of a revised standard linear solid (SLS) element and a thermal expansion element, is proposed for epoxy-SMP. The thermomechanical coupling effect and nonlinear viscous flowing rules are considered in the model. Then, the model is used to predict the measured rubbery and time-dependent response of the material, and different thermomechanical loading histories are adopted to verify the shape memory behavior of the model. The results of the calculation agree with experiments satisfactorily. The proposed shape memory model is practical for the design of SMP smart structures.

  7. Cyclic behaviors of amorphous shape memory polymers.

    PubMed

    Yu, Kai; Li, Hao; McClung, Amber J W; Tandon, Gyaneshwar P; Baur, Jeffery W; Qi, H Jerry

    2016-04-01

    Cyclic loading conditions are commonly encountered in the applications of shape memory polymers (SMPs), where the cyclic characteristics of the materials determine their performance during the service life, such as deformation resistance, shape recovery speed and shape recovery ratio. Recent studies indicate that in addition to the physical damage or some other irreversible softening effects, the viscoelastic nature could also be another possible reason for the degraded cyclic behavior of SMPs. In this paper, we explore in detail the influence of the viscoelastic properties on the cyclic tension and shape memory (SM) behavior of an epoxy based amorphous thermosetting polymer. Cyclic experiments were conducted first, which show that although the epoxy material does not have any visible damage or irreversible softening effect during deformation, it still exhibits obvious degradation in the cyclic tension and SM behaviors. A linear multi-branched model is utilized to assist in the prediction and understanding of the mechanical responses of amorphous SMPs. Parametric studies based on the applied model suggest that the shape memory performance can be improved by adjusting programming and recovery conditions, such as lowering the loading rate, increasing the programming temperature, and reducing the holding time. PMID:26924339

  8. Thermomechanical indentation of shape memory polymers.

    SciTech Connect

    Long, Kevin N.; Nguyen, Thao D.; Castro, Francisco; Qi, H. Jerry; Dunn, Martin L.; Shandas, Robin

    2007-04-01

    Shape memory polymers (SMPs) are receiving increasing attention because of their ability to store a temporary shape for a prescribed period of time, and then when subjected to an environmental stimulus, recover an original programmed shape. They are attractive candidates for a wide range of applications in microsystems, biomedical devices, deployable aerospace structures, and morphing structures. In this paper we investigate the thermomechanical behavior of shape memory polymers due to instrumented indentation, a loading/deformation scenario that represents complex multiaxial deformation. The SMP sample is indented using a spherical indenter at a temperature T{sub 1} (>T{sub g}). The temperature is then lowered to T{sub 2} (memory is then activated by increasing the temperature to T{sub 1} (>T{sub g}) during free recovery the indentation impression disappears and the surface of the SMP recovers to its original profile. A recently-developed three-dimensional finite deformation constitutive model for the thermomechanical behavior of SMPs is then used with the finite element method to simulate this process. Measurement and simulation results are compared for cases of free and constrained recovery and good agreement is obtained, suggesting the appropriateness of the simulation approach for complex multiaxial loading/deformations that are likely to occur in applications.

  9. Autobiographical Memory Disturbances in Depression: A Novel Therapeutic Target?

    PubMed Central

    Köhler, Cristiano A.; Carvalho, André F.; Alves, Gilberto S.; McIntyre, Roger S.; Hyphantis, Thomas N.; Cammarota, Martín

    2015-01-01

    Major depressive disorder (MDD) is characterized by a dysfunctional processing of autobiographical memories. We review the following core domains of deficit: systematic biases favoring materials of negative emotional valence; diminished access and response to positive memories; a recollection of overgeneral memories in detriment of specific autobiographical memories; and the role of ruminative processes and avoidance when dealing with autobiographical memories. Furthermore, we review evidence from functional neuroimaging studies of neural circuits activated by the recollection of autobiographical memories in both healthy and depressive individuals. Disruptions in autobiographical memories predispose and portend onset and maintenance of depression. Thus, we discuss emerging therapeutics that target memory difficulties in those with depression. We review strategies for this clinical domain, including memory specificity training, method-of-loci, memory rescripting, and real-time fMRI neurofeedback training of amygdala activity in depression. We propose that the manipulation of the reconsolidation of autobiographical memories in depression might represent a novel yet largely unexplored, domain-specific, therapeutic opportunity for depression treatment. PMID:26380121

  10. Porous inorganic—organic shape memory polymers

    PubMed Central

    Zhang, Dawei; Burkes, William L.; Schoener, Cody A.; Grunlan, Melissa A.

    2012-01-01

    Thermoresponsive shape memory polymers (SMPs) are a type of stimuli-sensitive materials that switch from a temporary shape back to their permanent shape upon exposure to heat. While the majority of SMPs have been fabricated in the solid form, porous SMP foams exhibit distinct properties and are better suited for certain applications, including some in the biomedical field. Like solid SMPs, SMP foams have been restricted to a limited group of organic polymer systems. In this study, we prepared inorganic–organic SMP foams based on the photochemical cure of a macromer comprised of inorganic polydimethylsiloxane (PDMS) segments and organic poly(ε-caprolactone) (PCL) segments, diacrylated PCL40-block-PDMS37-block-PCL40. To achieve tunable pore size with high interconnectivity, the SMP foams were prepared via a refined solvent-casting/particulate-leaching (SCPL) method. By varying design parameters such as degree of salt fusion, macromer concentration in the solvent and salt particle size, the SMP foams with excellent shape memory behavior and tunable pore size, pore morphology, and modulus were obtained. PMID:22956854

  11. Methods of Making and Using Shape Memory Polymer Composite Patches

    NASA Technical Reports Server (NTRS)

    Hood, Patrick J.

    2011-01-01

    A method of repairing a composite component having a damaged area including: laying a composite patch over the damaged area: activating the shape memory polymer resin to easily and quickly mold said patch to said damaged area; deactivating said shape memory polymer so that said composite patch retains the molded shape; and bonding said composite patch to said damaged part.

  12. High-Temperature Shape Memory Polymers

    NASA Technical Reports Server (NTRS)

    Yoonessi, Mitra; Weiss, Robert A.

    2012-01-01

    physical conformation changes when exposed to an external stimulus, such as a change in temperature. Such materials have a permanent shape, but can be reshaped above a critical temperature and fixed into a temporary shape when cooled under stress to below the critical temperature. When reheated above the critical temperature (Tc, also sometimes called the triggering or switching temperature), the materials revert to the permanent shape. The current innovation involves a chemically treated (sulfonated, carboxylated, phosphonated, or other polar function group), high-temperature, semicrystalline thermoplastic poly(ether ether ketone) (Tg .140 C, Tm = 340 C) mix containing organometallic complexes (Zn++, Li+, or other metal, ammonium, or phosphonium salts), or high-temperature ionic liquids (e.g. hexafluorosilicate salt with 1-propyl-3- methyl imidazolium, Tm = 210 C) to form a network where dipolar or ionic interactions between the polymer and the low-molecular-weight or inorganic compound forms a complex that provides a physical crosslink. Hereafter, these compounds will be referred to as "additives". The polymer is semicrystalline, and the high-melt-point crystals provide a temporary crosslink that acts as a permanent crosslink just so long as the melting temperature is not exceeded. In this example case, the melting point is .340 C, and the shape memory critical temperature is between 150 and 250 C. PEEK is an engineering thermoplastic with a high Young fs modulus, nominally 3.6 GPa. An important aspect of the invention is the control of the PEEK functionalization (in this example, the sulfonation degree), and the thermal properties (i.e. melting point) of the additive, which determines the switching temperature. Because the compound is thermoplastic, it can be formed into the "permanent" shape by conventional plastics processing operations. In addition, the compound may be covalently cross - linked after forming the permanent shape by S-PEEK by applying ionizing radiation ( radiation, neutrons), or by chemical crosslinking to form a covalent permanent network. With respect to other shape memory polymers, this invention is novel in that it describes the use of a thermoplastic composition that can be thermally molded or solution-cast into complex "permanent" shapes, and then reheated or redissolved and recast from solution to prepare another shape. It is also unique in that the shape memory behavior is provided by a non-polymer additive.

  13. Memristive learning and memory functions in polyvinyl alcohol polymer memristors

    NASA Astrophysics Data System (ADS)

    Lei, Yan; Liu, Yi; Xia, Yidong; Gao, Xu; Xu, Bo; Wang, Suidong; Yin, Jiang; Liu, Zhiguo

    2014-07-01

    Polymer based memristive devices can offer simplicity in fabrication and at the same time promise functionalities for artificial neural applications. In this work, inherent learning and memory functions have been achieved in polymer memristive devices employing Polyvinyl Alcohol. The change in conduction in such polymer devices strongly depends on the pulse amplitude, duration and time interval. Through repetitive stimuli training, temporary short-term memory can transfer into consolidated long-term memory. These behaviors bear remarkable similarities to certain learning and memory functions of biological systems.

  14. Bioreducible Polymers for Therapeutic Gene Delivery

    PubMed Central

    Lee, Young Sook; Kim, Sung Wan

    2014-01-01

    Most currently available cationic polymers have significant acute toxicity concerns such as cellular toxicity, aggregation of erythrocytes, and entrapment in the lung capillary bed, largely due to their poor biocompatibility and non-degradability under physiological conditions. To develop more intelligent polymers, disulfide bonds are introduced in the design of biodegradable polymers. Herein, the sustained innovations of biomimetic nanosized constructs with bioreducible poly(disulfide amine)s demonstrate a viable clinical tool for the treatment of cardiovascular disease, anemia, diabetes, and cancer. PMID:24746626

  15. Lignin-Based Triple Shape Memory Polymers.

    PubMed

    Sivasankarapillai, Gopakumar; Li, Hui; McDonald, Armando G

    2015-09-14

    Lignin-based triple shape memory polymers comprised of both permanent covalent cross-links and physical cross-links have been synthesized. A mixing phase with poly(ester-amine) and poly(ester-amide) network having two distinct glass transitions was hot mixed with more structurally homogenized methanol soluble lignin fraction by one-pot, two-step method. Triple shape properties arise from the combined effect of the glass transition of polyester copolymers and lignin and the dissociation of self-complementary hydrogen bonding and cross-link density. The percentage of recovery in each stage was investigated and it was proved that the first recovery is related with lignin-poly(ester-amine) rich network and the second recovery stage is related with lignin-poly(ester-amide) rich network. The thermal and mechanical properties of the lignin-copolymer networks were also investigated using differential scanning calorimetry and dynamic mechanical analysis. PMID:26214041

  16. Metal complex modified azo polymers for multilevel organic memories

    NASA Astrophysics Data System (ADS)

    Ma, Yong; Chen, Hong-Xia; Zhou, Feng; Li, Hua; Dong, Huilong; Li, You-Yong; Hu, Zhi-Jun; Xu, Qing-Feng; Lu, Jian-Mei

    2015-04-01

    Multilevel organic memories have attracted considerable interest due to their high capacity of data storage. Despite advances, the search for multilevel memory materials still remains a formidable challenge. Herein, we present a rational design and synthesis of a class of polymers containing an azobenzene-pyridine group (PAzo-py) and its derivatives, for multilevel organic memory storage. In this design, a metal complex (M(Phen)Cl2, M = Cu, Pd) is employed to modify the HOMO-LUMO energy levels of azo polymers, thereby converting the memory state from binary to ternary. More importantly, this approach enables modulating the energy levels of azo polymers by varying the coordination metal ions. This makes the achievement of high performance multilevel memories possible. The ability to tune the bandgap energy of azo polymers provides new exciting opportunities to develop new materials for high-density data storage.Multilevel organic memories have attracted considerable interest due to their high capacity of data storage. Despite advances, the search for multilevel memory materials still remains a formidable challenge. Herein, we present a rational design and synthesis of a class of polymers containing an azobenzene-pyridine group (PAzo-py) and its derivatives, for multilevel organic memory storage. In this design, a metal complex (M(Phen)Cl2, M = Cu, Pd) is employed to modify the HOMO-LUMO energy levels of azo polymers, thereby converting the memory state from binary to ternary. More importantly, this approach enables modulating the energy levels of azo polymers by varying the coordination metal ions. This makes the achievement of high performance multilevel memories possible. The ability to tune the bandgap energy of azo polymers provides new exciting opportunities to develop new materials for high-density data storage. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00871a

  17. Disruptions in autobiographical memory processing in depression and the emergence of memory therapeutics.

    PubMed

    Dalgleish, Tim; Werner-Seidler, Aliza

    2014-11-01

    Depression is characterized by distinct profiles of disturbance in ways autobiographical memories are represented, recalled, and maintained. We review four core domains of difficulty: systematic biases in favor of negative material; impoverished access and responses to positive memories; reduced access to the specific details of the personal past; and dysfunctional processes of rumination and avoidance around personal autobiographical material. These difficulties drive the onset and maintenance of depression; consequently, interventions targeted at these maladaptive processes have clinical potential. Memory therapeutics is the development of novel clinical techniques, translated from basic research, that target memory difficulties in those with emotional disorders. We discuss prototypical examples from this clinical domain including MEmory Specificity Training, positive memory elaboration, memory rescripting, and the method-of-loci (MoL). PMID:25060510

  18. Shape memory polymers for active cell culture.

    PubMed

    Davis, Kevin A; Luo, Xiaofan; Mather, Patrick T; Henderson, James H

    2011-01-01

    Shape memory polymers (SMPs) are a class of "smart" materials that have the ability to change from a fixed, temporary shape to a pre-determined permanent shape upon the application of a stimulus such as heat(1-5). In a typical shape memory cycle, the SMP is first deformed at an elevated temperature that is higher than its transition temperature, T(trans;) [either the melting temperature (T(m;)) or the glass transition temperature (T(g;))]. The deformation is elastic in nature and mainly leads to a reduction in conformational entropy of the constituent network chains (following the rubber elasticity theory). The deformed SMP is then cooled to a temperature below its T(trans;) while maintaining the external strain or stress constant. During cooling, the material transitions to a more rigid state (semi-crystalline or glassy), which kinetically traps or "freezes" the material in this low-entropy state leading to macroscopic shape fixing. Shape recovery is triggered by continuously heating the material through T(trans;) under a stress-free (unconstrained) condition. By allowing the network chains (with regained mobility) to relax to their thermodynamically favored, maximal-entropy state, the material changes from the temporary shape to the permanent shape. Cells are capable of surveying the mechanical properties of their surrounding environment(6). The mechanisms through which mechanical interactions between cells and their physical environment control cell behavior are areas of active research. Substrates of defined topography have emerged as powerful tools in the investigation of these mechanisms. Mesoscale, microscale, and nanoscale patterns of substrate topography have been shown to direct cell alignment, cell adhesion, and cell traction forces(7-14). These findings have underscored the potential for substrate topography to control and assay the mechanical interactions between cells and their physical environment during cell culture, but the substrates used to date have generally been passive and could not be programmed to change significantly during culture. This physical stasis has limited the potential of topographic substrates to control cells in culture. Here, active cell culture (ACC) SMP substrates are introduced that employ surface shape memory to provide programmed control of substrate topography and deformation. These substrates demonstrate the ability to transition from a temporary grooved topography to a second, nearly flat memorized topography. This change in topography can be used to control cell behavior under standard cell culture conditions. PMID:21750496

  19. Shape memory polymer foams for endovascular therapies

    SciTech Connect

    Wilson, Thomas S.; Maitland, Duncan J.

    2015-05-26

    A system for occluding a physical anomaly. One embodiment comprises a shape memory material body wherein the shape memory material body fits within the physical anomaly occluding the physical anomaly. The shape memory material body has a primary shape for occluding the physical anomaly and a secondary shape for being positioned in the physical anomaly.

  20. Shape memory polymer foams for endovascular therapies

    DOEpatents

    Wilson, Thomas S.; Maitland, Duncan J.

    2012-03-13

    A system for occluding a physical anomaly. One embodiment comprises a shape memory material body wherein the shape memory material body fits within the physical anomaly occluding the physical anomaly. The shape memory material body has a primary shape for occluding the physical anomaly and a secondary shape for being positioned in the physical anomaly.

  1. AC Electric Field Activated Shape Memory Polymer Composite

    NASA Technical Reports Server (NTRS)

    Kang, Jin Ho; Siochi, Emilie J.; Penner, Ronald K.; Turner, Travis L.

    2011-01-01

    Shape memory materials have drawn interest for applications like intelligent medical devices, deployable space structures and morphing structures. Compared to other shape memory materials like shape memory alloys (SMAs) or shape memory ceramics (SMCs), shape memory polymers (SMPs) have high elastic deformation that is amenable to tailored of mechanical properties, have lower density, and are easily processed. However, SMPs have low recovery stress and long response times. A new shape memory thermosetting polymer nanocomposite (LaRC-SMPC) was synthesized with conductive fillers to enhance its thermo-mechanical characteristics. A new composition of shape memory thermosetting polymer nanocomposite (LaRC-SMPC) was synthesized with conductive functionalized graphene sheets (FGS) to enhance its thermo-mechanical characteristics. The elastic modulus of LaRC-SMPC is approximately 2.7 GPa at room temperature and 4.3 MPa above its glass transition temperature. Conductive FGSs-doped LaRC-SMPC exhibited higher conductivity compared to pristine LaRC SMP. Applying an electric field at between 0.1 Hz and 1 kHz induced faster heating to activate the LaRC-SMPC s shape memory effect relative to applying DC electric field or AC electric field at frequencies exceeding1 kHz.

  2. Evaluation of a degradable shape-memory polymer network as matrix for controlled drug release.

    PubMed

    Wischke, Christian; Neffe, Axel T; Steuer, Susi; Lendlein, Andreas

    2009-09-15

    Degradable shape-memory polymers are multifunctional materials with broad applicability for medical devices. They are designed to acquire their therapeutically relevant shape and mechanical properties after implantation. In this study, the potential of a completely amorphous shape-memory polymer matrix for controlled drug release was comprehensively characterized according to a four step general strategy which provides concepts for validating multifunctional materials for pharmaceutical applications. Independent functionalities are thereby crucial for fully exploiting the potential of the materials. The copolyester urethane network was synthesized by crosslinking star-shaped tetrahydroxy telechelics of oligo[(rac-lactide)-co-glycolide] with an aliphatic diisocyanate. In step 1 of the four step characterization procedure, this material showed the thermal and mechanical properties, which are required for the shape-memory effect under physiological conditions. Shape recovery could be realized by a one-step or a multi-step methodology. In step 2, feasibility of drug loading of pre-formed shape-memory networks has been demonstrated with drugs of different hydrophobicities. The presence of drugs did not disturb the material's functionalities directly after loading (step 3) and under release conditions (step 4). A predictable release of about 90% of the payload in 80 days was observed. Overall, the synthesized amorphous polymer network showed three independent functionalities, i.e., a shape-memory effect combined with biodegradability and controlled drug release. PMID:19470395

  3. Nanoscale porosity in polymer films: fabrication and therapeutic applications

    PubMed Central

    Bernards, Daniel A.; Desai, Tejal A.

    2011-01-01

    This review focuses on current developments in the field of nanostructured bulk polymers and their application in bioengineering and therapeutic sciences. In contrast to well-established nanoscale materials, such as nanoparticles and nanofibers, bulk nanostructured polymers combine nanoscale structure in a macroscopic construct, which enables unique application of these materials. Contemporary fabrication and processing techniques capable of producing nanoporous polymer films are reviewed. Focus is placed on techniques capable of sub-100 nm features since this range approaches the size scale of biological components, such as proteins and viruses. The attributes of these techniques are compared, with an emphasis on the characteristic advantages and limitations of each method. Finally, application of these materials to biofiltration, immunoisolation, and drug delivery are reviewed. PMID:22140398

  4. Residual stresses in injection molded shape memory polymer parts

    NASA Astrophysics Data System (ADS)

    Katmer, Sukran; Esen, Huseyin; Karatas, Cetin

    2016-03-01

    Shape memory polymers (SMPs) are materials which have shape memory effect (SME). SME is a property which has the ability to change shape when induced by a stimulator such as temperature, moisture, pH, electric current, magnetic field, light, etc. A process, known as programming, is applied to SMP parts in order to alter them from their permanent shape to their temporary shape. In this study we investigated effects of injection molding and programming processes on residual stresses in molded thermoplastic polyurethane shape memory polymer, experimentally. The residual stresses were measured by layer removal method. The study shows that injection molding and programming process conditions have significantly influence on residual stresses in molded shape memory polyurethane parts.

  5. Shape memory polymers with high and low temperature resistant properties.

    PubMed

    Xiao, Xinli; Kong, Deyan; Qiu, Xueying; Zhang, Wenbo; Liu, Yanju; Zhang, Shen; Zhang, Fenghua; Hu, Yang; Leng, Jinsong

    2015-01-01

    High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to -150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed. PMID:26382318

  6. Shape memory polymers with high and low temperature resistant properties

    PubMed Central

    Xiao, Xinli; Kong, Deyan; Qiu, Xueying; Zhang, Wenbo; Liu, Yanju; Zhang, Shen; Zhang, Fenghua; Hu, Yang; Leng, Jinsong

    2015-01-01

    High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to −150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed. PMID:26382318

  7. Toward a self-deploying shape memory polymer neuronal electrode.

    PubMed

    Sharp, Andrew A; Panchawagh, Hrishikesh V; Ortega, Alicia; Artale, Ryan; Richardson-Burns, Sarah; Finch, Dudley S; Gall, Ken; Mahajan, Roop L; Restrepo, Diego

    2006-12-01

    The widespread application of neuronal probes for chronic recording of brain activity and functional stimulation has been slow to develop partially due to long-term biocompatibility problems with existing metallic and ceramic probes and the tissue damage caused during probe insertion. Stiff probes are easily inserted into soft brain tissue but cause astrocytic scars that become insulating sheaths between electrodes and neurons. In this communication, we explore the feasibility of a new approach to the composition and implantation of chronic electrode arrays. We demonstrate that softer polymer-based probes can be inserted into the olfactory bulb of a mouse and that slow insertion of the probes reduces astrocytic scarring. We further present the development of a micromachined shape memory polymer probe, which provides a vehicle to self-deploy an electrode at suitably slow rates and which can provide sufficient force to penetrate the brain. The deployment rate and composition of shape memory polymer probes can be tailored by polymer chemistry and actuator design. We conclude that it is feasible to fabricate shape memory polymer-based electrodes that would slowly self-implant compliant conductors into the brain, and both decrease initial trauma resulting from implantation and enhance long-term biocompatibility for long-term neuronal measurement and stimulation. PMID:17124327

  8. Thermo-Responsive Polymers for Cell-based Therapeutic Applications

    NASA Astrophysics Data System (ADS)

    James, Hodari-Sadiki

    Poly (N-isopropylacrylamide) (PNIPAAm) is a well-known thermo-responsive polymer that has be shown to be biocompatible, with surfaces coated with PNIPAAm supporting the culture of cells. These surfaces support the adhesion and proliferation of multiple cell phenotypes at 37 C, when surface is hydrophobic, as the polymer chains are collapse and lose their affinity for water. Reducing the temperature below the polymers lower critical solution temperature (LCST) elicits hydration and swelling of the polymer chains and leads to cell detachment. In vitro culture on thermo-responsive surfaces can be used to produce cell sheets for the use of different therapeutic treatments. PNIPAAm coated membranes were used to culture human keratinocyte cells to confluence, with cell release possible after exposing the membranes to room temperature (25 C) for 10 minutes. Cell sheet transfer was possible from the coated membrane to cell culture dishes using a protocol that we developed. There was also a trend towards similar cell apoptosis on both PNIPAAm coated and uncoated surfaces.

  9. Microscopic mechanisms of the shape memory effect in crosslinked polymers

    NASA Astrophysics Data System (ADS)

    Davidson, Jacob D.; Goulbourne, N. C.

    2015-05-01

    In this work we perform coarse-grained molecular dynamics (MD) simulations to study the molecular origins of the thermal shape memory effect in crosslinked polymer materials. Thermal shape memory polymers (SMPs) are materials able to hold a deformed shape when cooled below the glass transition temperature, and subsequently recover the initial shape when heated. To use SMPs in various applications requires materials which reliably hold and recover their shapes; this has sparked recent synthesis work to create new SMP materials with optimized properties. Here we use coarse-grained MD simulations with different polymer chain models to determine which parameters affect relevant SMP behavior and to investigate the molecular mechanisms at the level of individual chains during temperature cycling. The simulations show how temperature-dependent chain mobility leads to shape memory polymer behavior. In particular, we demonstrate the importance of attractive monomer interactions in leading to ‘good’ SMP behavior. The results suggest promising routes for material development. Additionally, the mechanisms identified with the simple simulation model can be used to inform multi-scale models of SMP material behavior.

  10. Biomedical Applications of Thermally Activated Shape Memory Polymers

    SciTech Connect

    Small IV, W; Singhal, P; Wilson, T S; Maitland, D J

    2009-04-10

    Shape memory polymers (SMPs) are smart materials that can remember a primary shape and can return to this primary shape from a deformed secondary shape when given an appropriate stimulus. This property allows them to be delivered in a compact form via minimally invasive surgeries in humans, and deployed to achieve complex final shapes. Here we review the various biomedical applications of SMPs and the challenges they face with respect to actuation and biocompatibility. While shape memory behavior has been demonstrated with heat, light and chemical environment, here we focus our discussion on thermally stimulated SMPs.

  11. Ultra-flexible nonvolatile memory based on donor-acceptor diketopyrrolopyrrole polymer blends

    PubMed Central

    Zhou, Ye; Han, Su-Ting; Yan, Yan; Zhou, Li; Huang, Long-Biao; Zhuang, Jiaqing; Sonar, Prashant; Roy, V. A. L.

    2015-01-01

    Flexible memory cell array based on high mobility donor-acceptor diketopyrrolopyrrole polymer has been demonstrated. The memory cell exhibits low read voltage, high cell-to-cell uniformity and good mechanical flexibility, and has reliable retention and endurance memory performance. The electrical properties of the memory devices are systematically investigated and modeled. Our results suggest that the polymer blends provide an important step towards high-density flexible nonvolatile memory devices. PMID:26029856

  12. Ultra-flexible nonvolatile memory based on donor-acceptor diketopyrrolopyrrole polymer blends.

    PubMed

    Zhou, Ye; Han, Su-Ting; Yan, Yan; Zhou, Li; Huang, Long-Biao; Zhuang, Jiaqing; Sonar, Prashant; Roy, V A L

    2015-01-01

    Flexible memory cell array based on high mobility donor-acceptor diketopyrrolopyrrole polymer has been demonstrated. The memory cell exhibits low read voltage, high cell-to-cell uniformity and good mechanical flexibility, and has reliable retention and endurance memory performance. The electrical properties of the memory devices are systematically investigated and modeled. Our results suggest that the polymer blends provide an important step towards high-density flexible nonvolatile memory devices. PMID:26029856

  13. Targeting Angiogenesis-Dependent Calcified Neoplasms Using Combined Polymer Therapeutics

    PubMed Central

    Segal, Ehud; Pan, Huaizhong; Ofek, Paula; Udagawa, Taturo; Kope?kov, Pavla; Kope?ek, Jind?ich; Satchi-Fainaro, Ronit

    2009-01-01

    Background There is an immense clinical need for novel therapeutics for the treatment of angiogenesis-dependent calcified neoplasms such as osteosarcomas and bone metastases. We developed a new therapeutic strategy to target bone metastases and calcified neoplasms using combined polymer-bound angiogenesis inhibitors. Using an advanced living polymerization technique, the reversible addition-fragmentation chain transfer (RAFT), we conjugated the aminobisphosphonate alendronate (ALN), and the potent anti-angiogenic agent TNP-470 with N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer through a Glycine-Glycine-Proline-Norleucine linker, cleaved by cathepsin K, a cysteine protease overexpressed at resorption sites in bone tissues. In this approach, dual targeting is achieved. Passive accumulation is possible due to the increase in molecular weight following polymer conjugation of the drugs, thus extravasating from the tumor leaky vessels and not from normal healthy vessels. Active targeting to the calcified tissues is achieved by ALN's affinity to bone mineral. Methods and Finding The anti-angiogenic and antitumor potency of HPMA copolymer-ALN-TNP-470 conjugate was evaluated both in vitro and in vivo. We show that free and conjugated ALN-TNP-470 have synergistic anti-angiogenic and antitumor activity by inhibiting proliferation, migration and capillary-like tube formation of endothelial and human osteosarcoma cells in vitro. Evaluation of anti-angiogenic, antitumor activity and body distribution of HPMA copolymer-ALN-TNP-470 conjugate was performed on severe combined immunodeficiency (SCID) male mice inoculated with mCherry-labeled MG-63-Ras human osteosarcoma and by modified Miles permeability assay. Our targeted bi-specific conjugate reduced VEGF-induced vascular hyperpermeability by 92% and remarkably inhibited osteosarcoma growth in mice by 96%. Conclusions This is the first report to describe a new concept of a narrowly-dispersed combined polymer therapeutic designed to target both tumor and endothelial compartments of bone metastases and calcified neoplasms at a single administration. This new approach of co-delivery of two synergistic drugs may have clinical utility as a potential therapy for angiogenesis-dependent cancers such as osteosarcoma and bone metastases. PMID:19381291

  14. Strong, Tailored, Biocompatible Shape-Memory Polymer Networks**

    PubMed Central

    Shandas, Robin; Safranski, David; Ortega, Alicia M.; Sassaman, Katie; Gall, Ken

    2009-01-01

    Shape-memory polymers are a class of smart materials that have recently been used in intelligent biomedical devices and industrial applications for their ability to change shape under a predetermined stimulus. In this study, photopolymerized thermoset shape-memory networks with tailored thermomechanics are evaluated to link polymer structure to recovery behavior. Methyl methacrylate (MMA) and poly(ethylene glycol) dimethacrylate (PEGDMA) are copolymerized to create networks with independently adjusted glass transition temperatures (Tg) and rubbery modulus values ranging from 56 to 92 C and 9.3 to 23.0 MPa, respectively. Free-strain recovery under isothermal and transient temperature conditions is highly influenced by the Tg of the networks, while the rubbery moduli of the networks has a negligible effect on this response. The magnitude of stress generation of fixed-strain recovery correlates with network rubbery moduli, while fixed-strain recovery under isothermal conditions shows a complex evolution for varying Tg. The results are intended to help aid in future shape-memory device design and the MMA-co-PEGDMA network is presented as a possible high strength shape-memory biomaterial. PMID:19633727

  15. Strong, Tailored, Biocompatible Shape-Memory Polymer Networks.

    PubMed

    Yakacki, Christopher M; Shandas, Robin; Safranski, David; Ortega, Alicia M; Sassaman, Katie; Gall, Ken

    2008-08-22

    Shape-memory polymers are a class of smart materials that have recently been used in intelligent biomedical devices and industrial applications for their ability to change shape under a predetermined stimulus. In this study, photopolymerized thermoset shape-memory networks with tailored thermomechanics are evaluated to link polymer structure to recovery behavior. Methyl methacrylate (MMA) and poly(ethylene glycol) dimethacrylate (PEGDMA) are copolymerized to create networks with independently adjusted glass transition temperatures (T(g)) and rubbery modulus values ranging from 56 to 92 °C and 9.3 to 23.0 MPa, respectively. Free-strain recovery under isothermal and transient temperature conditions is highly influenced by the T(g) of the networks, while the rubbery moduli of the networks has a negligible effect on this response. The magnitude of stress generation of fixed-strain recovery correlates with network rubbery moduli, while fixed-strain recovery under isothermal conditions shows a complex evolution for varying T(g). The results are intended to help aid in future shape-memory device design and the MMA-co-PEGDMA network is presented as a possible high strength shape-memory biomaterial. PMID:19633727

  16. Design of a deployable structure with shape memory polymers

    NASA Astrophysics Data System (ADS)

    Rossiter, Jonathan; Scarpa, Fabrizio; Takashima, Kazuto; Walters, Peter

    2012-04-01

    Auxetic (negative Poisson's ratio) configurations have recently been used to build prototypes of deployable structures using classical shape memory alloys (Nickel-Titanium-Copper). Chiral configurations, featuring three or more inter-connected spiral-wound hubs, exploit efficient tensile-rotational mechanisms. These structures offer high deployability ratios in structural elements with load-bearing characteristics. Shape memory polymers have the potential to replace these shape memory alloys and other stored-energy actuators, and have the attractive properties of low mass, high actuation strain, easy fabrication and tuneable thermal properties. In this work we discuss how shape memory polymers (SMP) integrated into a chiral core could offer enhanced deployable characteristics and increase the efficiency of the auxetic deformations in these unusual cellular structures. We consider the spiral-wound fundamental component needed for SMP n-chiral prototypes and present test results showing actuation motion of expanding SMP deployable structures. Applications likely to benefit from these structures include lightweight elements for structural engineering applications, deployable structures for space applications and implantable medical devices.

  17. Shape memory polymers based on uniform aliphatic urethane networks

    SciTech Connect

    Wilson, T S; Bearinger, J P; Herberg, J L; Marion III, J E; Wright, W J; Evans, C L; Maitland, D J

    2007-01-19

    Aliphatic urethane polymers have been synthesized and characterized, using monomers with high molecular symmetry, in order to form amorphous networks with very uniform supermolecular structures which can be used as photo-thermally actuable shape memory polymers (SMPs). The monomers used include hexamethylene diisocyanate (HDI), trimethylhexamethylenediamine (TMHDI), N,N,N{prime},N{prime}-tetrakis(hydroxypropyl)ethylenediamine (HPED), triethanolamine (TEA), and 1,3-butanediol (BD). The new polymers were characterized by solvent extraction, NMR, XPS, UV/VIS, DSC, DMTA, and tensile testing. The resulting polymers were found to be single phase amorphous networks with very high gel fraction, excellent optical clarity, and extremely sharp single glass transitions in the range of 34 to 153 C. Thermomechanical testing of these materials confirms their excellent shape memory behavior, high recovery force, and low mechanical hysteresis (especially on multiple cycles), effectively behaving as ideal elastomers above T{sub g}. We believe these materials represent a new and potentially important class of SMPs, and should be especially useful in applications such as biomedical microdevices.

  18. Shape memory polymer network with thermally distinct elasticity and plasticity.

    PubMed

    Zhao, Qian; Zou, Weike; Luo, Yingwu; Xie, Tao

    2016-01-01

    Stimuli-responsive materials with sophisticated yet controllable shape-changing behaviors are highly desirable for real-world device applications. Among various shape-changing materials, the elastic nature of shape memory polymers allows fixation of temporary shapes that can recover on demand, whereas polymers with exchangeable bonds can undergo permanent shape change via plasticity. We integrate the elasticity and plasticity into a single polymer network. Rational molecular design allows these two opposite behaviors to be realized at different temperature ranges without any overlap. By exploring the cumulative nature of the plasticity, we demonstrate easy manipulation of highly complex shapes that is otherwise extremely challenging. The dynamic shape-changing behavior paves a new way for fabricating geometrically complex multifunctional devices. PMID:26824077

  19. Shape memory polymer network with thermally distinct elasticity and plasticity

    PubMed Central

    Zhao, Qian; Zou, Weike; Luo, Yingwu; Xie, Tao

    2016-01-01

    Stimuli-responsive materials with sophisticated yet controllable shape-changing behaviors are highly desirable for real-world device applications. Among various shape-changing materials, the elastic nature of shape memory polymers allows fixation of temporary shapes that can recover on demand, whereas polymers with exchangeable bonds can undergo permanent shape change via plasticity. We integrate the elasticity and plasticity into a single polymer network. Rational molecular design allows these two opposite behaviors to be realized at different temperature ranges without any overlap. By exploring the cumulative nature of the plasticity, we demonstrate easy manipulation of highly complex shapes that is otherwise extremely challenging. The dynamic shape-changing behavior paves a new way for fabricating geometrically complex multifunctional devices. PMID:26824077

  20. Light-activated shape memory polymers and associated applications

    NASA Astrophysics Data System (ADS)

    Havens, Ernie; Snyder, Emily A.; Tong, Tat H.

    2005-05-01

    Continuous product development and technology integration efforts using shape memory polymers (SMPs) have uncovered a need for faster response times. As with most smart materials, SMP responds to a specific stimulus. Traditionally SMP is triggered by thermal stimulus; increasing the temperature of the SMP above a Tg will transition the polymer from a glassy state to a rubbery state. The transition is reversible upon cooling below the Tg. It has been determined that many SMP applications can be significantly enhanced with non-thermal triggering. Non-thermal triggering eliminates the need for heating mechanisms and reduces cycle time. Furthermore, it has been found that with a faster response time many new applications become viable. Previous successful attempts have been made to improve response time of SMP by increasing its thermal conductivity with various thermally conductive additives1. However, thermal heating and cooling of polymers and composites of substantial thickness, thermally conductive or not, takes time. In an effort to facilitate system integration and increase the response time of SMP, researchers at Cornerstone Research Group, Inc. (CRG) have sought to eliminate the thermal dependency of SMP by developing light-activated shape memory polymer (LASMP). In this work, monomers which contain photo-crosslinkable groups in addition to the primary polymerizable groups were developed. These monomers were formulated and cured with other monomers to form LASMP. The mechanical properties of these materials, the kinetics, and the reversibility of the light-activated shape memory effect were studied. The near-, mid-, and far-term potential of this new material technology for system level applications is discussed.

  1. Tunable thiol-epoxy shape memory polymer foams

    NASA Astrophysics Data System (ADS)

    Ellson, Gregory; Di Prima, Matthew; Ware, Taylor; Tang, Xiling; Voit, Walter

    2015-05-01

    Shape memory polymers (SMPs) are uniquely suited to a number of applications due to their shape storage and recovery abilities and the wide range of available chemistries. However, many of the desired performance properties are tied to the polymer chemistry which can make optimization difficult. The use of foaming techniques is one way to tune mechanical response of an SMP without changing the polymer chemistry. In this work, a novel thiol-epoxy SMP was foamed using glass microspheres (40 and 50% by volume Q-Cel 6019), using expandable polymer microspheres (1% 930 DU 120), and by a chemical blowing agent (1% XOP-341). Each approach created SMP foam with a differing density and microstructure from the others. Thermal and thermomechanical analysis was performed to observe the behavioral difference between the foaming techniques and to confirm that the glass transition (Tg) was relatively unchanged near 50 °C while the glassy modulus varied from 19.1 to 345 MPa and the rubbery modulus varied from 0.04 to 2.2 MPa. The compressive behavior of the foams was characterized through static compression testing at different temperatures, and cyclic compression testing at Tg. Constrained shape recovery testing showed a range of peak recovery stress from 5 MPa for the syntactic Q-Cel foams to ˜0.1 MPa for the chemically blown XOP-341 foam. These results showed that multiple foaming approaches can be used with a novel SMP to vary the mechanical response independent of Tg and polymer chemistry.

  2. Thermal response of novel shape memory polymer-shape memory alloy hybrids

    NASA Astrophysics Data System (ADS)

    Rossiter, Jonathan; Takashima, Kazuto; Mukai, Toshiharu

    2014-03-01

    Shape memory polymers (SMP) and shape memory alloys (SMA) have both been proven important smart materials in their own fields. Shape memory polymers can be formed into complex three-dimensional structures and can undergo shape programming and large strain recovery. These are especially important for deployable structures including those for space applications and micro-structures such as stents. Shape memory alloys on the other hand are readily exploitable in a range of applications where simple, silent, light-weight and low-cost repeatable actuation is required. These include servos, valves and mobile robotic artificial muscles. Despite their differences, one important commonality between SMPs and SMAs is that they are both typically activated by thermal energy. Given this common characteristic it is important to consider how these two will behave when in close environmental proximity, and hence exposed to the same thermal stimulus, and when they are incorporated into a hybrid SMA-SMP structure. In this paper we propose and examine the operation of SMA-SMP hybrids. The relationship between the two temperatures Tg, the glass transition temperature of the polymer, and Ta, the nominal austenite to martensite transition temperature of the alloy is considered. We examine how the choice of these two temperatures affects the thermal response of the hybrid. Electrical stimulation of the SMA is also considered as a method not only of actuating the SMA but also of inducing heating in the surrounding polymer, with consequent effects on actuator behaviour. Likewise by varying the rate and degree of thermal stimulation of the SMA significantly different actuation and structural stiffness can be achieved. Novel SMP-SMA hybrid actuators and structures have many ready applications in deployable structures, robotics and tuneable engineering systems.

  3. Memory loss in Alzheimer's disease: implications for development of therapeutics

    PubMed Central

    Gold, Carl A; Budson, Andrew E

    2009-01-01

    Alzheimer's disease (AD) is a progressive neurodegenerative disease marked by a constellation of cognitive disturbances, the earliest and most prominent being impaired episodic memory. Episodic memory refers to the memory system that allows an individual to consciously retrieve a previously experienced item or episode of life. Many recent studies have focused on characterizing how AD pathology impacts particular aspects of episodic memory and underlying mental and neural processes. This review summarizes the findings of those studies and discusses the effects of current and promising treatments for AD on episodic memory. The goal of this review is to raise awareness of the strides that cognitive neuroscientists have made in understanding intact and dysfunctional memory. Knowledge of the specific memorial processes that are impaired in AD may be of great value to basic scientists developing novel therapies and to clinical researchers assessing the efficacy of those therapies. PMID:19086882

  4. Thiol-vinyl systems as shape memory polymers and novel two-stage reactive polymer systems

    NASA Astrophysics Data System (ADS)

    Nair, Devatha P.

    2011-12-01

    The focus of this research was to formulate, characterize and tailor the reaction methodologies and material properties of thiol-vinyl systems to develop novel polymer platforms for a range of engineering applications. Thiol-ene photopolymers were demonstrated to exhibit several advantageous characteristics for shape memory polymer systems for a range of biomedical applications. The thiol-ene shape memory polymer systems were tough and flexible as compared to the acrylic control systems with glass transition temperatures between 30 and 40 C; ideal for actuation at body temperature. The thiol-ene polymers also exhibited excellent shape fixity and a rapid and distinct shape memory actuation response along with free strain recoveries of greater than 96% and constrained stress recoveries of 100%. Additionally, two-stage reactive thiol-acrylate systems were engineered as a polymer platform technology enabling two independent sets of polymer processing and material properties. There are distinct advantages to designing polymer systems that afford two distinct sets of material properties -- an intermediate polymer that would enable optimum handling and processing of the material (stage 1), while maintaining the ability to tune in different, final properties that enable the optimal functioning of the polymeric material (stage 2). To demonstrate the range of applicability of the two-stage reactive systems, three specific applications were demonstrated; shape memory polymers, lithographic impression materials, and optical materials. The thiol-acrylate reactions exhibit a wide range of application versatility due to the range of available thiol and acrylate monomers as well as reaction mechanisms such as Michael Addition reactions and free radical polymerizations. By designing a series of non-stoichiometeric thiol-acrylate systems, a polymer network is initially formed via a base catalyzed 'click' Michael addition reaction. This self-limiting reaction results in a Stage 1 polymer with excess acrylic functional groups within the network. At a later point in time, the photoinitiated, free radical polymerization of the excess acrylic functional groups results in a highly crosslinked, robust material system. By varying the monomers within the system as well as the stoichiometery of thiol to acrylate functional groups, the ability of the two-stage reactive systems to encompass a wide range of properties at the end of both the stage 1 and stage 2 polymerizations was demonstrated. The thiol-acrylate networks exhibited intermediate Stage 1 rubbery moduli and glass transition temperatures that range from 0.5 MPa and -10 C to 22 MPa and 22 C respectively. The same polymer networks can then attain glass transition temperatures that range from 5 C to 195 C and rubbery moduli of up to 200 MPa after the subsequent photocure stage. Two-stage reactive polymer composite systems were also formulated and characterized for thermomechanical and mechanical properties. Thermomechanical analysis showed that the fillers resulted in a significant increase in the modulus at both stage 1 and stage 2 polymerizations without a significant change in the glass transition temperatures (Tg). The two-stage reactive matrix composite formed with a hexafunctional acrylate matrix and 20 volume % silica particles showed a 125% increase in stage 1 modulus and 101% increase in stage 2 modulus, when compared with the modulus of the neat matrix. Finally, the two-stage reactive polymeric devices were formulated and designed as orthopedic suture anchors for arthroscopic surgeries and mechanically characterized. The Stage 1 device was designed to exhibit properties ideal for arthroscopic delivery and device placement with glass transition temperatures 25 -- 30 C and rubbery moduli 95 MPa. The subsequent photopolymerization generated Stage 2 polymers designed to match the local bone environment with moduli ranging up to 2 GPa. Additionally, pull-out strengths of 140 N were demonstrated and are equivalent to the pull-strengths achieved by other commercially available suture anchors.

  5. Smart medical stocking using memory polymer for chronic venous disorders.

    PubMed

    Kumar, Bipin; Hu, Jinlian; Pan, Ning

    2016-01-01

    Proper level of pressure or compression generated by medical stocking or hosiery is the key element for successful treatment or management of chronic venous disorders such as oedema, leg ulcers, etc. However achieving the recommended compression level and, more importantly, sustaining it using stockings has been a major challenge to the health practitioners supervising the treatment. This work aims to investigate and design a smart compression stocking using shape-memory polymer that allows externally controlling the pressure level in the wrapped position on the leg. Based on thermodynamical rubber theories, we first derived several criteria that have to be satisfied simultaneously in order to achieve the controlled pressure adjustment using external heat stimuli. We then presented a case where such a stocking is developed using a blend yarn consists of selected shape-memory polyurethane and nylon filaments. Extensive experimental work has also been conducted to demonstrate the feasibility and explore the influencing factors involved. PMID:26513411

  6. Internal stress storage in shape memory polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Gall, Ken; Dunn, Martin L.; Liu, Yiping; Stefanic, Goran; Balzar, Davor

    2004-07-01

    We examine the storage and release of internal stresses in shape memory polymers reinforced with a dispersion of nanometer-scale SiC particles. A quantitative Rietveld analysis of diffraction peaks was used to measure changes in the lattice parameter of the SiC particles after permanent deformation at 25C, and subsequent shape recovery induced by heating to 120C. Under 50% compression of the composite material, the nanoparticles store a finite compressive stress, which is almost completely released during heated strain recovery. The values of the stored internal stresses in the particles are compared to values based on micromechanic calculations.

  7. Investigation of mechanical behavior of epoxy shape memory polymers

    NASA Astrophysics Data System (ADS)

    Wu, Xuelian; Liu, Yanju; Leng, Jinsong

    2009-03-01

    Shape memory polymer (SMP) is a new class of smart material which attracts great interest in recent years. In this paper, in addition to the synthesizing of three types of epoxy SMPs with various linear epoxy monomer contents, their mechanical properties are focused on. Structure characteristic, dynamic mechanical property and quasi-static tension property and shape memory behavior of the epoxy SMPs are presented. Results indicate that glass transition temperature determined by dynamic mechanical analysis (loss modulus) varies from 69 to 113 C for the epoxy SMPs. And it should be noted that the linear monomer has no effect on storage modulus in glass state but decrease the storage modulus in rubber state for the polymers. From tensile test, it is found that the content of linear monomer has significant effect on the tensile deformation behavior which varies from a brittle response to elastomeric response at room temperature. And the strength varies from 15 to 62MPa with the corresponding elastic modulus ranging from 2.5 to 1.7GPa for the epoxy system. Characterization of the shape memory effect in epoxy SMP suggests a high (above 99%) shape recovery ratio at 100 C, besides, the epoxy SMP with higher linear monomer content shows a quicker shape recovery speed. Moreover, effect of linear monomer content on glass transition temperature and thermo-mechanical property is also investigated. Results indicate that, epoxy SMP fabricated in this study possess not only unique shape memory effect but also excellent mechanical properties, which will be the leading candidate for applications in engineering fields.

  8. Characterization of Nonlinear Rate Dependent Response of Shape Memory Polymers

    NASA Technical Reports Server (NTRS)

    Volk, Brent; Lagoudas, Dimitris C.; Chen, Yi-Chao; Whitley, Karen S.

    2007-01-01

    Shape Memory Polymers (SMPs) are a class of polymers, which can undergo deformation in a flexible state at elevated temperatures, and when cooled below the glass transition temperature, while retaining their deformed shape, will enter and remain in a rigid state. Upon heating above the glass transition temperature, the shape memory polymer will return to its original, unaltered shape. SMPs have been reported to recover strains of over 400%. It is important to understand the stress and strain recovery behavior of SMPs to better develop constitutive models which predict material behavior. Initial modeling efforts did not account for large deformations beyond 25% strain. However, a model under current development is capable of describing large deformations of the material. This model considers the coexisting active (rubber) and frozen (glass) phases of the polymer, as well as the transitions between the material phases. The constitutive equations at the continuum level are established with internal state variables to describe the microstructural changes associated with the phase transitions. For small deformations, the model reduces to a linear model that agrees with those reported in the literature. Thermomechanical characterization is necessary for the development, calibration, and validation of a constitutive model. The experimental data reported in this paper will assist in model development by providing a better understanding of the stress and strain recovery behavior of the material. This paper presents the testing techniques used to characterize the thermomechanical material properties of a shape memory polymer (SMP) and also presents the resulting data. An innovative visual-photographic apparatus, known as a Vision Image Correlation (VIC) system was used to measure the strain. The details of this technique will also be presented in this paper. A series of tensile tests were performed on specimens such that strain levels of 10, 25, 50, and 100% were applied to the material while it was above its glass transition temperature. After deforming the material to a specified applied strain, the material was then cooled to below the glass transition temperature (Tg) while retaining the deformed shape. Finally, the specimen was heated again to above the transition temperature, and the resulting shape recovery profile was measured. Results show that strain recovery occurs at a nonlinear rate with respect to time. Results also indicate that the ratio of recoverable strain/applied strain increases as the applied strain increases.

  9. Active material reversible attachments: shape memory polymer based

    NASA Astrophysics Data System (ADS)

    Stanford, Thomas; Barvosa-Carter, William; Browne, Alan L.; Johnson, Nancy L.

    2008-03-01

    We detail the joint concept generation and embodiment development by HRL and GMR&D of shape memory polymer (SMP) based reversible-on-demand attachments. In this initial study of active material enabled reversible-on-demand attachments, our primary focus was on hook-and-loop type fasteners. The approach followed, in broader context, was to incorporate an active material, defined as a material which changes a fundamental mechanical property upon exposure to an appropriate field, in at least one component of the hook-and-loop assembly, in this way allowing a field activated change in the stiffness (raising/lowering) and/or geometry (straightening of the hook) of the component and thus on-demand release of the attachment This paper describes the fabrication method and properties of one of the two principle classes of embodiments made during the development of the concept. This class of embodiments, which utilized thermally activated shape memory polymer materials, was shown to exhibit pull-off forces similar to conventional "non-active" hook-and-loop fasteners, and significantly, as desired, was reversible with a reduction in the pull-off force of a factor of ~100. This study was thus successful in demonstrating the feasibility of a thermally activated SMP based reversible-on-demand distributed attachment.

  10. Post-Polymerization Crosslinked Polyurethane Shape-Memory Polymers

    PubMed Central

    Hearon, K.; Gall, K.; Ware, T.; Maitland, D. J.; Bearinger, J. P.; Wilson, T. S.

    2011-01-01

    Novel urethane shape-memory polymers (SMPs) of significant industrial relevance have been synthesized and characterized. Chemically crosslinked SMPs have traditionally been made in a one-step polymerization of monomers and crosslinking agents. However, these new post-polymerization crosslinked SMPs can be processed into complex shapes by thermoplastic manufacturing methods and later crosslinked by heat exposure or by electron beam irradiation. Several series of linear, olefinic urethane polymers were made from 2-butene-1,4-diol, other saturated diols, and various aliphatic diisocyanates. These thermoplastics were melt-processed into desired geometries and thermally crosslinked at 200C or radiation crosslinked at 50 kGy. The SMPs were characterized by solvent swelling and extraction, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile testing, and qualitative shape-recovery analysis. Swelling and DMA results provided concrete evidence of chemical crosslinking, and further characterization revealed that the urethanes had outstanding mechanical properties. Key properties include tailorable transitions between 25 and 80C, tailorable rubbery moduli between 0.2 and 4.2 MPa, recoverable strains approaching 100%, failure strains of over 500% at Tg, and qualitative shape-recovery times of less than 12 seconds at body temperature (37C). Because of its outstanding thermo-mechanical properties, one polyurethane was selected for implementation in the design of a complex medical device. These post-polymerization crosslinked urethane SMPs are an industrially relevant class of highly processable shape-memory materials. PMID:21572577

  11. Biomedical applications of electroactive polymers and shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Lee, Seung-Ki; Lee, Sang-Jo; An, Ho-Jeong; Cha, Seung-Eun; Chang, Jun Keun; Kim, Byungkyu; Pak, James Jungho

    2002-07-01

    Among many kinds of polymer materials, electronic conductive material, that is polypyrrole, shows potential possibility for bio-relate actuator materials. However, it may be an impediment for practical use in polypyrrole actuator that polypyrrole usually requires electrolyte solution for actuation. Our first research theme is focused on this problem solving. We have investigated many kinds of solid polymer electrolyes for the substitution of electrolyte solution. Our goals are to find the stable solid electrolyte in the air, to establish the reliable fabrication process of it and to apply it for micropump application. Besides actuators, the reduction and oxidation property of polypyrrole can be exploited for active drug delivery systems by the control of structural deformation of it. We have investigated this kind of new and bio-related possibility of polypyrrole. Shape memory alloy has another possibility in the biomedical field. Due to its inherent excellent advantages as actuator materials, it can be used for micro active intravascular catheter. We have developed thin tube type bending actuator using shape memory alloy and characterized its performance by in-vivo test.

  12. Shape memory-based tunable resistivity of polymer composites

    NASA Astrophysics Data System (ADS)

    Luo, Hongsheng; Zhou, Xingdong; Ma, Yuanyuan; Yi, Guobin; Cheng, Xiaoling; Zhu, Yong; Zu, Xihong; Zhang, Nanjun; Huang, Binghao; Yu, Lifang

    2016-02-01

    A conductive composite in bi-layer structure was fabricated by embedding hybrid nanofillers, namely carbon nanotubes (CNTs) and silver nanoparticles (AgNPs), into a shape memory polyurethane (SMPU). The CNT/AgNP-SMPU composites exhibited a novel tunable conductivity which could be facially tailored in wide range via the compositions or a specifically designed thermo-mechanical shape memory programming. The morphologies of the conductive fillers and the composites were investigated by scanning electron microscope (SEM). The mechanical and thermal measurements were performed by tensile tests and differential scanning calorimetry (DSC). By virtue of a specifically explored shape memory programming, the composites were stretched and fixed into different temporary states. The electrical resistivity (Rs) varied accordingly, which was able to be stabilized along with the shape fixing. Theoretical prediction based upon the tunneling model was performed. The Rs-strain curves of the composites with different compositions were well fitted. Furthermore, the relative resistivity and the Gauge factor along with the elongation were calculated. The influence of the compositions on the strain-dependent Rs was disclosed. The findings provided a new avenue to tailor the conductivity of the polymeric nano-composites by combining the composition method and a thermo-mechanical programming, which may greatly benefit the application of intelligent polymers in flexible electronics and sensors fields.

  13. Numerical simulations for microvascular shape memory polymer composites

    NASA Astrophysics Data System (ADS)

    Li, Y.; Goulbourne, N. C.

    2015-05-01

    Microvascular shape memory polymer (SMP) composites are a new class of active composites consisting of an embedded microvascular network in a SMP matrix. The microvascular network can be used to deliver thermal, chemical, electrical, and magnetic stimulation to the SMP matrix thus integrating the activation/deactivation mechanism and opening up a new functional space for active polymers. Here, we focus on thermomechanical coupling triggered through fluid transport within the polymer. A modified thermo-viscoelastic model is used to simulate the response of microvascular SMP composites. The model is developed within a finite deformation continuum mechanics framework and captures the free recovery response of the SMP composite. The present model includes two glass transition temperatures to describe the structural relaxation time and the stress relaxation time, respectively. The model results are calibrated with experimental data from the literature. Lined and unlined microvascular composites fabricated with a varying number of channels and thermal profiles were recorded by infrared camera. Using a range of thermal inputs, we calculate the corresponding free recovery response of microvascular SMP composites. We show that the response can be optimized by tailoring a number of controllable parameters including channel spacing, inlet temperature, fluid flow rate, and the heating/cooling protocol.

  14. Shape memory polymers: three-dimensional isotropic modeling

    NASA Astrophysics Data System (ADS)

    Balogun, Olaniyi; Mo, Changki

    2014-04-01

    This paper presents a comprehensive three-dimensional isotropic numerical simulation for a thermo-mechanical constitutive model of shape memory polymers (SMPs). In order to predict the thermo-mechanical behavior of SMPs, a one-dimensional rheological thermo-mechanical constitutive model is adopted, translated into a three-dimensional form and a time discrete form of the three-dimensional model is then presented. Numerical simulation of this model was developed using the UMAT subroutine capabilities of the finite element software ABAQUS. Evolution of the analysis was conducted by making use of the backward difference scheme, which was applied to all quantities within the model, including the material properties. A comparison of the numerical simulation results was carried out with the available experimental data. Numerical simulation results clearly exhibit the thermo-mechanical properties of the material which include shape fixity, shape recovery, and recovery stress. Finally, a prediction for the transverse and shear directions of the material is presented.

  15. Magnetic Resonance Flow Velocity and Temperature Mapping of a Shape Memory Polymer Foam Device

    SciTech Connect

    Small IV, W; Gjersing, E; Herberg, J L; Wilson, T S; Maitland, D J

    2008-10-29

    Interventional medical devices based on thermally responsive shape memory polymer (SMP) are under development to treat stroke victims. The goals of these catheter-delivered devices include re-establishing blood flow in occluded arteries and preventing aneurysm rupture. Because these devices alter the hemodynamics and dissipate thermal energy during the therapeutic procedure, a first step in the device development process is to investigate fluid velocity and temperature changes following device deployment. A laser-heated SMP foam device was deployed in a simplified in vitro vascular model. Magnetic resonance imaging (MRI) techniques were used to assess the fluid dynamics and thermal changes associated with device deployment. Spatial maps of the steady-state fluid velocity and temperature change inside and outside the laser-heated SMP foam device were acquired. Though non-physiological conditions were used in this initial study, the utility of MRI in the development of a thermally-activated SMP foam device has been demonstrated.

  16. An investigation of a thermally steerable electroactive polymer/shape memory polymer hybrid actuator

    NASA Astrophysics Data System (ADS)

    Ren, Kailiang; Bortolin, Robert S.; Zhang, Q. M.

    2016-02-01

    This paper investigates the thermal response of a hybrid actuator composed of an electroactive polymer (EAP) and a shape memory polymer (SMP). This study introduces the concept of using the large strain from a phase transition (ferroelectric to paraelectric phase) induced by temperature change in a poly(vinylidene fluoride-trifluoroethylene) film to tune the shape of an SMP film above its glass transition temperature (Tg). Based on the material characterization data, it is revealed that the thickness ratio of the EAP/SMP films plays a critical role in the displacement of the actuator. Further, it is also demonstrated that the displacement of the hybrid actuator can be tailored by varying the temperature, and finite element method simulation results fit well with the measurement data. This specially designed hybrid actuator shows great promise for future morphing aircraft applications.

  17. Digital memory versatility of fully ?-conjugated donor-acceptor hybrid polymers.

    PubMed

    Ko, Yong-Gi; Kim, Dong Min; Kim, Kyungtae; Jung, Sungmin; Wi, Dongwoo; Michinobu, Tsuyoshi; Ree, Moonhor

    2014-06-11

    The fully ?-conjugated donor-acceptor hybrid polymers Fl-TPA, Fl-TPA-TCNE, and Fl-TPA-TCNQ, which are composed of fluorene (Fl), triphenylamine (TPA), dimethylphenylamine, alkyne, alkyne-tetracyanoethylene (TCNE) adduct, and alkyne-7,7,8,8-tetracyanoquinodimethane (TCNQ) adduct, were synthesized. These polymers are completely amorphous in the solid film state and thermally stable up to 291-409 C. Their molecular orbital levels and band gaps vary with their compositions. The TCNE and TCNQ units, despite their electron-acceptor characteristics, were found to enhance the ?-conjugation lengths of Fl-TPA-TCNE and Fl-TPA-TCNQ (i.e., to produce red shifts in their absorption spectra and significant reductions in their band gaps). These changes are reflected in the electrical digital memory behavior of the polymers. Moreover, the TCNE and TCNQ units were found to diversify the digital memory modes and to widen the active polymer layer thickness window. In devices with aluminum top and bottom electrodes, the Fl-TPA polymer exhibits stable unipolar permanent memory behavior with high reliability. The Fl-TPA-TCNE and Fl-TPA-TCNQ devices exhibit stable unipolar permanent memory behavior as well as dynamic random access memory behavior with excellent reliability. These polymer devices were found to operate by either hole injection or hole injection along with electron injection, depending on the polymer composition. Overall, this study demonstrated that the incorporation of ?-conjugated cyano moieties, which control both the ?-conjugation length and electron-accepting power, is a sound approach for the design and synthesis of high-performance digital memory polymers. The TCNE and TCNQ polymers synthesized in this study are highly suitable active materials for the low-cost mass production of high-performance, polarity-free, programmable, volatile, and permanent memory devices that can be operated with very low power consumption, high ON/OFF current ratios, and high reliability. PMID:24779635

  18. The Holy Grail of Polymer Therapeutics for Cancer Therapy: An Overview on the Pharmacokinetics and Bio Distribution.

    PubMed

    Dyawanapelly, Sathish; Junnuthula, Vijayabhaskar Reddy; Singh, AkhileshVikram

    2015-01-01

    In recent years, multifaceted clinical benefits of polymeric therapeutics have been reported. Over the past decades, cancer has been one of the leading causes of mortality in the world. Many clinically approved chemotherapeutics encounter potential challenges against deadly cancer. Moreover, safety and efficacy of anticancer agents have been limited by undesirable pharmacokinetics and biodistribution. To address these limitations, various polymer drug conjugates are being studied and developed to improve the antitumor efficacy. Among other therapeutics, polymer therapeutics are well established platforms that circumvent anticancer therapeutics from enzymatic metabolism via direct conjugation to therapeutic molecules. Interestingly, polymer therapeutics meets an unmet need of small molecules. Further clinical study showed that polymer-drug conjugation can achieve desired pharmacokinetics and biodistribution properties of several anticancer drugs. The present retrospective review mainly enlightens the most recent preclinical and clinical studies include safety, stability, pharmacokinetic behavior and distribution of polymer therapeutics. PMID:25523548

  19. Virtual Treatment of Basilar Aneurysms Using Shape Memory Polymer Foam

    PubMed Central

    Ortega, J.M.; Hartman, J.; Rodriguez, J.N.; Maitland, D.J.

    2013-01-01

    Numerical simulations are performed on patient-specific basilar aneurysms that are treated with shape memory polymer (SMP) foam. In order to assess the post-treatment hemodynamics, two modeling approaches are employed. In the first, the foam geometry is obtained from a micro-CT scan and the pulsatile blood flow within the foam is simulated for both Newtonian and non-Newtonian viscosity models. In the second, the foam is represented as a porous media continuum, which has permeability properties that are determined by computing the pressure gradient through the foam geometry over a range of flow speeds comparable to those of in vivo conditions. Virtual angiography and additional post-processing demonstrate that the SMP foam significantly reduces the blood flow speed within the treated aneurysms, while eliminating the high-frequency velocity fluctuations that are present within the pre-treatment aneurysms. An estimation of the initial locations of thrombus formation throughout the SMP foam is obtained by means of a low fidelity thrombosis model that is based upon the residence time and shear rate of blood. The Newtonian viscosity model and the porous media model capture similar qualitative trends, though both yield a smaller volume of thrombus within the SMP foam. PMID:23329002

  20. Virtual Treatment of Basilar Aneurysms Using Shape Memory Polymer Foam

    NASA Astrophysics Data System (ADS)

    Ortega, J. M.; Hartman, J.; Rodriguez, J. N.; Maitland, D. J.

    2012-11-01

    Numerical simulations are performed on patient-specific basilar aneurysms that are treated with shape memory polymer (SMP) foam. In order to assess the post-treatment hemodynamics, two modeling approaches are employed. In the first, the foam geometry is obtained from a micro-CT scan and the pulsatile blood flow within the foam is simulated for both Newtonian and non-Newtonian viscosity models. In the second, the foam is represented as a porous media continuum, which has permeability properties that are determined by computing the pressure gradient through the foam geometry over a range of flow speeds comparable to those of in vivo conditions. Virtual angiography and additional post-processing demonstrate that the SMP foam significantly reduces the blood flow speed within the treated aneurysms, while eliminating the high-frequency velocity fluctuations that are present prior to treatment. A prediction of the initial locations of thrombus formation throughout the SMP foam is obtained by means of a low fidelity thrombosis model that is based upon the residence time and shear rate of blood. The two modeling approaches capture similar qualitative trends for the initial locations of thrombus within the SMP foam.

  1. Micro devices using shape memory polymer patches for mated connections

    DOEpatents

    Lee, Abraham P. (Walnut Creek, CA); Fitch, Joseph P. (Livermore, CA)

    2000-01-01

    A method and micro device for repositioning or retrieving miniature devices located in inaccessible areas, such as medical devices (e.g., stents, embolic coils, etc.) located in a blood vessel. The micro repositioning or retrieving device and method uses shape memory polymer (SMP) patches formed into mating geometries (e.g., a hoop and a hook) for re-attachment of the deposited medical device to a catheter or guidewire. For example, SMP or other material hoops are formed on the medical device to be deposited in a blood vessel, and SMP hooks are formed on the micro device attached to a guidewire, whereby the hooks on the micro device attach to the hoops on the medical device, or vice versa, enabling deposition, movement, re-deposit, or retrieval of the medical device. By changing the temperature of the SMP hooks, the hooks can be attached to or released from the hoops located on the medical device. An exemplary method for forming the hooks and hoops involves depositing a sacrificial thin film on a substrate, patterning and processing the thin film to form openings therethrough, depositing or bonding SMP materials in the openings so as to be attached to the substrate, and removing the sacrificial thin film.

  2. Component assembly with shape memory polymer fastener for microrobots

    NASA Astrophysics Data System (ADS)

    Kim, Ji-Suk; Lee, Dae-Young; Koh, Je-Sung; Jung, Gwang-Pil; Cho, Kyu-Jin

    2014-01-01

    Adhesives are generally used for the assembly of microrobots, whereas bolts, screws, or rivets are used for larger robots. Although adhesives are easy to apply, lightweight, and small, they cannot be used for repeated assembly and disassembly of parts. In this paper, we present a novel microfastener composed of a polyurethane-based shape memory polymer (SMP) that is lightweight and small but that is easily detached for disassembly. This was achieved by using the shape recovery and modulus change of the SMP. A sheet of macromolded SMP was laser machined into an I-beam-shaped rivet, and notches were added to the structure to prevent stress concentration. Pull-off tests showed that, as the notch radius increased, the disengagement strength of the rivet fastener decreased and the reusability increased. Through the elastoplastic model, a single SMP rivet was calculated to have maximum disengagement strength of 150 N cm-2 in the elastic range, depending on the notch radius. The fasteners were applied to a jumping microrobot. The legs and body were assembled with ten fasteners, which showed no permanent deformation after impact during jumping movements. The legs were easily replaced with ones of different stiffness by heating the engaged sites to make the fasteners compliant and detachable. The proposed detachable SMP microfasteners are particularly useful for testing the isolated performance of microrobot components to determine the optimal designs for these components.

  3. Self-Deploying Trusses Containing Shape-Memory Polymers

    NASA Technical Reports Server (NTRS)

    Schueler, Robert M.

    2008-01-01

    Composite truss structures are being developed that can be compacted for stowage and later deploy themselves to full size and shape. In the target applications, these smart structures will precisely self-deploy and support a large, lightweight space-based antenna. Self-deploying trusses offer a simple, light, and affordable alternative to articulated mechanisms or inflatable structures. The trusses may also be useful in such terrestrial applications as variable-geometry aircraft components or shelters that can be compacted, transported, and deployed quickly in hostile environments. The truss technology uses high-performance shape-memory-polymer (SMP) thermoset resin reinforced with fibers to form a helical composite structure. At normal operating temperatures, the truss material has the structural properties of a conventional composite. This enables truss designs with required torsion, bending, and compression stiffness. However, when heated to its designed glass transition temperature (Tg), the SMP matrix acquires the flexibility of an elastomer. In this state, the truss can be compressed telescopically to a configuration encompassing a fraction of its original volume. When cooled below Tg, the SMP reverts to a rigid state and holds the truss in the stowed configuration without external constraint. Heating the materials above Tg activates truss deployment as the composite material releases strain energy, driving the truss to its original memorized configuration without the need for further actuation. Laboratory prototype trusses have demonstrated repeatable self-deployment cycles following linear compaction exceeding an 11:1 ratio (see figure).

  4. Method for loading shape memory polymer gripper mechanisms

    DOEpatents

    Lee, Abraham P. (Walnut Creek, CA); Benett, William J. (Livermore, CA); Schumann, Daniel L. (Concord, CA); Krulevitch, Peter A. (Pleasanton, CA); Fitch, Joseph P. (Livermore, CA)

    2002-01-01

    A method and apparatus for loading deposit material, such as an embolic coil, into a shape memory polymer (SMP) gripping/release mechanism. The apparatus enables the application of uniform pressure to secure a grip by the SMP mechanism on the deposit material via differential pressure between, for example, vacuum within the SMP mechanism and hydrostatic water pressure on the exterior of the SMP mechanism. The SMP tubing material of the mechanism is heated to above the glass transformation temperature (Tg) while reshaping, and subsequently cooled to below Tg to freeze the shape. The heating and/or cooling may, for example, be provided by the same water applied for pressurization or the heating can be applied by optical fibers packaged to the SMP mechanism for directing a laser beam, for example, thereunto. At a point of use, the deposit material is released from the SMP mechanism by reheating the SMP material to above the temperature Tg whereby it returns to its initial shape. The reheating of the SMP material may be carried out by injecting heated fluid (water) through an associated catheter or by optical fibers and an associated beam of laser light, for example.

  5. A Processable Shape Memory Polymer System for Biomedical Applications.

    PubMed

    Hearon, Keith; Wierzbicki, Mark A; Nash, Landon D; Landsman, Todd L; Laramy, Christine; Lonnecker, Alexander T; Gibbons, Michael C; Ur, Sarah; Cardinal, Kristen O; Wilson, Thomas S; Wooley, Karen L; Maitland, Duncan J

    2015-06-24

    Polyurethane shape memory polymers (SMPs) with tunable thermomechanical properties and advanced processing capabilities are synthesized, characterized, and implemented in the design of a microactuator medical device prototype. The ability to manipulate glass transition temperature (Tg ) and crosslink density in low-molecular weight aliphatic thermoplastic polyurethane SMPs is demonstrated using a synthetic approach that employs UV catalyzed thiol-ene "click" reactions to achieve postpolymerization crosslinking. Polyurethanes containing varying C=C functionalization are synthesized, solution blended with polythiol crosslinking agents and photoinitiator and subjected to UV irradiation, and the effects of number of synthetic parameters on crosslink density are reported. Thermomechanical properties are highly tunable, including glass transitions tailorable between 30 and 105 °C and rubbery moduli tailorable between 0.4 and 20 MPa. This new SMP system exhibits high toughness for many formulations, especially in the case of low crosslink density materials, for which toughness exceeds 90 MJ m(-3) at select straining temperatures. To demonstrate the advanced processing capability and synthetic versatility of this new SMP system, a laser-actuated SMP microgripper device for minimally invasive delivery of endovascular devices is fabricated, shown to exhibit an average gripping force of 1.43 ± 0.37 N and successfully deployed in an in vitro experimental setup under simulated physiological conditions. PMID:25925212

  6. Chromogenic Photonic Crystals Enabled by Novel Vapor-Responsive Shape-Memory Polymers.

    PubMed

    Fang, Yin; Ni, Yongliang; Choi, Baeck; Leo, Sin-Yen; Gao, Jian; Ge, Beverly; Taylor, Curtis; Basile, Vito; Jiang, Peng

    2015-06-24

    A new type of shape-memory polymer (SMP) is developed by integrating scientific principles drawn from two disparate fields: the fast-growing photonic crystal and SMP technologies. This new SMP enables room-temperature operation for the entire shape-memory cycle and instantaneous shape recovery triggered by exposure to a variety of organic vapors. PMID:25981680

  7. Anomalous polymer dynamics is non-Markovian: memory effects and the generalized Langevin equation formulation

    NASA Astrophysics Data System (ADS)

    Panja, Debabrata

    2010-06-01

    Any first course on polymer physics teaches that the dynamics of a tagged monomer of a polymer is anomalously subdiffusive, i.e., the mean-square displacement of a tagged monomer increases as tα for some α < 1 until the terminal relaxation time τ of the polymer. Beyond time τ the motion of the tagged monomer becomes diffusive. Classical examples of anomalous dynamics in polymer physics are single polymeric systems, such as phantom Rouse, self-avoiding Rouse, self-avoiding Zimm, reptation, translocation through a narrow pore in a membrane, and many-polymeric systems such as polymer melts. In this pedagogical paper I report that all these instances of anomalous dynamics in polymeric systems are robustly characterized by power-law memory kernels within a unified generalized Langevin equation (GLE) scheme, and therefore are non-Markovian. The exponents of the power-law memory kernels are related to the relaxation response of the polymers to local strains, and are derived from the equilibrium statistical physics of polymers. The anomalous dynamics of a tagged monomer of a polymer in these systems is then reproduced from the power-law memory kernels of the GLE via the fluctuation-dissipation theorem (FDT). Using this GLE formulation I further show that the characteristics of the drifts caused by a (weak) applied field on these polymeric systems are also obtained from the corresponding memory kernels.

  8. The future orientation of constructive memory: an evolutionary perspective on therapeutic hypnosis and brief psychotherapy.

    PubMed

    Rossi, Ernest; Erickson-Klein, Roxanna; Rossi, Kathryn

    2008-04-01

    We explore a new distinction between the future, prospective memory system being investigated in current neuroscience and the past, retrospective memory system, which was the original theoretical foundation of therapeutic hypnosis, classical psychoanalysis, and psychotherapy. We then generalize a current evolutionary theory of sleep and dreaming, which focuses on the future, prospective memory system, to conceptualize a new evolutionary perspective on therapeutic hypnosis and brief psychotherapy. The implication of current neuroscience research is that activity-dependent gene expression and brain plasticity are the psychobiological basis of adaptive behavior, consciousness, and creativity in everyday life as well as psychotherapy. We summarize a case illustrating how this evolutionary perspective can be used to quickly resolve problems with past obstructive procrastination in school to facilitate current and future academic success. PMID:18524301

  9. Reconfigurable photonic crystals enabled by pressure-responsive shape-memory polymers.

    PubMed

    Fang, Yin; Ni, Yongliang; Leo, Sin-Yen; Taylor, Curtis; Basile, Vito; Jiang, Peng

    2015-01-01

    Smart shape-memory polymers can memorize and recover their permanent shape in response to an external stimulus (for example, heat). They have been extensively exploited for a wide spectrum of applications ranging from biomedical devices to aerospace morphing structures. However, most of the existing shape-memory polymers are thermoresponsive and their performance is hindered by heat-demanding programming and recovery steps. Although pressure is an easily adjustable process variable such as temperature, pressure-responsive shape-memory polymers are largely unexplored. Here we report a series of shape-memory polymers that enable unusual 'cold' programming and instantaneous shape recovery triggered by applying a contact pressure at ambient conditions. Moreover, the interdisciplinary integration of scientific principles drawn from two disparate fields--the fast-growing photonic crystal and shape-memory polymer technologies--enables fabrication of reconfigurable photonic crystals and simultaneously provides a simple and sensitive optical technique for investigating the intriguing shape-memory effects at nanoscale. PMID:26074349

  10. Reconfigurable photonic crystals enabled by pressure-responsive shape-memory polymers

    NASA Astrophysics Data System (ADS)

    Fang, Yin; Ni, Yongliang; Leo, Sin-Yen; Taylor, Curtis; Basile, Vito; Jiang, Peng

    2015-06-01

    Smart shape-memory polymers can memorize and recover their permanent shape in response to an external stimulus (for example, heat). They have been extensively exploited for a wide spectrum of applications ranging from biomedical devices to aerospace morphing structures. However, most of the existing shape-memory polymers are thermoresponsive and their performance is hindered by heat-demanding programming and recovery steps. Although pressure is an easily adjustable process variable such as temperature, pressure-responsive shape-memory polymers are largely unexplored. Here we report a series of shape-memory polymers that enable unusual `cold' programming and instantaneous shape recovery triggered by applying a contact pressure at ambient conditions. Moreover, the interdisciplinary integration of scientific principles drawn from two disparate fields--the fast-growing photonic crystal and shape-memory polymer technologies--enables fabrication of reconfigurable photonic crystals and simultaneously provides a simple and sensitive optical technique for investigating the intriguing shape-memory effects at nanoscale.

  11. Reconfigurable photonic crystals enabled by pressure-responsive shape-memory polymers

    PubMed Central

    Fang, Yin; Ni, Yongliang; Leo, Sin-Yen; Taylor, Curtis; Basile, Vito; Jiang, Peng

    2015-01-01

    Smart shape-memory polymers can memorize and recover their permanent shape in response to an external stimulus (for example, heat). They have been extensively exploited for a wide spectrum of applications ranging from biomedical devices to aerospace morphing structures. However, most of the existing shape-memory polymers are thermoresponsive and their performance is hindered by heat-demanding programming and recovery steps. Although pressure is an easily adjustable process variable such as temperature, pressure-responsive shape-memory polymers are largely unexplored. Here we report a series of shape-memory polymers that enable unusual cold' programming and instantaneous shape recovery triggered by applying a contact pressure at ambient conditions. Moreover, the interdisciplinary integration of scientific principles drawn from two disparate fieldsthe fast-growing photonic crystal and shape-memory polymer technologiesenables fabrication of reconfigurable photonic crystals and simultaneously provides a simple and sensitive optical technique for investigating the intriguing shape-memory effects at nanoscale. PMID:26074349

  12. Modified shape memory cyanate polymers with a wide range of high glass transition temperatures

    NASA Astrophysics Data System (ADS)

    Xie, Fang; Huang, Longnan; Liu, Yanju; Leng, Jinsong

    2012-04-01

    Shape memory cyanate polymers (SMCPs) are a new kind of smart materials, which have huge development potential and a promising future. A series of shape memory cyanate polymers were prepared by cyanate ester and varying content of a linear modifier. The thermal properties of the SMCPs were investigated by Differential Scanning Calorimetry (DSC), Thermal Gravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA). The SMCPs we prepared have high glass transition temperature and show good heat resistance. The glass transition temperature Tg can be adjusted from 156.9°C to 259.6°C with the modifier. The initial temperature of thermal decomposition comes up to 300°C, which is enough high for the application in aerospace fields. The shape memory polymer we prepared shows a good shape memory effect, as the shape recovery time is less than 65s and the shape recovery rate reaches 95%.

  13. Self-assembly of Nanopatterns on Shape Memory Polymer Substrates

    NASA Astrophysics Data System (ADS)

    Chen, Zhongbi

    Periodic surface nanostructures provide unique acoustic, electronic, optical and mechanical properties, with potential applications to metamaterials, sensors, catalysis, medicine, etc. However, assembling nanometer scale constituents into engineering scale components or devices poses tremendous challenges such as cost reduction and scalability. In this work, we will introduce a novel directed self-assembly method that has the potential to address these challenges by forming unidirectional micro- and nano-wrinkles on engineering scale polymer substrates. The approach utilizes a smart material, shape memory polymer (SMP), as the substrate in a bi-layer thin-film/substrate system. With a specially-designed programming scheme, the SMP substrate can retract in one direction while expand in the perpendicular direction in a heating process. Consequently, the thin film corrugates and the wrinkling patterns are aligned. A parametric study that investigates how the system parameters influence the surface topology will be presented. Besides wrinkles, surface defects that occurred concurrently were also observed. We will present a progressive damage scheme and a microdomain-based model to understand and possibly help preventing the formation of defects. In addition, this work will also address our efforts in shrinking the wrinkle feature size from several microns to the tens of nanometer range. Two methods, through which the minimum wrinkle wavelength was reduced from one micron to 300 nm and further down to 35 nm will be elaborated. Such aligned wrinkles whose wavelength spanning two orders of magnitude from as small as 35 nm to as large as 5 mum will open up avenues for numerous exciting applications. The application of using the self-assembled wrinkled surface as the back-reflector in solar cells to improve the power conversion efficiency will be discussed as a case study. The long-term stability of the wrinkle topology, which is essential to efficiency boost will be examined through a viscoelastic model. Another application of using wrinkled surfaces as templates to obtain one-dimensional nanoparticle arrays will be demonstrated. This complete bottom-up approach is simple, cost-effective and has the potential of large-scale fabrication. It is also expected to bring us much closer to transforming nanostructures into real products.

  14. Reversible shape memory of nanoscale deformations in inherently conducting polymers without reprogramming.

    PubMed

    Higgins, Michael J; Grosse, Willo; Wagner, Klaudia; Molino, Paul J; Wallace, Gordon G

    2011-04-01

    By using inherently conducting polymers, we introduce new shape memory functionality for stimuli-responsive polymers. The shape memory process is unique in that it utilizes electrochemical control of the polymer redox state to conceal, and temporarily store, preformed nanoscale surface patterns, which can later be recalled. Unlike classical thermoset and thermoplastic shape memory polymers, the electrochemical control does not completely perturb the low entropy state of the deformed polymer chains, thus enabling the concept of reversible transition between the permanent and temporary shapes. This is demonstrated using electrochemical-atomic force microscopy/quartz crystal microbalance to characterize the modulation of nanoscale deformations in electroactive polybithiophene films. Experimental results reveal that cation/solvent exchange with the electrolyte and its effect on reconfiguration of the film structure is the mechanism behind the process. In addition to incorporating conductive properties into shape-memory polymers, the ability to reversibly modulate surface nanopatterns in a liquid environment is also of significant interest in tribology and biointerface applications. PMID:21401135

  15. Therapeutic Intervention of Learning and Memory Decays by Salidroside Stimulation of Neurogenesis in Aging.

    PubMed

    Jin, Huijuan; Pei, Lei; Shu, Xiaogang; Yang, Xin; Yan, Tianhua; Wu, Yan; Wei, Na; Yan, Honglin; Wang, Shan; Yao, Chengye; Liu, Dan; Tian, Qing; Wang, Lin; Lu, Youming

    2016-03-01

    Cognition in all mammals including human beings declines during aging. The cellular events responsible for this decay involve a reduction of neurogenesis in the dentate gyrus. Here, we show that treatment with a nature product from a traditional Chinese medicine, namely salidroside restores the capacity of the dentate gyrus to generate new neurons and intercepts learning and memory decays in mice during aging. We uncover that new neurons in aging mice have functional features of an adult granule neuron by forming excitatory synapses with their putative targeting neurons. Genetic inhibition of synaptic transmission from new neurons abolishes the therapeutic effects of salidroside in behavioral tests. We also identify that salidroside targets CREB transcription for the survival of new neurons in the dentate gyrus of old mice. Thus, salidroside is therapeutically effective against learning and memory decays via stimulation of CREB-dependent functional neurogenesis in aging. PMID:25520005

  16. Shape memory composites based on glass-fibre-reinforced poly(ethylene)-like polymers

    NASA Astrophysics Data System (ADS)

    Cuevas, J. M.; Rubio, R.; Laza, J. M.; Vilas, J. L.; Rodriguez, M.; Len, L. M.

    2012-03-01

    The mechanical response of a series of semicrystalline shape memory polymers was considerably enhanced by incorporating short glass fibres without modifying the thermo-responsive actuation based on balanced crystallinity and elasticity. The effect of different fractions of inorganic reinforcement on thermo-mechanical properties was evaluated using different instrument techniques such as differential scanning calorimetry (DSC), thermogravimetry (TGA), dynamic mechanical thermal analysis (DMTA) and three-point flexural tests. Moreover, we studied the inorganic reinforcement influence on the shape memory actuation capabilities by thermo-mechanical bending cycle experiments. As demonstrated, the manufactured polymer composites showed excellent shape memory capacities, similar to neat active polymer matrices, but with outstanding improvements in static and recovering mechanical performance.

  17. Bioactive factor delivery strategies from engineered polymer hydrogels for therapeutic medicine

    PubMed Central

    Nguyen, Minh Khanh; Alsberg, Eben

    2014-01-01

    Polymer hydrogels have been widely explored as therapeutic delivery matrices because of their ability to present sustained, localized and controlled release of bioactive factors. Bioactive factor delivery from injectable biopolymer hydrogels provides a versatile approach to treat a wide variety of diseases, to direct cell function and to enhance tissue regeneration. The innovative development and modification of both natural-(e.g., alginate (ALG), chitosan, hyaluronic acid (HA), gelatin, heparin (HEP), etc.) and synthetic-(e.g., polyesters, polyethyleneimine (PEI), etc.) based polymers has resulted in a variety of approaches to design drug delivery hydrogel systems from which loaded therapeutics are released. This review presents the state-of-the-art in a wide range of hydrogels that are formed though self-assembly of polymers and peptides, chemical crosslinking, ionic crosslinking and biomolecule recognition. Hydrogel design for bioactive factor delivery is the focus of the first section. The second section then thoroughly discusses release strategies of payloads from hydrogels for therapeutic medicine, such as physical incorporation, covalent tethering, affinity interactions, on demand release and/or use of hybrid polymer scaffolds, with an emphasis on the last 5 years. PMID:25242831

  18. Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers

    NASA Astrophysics Data System (ADS)

    Mohr, R.; Kratz, K.; Weigel, T.; Lucka-Gabor, M.; Moneke, M.; Lendlein, A.

    2006-03-01

    In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, Tswitch. If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(-caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25C resulted in temporary fixation of the mechanical deformation by 50-60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f = 258 kHz; H = 30 kAm-1). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature. nanocomposite | shape-memory polymer | stimuli-sensitive polymer


  19. Magnetic resonance flow velocity and temperature mapping of a shape memory polymer foam device

    PubMed Central

    2009-01-01

    Background Interventional medical devices based on thermally responsive shape memory polymer (SMP) are under development to treat stroke victims. The goals of these catheter-delivered devices include re-establishing blood flow in occluded arteries and preventing aneurysm rupture. Because these devices alter the hemodynamics and dissipate thermal energy during the therapeutic procedure, a first step in the device development process is to investigate fluid velocity and temperature changes following device deployment. Methods A laser-heated SMP foam device was deployed in a simplified in vitro vascular model. Magnetic resonance imaging (MRI) techniques were used to assess the fluid dynamics and thermal changes associated with device deployment. Results Spatial maps of the steady-state fluid velocity and temperature change inside and outside the laser-heated SMP foam device were acquired. Conclusions Though non-physiological conditions were used in this initial study, the utility of MRI in the development of a thermally-activated SMP foam device has been demonstrated. PMID:20043833

  20. Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers

    PubMed Central

    Mohr, R.; Kratz, K.; Weigel, T.; Lucka-Gabor, M.; Moneke, M.; Lendlein, A.

    2006-01-01

    In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, Tswitch. If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(?-caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25C resulted in temporary fixation of the mechanical deformation by 5060%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f = 258 kHz; H = 30 kAm?1). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature. PMID:16537442

  1. Influence of strain rates on the mechanical behaviors of shape memory polymer

    NASA Astrophysics Data System (ADS)

    Guo, Xiaogang; Liu, Liwu; Zhou, Bo; Liu, Yanju; Leng, Jinsong

    2015-09-01

    In the last few decades, shape memory polymers have demonstrated their major advantages of extremely high recovery strain, low density and low cost. Generally, the mechanical behavior of shape memory polymers is strongly dependent on the loading strain rates. Uniaxial tensile experiments were conducted on one kind of typical shape memory polymer (epoxy) at several different temperatures (348 K, 358 K, 368 K and 378 K) and true strain rates (0.25% s-1, 1.25% s-1 and 2.5% s-1). Thus, the influence of strain rate and temperature on the mechanical behavior of epoxy, in particular on the post yield stresses and the strain hardening behavior, were investigated through this experimental study. Based on our previous work Guo (2014 Smart Mater. Struct. 23 105019), a simplified model which can explain the shape memory effect of epoxy was proposed to predict the strain hardening behavior of the shape memory polymer. Based on the suggestion of Rault (1998 J. Non-Cryst. Solids 235-7 737-41), a linear compensation model was introduced to indicate the change in yield stresses with the increase of strain rate and temperature. Finally, the new model predictions for the true strain and stress behavior of epoxy were compared with the experimental results.

  2. A molecular dynamics investigation of the deformation mechanism and shape memory effect of epoxy shape memory polymers

    NASA Astrophysics Data System (ADS)

    Yang, Hua; Wang, ZhengDao; Guo, YaFang; Shi, XingHua

    2016-03-01

    Following deformation, thermally induced shape memory polymers (SMPs) have the ability to recover their original shape with a change in temperature. In this work, the thermomechanical properties and shape memory behaviors of three types of epoxy SMPs with varying curing agent contents were investigated using a molecular dynamics (MD) method. The mechanical properties under uniaxial tension at different temperatures were obtained, and the simulation results compared reasonably with experimental data. In addition, in a thermomechanical cycle, ideal shape memory effects for the three types of SMPs were revealed through the shape frozen and shape recovery responses at low and high temperatures, respectively, indicating that the recovery time is strongly influenced by the ratio of E-51 to 4,4'-Methylenedianiline.

  3. Investigation of interfacial shear stresses, shape fixity, and actuation strain in composites incorporating shape memory polymers and shape memory alloys

    NASA Astrophysics Data System (ADS)

    Park, Jungkyu; Headings, Leon; Dapino, Marcelo; Baur, Jeffery; Tandon, Gyaneshwar

    2015-03-01

    Shape memory composites (SMCs) based on shape memory alloys (SMAs) and shape memory polymers (SMPs) allow many design possibilities due to their controllable temperature-dependent mechanical properties. The complementary characteristics of SMAs and SMPs can be utilized in systems with shape recovery created by the SMA and shape fixity provided by the SMP. In this research, three SMC operating regimes are identified and the behavior of SMC structures is analyzed by focusing on composite shape fixity and interfacial stresses. Analytical models show that SMPs can be used to adequately fix the shape of SMA actuators and springs. COMSOL finite element simulations are in agreement with analytical expressions for shape fixity and interfacial stresses. Analytical models are developed for an end-coupled linear SMP-SMA two-way actuator and the predicted strain is shown to be in good agreement with experimental test results.

  4. Therapeutic polymers for dental adhesives: Loading resins with bio-active components

    PubMed Central

    Imazato, Satoshi; Ma, Sai; Chen, Ji-hua; Xu, Hockin H.K.

    2014-01-01

    Objectives Many recent adhesives on the market exhibit reasonable clinical performance. Future innovations in adhesive materials should therefore seek out novel properties rather than simply modifying existing technologies. It is proposed that adhesive materials that are “bio-active” could contribute to better prognosis of restorative treatments. Methods This review examines the recent approaches used to achieve therapeutic polymers for dental adhesives by incorporating bio-active components. A strategy to maintain adhesive restorations is the focus of this paper. Results Major trials on therapeutic dental adhesives have looked at adding antibacterial activities or remineralization effects. Applications of antibacterial resin monomers based on quaternary ammonium compounds have received much research attention, and the loading of nano-sized bioactive particles or multiple ion-releasing glass fillers have been perceived as advantageous since they are not expected to influence the mechanical properties of the carrier polymer. Significance The therapeutic polymer approaches described here have the potential to provide clinical benefits. However, not many technological applications in this category have been successfully commercialized. Clinical evidence as well as further advancement of these technologies can be a driving force to make these new types of materials clinically available. PMID:23899387

  5. Electrochromic conductive polymer fuses for hybrid organic/inorganic semiconductor memories

    NASA Astrophysics Data System (ADS)

    Mller, Sven; Forrest, Stephen R.; Perlov, Craig; Jackson, Warren; Taussig, Carl

    2003-12-01

    We demonstrate a nonvolatile, write-once-read-many-times (WORM) memory device employing a hybrid organic/inorganic semiconductor architecture consisting of thin film p-i-n silicon diode on a stainless steel substrate integrated in series with a conductive polymer fuse. The nonlinearity of the silicon diodes enables a passive matrix memory architecture, while the conductive polyethylenedioxythiophene:polystyrene sulfonic acid polymer serves as a reliable switch with fuse-like behavior for data storage. The polymer can be switched at 2 ?s, resulting in a permanent decrease of conductivity of the memory pixel by up to a factor of 103. The switching mechanism is primarily due to a current and thermally dependent redox reaction in the polymer, limited by the double injection of both holes and electrons. The switched device performance does not degrade after many thousand read cycles in ambient at room temperature. Our results suggest that low cost, organic/inorganic WORM memories are feasible for light weight, high density, robust, and fast archival storage applications.

  6. Unconstrained Recovery Characterization of Shape-Memory Polymer Networks for Cardiovascular Applications

    PubMed Central

    Yakacki, Christopher M.; Shandas, Robin; Lanning, Craig; Rech, Bryan; Eckstein, Alex; Gall, Ken

    2009-01-01

    Shape-memory materials have been proposed in biomedical device design due to their ability to facilitate minimally invasive surgery and recover to a predetermined shape in-vivo. Use of the shape-memory effect in polymers is proposed for cardiovascular stent interventions to reduce the catheter size for delivery and offer highly controlled and tailored deployment at body temperature. Shape-memory polymer networks were synthesized via photopolymerization of tert-butyl acrylate and poly (ethylene glycol) dimethacrylate to provide precise control over the thermomechanical response of the system. The free recovery response of the polymer stents at body temperature was studied as a function of glass transition temperature (Tg), crosslink density, geometrical perforation, and deformation temperature, all of which can be independently controlled. Room temperature storage of the stents was shown to be highly dependent on Tg and crosslink density. The pressurized response of the stents is also demonstrated to depend on crosslink density. This polymer system exhibits a wide range of shape-memory and thermomechanical responses to adapt and meet specific needs of minimally invasive cardiovascular devices. PMID:17296222

  7. Shape Memory as a Process: Optimizing Polymer Design for Shape Recovery

    NASA Astrophysics Data System (ADS)

    Vaia, Richard; Koerner, Hilmar; Lee, Kyungmin; Strong, Robert; Smith, Mattew; Wang, Huabin; White, Tim; Tan, Loon-Seng

    2012-02-01

    Shape memory is a process that enables the reversible storage and recovery of mechanical energy through a change in shape. Polymers provide a unique alternative to kinematic designs and other materials (e.g. metallic alloys) for applications requiring large deformation and novel control options. The effect control of storage and relaxation of strain energy associated with chain deformation depends on the nonlinear visco-elasitc behavior and glassy dynamics of the polymer network. Considering the molecular understanding of rubbery elasticity, chain entanglements in concentrated polymer liquids, affine deformation of networks, and glass fragility, heuristic guidelines can be formulated to optimize the molecular design of a polymer for shape memory. These are applied to the development of a polymer system for shape memory processes at high-temperature (200^oC). The low-crosslink density polyimide exhibits very rapid shape recovery, excellent fixity, high creep resistance, and good cyclability. Furthermore, the molecular design affords a very narrow temperature range for programming and triggering shape change that can also be accessed by photo-isomerization of the cross-link nodes.

  8. COMMUNICATION: Toward a self-deploying shape memory polymer neuronal electrode

    NASA Astrophysics Data System (ADS)

    Sharp, Andrew A.; Panchawagh, Hrishikesh V.; Ortega, Alicia; Artale, Ryan; Richardson-Burns, Sarah; Finch, Dudley S.; Gall, Ken; Mahajan, Roop L.; Restrepo, Diego

    2006-12-01

    The widespread application of neuronal probes for chronic recording of brain activity and functional stimulation has been slow to develop partially due to long-term biocompatibility problems with existing metallic and ceramic probes and the tissue damage caused during probe insertion. Stiff probes are easily inserted into soft brain tissue but cause astrocytic scars that become insulating sheaths between electrodes and neurons. In this communication, we explore the feasibility of a new approach to the composition and implantation of chronic electrode arrays. We demonstrate that softer polymer-based probes can be inserted into the olfactory bulb of a mouse and that slow insertion of the probes reduces astrocytic scarring. We further present the development of a micromachined shape memory polymer probe, which provides a vehicle to self-deploy an electrode at suitably slow rates and which can provide sufficient force to penetrate the brain. The deployment rate and composition of shape memory polymer probes can be tailored by polymer chemistry and actuator design. We conclude that it is feasible to fabricate shape memory polymer-based electrodes that would slowly self-implant compliant conductors into the brain, and both decrease initial trauma resulting from implantation and enhance long-term biocompatibility for long-term neuronal measurement and stimulation.

  9. Ultra-low power, highly uniform polymer memory by inserted multilayer graphene electrode

    NASA Astrophysics Data System (ADS)

    Jang, Byung Chul; Seong, Hyejeong; Kim, Jong Yun; Koo, Beom Jun; Kim, Sung Kyu; Yang, Sang Yoon; Gap Im, Sung; Choi, Sung-Yool

    2015-12-01

    Filament type resistive random access memory (RRAM) based on polymer thin films is a promising device for next generation, flexible nonvolatile memory. However, the resistive switching nonuniformity and the high power consumption found in the general filament type RRAM devices present critical issues for practical memory applications. Here, we introduce a novel approach not only to reduce the power consumption but also to improve the resistive switching uniformity in RRAM devices based on poly(1,3,5-trimethyl-3,4,5-trivinyl cyclotrisiloxane) by inserting multilayer graphene (MLG) at the electrode/polymer interface. The resistive switching uniformity was thereby significantly improved, and the power consumption was markedly reduced by 250 times. Furthermore, the inserted MLG film enabled a transition of the resistive switching operation from unipolar resistive switching to bipolar resistive switching and induced self-compliance behavior. The findings of this study can pave the way toward a new area of application for graphene in electronic devices.

  10. Shape memory polymer nanofibers and their composites: electrospinning, structure, performance and applications

    NASA Astrophysics Data System (ADS)

    Zhang, Fenghua; Zhang, Zhichun; Zhou, Tianyang; Liu, Yanju; Leng, Jinsong

    2015-10-01

    Shape memory polymers (SMPs) have been defined as a kind of smart materials under great investigation from academic research to industry applications. Research on SMPs and their composites, now incorporates a growing focus on nanofibers which offers new structures in microscopic level and the potential of enhanced performance of SMPs. This paper presents a comprehensive review of the development of shape memory polymer nanofibers and their composites, including the introduction of electrospinning technology, the morphology and structures of nanofibers (non-woven fibers, oriented fibers, core/shell fibers and functional particles added in the fibers), shape memory performance (thermal and mechanical properties, stimulus responsive behavior, multiple and two-way shape changing performance), as well as their potential applications in the fields of biomedical and tissue engineering.

  11. Multi-stimulus-responsive shape-memory polymer nanocomposite network cross-linked by cellulose nanocrystals.

    PubMed

    Liu, Ye; Li, Ying; Yang, Guang; Zheng, Xiaotong; Zhou, Shaobing

    2015-02-25

    In this study, we developed a thermoresponsive and water-responsive shape-memory polymer nanocomposite network by chemically cross-linking cellulose nanocrystals (CNCs) with polycaprolactone (PCL) and polyethylene glycol (PEG). The nanocomposite network was fully characterized, including the microstructure, cross-link density, water contact angle, water uptake, crystallinity, thermal properties, and static and dynamic mechanical properties. We found that the PEG[60]-PCL[40]-CNC[10] nanocomposite exhibited excellent thermo-induced and water-induced shape-memory effects in water at 37 C (close to body temperature), and the introduction of CNC clearly improved the mechanical properties of the mixture of both PEG and PCL polymers with low molecular weights. In addition, Alamar blue assays based on osteoblasts indicated that the nanocomposites possessed good cytocompatibility. Therefore, this thermoresponsive and water-responsive shape-memory nanocomposite could be potentially developed into a new smart biomaterial. PMID:25647407

  12. Experimental and modelling studies of the shape memory properties of amorphous polymer network composites

    NASA Astrophysics Data System (ADS)

    Arrieta, J. S.; Diani, J.; Gilormini, P.

    2014-09-01

    Shape memory polymer composites (SMPCs) have become an important way to leverage improvements in the development of applications featuring shape memory polymers (SMPs). In this study, an amorphous SMP matrix has been filled with different types of reinforcements. An experimental set of results is presented and then compared to three-dimensional (3D) finite-element simulations. Thermomechanical shape memory cycles were performed in uniaxial tension. The fillers effect was studied in stress-free and constrained-strain recoveries. Experimental observations indicate complete shape recovery and put in evidence the increased sensitivity of constrained length stress recoveries to the heating ramp on the tested composites. The simulations reproduced a simplified periodic reinforced composite and used a model for the matrix material that has been previously tested on regular SMPs. The latter combines viscoelasticity at finite strain and time-temperature superposition. The simulations easily allow representation of the recovery properties of a reinforced SMP.

  13. Controlled wettability based on reversible micro-cracking on a shape memory polymer surface.

    PubMed

    Han, Yu; Liu, Yuxuan; Wang, Wenxin; Leng, Jinsong; Jin, Peng

    2016-03-14

    Wettability modification on a polymer surface is of immense importance for flexible electronics and biomedical applications. Herein, controlled wettability of a styrene-based shape memory polymer has been realized by introducing micro-cracks on the polymer surface for the first time. The cracks were purposely prepared by thin metal film constrained deformation on the polymer. After the removal of the metallic film, wettability was dramatically enhanced by showing a remarkable reduction in the contact angle with water droplets from 85° to 25°. Subsequent systematic characterization techniques like XPS and SEM revealed that such observation could be attributed to the increased density of hydrophilic groups and the roughened surface. In addition, by controlling the temperature for annealing the treated polymer, the surface could be switched reversely to water-repellent. Therefore, this paper offers a smart tactic to manipulate the surface wettability of a shape memory polymer freely. The features of the controlled wettability surface such as high tenability, high stability and easy fabrication are promising for microfluidic switching and molecule/cell capture-release. PMID:26865175

  14. Estimation of aneurysm wall stresses created by treatment with a shape memory polymer foam device

    PubMed Central

    Hwang, Wonjun; Volk, Brent L.; Akberali, Farida; Singhal, Pooja; Criscione, John C.

    2012-01-01

    In this study, compliant latex thin-walled aneurysm models are fabricated to investigate the effects of expansion of shape memory polymer foam. A simplified cylindrical model is selected for the in-vitro aneurysm, which is a simplification of a real, saccular aneurysm. The studies are performed by crimping shape memory polymer foams, originally 6 and 8 mm in diameter, and monitoring the resulting deformation when deployed into 4-mm-diameter thin-walled latex tubes. The deformations of the latex tubes are used as inputs to physical, analytical, and computational models to estimate the circumferential stresses. Using the results of the stress analysis in the latex aneurysm model, a computational model of the human aneurysm is developed by changing the geometry and material properties. The model is then used to predict the stresses that would develop in a human aneurysm. The experimental, simulation, and analytical results suggest that shape memory polymer foams have potential of being a safe treatment for intracranial saccular aneurysms. In particular, this work suggests oversized shape memory foams may be used to better fill the entire aneurysm cavity while generating stresses below the aneurysm wall breaking stresses. PMID:21901546

  15. Estimation of aneurysm wall stresses created by treatment with a shape memory polymer foam device.

    PubMed

    Hwang, Wonjun; Volk, Brent L; Akberali, Farida; Singhal, Pooja; Criscione, John C; Maitland, Duncan J

    2012-05-01

    In this study, compliant latex thin-walled aneurysm models are fabricated to investigate the effects of expansion of shape memory polymer foam. A simplified cylindrical model is selected for the in-vitro aneurysm, which is a simplification of a real, saccular aneurysm. The studies are performed by crimping shape memory polymer foams, originally 6 and 8 mm in diameter, and monitoring the resulting deformation when deployed into 4-mm-diameter thin-walled latex tubes. The deformations of the latex tubes are used as inputs to physical, analytical, and computational models to estimate the circumferential stresses. Using the results of the stress analysis in the latex aneurysm model, a computational model of the human aneurysm is developed by changing the geometry and material properties. The model is then used to predict the stresses that would develop in a human aneurysm. The experimental, simulation, and analytical results suggest that shape memory polymer foams have potential of being a safe treatment for intracranial saccular aneurysms. In particular, this work suggests oversized shape memory foams may be used to better fill the entire aneurysm cavity while generating stresses below the aneurysm wall breaking stresses. PMID:21901546

  16. Optical Input/Electrical Output Memory Elements based on a Liquid Crystalline Azobenzene Polymer.

    PubMed

    Mosciatti, Thomas; Bonacchi, Sara; Gobbi, Marco; Ferlauto, Laura; Liscio, Fabiola; Giorgini, Loris; Orgiu, Emanuele; Samorì, Paolo

    2016-03-16

    Responsive polymer materials can change their properties when subjected to external stimuli. In this work, thin films of thermotropic poly(metha)acrylate/azobenzene polymers are explored as active layer in light-programmable, electrically readable memories. The memory effect is based on the reversible modifications of the film morphology induced by the photoisomerization of azobenzene mesogenic groups. When the film is in the liquid crystalline phase, the trans → cis isomerization induces a major surface reorganization on the mesoscopic scale that is characterized by a reduction in the effective thickness of the film. The film conductivity is measured in vertical two-terminal devices in which the polymer is sandwiched between a Au contact and a liquid compliant E-GaIn drop. We demonstrate that the trans → cis isomerization is accompanied by a reversible 100-fold change in the film conductance. In this way, the device can be set in a high- or low-resistance state by light irradiation at different wavelengths. This result paves the way toward the potential use of poly(metha)acrylate/azobenzene polymer films as active layer for optical input/electrical output memory elements. PMID:26890532

  17. Preparation and characterization of shape memory composite foams with interpenetrating polymer networks

    NASA Astrophysics Data System (ADS)

    Yao, Yongtao; Zhou, Tianyang; Yang, Cheng; Liu, Yanju; Leng, Jinsong

    2016-03-01

    The present study reports a feasible approach of fabricating shape memory composite foams with an interpenetrating polymer network (IPN) based on polyurethane (PU) and shape memory epoxy resin (SMER) via a simultaneous polymerization technique. The PU component is capable of constructing a foam structure and the SMER is grafted on the PU network to offer its shape memory property in the final IPN foams. A series of IPN foams without phase separation were produced due to good compatibility and a tight chemical interaction between PU and SMER components. The relationships of the geometry of the foam cell were investigated via varying compositions of PU and SMER. The physical property and shape memory property were also evaluated. The stimulus temperature of IPN shape memory composite foams, glass temperature (Tg), could be tunable by varying the constituents and Tg of PU and SMER. The mechanism of the shape memory effect of IPN foams has been proposed. The shape memory composite foam with IPN developed in this study has the potential to extend its application field.

  18. Direct Writing of Three-Dimensional Macroporous Photonic Crystals on Pressure-Responsive Shape Memory Polymers.

    PubMed

    Fang, Yin; Ni, Yongliang; Leo, Sin-Yen; Wang, Bingchen; Basile, Vito; Taylor, Curtis; Jiang, Peng

    2015-10-28

    Here we report a single-step direct writing technology for making three-dimensional (3D) macroporous photonic crystal patterns on a new type of pressure-responsive shape memory polymer (SMP). This approach integrates two disparate fields that do not typically intersect: the well-established templating nanofabrication and shape memory materials. Periodic arrays of polymer macropores templated from self-assembled colloidal crystals are squeezed into disordered arrays in an unusual shape memory "cold" programming process. The recovery of the original macroporous photonic crystal lattices can be triggered by direct writing at ambient conditions using both macroscopic and nanoscopic tools, like a pencil or a nanoindenter. Interestingly, this shape memory disorder-order transition is reversible and the photonic crystal patterns can be erased and regenerated hundreds of times, promising the making of reconfigurable/rewritable nanooptical devices. Quantitative insights into the shape memory recovery of collapsed macropores induced by the lateral shear stresses in direct writing are gained through fundamental investigations on important process parameters, including the tip material, the critical pressure and writing speed for triggering the recovery of the deformed macropores, and the minimal feature size that can be directly written on the SMP membranes. Besides straightforward applications in photonic crystal devices, these smart mechanochromic SMPs that are sensitive to various mechanical stresses could render important technological applications ranging from chromogenic stress and impact sensors to rewritable high-density optical data storage media. PMID:26447681

  19. Anionic surfactant with hydrophobic and hydrophilic chains for nanoparticle dispersion and shape memory polymer nanocomposites.

    PubMed

    Iijima, Motoyuki; Kobayakawa, Murino; Yamazaki, Miwa; Ohta, Yasuhiro; Kamiya, Hidehiro

    2009-11-18

    An anionic surfactant comprising a hydrophilic poly(ethylene glycol) (PEG) chain, hydrophobic alkyl chain, and polymerizable vinyl group was synthesized as a capping agent of nanoparticles. TiO(2) nanoparticles modified by this surfactant were completely dispersible in various organic solvents with a wide range of polarities, such as nitriles, alcohols, ketones, and acetates. Furthermore, these particles were found to be dispersible in various polymers with different properties, such as thermosetting epoxy resins and radical polymerized poly(methylmethacrylate) (PMMA). A polymer composite of surface-modified TiO(2) nanoparticles in epoxy resins prepared by using the developed surfactant also possessed temperature-induced shape memory properties. PMID:19852463

  20. Electron Beam Crosslinked Polyurethane Shape Memory Polymers with Tunable Mechanical Properties

    PubMed Central

    Hearon, Keith; Nash, Landon D.; Volk, Brent L.; Ware, Taylor; Lewicki, James P.; Voit, Walter E.; Wilson, Thomas S.

    2014-01-01

    Novel electron beam crosslinked polyurethane shape memory polymers with advanced processing capabilities and tunable thermomechanical properties have been synthesized and characterized. We demonstrate the ability to manipulate crosslink density in order to finely tune rubbery modulus, strain capacity, ultimate tensile strength, recovery stress, and glass transition temperature. This objective is accomplished for the first time in a low-molecular-weight polymer system through the precise engineering of thermoplastic resin precursors suitable for mass thermoplastic processing. Neurovascular stent prototypes were fabricated by dip-coating and laser machining to demonstrate processability. PMID:25411531

  1. Electron Beam Crosslinked Polyurethane Shape Memory Polymers with Tunable Mechanical Properties.

    PubMed

    Hearon, Keith; Nash, Landon D; Volk, Brent L; Ware, Taylor; Lewicki, James P; Voit, Walter E; Wilson, Thomas S; Maitland, Duncan J

    2013-06-01

    Novel electron beam crosslinked polyurethane shape memory polymers with advanced processing capabilities and tunable thermomechanical properties have been synthesized and characterized. We demonstrate the ability to manipulate crosslink density in order to finely tune rubbery modulus, strain capacity, ultimate tensile strength, recovery stress, and glass transition temperature. This objective is accomplished for the first time in a low-molecular-weight polymer system through the precise engineering of thermoplastic resin precursors suitable for mass thermoplastic processing. Neurovascular stent prototypes were fabricated by dip-coating and laser machining to demonstrate processability. PMID:25411531

  2. Polymer ferroelectric field-effect memory device with SnO channel layer exhibits record hole mobility

    PubMed Central

    Caraveo-Frescas, J. A.; Khan, M. A.; Alshareef, H. N.

    2014-01-01

    Here we report for the first time a hybrid p-channel polymer ferroelectric field-effect transistor memory device with record mobility. The memory device, fabricated at 200C on both plastic polyimide and glass substrates, uses ferroelectric polymer P(VDF-TrFE) as the gate dielectric and transparent p-type oxide (SnO) as the active channel layer. A record mobility of 3.3?cm2V?1s?1, large memory window (?16?V), low read voltages (??1?V), and excellent retention characteristics up to 5000?sec have been achieved. The mobility achieved in our devices is over 10 times higher than previously reported polymer ferroelectric field-effect transistor memory with p-type channel. This demonstration opens the door for the development of non-volatile memory devices based on dual channel for emerging transparent and flexible electronic devices. PMID:24912617

  3. Viscosity-Based Constitutive Model for the Nonlinear Deformations of Shape Memory Network Polymers

    NASA Astrophysics Data System (ADS)

    Westbrook, Kristofer; Castro, Francisco; Qi, H. Jerry

    2010-03-01

    Shape memory polymers (SMP) are materials that can recover a large pre-deformed shape in response to environmental stimuli. This capability makes SMPs suitable materials for applications such as smart fabrics, biomedical devices and deployable structures. For a thermally induced amorphous SMP, the pre-deformation and recovery of the shape require the SMP to traverse its glass transition temperature (Tg) to complete the shape memory (SM) cycle. The dramatic change in viscosity (molecular chain mobility) as the temperature traverses the Tg is the underlying mechanism of the SM effect. As the temperature decreases from above to below the Tg, the material exhibits a transition from a low to high viscosity and the material relaxation increases substantially. Here, the mechanical response of an acrylate-based polymer network is characterized under various thermomechanical histories. A constitutive model is developed to capture the material behavior and implemented to predict responses of the material in specific biomedical applications.

  4. Shape Memory Polymers from Blends of Elastomers and Crystalline Small Molecules

    NASA Astrophysics Data System (ADS)

    Cavicchi, Kevin; Brostowitz, Nicole; Hukill, Brent; Fairbairn, Heather

    2015-03-01

    This talk will present work on the fabrication of shape memory polymers (SMPs) by swelling natural with molten fatty acids. By this method a SMPs with excellent shape fixity and recovery can be obtained during free recovery after uniaxial deformation to 100% strain. Experiments to measure the shape memory properties under both stress and strain controlled conditions will be reported and compared. This fabrication method offers a number of advantages for preparing SMPs. First, it utilizes natural rubber as the base material for the SMP, which capitalizes on a high performance, commodity elastomer. Second, by blending a commercial polymer with a small molecule additive no additional chemistry is needed for the preparation of the SMP. Third, this route inverts the typically processing steps by crosslinking the permanent network prior to formation of the physically crosslinked reversible network. This offers a means to potentially generate a SMP from any preformed elastomeric article.

  5. High performance shape memory polymer networks based on rigid nanoparticle cores.

    PubMed

    Xu, Jianwen; Song, Jie

    2010-04-27

    Smart materials that can respond to external stimuli are of widespread interest in biomedical science. Thermal-responsive shape memory polymers, a class of intelligent materials that can be fixed at a temporary shape below their transition temperature (T(trans)) and thermally triggered to resume their original shapes on demand, hold great potential as minimally invasive self-fitting tissue scaffolds or implants. The intrinsic mechanism for shape memory behavior of polymers is the freezing and activation of the long-range motion of polymer chain segments below and above T(trans), respectively. Both T(trans) and the extent of polymer chain participation in effective elastic deformation and recovery are determined by the network composition and structure, which are also defining factors for their mechanical properties, degradability, and bioactivities. Such complexity has made it extremely challenging to achieve the ideal combination of a T(trans) slightly above physiological temperature, rapid and complete recovery, and suitable mechanical and biological properties for clinical applications. Here we report a shape memory polymer network constructed from a polyhedral oligomeric silsesquioxane nanoparticle core functionalized with eight polyester arms. The cross-linked networks comprising this macromer possessed a gigapascal-storage modulus at body temperature and a T(trans) between 42 and 48 degrees C. The materials could stably hold their temporary shapes for > 1 year at room temperature and achieve full shape recovery

  6. Triple-Shape Memory Polymers Based on Self-Complementary Hydrogen Bonding

    PubMed Central

    Ware, Taylor; Hearon, Keith; Lonnecker, Alexander; Wooley, Karen L.; Maitland, Duncan J.; Voit, Walter

    2012-01-01

    Triple shape memory polymers (TSMPs) are a growing subset of a class of smart materials known as shape memory polymers, which are capable of changing shape and stiffness in response to a stimulus. A TSMP can change shapes twice and can fix two metastable shapes in addition to its permanent shape. In this work, a novel TSMP system comprised of both permanent covalent cross-links and supramolecular hydrogen bonding cross-links has been synthesized via a one-pot method. Triple shape properties arise from the combination of the glass transition of (meth)acrylate copolymers and the dissociation of self-complementary hydrogen bonding moieties, enabling broad and independent control of both glass transition temperature (Tg) and cross-link density. Specifically, ureidopyrimidone methacrylate and a novel monomer, ureidopyrimidone acrylate, were copolymerized with various alkyl acrylates and bisphenol A ethoxylate diacrylate. Control of Tg from 0 to 60 °C is demonstrated: concentration of hydrogen bonding moieties is varied from 0 to 40 wt %; concentration of the diacrylate is varied from 0 to 30 wt %. Toughness ranges from 0.06 to 0.14 MPa and is found to peak near 20 wt % of the supramolecular cross-linker. A widely tunable class of amorphous triple-shape memory polymers has been developed and characterized through dynamic and quasi-static thermomechanical testing to gain insights into the dynamics of supramolecular networks. PMID:22287811

  7. Constitutive model for photo-mechanical behaviors of photo-induced shape memory polymers

    NASA Astrophysics Data System (ADS)

    Long, Kevin N.; Scott, Timothy F.; Qi, H. Jerry; Dunn, Martin L.; Bowman, Christopher N.

    2009-03-01

    Light-activated polymers are an exciting class of materials that respond mechanically when irradiated at particular wavelengths. Recent demonstrations include two novel polymers developed by Scott et al (2006) and Lendlein et al (2005). In these polymers, photochemistry alters the microstructure of the cross-linked polymer network, which is further translated as light-induced deformation and when properly used light-induced shape memory effect. In this work, we develop a model framework to simulate the photomechanical response of light-activated polymer systems. This framework breaks down the observed macroscopic photomechanical phenomenon into four coupled sets of underlying physics, which occur throughout the material during irradiation and mechanical deformation. In the context of this framework, a basic photomechanical phenomenon involves simultaneously modeling photophysics, photochemistry, chemomechanical coupling, and mechanical behavior. Furthermore, network alteration are accounted for through the parallel decomposition of the cross-linked network into two components, an original network and a photochemically altered network, which allows to capture the observed photomechanical behaviors demonstrated in these materials. One of the principal strengths of this model framework is its generality as it can be applied to light activated polymer systems with fundamentally different of photophysics, photochemistry, and chemomechanical behaviors simply by choosing different field equations for the four sets of physics specific to a material system.

  8. A preliminary study on anti-irradiation performance of epoxy shape memory polymer

    NASA Astrophysics Data System (ADS)

    Wu, Xuelian; Liu, Yanju; Leng, Jinsong

    2009-07-01

    As a new class of smart material, shape memory polymer (SMP) receives more and more attention. In this paper, in addition to the fabrication of a new type of epoxy SMP, the thermo-mechanical properties of the polymer with/without gamma irradiation were investigated and compared systematically. The radiation source is Co-60 and the total dosage of radiation is 1104Gy. Changes of network structures of the polymer were investigated by Fourier Transform Infrared (FTIR) spectroscopy. The influence of gamma irradiation on thermo and mechanical properties of the polymer were investigated by Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and tensile test, respectively. Furthermore, shape recovery behaviors of the polymer before/after the irradiation were compared too. Results show that the epoxy SMP possesses good chemical stability, glass transition temperature (Tg) determined by DSC decreased by 7C after the irradiation. The gamma radiation has a slight influence on storage modulus, loss modulus and tan delta, respectively. No considerable change was found both in tensile strength and elongation at break after the gamma radiation. Finally, the shape recovery ratio of the polymer is near 100% with and without the gamma irradiation. Based on the above results, it can be demonstrated that the epoxy SMP prepared in the study possesses not only good thermo-mechanical properties but unique anti irradiation performance. The epoxy SMP shows potential for application of aerospace fields.

  9. Thermally responsive polymer systems for self-healing, reversible adhesion and shape memory applications

    NASA Astrophysics Data System (ADS)

    Luo, Xiaofan

    Responsive polymers are "smart" materials that are capable of performing prescribed, dynamic functions under an applied stimulus. In this dissertation, we explore several novel design strategies to develop thermally responsive polymers and polymer composites for self-healing, reversible adhesion and shape memory applications. In the first case described in Chapters 2 and 3, a thermally triggered self-healing material was prepared by blending a high-temperature epoxy resin with a thermoplastic polymer, poly(epsilon-caprolactone) (PCL). The initially miscible system undergoes polymerization induced phase separation (PIPS) during the curing of epoxy and yields a variety of compositionally dependent morphologies. At a particular PCL loading, the cured blend displays a "bricks-and-mortar" morphology in which epoxy exists as interconnected spheres ("bricks") within a continuous PCL matrix ("mortar"). A heat induced "bleeding" phenomenon was observed in the form of spontaneous wetting of all free surfaces by the molten PCL, and is attributed to the volumetric thermal expansion of PCL above its melting point in excess of epoxy brick expansion, which we term differential expansive bleeding (DEB). This DEB is capable of healing damage such as cracks. In controlled self-healing experiments, heating of a cracked specimen led to PCL bleeding from the bulk that yields a liquid layer bridging the crack gap. Upon cooling, a "scar" composed of PCL crystals was formed at the site of the crack, restoring a significant portion of mechanical strength. We further utilized DEB to enable strong and thermally-reversible adhesion of the material to itself and to metallic substrates, without any requirement for macroscopic softening or flow. After that, Chapters 4--6 present a novel composite strategy for the design and fabrication of shape memory polymer composites. The basic approach involves physically combining two or more functional components into an interpenetrating fiber/matrix structure, allowing them to function in a synergistic fashion yet remain physically separated. This latter aspect is critical since it enables the control of overall composite properties and functions by separately tuning each component. Utilizing the intrinsic versatility of this approach, composites with novel properties and functions (in addition to "regular" shape memory) have been developed, including (1) shape memory elastomeric composites (SMECs; Chapter 4), (2) triple-shape polymeric composites (TSPCs; Chapter 5), and (3) electrically conductive nanocomposites (Chapter 6). Then in Chapter 7, by combining the success in both thermoplastic based self-healing and shape memory polymer composites, we demonstrate a thermally triggered self-healing coating. This coating features a unique "shape memory assisted self-healing" mechanism in which crack closure (via shape memory) and crack re-bonding (via melting and diffusion of the thermoplastic healing agent) are achieved simultaneously upon a single heating step, leading to both structural and functional (corrosion resistance) recovery. Finally, Chapter 8 presents for the first time the preparation of functionally graded shape memory polymers (SMPs) that, unlike conventional SMPs, have a range of glass transition temperatures that are spatially graded. This was achieved using a temperature gradient curing method that imposes different vitrification limits at different positions along the gradient. The resulting material is capable of responding to a wide range of thermal triggers and a good candidate for low-cost, material based temperature sensors. All the aforementioned materials and methods show great potential for practical applications due to their high performance, low cost and broad applicability. Some recommendations for future research and development are given in Chapter 9.

  10. Investigation of buckling behavior of carbon nanotube/shape memory polymer composite shell

    NASA Astrophysics Data System (ADS)

    Shi, Guanghui; Yang, Qingsheng; Zhang, Qiang

    2011-11-01

    Shape memory polymer(SMP) is a class of smart materials used in intelligent biomedical devices and industrial application as sensors or actuators for their ability to change shape under a predetermined stimulus. Carbon nanotube (CNT)/shape memory polymer (SMP) composites demonstrate good mechanical properties and shape memory effect. In this work, a model of CNT/SMP composite shell with a vaulted cross-section was established. This composite shell structure could further elevate the recovery stress of CNT/SMP composites. The folding properties of CNT/SMP composite shell structure were analyzed by finite element method and the influence of structural parameters on the buckling behavior of the shell was studied using the energy conservation principle. The results indicate that vaulted cross-section shell had unique mechanical properties. The structural parameters, such as the vaulted radius and the total length have a great impact on buckling moment of the shell. This shell structure is expected to achieve effective control of buckling and deploying process, relying on the special shape memory property of SMP and high elastic modulus CNTs. Moreover, it could also largely avoid the vibration problem during the deploying process.

  11. Investigation of buckling behavior of carbon nanotube/shape memory polymer composite shell

    NASA Astrophysics Data System (ADS)

    Shi, Guanghui; Yang, Qingsheng; Zhang, Qiang

    2012-04-01

    Shape memory polymer(SMP) is a class of smart materials used in intelligent biomedical devices and industrial application as sensors or actuators for their ability to change shape under a predetermined stimulus. Carbon nanotube (CNT)/shape memory polymer (SMP) composites demonstrate good mechanical properties and shape memory effect. In this work, a model of CNT/SMP composite shell with a vaulted cross-section was established. This composite shell structure could further elevate the recovery stress of CNT/SMP composites. The folding properties of CNT/SMP composite shell structure were analyzed by finite element method and the influence of structural parameters on the buckling behavior of the shell was studied using the energy conservation principle. The results indicate that vaulted cross-section shell had unique mechanical properties. The structural parameters, such as the vaulted radius and the total length have a great impact on buckling moment of the shell. This shell structure is expected to achieve effective control of buckling and deploying process, relying on the special shape memory property of SMP and high elastic modulus CNTs. Moreover, it could also largely avoid the vibration problem during the deploying process.

  12. Shape-Memory Polymers Based on Fatty Acid-Filled Elastomeric Ionomers

    NASA Astrophysics Data System (ADS)

    Izzo, Elise; Weiss, Robert

    2009-03-01

    Shape memory polymers (SMPs) have applications as medical devices, actuators, sensors, artificial muscles, switches, smart textiles, and self-deployable structures. All previous design of SMPs has involved synthesizing new polymers or modifying existing polymers. This paper describes a new type of SMP based on blends of an elastomeric ionomer and low molar mass fatty acids or their salts (FAS). Shape memory elastomers were prepared from mixtures of a sulfonated EPDM ionomer and various amounts of a FAS (e.g., zinc stearate, zinc oleate, and various aliphalic acids). Nanophase separation of the metal sulfonate groups provided the ``permanent'' crosslinks, while sub-microscopic crystals of the low molecular weight FAS provided a physical crosslink needed for the temporary shape. The material was deformed above the melting point of the FAS and the new shape was fixed by cooling the material while under stress to below the melting point of the FAS. Polar interactions between the ionomer and the FAS stabilized the dispersion of the FAS in the polymer and provided the continuity between the phases that allowed the crystals of the FAS to provide a second network of physical crosslinks. The temporary shape was erased and the material returned to the primary shape by heating above the melting point of the FAS.

  13. Shape memory polymer (SMP) gripper with a release sensing system

    DOEpatents

    Maitland, Duncan J.; Lee, Abraham P.; Schumann, Daniel L.; Silva, Luiz Da

    2000-01-01

    A system for releasing a target material, such as an embolic coil from an SMP located at the end of a catheter utilizing an optical arrangement for releasing the material. The system includes a laser, laser driver, display panel, photodetector, fiber optics coupler, fiber optics and connectors, a catheter, and an SMP-based gripper, and includes a release sensing and feedback arrangement. The SMP-based gripper is heated via laser light through an optic fiber causing the gripper to release a target material (e.g., embolic coil for therapeutic treatment of aneurysms). Various embodiments are provided for coupling the laser light into the SMP, which includes specific positioning of the coils, removal of the fiber cladding adjacent the coil, a metal coating on the SMP, doping the SMP with a gradient absorbing dye, tapering the fiber optic end, coating the SMP with low refractive index material, and locating an insert between the fiber optic and the coil.

  14. Cancer-reactive memory T cells from bone marrow: Spontaneous induction and therapeutic potential (Review).

    PubMed

    Schirrmacher, Volker

    2015-12-01

    Cognate interactions between nave tumor antigen (TA)-specific T cells and TA-presenting dendritic cells (DCs) are facilitated by secondary lymphoid organs such as lymph nodes or the spleen. These can result either in TA-specific tolerance or, depending on environmental costimulatory signals, in TA-specific immune responses. In the present review, we describe such events for the bone marrow (BM) when blood-borne TA, released from the primary tumor or expressed by blood circulating tumor cells or DCs enters the BM stroma and parenchyma. We argue that cognate T-DC interactions in the BM result in immune responses and generation of memory T cells (MTCs) rather than tolerance because T cells in the BM show an increased level of pre-activation. The review starts with the spontaneous induction of cancer-reactive MTCs in the BM and the involvement of such MTCs in the control of tumor dormancy. The main part deals with the therapeutic potency of BM MTCs. This is a new area of research in which the authors research group has performed pioneering studies which are summarized. These include studies in animal tumor models, studies with human cells in tumor xenotransplant models and clinical studies. Based on observations of an enormous expansion capacity, longevity and therapeutic capacity of BM MTCs, a hypothesis is presented which suggests the involvement of stem-like MTCs. PMID:26459860

  15. Field enhanced charge carrier reconfiguration in electronic and ionic coupled dynamic polymer resistive memory

    NASA Astrophysics Data System (ADS)

    Zhao, Jun Hui; Thomson, Douglas J.; Pilapil, Matt; Pillai, Rajesh G.; Aminur Rahman, G. M.; Freund, Michael S.

    2010-04-01

    Dynamic resistive memory devices based on a conjugated polymer composite (PPy0DBS - Li + (PPy: polypyrrole; DBS - : dodecylbenzenesulfonate)), with field-driven ion migration, have been demonstrated. In this work the dynamics of these systems has been investigated and it has been concluded that increasing the applied field can dramatically increase the rate at which information can be 'written' into these devices. A conductance model using space charge limited current coupled with an electric field induced ion reconfiguration has been successfully utilized to interpret the experimentally observed transient conducting behaviors. The memory devices use the rising and falling transient current states for the storage of digital states. The magnitude of these transient currents is controlled by the magnitude and width of the write/read pulse. For the 500 nm length devices used in this work an increase in 'write' potential from 2.5 to 5.5 V decreased the time required to create a transient conductance state that can be converted into the digital signal by 50 times. This work suggests that the scaling of these devices will be favorable and that 'write' times for the conjugated polymer composite memory devices will decrease rapidly as ion driving fields increase with decreasing device size.

  16. Investigation of mechanical and conductive properties of shape memory polymer composite (SMPC)

    NASA Astrophysics Data System (ADS)

    Leng, Jinsong; Lan, Xin; Lv, Haibao; Zhang, Dawei; Liu, Yanju; Du, Shanyi

    2007-04-01

    This paper is concerned about an investigation of mechanical and electrical conductive properties of carbon fiber fabric reinforced shape memory polymer composite (SMPC). The shape memory polymer (SMP) is a thermoset styrene-based resin. SMP is a promising smart material, which is under intensive investigation at present. Its primary advantages over other smart materials are the high strain capacity (200% reversible strain), low density and low cost etc.. But its major drawbacks are low strength, low modulus and low recovery stress. So the fiber reinforced SMPC was naturally considered to be investigated in this paper, which may overcome the disadvantages mentioned above. The investigation was conducted with experimental methods: Dynamic Mechanical Analyzer (DMA), static and mechanical cycle loading tests, microscope observation of microstructural deformation mechanism, conductivity and shape recovery tests. Results indicated that SMPC showed higher glass transition temperature (T g) than neat SMP and improved the storage modulus, bending modulus, strength and resistance against relaxation and creep. Both fiber microbuckling and fracture of SMPC were observed after the static 3-ponit bending test at the constant room temperature. SMPC showed favorable recovery performances during thermomechanical cycles of the bending recovery test and the fiber microbuckling was obvious. Moreover, the conductive SMPC of this study experienced low electrical resistivity and performed a good shape memory effect during numerous thermomechanical cycles.

  17. Reticulation of low density shape memory polymer foam with an in vivo demonstration of vascular occlusion

    PubMed Central

    Rodriguez, Jennifer N.; Miller, Matthew W.; Boyle, Anthony; Horn, John; Yang, Cheng-Kang; Wilson, Thomas S.; Ortega, Jason M.; Small, Ward; Nash, Landon; Skoog, Hunter; Maitland, Duncan J.

    2014-01-01

    Predominantly closed-cell low density shape memory polymer (SMP) foam was recently reported to be an effective aneurysm filling device in a porcine model (Rodriguez et al., Journal of Biomedical Materials Research Part A 2013: (http://dx.doi.org/10.1002/jbm.a.34782)). Because healing involves blood clotting and cell migration throughout the foam volume, a more open-cell structure may further enhance the healing response. This research sought to develop a non-destructive reticulation process for this SMP foam to disrupt the membranes between pore cells. Non-destructive mechanical reticulation was achieved using a gravity-driven floating nitinol pin array coupled with vibratory agitation of the foam and supplemental chemical etching. Reticulation resulted in a reduced elastic modulus and increased permeability, but did not impede shape memory behavior. Reticulated foams were capable of achieving rapid vascular occlusion in an in vivo porcine model. PMID:25222869

  18. Efficient tristable resistive memory based on single layer graphene/insulating polymer multi-stacking layer

    NASA Astrophysics Data System (ADS)

    Wu, Chaoxing; Li, Fushan; Guo, Tailiang

    2014-05-01

    Tristable resistive memories based on single layer graphene (SLG)/insulating polymer multi-stacking layer were fabricated. By using the traditional transfer method, the chemical vapor deposition-synthesized SLG serving as charging layers were combined with poly(methyl methacrylate) (PMMA) layers and polystyrene (PS) layers to form charge traps with various depth. Based on the PS/SLG/PMMA/SLG/PMMA multi-stacking layer, the devices exhibited efficient tristable memory performances. The ratios as large as 104 between different resistive states were maintained for a retention time of more than 104 s. The operation mechanisms of stepping-charging in the multi-stacking layer for the tristable resistive switching were proposed on the basis of the current-voltage analysis.

  19. Reticulation of low density shape memory polymer foam with an in vivo demonstration of vascular occlusion.

    PubMed

    Rodriguez, Jennifer N; Miller, Matthew W; Boyle, Anthony; Horn, John; Yang, Cheng-Kang; Wilson, Thomas S; Ortega, Jason M; Small, Ward; Nash, Landon; Skoog, Hunter; Maitland, Duncan J

    2014-12-01

    Predominantly closed-cell low density shape memory polymer (SMP) foam was recently reported to be an effective aneurysm filling device in a porcine model (Rodriguez et al., Journal of Biomedical Materials Research Part A 2013: (http://dx.doi.org/10.1002/jbm.a.34782)). Because healing involves blood clotting and cell migration throughout the foam volume, a more open-cell structure may further enhance the healing response. This research sought to develop a non-destructive reticulation process for this SMP foam to disrupt the membranes between pore cells. Non-destructive mechanical reticulation was achieved using a gravity-driven floating nitinol pin array coupled with vibratory agitation of the foam and supplemental chemical etching. Reticulation resulted in a reduced elastic modulus and increased permeability, but did not impede the shape memory behavior. Reticulated foams were capable of achieving rapid vascular occlusion in an in vivo porcine model. PMID:25222869

  20. Current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury using polymer scaffolds?

    PubMed Central

    Madigan, Nicolas N.; McMahon, Siobhan; OBrien, Timothy; Yaszemski, Michael J.; Windebank, Anthony J.

    2010-01-01

    This review highlights current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury. The concept of developing 3-dimensional polymer scaffolds for placement into a spinal cord transection model has recently been more extensively explored as a solution for restoring neurologic function after injury. Given the patient morbidity associated with respiratory compromise, the discrete tracts in the spinal cord conveying innervation for breathing represent an important and achievable therapeutic target. The aim is to derive new neuronal tissue from the surrounding, healthy cord that will be guided by the polymer implant through the injured area to make functional reconnections. A variety of naturally derived and synthetic biomaterial polymers have been developed for placement in the injured spinal cord. Axonal growth is supported by inherent properties of the selected polymer, the architecture of the scaffold, permissive microstructures such as pores, grooves or polymer fibres, and surface modifications to provide improved adherence and growth directionality. Structural support of axonal regeneration is combined with integrated polymeric and cellular delivery systems for therapeutic drugs and for neurotrophic molecules to regionalize growth of specific nerve populations. PMID:19737633

  1. Femtosecond-laser direct writing in polymers and potential applications in microfluidics and memory devices

    NASA Astrophysics Data System (ADS)

    Kallepalli, Lakshmi Narayana Deepak; Soma, Venugopal Rao; Desai, Narayana Rao

    2012-07-01

    We have investigated femtosecond-laser-induced microstructures (on the surface and within the bulk), gratings, and craters in four different polymers: polymethyl methacrylate, polydimethylsiloxane, polystyrene, and polyvinyl alcohol. The structures were achieved using a Ti:sapphire laser delivering 100-fs pulses at 800 nm with a repetition rate of 1 kHz and a maximum pulse energy of 1 mJ. Local chemical modifications leading to the formation of optical centers and peroxide radicals were studied using ultraviolet-visible absorption and emission, confocal micro-Raman and electron spin resonance spectroscopic techniques. Potential applications of these structures in microfluidics, waveguides, and memory-based devices are demonstrated.

  2. Electroactivate shape-memory polymer filled with nanocarbon particles and short carbon fibers

    NASA Astrophysics Data System (ADS)

    Leng, Jinsong; Lv, Haibao; Liu, Yanju; Du, Shanyi

    2007-10-01

    In addition to the fabrication of shape-memory thermoset polymer nanocomposites filled with conductive nanoparticles and fiber fillers, this paper is focused on factors which would influence the electrical property of this type of material. It is shown that the particulate additives are dispersed homogeneously within the matrix and served as interconnections between the fibers, while the fibrous additives act as long distance charge transporter by forming local conductive paths. The electrical conductivity of the nanocomposite which contains 5wt% carbon nanoparticles and 2wt% short carbon fiber is 2.32S/cm by four-point van der Pauw method, and can be induced by 24V voltages.

  3. Swelling effect actuation of shape-memory polymer: mechanism and demonstration

    NASA Astrophysics Data System (ADS)

    Lu, Haibao; Leng, Jinsong; Liu, Yanju; Du, Shanyi

    2009-03-01

    Recently, there is increasing interest in triggering shape recovery of shape-memory polymers (SMPs) by novel inductive effect. In this paper, many hard works have been carried out to make SMP induced while along with swelling effect. Based on the Free-volume theory, Rubber Elasticity Theory and Mooney-Rivlin Equation, it is theoretically and experimentally demonstrated the feasibility of SMP activated by swelling effect. The mechanism behind it is solvent acting as plasticizer, to reduce the glass transition temperature (Tg) and melting temperature (Tm) of polymers, make them softer and more flexible, facilitating the diffusion of the molecules to polymer chains, and then separating them. In addition to this physical action, the intermolecular interactions among the chains are weakened, because interactions are hindered at the points where the plasticizer is located. Finally, the Dynamic mechanical analysis (DMA), FTIR study and glass transition temperature measurement tests were used to exemplify the feasibility of SMP driven by swelling effect. And it is qualitatively identified the role of swelling effect playing in influencing the transition temperature. Swelling effect occurs due to the interaction between macromolecules and solvent molecules, leading to free volume of polymeric chains increasing (namely the flexibility of polymer chains increasing), resulting in the Tg decreasing. All above mentioned investigation can be used to confirm that the shape recovery is induced by swelling effect. This actuation almost is applicable for all the SMP and SMP composite, as the swelling theory is almost applicable for all the polymeric materials.

  4. Improved delivery of polymer therapeutics to prostate tumors using plasmonic photothermal therapy

    NASA Astrophysics Data System (ADS)

    Gormley, Adam Joseph

    When a patient is presented with locally advanced prostate cancer, it is possible to provide treatment with curative intent. However, once the disease has formed distant metastases, the chances of survival drops precipitously. For this reason, proper management of the disease while it remains localized is of critical importance. Treating these malignant cells with cytotoxic agents is effective at cell killing; however, the nonspecific toxicity profiles of these drugs often limit their use until the disease has progressed and symptom palliation is required. Incorporation of these drugs in nanocarriers such as polymers help target them to tumors with a degree of specificity, though major vascular barriers limit their effective delivery. In this dissertation, it is shown that plasmonic photothermal therapy (PPTT) can be used to help overcome some of these barriers and improve delivery to prostate tumors. First, the concept of using PPTT to improve the delivery of macromolecules to solid tumors was validated. This was done by measuring the tumor uptake of albumin. Next, the concept of targeting gold nanorods (GNRs) directly to the tumor's vasculature to better modulate vascular response to heating was tested. Surface conjugation of cyclic RGD (Arg-Gly-Asp) to GNRs improved their binding and uptake to endothelial cells in vitro, but not in vivo. Nontargeted GNRs and PPTT were then utilized to guide the location of polymer therapeutic delivery to prostate tumors. N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers, which were designed to be targeted to cells previously exposed to heat shock, were used in this study. Treatment of tumors with PPTT facilitated a burst accumulation of the copolymers over 4 hours, and heat shock targeting to cells allowed them to be retained for an extended period of time. Finally, the tumor localization of the HPMA copolymers following PPTT was evaluated by magnetic resonance imaging (MRI). These results show that PPTT may be a useful tool to enhance delivery of polymeric drug carriers to locally advanced prostate tumors.

  5. Integrin-assisted drug delivery of nano-scaled polymer therapeutics bearing paclitaxel

    PubMed Central

    Eldar-Boock, Anat; Miller, Keren; Sanchis, Joaquin; Lupu, Ruth; Vicent, Mara J.; Satchi-Fainaro, Ronit

    2011-01-01

    Angiogenesis plays a prominent role in cancer progression. Anti-angiogenic therapy therefore, either alone or in combination with conventional cytotoxic therapy, offers a promising therapeutic approach. Paclitaxel (PTX) is a widely-used potent cytotoxic drug that also exhibits anti-angiogenic effects at low doses. However, its use, at its full potential, is limited by severe side effects. Here we designed and synthesized a targeted conjugate of PTX, a polymer and an integrin-targeted moiety resulting in a polyglutamic acid (PGA)-PTX-E-[c(RGDfK)2] nano-scaled conjugate. Polymer conjugation converted PTX to a macromolecule, which passively targets the tumor tissue exploiting the enhanced permeability and retention effect, while extravasating via the leaky tumor neovasculature. The cyclic RGD peptidomimetic enhanced the effects previously seen for PGA-PTX alone, utilizing the additional active targeting to the ?v?3 integrin overexpressed on tumor endothelial and epithelial cells. This strategy is particularly valuable when tumors are well-vascularized, but they present poor vascular permeability. We show that PGA is enzymatically-degradable leading to PTX release under lysosomal acidic pH. PGA-PTX-E-[c(RGDfK)2] inhibited the growth of proliferating ?v?3-expressing endothelial cells and several cancer cells. We also showed that PGA-PTX-E-[c(RGDfK)2] blocked endothelial cells migration towards vascular endothelial growth factor; blocked capillary-like tube formation; and inhibited endothelial cells attachment to fibrinogen. Orthotopic studies in mice demonstrated preferential tumor accumulation of the RGD-bearing conjugate, leading to enhanced antitumor efficacy and a marked decrease in toxicity as compared with free PTX-treated mice. PMID:21376390

  6. Sequential Self-Folding Structures by 3D Printed Digital Shape Memory Polymers

    PubMed Central

    Mao, Yiqi; Yu, Kai; Isakov, Michael S.; Wu, Jiangtao; Dunn, Martin L.; Jerry Qi, H.

    2015-01-01

    Folding is ubiquitous in nature with examples ranging from the formation of cellular components to winged insects. It finds technological applications including packaging of solar cells and space structures, deployable biomedical devices, and self-assembling robots and airbags. Here we demonstrate sequential self-folding structures realized by thermal activation of spatially-variable patterns that are 3D printed with digital shape memory polymers, which are digital materials with different shape memory behaviors. The time-dependent behavior of each polymer allows the temporal sequencing of activation when the structure is subjected to a uniform temperature. This is demonstrated via a series of 3D printed structures that respond rapidly to a thermal stimulus, and self-fold to specified shapes in controlled shape changing sequences. Measurements of the spatial and temporal nature of self-folding structures are in good agreement with the companion finite element simulations. A simplified reduced-order model is also developed to rapidly and accurately describe the self-folding physics. An important aspect of self-folding is the management of self-collisions, where different portions of the folding structure contact and then block further folding. A metric is developed to predict collisions and is used together with the reduced-order model to design self-folding structures that lock themselves into stable desired configurations. PMID:26346202

  7. Sequential Self-Folding Structures by 3D Printed Digital Shape Memory Polymers

    NASA Astrophysics Data System (ADS)

    Mao, Yiqi; Yu, Kai; Isakov, Michael S.; Wu, Jiangtao; Dunn, Martin L.; Jerry Qi, H.

    2015-09-01

    Folding is ubiquitous in nature with examples ranging from the formation of cellular components to winged insects. It finds technological applications including packaging of solar cells and space structures, deployable biomedical devices, and self-assembling robots and airbags. Here we demonstrate sequential self-folding structures realized by thermal activation of spatially-variable patterns that are 3D printed with digital shape memory polymers, which are digital materials with different shape memory behaviors. The time-dependent behavior of each polymer allows the temporal sequencing of activation when the structure is subjected to a uniform temperature. This is demonstrated via a series of 3D printed structures that respond rapidly to a thermal stimulus, and self-fold to specified shapes in controlled shape changing sequences. Measurements of the spatial and temporal nature of self-folding structures are in good agreement with the companion finite element simulations. A simplified reduced-order model is also developed to rapidly and accurately describe the self-folding physics. An important aspect of self-folding is the management of self-collisions, where different portions of the folding structure contact and then block further folding. A metric is developed to predict collisions and is used together with the reduced-order model to design self-folding structures that lock themselves into stable desired configurations.

  8. Sequential Self-Folding Structures by 3D Printed Digital Shape Memory Polymers.

    PubMed

    Mao, Yiqi; Yu, Kai; Isakov, Michael S; Wu, Jiangtao; Dunn, Martin L; Jerry Qi, H

    2015-01-01

    Folding is ubiquitous in nature with examples ranging from the formation of cellular components to winged insects. It finds technological applications including packaging of solar cells and space structures, deployable biomedical devices, and self-assembling robots and airbags. Here we demonstrate sequential self-folding structures realized by thermal activation of spatially-variable patterns that are 3D printed with digital shape memory polymers, which are digital materials with different shape memory behaviors. The time-dependent behavior of each polymer allows the temporal sequencing of activation when the structure is subjected to a uniform temperature. This is demonstrated via a series of 3D printed structures that respond rapidly to a thermal stimulus, and self-fold to specified shapes in controlled shape changing sequences. Measurements of the spatial and temporal nature of self-folding structures are in good agreement with the companion finite element simulations. A simplified reduced-order model is also developed to rapidly and accurately describe the self-folding physics. An important aspect of self-folding is the management of self-collisions, where different portions of the folding structure contact and then block further folding. A metric is developed to predict collisions and is used together with the reduced-order model to design self-folding structures that lock themselves into stable desired configurations. PMID:26346202

  9. Two-way actuation behavior of shape memory polymer/elastomer core/shell composites

    NASA Astrophysics Data System (ADS)

    Kang, Tae-Hyung; Lee, Jeong-Min; Yu, Woong-Ryeol; Youk, Ji Ho; Ryu, Hee Wook

    2012-03-01

    Semi-crystalline shape memory polymers (SMPs) show net two-way shape memory (2W-SM) behavior under constant stresses by the recoverable creep strain upon heating and stress-induced crystallization under the application of creep stress upon cooling. The applied constant stress is the key factor in this 2W-SM behavior. A core/shell structure is manufactured for the purpose of imparting a constant stress upon SMPs. An SMP in film or fiber form is dipped into a solution of an elastomer, photoinitiator, and curing agent and then dried out. After this dip coating process is repeatedly carried out, the SMP/elastomer core/shell composite is deformed into a temporary shape after being heated up above the transition temperature of the SMP. Under constant strain conditions, the composite is cooled down, after which the shell elastomer is cured using ultraviolet light. Then, the SMP/elastomer core/shell composite extends and contracts upon cooling and heating, respectively, without any external load. This cyclic deformation behavior is characterized, demonstrating that the current method offers a simple macroscopic processing technique to manufacture 2W-SM polymer composites.

  10. Self-healing nanocomposite using shape memory polymer and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Liu, Yingtao; Rajadas, Abhishek; Chattopadhyay, Aditi

    2013-04-01

    Carbon fiber reinforced composites are used in a wide range of applications in aerospace, mechanical, and civil structures. Due to the nature of material, most damage in composites, such as delaminations, are always barely visible to the naked eye, which makes it difficult to detect and repair. The investigation of biological systems has inspired the development and characterization of self-healing composites. This paper presents the development of a new type of self-healing material in order to impede damage progression and conduct in-situ damage repair in composite structures. Carbon nanotubes, which are highly conductive materials, are mixed with shape memory polymer to develop self-healing capability. The developed polymeric material is applied to carbon fiber reinforced composites to automatically heal the delamination between different layers. The carbon fiber reinforced composite laminates are manufactured using high pressure molding techniques. Tensile loading is applied to double cantilever beam specimens using an MTS hydraulic test frame. A direct current power source is used to generate heat within the damaged area. The application of thermal energy leads to re-crosslinking in shape memory polymers. Experimental results showed that the developed composite materials are capable of healing the matrix cracks and delaminations in the bonded areas of the test specimens. The developed self-healing material has the potential to be used as a novel structural material in mechanical, civil, aerospace applications.

  11. Highly compliant shape memory polymer gels for tunable damping and reversible adhesion

    NASA Astrophysics Data System (ADS)

    Mrozek, Randy A.; Berg, Michael C.; Gold, Christopher S.; Leighliter, Brad; Morton, Jeffrey T.; Lenhart, Joseph L.

    2016-02-01

    Materials that can dynamically change their properties to better adapt to the local environment have potential utility in robotics, aerospace, and coatings. For some of these applications, most notably robotics, it is advantageous for these responsive materials to be highly compliant in an effort to provide dynamic changes in adhesion and mechanical damping within a broad temperature operational environment. In this report, non-aqueous, highly compliant shape-memory polymer gels are developed by incorporating a low density of chemical cross-links into a physically cross-linked thermoplastic elastomer gel. Chemical cross-linkers were evaluated by varying there size and degree of functionality to determine the impact on the mechanical and adhesive properties. As a result of the chemical cross-linking, the gels exhibit modulus plateaus around room temperature and at elevated temperatures above 100 °C, where the thermoplastic elastomer gel typically melts. The materials were designed so that moduli in the plateaued regions were above and below the Dahlquist criteria of 4 × 104 Pa, respectively, where materials with a modulus below this value typically exhibit an increase in adhesion. The shape memory polymer gels were also integrated into fiber-reinforced composites to determine the temperature-dependent changes in mechanical damping. It is anticipated that this work will provide insight into materials design to provide dynamic changes in adhesion and damping to improve robotic appendage manipulation and platform mobility.

  12. Electroactive polymer and shape memory alloy actuators in biomimetics and humanoids

    NASA Astrophysics Data System (ADS)

    Tadesse, Yonas

    2013-04-01

    There is a strong need to replicate natural muscles with artificial materials as the structure and function of natural muscle is optimum for articulation. Particularly, the cylindrical shape of natural muscle fiber and its interconnected structure promote the critical investigation of artificial muscles geometry and implementation in the design phase of certain platforms. Biomimetic robots and Humanoid Robot heads with Facial Expressions (HRwFE) are some of the typical platforms that can be used to study the geometrical effects of artificial muscles. It has been shown that electroactive polymer and shape memory alloy artificial muscles and their composites are some of the candidate materials that may replicate natural muscles and showed great promise for biomimetics and humanoid robots. The application of these materials to these systems reveals the challenges and associated technologies that need to be developed in parallel. This paper will focus on the computer aided design (CAD) models of conductive polymer and shape memory alloys in various biomimetic systems and Humanoid Robot with Facial Expressions (HRwFE). The design of these systems will be presented in a comparative manner primarily focusing on three critical parameters: the stress, the strain and the geometry of the artificial muscle.

  13. Pneumatic artificial rubber muscle using shape-memory polymer sheet with embedded electrical heating wire

    NASA Astrophysics Data System (ADS)

    Takashima, Kazuto; Sugitani, Kazuhiro; Morimoto, Naohiro; Sakaguchi, Seiya; Noritsugu, Toshiro; Mukai, Toshiharu

    2014-12-01

    Shape-memory polymer (SMP) can be deformed by applying a small load above its glass transition temperature (Tg). Shape-memory polymer maintains its shape after it has cooled below Tg and returns to a predefined shape when subsequently heated above Tg. The reversible change in the elastic modulus between the glassy and rubbery states of an SMP can be on the order of several hundred times. Based on the change in stiffness of the SMP in relation to the change in temperature, the present study attempts to evaluate the application of the SMP to soft actuators of a robot. In order to control the temperature of the SMP, we developed an SMP sheet with an embedded electrical heating wire. We formed a uniform, thin SMP sheet without air bubbles using a heat press. The SMP sheet with a heating wire can be heated quickly and can be maintained at a constant temperature. Moreover, the effects of the embedded wire on the mechanical properties in bending and tensile tests were small. Then, we applied the SMP sheet with the embedded electrical heating wire to a pneumatic artificial rubber muscle. The enhanced versatility of SMP sheet applications is demonstrated through a series of experiments conducted using a prototype. The initial shape and bending displacement of the pneumatic artificial rubber muscle can be changed by controlling the temperature of the SMP sheet.

  14. Tumortropic monocyte-mediated delivery of echogenic polymer bubbles and therapeutic vesicles for chemotherapy of tumor hypoxia.

    PubMed

    Huang, Wen-Chia; Chiang, Wen-Hsuan; Cheng, Ya-Hui; Lin, Wan-Chi; Yu, Ching-Fang; Yen, Chia-Yi; Yeh, Chih-Kuang; Chern, Chorng-Shyan; Chiang, Chi-Shiun; Chiu, Hsin-Cheng

    2015-12-01

    Overcoming limitations often experienced in nanomedicine delivery toward hypoxia regions of malignant tumors remains a great challenge. In this study, a promising modality for active hypoxia drug delivery was developed by adopting tumortropic monocytes/macrophages as a cellular vehicle for co-delivery of echogenic polymer/C5F12 bubbles and doxorubicin-loaded polymer vesicles. Through the remote-controlled focused ultrasound (FUS)-triggered drug liberation, therapeutic monocytes show prominent capability of inducing apoptosis of cancer cells. The invivo and exvivo fluorescence imaging shows appreciable accumulation of cell-mediated therapeutics in tumor as compared to the nanoparticle counterpart residing mostly in liver. Inhibition of tumor recurrence with ?-ray pre-irradiated Tramp-C1-bearing mice receiving therapeutic monocytes intravenously alongside the FUS activation at tumor site was significantly observed. Immunohistochemical examination of tumor sections confirms successful cellular transport of therapeutic payloads to hypoxic regions and pronounced cytotoxic action against hypoxic cells. Following the intravenous administration, the cellular-mediated therapeutics can penetrate easily to a depth beyond 150?m from the nearest blood vessels within pre-irradiated tumor while nanoparticles are severely limited to a depth of ca 10-15?m. This work demonstrates the great promise of cellular delivery to carry therapeutic payloads for improving chemotherapy in hypoxia by combining external trigger for drug release. PMID:26318818

  15. Towards Therapeutic Applications of Arthropod Venom K+-Channel Blockers in CNS Neurologic Diseases Involving Memory Acquisition and Storage

    PubMed Central

    Gati, Christiano D. C.; Mortari, Mrcia R.; Schwartz, Elisabeth F.

    2012-01-01

    Potassium channels are the most heterogeneous and widely distributed group of ion channels and play important functions in all cells, in both normal and pathological mechanisms, including learning and memory processes. Being fundamental for many diverse physiological processes, K+-channels are recognized as potential therapeutic targets in the treatment of several Central Nervous System (CNS) diseases, such as multiple sclerosis, Parkinson's and Alzheimer's diseases, schizophrenia, HIV-1-associated dementia, and epilepsy. Blockers of these channels are therefore potential candidates for the symptomatic treatment of these neuropathies, through their neurological effects. Venomous animals have evolved a wide set of toxins for prey capture and defense. These compounds, mainly peptides, act on various pharmacological targets, making them an innumerable source of ligands for answering experimental paradigms, as well as for therapeutic application. This paper provides an overview of CNS K+-channels involved in memory acquisition and storage and aims at evaluating the use of highly selective K+-channel blockers derived from arthropod venoms as potential therapeutic agents for CNS diseases involving learning and memory mechanisms. PMID:22701481

  16. Micro-mechanics of nanostructured carbon/shape memory polymer hybrid thin film.

    PubMed

    Lei, Ming; Xu, Ben; Pei, Yutao; Lu, Haibao; Fu, Yong Qing

    2015-12-16

    This paper investigates the mechanics of hybrid shape memory polymer polystrene (PS) based nanocomposites with skeletal structures of CNFs/MWCNTs formed inside. Experimental results showed an increase of glass transition temperature (Tg) with CNF/MWCNT concentrations instead of a decrease of Tg in nanocomposites filled by spherical particles, and an increase in mechanical properties on both macro- and ?m-scales. Compared with CNFs, MWCNTs showed a better mechanical enhancement for PS nanocomposites due to their uniform distribution in the nanocomposites. In nanoindentation tests using the Berkovich tips, indentation size effects and pile-up effects appeared obviously for the nanocomposites, but not for pure PS. Experimental results revealed the enhancement mechanisms of CNFs/MWCNTs related to the secondary structures formed by nanofillers, including two aspects, i.e., filler-polymer interfacial connections and geometrical factors of nanofillers. The filler-polymer interfacial connections were strongly dependent on temperature, thus leading to the opposite changing trend of loss tangent with nanofiller concentrations, respectively, at low and high temperature. The geometrical factors of nanofillers were related to testing scales, further leading to the appearance of pile-up effects for nanocomposites in the nanoindentation tests, in which the size of indents was close to the size of the nanofiller skeleton. PMID:26448555

  17. Polymer (PTFE) and shape memory alloy (NiTi) intercalated nano-biocomposites

    NASA Astrophysics Data System (ADS)

    Anjum, S. S.; Rao, J.; Nicholls, J. R.

    2012-09-01

    Engineering on a nano-scale has been undertaken to mimic a biomaterial by forming an intercalated nano-composite structure by PVD sputtering of a polymer with a nickel-titanium (NiTi) shape memory alloy (SMA). A PTFE polymer has been selected due to its elastic properties, low interactions with water, optimum surface energies, stability and chemical resistance. NiTi SMAs allow the coatings to be energy absorbent and thus suitable in load bearing situations. The coatings are aimed to constantly withstand variable adverse biological environments whilst maintaining their characteristics. The nano-intercalated structures have been characterised for their wettability, friction coefficients, chemical composition, and morphology. Intercalation of a polymer with energy-absorbing alloys uncovers a set of material systems that will offer characteristics such as self-healing of hierarchal tissue in the body. The reformation of PTFE following sputter deposition was confirmed by FTIR spectra. According to SEM analysis PTFE shows a promising surface interaction with NiTi, forming stable coatings. Surface interactions are evident by the hydrophobic behaviour of films as the composite's water contact angle is around 86 which lies in-between that of PTFE and NiTi. The nano composite films are lubricious and have a measured CoF below 0.2 which does not vary with layer thickness.

  18. Method for preparation, programming, and characterization of miniaturized particulate shape-memory polymer matrices.

    PubMed

    Wischke, Christian; Lendlein, Andreas

    2014-03-18

    Their capability to change their shape on demand has created significant interest for shape-memory polymers (SMPs) in minimally invasive surgery. To evaluate the miniaturization of SMP matrices for small-sized implants or controlled release systems, a strategy to prepare and evaluate microsized SMP model particles is required. This methodological study reports the emulsion-based preparation of ~30 μm microparticles (MPs) from a phase-segregated SMP, poly(ε-caprolactone) [PCL] and poly(ω-pentadecalactone) [PPDL], with a particular focus on the effects of process parameters such as polymer solvents or stabilizer type/concentration on formation and size distribution of SMP MPs. Processes for the preparation of SMP MP-loaded water-soluble polymer films with tailored mechanical properties were developed and applied for programming the SMP MP to a temporary ellipsoid shape by film stretching. For the functional evaluation of shape recovery of MPs, a light microscopy-based setup with temperature control is proposed by which the stimuli-induced switching of the microsized SMP matrices could be confirmed. Overall, by applying this methodological strategy to various thermoplastic SMPs, a routine to identify and characterize the microscale functionality of SMPs in miniaturized applications will be broadly accessible. PMID:24564390

  19. Therapeutic Potential of Cell Penetrating Peptides (CPPs) and Cationic Polymers for Chronic Hepatitis B.

    PubMed

    Ndeboko, Bndicte; Lemamy, Guy Joseph; Nielsen, Peter E; Cova, Lucyna

    2015-01-01

    Chronic hepatitis B virus (HBV) infection remains a major health problem worldwide. Because current anti-HBV treatments are only virostatic, there is an urgent need for development of alternative antiviral approaches. In this context, cell-penetrating peptides (CPPs) and cationic polymers, such as chitosan (CS), appear of particular interest as nonviral vectors due to their capacity to facilitate cellular delivery of bioactive cargoes including peptide nucleic acids (PNAs) or DNA vaccines. We have investigated the ability of a PNA conjugated to different CPPs to inhibit the replication of duck hepatitis B virus (DHBV), a reference model for human HBV infection. The in vivo administration of PNA-CPP conjugates to neonatal ducklings showed that they reached the liver and inhibited DHBV replication. Interestingly, our results indicated also that a modified CPP (CatLip) alone, in the absence of its PNA cargo, was able to drastically inhibit late stages of DHBV replication. In the mouse model, conjugation of HBV DNA vaccine to modified CS (Man-CS-Phe) improved cellular and humoral responses to plasmid-encoded antigen. Moreover, other systems for gene delivery were investigated including CPP-modified CS and cationic nanoparticles. The results showed that these nonviral vectors considerably increased plasmid DNA uptake and expression. Collectively promising results obtained in preclinical studies suggest the usefulness of these safe delivery systems for the development of novel therapeutics against chronic hepatitis B. PMID:26633356

  20. Synthesis and Characterization of Polymer Nanocarriers for the Targeted Delivery of Therapeutic Enzymes

    PubMed Central

    Simone, Eric; Dziubla, Thomas; Shuvaev, Vladimir; Muzykantov, Vladimir R.

    2011-01-01

    Protein drugs, such as recombinant enzymes useful for detoxification and replacement therapies, have extraordinary specificity and potency. However, inherently inadequate delivery to target sites and rapid inactivation limit their medical utility. Using chaperone polymeric particles designed within an injectible size range (sub-micron) may help solve these shortcomings. Such nanocarriers would (i) prevent premature inactivation of encapsulated therapeutic protein cargoes, (ii) provide a carrier that can be surface decorated by targeting ligands, and (iii) optimize sub-cellular localization of the drug. This chapter describes the techniques successfully employed for the preparation of polymer nanocarriers (PNC) loaded with the antioxidant enzyme, catalase, and targeted to endothelial cells. Methods of PNC synthesis, loading with catalase, characterization, coupling of a targeting moiety, and in vitro testing of the enzymatic and targeting activities are provided here. Advantages and disadvantages of specific designs are discussed. Due to the modular nature of the targeting methodology employed, it is believed that these protocols will provide a solid foundation for the formulation of a wide variety of enzymatic drug targeting strategies. PMID:20013177

  1. Therapeutic Potential of Cell Penetrating Peptides (CPPs) and Cationic Polymers for Chronic Hepatitis B

    PubMed Central

    Ndeboko, Bénédicte; Lemamy, Guy Joseph; Nielsen, Peter. E; Cova, Lucyna

    2015-01-01

    Chronic hepatitis B virus (HBV) infection remains a major health problem worldwide. Because current anti-HBV treatments are only virostatic, there is an urgent need for development of alternative antiviral approaches. In this context, cell-penetrating peptides (CPPs) and cationic polymers, such as chitosan (CS), appear of particular interest as nonviral vectors due to their capacity to facilitate cellular delivery of bioactive cargoes including peptide nucleic acids (PNAs) or DNA vaccines. We have investigated the ability of a PNA conjugated to different CPPs to inhibit the replication of duck hepatitis B virus (DHBV), a reference model for human HBV infection. The in vivo administration of PNA-CPP conjugates to neonatal ducklings showed that they reached the liver and inhibited DHBV replication. Interestingly, our results indicated also that a modified CPP (CatLip) alone, in the absence of its PNA cargo, was able to drastically inhibit late stages of DHBV replication. In the mouse model, conjugation of HBV DNA vaccine to modified CS (Man-CS-Phe) improved cellular and humoral responses to plasmid-encoded antigen. Moreover, other systems for gene delivery were investigated including CPP-modified CS and cationic nanoparticles. The results showed that these nonviral vectors considerably increased plasmid DNA uptake and expression. Collectively promising results obtained in preclinical studies suggest the usefulness of these safe delivery systems for the development of novel therapeutics against chronic hepatitis B. PMID:26633356

  2. Acid-Responsive Therapeutic Polymer for Prolonging Nanoparticle Circulation Lifetime and Destroying Drug-Resistant Tumors.

    PubMed

    Piao, Ji-Gang; Gao, Feng; Yang, Lihua

    2016-01-13

    How to destroy drug-resistant tumor cells remains an ongoing challenge for cancer treatment. We herein report on a therapeutic nanoparticle, aHLP-PDA, which has an acid-activated hemolytic polymer (aHLP) grafted onto photothermal polydopamine (PDA) nanosphere via boronate ester bond, in efforts to ablate drug-resistant tumors. Upon exposure to oxidative stress and/or near-infrared laser irradiation, aHLP-PDA nanoparticle responsively releases aHLP, likely via responsive cleavage of boronate ester bond, and thus responsively exhibits acid-facilitated mammalian-membrane-disruptive activity. In vitro cell studies with drug-resistant and/or thermo-tolerant cancer cells show that the aHLP-PDA nanoparticle demonstrates preferential cytotoxicity at acidic pH over physiological pH. When administered intravenously, the aHLP-PDA nanoparticle exhibits significantly prolonged blood circulation lifetime and enhanced tumor uptake compared to bare PDA nanosphere, likely owing to aHLP's stealth effects conferred by its zwitterionic nature at blood pH. As a result, the aHLP-PDA nanoparticle effectively ablates drug-resistant tumors, leading to 100% mouse survival even on the 32nd day after suspension of photothermal treatment, as demonstrated with the mouse model. This work suggests that a combination of nanotechnology with lessons learned in bacterial antibiotic resistance may offer a feasible and effective strategy for treating drug-resistant cancers often found in relapsing patients. PMID:26654626

  3. A Shape Memory Polymer Dialysis Needle Adapter for the Reduction of Hemodynamic Stress within Arteriovenous Grafts

    SciTech Connect

    Ortega, J M; Small, W; Wilson, T S; Benett, W; Loge, J; Maitland, D J

    2006-08-16

    A deployable, shape memory polymer adapter is investigated for reducing the hemodynamic stress caused by a dialysis needle flow within an arteriovenous graft. Computational fluid dynamics simulations of dialysis sessions with and without the adapter demonstrate that the adapter provides a significant decrease in the wall shear stress. In vitro flow visualization measurements are made within a graft model following delivery and actuation of a prototype shape memory polymer adapter. Vascular access complications resulting from arteriovenous (AV) graft failures account for over $1 billion per year in the health care costs of dialysis patients in the U.S.[1] The primary mode of failure of arteriovenous fistulas (AVF's) and polytetrafluoroethylene (PTFE) grafts is the development of intimal hyperplasia (IH) and the subsequent formation of stenotic lesions, resulting in a graft flow decline. The hemodynamic stresses arising within AVF's and PTFE grafts play an important role in the pathogenesis of IH. Studies have shown that vascular damage can occur in regions where there is flow separation, oscillation, or extreme values of wall shear stress (WSS).[2] Nevaril et al.[3] show that exposure of red blood cells to WSS's on the order of 1500 dynes/cm2 can result in hemolysis. Hemodynamic stress from dialysis needle flow has recently been investigated for the role it plays in graft failure. Using laser Doppler velocimetry measurements, Unnikrishnan et al.[4] show that turbulence intensities are 5-6 times greater in the AV flow when the needle flow is present and that increased levels of turbulence exist for approximately 7-8cm downstream of the needle. Since the AVF or PTFE graft is exposed to these high levels of hemodynamic stress several hours each week during dialysis sessions, it is quite possible that needle flow is an important contributor to vascular access occlusion.[4] We present a method for reducing the hemodynamic stress in an AV graft by tailoring the fluid dynamics of the dialysis needle flow using a deployable shape memory polymer (SMP) dialysis needle adapter. Such an adapter is deployed through the needle into the graft where it is actuated into an expanded shape using thermal energy. The expanded adapter has a tube-like shape, in which the distal end has a larger cross-sectional area than that of the needle. When the dialysis session is completed, the adapter is retracted through the needle. In this initial study, we conduct computational fluid dynamics (CFD) simulations to assess the changes in the hemodynamic stress on a graft wall when the SMP adapter is utilized. Additionally, we fabricate a prototype SMP adapter and deploy it in an in vitro model of an AV graft.

  4. Coarse-grained simulation of molecular mechanisms of recovery in thermally activated shape-memory polymers

    NASA Astrophysics Data System (ADS)

    Abberton, Brendan C.; Liu, Wing Kam; Keten, Sinan

    2013-12-01

    Thermally actuated shape-memory polymers (SMPs) are capable of being programmed into a temporary shape and then recovering their permanent reference shape upon exposure to heat, which facilitates a phase transition that allows dramatic increase in molecular mobility. Experimental, analytical, and computational studies have established empirical relations of the thermomechanical behavior of SMPs that have been instrumental in device design. However, the underlying mechanisms of the recovery behavior and dependence on polymer microstructure remain to be fully understood for copolymer systems. This presents an opportunity for bottom-up studies through molecular modeling; however, the limited time-scales of atomistic simulations prohibit the study of key performance metrics pertaining to recovery. In order to elucidate the effects of phase fraction, recovery temperature, and deformation temperature on shape recovery, here we investigate the shape-memory behavior in a copolymer model with coarse-grained potentials using a two-phase molecular model that reproduces physical crosslinking. Our simulation protocol allows observation of upwards of 90% strain recovery in some cases, at time-scales that are on the order of the timescale of the relevant relaxation mechanism (stress relaxation in the unentangled soft-phase). Partial disintegration of the glassy phase during mechanical deformation is found to contribute to irrecoverable strain. Temperature dependence of the recovery indicates nearly full elastic recovery above the trigger temperature, which is near the glass-transition temperature of the rubbery switching matrix. We find that the trigger temperature is also directly correlated with the deformation temperature, indicating that deformation temperature influences the recovery temperatures required to obtain a given amount of shape recovery, until the plateau regions overlap above the transition region. Increasing the fraction of glassy phase results in higher strain recovery at low to intermediate temperatures, a widening of the transition region, and an eventual crossover at high temperatures. Our results corroborate experimental findings on shape-memory behavior and provide new insight into factors governing deformation recovery that can be leveraged in biomaterials design. The established computational methodology can be extended in straightforward ways to investigate the effects of monomer chemistry, low-molecular-weight solvents, physical and chemical crosslinking, different phase-separation morphologies, and more complicated mechanical deformation toward predictive modeling capabilities for stimuli-responsive polymers.

  5. Study on the activation of styrene-based shape memory polymer by medium-infrared laser light

    SciTech Connect

    Leng Jinsong; Yu Kai; Lan Xin; Zhang Dawei; Liu Yanju

    2010-03-15

    This paper demonstrates the feasibility of shape memory polymer (SMP) activation by medium-infrared laser light. Medium-infrared light is transmitted by an optical fiber embedded in the SMP matrix, and the shape recovery process and temperature distribution are recorded by an infrared camera. Light-induced SMP exhibits potential applications in biomedicines and flexible displays.

  6. Adjusting the Proportion of Electron-Withdrawing Groups in a Graft Functional Polymer for Multilevel Memory Performance.

    PubMed

    Wu, Linxin; Wang, Peng; Zhang, Chunyu; He, Jinghui; Chen, Dongyun; Jun, Jiang; Xu, Qingfeng; Lu, Jianmei

    2016-01-01

    A polymer containing aldehyde active groups (PVB) was synthesized by atom transfer radical polymerization (ATRP), acting as a polymer precursor to graft a functional moiety via nucleophilic addition reaction. DHI (2-(1,5-dimethyl-hexyl)-6-hydrazino-benzo[de]isoquinoline-1,3-dione) and NPH (nitrophenyl hydrazine) groups, which contain naphthalimides that act as narrow traps and nitro groups that act as deep traps, were anchored onto the PVB at different ratios. A series of graft polymers were obtained and named PVB-DHI, PVB-DHI4 -NPH, PVB-DHI-NPH4 , and PVB-NPH. The chemical composition of the polymers was analyzed by (1) H-NMR spectroscopy and X-ray photoelectron spectroscopy (XPS). Memory devices were prepared from the polymers, and I-V characteristics were measured to determine the performance. By adjusting the ratio of different electron acceptors (DHI and NPH) to 4:1, ternary memory behavior was achieved. The relationship between memory behavior of PVB-DHIx NPHy and acceptor groups as well as their conduction mechanism were studied in detail. PMID:26395326

  7. Fabrication and Characterization of Cylindrical Light Diffusers Comprised of Shape Memory Polymer

    SciTech Connect

    Small IV, W; Buckley, P R; Wilson, T S; Loge, J M; Maitland, K D; Maitland, D J

    2007-01-29

    We have developed a technique for constructing light diffusing devices comprised of a flexible shape memory polymer (SMP) cylindrical diffuser attached to the tip of an optical fiber. Devices were fabricated by casting an SMP rod over the cleaved tip of an optical fiber and media blasting the SMP rod to create a light diffusing surface. The axial and polar emission profiles and circumferential (azimuthal) uniformity were characterized for various blasting pressures, nozzle-to-sample distances, and nozzle translation speeds. The diffusers were generally strongly forward-directed and consistently withstood over 8 W of incident infrared laser light without suffering damage when immersed in water. These devices are suitable for various endoluminal and interstitial biomedical applications.

  8. Thermomechanical Properties, Collapse Pressure, and Expansion of Shape Memory Polymer Neurovascular Stent Prototypes

    PubMed Central

    Baer, Graldine M.; Wilson, Thomas S.; Small, Ward; Hartman, Jonathan; Benett, William J.; Matthews, Dennis L.; Maitland, Duncan J.

    2011-01-01

    Shape memory polymer stent prototypes were fabricated from thermoplastic polyurethane. Commercial stents are generally made of stainless steel or other alloys. These alloys are too stiff and prevent most stent designs from being able to navigate small and tortuous vessels to reach intracranial lesions. A solid tubular model and a high flexibility laser etched model are presented. The stents were tested for collapse in a pressure chamber. At 37C, the full collapse pressure was comparable to that of commercially available stents, and higher than the estimated maximum pressure exerted by intracranial arteries. However, there is a potential for onset of collapse, which needs further study. The stents were crimped and expanded, the laser-etched stent showed full recovery with an expansion ratio of 2.7 and a 1% axial shortening. PMID:19107804

  9. Self-healing of sandwich structures with a grid stiffened shape memory polymer syntactic foam core

    NASA Astrophysics Data System (ADS)

    John, Manu; Li, Guoqiang

    2010-07-01

    In this paper, a new sandwich with an orthogrid stiffened shape memory polymer (SMP) based syntactic foam core was proposed, fabricated, programmed, impacted, healed (sealed), and compression tested, for the purposes of healing impact damage repeatedly and almost autonomously. Two prestrain levels (3% and 20%), two impact energy levels (30.0 and 53.3 J), and two recovery (healing) conditions (2D confined and 3D confined) were employed in this paper. Up to seven impact-healing cycles were conducted. Macroscopic and microscopic damage-healing observation and analysis were implemented. Residual strength was evaluated using an anti-buckling compression test fixture. It was found that the healing efficiency was over 100% for almost all the impact-healing cycles; programming using 20% prestrain led to higher residual strength than that with 3% prestrain; 3D confined recovery resulted in higher residual strength than 2D confined recovery; and as the impact energy increased, the healing efficiency slightly decreased.

  10. a Glass Transition Model for Shape Memory Polymer and its Composite

    NASA Astrophysics Data System (ADS)

    Zhou, Bo; Liu, Yan-Ju; Lan, Xin; Leng, Jin-Song; Yoon, Sung-Ho

    As novel smart materials, shape memory polymer (SMP) and its composite (SMPC) have the ability to regain its original shape after undergoing significant deformation upon heating or other external stimuli such as light, chemic condition and so on. Their special behaviors much depends on the glass transitions due to the increasing of material temperature. Dynamic Mechanical Analysis (DMA) tests are performed on the styrene-based SMP and its carbon fiber fabric reinforced SMPC to investigate their glass transition behaviors. Three glass transition critical temperatures of SMP or SMPC are defined and a method to determine their values from DMA tests is supposed. A glass transition model is developed to describe the glass transition behaviors of SMP or SMPC based on the results of DMA tests. Numerical calculations illustrate the method determining the glass transition critical temperature is reasonable and the model can well predict the glass transition behaviors of SMP or SMPC.

  11. Effect of Biodegradable Shape-Memory Polymers on Proliferation of 3T3 Cells

    NASA Astrophysics Data System (ADS)

    Xu, Shuo-Gui; Zhang, Peng; Zhu, Guang-Ming; Jiang, Ying-Ming

    2011-07-01

    This article evaluates the in vitro biocompatibility for biodegradable shape-memory polymers (BSMP) invented by the authors. 3T3 cells (3T3-Swiss albino GNM 9) of primary and passaged cultures were inoculated into two kinds of carriers: the BSMP carrier and the control group carrier. Viability, proliferation, and DNA synthesis (the major biocompatibility parameters), were measured and evaluated for both the BSMP and naked carrier via cell growth curve analysis, MTT colorimetry and addition of 3H-TdR to culture media. The results showed that there was no difference between the BSMP carrier and the control dish in terms of viability, proliferation, and metabolism of the 3T3 cells. Overall, the BSMP carrier provides good biocompatibility and low toxicity to cells in vitro, and could indicate future potential for this medium as a biological material for implants in vivo.

  12. A constitutive theory for shape memory polymers: coupling of small and large deformation

    NASA Astrophysics Data System (ADS)

    Tan, Qiao; Liu, Liwu; Liu, Yanju; Leng, Jinsong; Yan, Xiangqiao; Wang, Haifang

    2013-04-01

    At high temperatures, SMPs share attributes like rubber and exhibit long-range reversibility. In contrast, at low temperatures they become very rigid and are susceptible to plastic, only small strains are allowable. But there relatively little literature has considered the unique small stain (rubber phase) and large stain (glass phase) coupling in SMPs when developing the constitutive modeling. In this work, we present a 3D constitutive model for shape memory polymers in both low temperature small strain regime and high temperature large strain regime. The theory is based on the work of Liu et al. [15]. Four steps of SMP's thermomechanical loadings cycle are considered in the constitutive model completely. The linear elastic and hyperelastic effects of SMP in different temperatures are also fully accounted for in the proposed model by adopt the neo-Hookean model and the Generalized Hooke's laws.

  13. Synergic effect of carbon black and short carbon fiber on shape memory polymer actuation by electricity

    NASA Astrophysics Data System (ADS)

    Leng, Jinsong; Lv, Haibao; Liu, Yanju; Du, Shanyi

    2008-11-01

    This paper presents a study on the effect of carbon black (CB) and short carbon fibers (SCFs) on shape memory polymer (SMP) actuation by applying electric current. The coexistence of CB and SCF electrically conductive networks, supporting each other, resulting in significant improvement of electrical properties, was supported by optical microscopy, while the roles of particulate and fibrous fillers were distinguished by scanning electron microscopy. In sequence, the volume resistivity curves of one filler systems and two fillers systems were figured out and compared. Moreover, experimental results substantiated that the actuation voltage of two-filler SMP composites' shape recovery was prominently lower in comparison with that of one-filler systems at the same filler content. Additional, the response of glass transition temperature (Tg) and thermomechanical properties to filler content and two fillers' synergic effect were characterized and illuminated experimentally.

  14. An annulus fibrosus closure device based on a biodegradable shape-memory polymer network.

    PubMed

    Sharifi, Shahriar; van Kooten, Theo G; Kranenburg, Hendrik-Jan C; Meij, Bjrn P; Behl, Marc; Lendlein, Andreas; Grijpma, Dirk W

    2013-11-01

    Injuries to the intervertebral disc caused by degeneration or trauma often lead to tearing of the annulus fibrosus (AF) and extrusion of the nucleus pulposus (NP). This can compress nerves and cause lower back pain. In this study, the characteristics of poly(D,L-lactide-co-trimethylene carbonate) networks with shape-memory properties have been evaluated in order to prepare biodegradable AF closure devices that can be implanted minimally invasively. Four different macromers with (D,L-lactide) to trimethylene carbonate (DLLA:TMC) molar ratios of 80:20, 70:30, 60:40 and 40:60 with terminal methacrylate groups and molecular weights of approximately 30 kg mol(-1) were used to prepare the networks by photo-crosslinking. The mechanical properties of the samples and their shape-memory properties were determined at temperatures of 0 C and 40 C by tensile tests- and cyclic, thermo-mechanical measurements. At 40 C all networks showed rubber-like behavior and were flexible with elastic modulus values of 1.7-2.5 MPa, which is in the range of the modulus values of human annulus fibrosus tissue. The shape-memory characteristics of the networks were excellent with values of the shape-fixity and the shape-recovery ratio higher than 98 and 95%, respectively. The switching temperatures were between 10 and 39 C. In vitro culture and qualitative immunocytochemistry of human annulus fibrosus cells on shape-memory films with DLLA:TMC molar ratios of 60:40 showed very good ability of the networks to support the adhesion and growth of human AF cells. When the polymer network films were coated by adsorption of fibronectin, cell attachment, cell spreading, and extracellular matrix production was further improved. Annulus fibrosus closure devices were prepared from these AF cell-compatible materials by photo-polymerizing the reactive precursors in a mold. Insertion of the multifunctional implant in the disc of a cadaveric canine spine showed that these shape-memory devices could be implanted through a small slit and to some extent deploy self-sufficiently within the disc cavity. PMID:23932501

  15. Thermo-mechanical and micro-structural characterization of shape memory polymer foams

    NASA Astrophysics Data System (ADS)

    di Prima, Matthew Allen

    The need for a set of design criteria, models, and limits for the use of shape memory polymer foams was proposed. The effect of temperature and strain on the mechanical behavior; compression, tensile, cyclic compression, constrained recovery, and free strain recovery of the material was used to determine the operational limits of the material. Next, the damage mechanism and viscoelastic effects in compressive cycling were determined through further mechanical testing and with the incorporation of three dimensional structure mapping via micro-CT scanning. The influence of microstructure was determined by testing the basic thermomechanical, viscoelactic, and shape recovery behavior of foams with relative densities of 20, 30, and 40 percent. A similar suite of tests were then performed with the base epoxy material to generate the material properties for computational modeling. This data was then combined with three dimensional microstructures generated from micro-CT scans to develop material models for shape memory foams. These models were then validated by comparing model results to the experimental results under similar conditions.

  16. Fabrication of a Bioactive, PCL-based "Self-fitting" Shape Memory Polymer Scaffold.

    PubMed

    Nail, Lindsay N; Zhang, Dawei; Reinhard, Jessica L; Grunlan, Melissa A

    2015-01-01

    Tissue engineering has been explored as an alternative strategy for the treatment of critical-sized cranio-maxillofacial (CMF) bone defects. Essential to the success of this approach is a scaffold that is able to conformally fit within an irregular defect while also having the requisite biodegradability, pore interconnectivity and bioactivity. By nature of their shape recovery and fixity properties, shape memory polymer (SMP) scaffolds could achieve defect "self-fitting." In this way, following exposure to warm saline (~60 C), the SMP scaffold would become malleable, permitting it to be hand-pressed into an irregular defect. Subsequent cooling (~37 C) would return the scaffold to its relatively rigid state within the defect. To meet these requirements, this protocol describes the preparation of SMP scaffolds prepared via the photochemical cure of biodegradable polycaprolactone diacrylate (PCL-DA) using a solvent-casting particulate-leaching (SCPL) method. A fused salt template is utilized to achieve pore interconnectivity. To realize bioactivity, a polydopamine coating is applied to the surface of the scaffold pore walls. Characterization of self-fitting and shape memory behaviors, pore interconnectivity and in vitro bioactivity are also described. PMID:26556112

  17. Multiple shape memory polymers based on laminates formed from thiol-click chemistry based polymerizations.

    PubMed

    Podgórski, M; Wang, C; Bowman, C N

    2015-09-14

    This investigation details the formation of polymer network trilayer laminates formed by thiol-X click chemistries, and their subsequent implementation and evaluation for quadruple shape memory behavior. Thiol-Michael addition and thiol-isocyanate-based crosslinking reactions were employed to fabricate each of the laminate's layers with independent control of the chemistry and properties of each layer and outstanding interlayer adhesion and stability. The characteristic features of step-growth thiol-X reactions, such as excellent network uniformity and narrow thermal transitions as well as their stoichiometric nature, enabled fabrication of trilayer laminates with three distinctly different glass transition temperatures grouped within a narrow range of 100 °C. Through variations in the layer thicknesses, a step-wise modulus drop as a function of temperature was achieved. This behavior allowed multi-step programming and the demonstration and quantification of quadruple shape memory performance. As is critical for this performance, the interface connecting the layers was evaluated in stoichiometric as well as off-stoichiometric systems. It was shown that the laminated structures exhibit strong interfacial binding and hardly suffer any delamination during cyclic material testing and deformation. PMID:26234205

  18. PCL-based Shape Memory Polymers with Variable PDMS Soft Segment Lengths

    PubMed Central

    Zhang, Dawei; Giese, Melissa L.; Prukop, Stacy L.; Grunlan, Melissa A.

    2012-01-01

    Thermoresponsive shape memory polymers (SMPs) are stimuli-responsive materials that return to their permanent shape from a temporary shape in response to heating. The design of new SMPs which obtain a broader range of properties including mechanical behavior is critical to realize their potential in biomedical as well as industrial and aerospace applications. To tailor the properties of SMPs, AB networks comprised of two distinct polymer components have been investigated but are overwhelmingly limited to those in which both components are organic. In this present work, we prepared inorganic-organic SMPs comprised of inorganic polydimethyl-siloxane (PDMS) segments of varying lengths and organic poly(?-caprolactone) (PCL) segments. PDMS has a particularly low Tg (?125 C) which makes it a particularly effective soft segment to tailor the mechanical properties of PCL-based SMPs. The SMPs were prepared via the rapid photocure of solutions of diacrylated PCL40-block-PDMSm-block-PCL40 macromers (m = 20, 37, 66 and 130). The resulting inorganic-organic SMP networks exhibited excellent shape fixity and recovery. By changing the PDMS segment length, the thermal, mechanical, and surface properties were systematically altered. PMID:22904597

  19. Silicone Membranes to Inhibit Water Uptake into Thermoset Polyurethane Shape-Memory Polymer Conductive Composites

    PubMed Central

    Yu, Ya-Jen; Infanger, Stephen; Grunlan, Melissa A.; Maitland, Duncan J.

    2014-01-01

    Electroactive shape memory polymer (SMP) composites capable of shape actuation via resistive heating are of interest for various biomedical applications. However, water uptake into SMPs will produce a depression of the glass transition temperature (Tg) resulting in shape recovery in vivo. While water actuated shape recovery may be useful, it is foreseen to be undesirable during early periods of surgical placement into the body. Silicone membranes have been previously reported to prevent release of conductive filler from an electroactive polymer composite in vivo. In this study, a silicone membrane was used to inhibit water uptake into a thermoset SMP composite containing conductive filler. Thermoset polyurethane (PU) SMPs were loaded with either 5 wt% carbon black (CB) or 5 wt% carbon nanotubes (CNT) and subsequently coated with either an Al2O3- or silica-filled silicone membrane. It was observed that the silicone membranes, particularly the silica-filled membrane, reduced the rate of water absorption (37 °C) and subsequent Tg depression versus uncoated composites. In turn, this led to a reduction in the rate of recovery of the permanent shape when exposed to water at 37 °C. PMID:25663711

  20. Laser Chemosensor with Rapid Responsivity and Inherent Memory Based on a Polymer of Intrinsic Microporosity

    PubMed Central

    Wang, Yue; McKeown, Neil B.; Msayib, Kadhum J.; Turnbull, Graham A.; Samuel, Ifor D. W.

    2011-01-01

    This work explores the use of a polymer of intrinsic microporosity (PIM-1) as the active layer within a laser sensor to detect nitroaromatic-based explosive vapors. We show successful detection of dinitrobenzene (DNB) by monitoring the real-time photoluminescence. We also show that PIM-1 has an inherent memory, so that it accumulates the analyte during exposure. In addition, the optical gain and refractive index of the polymer were studied by amplified spontaneous emission and variable-angle ellipsometry, respectively. A second-order distributed feedback PIM-1 laser sensor was fabricated and found to show an increase in laser threshold of 2.5 times and a reduction of the laser slope efficiency by 4.4 times after a 5-min exposure to the DNB vapor. For pumping at 2 times threshold, the lasing action was stopped within 30 s indicating that PIM-1 has a very fast responsivity and as such has a potential sensing ability for ultra-low-concentration explosives. PMID:22163750

  1. S 17092: a prolyl endopeptidase inhibitor as a potential therapeutic drug for memory impairment. Preclinical and clinical studies.

    PubMed

    Morain, Philippe; Lestage, Pierre; De Nanteuil, Guillaume; Jochemsen, Roeline; Robin, Jean-Loc; Guez, David; Boyer, Pierre-Alain

    2002-01-01

    Any treatment that could positively modulate central neuropeptides levels would provide a promising therapeutic approach to the treatment of cognitive deficits associated with aging and/or neurodegenerative diseases. Therefore, based on the activity in rodents, S 17092 (2S,3aS,7aS)-1][(R,R)-2-phenylcyclopropyl]carbonyl]-2-[(thiazolidin-3-yl)carbonyl]octahydro-1H-indole) has been selected as a potent inhibitor of cerebral prolyl-endopeptidase (PEP). By retarding the degradation of neuroactive peptides, S 17092 was successfully used in a variety of memory tasks. These tasks explored short-term, long-term, reference and working memory in aged mice, as well as in rodents and monkeys with chemically induced amnesia or spontaneous memory deficits. S 17092 has also been safely administered to humans, and showed a clear peripheral expression of its mechanism of action through its inhibitory effect upon PEP activity in plasma. S 17092 exhibited central effects, as evidenced by EEG recording in healthy volunteers, and could improve a delayed verbal memory task. Collectively, the preclinical and clinical effects of S 17092 have suggested a promising role for this compound as an agent for the treatment of cognitive disorders associated with cerebral aging. PMID:12070525

  2. Estimation of creep and recovery behavior of a shape memory polymer

    NASA Astrophysics Data System (ADS)

    Sakai, Takenobu; Tao, Takayuki; Somiya, Satoshi

    2015-09-01

    The shape recovery and shape fixity properties of shape memory polymers (SMPs), advanced functional materials, were investigated in this study. Although the shape recovery behavior of these polymers has been examined from a viscoelastic point of view, questions remain with regard to quantifying the recovery behavior of SMPs. SMPs can recover their shape after the molding process; this recovery occurs via creep recovery and/or shape recovery; an estimation of SMP recovery requires a good understanding of both processes. In this study, the time-temperature superposition principle was applied to the creep and shape recovery behavior of SMPs. The creep behavior was estimated using an experimentally obtained master curve and time-temperature shift factors. Our estimated results were in good agreement with the experimental data. However, the estimation of the creep recovery with changing temperature below or above the glass transition temperature was not successful due to the lack of consideration of the shape recovery behavior. The time and temperature dependency of the shape recovery were confirmed for creep behavior, using the master curve for the recovery ratio and the corresponding shift factors for shape recovery. The values of the shape recovery shift factors differed from those for the time-temperature shift factors obtained for creep behavior. Therefore, these shape recovery shift factors were used in the estimation of creep and shape recovery behavior using the master curve for the creep tests. The estimated results were closer to the results obtained experimentally. Moreover, our results indicated that the recovery behavior above Tg was dominated by shape recovery as a result of polymer viscoelasticity.

  3. Estimation of creep and recovery behavior of a shape memory polymer

    NASA Astrophysics Data System (ADS)

    Sakai, Takenobu; Tao, Takayuki; Somiya, Satoshi

    2015-11-01

    The shape recovery and shape fixity properties of shape memory polymers (SMPs), advanced functional materials, were investigated in this study. Although the shape recovery behavior of these polymers has been examined from a viscoelastic point of view, questions remain with regard to quantifying the recovery behavior of SMPs. SMPs can recover their shape after the molding process; this recovery occurs via creep recovery and/or shape recovery; an estimation of SMP recovery requires a good understanding of both processes. In this study, the time-temperature superposition principle was applied to the creep and shape recovery behavior of SMPs. The creep behavior was estimated using an experimentally obtained master curve and time-temperature shift factors. Our estimated results were in good agreement with the experimental data. However, the estimation of the creep recovery with changing temperature below or above the glass transition temperature was not successful due to the lack of consideration of the shape recovery behavior. The time and temperature dependency of the shape recovery were confirmed for creep behavior, using the master curve for the recovery ratio and the corresponding shift factors for shape recovery. The values of the shape recovery shift factors differed from those for the time-temperature shift factors obtained for creep behavior. Therefore, these shape recovery shift factors were used in the estimation of creep and shape recovery behavior using the master curve for the creep tests. The estimated results were closer to the results obtained experimentally. Moreover, our results indicated that the recovery behavior above Tg was dominated by shape recovery as a result of polymer viscoelasticity.

  4. An approach to predict the shape-memory behavior of amorphous polymers from Dynamic Mechanical Analysis (DMA) data

    NASA Astrophysics Data System (ADS)

    Kuki, Ákos; Czifrák, Katalin; Karger-Kocsis, József; Zsuga, Miklós; Kéki, Sándor

    2015-02-01

    The prediction of shape-memory behavior is essential regarding the design of a smart material for different applications. This paper proposes a simple and quick method for the prediction of shape-memory behavior of amorphous shape memory polymers (SMPs) on the basis of a single dynamic mechanical analysis (DMA) temperature sweep at constant frequency. All the parameters of the constitutive equations for linear viscoelasticity are obtained by fitting the DMA curves. The change with the temperature of the time-temperature superposition shift factor ( a T ) is expressed by the Williams-Landel-Ferry (WLF) model near and above the glass transition temperature ( T g ), and by the Arrhenius law below T g . The constants of the WLF and Arrhenius equations can also be determined. The results of our calculations agree satisfactorily with the experimental free recovery curves from shape-memory tests.

  5. Solution-processable low-voltage and flexible floating-gate memories based on an n-type polymer semiconductor and high-k polymer gate dielectrics.

    PubMed

    Li, Jinhua; Yan, Feng

    2014-08-13

    High-performance low-voltage flash memories based on organic floating-gate field-effect transistors are prepared by a solution process for the first time. Transistors with a high-mobility n-type polymer semiconductor, poly{[N,N(')-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)}, and a high-k polymer gate dielectric, poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (k ≈ 60), are successfully fabricated on flexible substrates. A thin layer of Au nanoparticles is embedded in the gate dielectric, which can store injected charge from the channel and result in a memory effect. The organic memories demonstrate high carrier mobilities (>0.3 cm(2)/(V s)), low program/erase voltages (±6 V), little degradation after 10(5) program/erase cycles, and good retention after 10(5) s, which suggest great promise in the application of nonvolatile memories in flexible electronics. PMID:25026221

  6. Inorganic-organic shape memory polymers and foams for bone defect repairs

    NASA Astrophysics Data System (ADS)

    Zhang, Dawei

    The ultimate goal of this research was to develop a "self-fitting" shape memory polymer (SMP) scaffold for the repair of craniomaxillofacial (CMF) bone defects. CMF defects may be caused by trauma, tumor removal or congenital abnormalities and represent a major class of bone defects. Their repair with autografts is limited by availability, donor site morbidity and complex surgical procedures. In addition, shaping and positioning of these rigid grafts into irregular defects is difficult. Herein, we have developed SMP scaffolds which soften at T > 56 C, allowing them to conformally fit into a bone defect. Upon cooling to body temperature, the scaffold becomes rigid and mechanically locks in place. This research was comprised of four major studies. In the first study, photocrosslinkable acrylated (AcO) SMP macromers containing a poly(epsilon-caprolactone) (PCL) segment and polydimethylsiloxane (PDMS) segments were synthesized with the general formula: AcO-PCL40-block-PDMS m-block-PCL40-OAc. By varying the PDMS segment length (m), solid SMPs with highly tunable mechanical properties and excellent shape memory abilities were prepared. In the second study, porous SMP scaffolds were fabricated based on AcO-PCL 40-block-PDMS37-block-PCL 40-OAc via a revised solvent casting particulate leaching (SCPL) method. By tailoring scaffold parameters including salt fusion, macromer concentration and salt size, scaffold properties (e.g. pore features, compressive modulus and shape memory behavior) were tuned. In the third study, porous SMP scaffolds were produced from macromers with variable PDMS segment lengths (m = 0 -- 130) via an optimized SCPL method. The impact on pore features, thermal, mechanical, and shape memory properties as well as degradation rates were investigated. In the final study, a bioactive polydopamine coating was applied onto pore surfaces of the SMP scaffold prepared from PCL diacrylate. The thin coating did not affect intrinsic bulk properties of the scaffold. However, the coating significantly increased its bioactivity, giving rise to the formation of "bone-bonding" hydroxyapatite (HAp) when exposed to simulated body fluid (SBF). It was also shown that the coating largely enhanced the scaffold's capacities to support osteoblasts adhesion, proliferation and osteogenesis. Thus, the polydopamine coating should enhance the performance of the "self-fitting" SMP scaffolds for the repair of bone defects.

  7. Memory.

    ERIC Educational Resources Information Center

    McKean, Kevin

    1983-01-01

    Discusses current research (including that involving amnesiacs and snails) into the nature of the memory process, differentiating between and providing examples of "fact" memory and "skill" memory. Suggests that three brain parts (thalamus, fornix, mammilary body) are involved in the memory process. (JN)

  8. High Performance Transparent Transistor Memory Devices Using Nano-Floating Gate of Polymer/ZnO Nanocomposites

    PubMed Central

    Shih, Chien-Chung; Lee, Wen-Ya; Chiu, Yu-Cheng; Hsu, Han-Wen; Chang, Hsuan-Chun; Liu, Cheng-Liang; Chen, Wen-Chang

    2016-01-01

    Nano-floating gate memory devices (NFGM) using metal nanoparticles (NPs) covered with an insulating polymer have been considered as a promising electronic device for the next-generation nonvolatile organic memory applications NPs. However, the transparency of the device with metal NPs is restricted to 60~70% due to the light absorption in the visible region caused by the surface plasmon resonance effects of metal NPs. To address this issue, we demonstrate a novel NFGM using the blends of hole-trapping poly (9-(4-vinylphenyl) carbazole) (PVPK) and electron-trapping ZnO NPs as the charge storage element. The memory devices exhibited a remarkably programmable memory window up to 60 V during the program/erase operations, which was attributed to the trapping/detrapping of charge carriers in ZnO NPs/PVPK composite. Furthermore, the devices showed the long-term retention time (>105 s) and WRER test (>200 cycles), indicating excellent electrical reliability and stability. Additionally, the fabricated transistor memory devices exhibited a relatively high transparency of 90% at the wavelength of 500 nm based on the spray-coated PEDOT:PSS as electrode, suggesting high potential for transparent organic electronic memory devices. PMID:26831222

  9. High Performance Transparent Transistor Memory Devices Using Nano-Floating Gate of Polymer/ZnO Nanocomposites

    NASA Astrophysics Data System (ADS)

    Shih, Chien-Chung; Lee, Wen-Ya; Chiu, Yu-Cheng; Hsu, Han-Wen; Chang, Hsuan-Chun; Liu, Cheng-Liang; Chen, Wen-Chang

    2016-02-01

    Nano-floating gate memory devices (NFGM) using metal nanoparticles (NPs) covered with an insulating polymer have been considered as a promising electronic device for the next-generation nonvolatile organic memory applications NPs. However, the transparency of the device with metal NPs is restricted to 60~70% due to the light absorption in the visible region caused by the surface plasmon resonance effects of metal NPs. To address this issue, we demonstrate a novel NFGM using the blends of hole-trapping poly (9-(4-vinylphenyl) carbazole) (PVPK) and electron-trapping ZnO NPs as the charge storage element. The memory devices exhibited a remarkably programmable memory window up to 60 V during the program/erase operations, which was attributed to the trapping/detrapping of charge carriers in ZnO NPs/PVPK composite. Furthermore, the devices showed the long-term retention time (>105 s) and WRER test (>200 cycles), indicating excellent electrical reliability and stability. Additionally, the fabricated transistor memory devices exhibited a relatively high transparency of 90% at the wavelength of 500 nm based on the spray-coated PEDOT:PSS as electrode, suggesting high potential for transparent organic electronic memory devices.

  10. Epitaxial Growth of Thin Ferroelectric Polymer Films on Graphene Layer for Fully Transparent and Flexible Nonvolatile Memory.

    PubMed

    Kim, Kang Lib; Lee, Wonho; Hwang, Sun Kak; Joo, Se Hun; Cho, Suk Man; Song, Giyoung; Cho, Sung Hwan; Jeong, Beomjin; Hwang, Ihn; Ahn, Jong-Hyun; Yu, Young-Jun; Shin, Tae Joo; Kwak, Sang Kyu; Kang, Seok Ju; Park, Cheolmin

    2016-01-13

    Enhancing the device performance of organic memory devices while providing high optical transparency and mechanical flexibility requires an optimized combination of functional materials and smart device architecture design. However, it remains a great challenge to realize fully functional transparent and mechanically durable nonvolatile memory because of the limitations of conventional rigid, opaque metal electrodes. Here, we demonstrate ferroelectric nonvolatile memory devices that use graphene electrodes as the epitaxial growth substrate for crystalline poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) polymer. The strong crystallographic interaction between PVDF-TrFE and graphene results in the orientation of the crystals with distinct symmetry, which is favorable for polarization switching upon the electric field. The epitaxial growth of PVDF-TrFE on a graphene layer thus provides excellent ferroelectric performance with high remnant polarization in metal/ferroelectric polymer/metal devices. Furthermore, a fully transparent and flexible array of ferroelectric field effect transistors was successfully realized by adopting transparent poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] semiconducting polymer. PMID:26618802

  11. Strong electroactive biodegradable shape memory polymer networks based on star-shaped polylactide and aniline trimer for bone tissue engineering.

    PubMed

    Xie, Meihua; Wang, Ling; Ge, Juan; Guo, Baolin; Ma, Peter X

    2015-04-01

    Preparation of functional shape memory polymer (SMP) for tissue engineering remains a challenge. Here the synthesis of strong electroactive shape memory polymer (ESMP) networks based on star-shaped polylactide (PLA) and aniline trimer (AT) is reported. Six-armed PLAs with various chain lengths were chemically cross-linked to synthesize SMP. After addition of an electroactive AT segment into the SMP, ESMP was obtained. The polymers were characterized by (1)H NMR, GPC, FT-IR, CV, DSC, DMA, tensile test, and degradation test. The SMP and ESMP exhibited strong mechanical properties (modulus higher than GPa) and excellent shape memory performance: short recovery time (several seconds), high recovery ratio (over 94%), and high fixity ratio (almost 100%). Moreover, cyclic voltammetry test confirmed the electroactivity of the ESMP. The ESMP significantly enhanced the proliferation of C2C12 cells compared to SMP and linear PLA (control). In addition, the ESMP greatly improved the osteogenic differentiation of C2C12 myoblast cells compared to PH10 and PLA in terms of ALP enzyme activity, immunofluorescence staining, and relative gene expression by quantitative real-time polymerase chain reaction (qRT-PCR). These intelligent SMPs and electroactive SMP with strong mechanical properties, tunable degradability, good electroactivity, biocompatibility, and enhanced osteogenic differentiation of C2C12 cells show great potential for bone regeneration. PMID:25742188

  12. A simplified constitutive model for predicting shape memory polymers deformation behavior

    NASA Astrophysics Data System (ADS)

    Li, Yunxin; Guo, Siu-Siu; He, Yuhao; Liu, Zishun

    2015-12-01

    Shape memory polymers (SMPs) can keep a temporary shape after pre-deformation at a higher temperature and subsequent cooling. When they are reheated, their original shapes can be recovered. Such special characteristics of SMPs make them widely used in aerospace structures, biomedical devices, functional textiles and other devices. Increasing usefulness of SMPs motivates us to further understand their thermomechanical properties and deformation behavior, of which the development of appropriate constitutive models for SMPs is imperative. There is much work in literatures that address constitutive models of the thermo-mechanical coupling in SMPs. However, due to their complex forms, it is difficult to apply these constitutive models in the real world. In this paper, a three-element model with simple form is proposed to investigate the thermo-mechanical small strain (within 10%) behavior of polyurethane under uniaxial tension. Two different cases of heated recovery are considered: (1) unconstrained free strain recovery and (2) stress recovery under full constraint at a strain level fixed during low temperature unloading. To validate the model, simulated and predicted results are compared with Tobushi's experimental results and good agreement can be observed.

  13. Fabrication and in vitro deployment of a laser-activated shape memory polymer vascular stent

    PubMed Central

    Baer, Graldine M; Small, Ward; Wilson, Thomas S; Benett, William J; Matthews, Dennis L; Hartman, Jonathan; Maitland, Duncan J

    2007-01-01

    Background Vascular stents are small tubular scaffolds used in the treatment of arterial stenosis (narrowing of the vessel). Most vascular stents are metallic and are deployed either by balloon expansion or by self-expansion. A shape memory polymer (SMP) stent may enhance flexibility, compliance, and drug elution compared to its current metallic counterparts. The purpose of this study was to describe the fabrication of a laser-activated SMP stent and demonstrate photothermal expansion of the stent in an in vitro artery model. Methods A novel SMP stent was fabricated from thermoplastic polyurethane. A solid SMP tube formed by dip coating a stainless steel pin was laser-etched to create the mesh pattern of the finished stent. The stent was crimped over a fiber-optic cylindrical light diffuser coupled to an infrared diode laser. Photothermal actuation of the stent was performed in a water-filled mock artery. Results At a physiological flow rate, the stent did not fully expand at the maximum laser power (8.6 W) due to convective cooling. However, under zero flow, simulating the technique of endovascular flow occlusion, complete laser actuation was achieved in the mock artery at a laser power of ~8 W. Conclusion We have shown the design and fabrication of an SMP stent and a means of light delivery for photothermal actuation. Though further studies are required to optimize the device and assess thermal tissue damage, photothermal actuation of the SMP stent was demonstrated. PMID:18042294

  14. Sensing and actuating capabilities of a shape memory polymer composite integrated with hybrid filler

    NASA Astrophysics Data System (ADS)

    Lu, Haibao; Yu, Kai; Liu, Yanju; Leng, Jinsong

    2010-06-01

    In this paper, hybrid fillers, including carbon black (CB) and chopped short carbon fibers (SCF), are integrated into a styrene-based shape memory polymer (SMP) with sensing and actuating capabilities. The hybrid filler is expected to transform insulating SMP into conducting. Static mechanical properties of the SMP composites containing various filler concentrations of hybrid filler reinforcement are studied first, and it is theoretically and experimentally confirmed that the mechanical properties are significantly improved by a factor of filler content of SCF. The excellent electrical properties of this novel type of SMP composite are determined by a four-point-probe method. As a consequence, the sensing properties of SMP composite filled with 5 wt% CB and 2 wt% SCF are characterized by functions of temperature and strain. These two experimental results both aid the use of SMP composites as sensors that respond to changes in temperature or mechanical loads. On the other hand, the actuating capability of SMP composites is also validated and demonstrated. The dynamic mechanical analysis result reveals that the output strength of SMP composites is improved with an increase in filler content of SCF. The actuating capability of SMP composites is subsequently demonstrated in a series of photographs.

  15. Fabrication and In Vitro Deployment of a Laser-Activated Shape Memory Polymer Vascular Stent

    SciTech Connect

    Baer, G M; Small IV, W; Wilson, T S; Benett, W J; Matthews, D L; Hartman, J; Maitland, D J

    2007-04-25

    Vascular stents are small tubular scaffolds used in the treatment of arterial stenosis (narrowing of the vessel). Most vascular stents are metallic and are deployed either by balloon expansion or by self-expansion. A shape memory polymer (SMP) stent may enhance flexibility, compliance, and drug elution compared to its current metallic counterparts. The purpose of this study was to describe the fabrication of a laser-activated SMP stent and demonstrate photothermal expansion of the stent in an in vitro artery model. A novel SMP stent was fabricated from thermoplastic polyurethane. A solid SMP tube formed by dip coating a stainless steel pin was laser-etched to create the mesh pattern of the finished stent. The stent was crimped over a fiber-optic cylindrical light diffuser coupled to an infrared diode laser. Photothermal actuation of the stent was performed in a water-filled mock artery. At a physiological flow rate, the stent did not fully expand at the maximum laser power (8.6 W) due to convective cooling. However, under zero flow, simulating the technique of endovascular flow occlusion, complete laser actuation was achieved in the mock artery at a laser power of {approx}8 W. We have shown the design and fabrication of an SMP stent and a means of light delivery for photothermal actuation. Though further studies are required to optimize the device and assess thermal tissue damage, photothermal actuation of the SMP stent was demonstrated.

  16. Opacification of Shape Memory Polymer Foam Designed for Treatment of Intracranial Aneurysms

    PubMed Central

    Rodriguez, Jennifer N.; Yu, Ya-Jen; Miller, Matthew W.; Wilson, Thomas S.; Hartman, Jonathan; Clubb, Fred J.; Gentry, Brandon; Maitland, Duncan J.

    2012-01-01

    Shape memory polymer (SMP) foam possesses structural and mechanical characteristics that make them very promising as an alternative treatment for intracranial aneurysms. Our SMP foams have low densities, with porosities as high as 98.8%; favorable for catheter delivery and aneurysm filling, but unfavorable for attenuating X-rays. This lack of contrast impedes the progression of this material becoming a viable medical device. This paper reports on increasing radioopacity by incorporating a high-Z element, tungsten particulate filler to attenuate X-rays, while conserving similar physical properties of the original non-opacified SMP foams. The minimal amount of tungsten for visibility was determined and subsequently incorporated into SMP foams, which were then fabricated into samples of increasing thicknesses. These samples were imaged through a pigs skull to demonstrate radio-opacity in situ. Quantification of the increase in image contrast was performed via image processing methods and standard curves were made for varying concentrations of tungsten doped solid and foam SMP. 4% by volume loading of tungsten incorporated into our SMP foams has proven to be an effective method for improving radio-opacity of this material while maintaining the mechanical, physical and chemical properties of the original formulation. PMID:22101759

  17. Shape memory polymers and their composites in aerospace applications: a review

    NASA Astrophysics Data System (ADS)

    Liu, Yanju; Du, Haiyang; Liu, Liwu; Leng, Jinsong

    2014-02-01

    As a new class of smart materials, shape memory polymers and their composites (SMPs and SMPCs) can respond to specific external stimulus and remember the original shape. There are many types of stimulus methods to actuate the deformation of SMPs and SMPCs, of which the thermal- and electro-responsive components and structures are common. In this review, the general mechanism of SMPs and SMPCs are first introduced, the stimulus methods are then discussed to demonstrate the shape recovery effect, and finally, the applications of SMPs and SMPCs that are reinforced with fiber materials in aerospace are reviewed. SMPC hinges and booms are discussed in the part on components; the booms can be divided again into foldable SMPC truss booms, coilable SMPC truss booms and storable tubular extendible member (STEM) booms. In terms of SMPC structures, the solar array and deployable panel, reflector antenna and morphing wing are introduced in detail. Considering the factors of weight, recovery force and shock effect, SMPCs are expected to have great potential applications in aerospace.

  18. Characterizing and modeling the free recovery and constrained recovery behavior of a polyurethane shape memory polymer.

    PubMed

    Volk, Brent L; Lagoudas, Dimitris C; Maitland, Duncan J

    2011-09-01

    In this work, tensile tests and one-dimensional constitutive modeling are performed on a high recovery force polyurethane shape memory polymer that is being considered for biomedical applications. The tensile tests investigate the free recovery (zero load) response as well as the constrained displacement recovery (stress recovery) response at extension values up to 25%, and two consecutive cycles are performed during each test. The material is observed to recover 100% of the applied deformation when heated at zero load in the second thermomechanical cycle, and a stress recovery of 1.5 MPa to 4.2 MPa is observed for the constrained displacement recovery experiments.After performing the experiments, the Chen and Lagoudas model is used to simulate and predict the experimental results. The material properties used in the constitutive model - namely the coefficients of thermal expansion, shear moduli, and frozen volume fraction - are calibrated from a single 10% extension free recovery experiment. The model is then used to predict the material response for the remaining free recovery and constrained displacement recovery experiments. The model predictions match well with the experimental data. PMID:22003272

  19. Facile 3D Metal Electrode Fabrication for Energy Applications via Inkjet Printing and Shape Memory Polymer

    NASA Astrophysics Data System (ADS)

    Roberts, R. C.; Wu, J.; Hau, N. Y.; Chang, Y. H.; Feng, S. P.; Li, D. C.

    2014-11-01

    This paper reports on a simple 3D metal electrode fabrication technique via inkjet printing onto a thermally contracting shape memory polymer (SMP) substrate. Inkjet printing allows for the direct patterning of structures from metal nanoparticle bearing liquid inks. After deposition, these inks require thermal curing steps to render a stable conductive film. By printing onto a SMP substrate, the metal nanoparticle ink can be cured and substrate shrunk simultaneously to create 3D metal microstructures, forming a large surface area topology well suited for energy applications. Polystyrene SMP shrinkage was characterized in a laboratory oven from 150-240C, resulting in a size reduction of 1.97-2.58. Silver nanoparticle ink was patterned into electrodes, shrunk, and the topology characterized using scanning electron microscopy. Zinc-Silver Oxide microbatteries were fabricated to demonstrate the 3D electrodes compared to planar references. Characterization was performed using 10M potassium hydroxide electrolyte solution doped with zinc oxide (57g/L). After a 300s oxidation at 3Vdc, the 3D electrode battery demonstrated a 125% increased capacity over the reference cell. Reference cells degraded with longer oxidations, but the 3D electrodes were fully oxidized for 4 hours, and exhibited a capacity of 5.5mA-hr/cm2 with stable metal performance.

  20. A multi-branch finite deformation constitutive model for a shape memory polymer based syntactic foam

    NASA Astrophysics Data System (ADS)

    Gu, Jianping; Sun, Huiyu; Fang, Changqing

    2015-02-01

    A multi-branch thermoviscoelastic-themoviscoplastic finite deformation constitutive model incorporated with structural and stress relaxation is developed for a thermally activated shape memory polymer (SMP) based syntactic foam. In this paper, the total mechanical deformation of the foam is divided into the components of the SMP and the elastic glass microballoons by using the mixture rule. The nonlinear Adam-Gibbs model is used to describe the structural relaxation of the SMP as the temperature crosses the glass transition temperature (Tg). Further, a multi-branch model combined with the modified Eying model of viscous flow is used to capture the multitude of relaxation processes of the SMP. The deformation of the glass microballoons could be split into elastic and inelastic components. In addition, the phenomenological evolution rule is implemented in order to further characterize the macroscopic post-yield strain softening behaviors of the syntactic foam. A comparison between the numerical simulation and the thermomechanical experiment shows an acceptable agreement. Moreover, a parametric study is conducted to examine the predictability of the model and to provide guidance for reasonable design of the syntactic foam.

  1. Strain rate effect on the thermomechanical behavior of a thermoset shape memory polymer

    NASA Astrophysics Data System (ADS)

    Wang, Anqi; Li, Guoqiang; Meng, Harper

    2013-08-01

    Driven by conformational entropy, a shape memory polymer (SMP) is capable of memorizing typical programming information, such as level of induced strain, deformation sequence and temperature profile. Because strain rate is one of the variables during programming, it is desirable to know whether the strain rate effect can be memorized or not. In this study, the effects of programming strain rate on the thermomechanical behavior of a thermoset SMP were investigated. A polystyrene based thermoset SMP was programmed under various strain rates (1500, 0.1 and 0.0001 s-1) in the glassy state, with the same prestrain level and temperature profiles. The thermomechanical response and some crucial physical properties were investigated via multiple characterization techniques. The test results indicate that programming strain rate has an influence on the glass transition temperature. A higher strain rate consistently leads to higher relaxation of prestrain and thus lower strain fixity. Moreover, the recovery strain and recovery strain rate rely on the pseudo-plastic strain during programming, which is associated with the programming strain rate.

  2. Characterizing and modeling the free recovery and constrained recovery behavior of a polyurethane shape memory polymer

    PubMed Central

    Volk, Brent L; Lagoudas, Dimitris C; Maitland, Duncan J

    2011-01-01

    In this work, tensile tests and one-dimensional constitutive modeling are performed on a high recovery force polyurethane shape memory polymer that is being considered for biomedical applications. The tensile tests investigate the free recovery (zero load) response as well as the constrained displacement recovery (stress recovery) response at extension values up to 25%, and two consecutive cycles are performed during each test. The material is observed to recover 100% of the applied deformation when heated at zero load in the second thermomechanical cycle, and a stress recovery of 1.5 MPa to 4.2 MPa is observed for the constrained displacement recovery experiments. After performing the experiments, the Chen and Lagoudas model is used to simulate and predict the experimental results. The material properties used in the constitutive model namely the coefficients of thermal expansion, shear moduli, and frozen volume fraction are calibrated from a single 10% extension free recovery experiment. The model is then used to predict the material response for the remaining free recovery and constrained displacement recovery experiments. The model predictions match well with the experimental data. PMID:22003272

  3. A self-healing 3D woven fabric reinforced shape memory polymer composite for impact mitigation

    NASA Astrophysics Data System (ADS)

    Nji, Jones; Li, Guoqiang

    2010-03-01

    In this paper, a three-dimensional (3D) woven fabric reinforced shape memory polymer composite for impact mitigation was proposed, fabricated, programmed using a three-step strain-controlled thermomechanical cycle at a pre-strain level of 5% and machined to two groups of specimens (G1 and G2) with dimensions 152.4 mm 101.6 mm 12.7 mm. The specimens were impact tested, transversely, centrally and repeatedly with 32 and 42 J of energy. G1 specimens were healed after each impact until perforation occurred. G2 specimens were not healed after each impact and served as controls. At 32 J impact energy, G2 specimens were perforated at the 9th impact while G1 specimens lasted until the 15th impact; at 42 J impact energy, G2 specimens were perforated at the 5th impact while G1 specimens were perforated at the 7th impact. Visual inspection, C-scan, and scanning electron microscopy techniques were used to evaluate damage, failure modes, and healing efficiency.

  4. The effect of moisture absorption on the physical properties of polyurethane shape memory polymer foams

    NASA Astrophysics Data System (ADS)

    Yu, Ya-Jen; Hearon, Keith; Wilson, Thomas S.; Maitland, Duncan J.

    2011-08-01

    The effect of moisture absorption on the glass transition temperature (Tg) and the stress/strain behavior of network polyurethane shape memory polymer (SMP) foams has been investigated. With our ultimate goal of engineering polyurethane SMP foams for use in blood-contacting environments, we have investigated the effects of moisture exposure on the physical properties of polyurethane foams. To the best of our knowledge, this study is the first to investigate the effects of moisture absorption at varying humidity levels (non-immersion and immersion) on the physical properties of polyurethane SMP foams. The SMP foams were exposed to differing humidity levels for varying lengths of time, and they exhibited a maximum water uptake of 8.0% (by mass) after exposure to 100% relative humidity for 96 h. Differential scanning calorimetry results demonstrated that water absorption significantly decreased the Tg of the foam, with a maximum water uptake shifting the Tg from 67 to 5 C. Samples that were immersed in water for 96 h and immediately subjected to tensile testing exhibited 100% increases in failure strains and 500% decreases in failure stresses; however, in all cases of time and humidity exposure, the plasticization effect was reversible upon placing moisture-saturated samples in 40% humidity environments for 24 h.

  5. Development of a McKibben artificial muscle using a shape-memory polymer

    NASA Astrophysics Data System (ADS)

    Takashima, Kazuto; Rossiter, Jonathan; Mukai, Toshiharu

    2010-04-01

    When McKibben artificial muscle actuators are applied to robotic joints, the joints are driven by pairs of actuators located antagonistically to increase the joint stiffness. However, the force for shape fixity is not large. Therefore, the objective of this study is to develop a McKibben artificial muscle using a shape-memory polymer (SMP). SMPs can be deformed above their glass transition temperature (Tg) by applying a small load. They maintain their shape after they have been cooled to below Tg. They then return to the predefined shape when heated above Tg. Exploiting these characteristics, we coated the braided mesh shell of a commercial McKibben artificial muscle and made a prototype of the actuator using the SMP. When this new actuator is warmed above Tg, the SMP deforms. Then, when the internal bladder is pressurized, the actuator shortens and/or produces a load. After the actuator becomes the desirable length, the actuator is cooled to below Tg and the SMP is fixed in a rigid state even without the air supply. Consequently, this actuator can maintain its length more rigidly and accurately. The experimental results conducted on this prototype confirm the feasibility of this new actuator.

  6. Thermomechanical properties of polyurethane shape memory polymer-experiment and modelling

    NASA Astrophysics Data System (ADS)

    Pieczyska, E. A.; Maj, M.; Kowalczyk-Gajewska, K.; Staszczak, M.; Gradys, A.; Majewski, M.; Cristea, M.; Tobushi, H.; Hayashi, S.

    2015-04-01

    In this paper extensive research on the polyurethane shape memory polymer (PU-SMP) is reported, including its structure analysis, our experimental investigation of its thermomechanical properties and its modelling. The influence of the effects of thermomechanical couplings on the SMP behaviour during tension at room temperature is studied using a fast and sensitive infrared camera. It is shown that the thermomechanical behaviour of the SMP significantly depends on the strain rate: at a higher strain rate higher stress and temperature values are obtained. This indicates that an increase of the strain rate leads to activation of different deformation mechanisms at the micro-scale, along with reorientation and alignment of the molecular chains. Furthermore, influence of temperature on the SMPs mechanical behaviour is studied. It is observed during the loading in a thermal chamber that at the temperature 20 C below the glass transition temperature (Tg) the PU-SMP strengthens about six times compared to the material above Tg but does not exhibit the shape recovery. A finite-strain constitutive model is formulated, where the SMP is described as a two-phase material composed of a hyperelastic rubbery phase and elastic-viscoplastic glassy phase. The volume content of phases is governed by the current temperature. Finally, model predictions are compared with the experimental results.

  7. Using a single electrospun polymer nanofiber to enhance carrier mobility in organic field-effect transistors toward nonvolatile memory.

    PubMed

    Jian, Pei-Zhen; Chiu, Yu-Cheng; Sun, Han-Sheng; Chen, Tzu-Ying; Chen, Wen-Chang; Tung, Shih-Huang

    2014-04-23

    In this work, a single electrospun polymer nanofiber was employed as an additional dielectric in organic field-effect transistors where the active channel was a layer of pentacene. A high field-effect mobility (>1.50 cm(2)/(Vs)) and a high ON/OFF current ratio (>10(6)) could be achieved by the use of such a nanofiber. Probing by electron microscopy, atomic force microscopy, and scattering techniques, we found that the geometry of the fiber is key to induce a pentacene morphology with large and oriented grains that facilitates the charge transport in pentacene layer along the fiber. The feasibility of nonvolatile memory based on this new type of transistor has been explored and the devices showed a fairly high memory window and reliable memory characteristics. In addition to pure polymers, the effects of composite nanofibers with dispersed [6,6]-phenyl-C61-butyric acid methyl ester were also investigated, and the electrical properties and memory characteristics of the transistors were found to be further improved. This study highlights the importance of dielectric geometry to pentacene morphology that is decisive for the performances of organic field-effect transistors. PMID:24673527

  8. Self-adjuvanting polymer-peptide conjugates as therapeutic vaccine candidates against cervical cancer.

    PubMed

    Liu, Tzu-Yu; Hussein, Waleed M; Jia, Zhongfan; Ziora, Zyta M; McMillan, Nigel A J; Monteiro, Michael J; Toth, Istvan; Skwarczynski, Mariusz

    2013-08-12

    Dendrimers are structurally well-defined, synthetic polymers with sizes and physicochemical properties often resembling those of biomacromolecules (e.g., proteins). As a result, they are promising candidates for peptide-based vaccine delivery platforms. Herein, we established a synthetic pathway to conjugate a human papillomavirus (HPV) E7 protein-derived peptide antigen to a star-polymer to create a macromolecular vaccine candidate to treat HPV-related cancers. These conjugates were able to reduce tumor growth and eradicate E7-expressing TC-1 tumors in mice after a single immunization, without the help of any external adjuvant. PMID:23837675

  9. Swellable polymer films containing Au nanoparticles for point-of-care therapeutic drug monitoring using surface-enhanced Raman spectroscopy.

    PubMed

    Lee, Wendy W Y; McCoy, Colin P; Donnelly, Ryan F; Bell, Steven E J

    2016-03-17

    Large (10 × 10 cm) sheets of surface-enhanced Raman spectroscopy (SERS) active polymer have been prepared by stabilising metal nanoparticle aggregates within dry hydroxyethylcellulose (HEC) films. In these films the aggregates are protected by the polymer matrix during storage but in use they are released when aqueous analyte droplets cause the films to swell to their gel form. The fact that these "Poly-SERS" films can be prepared in bulk but then cut to size and stored in air before use means that they provide a cost effective and convenient method for routine SERS analysis. Here we have tested both Ag and Au Poly-SERS films for use in point-of-care monitoring of therapeutic drugs, using phenytoin as the test compound. Phenytoin in water could readily be detected using Ag Poly-SERS films but dissolving the compound in phosphate buffered saline (PBS) to mimic body fluid samples caused loss of the drug signal due to competition for metal surface sites from Cl(-) ions in the buffer solution. However, with Au Poly-SERS films there was no detectable interference from Cl(-) and these materials allowed phenytoin to be detected at 1.8 mg L(-1), even in PBS. The target range of detection of phenytoin in therapeutic drug monitoring is 10-20 mg L(-1). With the Au Poly-SERS films, the absolute signal generated by a given concentration of phenytoin was lower for the films than for the parent colloid but the SERS signals were still high enough to be used for therapeutic monitoring, so the cost in sensitivity for moving from simple aqueous colloids to films is not so large that it outweighs the advantages which the films bring for practical applications, in particular their ease of use and long shelf life. PMID:26920779

  10. A semi-analytical study on helical springs made of shape memory polymer

    NASA Astrophysics Data System (ADS)

    Baghani, M.; Naghdabadi, R.; Arghavani, J.

    2012-04-01

    In this paper, the responses of shape memory polymer (SMP) helical springs under axial force are studied both analytically and numerically. In the analytical solution, we first derive the response of a cylindrical tube under torsional loadings. This solution can be used for helical springs in which both the curvature and pitch effects are negligible. This is the case for helical springs with large ratios of the mean coil radius to the cross sectional radius (spring index) and also small pitch angles. Making use of this solution simplifies the analysis of the helical springs to that of the torsion of a straight bar with circular cross section. The 3D phenomenological constitutive model recently proposed for SMPs is also reduced to the 1D shear case. Thus, an analytical solution for the torsional response of SMP tubes in a full cycle of stress-free strain recovery is derived. In addition, the curvature effect is added to the formulation and the SMP helical spring is analyzed using the exact solution presented for torsion of curved SMP tubes. In this modified solution, the effect of the direct shear force is also considered. In the numerical analysis, the 3D constitutive equations are implemented in a finite element program and a full cycle of stress-free strain recovery of an SMP (extension or compression) helical spring is simulated. Analytical and numerical results are compared and it is shown that the analytical solution gives accurate stress distributions in the cross section of the helical SMP spring besides the global load-deflection response. Some case studies are presented to show the validity of the presented analytical method.

  11. Porous media properties of reticulated shape memory polymer foams and mock embolic coils for aneurysm treatment

    PubMed Central

    2013-01-01

    Background Shape memory polymer (SMP) foams are being investigated as an alternative aneurysm treatment method to embolic coils. The goal of both techniques is the reduction of blood flow into the aneurysm and the subsequent formation of a stable thrombus, which prevents future aneurysm rupture. The purpose of this study is to experimentally determine the parameters, permeability and form factor, which are related to the flow resistance imposed by both media when subjected to a pressure gradient. Methods The porous media propertiespermeability and form factorof SMP foams and mock embolic coils (MECs) were measured with a pressure gradient method by means of an in vitro closed flow loop. We implemented the Forchheimer-Hazen-Dupuit-Darcy equation to calculate these properties. Mechanically-reticulated SMP foams were fabricated with average cell sizes of 0.7E-3 and 1.1E-3m, while the MECs were arranged with volumetric packing densities of 11-28%. Results The permeability of the SMP foams was an order of magnitude lower than that of the MECs. The form factor differed by up to two orders of magnitude and was higher for the SMP foams in all cases. The maximum flow rate of all samples tested was within the inertial laminar flow regime, with Reynolds numbers ranging between 1 and 35. Conclusions The SMP foams impose a greater resistance to fluid flow compared to MECs, which is a result of increased viscous and inertial losses. These results suggest that aneurysms treated with SMP foam will have flow conditions more favorable for blood stasis than those treated with embolic coils having packing densities???28%. PMID:24120254

  12. Lipid-polymer hybrid nanoparticles as a new generation therapeutic delivery platform: a review.

    PubMed

    Hadinoto, Kunn; Sundaresan, Ajitha; Cheow, Wean Sin

    2013-11-01

    Lipid-polymer hybrid nanoparticles (LPNs) are core-shell nanoparticle structures comprising polymer cores and lipid/lipid-PEG shells, which exhibit complementary characteristics of both polymeric nanoparticles and liposomes, particularly in terms of their physical stability and biocompatibility. Significantly, the LPNs have recently been demonstrated to exhibit superior in vivo cellular delivery efficacy compared to that obtained from polymeric nanoparticles and liposomes. Since their inception, the LPNs have advanced significantly in terms of their preparation strategy and scope of applications. Their preparation strategy has undergone a shift from the conceptually simple two-step method, involving preformed polymeric nanoparticles and lipid vesicles, to the more principally complex, yet easier to perform, one-step method, relying on simultaneous self-assembly of the lipid and polymer, which has resulted in better products and higher production throughput. The scope of LPNs' applications has also been extended beyond single drug delivery for anticancer therapy, to include combinatorial and active targeted drug deliveries, and deliveries of genetic materials, vaccines, and diagnostic imaging agents. This review details the current state of development for the LPNs preparation and applications from which we identify future research works needed to bring the LPNs closer to its clinical realization. PMID:23872180

  13. Polymer-based delivery of RNA-based therapeutics in ovarian cancer.

    PubMed

    Weirauch, Ulrike; Gutsch, Daniela; Hbel, Sabrina; Aigner, Achim

    2013-01-01

    RNA interference (RNAi) is a naturally occurring, powerful mechanism for gene silencing, based on the cleavage of a given target mRNA. It relies on small interfering RNAs (siRNAs) in the cell. Being similar in structure, microRNAs (miRNAs) are important regulators of gene expression which mainly act by blocking mRNA translation. In cancer, certain miRNAs have been found to be pathologically downregulated. The therapeutic application of siRNAs or miRNAs for the induction of RNAi or miRNA replacement, respectively, relies on their efficient delivery through a non-viral formulation. Complexation of siRNAs/miRNAs in polymeric nanoparticles based on polyethylenimines (PEIs) offers protection against degradation, delivery to the target site, cellular uptake, and intracellular release. This chapter provides protocols for therapeutic gene silencing and miRNA replacement therapy, based on PEI complexes for in vitro and in vivo use. PMID:23913237

  14. Multistability, ionic doping, and charge dynamics in electrosynthesized polypyrrole, polymer-nanoparticle blend nonvolatile memory, and fixed p-i-n junction polymer light-emitting electrochemical cells

    NASA Astrophysics Data System (ADS)

    Simon, Daniel Theodore

    A variety of factors make semiconducting polymers a fascinating alternative for both device development and new areas of fundamental research. Among these are solution processability, low cost, flexibility, and the strong dependence of conduction on the presence of charge compensating ions. With the lack of a complete fundamental understanding of the materials, and the growing demand for novel solutions to semiconductor device design, research in the field can take many, often multifaceted, routes. Due to ion-mediated conduction and versatility of fabrication, conducting polymers can provide a route to the study of neural signaling. In the first of three research topics presented, junctions of polypyrrole electropolymenzed on microelectrode arrays are demonstrated. Indi vidual junctions, when synthesized in a three-electrode configuration, exhibit current switching behavior analogous to neural weighting. Junctions copolymerized with thiophene exhibit current rectification and the nonlinear current-voltage behavior requisite for complex neural systems. Applications to larger networks, and eventual use in analysis of signaling, are discussed. In the second research topic, nonvolatile resistive memory consisting of gold nanoparticles embedded in a polymer film is examined using admittance spectroscopy. The frequency dependence of the devices indicates space-charge-limited transport in the high-conductivity "on" state, and similar transport in the lower-conductivity "off' state. Furthermore, a larger do capacitance of the on state indicates that a greater amount of filling of midgap trap levels introduced by the nanoparticles increases conductivity, leading to the memory effect. Implications on the question as to whether or not the on state is the result of percolation pathways is discussed. The third and final research topic is a presentation of enhanced efficiency of polymer light-emitting electrochemical cells (LECs) by means of forming a doping self-assembled monolayer (SAM) at the cathode-polymer interface. The addition of the SAM causes a twofold increase in quantum efficiency. Photovoltaic analysis indicates that the SAM increases both open-circuit voltage and short-circuit current. Current versus voltage data are presented which indicate that the SAM does not simply introduce an interfacial dipole layer, but rather provides a fixed doping region, and thus a more stable p-i-n structure.

  15. Electrical switching and memory behaviors in organic diodes based on polymer blend films treated by ultraviolet ozone

    NASA Astrophysics Data System (ADS)

    Huang, Jinying; Ma, Dongge

    2014-09-01

    Resistive memory devices with resistive switching characteristics were fabricated based on poly (3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) doping with polyvinyl alcohol. It has been demonstrated that the resistive switching characteristics in the memory device was strongly dependent on the treatment of the polymer blend film by ultraviolet ozone (UV-ozone). The UV-ozone treated device exhibited improved performance with the ON/OFF current ratio of more than 102, and its ON and OFF states can be maintained over 96 h without deterioration. The resistive switching behavior in the UV-ozone treated device was attributed to the formation and rupture of the PEDOT:PSS filaments as well as the narrow conducting paths through the native oxide of aluminum.

  16. A phenomenological model for simulating the chemo-responsive shape memory effect in polymers undergoing a permeation transition

    NASA Astrophysics Data System (ADS)

    Lu, Haibao; Huang, Wei Min; Leng, Jinsong

    2014-04-01

    We present a phenomenological model for studying the constitutive relations and working mechanism of the chemo-responsive shape memory effect (SME) in shape memory polymers (SMPs). On the basis of the solubility parameter equation, diffusion model and permeation transition model, a phenomenological model is derived for quantitatively identifying the influential factors in the chemically induced SME in SMPs. After this, a permeability parallel model and series model are implemented in order to couple the constitutive relations of the permeability coefficient, stress and relaxation time as a function of stretch, separately. The inductive effect of the permeability transition on the transition temperature is confirmed as the driving force for the chemo-responsive SME. Furthermore, the analytical result from the phenomenological model is compared with the available experimental results and the simulation of a semi-empirical model reported in the literature for verification.

  17. Fabrication and static characterization of carbon-fiber-reinforced polymers with embedded NiTi shape memory wire actuators

    NASA Astrophysics Data System (ADS)

    de Arajo, C. J.; Rodrigues, L. F. A.; Coutinho Neto, J. F.; Reis, R. P. B.

    2008-12-01

    In this work, unidirectional carbon-fiber-reinforced polymers (CFRP) with embedded NiTi shape memory alloy (SMA) wire actuators were manufactured using a universal testing machine equipped with a thermally controlled chamber. Beam specimens containing cold-worked, annealed and trained NiTi SMA wires distributed along their neutral plane were fabricated. Several tests in a three-point bending mode at different constant temperatures were performed. To verify thermal buckling effects, electrical activation of the specimens was realized in a cantilevered beam mode and the influence of the SMA wire actuators on the tip deflection of the composite is demonstrated.

  18. Therapeutic effect of taurine against aluminum-induced impairment on learning, memory and brain neurotransmitters in rats.

    PubMed

    Wenting, Lu; Ping, Liu; Haitao, Jiao; Meng, Qiao; Xiaofei, Ren

    2014-10-01

    The aim of the study was to demonstrate the therapeutic effect of taurine against aluminum (Al)-induced neurological disorders in rats. Forty-two Wistar rats were randomly allotted into six groups: control (saline only), Al exposure (281.4 mg/kg/day for 1 month), Al + taurine (Al administration as previously plus taurine, doses were 200, 400 and 800 mg/kg/day, respectively, for the next 1 month) and prevention group (along with the Al administration as previously, 400 mg/kg/day taurine was treated for 1 month. During the next 1 month, rats were given taurine 400 mg/kg/day only). Starting from the sixth week, the body weight gain was significantly reduced in Al exposure group compared with saline (P < 0.05), and at the eighth week, the gain in prevention group was increased compared with Al (P < 0.05). Brain coefficient was gained in Al exposure compared with saline or prevention group (P < 0.05). Al exposure resulted in learning and memory impairment by increasing the escape latency and searching distance, meanwhile, decreasing the swimming time in the quadrant of platform and the numbers of crossing the platform (P < 0.05). Unsurprisingly, taurine treatment (400, 800 mg/kg/day and prevention) significantly protected against Al-induced brain dysfunction (P < 0.05). The Al exposure led to significant decreases in levels of ?-GABA and Tau, meanwhile, increased in level of Asp and Glu compared with saline (P < 0.05). And yet, taurine treatment partially reversed the deteriorated changes. The results suggested that taurine probably has neuroprotective effect against Al-induced learning, memory and brain neurotransmitters dysfunction. PMID:24770980

  19. Memory

    MedlinePLUS

    Your mind works a lot like a computer. Your brain puts information it judges to be important into "files." When you remember something, you pull up a file. Memory doesn't always work perfectly. As ...

  20. Neuroprotective effects of therapeutic hypercapnia on spatial memory and sensorimotor impairment via anti-apoptotic mechanisms after focal cerebral ischemia/reperfusion.

    PubMed

    Tao, Tao; Zhao, Meng; Yang, Wanchao; Bo, Yulong; Li, Wenzhi

    2014-06-24

    A number of studies have demonstrated that therapeutic hypercapnia ameliorates neurological deficits and attenuates the histological damage of cerebral ischemia-reperfusion injury. However, the effects of therapeutic hypercapnia on impaired spatial memory have not been reported. Here we aimed to investigate the effects and mechanisms of therapeutic hypercapnia on spatial memory in a rat model of focal cerebral ischemia induced by middle cerebral artery occlusion/reperfusion (MCAO/R). Adult male rats were randomly assigned into three experimental groups: sham (sham operation), IR (MCAO/R), and hypercapnia [arterial blood CO2 tension (PaCO2) 80-100 mmHg+IR] groups. Sensorimotor deficits and spatial memory testing were evaluated by an 18-point scoring system and an 8-arm radial maze task, respectively. The hippocampal histological damage and the percentage of apoptotic neurons were evaluated by hematoxylin and eosin (HE) staining as well as flow cytometry. Western blotting was used to investigate the changes of the apoptosis-related Bcl-2 and Bax proteins. The results indicated that hypercapnia treatment significantly improved the abilities of impaired sensorimotor and spatial memory after MCAO/R. Moreover, hypercapnia treatment significantly increased the percentage of surviving neurons and decreased the percentage of apoptotic neurons in the hippocampus after MCAO/R damage. The expressions of anti-apoptotic protein Bcl-2 and pro-apoptotic protein Bax were significantly increased and decreased in the hypercapnia treated rats, respectively. These findings suggest that therapeutic hypercapnia can attenuate neuronal apoptosis and improve impaired spatial memory and sensorimotor after MCAO/R, which may be attributable to its anti-apoptotic effects through modulation of apoptosis-related protein. PMID:24813106

  1. Influence of strain-holding conditions on shape recovery and secondary-shape forming in polyurethane-shape memory polymer

    NASA Astrophysics Data System (ADS)

    Tobushi, H.; Hayashi, S.; Hoshio, K.; Miwa, N.

    2006-08-01

    It was found in previous work on the thermomechanical properties of the polyurethane-shape memory polymer foam that the shape fixity and shape recovery become imperfect and that secondary-shape forming appears, depending on the strain-holding conditions. The main factors of the strain-holding conditions which affect the secondary-shape forming are the holding temperature, holding time and holding strain. In the present study, the influence of the strain-holding conditions on the shape recovery and secondary-shape forming was investigated for the polyurethane-shape memory polymer film. It was found that the secondary-shape forming appears markedly if the holding temperature is higher than the glass transition temperature and does not appear if the holding temperature is lower than the glass transition temperature. The rate of secondary-shape forming increases with an increase in the holding time if the holding temperature is higher than the glass transition temperature. The irrecoverable strain increases in proportion to the holding strain.

  2. A phenomenological model for the chemo-responsive shape memory effect in amorphous polymers undergoing viscoelastic transition

    NASA Astrophysics Data System (ADS)

    Lu, Haibao; Huang, Wei Min

    2013-11-01

    We present a phenomenological approach to study the viscoelastic transition and working mechanism of the chemo-responsive shape memory effect (SME) in amorphous shape memory polymers (SMPs). Both the copolymerization viscosity model and Doolittle equation are initially applied to quantitatively identify the influential factors behind the chemo-responsive SME in the SMPs exposure to a right solvent. After this, the Williams-Landel-Ferry (WLF) equation is employed to couple the viscosity (?), time-temperature shift factor (??) and glass transition temperature (Tg) in amorphous polymers. By means of combining the WLF and Arrhenius equations together, the inductively decreased transition temperature is confirmed as the driving force for the chemo-responsive SME. Finally, a phenomenological viscoelastic model is proposed and then verified by the available experimental data reported in the literature and then compared with the simulation results of a semi-empirical model. This phenomenological model is expected to provide a powerful simulation tool for theoretical prediction and experimental substantiation of the chemo-responsive SME in amorphous SMPs by viscoelastic transition.

  3. Biodegradable polymer nanocarriers for therapeutic antisense microRNA delivery in living animals

    NASA Astrophysics Data System (ADS)

    Paulmurugan, Ramasamy; Sekar, Narayana M.; Sekar, Thillai V.

    2012-03-01

    MicroRNAs are endogenous regulators of gene expression, deregulated in several cellular diseases including cancer. Altering the cellular microenvironment by modulating the microRNAs functions can regulate different genes involved in major cellular processes, and this approach is now being investigated as a promising new generation of molecularly targeted anti-cancer therapies. AntagomiRs (Antisense-miRNAs) are a novel class of chemically modified stable oligonucleotides used for blocking the functions of endogenous microRNAs, which are overexpressed. A key challenge in achieving effective microRNAbased therapeutics lies in the development of an efficient delivery system capable of specifically delivering antisense oligonucleotides and target cancer cells in living animals. We are now developing an effective delivery system designed to selectively deliver antagomiR- 21 and antagomiR-10b to triple negative breast cancer cells, and to revert tumor cell metastasis and invasiveness. The FDA-approved biodegradable PLGA-nanoparticles were selected as a carrier for antagomiRs delivery. Chemically modified antagomiRs (antagomiR-21 and antagomiR-10b) were co-encapsulated in PEGylated-PLGA-nanoparticles by using the double-emulsification (W/O/W) solvent evaporation method, and the resulting average particle size of 150-200nm was used for different in vitro and in vivo experiments. The antagomiR encapsulated PLGA-nanoparticles were evaluated for their in vitro antagomiRs delivery, intracellular release profile, and antagomiRs functional effects, by measuring the endogenous cellular targets, and the cell growth and metastasis. The xenografts of tumor cells in living mice were used for evaluating the anti-metastatic and anti-invasive properties of cells. The results showed that the use of PLGA for antagomiR delivery is not only efficient in crossing cell membrane, but can also maintain functional intracellular antagomiRs level for a extended period of time and achieve therapeutic effect in living animals.

  4. Photo-Mediated Copper(I)-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) Click Reactions for Forming Polymer Networks as Shape Memory Materials

    PubMed Central

    McBride, Matthew K.; Gong, Tao; Nair, Devatha P.; Bowman, Christopher N.

    2014-01-01

    The formation of polymer networks polymerized with the Copper (I) catalyzed azide alkyne cycloaddition (CuAAC) click reaction is described along with their accompanying utilization as shape memory polymers. Due to the click nature of the reaction and the synthetic accessibility of azide and alkyne functional-monomers, the polymer architecture was readily controlled through monomer design to manipulate crosslink density, ability for further functionalization, and the glass transition temperature (55 to 120C). Free strain recovery is used to quantify the shape memory properties of a model CuAAC network resulting in excellent shape fixity and recovery of 99%. The step growth nature of this polymerization results in homogenous network formation with narrow glass transitions ranges having half widths of the transition close to 15C for these materials resulting in shape recovery sharpness of 3.9 %/C in a model system comparable to similarly crosslinked chain growth polymers. Utilization of the CuAAC reaction to form shape memory materials opens a range of possibilities and behaviors that are not readily achieved in other shape memory materials such as (meth) acrylates, thiolene, thiol-Michael, and poly(caprolactone) based shape memory materials. PMID:25378717

  5. Theoretical model based on the memory effect for the strange photoisomerization kinetics of diarylethene derivatives dispersed on polymer films

    SciTech Connect

    Seki, Kazuhiko; Tachiya, M.

    2007-01-28

    In the present paper the authors present a theoretical model to explain the kinetics involving the induction period observed by Irie et al. [Nature (London) 420, 759 (2002)] for photoisomerization of diarylethene derivatives dispersed on polymer films at a single molecular level. In the model we assume that both ground state and excited state free energy landscapes which result from the interaction between the photochromic molecule and the surrounding polymer are rugged and have several local minima along the pathway to the critical point at which isomerization actually occurs. We assume that after one photoexcitation a fraction of the photochromic molecule moves to a new local minimum and stays there, although the other fraction returns to the original local minimum. The former effect is referred to as the memory effect. After repeated photoexcitations the photochromic molecule moves gradually from one local minimum to another in the pathway to the isomerization point. It finally reaches the isomerization point, where isomerization occurs. Their model successfully reproduces the kinetics of photoisomerization of diarylethene derivatives dispersed on polymer films observed experimentally.

  6. Theoretical model based on the memory effect for the strange photoisomerization kinetics of diarylethene derivatives dispersed on polymer films

    NASA Astrophysics Data System (ADS)

    Seki, Kazuhiko; Tachiya, M.

    2007-01-01

    In the present paper the authors present a theoretical model to explain the kinetics involving the induction period observed by Irie et al. [Nature (London) 420, 759 (2002)] for photoisomerization of diarylethene derivatives dispersed on polymer films at a single molecular level. In the model we assume that both ground state and excited state free energy landscapes which result from the interaction between the photochromic molecule and the surrounding polymer are rugged and have several local minima along the pathway to the critical point at which isomerization actually occurs. We assume that after one photoexcitation a fraction of the photochromic molecule moves to a new local minimum and stays there, although the other fraction returns to the original local minimum. The former effect is referred to as the memory effect. After repeated photoexcitations the photochromic molecule moves gradually from one local minimum to another in the pathway to the isomerization point. It finally reaches the isomerization point, where isomerization occurs. Their model successfully reproduces the kinetics of photoisomerization of diarylethene derivatives dispersed on polymer films observed experimentally.

  7. Memories.

    ERIC Educational Resources Information Center

    Brand, Judith, Ed.

    1998-01-01

    This theme issue of the journal "Exploring" covers the topic of "memories" and describes an exhibition at San Francisco's Exploratorium that ran from May 22, 1998 through January 1999 and that contained over 40 hands-on exhibits, demonstrations, artworks, images, sounds, smells, and tastes that demonstrated and depicted the biological,

  8. Effect of Ag doping and insulator buffer layer on the memory mechanism of polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Kaur, Ramneek; Kaur, Jagdish; Tripathi, S. K.

    2015-07-01

    Resistive memory devices based on nanocomposites have attracted great potential for future applications in electronic and optoelectronic devices. The successful synthesis of aqueous CdSe nanoparticles has been provided with UV-Vis and Photoluminescence spectroscopy. The two terminal planar devices of CdSe nanocomposite have been fabricated. The effect of Ag doping and additional dielectric buffer layers on the memory devices have been studied by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The devices show hysteresis loops in both positive and negative bias directions. The memory window has been found to be increased with both Ag doping and PVA layer addition. The charge carrier transport mechanism in the memory devices has been studied by fitting the I-V characteristics with the theoretical model, Space charge conduction model (SCLC). C-V hysteresis loop in both positive and negative bias directions indicate that both the electrons and holes are responsible for memory mechanism of the devices. The switching mechanism of the memory devices has been explained by charge trapping/detrapping model. The retention characteristics show good stability and reliability of the devices.

  9. Modelling of shape memory polymer sheets that self-fold in response to localized heating.

    PubMed

    Mailen, Russell W; Liu, Ying; Dickey, Michael D; Zikry, Mohammed; Genzer, Jan

    2015-10-21

    We report a nonlinear finite element analysis (FEA) of the thermo-mechanical shrinking and self-folding behavior of pre-strained polystyrene polymer sheets. Self-folding is useful for actuation, packaging, and remote deployment of flat surfaces that convert to 3D objects in response to a stimulus such as heat. The proposed FEA model accounts for the viscoelastic recovery of pre-strained polystyrene sheets in response to localized heating on the surface of the polymer. Herein, the heat results from the localized absorption of light by ink patterned on the surface of the sheet. This localized delivery of heat results in a temperature gradient through the thickness of the sheet, and thus a gradient of strain recovery, or shrinkage, develops causing the polymer sheet to fold. This process transforms a 2D pattern into a 3D shape through an origami-like behavior. The FEA predictions indicate that shrinking and folding are sensitive to the thermo-mechanical history of the polymer during pre-straining. The model also shows that shrinkage does not vary linearly through the thickness of the polymer during folding due to the accumulation of mass in the hinged region. Counterintuitively, the maximum shrinkage does not occur at the patterned surface. Rather, it occurs considerably below the top surface of the polymer. This investigation provides a fundamental understanding of shrinking, self-folding dynamics, and bending angles, and provides design guidelines for origami shapes and structures. PMID:26324954

  10. Polymers.

    ERIC Educational Resources Information Center

    Tucker, David C.

    1986-01-01

    Presents an open-ended experiment which has students exploring polymer chemistry and reverse osmosis. This activity involves construction of a polymer membrane, use of it in a simple osmosis experiment, and application of its principles in solving a science-technology-society problem. (ML)

  11. Production of bioinspired and rationally designed polymer hydrogels for controlled delivery of therapeutic proteins

    NASA Astrophysics Data System (ADS)

    Kim, Sung Hye

    Hydrogel systems for controlled delivery therapeutic growth factors have been developed in a wide spectrum of strategies: these systems aim for the release of growth factors via a passive diffusion, electrostatic interaction, degradation of hydrogels, and responsiveness to external stimuli. Heparin, a highly sulfated glycosaminoglycan (GAG), was employed for a targeted delivery system of vascular endothelial growth factor (VEGF) to endothelial cells overexpressing a relevant receptor VEGFR-2. Addition of dimeric VEGF to 4-arm star-shaped poly(ethylene glycol) (PEG) immobilized with low-molecular weight heparin (LMWH) afforded a non-covalently assembled hydrogel via interaction between heparin and VEGF, with storage modulus 10 Pa. The release of VEGF and hydrogel erosion reached maximum 100 % at day 4 in the presence of VEGFR-2 overexpressing pocine aortic endothelial cell (PAE/KDR), while those of 80% were achieved via passive release at day 5 in the presence of PAE cell lacking VEGFR-2 or in the absence of cell, indicating that the release of VEGF was in targeted manner toward cell receptor. The proliferation of PAE/KDR in the presence of [PEG-LMWH/VEGF] hydrogel was greater by ca. 30% at day 4 compared to that of PAE, confirming that the release of VEGF was in response to the cellular demand. The phosphorylation fraction of VEGFR-2 on PAE/KDR was greater in the presence of [PEG-LMWH/VEGF] hydrogel, increasing from 0.568 at day 1 to 0.790 at day 4, whereas it was maintained at 0.230 at day 4 in the presence of [PEG-LMWH] hydrogel. This study has proven that this hydrogel, assembled via bio-inspired non-covalent interaction, liberating VEGFon celluar demand to target cell, eroding upon VEGF release, and triggering endothelial cell proliferation, could be used in multiple applications including targeted delivery and angiogenesis. Heparin has been widely exploited in growth factor delivery systems owing to its ability to bind many growth factors through the flexible patterns of functional groups. However, heterogeneity in the composition and in the polydispersity of heparin has been problematic in controlled delivery system and thus motivated the development of homogeneous heparin mimics. Peptides of appropriate sequence and chemical function have therefore recently emerged as potential replacements for heparin in select applications. Studied was the assessment of the binding affinities of multiple sulfated peptides (SPs) for a set of heparin-binding peptides (HBPs) and for VEGF; these binding partners have application in the selective immobilization of proteins and in hydrogel formation through non-covalent interactions. Sulfated peptides were produced via solid-phase methods, and their affinity for the HBPs and VEGF was assessed via affinity liquid chromatography (ALC), surface plasmon resonance (SPR), and in select cases, isothermal titration calorimetry (ITC). The shortest peptide, SPa, showed the highest affinity binding of HBPs and VEGF165 in both ALC and SPR measurements, with slight exceptions. Of the investigated HBPs, a peptide based on the heparin-binding domain of human platelet factor 4 showed greatest binding affinities toward all of the SPs, consistent with its stronger binding to heparin. The affinity between SPa and PF4ZIP was indicated via SPR ( KD = 5.27 muM) and confirmed via ITC (KD = 8.09 muM). The binding by SPa of both VEGF and HBPs suggests its use as a binding partner to multiple species, and the use of these interactions in assembly of materials. Given that the peptide sequences can be varied to control binding affinity and selectivity, opportunities are also suggested for the production of a wider array of matrices with selective binding and release properties useful for biomaterials applications. Hydrogel consisting of SPa was formed via a covalent Michael Addition reaction between maleimide- and thiol-terminated multi-arm PEGs and Cys-SPa. The mechanical property of hydrogel was tunable from ca. 186 to 1940 Pa. by varing the cross-linking density, suggesting its flexible applications depending on matrix needs. The non-anti-coagulative property of SPa, assessed via activated partial thromboplastin time (APTT) and HeptestRTM in comparison to LMWH, implied its usefulness in applications without excessive bleeding. The VEGF released from [PEG-SPa] hydrogel showed up to ca. 400% greater bioactivity on proliferation of human umbilical vein endothelical cell (HUVEC) compared to the VEGF incubated in solution for the same period: this was significantly higher than that of [PEG] hydrogel (ca. 280%), suggesting the SPa may protect the bioactivity of VEGF when bound. The release of dual growth factor, i.e. VEGF and fibroblast growth factor-2 (FGF-2), were investigated on [PEG-SPa] hydrogel: the release of bFGF was lower than that of VEGF due to weaker binding affinity to matrix-bound SPa. The HUVEC culture on dual growth factor loaded [PEG-SPa] showed that the synergistic effects of dual system in select concentrations, suggesting the opportunity of manipulating cell responses. Given that sulfated peptides for various binding targets with desired affinity can be identified, applications are suggested in multiple growth factors delivery where an integrated action of multiple growth factors is required, such as angiogenesis.

  12. Programming Tilting Angles in Shape Memory Polymer Janus Pillar Arrays with Unidirectional Wetting against the Tilting Direction.

    PubMed

    Chen, Chi-Mon; Chiang, Chang-Lung; Yang, Shu

    2015-09-01

    By coating a thin layer of metal, including gold and gold-palladium alloy, of different thickness on the deformed shape memory polymer (SMP) pillars, we manipulate the degree of recovery of the SMP pillars. Pillars of different tilting angles were obtained as a result of balancing the strain recovery energy of the SMP pillars that favor the original straight state and the elastic energy of the metal layers that prefer the bent state. With this selective coating of a metal layer on the tilted pillars, we report a unique anisotropic liquid spreading behavior, where the water droplet is fully pinned in the direction of pillar tilting but advances in the reverse direction. This phenomenon is explained by the interplay of the surface chemistry and topography. PMID:26305291

  13. Transparent photostable ZnO nonvolatile memory transistor with ferroelectric polymer and sputter-deposited oxide gate

    SciTech Connect

    Park, C. H.; Im, Seongil; Yun, Jungheum; Lee, Gun Hwan; Lee, Byoung H.; Sung, Myung M.

    2009-11-30

    We report on the fabrication of transparent top-gate ZnO nonvolatile memory thin-film transistors (NVM-TFTs) with 200 nm thick poly(vinylidene fluoride/trifluoroethylene) ferroelectric layer; semitransparent 10 nm thin AgO{sub x} and transparent 130 nm thick indium-zinc oxide (IZO) were deposited on the ferroelectric polymer as gate electrode by rf sputtering. Our semitransparent NVM-TFT with AgO{sub x} gate operates under low voltage write-erase (WR-ER) pulse of {+-}20 V, but shows some degradation in retention property. In contrast, our transparent IZO-gated device displays very good retention properties but requires anomalously higher pulse of {+-}70 V for WR and ER states. Both devices stably operated under visible illuminations.

  14. Multi-shape memory polymers achieved by the spatio-assembly of 3D printable thermoplastic building blocks.

    PubMed

    Li, Hongze; Gao, Xiang; Luo, Yingwu

    2016-04-01

    Multi-shape memory polymers were prepared by the macroscale spatio-assembly of building blocks in this work. The building blocks were methyl acrylate-co-styrene (MA-co-St) copolymers, which have the St-block-(St-random-MA)-block-St tri-block chain sequence. This design ensures that their transition temperatures can be adjusted over a wide range by varying the composition of the middle block. The two St blocks at the chain ends can generate a crosslink network in the final device to achieve strong bonding force between building blocks and the shape memory capacity. Due to their thermoplastic properties, 3D printing was employed for the spatio-assembly to build devices. This method is capable of introducing many transition phases into one device and preparing complicated shapes via 3D printing. The device can perform a complex action via a series of shape changes. Besides, this method can avoid the difficult programing of a series of temporary shapes. The control of intermediate temporary shapes was realized via programing the shapes and locations of building blocks in the final device. PMID:26924759

  15. Biobased poly(propylene sebacate) as shape memory polymer with tunable switching temperature for potential biomedical applications.

    PubMed

    Guo, Baochun; Chen, Yongwen; Lei, Yanda; Zhang, Liqun; Zhou, Wen You; Rabie, A Bakr M; Zhao, Jianqing

    2011-04-11

    From the point of better biocompatibility and sustainability, biobased shape memory polymers (SMPs) are highly desired. We used 1,3-propanediol, sebacic acid, and itaconic acid, which have been industrially produced via fermentation or extraction with large quantities as the main raw materials for the synthesis of biobased poly(propylene sebacate). Diethylene glycol was used to tailor the flexibility of the polyester. The resulted polyesters were found to be promising SMPs with excellent shape recovery and fixity (near 100% and independent of thermomechanical cycles). The switching temperature and recovery speed of the SMPs are tunable by controlling the composition of the polyesters and their curing extent. The continuously changed switching temperature ranging from 12 to 54 °C was realized. Such temperature range is typical for biomedical applications in the human body. The molecular and crystalline structures were explored to correlate to the shape memory behavior. The combination of potential biocompatibility and biodegradability of the biobased SMPs makes them suitable for fabricating biomedical devices. PMID:21381645

  16. Dually actuated triple shape memory polymers of cross-linked polycyclooctene-carbon nanotube/polyethylene nanocomposites.

    PubMed

    Wang, Zhenwen; Zhao, Jun; Chen, Min; Yang, Minhao; Tang, Luyang; Dang, Zhi-Min; Chen, Fenghua; Huang, Miaoming; Dong, Xia

    2014-11-26

    In this work, electrically and thermally actuated triple shape memory polymers (SMPs) of chemically cross-linked polycyclooctene (PCO)-multiwalled carbon nanotube (MWCNT)/polyethylene (PE) nanocomposites with co-continuous structure and selective distribution of fillers in PCO phase are prepared. We systematically studied not only the microstructure including morphology and fillers' selective distribution in one phase of the PCO/PE blends, but also the macroscopic properties including thermal, mechanical, and electrical properties. The co-continuous window of the immiscible PCO/PE blends is found to be the volume fraction of PCO (vPCO) of ca. 40-70 vol %. The selective distribution of fillers in one phase of co-continuous blends is obtained by a masterbatch technique. The prepared triple SMP materials show pronounced triple shape memory effects (SMEs) on the dynamic mechanical thermal analysis (DMTA) and the visual observation by both thermal and electric actuations. Such polyolefin samples with well-defined microstructure, electrical actuation, and triple SMEs might have potential applications as, for example, multiple autochoke elements for engines, self-adjusting orthodontic wires, and ophthalmic devices. PMID:25347728

  17. Development of a self-stressing NiTiNb shape memory alloy (SMA)/fiber reinforced polymer (FRP) patch

    NASA Astrophysics Data System (ADS)

    El-Tahan, M.; Dawood, M.; Song, G.

    2015-06-01

    The objective of this research is to develop a self-stressing patch using a combination of shape memory alloys (SMAs) and fiber reinforced polymer (FRP) composites. Prestressed carbon FRP patches are emerging as a promising alternative to traditional methods to repair cracked steel structures and civil infrastructure. However, prestressing these patches typically requires heavy and complex fixtures, which is impractical in many applications. This paper presents a new approach in which the prestressing force is applied by restraining the shape memory effect of NiTiNb SMA wires. The wires are subsequently embedded in an FRP overlay patch. This method overcomes the practical challenges associated with conventional prestressing. This paper presents the conceptual development of the self-stressing patch with the support of experimental observations. The bond between the SMA wires and the FRP is evaluated using pull-out tests. The paper concludes with an experimental study that evaluates the patch response during activation subsequent monotonic tensile loading. The results demonstrate that the self-stressing patch with NiTiNb SMA is capable of generating a significant prestressing force with minimal tool and labor requirements.

  18. An electrical-heating and self-sensing shape memory polymer composite incorporated with carbon fiber felt

    NASA Astrophysics Data System (ADS)

    Gong, Xiaobo; Liu, Liwu; Liu, Yanju; Leng, Jinsong

    2016-03-01

    Shape memory polymers (SMPs) have the ability to adjust their stiffness, lock a temporary shape, and recover the permanent shape upon imposing an appropriate stimulus. They have found their way into the field of morphing structures. The electrically Joule resistive heating of the conductive composite can be a desirable stimulus to activate the shape memory effect of SMPs without external heating equipment. Electro-induced SMP composites incorporated with carbon fiber felt (CFF) were explored in this work. The CFF is an excellent conductive filler which can easily spread throughout the composite. It has a huge advantage in terms of low cost, simple manufacturing process, and uniform and tunable temperature distribution while heating. A continuous and compact conductive network made of carbon fibers and the overlap joints among them was observed from the microscopy images, and this network contributes to the high conductive properties of the CFF/SMP composites. The CFF/SMP composites can be electrical-heated rapidly and uniformly, and its’ shape recovery effect can be actuated by the electrical resistance Joule heating of the CFF without an external heater. The CFF/SMP composite get higher modulus and higher strength than the pure SMP without losing any strain recovery property. The high dependence of temperature and strain on the electrical resistance also make the composite a good self-sensing material. In general, the CFF/SMP composite shows great prospects as a potential material for the future morphing structures.

  19. Self-deploying shape memory polymer scaffolds for grafting and stabilizing complex bone defects: A mouse femoral segmental defect study.

    PubMed

    Baker, Richard M; Tseng, Ling-Fang; Iannolo, Maria T; Oest, Megan E; Henderson, James H

    2016-01-01

    Treatment of complex bone defects places a significant burden on the US health care system. Current strategies for treatment include grafting and stabilization using internal metal plates/screws, intramedullary rods, or external fixators. Here, we introduce the use of shape memory polymer (SMP) materials for grafting and adjunct stabilization of segmental defects. Self-deploying SMP grafts and SMP sleeves capable of expanding and contracting, respectively, under intraoperative conditions were developed and evaluated in a mouse segmental defect model invivo. Integration between grafts/sleeves and native bone was assessed using x-ray radiography, microcomputed tomography, and torsional mechanical testing. We found that SMP grafts were able to integrate with the native bone after 12 weeks, maintain defect stability, and provide torsional mechanical properties comparable to an allograft alone treatment; however no gross de novo bone formation was observed. SMP sleeves did not inhibit bony bridging at the margins, and limbs treated with a sleeve/allograft combination had torsional mechanical properties comparable to limbs treated with an allograft alone. Invitro torsional and bending tests suggest sleeves may provide additional torsional stability to defects. Incorporation of shape memory into synthetic bone graft substitutes and adjunct stabilization devices is anticipated to enhance functionality of synthetic materials employed in both applications. PMID:26561935

  20. Radiation-crosslinking of shape memory polymers based on poly(vinyl alcohol) in the presence of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Basfar, A. A.; Lotfy, S.

    2015-01-01

    Shape memory polymers based on poly(vinyl alcohol) (SM-PVA) in the presence of 2-carboxyethyl acrylate oligomers (CEA) and multi-wall carbon nanotubes (MWCNTs) crosslinked by ionizing radiation were investigated. Chemical-crosslinking of PVA by glutaraldehyde in the presence of CEA and MWCNTs was also studied. The swelling and gel fraction of the radiation-crosslinked SM-PVA and chemically crosslinked systems were evaluated. Analysis of the swelling and gel fraction revealed a significant reduction in swelling and an increase in the gel fraction of the material that was chemically crosslinked with glutaraldehyde. The radiation-crosslinked SM-PVA demonstrated 100% gelation at an irradiation dose of 50 kGy. In addition, radiation-crosslinked SM-PVA exhibited good temperature responsive shape-memory behavior. A scanning electron microscopy (SEM) analysis was performed. The thermal properties of radiation-crosslinked SM-PVA were investigated by a thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The ability of the material to return or store energy (E?), to its ability to lose energy (E?), and the ratio of these effects (Tan?), which is called damping were examined via DMA. The temperature of Tan? in the radiation-crosslinked SM-PVA decreased significantly by 6 and 13 C as a result of the addition of MWCNTs. In addition, the temperature of Tan? for SM-PVA increased as the irradiation dose increased. These radiation-crosslinked SM-PVA materials show promising shape-memory behavior based on the range of temperatures at which Tan? appears.

  1. Spider-silk-like shape memory polymer fiber for vibration damping

    NASA Astrophysics Data System (ADS)

    Yang, Qianxi; Li, Guoqiang

    2014-10-01

    In this study, the static and dynamic properties of shape memory polyurethane (SMPU) fiber are reported and compared to those of spider dragline silk. Although the polymeric fiber has a lower strength compared to spider dragline silks (0.2-0.3 GPa versus 1.1 GPa), it possesses much higher toughness (276-289 MJ m-3 versus 160 MJ m-3), due to its excellent extensibility. The dynamic mechanical tests reveal that SMPU fiber has a high damping capacity (tan ? = 0.10-0.35) which is comparable to or even higher than that of spider silks (tan ? = 0.15). In addition, we found that, different programming methods change the shape memory and damping properties of the fiber in different ways and cold-drawing programming is more advocated in structural applications. These results suggest that the SMPU fiber has similar vibration damping and mechanical properties as spider silk, and may find applications in lightweight engineering structures.

  2. Small-angle neutron scattering from polymer hydrogels with memory effect for medicine immobilization

    SciTech Connect

    Kulvelis, Yu. V. Lebedev, V. T.; Trunov, V. A.; Pavlyuchenko, V. N.; Ivanchev, S. S.; Primachenko, O. N.; Khaikin, S. Ya.

    2011-12-15

    Hydrogels synthesized based on cross-linked copolymers of 2-hydroxyethyl methacrylate and functional monomers (acrylic acid or dimethylaminoethyl methacrylate), having a memory effect with respect to target medicine (cefazolin), have been investigated by small-angle neutron scattering. The hydrogels are found to have a two-level structural organization: large (up to 100 nm) aggregates filled with network cells (4-7 nm in size). The structural differences in the anionic, cationic, and amphiphilic hydrogels and the relationship between their structure and the ability of hydrogels to absorb moisture are shown. A relationship between the memory effect during cefazolin immobilization and the internal structure of hydrogels, depending on their composition and type of functional groups, is established.

  3. Laser Fabrication of Polymer Ferroelectric Nanostructures for Nonvolatile Organic Memory Devices.

    PubMed

    Martnez-Tong, Daniel E; Rodrguez-Rodrguez, lvaro; Nogales, Aurora; Garca-Gutirrez, Mari-Cruz; Prez-Murano, Francesc; Llobet, Jordi; Ezquerra, Tiberio A; Rebollar, Esther

    2015-09-01

    Polymer ferroelectric laser-induced periodic surface structures (LIPSS) have been prepared on ferroelectric thin films of a poly(vinylidene fluoride-trifluoroethylene) copolymer. Although this copolymer does not absorb light at the laser wavelength, LIPSS on the copolymer can be obtained by forming a bilayer with other light-absorbing polymers. The ferroelectric nature of the structured bilayer was proven by piezoresponse force microscopy measurements. Ferroelectric hysteresis was found on both the bilayer and the laser-structured bilayer. We show that it is possible to write ferroelectric information at the nanoscale. The laser-structured ferroelectric bilayer showed an increase in the information storage density of an order of magnitude, in comparison to the original bilayer. PMID:26280158

  4. MACROMOLECULAR THERAPEUTICS

    PubMed Central

    Yang, Jiyuan; Kopeček, Jindřich

    2014-01-01

    This review covers water-soluble polymer-drug conjugates and macromolecules that possess biological activity without attached low molecular weight drugs. The main design principles of traditional and backbone degradable polymer-drug conjugates as well as the development of a new paradigm in nanomedicines – (low molecular weight) drug-free macromolecular therapeutics are discussed. To address the biological features of cancer, macromolecular therapeutics directed to stem/progenitor cells and the tumor microenvironment are deliberated. Finally, the future perspectives of the field are briefly debated. PMID:24747162

  5. Charge trapping at the polymer-metal oxide interface as a first step in the electroforming of organic-inorganic memory diodes

    NASA Astrophysics Data System (ADS)

    Bory, Benjamin F.; Rocha, Paulo; Gomes, Henrique L.; de Leeuw, Dago M.; Meskers, Stefan C. J.

    2015-09-01

    Diodes containing a layer of aluminum oxide combined with a layer of ?-conjugated polymer show nonvolatile memory effects after they have been electroformed. Electroforming is induced by application high bias voltage close to the limit for dielectric breakdown and can be performed reliably and with high yield on organic-inorganic hybrid diodes with controlled oxide thickness. Here we investigate the initial stage of the electroforming process and show through temperature dependent current-voltage characterization that electrons are trapped in deep traps at the interface between ?-conjugated polyspirofluorene polymer and the aluminum oxide.

  6. Anti-corrosive properties of an electropolymerized polymer coating on a shape memory alloy surface

    SciTech Connect

    de Cayeux, S.

    1996-01-01

    Acrylonitrile electropolymerization (in an aprotic and anhydrous medium) has been used as a way to build thin, homogeneous and covering polyacrylonitrile layers grafted on the surface of usual metals and specially on copper-based shape memory alloy: Cu-Zn-Al. The results of the study first confirm the possibility of grafting thin and covering polyacrylonitrile layers on Cu-Zn-Al surface. The morphology of the films however is influenced by the geometry of the polycristalline structure of the alloy and its superficial defects. Samples obtained after grafting polyacrylonitrile films were submitted to corrosion tests based on Electrochemical Impedance Spectroscopy (EIS) measurements in a NaCl/H{sub 2}O medium. Results show that some post-treatments of the grafted films are necessary to improve their protective role, while preserving the strong interfacial bondings. Actually, thermal and mechanical cycling of the shape memory alloy covered by electropolymerized polyacrylonitrile show that the adhesion of the film is better than for simply dipped films, and thus show the relevance of grafting. {copyright} {ital 1996 American Institute of Physics.}

  7. Therapeutic Antiviral Effect of the Nucleic Acid Polymer REP 2055 against Persistent Duck Hepatitis B Virus Infection

    PubMed Central

    Noordeen, Faseeha; Scougall, Catherine A.; Grosse, Arend; Qiao, Qiao; Ajilian, Behzad B.; Reaiche-Miller, Georget; Finnie, John; Werner, Melanie; Broering, Ruth; Schlaak, Joerg F.; Vaillant, Andrew; Jilbert, Allison R.

    2015-01-01

    Previous studies have demonstrated that nucleic acid polymers (NAPs) have both entry and post-entry inhibitory activity against duck hepatitis B virus (DHBV) infection. The inhibitory activity exhibited by NAPs prevented DHBV infection of primary duck hepatocytes in vitro and protected ducks from DHBV infection in vivo and did not result from direct activation of the immune response. In the current study treatment of primary human hepatocytes with NAP REP 2055 did not induce expression of the TNF, IL6, IL10, IFNA4 or IFNB1 genes, confirming the lack of direct immunostimulation by REP 2055. Ducks with persistent DHBV infection were treated with NAP 2055 to determine if the post-entry inhibitory activity exhibited by NAPs could provide a therapeutic effect against established DHBV infection in vivo. In all REP 2055-treated ducks, 28 days of treatment lead to initial rapid reductions in serum DHBsAg and DHBV DNA and increases in anti-DHBs antibodies. After treatment, 6/11 ducks experienced a sustained virologic response: DHBsAg and DHBV DNA remained at low or undetectable levels in the serum and no DHBsAg or DHBV core antigen positive hepatocytes and only trace amounts of DHBV total and covalently closed circular DNA (cccDNA) were detected in the liver at 9 or 16 weeks of follow-up. In the remaining 5/11 REP 2055-treated ducks, all markers of DHBV infection rapidly rebounded after treatment withdrawal: At 9 and 16 weeks of follow-up, levels of DHBsAg and DHBcAg and DHBV total and cccDNA in the liver had rebounded and matched levels observed in the control ducks treated with normal saline which remained persistently infected with DHBV. These data demonstrate that treatment with the NAP REP 2055 can lead to sustained control of persistent DHBV infection. These effects may be related to the unique ability of REP 2055 to block release of DHBsAg from infected hepatocytes. PMID:26560490

  8. The effect of free radical inhibitor on the sensitized radiation crosslinking and thermal processing stabilization of polyurethane shape memory polymers

    PubMed Central

    Hearon, Keith; Smith, Sarah E.; Maher, Cameron A.; Wilson, Thomas S.; Maitland, Duncan J.

    2012-01-01

    The effects of free radical inhibitor on the electron beam crosslinking and thermal processing stabilization of novel radiation crosslinkable polyurethane shape memory polymers (SMPs) blended with acrylic radiation sensitizers have been determined. The SMPs in this study possess novel processing capabilitiesthat is, the ability to be melt processed into complex geometries as thermoplastics and crosslinked in a secondary step using electron beam irradiation. To increase susceptibility to radiation crosslinking, the radiation sensitizer pentaerythritol triacrylate (PETA) was solution blended with thermoplastic polyurethane SMPs made from 2-butene-1,4-diol and trimethylhexamethylene diisocyanate (TMHDI). Because thermoplastic melt processing methods such as injection molding are often carried out at elevated temperatures, sensitizer thermal instability is a major processing concern. Free radical inhibitor can be added to provide thermal stabilization; however, inhibitor can also undesirably inhibit radiation crosslinking. In this study, we quantified both the thermal stabilization and radiation crosslinking inhibition effects of the inhibitor 1,4-benzoquinone (BQ) on polyurethane SMPs blended with PETA. Sol/gel analysis of irradiated samples showed that the inhibitor had little to no inverse effects on gel fraction at concentrations of 0-10,000 ppm, and dynamic mechanical analysis showed only a slight negative correlation between BQ composition and rubbery modulus. The 1,4-benzoquinone was also highly effective in thermally stabilizing the acrylic sensitizers. The polymer blends could be heated to 150C for up to five hours or to 125C for up to 24 hours if stabilized with 10,000 ppm BQ and could also be heated to 125C for up to 5 hours if stabilized with 1000 ppm BQ without sensitizer reaction occurring. We believe this study provides significant insight into methods for manipulation of the competing mechanisms of radiation crosslinking and thermal stabilization of radiation sensitizers, thereby facilitating further development of radiation crosslinkable thermoplastic SMPs. PMID:23226930

  9. Dependence of memory characteristics of fullerene-containing polymer on the kind of gate metal

    NASA Astrophysics Data System (ADS)

    Nakajima, Anri; Shoji, Atsushi; Nagano, Kohei; Kajihara, Jun

    2015-10-01

    The memory operation of [6,6]-phenyl-C61-butyric-acid-methyl-ester-containing polystyrene nanocomposites was investigated while varying the kind of gate metal used. Moderate magnitudes of flatband voltage shift were observed both after negative and positive programming voltages were applied to the Au gate. Excellent retention characteristics were obtained for electrons, whereas the retention time of holes was much shorter than that of electrons for the gate. An analysis of the band diagram indicated that carriers are injected and stored in the lowest unoccupied molecular orbital or highest occupied molecular orbital levels of fullerene. Au gates are promising from the practical viewpoint because they make the magnitudes of both the writing and erasing voltages small.

  10. Nanoporous capsules of block co-polymers of [(MeO-PEG-NH)-b-(L-GluA)]-PCL for the controlled release of anticancer drugs for therapeutic applications

    NASA Astrophysics Data System (ADS)

    Amgoth, Chander; Dharmapuri, Gangappa; Kalle, Arunasree M.; Paik, Pradip

    2016-03-01

    Herein, new nanoporous capsules of the block co-polymers of MeO-PEG-NH-(L-GluA)10 and polycaprolactone (PCL) have been synthesized through a surfactant-free cost-effective self-assembled soft-templating approach for the controlled release of drugs and for therapeutic applications. The nanoporous polymer capsules are designed to be biocompatible and are capable of encapsulating anticancer drugs (e.g., doxorubicin hydrochloride (DOX) and imatinib mesylate (ITM)) with a high extent (∼279 and ∼480 ng μg‑1, respectively). We have developed a nanoformulation of porous MeO-PEG-NH-(L-GluA)10-PCL capsules with DOX and ITM. The porous polymer nanoformulations have been programmed in terms of the release of anticancer drugs with a desired dose to treat the leukemia (K562) and human carcinoma cells (HepG2) in vitro and show promising IC50 values with a very high mortality of cancer cells (up to ∼96.6%). Our nanoformulation arrests the cell divisions due to ‘cellular scenescence’ and kills the cancer cells specifically. The present findings could enrich the effectiveness of idiosyncratic nanoporous polymer capsules for use in various other nanomedicinal and biomedical applications, such as for killing cancer cells, immune therapy, and gene delivery.

  11. Nanoporous capsules of block co-polymers of [(MeO-PEG-NH)-b-(L-GluA)]-PCL for the controlled release of anticancer drugs for therapeutic applications.

    PubMed

    Amgoth, Chander; Dharmapuri, Gangappa; Kalle, Arunasree M; Paik, Pradip

    2016-03-29

    Herein, new nanoporous capsules of the block co-polymers of MeO-PEG-NH-(L-GluA)10 and polycaprolactone (PCL) have been synthesized through a surfactant-free cost-effective self-assembled soft-templating approach for the controlled release of drugs and for therapeutic applications. The nanoporous polymer capsules are designed to be biocompatible and are capable of encapsulating anticancer drugs (e.g., doxorubicin hydrochloride (DOX) and imatinib mesylate (ITM)) with a high extent (∼279 and ∼480 ng μg(-1), respectively). We have developed a nanoformulation of porous MeO-PEG-NH-(L-GluA)10-PCL capsules with DOX and ITM. The porous polymer nanoformulations have been programmed in terms of the release of anticancer drugs with a desired dose to treat the leukemia (K562) and human carcinoma cells (HepG2) in vitro and show promising IC50 values with a very high mortality of cancer cells (up to ∼96.6%). Our nanoformulation arrests the cell divisions due to 'cellular scenescence' and kills the cancer cells specifically. The present findings could enrich the effectiveness of idiosyncratic nanoporous polymer capsules for use in various other nanomedicinal and biomedical applications, such as for killing cancer cells, immune therapy, and gene delivery. PMID:26891479

  12. Microfabricated therapeutic actuators

    DOEpatents

    Lee, A.P.; Northrup, M.A.; Ciarlo, D.R.; Krulevitch, P.A.; Benett, W.J.

    1999-06-15

    Microfabricated therapeutic actuators are fabricated using a shape memory polymer (SMP), a polyurethane-based material that undergoes a phase transformation at a specified temperature (Tg). At a temperature above temperature Tg material is soft and can be easily reshaped into another configuration. As the temperature is lowered below temperature Tg the new shape is fixed and locked in as long as the material stays below temperature Tg. Upon reheating the material to a temperature above Tg, the material will return to its original shape. By the use of such SMP material, SMP microtubing can be used as a release actuator for the delivery of embolic coils through catheters into aneurysms, for example. The microtubing can be manufactured in various sizes and the phase change temperature Tg is determinate for an intended temperature target and intended use. 8 figs.

  13. Microfabricated therapeutic actuators

    DOEpatents

    Lee, Abraham P. (Walnut Creek, CA); Northrup, M. Allen (Berkeley, CA); Ciarlo, Dino R. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA); Benett, William J. (Livermore, CA)

    1999-01-01

    Microfabricated therapeutic actuators are fabricated using a shape memory polymer (SMP), a polyurethane-based material that undergoes a phase transformation at a specified temperature (Tg). At a temperature above temperature Tg material is soft and can be easily reshaped into another configuration. As the temperature is lowered below temperature Tg the new shape is fixed and locked in as long as the material stays below temperature Tg. Upon reheating the material to a temperature above Tg, the material will return to its original shape. By the use of such SMP material, SMP microtubing can be used as a release actuator for the delivery of embolic coils through catheters into aneurysms, for example. The microtubing can be manufactured in various sizes and the phase change temperature Tg is determinate for an intended temperature target and intended use.

  14. Polyacetal-stilbene conjugates - The first examples of polymer therapeutics for the inhibition of HIF-1 in the treatment of solid tumours.

    PubMed

    England, Richard M; Masi, Esther; Gimnez, Vanessa; Lucas, Rut; Vicent, Mara J

    2012-12-28

    We report here the first examples of Polymer Therapeutics synthesised with the intention of inhibiting Hypoxia Inducible Factor-1 (HIF-1), a transcription factor heavily involved in numerous cell processes under a low oxygen environment. Four compounds were selected for use in these systems; Diethylstilbestrol (DES), Bisphenol A (BIS), Dienestrol (DIENES) and Hexestrol (HEX), which were chosen from a large family of similar molecules known as Stilbenes. These are non-steroidal molecules with structural similarities to oestrogen, and of which DES and BIS have previously been reported for HIF-1 inhibition. These molecules were incorporated into a poly(ethylene glycol) (PEG) based polyacetal system using a reaction of short PEG chains with di(ethylene glycol) divinyl ether units and an acid catalyst and without the need for biodegradable linkers. With an improved polyacetal synthesis strategy we obtained high yields of water soluble polymer conjugates with desirable drug loadings and tailored molecular weights (Mw 23,000-35,000g/mol) with relatively narrow polydispersities (pdi 1.3-1.5). These polymers were found to be hydrolytically cleaved under acid conditions (such as those found in endosomes, lysosomes or the extracellular fluid of some tumours) yielding the free drug. Additionally, they were found to be stable over prolonged periods of time at pH 7.4 mimicking blood plasma. Of the four polymers synthesised, the conjugates of DES and BIS displayed the best activity for HIF-1? inhibition in HeLa 9xHRE-Luc tumour cells. More importantly, these conjugates were found to exhibit little to no cell toxicity, contrary to the free drugs, and consequently, they significantly enhanced drug therapeutic index (TI 3.5 vs. 7.2 for free DES vs. DES-polyacetal 2a, and TI 1.1 vs. >20 for free BIS vs. BIS-polyacetal 1b). PMID:22940127

  15. Implementation of poly(?-caprolactone) sheet-based shape-memory polymer microvalves into plastic-based microfluidic devices

    NASA Astrophysics Data System (ADS)

    Jiang, Chenyang; Uto, Koichiro; Ebara, Mitsuhiro; Aoyagi, Takao; Ichiki, Takanori

    2015-06-01

    Implementation of shape-memory polymer (SMP) sheet-based microvalves into plastic-based microfluidic devices has been studied toward the use in disposable and mass producible micro total analysis devices. Poly(?-caprolactone) (PCL) and poly(methyl methacrylate-co-styrene) (MS) were used as SMP and main substrate materials, respectively. Bonding between PCL sheets and MS plates was the critical issue in the practical implementation. We found the pristine PCL sheet has relatively rough surface with Ra of 85.14 nm, which is the cause of poor bonding. Hence, by introducing the post-anneal treatment with sandwiched between two flat glass plates, the PCL surface could be smoothed to Ra of 12.50 nm, and tight bonding could be obtained. Consequently, microfluidic devices consisting of plastic/PCL/plastic layers were successfully fabricated and therein the actuation of SMP valves without any leakage was demonstrated. The present technology is expected to be applicable to disposable microfluidic devices as required for point-of-care testing.

  16. Switching and memory effects governed by the hopping mechanism of charge carrier transfer in composite films based on conducting polymers and inorganic nanoparticles

    NASA Astrophysics Data System (ADS)

    Aleshin, A. N.; Alexandrova, E. L.

    2008-10-01

    The switching and memory effects in composite films based on conducting polymers [poly(phenylenevinylene), thiophene, and carbazole derivatives] and inorganic nanoparticles (ZnO, Si) are investigated. It is established that the introduction of inorganic nanoparticles (ZnO, Si) exhibiting strong acceptor properties into polymer materials leads to the appearance of memory effects, which manifest themselves in the transition of the polymer from a low-conductivity state to a high-conductivity state. For a number of composites, this transition is accompanied by the formation of a region with a negative differential resistance and a hysteresis in the current-voltage characteristics. It is demonstrated that the observed effects are determined by the mechanism of charge carrier transfer in the composite. In particular, the main mechanism of transport in films based on thiophene derivatives is associated with electrical conduction due to the tunneling of charge carriers between conducting regions embedded in a nonconducting matrix, whereas the dominant mechanism of transport in “polymer-semiconductor nanoparticle” composite films is hopping conduction, which is responsible for the effects observed in these objects.

  17. Configuration control on the shape memory stiffness of molecularly imprinted polymer for specific uptake of creatinine

    NASA Astrophysics Data System (ADS)

    Ang, Qian Yee; Zolkeflay, Muhammad Helmi; Low, Siew Chun

    2016-04-01

    In this study, sol-gel processing was proposed to prepare a creatinine (Cre)-imprinted molecularly imprinted polymer (MIP). The intermolecular interaction constituted by the cross-linkers, i.e., 2-acrylamido-2-methylpropane-sulfonic acid (AMPS) and aluminium ion (Al3+), was studied and compared in order to form a confined matrix that promises the effectiveness of molecular imprinting. In view of the shape recognition, the hydrogen bonded Cre-AMPS did not demonstrate good recognition of Cre, with Cre binding found only at 5.70 ± 0.15 mg g-1 of MIP. Whilst, MIP cross-linked using Al3+ was able to attain an excellent Cre adsorption capacity of 19.48 ± 0.64 mg g-1 of MIP via the stronger ionic interaction of Cre-Al3+. Based on the Scatchard analysis, a higher Cre concentration in testing solution required greater driving force to resolve the binding resistance of Cre molecules, so as to have a precise Cre binding with shape factor. The molecular recognition ability of Cre-MIP in present work was shape-specific for Cre as compared to its structural analogue, 2-pyrrolidinone (2-pyr), by an ideal selectivity coefficient of 6.57 ± 0.10. In overall, this study has come up with a practical approach on the preparation of MIP for the detection of renal dysfunction by point-of-care Cre testing.

  18. Degree of Vertical Integration Between the Undergraduate Program and Clinical Internship With Respect to Cervical and Cranial Diagnostic and Therapeutic Procedures Taught at the Canadian Memorial Chiropractic College

    PubMed Central

    Leppington, Charmody; Gleberzon, Brian; Fortunato, Lisa; Doucet, Nicolea; Vandervalk, Kyle

    2012-01-01

    Objective: The purpose of this study was to determine if diagnostic and therapeutic procedures for the cervical and cranial spine taught to students during the undergraduate program at Canadian Memorial Chiropractic College are required to be used during their internship by their supervising clinicians and, if so, to what extent these procedures are used. Methods: Course manuals and course syllabi from the Applied Chiropractic and Clinical Diagnosis faculty of the undergraduate chiropractic program for the academic year 20092010 were consulted and a list of all diagnostic and therapeutic procedures for the cranial and cervical spine was compiled. This survey asked clinicians to indicate if they themselves used or if they required the students they were supervising to use each procedure listed and, if so, to what extent each procedure was used. Demographic information of each clinician was also obtained. Results: In general, most diagnostic procedures of the head and neck were seldom used, with the exception of postural observation and palpation. By contrast, most cervical orthopaedic tests were often used, with the exception of tests for vertigo. Most therapeutic procedures were used frequently with the exception of prone cervical and muscle adjustments. Conclusion: There was a low degree of vertical integration for cranial procedures as compared to a much higher degree of vertical integration for cervical procedures between the undergraduate and clinical internship programs taught. Vertical integration is an important element of curricular planning and these results may be helpful to aid educators to more appropriately allocate classroom instruction PMID:22778531

  19. A Structural Approach to Establishing a Platform Chemistry for the Tunable, Bulk Electron Beam Cross-Linking of Shape Memory Polymer Systems.

    PubMed

    Hearon, Keith; Besset, Celine J; Lonnecker, Alexander T; Ware, Taylor; Voit, Walter E; Wilson, Thomas S; Wooley, Karen L; Maitland, Duncan J

    2013-11-26

    The synthetic design and thermomechanical characterization of shape memory polymers (SMPs) built from a new polyurethane chemistry that enables facile, bulk and tunable cross-linking of low-molecular weight thermoplastics by electron beam irradiation is reported in this study. SMPs exhibit stimuli-induced geometry changes and are being proposed for applications in numerous fields. We have previously reported a polyurethane SMP system that exhibits the complex processing capabilities of thermoplastic polymers and the mechanical robustness and tunability of thermomechanical properties that are often characteristic of thermoset materials. These previously reported polyurethanes suffer practically because the thermoplastic molecular weights needed to achieve target cross-link densities severely limit high-throughput thermoplastic processing and because thermally unstable radiation-sensitizing additives must be used to achieve high enough cross-link densities to enable desired tunable shape memory behavior. In this study, we demonstrate the ability to manipulate cross-link density in low-molecular weight aliphatic thermoplastic polyurethane SMPs (M w as low as ~1.5 kDa) without radiation-sensitizing additives by incorporating specific structural motifs into the thermoplastic polymer side chains that we hypothesized would significantly enhance susceptibility to e-beam cross-linking. A custom diol monomer was first synthesized and then implemented in the synthesis of neat thermoplastic polyurethane SMPs that were irradiated at doses ranging from 1 to 500 kGy. Dynamic mechanical analysis (DMA) demonstrated rubbery moduli to be tailorable between 0.1 and 55 MPa, and both DMA and sol/gel analysis results provided fundamental insight into our hypothesized mechanism of electron beam cross-linking, which enables controllable bulk cross-linking to be achieved in highly processable, low-molecular weight thermoplastic shape memory polymers without sensitizing additives. PMID:25411511

  20. A Structural Approach to Establishing a Platform Chemistry for the Tunable, Bulk Electron Beam Cross-Linking of Shape Memory Polymer Systems

    PubMed Central

    Hearon, Keith; Besset, Celine J.; Lonnecker, Alexander T.; Ware, Taylor; Voit, Walter E.; Wilson, Thomas S.; Wooley, Karen L.; Maitland, Duncan J.

    2014-01-01

    The synthetic design and thermomechanical characterization of shape memory polymers (SMPs) built from a new polyurethane chemistry that enables facile, bulk and tunable cross-linking of low-molecular weight thermoplastics by electron beam irradiation is reported in this study. SMPs exhibit stimuli-induced geometry changes and are being proposed for applications in numerous fields. We have previously reported a polyurethane SMP system that exhibits the complex processing capabilities of thermoplastic polymers and the mechanical robustness and tunability of thermomechanical properties that are often characteristic of thermoset materials. These previously reported polyurethanes suffer practically because the thermoplastic molecular weights needed to achieve target cross-link densities severely limit high-throughput thermoplastic processing and because thermally unstable radiation-sensitizing additives must be used to achieve high enough cross-link densities to enable desired tunable shape memory behavior. In this study, we demonstrate the ability to manipulate cross-link density in low-molecular weight aliphatic thermoplastic polyurethane SMPs (Mw as low as ~1.5 kDa) without radiation-sensitizing additives by incorporating specific structural motifs into the thermoplastic polymer side chains that we hypothesized would significantly enhance susceptibility to e-beam cross-linking. A custom diol monomer was first synthesized and then implemented in the synthesis of neat thermoplastic polyurethane SMPs that were irradiated at doses ranging from 1 to 500 kGy. Dynamic mechanical analysis (DMA) demonstrated rubbery moduli to be tailorable between 0.1 and 55 MPa, and both DMA and sol/gel analysis results provided fundamental insight into our hypothesized mechanism of electron beam cross-linking, which enables controllable bulk cross-linking to be achieved in highly processable, low-molecular weight thermoplastic shape memory polymers without sensitizing additives. PMID:25411511

  1. Facile fabrication of uniaxial nanopatterns on shape memory polymer substrates using a complete bottom-up approach

    NASA Astrophysics Data System (ADS)

    Chen, Zhongbi; Krishnaswamy, Sridhar

    2014-03-01

    In earlier work, we have demonstrated an assisted self-assembly fabrication method for unidirectional submicron patterns using pre-programmed shape memory polymers (SMP) as the substrate in an organic/inorganic bilayer structure. In this paper, we propose a complete bottom-up method for fabrication of uniaxial wrinkles whose wavelength is below 300 nm. The method starts with using the aforementioned self-assembled bi-layer wrinkled surface as the template to make a replica of surface wrinkles on a PDMS layer which is spin-coated on a pre-programmed SMP substrate. When the shape recovery of the substrate is triggered by heating it to its transition temperature, the substrate has been programmed in such a way that it shrinks uniaxially to return to its permanent shape. Consequently, the wrinkle wavelength on PDMS reduces accordingly. A subsequent contact molding process is carried out on the PDMS layer spin-coated on another pre-programmed SMP substrate, but using the wrinkled PDMS surface obtained in the previous step as the master. By activating the shape recovery of the substrate, the wrinkle wavelength is further reduced a second time in a similar fashion. Our experiments showed that the starting wavelength of 640 nm decreased to 290 nm after two cycles of recursive molding. We discuss the advantages and limitations of our recursive molding approach compared to the prevalent top-down fabrication methods represented by lithography. The present study is expected to o er a simple and cost-e ective fabrication method of nano-scale uniaxial wrinkle patterns with the potential for large-scale mass-production.

  2. Degree of Vertical Integration Between the Undergraduate Program and Clinical Internship with Respect to Lumbopelvic Diagnostic and Therapeutic Procedures Taught at the Canadian Memorial Chiropractic College

    PubMed Central

    Vermet, Shannon; McGinnis, Karen; Boodham, Melissa; Gleberzon, Brian J.

    2010-01-01

    Purpose: The objective of this study was to determine to what extent the diagnostic and therapeutic procedures taught in the undergraduate program used for patients with lumbopelvic conditions are expected to be utilized by students during their clinical internship program at Canadian Memorial Chiropractic College or are being used by the clinical faculty. Methods: A confidential survey was distributed to clinical faculty at the college. It consisted of a list of diagnostic and therapeutic procedures used for lumbopelvic conditions taught at that college. Clinicians were asked to indicate the frequency with which they performed or they required students to perform each item. Results: Seventeen of 23 clinicians responded. The following procedures were most likely required to be performed by clinicians: posture; ranges of motion; lower limb sensory, motor, and reflex testing; and core orthopedic tests. The following were less likely to be required to be performed: Waddell testing, Schober's test, Gillet tests, and abdominal palpation. Students were expected to perform (or clinicians performed) most of the mobilization (in particular, iliocostal, iliotransverse, and iliofemoral) and spinal manipulative therapies (in particular, the procedures referred to as the lumbar roll, lumbar pull/hook, and upper sacroiliac) taught at the college. Conclusion: This study suggests that there was considerable, but not complete, vertical integration between the undergraduate and clinical education program at this college. PMID:20480014

  3. Fabrication and characterization of a foamed polylactic acid (PLA)/ thermoplastic polyurethane (TPU) shape memory polymer (SMP) blend for biomedical and clinical applications

    NASA Astrophysics Data System (ADS)

    Song, Janice J.; Srivastava, Ijya; Kowalski, Jennifer; Naguib, Hani E.

    2014-03-01

    Shape memory polymers (SMP) are a class of stimuli-responsive materials that are able to respond to external stimulus such as heat by altering their shape. Bio-compatible SMPs have a number of advantages over static materials and are being studied extensively for biomedical and clinical applications (such as tissue stents and scaffolds). A previous study has demonstrated that the bio-compatible polymer blend of polylactic acid (PLA)/ thermoplastic polyurethane (TPU) (50/50 and 70/30) exhibit good shape memory properties. In this study, the mechanical and thermo-mechanical (shape memory) properties of TPU/PLA SMP blends were characterized; the compositions studied were 80/20, 65/35, and 50/50 TPU/PLA. In addition, porous TPU/PLA SMP blends were fabricated with a gas-foaming technique; and the morphology of the porous structure of these SMPs foams were characterized with scanning electron microscopy (SEM). The TPU/PLA bio-compatible SMP blend was fabricated with melt-blending and compression molding. The glass transition temperature (Tg) of the SMP blends was determined with a differential scanning calorimeter (DSC). The mechanical properties studied were the stress-strain behavior, tensile strength, and elastic modulus; and the thermomechanical (or shape memory) properties studied were the shape fixity rate (Rf), shape recovery rate (Rr), response time, and the effect of recovery temperature on Rr. The porous 80/20 PLA/TPU SMP blend was found to have the highest tensile strength, toughness and percentage extension, as well as the lowest density and uniform pore structure in the micron and submicron scale. The porous 80/20 TPU/PLA SMP blend may be further developed for specific biomedical and clinical applications where a combination of tensile strength, toughness, and low density are required.

  4. Integrating a novel shape memory polymer into surgical meshes to improve device performance during laparoscopic hernia surgery

    NASA Astrophysics Data System (ADS)

    Zimkowski, Michael M.

    About 600,000 hernia repair surgeries are performed each year. The use of laparoscopic minimally invasive techniques has become increasingly popular in these operations. Use of surgical mesh in hernia repair has shown lower recurrence rates compared to other repair methods. However in many procedures, placement of surgical mesh can be challenging and even complicate the procedure, potentially leading to lengthy operating times. Various techniques have been attempted to improve mesh placement, including use of specialized systems to orient the mesh into a specific shape, with limited success and acceptance. In this work, a programmed novel Shape Memory Polymer (SMP) was integrated into commercially available polyester surgical meshes to add automatic unrolling and tissue conforming functionalities, while preserving the intrinsic structural properties of the original surgical mesh. Tensile testing and Dynamic Mechanical Analysis was performed on four different SMP formulas to identify appropriate mechanical properties for surgical mesh integration. In vitro testing involved monitoring the time required for a modified surgical mesh to deploy in a 37°C water bath. An acute porcine model was used to test the in vivo unrolling of SMP integrated surgical meshes. The SMP-integrated surgical meshes produced an automated, temperature activated, controlled deployment of surgical mesh on the order of several seconds, via laparoscopy in the animal model. A 30 day chronic rat model was used to test initial in vivo subcutaneous biocompatibility. To produce large more clinical relevant sizes of mesh, a mold was developed to facilitate manufacturing of SMP-integrated surgical mesh. The mold is capable of manufacturing mesh up to 361 cm2, which is believed to accommodate the majority of clinical cases. Results indicate surgical mesh modified with SMP is capable of laparoscopic deployment in vivo, activated by body temperature, and possesses the necessary strength and biocompatibility to function as suitable ventral hernia repair mesh, while offering a reduction in surgical operating time and improving mesh placement characteristics. Future work will include ball-burst tests similar to ASTM D3787-07, direct surgeon feedback studies, and a 30 day chronic porcine model to evaluate the SMP surgical mesh in a realistic hernia repair environment, using laparoscopic techniques for typical ventral hernia repair.

  5. VEGF therapeutic gene delivery using dendrimer type bio-reducible polymer into human mesenchymal stem cells (hMSCs).

    PubMed

    Kim, Hyojung; Nam, Kihoon; Nam, Joung-Pyo; Kim, Hyun Soo; Kim, Yong Man; Joo, Wan Seok; Kim, Sung Wan

    2015-12-28

    The therapeutic potential of mesenchymal stem cells (MSCs) has garnered great attention in the expansive diversity of biomedical research. Despite this broad interest in stem cells, limited incorporation and poor viability are major disadvantages for accomplishing therapeutic success in the field of hMSC-based cell therapy, and an optimal approach for hMSC-based cell therapy using non-viral vectors has not been established. Hence, we examined the possibility of performing gene therapy using the biodegradable polymeric non-viral vector Arginine-grafted poly (cystaminebisacrylamide-diaminohexane) (ABP)-conjugated poly (amidoamine) (PAMAM) dendrimer (PAM-ABP) in hMSCs. PAM-ABP formed compact nanosized polyplexes and showed low cytotoxicity compared to bPEI 25k and Lipofectamine 2000 in hMSCs. Although the cellular uptake was similar, the transfection efficiency and VEGF expression of PAM-ABP using gWiz-Luc and p?-VEGF were higher than those of the control groups. Although hMSCs were transfected, their stem cell characteristics were retained. Our results suggest that PAM-ABP has the ability to deliver a therapeutic gene in hMSCs. PMID:26368313

  6. Examination of nanoformulated crosslinked polymers complexed with copper/zinc superoxide dismutase as a therapeutic strategy for angiotensin II-mediated hypertension

    NASA Astrophysics Data System (ADS)

    Savalia, Krupa

    Excessive generation of superoxide (O2·-) has been extensively implicated as a signaling molecule in cardiovascular pathologies, including hypertension. As a major risk factor for myocardial infarction, stroke, and heart failure, the morbidity and mortality associated with hypertension is a worldwide epidemic. Although there are several standard therapies that effectively lower blood pressure, many hypertensive patients have uncontrolled blood pressure despite taking available medications. Thus, there is a necessity to develop new pharmacotherapies that target novel molecular effectors (e.g. O2·-) that have been implicated to be integral in the pathogenesis of hypertension. To overcome the failed therapeutic impact of currently available antioxidants in cardiovascular disease, we developed a nanomedicine-based delivery system for the O2 ·- scavenging enzyme, copper/zinc superoxide dismutase (CuZnSOD), in which CuZnSOD protein is electrostatically bound to poly-L-lysine (PLL 50)-polyethylene glycol (PEG) block co-polymer to form CuZnSOD nanozyme. Different formulations of CuZnSOD nanozyme are covalently stabilized by either reducible or non-reducible crosslinked bonds between the PLL50-PEG polymers. Herein, we tested the overall hypothesis that PLL50-PEG CuZnSOD nanozyme delivers active CuZnSOD protein to neurons and decreases blood pressure in a model of Angll-dependent hypertension. As determined by electron paramagnetic resonance (EPR) spectroscopy, nanozymes retain full SOD enzymatic activity. Furthermore, non-reducible crosslinked nanozyme delivers active CuZnSOD protein to central neurons in culture (CATH.a neurons) without inducing significant neuronal toxicity. In vivo studies conducted in Angll-mediated hypertensive adult male C57BL/6 mice demonstrate that the non-reducible crosslinked nanozyme significantly attenuates blood pressure when given directly into the brain and prevents the further increase in hypertension when intravenously (IV) administered. While these physiologic data are promising, it was essential to determine the biological distribution of our nanozymes. The experimental data provided herein implicate the proximal tubules in the kidney cortex as a primary target for CuZnSOD nanozyme following IV administration. Collectively, these studies support the further development of PLL50 -PEG CuZnSOD nanozyme as an antioxidant-based therapeutic option for the improved treatment of hypertension. Furthermore, the therapeutic impact of CuZnSOD nanozyme could be investigated in additional pathologies in which there are excessive levels of O2·- present in the kidney.

  7. Influence of long-term storage in cold hibernation on strain recovery and recovery stress of polyurethane shape memory polymer foam

    NASA Astrophysics Data System (ADS)

    Tey, S. J.; Huang, W. M.; Sokolowski, W. M.

    2001-04-01

    In this paper, the effects of long-term storage in compressed cold hibernated elastic memory (CHEM) polyurethane foam, a kind of shape memory polymer, are investigated experimentally. The foams were pre-strained at a high temperature, which was above the glass transition temperature, to 80% and 93.4%, respectively, and then cooled back to room temperature. After various periods of cold hibernation (up to two months), they were heated up at fixed length or against different constant loads. It is found that: (1) the maximum stress that the foam could exert at fixed length depends heavily on the amount of pre-strain; (2) expansion rates of 380 and 1273% from the hibernated size against a 1 N load (pre-strained by 80 and 93.4%, respectively) are achievable. However, upon further increases in load, the expansion is reduced dramatically. It appears that the tested CHEM polyurethane foam retains its shape memory properties even after being stored in a compacted state for a long period. Complete strain recovery is attainable for a hibernation period of up to two months.

  8. Surface modification of a ferroelectric polymer insulator for low-voltage readable nonvolatile memory in an organic field-effect transistor

    NASA Astrophysics Data System (ADS)

    Kim, Won-Ho; Bae, Jin-Hyuk; Kim, Min-Hoi; Keum, Chang-Min; Park, Jaehoon; Lee, Sin-Doo

    2011-01-01

    We demonstrate that the sequential surface modification of a ferroelectric polymer insulator plays an essential role in both the enhancement of the carrier mobility and the shift in the turn-on voltage (Von) in an organic ferroelectric field-effect transistor (FeFET) for nonvolatile memory. The surface of a ferroelectric polymer insulator, poly(vinylidene fluoride-trifluoroethylene), is physicochemically modified by the successive treatments of ultraviolet-ozone (UVO) and CF4 plasma to understand how the surface morphology and the hydrophobicity affect the grain size, the mobility, and Von in the FeFET. In a pentacene-based FeFET, the CF4 plasma irradiation leads to the mobility enhancement by a factor of about 5 as well as the shift in Von toward a positive voltage direction while the UVO treatment results in only the shift in Von toward a negative voltage direction. It is found that the sequence of the two successive treatments is critical for tailoring interfacial interactions between the ferroelectric polymer insulator and the pentacene layer. The underlying mechanism for the mobility enhancement and the shift in Von is described in terms of the surface morphology and the nature of the built-in electric field.

  9. Response of the medial temporal lobe network in amnestic mild cognitive impairment to therapeutic intervention assessed by fMRI and memory task performance.

    PubMed

    Bakker, Arnold; Albert, Marilyn S; Krauss, Gregory; Speck, Caroline L; Gallagher, Michela

    2015-01-01

    Studies of individuals with amnestic mild cognitive impairment (aMCI) have detected hyperactivity in the hippocampus during task-related functional magnetic resonance imaging (fMRI). Such elevated activation has been localized to the hippocampal dentate gyrus/CA3 (DG/CA3) during performance of a task designed to detect the computational contributions of those hippocampal circuits to episodic memory. The current investigation was conducted to test the hypothesis that greater hippocampal activation in aMCI represents a dysfunctional shift in the normal computational balance of the DG/CA3 regions, augmenting CA3-driven pattern completion at the expense of pattern separation mediated by the dentate gyrus. We tested this hypothesis using an intervention based on animal research demonstrating a beneficial effect on cognition by reducing excess hippocampal neural activity with low doses of the atypical anti-epileptic levetiracetam. In a within-subject design we assessed the effects of levetiracetam in three cohorts of aMCI participants, each receiving a different dose of levetiracetam. Elevated activation in the DG/CA3 region, together with impaired task performance, was detected in each aMCI cohort relative to an aged control group. We observed significant improvement in memory task performance under drug treatment relative to placebo in the aMCI cohorts at the 62.5 and 125 mg BID doses of levetiracetam. Drug treatment in those cohorts increased accuracy dependent on pattern separation processes and reduced errors attributable to an over-riding effect of pattern completion while normalizing fMRI activation in the DG/CA3 and entorhinal cortex. Similar to findings in animal studies, higher dosing at 250 mg BID had no significant benefit on either task performance or fMRI activation. Consistent with predictions based on the computational functions of the DG/CA3 elucidated in basic animal research, these data support a dysfunctional encoding mechanism detected by fMRI in individuals with aMCI and therapeutic intervention using fMRI to detect target engagement in response to treatment. PMID:25844322

  10. Response of the medial temporal lobe network in amnestic mild cognitive impairment to therapeutic intervention assessed by fMRI and memory task performance

    PubMed Central

    Bakker, Arnold; Albert, Marilyn S.; Krauss, Gregory; Speck, Caroline L.; Gallagher, Michela

    2015-01-01

    Studies of individuals with amnestic mild cognitive impairment (aMCI) have detected hyperactivity in the hippocampus during task-related functional magnetic resonance imaging (fMRI). Such elevated activation has been localized to the hippocampal dentate gyrus/CA3 (DG/CA3) during performance of a task designed to detect the computational contributions of those hippocampal circuits to episodic memory. The current investigation was conducted to test the hypothesis that greater hippocampal activation in aMCI represents a dysfunctional shift in the normal computational balance of the DG/CA3 regions, augmenting CA3-driven pattern completion at the expense of pattern separation mediated by the dentate gyrus. We tested this hypothesis using an intervention based on animal research demonstrating a beneficial effect on cognition by reducing excess hippocampal neural activity with low doses of the atypical anti-epileptic levetiracetam. In a within-subject design we assessed the effects of levetiracetam in three cohorts of aMCI participants, each receiving a different dose of levetiracetam. Elevated activation in the DG/CA3 region, together with impaired task performance, was detected in each aMCI cohort relative to an aged control group. We observed significant improvement in memory task performance under drug treatment relative to placebo in the aMCI cohorts at the 62.5 and 125 mg BID doses of levetiracetam. Drug treatment in those cohorts increased accuracy dependent on pattern separation processes and reduced errors attributable to an over-riding effect of pattern completion while normalizing fMRI activation in the DG/CA3 and entorhinal cortex. Similar to findings in animal studies, higher dosing at 250 mg BID had no significant benefit on either task performance or fMRI activation. Consistent with predictions based on the computational functions of the DG/CA3 elucidated in basic animal research, these data support a dysfunctional encoding mechanism detected by fMRI in individuals with aMCI and therapeutic intervention using fMRI to detect target engagement in response to treatment. PMID:25844322

  11. n-Channel Organic Thin-Film Transistors based on Naphthalene-Bis(dicarboximide) Polymer for Organic Transistor Memory Using Hole-Acceptor Layer

    NASA Astrophysics Data System (ADS)

    Anuar Mohamad, Khairul; Yousuke, Kakuta; Uesugi, Katsuhiro; Fukuda, Hisashi

    2011-09-01

    An investigation of threshold voltage shifts in organic thin-film transistors (OTFTs) based on poly[N,N '-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene) [P(NDI2OD-T2)] with additional poly(3-hexylthiophene) (P3HT) films on a poly(methyl methacrylate) (PMMA) organic dielectric layer is reported. With a top source-drain contact structure, the device exhibited a unipolar property with n-channel characteristics similar to those of the P(NDI2OD-T2)-only device. Furthermore, the existence of P3HT films as hole acceptor-like storage layers resulted in reversible Vth shift upon the application of external gate bias (Vbias) for a certain bias time (Tbias). Hence, the P(NDI2OD-T2)/P3HT-OTFTs exhibited a large memory window (ΔVth = 10.7 V) for write and erase electrically without major degradation in saturation mobility [µsat = (1.8-2.8) ×10-4 cm2 V-1 s-1]. These results clearly indicate the utility of the naphthalene-bis(dicarboximide) (NDI)-based polymer-hole acceptor layer in the development of n-channel organic transistor memories.

  12. n-Channel Organic Thin-Film Transistors based on Naphthalene--Bis(dicarboximide) Polymer for Organic Transistor Memory Using Hole-Acceptor Layer

    NASA Astrophysics Data System (ADS)

    Mohamad, Khairul Anuar; Yousuke, Kakuta; Uesugi, Katsuhiro; Fukuda, Hisashi

    2011-09-01

    An investigation of threshold voltage shifts in organic thin-film transistors (OTFTs) based on poly{[N,N\\aku '-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} [P(NDI2OD-T2)] with additional poly(3-hexylthiophene) (P3HT) films on a poly(methyl methacrylate) (PMMA) organic dielectric layer is reported. With a top source-drain contact structure, the device exhibited a unipolar property with n-channel characteristics similar to those of the P(NDI2OD-T2)-only device. Furthermore, the existence of P3HT films as hole acceptor-like storage layers resulted in reversible Vth shift upon the application of external gate bias (Vbias) for a certain bias time (Tbias). Hence, the P(NDI2OD-T2)/P3HT-OTFTs exhibited a large memory window (Δ Vth = 10.7 V) for write and erase electrically without major degradation in saturation mobility [μsat = (1.8{--}2.8) × 10-4 cm2 V-1 s-1]. These results clearly indicate the utility of the naphthalene--bis(dicarboximide) (NDI)-based polymer--hole acceptor layer in the development of n-channel organic transistor memories.

  13. Electrospun biomimetic fibrous scaffold from shape memory polymer of PDLLA-co-TMC for bone tissue engineering.

    PubMed

    Bao, Min; Lou, Xiangxin; Zhou, Qihui; Dong, Wen; Yuan, Huihua; Zhang, Yanzhong

    2014-02-26

    Multifunctional fibrous scaffolds, which combine the capabilities of biomimicry to the native tissue architecture and shape memory effect (SME), are highly promising for the realization of functional tissue-engineered products with minimally invasive surgical implantation possibility. In this study, fibrous scaffolds of biodegradable poly(d,l-lactide-co-trimethylene carbonate) (denoted as PDLLA-co-TMC, or PLMC) with shape memory properties were fabricated by electrospinning. Morphology, thermal and mechanical properties as well as SME of the resultant fibrous structure were characterized using different techniques. And rat calvarial osteoblasts were cultured on the fibrous PLMC scaffolds to assess their suitability for bone tissue engineering. It is found that by varying the monomer ratio of DLLA:TMC from 5:5 to 9:1, fineness of the resultant PLMC fibers was attenuated from ca. 1500 down to 680 nm. This also allowed for readily modulating the glass transition temperature Tg (i.e., the switching temperature for actuating shape recovery) of the fibrous PLMC to fall between 19.2 and 44.2 C, a temperature range relevant for biomedical applications in the human body. The PLMC fibers exhibited excellent shape memory properties with shape recovery ratios of Rr > 94% and shape fixity ratios of Rf > 98%, and macroscopically demonstrated a fast shape recovery (?10 s at 39 C) in the pre-deformed configurations. Biological assay results corroborated that the fibrous PLMC scaffolds were cytocompatible by supporting osteoblast adhesion and proliferation, and functionally promoted biomineralization-relevant alkaline phosphatase expression and mineral deposition. We envision the wide applicability of using the SME-capable biomimetic scaffolds for achieving enhanced efficacy in repairing various bone defects (e.g., as implants for healing bone screw holes or as barrier membranes for guided bone regeneration). PMID:24476093

  14. Nitrogen-doped, boron-doped and undoped multiwalled carbon nanotube/polymer composites in WORM memory devices

    NASA Astrophysics Data System (ADS)

    Mamo, Messai A.; Sustaita, Alan O.; Tetana, Zikhona N.; Coville, Neil J.; Hmmelgen, Ivo A.

    2013-03-01

    We report the preparation of write-once-read-many times memory devices using composites of carbon nanotubes and poly(vinyl phenol) sandwiched between Al electrodes. Three types of nanotubes (undoped multiwalled carbon nanotubes, nitrogen-doped multiwalled carbon nanotubes and boron-doped multiwalled carbon nanotubes) are investigated for this application. The OFF to ON state switching threshold is only slightly dependent on nanotube type, but the ON/OFF current ratio depends on both nanotube type and concentration and varies up to 106, decreasing for nanotube concentrations larger than 0.50 wt% in the composite.

  15. Switching and memory effects in composite films of semiconducting polymers with particles of graphene and graphene oxide

    NASA Astrophysics Data System (ADS)

    Krylov, P. S.; Berestennikov, A. S.; Aleshin, A. N.; Komolov, A. S.; Shcherbakov, I. P.; Petrov, V. N.; Trapeznikova, I. N.

    2015-08-01

    The effects of switching were investigated in composite films based on multifunctional polymers. i.e., derivatives of carbazole (PVK) and fluorene (PFD), as well as based on particles of graphene (Gr) and graphene oxide (GO). The concentration of Gr and GO particles in the PVK(PFD) matrix was varied in the range of 2-3 wt %, which corresponded to the percolation threshold in these systems. The atomic composition of the composite films PVK: GO was examined using X-ray photoelectron spectroscopy. It was found that the effect of switching in structures of the form Al/PVK(PFD): GO(Gr)/ITO/PET manifests itself in a sharp change of the electrical resistance of the composite film from a low-conducting state to a relatively high-conducting state when applying a bias to Al-ITO electrodes of ˜0.1-0.3 V ( E ˜ 3-5 × 104 V/cm), which is below the threshold switching voltages for similar composites. The mechanism of resistance switching, which is associated with the processes of capture and accumulation of charge carriers by Gr (GO) particles introduced into the matrices of the high-molecular-weight (PVK) and relatively low-molecular-weight (PFD) polymers, was discussed.

  16. dc- and ac-magnetic field-induced strain effects in ferromagnetic shape memory composites of Ni-Mn-Ga single crystal and polyurethane polymer

    NASA Astrophysics Data System (ADS)

    Zeng, Min; Or, Siu Wing; Chan, Helen Lai Wa

    2010-05-01

    Ferromagnetic shape memory composites of multilayer and sandwich types were fabricated by laminating Ni-Mn-Ga single-crystal plates with polyurethane (PU) polymer plates. The dc- and ac-magnetic field-induced strains (MFISs) in the composites were measured as functions of both magnetic field and mechanical load, and the results were compared with those of the single crystal. It was found that the load-free dc-MFISs were 5.6%, 1.5%, and 0.8%, while the load-free ac-MFISs were 0.3%, 0.8%, and 0.5% in the single crystal, multilayer composite, and sandwich composite, respectively. The relatively smaller load-free dc-MFISs and larger load-free ac-MFISs in the composites than the single crystal originated from the stress bias of the Ni-Mn-Ga plates by the PU plates in the composites. The dc-MFISs of all samples and the ac-MFISs of the composites decreased with the increase in mechanical load amplitude, while the ac-MFIS of the single crystal peaked at 1.6 MPa load.

  17. Building a better hormone therapy?: How understanding the rapid effects of sex steroid hormones could lead to new therapeutics for age-related memory decline

    PubMed Central

    Frick, Karyn M.

    2012-01-01

    A wealth of data collected in recent decades has demonstrated that ovarian sex-steroid hormones, particularly 17β-estradiol (E2), are important trophic factors that regulate the function of cognitive regions of the brain such as the hippocampus. The loss of hormone cycling at menopause is associated with cognitive decline and dementia in women, and the onset of memory decline in animal models. However, hormone therapy is not currently recommended to prevent or treat cognitive decline, in part because of its detrimental side effects. In this article, it is proposed that investigations of the rapid effects of E2 on hippocampal function be used to further the design of new drugs that mimic the beneficial effects of E2 on memory without the side effects of current therapies. A conceptual model is presented for elucidating the molecular and biochemical mechanisms through which sex-steroid hormones modulate memory, and a specific hypothesis is proposed to account for the rapid memory-enhancing effects of E2. Empirical support for this hypothesis is discussed as a means of stimulating the consideration of new directions for the development of hormone-based therapies to preserve memory function in menopausal women. PMID:22289043

  18. Study on reinforced concrete beams strengthened using shape memory alloy wires in combination with carbon-fiber-reinforced polymer plates

    NASA Astrophysics Data System (ADS)

    Li, Hui; Liu, Zhi-qiang; Ou, Jin-ping

    2007-12-01

    It has been proven that carbon-fiber-reinforced polymer (CFRP) sheets or plates are capable of improving the strength of reinforced concrete (RC) structures. However, residual deformation of RC structures in service reduces the effect of CFRP strengthening. SMA can be applied to potentially decrease residual deformation and even close concrete cracks because of its recovery forces imposed on the concrete when heated. Therefore, a method of a RC structure strengthened by CFRP plates in combination with SMA wires is proposed in this paper. The strengthening effect of this method is investigated through experiments and numerical study based on the nonlinear finite element software ABAQUS in simple RC beams. Parametric analysis and assessment of damage by defining a damage index are carried out. The results indicate that recovery forces of SMA wires can decrease deflections and even close cracks in the concrete. The recovery rate of deflection of the beam increases with increasing the ratio of SMA wires. The specimen strengthened with CFRP plates has a relatively large stiffness and smaller damage index value when the residual deformation of the beam is first reduced by activation of the SMA wires. The effectiveness of this strengthening method for RC beams is verified by experimental and numerical results.

  19. Establishment of subcellular fractionation techniques to monitor the intracellular fate of polymer therapeutics II. Identification of endosomal and lysosomal compartments in HepG2 cells combining single-step subcellular fractionation with fluorescent imaging.

    PubMed

    Manunta, Maria; Izzo, Lorella; Duncan, Ruth; Jones, Arwyn Tomos

    2007-01-01

    As they are often designed for lysosomotropic, endosomotropic and/or transcellular delivery, an understanding of intracellular trafficking pathways is essential to enable optimised design of novel polymer therapeutics. Here, we describe a single-step density gradient subcellular fractionation method combined with fluorescent detection analysis that provides a new tool for characterisation of endocytic traffic of polymer therapeutics. Hepatoma (HepG2) cells were used as a model and cell breakage was optimised using a cell cracker to ensure assay of the whole cell population. After removal of unbroken cells and nuclei, the cell lysate as a post-nuclear supernatant (PNS) was layered onto an iodixanol (OptiPrep) density gradient optimised to 5-20%. Early endosomes, late endosomes and lysosomes were identified from gradient fractions by immunoblotting for marker proteins early endosome antigen 1 (EEA 1) and lysosomal associated membrane protein 1 (LAMP 1) using horseradish peroxidase or fluorescently-labelled secondary antibodies. Lysosomes were also detected using N-acetyl-beta-glucosamindase (Hex A) activity. In addition, cells were incubated with Texas-red labelled transferrin (TxR-Tf) for 5 min to specifically label early endosomes and this was directly detected from SDS-PAGE gels. Internalised macromolecules and colloidal particles can potentially alter vesicle buoyant density. To see if typical macromolecules of interest would alter vesicle density or perturb vesicle traffic, HepG2 cells were incubated with dextran or a polyethyleneglycol (PEG)-polyester dendron G4 (1 mg/ml for 24 h). The PEG-polyester dendron G4 caused a slight redistribution of endocytic structures to lower density fractions but immunofluorescence microscopy showed no obvious dendron effects. In conclusion, the combined subcellular fractionation with fluorescent imaging approach described here can be used as a tool for both fundamental cell biology research and/or the quantitative localisation of polymer therapeutics in the endocytic pathway. PMID:17365272

  20. Exploration of use of SenseCam to support autobiographical memory retrieval within a cognitive-behavioural therapeutic intervention following acquired brain injury.

    PubMed

    Brindley, Rob; Bateman, Andrew; Gracey, Fergus

    2011-10-01

    Delivering effective psychotherapy to address the significant emotional consequences of acquired brain injury (ABI) is challenged by the presence of acquired cognitive impairments, especially retrieval of detailed autobiographical memories of emotional trigger events. Initial studies using a wearable camera (SenseCam) suggest long-term improvements in autobiographical retrieval of recorded events. In this study a single-case experimental design was implemented to explore the use of SenseCam as a memory aid for a man with a specific anxiety disorder and memory and executive difficulties following ABI. We predicted that SenseCam supported rehearsal of memories of events that trigger high levels of anxiety would yield improved retrieval of both factual detail and internal state information (thoughts and feelings) compared with a conventional psychotherapy aid (automatic thought record sheets, ATRs) and no strategy. The findings indicated SenseCam supported retrieval of anxiety trigger events was superior to ATRs or no strategy in terms of both detail and internal state information, with 94% of the information being recalled in the SenseCam condition, compared to 39% for the "no strategy" and 22% for the ATR conditions. It is concluded that SenseCam may be of use as a compensatory aid in psychotherapies relying on retrieval of emotionally salient trigger events. PMID:20635299

  1. Integrating a novel shape memory polymer into surgical meshes decreases placement time in laparoscopic surgery: An in vitro and acute in vivo study

    PubMed Central

    Zimkowski, Michael M.; Rentschler, Mark E.; Schoen, Jonathan; Rech, Bryan A.; Mandava, Nageswara; Shandas, Robin

    2014-01-01

    About 600,000 hernia repair surgeries are performed each year; recently, the use of laparoscopic minimally invasive techniques has become increasingly popular in these operations. Use of surgical mesh in hernia repair has shown lower recurrence rates compared to other repair methods. However in many procedures, placement of surgical mesh can be challenging and even complicate the procedure, potentially leading to lengthy operating times. Various techniques have been attempted to improve mesh placement, including use of specialized systems to orient the mesh into a specific shape, with limited success and acceptance. In this study, a programmed novel Shape Memory Polymer (SMP) was integrated into commercially available polyester surgical meshes to add automatic unrolling and tissue conforming functionalities, while preserving the intrinsic structural properties of the original surgical mesh. Tensile testing and Dynamic Mechanical Analysis was performed on four different SMP formulas to identify appropriate mechanical properties for surgical mesh integration. In vitro testing involved monitoring the time required for a modified surgical mesh to deploy in a 37C water bath. An acute porcine model was used to test the in vivo unrolling of SMP integrated surgical meshes. The SMP-integrated surgical meshes produced an automated, temperature activated, controlled deployment of surgical mesh on the order of several seconds, via laparoscopy in the animal model. Results indicate surgical mesh modified with SMP is capable of laparoscopic deployment in vivo, activated by body temperature. This suggests a reduction in surgical operating time and improved mesh placement characteristics is possible with SMP-integrated surgical meshes. PMID:23412974

  2. Application of a novel 3-fluid nozzle spray drying process for the microencapsulation of therapeutic agents using incompatible drug-polymer solutions.

    PubMed

    Sunderland, Tara; Kelly, John G; Ramtoola, Zebunnissa

    2015-04-01

    The aim of this study was to evaluate a novel 3-fluid concentric nozzle (3-N) spray drying process for the microencapsulation of omeprazole sodium (OME) using Eudragit L100 (EL100). Feed solutions containing OME and/or EL100 in ethanol were assessed visually for OME stability. Addition of OME solution to EL100 solution resulted in precipitation of OME followed by degradation of OME reflected by a colour change from colourless to purple and brown. This was related to the low pH of 2.8 of the EL100 solution at which OME is unstable. Precipitation and progressive discoloration of the 2-fluid nozzle (2-N) feed solution was observed over the spray drying time course. In contrast, 3-N solutions of EL100 or OME in ethanol were stable over the spray drying period. Microparticles prepared using either nozzle showed similar characteristics and outer morphology however the internal morphology was different. DSC showed a homogenous matrix of drug and polymer for 2-N microparticles while 3-N microparticles had defined drug and polymer regions distributed as core and coat. The results of this study demonstrate that the novel 3-N spray drying process can allow the microencapsulation of a drug using an incompatible polymer and maintain the drug and polymer in separate regions of the microparticles. PMID:24170510

  3. Psychotherapy and Memories of Childhood Sexual Abuse.

    ERIC Educational Resources Information Center

    Lindsay, D. Stephen

    This conference address examines the question of whether "memory work"--using therapeutic techniques to help clients recover suspected hidden memories of childhood sexual abuse--has led some clients to develop illusory memories or false beliefs. Prospective research on memory for childhood trauma indicates that the gist of traumatic childhood

  4. Nonvolatile Ferroelectric Memory Circuit Using Black Phosphorus Nanosheet-Based Field-Effect Transistors with P(VDF-TrFE) Polymer.

    PubMed

    Lee, Young Tack; Kwon, Hyeokjae; Kim, Jin Sung; Kim, Hong-Hee; Lee, Yun Jae; Lim, Jung Ah; Song, Yong-Won; Yi, Yeonjin; Choi, Won-Kook; Hwang, Do Kyung; Im, Seongil

    2015-10-27

    Two-dimensional van der Waals (2D vdWs) materials are a class of new materials that can provide important resources for future electronics and materials sciences due to their unique physical properties. Among 2D vdWs materials, black phosphorus (BP) has exhibited significant potential for use in electronic and optoelectronic applications because of its allotropic properties, high mobility, and direct and narrow band gap. Here, we demonstrate a few-layered BP-based nonvolatile memory transistor with a poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) ferroelectric top gate insulator. Experiments showed that our BP-based ferroelectric transistors operate satisfactorily at room temperature in ambient air and exhibit a clear memory window. Unlike conventional ambipolar BP transistors, our ferroelectric transistors showed only p-type characteristics due to the carbon-fluorine (C-F) dipole effect of the P(VDF-TrFE) layer, as well as the highest linear mobility value of 1159 cm(2) V(-1) s(-1) with a 10(3) on/off current ratio. For more advanced memory applications beyond unit memory devices, we implemented two memory inverter circuits, a resistive-load inverter circuit and a complementary inverter circuit, combined with an n-type molybdenum disulfide (MoS2) nanosheet. Our memory inverter circuits displayed a clear memory window of 15 V and memory output voltage efficiency of 95%. PMID:26370537

  5. Electrical stimulation during skill training with a therapeutic glove enhances the induction of cortical plasticity and has a positive effect on motor memory.

    PubMed

    Christova, Monica; Rafolt, Dietmar; Golaszewski, Stefan; Nardone, Raffaele; Gallasch, Eugen

    2014-08-15

    To examine whether afferent stimulation of hand muscles has a facilitating effect on motor performance, learning and cortical excitability, healthy subjects were trained on the grooved pegboard test (GTP) while wearing a mesh glove (MG) with incorporated electrical stimulation. Three study groups (n=12) were compared in a between subjects design, the bare handed (BH), gloved (MG) and gloved with electrical stimulation (MGS) groups. Motor performance was assessed by the GPT completion time across 4 training blocks, and further one block was retested 7 days later to determine the off-line effects. On-line learning was obtained by normalizing the completion time values to the first training block, and off-line learning was obtained by normalizing the retest values to the last training block. Cortical excitability was assessed via single and paired-pulse transcranial magnetic stimulation (TMS) at pre-training, post-training and 30 min post-training. Motor evoked potential recruitment curve, short-latency intracortical inhibition and intracortical facilitation were estimated from the TMS assessments. Motor performance across all 4 training blocks was poor in the MG and MGS groups, while on-line learning was not affected by wearing the glove or by afferent stimulation. However, off-line learning, tested 7 days after training, was improved in the MGS group compared to the MG group. In addition, post-training corticospinal excitability was increased in the MGS group. It can be concluded that afferent stimulation improves off-line learning and thus has a positive effect on motor memory, likely due to LTP-like cortical plasticity in the consolidation phase. PMID:24844752

  6. Mechanical memory

    DOEpatents

    Gilkey, Jeffrey C.; Duesterhaus, Michelle A.; Peter, Frank J.; Renn, Rosemarie A.; Baker, Michael S.

    2006-05-16

    A first-in-first-out (FIFO) microelectromechanical memory apparatus (also termed a mechanical memory) is disclosed. The mechanical memory utilizes a plurality of memory cells, with each memory cell having a beam which can be bowed in either of two directions of curvature to indicate two different logic states for that memory cell. The memory cells can be arranged around a wheel which operates as a clocking actuator to serially shift data from one memory cell to the next. The mechanical memory can be formed using conventional surface micromachining, and can be formed as either a nonvolatile memory or as a volatile memory.

  7. Mechanical memory

    DOEpatents

    Gilkey, Jeffrey C.; Duesterhaus, Michelle A.; Peter, Frank J.; Renn, Rosemarie A.; Baker, Michael S.

    2006-08-15

    A first-in-first-out (FIFO) microelectromechanical memory apparatus (also termed a mechanical memory) is disclosed. The mechanical memory utilizes a plurality of memory cells, with each memory cell having a beam which can be bowed in either of two directions of curvature to indicate two different logic states for that memory cell. The memory cells can be arranged around a wheel which operates as a clocking actuator to serially shift data from one memory cell to the next. The mechanical memory can be formed using conventional surface micromachining, and can be formed as either a nonvolatile memory or as a volatile memory.

  8. Neuroepigenetic Regulation of Pathogenic Memories

    PubMed Central

    Sillivan, Stephanie E.; Vaissire, Thomas; Miller, Courtney A.

    2014-01-01

    Our unique collection of memories determines our individuality and shapes our future interactions with the world. Remarkable advances into the neurobiological basis of memory have identified key epigenetic mechanisms that support the stability of memory. Various forms of epigenetic regulation at the levels of DNA methylation, histone modification, and non-coding RNAs (ncRNAs) can modulate transcriptional and translational events required for memory processes. By changing the cellular profile in the brains emotional, reward, and memory circuits, these epigenetic modifications have also been linked to perseverant, pathogenic memories. In this review, we will delve into the relevance of epigenetic dysregulation to pathogenic memory mechanisms by focusing on two neuropsychiatric disorders perpetuated by aberrant memory associations: substance use disorder (SUD) and post-traumatic stress disorder (PTSD). As our understanding improves, neuroepigenetic mechanisms may someday be harnessed to develop novel therapeutic targets for the treatment of these chronic, relapsing disorders. PMID:25642412

  9. Therapeutic effect for liver-metastasized tumor by sequential intravenous injection of anionic polymer and cationic lipoplex of siRNA.

    PubMed

    Hattori, Yoshiyuki; Arai, Shohei; Kikuchi, Takuto; Ozaki, Kei-Ichi; Kawano, Kumi; Yonemochi, Etsuo

    2016-04-01

    Previously, we developed a novel siRNA transfer method to the liver by sequential intravenous injection of anionic polymer and cationic liposome/siRNA complex (cationic lipoplex). In this study, we investigated whether siRNA delivered by this sequential injection could significantly suppress mRNA expression of the targeted gene in liver metastasis and inhibit tumor growth. When cationic lipoplex was intravenously injected into mice bearing liver metastasis of human breast tumor MCF-7 at 1?min after intravenous injection of chondroitin sulfate C (CS) or poly-l-glutamic acid (PGA), siRNA was accumulated in tumor-metastasized liver. In terms of a gene silencing effect, sequential injections of CS or PGA plus cationic lipoplex of luciferase siRNA could reduce luciferase activity in liver MCF-7-Luc metastasis. Regarding the side effects, sequential injections of CS plus cationic lipoplex did not exhibit hepatic damage or induction of inflammatory cytokines in serum after repeated injections, but sequential injections of PGA plus cationic lipoplex did. Finally, sequential injections of CS plus cationic lipoplex of protein kinase N3 siRNA could suppress tumor growth in the mice bearing liver metastasis. From these findings, sequential injection of CS and cationic lipoplex of siRNA might be a novel systemic method of delivering siRNA to liver metastasis. PMID:26325230

  10. Soluble porphyrin polymers

    DOEpatents

    Gust, Jr., John Devens; Liddell, Paul Anthony

    2015-07-07

    Porphyrin polymers of Structure 1, where n is an integer (e.g., 1, 2, 3, 4, 5, or greater) ##STR00001## are synthesized by the method shown in FIGS. 2A and 2B. The porphyrin polymers of Structure 1 are soluble in organic solvents such as 2-MeTHF and the like, and can be synthesized in bulk (i.e., in processes other than electropolymerization). These porphyrin polymers have long excited state lifetimes, making the material suitable as an organic semiconductor for organic electronic devices including transistors and memories, as well as solar cells, sensors, light-emitting devices, and other opto-electronic devices.

  11. Polymers for Drug Delivery Systems

    PubMed Central

    Liechty, William B.; Kryscio, David R.; Slaughter, Brandon V.; Peppas, Nicholas A.

    2012-01-01

    Polymers have played an integral role in the advancement of drug delivery technology by providing controlled release of therapeutic agents in constant doses over long periods, cyclic dosage, and tunable release of both hydrophilic and hydrophobic drugs. From early beginnings using off-the-shelf materials, the field has grown tremendously, driven in part by the innovations of chemical engineers. Modern advances in drug delivery are now predicated upon the rational design of polymers tailored for specific cargo and engineered to exert distinct biological functions. In this review, we highlight the fundamental drug delivery systems and their mathematical foundations and discuss the physiological barriers to drug delivery. We review the origins and applications of stimuli-responsive polymer systems and polymer therapeutics such as polymer-protein and polymer-drug conjugates. The latest developments in polymers capable of molecular recognition or directing intracellular delivery are surveyed to illustrate areas of research advancing the frontiers of drug delivery. PMID:22432577

  12. Therapeutic hypothermia.

    PubMed

    Alzaga, Ana G; Cerdan, Mario; Varon, Joseph

    2006-09-01

    Therapeutic hypothermia has been used for millennia, but in recent years was not in much clinical use due to an apparent high risk of complications. More recently, the benefits of induced therapeutic hypothermia have been rediscovered, mainly with the improvement in neurological outcome in out-of-hospital cardiac arrest victims. In addition, therapeutic hypothermia has been suggested to improve outcome in other neurological conditions such as traumatic brain injury, neonatal asphyxia, cerebrovascular accidents and intracranial hypertension. This article reviews the history of the discovery of therapeutic hypothermia, as well as the current therapeutic applications and ways to deliver this treatment. Cooling techniques and recovery processes, as well as potential complications are also reviewed. Clinicians caring for a wide variety of critically ill patients should be familiar with the use of therapeutic hypothermia. PMID:16930801

  13. Nanoreinforced shape memory polyurethane

    NASA Astrophysics Data System (ADS)

    Richardson, Tara Beth

    Shape memory polymers (SMPs) are functional materials, which find applications in a broad range of temperature sensing elements and biological micro-electro-mechanical systems (MEMS). These polymers are capable of fixing a transient shape and recovering to their original shape after a series of thermo-mechanical treatments. Generally, these materials are thermoplastic segmented polyurethanes composed of soft segments, usually formed by a polyether macroglycol, and hard segments formed from the reaction of a diisocyanate with a low molecular mass diol. The hard segment content is a key parameter to control the final properties of the polymer, such as rubbery plateau modulus, melting point, hardness, and tensile strength. The long flexible soft segment largely controls the low temperature properties, solvent resistance, and weather resistance properties. The morphology and properties of polyurethanes (PU) are greatly influenced by the ratio of hard and soft block components and the average block lengths. However, in some applications, SMPs may not generate enough recovery force to be useful. The reinforcement of SMPs using nanofillers represents a novel approach of enhancing the performance of these materials. The incorporation of these fillers into SMPs can produce performance enhancements (particularly elastic modulus) at small nanoparticle loadings (1-2 wt %). An optimal performance of nanofiller-polymer nanocomposites requires uniform dispersion of filler in polymers and good interfacial adhesion. The addition of nanofillers like cellulose nanofibers (CNF), conductive cellulose nanofibers (C-CNF), and carbon nanotubes (CNTs) allows for the production of stiffer materials with deformation capacity comparable to that of the unfilled polymer. Additionally, the use of conductive nanoreinforcements such as C-CNF and CNTs leads to new pathways for actuation of the shape memory effect. During this work, thermoplastic shape memory polyurethanes were synthesized with varying chemical composition and molecular weight. This was achieved by controlling the moles of reactants used, by using polyols with different molecular weights, and by using different diisocyanates. Using these controls, polymer matrices with different but controlled structures were synthesized and then reinforced with CNF, C-CNF, and CNTs in order to study the influence of chemical structure and polymer-nanoreinforcement interactions on polymer nanocomposite morphology, thermal and mechanical properties, and shape memory behavior.

  14. Memory Matters

    MedlinePLUS

    ... different parts. Some of them are important for memory. The hippocampus (say: hih-puh-KAM-pus) is one of the more important parts of the brain that processes memories. Old information and new information, or memories, are ...

  15. Memory loss

    MedlinePLUS

    ... loss. Such memory loss is due to other diseases. Memory loss can be caused by many things. To ... event Bipolar disorder Depression or other mental health disorders, such as schizophrenia Memory loss may be a sign of dementia . Dementia ...

  16. Polymer films

    DOEpatents

    Granick, Steve; Sukhishvili, Svetlana A.

    2008-12-30

    A film contains a first polymer having a plurality of hydrogen bond donating moieties, and a second polymer having a plurality of hydrogen bond accepting moieties. The second polymer is hydrogen bonded to the first polymer.

  17. Polymer films

    DOEpatents

    Granick, Steve; Sukhishvili, Svetlana A.

    2004-05-25

    A film contains a first polymer having a plurality of hydrogen bond donating moieties, and a second polymer having a plurality of hydrogen bond accepting moieties. The second polymer is hydrogen bonded to the first polymer.

  18. Microfabricated therapeutic actuators and release mechanisms therefor

    SciTech Connect

    Lee, A.P.; Fitch, J.P.; Schumann, D.L.; Da Silva, L.; Benett, W.J.; Krulevitch, P.A.

    2000-05-09

    Microfabricated therapeutic actuators are fabricated using a shape memory polymer (SMP), a polyurethane-based material that undergoes a phase transformation at a specified temperature (Tg). At a temperature above temperature Tg material is soft and can be easily reshaped into another configuration. As the temperature is lowered below temperature Tg the new shape is fixed and locked in as long as the material stays below temperature Tg. Upon reheating the material to a temperature above Tg, the material will return to its original shape. By the use of such SMP material, SMP microtubing can be used as a retaining/release actuator for the delivery of material, such as embolic coils, for example, through catheters into aneurysms, for example. The microtubing can be manufactured in various sizes and the phase change temperature Tg is determinate for an intended temperature target and intended use. The SMP microtubing can be positioned around or within an end of a deposit material. Various heating arrangements can be utilized with the SMP release mechanism, and the SMP microtubing can include a metallic coating for enhanced light absorption.

  19. Microfabricated therapeutic actuators and release mechanisms therefor

    DOEpatents

    Lee, Abraham P. (Walnut Creek, CA); Fitch, Joseph P. (Livermore, CA); Schumann, Daniel L. (Concord, CA); Da Silva, Luiz (Danville, CA); Benett, William J. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

    2000-01-01

    Microfabricated therapeutic actuators are fabricated using a shape memory polymer (SMP), a polyurethane-based material that undergoes a phase transformation at a specified temperature (Tg). At a temperature above temperature Tg material is soft and can be easily reshaped into another configuration. As the temperature is lowered below temperature Tg the new shape is fixed and locked in as long as the material stays below temperature Tg. Upon reheating the material to a temperature above Tg, the material will return to its original shape. By the use of such SMP material, SMP microtubing can be used as a retaining/release actuator for the delivery of material, such as embolic coils, for example, through catheters into aneurysms, for example. The microtubing can be manufactured in various sizes and the phase change temperature Tg is determinate for an intended temperature target and intended use. The SMP microtubing can be positioned around or within an end of a deposit material. Various heating arrangements can be utilized with the SMP release mechanism, and the SMP microtubing can include a metallic coating for enhanced light absorption.

  20. High-performance a MoS2 nanosheet-based nonvolatile memory transistor with a ferroelectric polymer and graphene source-drain electrode

    NASA Astrophysics Data System (ADS)

    Lee, Young Tack; Hwang, Do Kyung; Im, Seongil

    2015-11-01

    Two-dimensional (2D) van der Waals (vdWs) materials are a class of new materials due to their unique physical properties. Of the many 2D vdWs materials, molybdenum disulfide (MoS2) is a representative n-type transition-metal dichalcogenide (TMD) semiconductor. Here, we report on a high-performance MoS2 nanosheet-based nonvolatile memory transistor with a poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) ferroelectric top gate insulator. In order to enhance the ohmic contact property, we use graphene flakes as source/drain electrodes prepared by using the direct imprinting method with an elastomer stamp. The MoS2 ferroelectric field-effect transistor (FeFET) shows the highest linear electron mobility value of 175 cm2/Vs with a high on/off current ratio of more than 107, and a very clear memory window of more than 15 V. The program and erase dynamics and the static retention properties are also well demonstrated.

  1. Therapeutic Nanodevices

    NASA Astrophysics Data System (ADS)

    Lee, Stephen; Ruegsegger, Mark; Barnes, Philip; Smith, Bryan; Ferrari, Mauro

    Therapeutic nanotechnology offers minimally invasive therapies with high densities of function concentrated in small volumes, features that may reduce patient morbidity and mortality. Unlike other areas of nanotechnology, novel physical properties associated with nanoscale dimensionality are not the raison d'tre of therapeutic nanotechnology, whereas the aggregation of multiple biochemical (or comparably precise) functions into controlled nanoarchitectures is. Multifunctionality is a hallmark of emerging nanotherapeutic devices, and multifunctionality can allow nanotherapeutic devices to perform multistep work processes, with each functional component contributing to one or more nanodevice subroutine such that, in aggregate, subroutines sum to a cogent work process. Cannonical nanotherapeutic subroutines include tethering (targeting) to sites of disease, dispensing measured doses of drug (or bioactive compound), detection of residual disease after therapy and communication with an external clinician/operator. Emerging nanotherapeutics thus blur the boundaries between medical devices and traditional pharmaceuticals. Assembly of therapeutic nanodevices generally exploits either (bio)material self-assembly properties or chemoselective bioconjugation techniques, or both. Given the complexity, composition, and the necessity for their tight chemical and structural definition inherent in the nature of nanotherapeutics, their cost of goods (COGs) might exceed that of (already expensive) biologics. Early therapeutic nanodevices will likely be applied to disease states which exhibit significant unmet patient need (cancer and cardiovascular disease), while application to other disease states well-served by conventional therapy may await perfection of nanotherapeutic design and assembly protocols.

  2. Therapeutic Nanodevices

    NASA Astrophysics Data System (ADS)

    Lee, Stephen C.; Ruegsegger, Mark; Barnes, Philip D.; Smith, Bryan R.; Ferrari, Mauro

    Therapeutic nanotechnology offers minimally invasive therapies with high densities of function concentrated in small volumes, features that may reduce patient morbidity and mortality. Unlike other areas of nanotechnology, novel physical properties associated with nanoscale dimensionality are not the raison d'etre of therapeutic nanotechnology, whereas the aggregation of multiple biochemical (or comparably precise) functions into controlled nanoarchitectures is. Multifunctionality is a hallmark of emerging nanotherapeutic devices, and multifunctionality can allow nanotherapeutic devices to perform multi-step work processes, with each functional component contributing to one or more nanodevice subroutine such that, in aggregate, subroutines sum to a cogent work process. Cannonical nanotherapeutic subroutines include tethering (targeting) to sites of disease, dispensing measured doses of drug (or bioactive compound), detection of residual disease after therapy and communication with an external clinician/operator. Emerging nanotherapeutics thus blur the boundaries between medical devices and traditional pharmaceuticals. Assembly of therapeutic nanodevices generally exploits either (bio)material self assembly properties or chemoselective bioconjugation techniques, or both. Given the complexity, composition, and the necessity for their tight chemical and structural definition inherent in the nature of nanotherapeutics, their cost of goods (COGs) might exceed that of (already expensive) biologics. Early therapeutic nanodevices will likely be applied to disease states which exhibit significant unmet patient need (cancer and cardiovascular disease), while application to other disease states well-served by conventional therapy may await perfection of nanotherapeutic design and assembly protocols.

  3. Memory Matters

    MedlinePLUS

    ... Digestive System How the Body Works Main Page Memory Matters KidsHealth > Kids > Health Problems > Brain & Nervous System > ... of your complex and multitalented brain. What Is Memory? When an event happens, when you learn something, ...

  4. Cognitive memory.

    PubMed

    Widrow, Bernard; Aragon, Juan Carlos

    2013-05-01

    Regarding the workings of the human mind, memory and pattern recognition seem to be intertwined. You generally do not have one without the other. Taking inspiration from life experience, a new form of computer memory has been devised. Certain conjectures about human memory are keys to the central idea. The design of a practical and useful "cognitive" memory system is contemplated, a memory system that may also serve as a model for many aspects of human memory. The new memory does not function like a computer memory where specific data is stored in specific numbered registers and retrieval is done by reading the contents of the specified memory register, or done by matching key words as with a document search. Incoming sensory data would be stored at the next available empty memory location, and indeed could be stored redundantly at several empty locations. The stored sensory data would neither have key words nor would it be located in known or specified memory locations. Sensory inputs concerning a single object or subject are stored together as patterns in a single "file folder" or "memory folder". When the contents of the folder are retrieved, sights, sounds, tactile feel, smell, etc., are obtained all at the same time. Retrieval would be initiated by a query or a prompt signal from a current set of sensory inputs or patterns. A search through the memory would be made to locate stored data that correlates with or relates to the prompt input. The search would be done by a retrieval system whose first stage makes use of autoassociative artificial neural networks and whose second stage relies on exhaustive search. Applications of cognitive memory systems have been made to visual aircraft identification, aircraft navigation, and human facial recognition. Concerning human memory, reasons are given why it is unlikely that long-term memory is stored in the synapses of the brain's neural networks. Reasons are given suggesting that long-term memory is stored in DNA or RNA. Neural networks are an important component of the human memory system, and their purpose is for information retrieval, not for information storage. The brain's neural networks are analog devices, subject to drift and unplanned change. Only with constant training is reliable action possible. Good training time is during sleep and while awake and making use of one's memory. A cognitive memory is a learning system. Learning involves storage of patterns or data in a cognitive memory. The learning process for cognitive memory is unsupervised, i.e. autonomous. PMID:23453302

  5. Immunological memory.

    PubMed

    Gray, D

    1993-01-01

    The past five or six years has seen a resurgence of interest in immunological memory. Areas in which important advances have been made of late or in which problems in understanding persist are covered here: (i) Selection of virgin B cells for entry into the peripheral pool. (ii) Expression of immunoglobulin isotypes and other markers on memory B cells. (iii) Development of memory B cells as a separate lineage from primary response B cells. (iv) Sites of production of memory B cells. (v) Signals that rescue mutating B cells in germinal centers, forming the basis of affinity selection, and programming further differentiation. (vi) The myriad markers of memory T cells, in particular CD45R isoforms. (vii) Selective migration pathways of memory T cells and its possible molecular basis. (viii) The lifespan of memory cells and factors that influence their long-term survival. The data accumulated during this period which have vastly increased our understanding of memory have at the same time highlighted unresolved problems that could block further progress in the field. The thorny question that we cannot at present answer is: How does a memory cell differ from an activated cell and, in the case of T cells, from an effector cell? The problem bears on the interpretation of any study that sets out to correlate memory phenotype with memory function. Immunologists may have donned an intellectual straitjacket in their search for the memory cell. PMID:8476570

  6. Targeted polymer-drug conjugates: Current progress and future perspective.

    PubMed

    Xu, Hongyan; Ma, Haifeng; Yang, Peimin; Zhang, Xia; Wu, Xiangxia; Yin, Weidong; Wang, Hui; Xu, Dongmei

    2015-12-01

    The combination of polymer technology and targeted drug delivery may pave the way for more effective yet safer therapeutic options for cancer therapy. Polymer-drug conjugates belonging to polymer therapeutics represent an emerging approach for drug delivery. The development of smart targeted polymer-drug conjugates that can specifically deliver drugs at a sustained rate to tumor cells may substantially improve the therapeutic index of anticancer agents. In this update, we provide an overview of the most important targeting molecules, and systemically summarize the recent advances in the development of tumor-targeted polymer-drug conjugates. Additionally, several promising approaches for the future will also be presented. PMID:26513756

  7. Microgravity Polymers

    NASA Technical Reports Server (NTRS)

    1986-01-01

    A one-day, interactive workshop considering the effects of gravity on polymer materials science was held in Cleveland, Ohio, on May 9, 1985. Selected programmatic and technical issues were reviewed to introduce the field to workshop participants. Parallel discussions were conducted in three disciplinary working groups: polymer chemistry, polymer physics, and polymer engineering. This proceedings presents summaries of the workshop discussions and conclusions.

  8. Emerging memories

    NASA Astrophysics Data System (ADS)

    Baldi, Livio; Bez, Roberto; Sandhu, Gurtej

    2014-12-01

    Memory is a key component of any data processing system. Following the classical Turing machine approach, memories hold both the data to be processed and the rules for processing them. In the history of microelectronics, the distinction has been rather between working memory, which is exemplified by DRAM, and storage memory, exemplified by NAND. These two types of memory devices now represent 90% of all memory market and 25% of the total semiconductor market, and have been the technology drivers in the last decades. Even if radically different in characteristics, they are however based on the same storage mechanism: charge storage, and this mechanism seems to be near to reaching its physical limits. The search for new alternative memory approaches, based on more scalable mechanisms, has therefore gained new momentum. The status of incumbent memory technologies and their scaling limitations will be discussed. Emerging memory technologies will be analyzed, starting from the ones that are already present for niche applications, and which are getting new attention, thanks to recent technology breakthroughs. Maturity level, physical limitations and potential for scaling will be compared to existing memories. At the end the possible future composition of memory systems will be discussed.

  9. Memory protection

    NASA Technical Reports Server (NTRS)

    Denning, Peter J.

    1988-01-01

    Accidental overwriting of files or of memory regions belonging to other programs, browsing of personal files by superusers, Trojan horses, and viruses are examples of breakdowns in workstations and personal computers that would be significantly reduced by memory protection. Memory protection is the capability of an operating system and supporting hardware to delimit segments of memory, to control whether segments can be read from or written into, and to confine accesses of a program to its segments alone. The absence of memory protection in many operating systems today is the result of a bias toward a narrow definition of performance as maximum instruction-execution rate. A broader definition, including the time to get the job done, makes clear that cost of recovery from memory interference errors reduces expected performance. The mechanisms of memory protection are well understood, powerful, efficient, and elegant. They add to performance in the broad sense without reducing instruction execution rate.

  10. Quantum memory Quantum memory

    NASA Astrophysics Data System (ADS)

    Le Gout, Jean-Louis; Moiseev, Sergey

    2012-06-01

    Interaction of quantum radiation with multi-particle ensembles has sparked off intense research efforts during the past decade. Emblematic of this field is the quantum memory scheme, where a quantum state of light is mapped onto an ensemble of atoms and then recovered in its original shape. While opening new access to the basics of light-atom interaction, quantum memory also appears as a key element for information processing applications, such as linear optics quantum computation and long-distance quantum communication via quantum repeaters. Not surprisingly, it is far from trivial to practically recover a stored quantum state of light and, although impressive progress has already been accomplished, researchers are still struggling to reach this ambitious objective. This special issue provides an account of the state-of-the-art in a fast-moving research area that makes physicists, engineers and chemists work together at the forefront of their discipline, involving quantum fields and atoms in different media, magnetic resonance techniques and material science. Various strategies have been considered to store and retrieve quantum light. The explored designs belong to three mainwhile still overlappingclasses. In architectures derived from photon echo, information is mapped over the spectral components of inhomogeneously broadened absorption bands, such as those encountered in rare earth ion doped crystals and atomic gases in external gradient magnetic field. Protocols based on electromagnetic induced transparency also rely on resonant excitation and are ideally suited to the homogeneous absorption lines offered by laser cooled atomic clouds or ion Coulomb crystals. Finally off-resonance approaches are illustrated by Faraday and Raman processes. Coupling with an optical cavity may enhance the storage process, even for negligibly small atom number. Multiple scattering is also proposed as a way to enlarge the quantum interaction distance of light with matter. The quest for higher efficiency, better fidelity, broader bandwidth, multimode capacity and longer storage lifetime is pursued in all those approaches, as shown in this special issue. The improvement of quantum memory operation specifically requires in-depth study and control of numerous physical processes leading to atomic decoherence. The present issue reflects the development of rare earth ion doped matrices offering long lifetime superposition states, either as bulk crystals or as optical waveguides. The need for quantum sources and high efficiency detectors at the single photon level is also illustrated. Several papers address the networking of quantum memories either in long-haul cryptography or in the prospect of quantum processing. In this context, much attention has been paid recently to interfacing quantum light with superconducting qubits and with nitrogen-vacancy centers in diamond. Finally, the quantum interfacing of light with matter raises questions on entanglement. The last two papers are devoted to the generation of entanglement by dissipative processes. It is shown that long lifetime entanglement may be built in this way. We hope this special issue will help readers to become familiar with the exciting field of ensemble-based quantum memories and will stimulate them to bring deeper insights and new ideas to this area.

  11. Declarative memory.

    PubMed

    Riedel, Wim J; Blokland, Arjan

    2015-01-01

    Declarative Memory consists of memory for events (episodic memory) and facts (semantic memory). Methods to test declarative memory are key in investigating effects of potential cognition-enhancing substances--medicinal drugs or nutrients. A number of cognitive performance tests assessing declarative episodic memory tapping verbal learning, logical memory, pattern recognition memory, and paired associates learning are described. These tests have been used as outcome variables in 34 studies in humans that have been described in the literature in the past 10 years. Also, the use of episodic tests in animal research is discussed also in relation to the drug effects in these tasks. The results show that nutritional supplementation of polyunsaturated fatty acids has been investigated most abundantly and, in a number of cases, but not all, show indications of positive effects on declarative memory, more so in elderly than in young subjects. Studies investigating effects of registered anti-Alzheimer drugs, cholinesterase inhibitors in mild cognitive impairment, show positive and negative effects on declarative memory. Studies mainly carried out in healthy volunteers investigating the effects of acute dopamine stimulation indicate enhanced memory consolidation as manifested specifically by better delayed recall, especially at time points long after learning and more so when drug is administered after learning and if word lists are longer. The animal studies reveal a different picture with respect to the effects of different drugs on memory performance. This suggests that at least for episodic memory tasks, the translational value is rather poor. For the human studies, detailed parameters of the compositions of word lists for declarative memory tests are discussed and it is concluded that tailored adaptations of tests to fit the hypothesis under study, rather than "off-the-shelf" use of existing tests, are recommended. PMID:25977084

  12. Scope of nanotechnology in ovarian cancer therapeutics.

    PubMed

    Yallapu, Murali M; Jaggi, Meena; Chauhan, Subhash C

    2010-01-01

    This review describes the use of polymer micelle nanotechnology based chemotherapies for ovarian cancer. While various chemotherapeutic agents can be utilized to improve the survival rate of patients with ovarian cancer, their distribution throughout the entire body results in high normal organ toxicity. Polymer micelle nanotechnology aims to improve the therapeutic efficacy of anti-cancer drugs while minimizing the side effects. Herein, different types of polymer micelle technology based nanotherapies such as PLGA, polymerosomes, acid cleavable, thermosensitive, pH sensitive, and cross-linked micelles are introduced and structural differences are explained. Additionally, production methods, stability, sustainability, drug incorporation and drug release profiles of various polymer micelle based nanoformulations are discussed. An important feature of polymer micelle nanotechnology is the small size (10-100 nm) of particles which improves circulation and enables superior accumulation of the therapeutic drugs at the tumor sites. This review provides a comprehensive evaluation of different types of polymer micelles and their implications in ovarian cancer therapeutics. PMID:20691083

  13. The Evolving Roles of Memory Immune Cells in Transplantation.

    PubMed

    Chen, Wenhao; Ghobrial, Rafik M; Li, Xian C

    2015-10-01

    Memory cells are the products of immune responses but also exert significant impact on subsequent immunity and immune tolerance, thus placing them in a unique position in transplant research. Memory cells are heterogeneous, including not only memory T cells but also memory B cells and innate memory cells. Memory cells are a critical component of protective immunity against invading pathogens, especially in immunosuppressed patients, but they also mediate graft loss and tolerance resistance. Recent studies suggest that some memory cells unexpectedly act as regulatory cells, promoting rather than hindering transplant survival. This functional diversity makes therapeutic targeting of memory cells a challenging task in transplantation. In this article, we highlight recent advances in our understanding of memory cells, focusing on diversity of memory cells and mechanisms involved in their induction and functions. We also provide a broad overview on the challenges and opportunities in targeting memory cells in the induction of transplant tolerance. PMID:26102615

  14. Robust Vacuum-/Air-Dried Graphene Aerogels and Fast Recoverable Shape-Memory Hybrid Foams.

    PubMed

    Li, Chenwei; Qiu, Ling; Zhang, Baoqing; Li, Dan; Liu, Chen-Yang

    2016-02-01

    New graphene aerogels can be fabricated by vacuum/air drying, and because of the mechanical robustness of the graphene aerogels, shape-memory polymer/graphene hybrid foams can be fabricated by a simple infiltration-air-drying-crosslinking method. Due to the superelasticity, high strength, and good electrical conductivity of the as-prepared graphene aerogels, the shape-memory hybrid foams exhibit excellent thermotropical and electrical shape-memory properties, outperforming previously reported shape-memory polymer foams. PMID:26643876

  15. Variable-Resistivity Material For Memory Circuits

    NASA Technical Reports Server (NTRS)

    Nagasubramanian, Ganesan; Distefano, Salvador; Moacanin, Jovan

    1989-01-01

    Nonvolatile memory elements packed densely. Electrically-erasable, programmable, read-only memory matrices made with newly-synthesized organic material of variable electrical resistivity. Material, polypyrrole doped with tetracyanoquinhydrone (TCNQ), changes reversibly between insulating or higher-resistivity state and conducting or low-resistivity state. Thin film of conductive polymer separates layer of row conductors from layer of column conductors. Resistivity of film at each intersection and, therefore, resistance of memory element defined by row and column, increased or decreased by application of suitable switching voltage. Matrix circuits made with this material useful for experiments in associative electronic memories based on models of neural networks.

  16. Memory reconsolidation keeps track of emotional changes, but what will explain the actual "processing"?

    PubMed

    Pascual-Leone, Antonio; Pascual-Leone, Juan

    2015-01-01

    We question memory reconsolidation and emotional arousal as sufficient determinants of therapeutic change. Generating new feelings and meanings must be contrasted with activating and stabilizing the evolving memories that reflect those novel experiences. Some therapeutic changes are not attributable to a memory model alone. "Emotional processing" is also needed and is often an undeclared form of complex executive problem solving. PMID:26050684

  17. Virtual memory

    NASA Technical Reports Server (NTRS)

    Denning, P. J.

    1986-01-01

    Virtual memory was conceived as a way to automate overlaying of program segments. Modern computers have very large main memories, but need automatic solutions to the relocation and protection problems. Virtual memory serves this need as well and is thus useful in computers of all sizes. The history of the idea is traced, showing how it has become a widespread, little noticed feature of computers today.

  18. CCD Memory

    NASA Technical Reports Server (NTRS)

    Janesick, James R.; Elliot, Tom; Norris, Dave; Vescelus, Fred

    1987-01-01

    CCD memory device yields over 6.4 x 10 to the eighth power levels of information on single chip. Charge-coupled device (CCD) demonstrated to operate as either read-only-memory (ROM) or photon-programmable memory with capacity of 640,000 bits, with each bit capable of being weighted to more than 1,000 discrete analog levels. Larger memory capacities now possible using proposed approach in conjunction with CCD's now being fabricated, which yield over 4 x 10 to the ninth power discrete levels of information on single chip.

  19. Episodic Memories in Anxiety Disorders: Clinical Implications

    PubMed Central

    Zlomuzica, Armin; Dere, Dorothea; Machulska, Alla; Adolph, Dirk; Dere, Ekrem; Margraf, Jürgen

    2014-01-01

    The aim of this review is to summarize research on the emerging role of episodic memories in the context of anxiety disorders (AD). The available literature on explicit, autobiographical, and episodic memory function in AD including neuroimaging studies is critically discussed. We describe the methodological diversity of episodic memory research in AD and discuss the need for novel tests to measure episodic memory in a clinical setting. We argue that alterations in episodic memory functions might contribute to the etiology of AD. We further explain why future research on the interplay between episodic memory function and emotional disorders as well as its neuroanatomical foundations offers the promise to increase the effectiveness of modern psychological treatments. We conclude that one major task is to develop methods and training programs that might help patients suffering from AD to better understand, interpret, and possibly actively use their episodic memories in a way that would support therapeutic interventions and counteract the occurrence of symptoms. PMID:24795583

  20. DNA Polymerases as Therapeutic Targets

    PubMed Central

    Berdis, Anthony J.

    2009-01-01

    Numerous pathological states including cancer, autoimmune diseases, and viral/bacterial infections are often attributed to uncontrollable DNA replication. Inhibiting this essential biological process provides an obvious therapeutic target against these diseases. A logical target is the DNA polymerase, the enzyme responsible for catalyzing the addition of mononucleotides into a growing polymer using a DNA or RNA template as a guide for directing each incorporation event. This review provides a summary of therapeutic agents that target polymerase activity. A discussion of the biological function and mechanism of polymerases is first provided to illustrate the strategy for therapeutic intervention as well as the rational design of various nucleoside analogs that inhibit various polymerases associated with viral infections and cancer. The development of nucleoside and non-nucleoside inhibitors as anti-viral agents is discussed with particular emphasis on their mechanism of action, structure-activity relationships, toxicity, and mechanism of resistance. In addition, commonly used anti-cancer agents are described to illustrate the similarities and differences associated with various nucleoside analogs as therapeutic agents. Finally, new therapeutic approaches are discussed that include the inhibition of selective polymerases involved in DNA repair and/or translesion DNA synthesis as anti-cancer agents. PMID:18642851

  1. Piezoelectric Polymers

    NASA Technical Reports Server (NTRS)

    Harrison, J. S.; Ounaies, Z.; Bushnell, Dennis M. (Technical Monitor)

    2001-01-01

    The purpose of this review is to detail the current theoretical understanding of the origin of piezoelectric and ferroelectric phenomena in polymers; to present the state-of-the-art in piezoelectric polymers and emerging material systems that exhibit promising properties; and to discuss key characterization methods, fundamental modeling approaches, and applications of piezoelectric polymers. Piezoelectric polymers have been known to exist for more than forty years, but in recent years they have gained notoriety as a valuable class of smart materials.

  2. Collaging Memories

    ERIC Educational Resources Information Center

    Wallach, Michele

    2011-01-01

    Even middle school students can have memories of their childhoods, of an earlier time. The art of Romare Bearden and the writings of Paul Auster can be used to introduce ideas about time and memory to students and inspire works of their own. Bearden is an exceptional role model for young artists, not only because of his astounding art, but also…

  3. Collaging Memories

    ERIC Educational Resources Information Center

    Wallach, Michele

    2011-01-01

    Even middle school students can have memories of their childhoods, of an earlier time. The art of Romare Bearden and the writings of Paul Auster can be used to introduce ideas about time and memory to students and inspire works of their own. Bearden is an exceptional role model for young artists, not only because of his astounding art, but also

  4. Childhood Memories.

    ERIC Educational Resources Information Center

    Danielson, Kathy Everts

    1989-01-01

    Provides numerous ideas for helping students write about special memories in the following categories: growing up--future dreams; authors and illustrators; family history; special places; and special memories. Describes how to write a "bio poem," and includes a bibliography of children's books that enhance and enrich student learning and writing.

  5. Episodic Memories

    ERIC Educational Resources Information Center

    Conway, Martin A.

    2009-01-01

    An account of episodic memories is developed that focuses on the types of knowledge they represent, their properties, and the functions they might serve. It is proposed that episodic memories consist of "episodic elements," summary records of experience often in the form of visual images, associated to a "conceptual frame" that provides a…

  6. Epigenetic memory: the Lamarckian brain

    PubMed Central

    Fischer, Andre

    2014-01-01

    Recent data support the view that epigenetic processes play a role in memory consolidation and help to transmit acquired memories even across generations in a Lamarckian manner. Drugs that target the epigenetic machinery were found to enhance memory function in rodents and ameliorate disease phenotypes in models for brain diseases such as Alzheimer's disease, Chorea Huntington, Depression or Schizophrenia. In this review, I will give an overview on the current knowledge of epigenetic processes in memory function and brain disease with a focus on Morbus Alzheimer as the most common neurodegenerative disease. I will address the question whether an epigenetic therapy could indeed be a suitable therapeutic avenue to treat brain diseases and discuss the necessary steps that should help to take neuroepigenetic research to the next level. PMID:24719207

  7. Therapeutic misadventure.

    PubMed

    Langford, N J

    2010-10-01

    Therapeutic misadventure can be defined as an injury or an adverse event caused by medical management rather than by an underlying disease. Within the National Health Service there were over 86,000 reported adverse incidents in 2007. In the USA medication errors have been rated as the fourth highest cause of death. Unfortunately one of the greatest contributors to iatrogenic injury is human error. The potential types of misadventure are infinite. Medication errors are a major part of this, being responsible for over 70% of cases that cause serious harm. However, many medication errors caused by slips, lapses, technical errors and mistakes are preventable; intentional violations of safe operating procedures are not. While medication errors were tolerated by society in the past, the readiness to institute criminal proceedings against health-care professionals has increased greatly in the UK over the last decade. The medication process consists of writing prescriptions, dispensing the product, administering it and monitoring its effects. Prescription errors arise owing to incomplete information, lack of appropriate labelling, environmental factors and human blunders. Even with a perfect prescription the right medication must be dispensed and appropriately labelled. Dispensing errors are not uncommon and may be compounded by non-clinical considerations. Administration of a drug by injection is one of the most dangerous aspects of the medication process, especially in inexperienced hands. The final component of medication supply is monitoring the effect of the medication. With short courses of medication such monitoring is easy, but with long-term medication, particularly with potent drugs where the margin between efficacy and toxicity is small, active procedures may be required to ensure toxicity does not ensue. Despite the endeavour of health-care professions to stick to the rule of 'first, do no harm', in reality this is difficult to achieve all of the time. When errors occur the natural thoughts of wanting to blame an individual at the sharp end (active error) should be tempered. Identifying and correcting system (latent) errors will, in the end, provide a safer health-care system. PMID:21539282

  8. Conjugated polymers: Watching polymers dance

    NASA Astrophysics Data System (ADS)

    Rothberg, Lewis

    2011-06-01

    Single-molecule spectroscopy allows fluctuations of conjugated polymer conformation to be monitored during solvent vapour annealing. Dramatic changes in fluorescence behaviour are observed and interpreted in terms of transformations between extended and collapsed polymer geometries.

  9. Frontiers in Alzheimer's Disease Therapeutics

    PubMed Central

    Stone, Jeremy G.; Casadesus, Gemma; Gustaw-Rothenberg, Kasia; Siedlak, Sandra L.; Wang, Xinglong; Zhu, Xiongwei; Perry, George; Castellani, Rudy J.; Smith, Mark A.

    2011-01-01

    Alzheimer's disease (AD) is a progressive neurodegenerative disease which begins with insidious deterioration of higher cognition and progresses to severe dementia. Clinical symptoms typically involve impairment of memory and at least one other cognitive domain. Owing to the exponential increase in the incidence of AD with age, the aging population across the world has seen a congruous increase in AD, emphasizing the importance of disease-altering therapy. Current therapeutics on the market, including cholinesterase inhibitors and N-methyl-D-aspartate receptor antagonists, provide symptomatic relief but do not alter progression of the disease. Therefore, progress in the areas of prevention and disease modification may be of critical interest. In this review, we summarize novel AD therapeutics that are currently being explored, and also mechanisms of action of specific drugs within the context of current knowledge of AD pathologic pathways. PMID:21743833

  10. Updating stored memory requires adult hippocampal neurogenesis

    PubMed Central

    Suárez-Pereira, Irene; Carrión, Ángel M

    2015-01-01

    Adult hippocampal neurogenesis appears to influence hippocampal functions, such as memory formation for example. While adult hippocampal neurogenesis is known to be involved in hippocampal-dependent learning and consolidation processes, the role of such immature neurons in memory reconsolidation, a process involved in the modification of stored memories, remains unclear. Here, using a novel fast X-ray ablation protocol to deplete neurogenic cells, we have found that adult hippocampal neurogenesis is required to update object recognition stored memory more than to reinforce it. Indeed, we show that immature neurons were selectively recruited to hippocampal circuits during the updating of stored information. Thus, our data demonstrate a new role for neurogenesis in cognitive processes, adult hippocampal neurogenesis being required for the updating of stored OR memories. These findings suggest that manipulating adult neurogenesis may have a therapeutic application in conditions associated with traumatic stored memory, for example. PMID:26358557

  11. TCR Signaling in T Cell Memory

    PubMed Central

    Daniels, Mark A.; Teixeiro, Emma

    2015-01-01

    T cell memory plays a critical role in our protection against pathogens and tumors. The antigen and its interaction with the T cell receptor (TCR) is one of the initiating elements that shape T cell memory together with inflammation and costimulation. Over the last decade, several transcription factors and signaling pathways that support memory programing have been identified. However, how TCR signals regulate them is still poorly understood. Recent studies have shown that the biochemical rules that govern T cell memory, strikingly, change depending on the TCR signal strength. Furthermore, TCR signal strength regulates the input of cytokine signaling, including pro-inflammatory cytokines. These highlight how tailoring antigenic signals can improve immune therapeutics. In this review, we focus on how TCR signaling regulates T cell memory and how the quantity and quality of TCR–peptide–MHC interactions impact the multiple fates a T cell can adopt in the memory pool. PMID:26697013

  12. Polymer adsorption

    NASA Astrophysics Data System (ADS)

    Joanny, Jean-Francois

    2008-03-01

    The aim of this talk is to review Pierre-Gilles deGennes' work on polymer adsorption and the impact that it has now in our understanding of this problem. We will first present the self-consistent mean-field theory and its applications to adsorption and depletion. De Gennes most important contribution is probably the derivation of the self-similar power law density profile for adsorbed polymer layers that we will present next, emphasizing the differences between the tail sections and the loop sections of the adsorbed polymers. We will then discuss the kinetics of polymer adsorption and the penetration of a new polymer chain in an adsobed layer that DeGennes described very elegantly in analogy with a quantum tunneling problem. Finally, we will discuss the role of polymer adsorption for colloid stabilization.

  13. Electrochemical Sensors Based on Organic Conjugated Polymers

    PubMed Central

    Rahman, Md. Aminur; Kumar, Pankaj; Park, Deog-Su; Shim, Yoon-Bo

    2008-01-01

    Organic conjugated polymers (conducting polymers) have emerged as potential candidates for electrochemical sensors. Due to their straightforward preparation methods, unique properties, and stability in air, conducting polymers have been applied to energy storage, electrochemical devices, memory devices, chemical sensors, and electrocatalysts. Conducting polymers are also known to be compatible with biological molecules in a neutral aqueous solution. Thus, these are extensively used in the fabrication of accurate, fast, and inexpensive devices, such as biosensors and chemical sensors in the medical diagnostic laboratories. Conducting polymer-based electrochemical sensors and biosensors play an important role in the improvement of public health and environment because rapid detection, high sensitivity, small size, and specificity are achievable for environmental monitoring and clinical diagnostics. In this review, we summarized the recent advances in conducting polymer-based electrochemical sensors, which covers chemical sensors (potentiometric, voltammetric, amperometric) and biosensors (enzyme based biosensors, immunosensors, DNA sensors).

  14. Polymer Electrolytes

    NASA Astrophysics Data System (ADS)

    Hallinan, Daniel T.; Balsara, Nitash P.

    2013-07-01

    This review article covers applications in which polymer electrolytes are used: lithium batteries, fuel cells, and water desalination. The ideas of electrochemical potential, salt activity, and ion transport are presented in the context of these applications. Potential is defined, and we show how a cell potential measurement can be used to ascertain salt activity. The transport parameters needed to fully specify a binary electrolyte (salt + solvent) are presented. We define five fundamentally different types of homogeneous electrolytes: type I (classical liquid electrolytes), type II (gel electrolytes), type III (dry polymer electrolytes), type IV (dry single-ion-conducting polymer electrolytes), and type V (solvated single-ion-conducting polymer electrolytes). Typical values of transport parameters are provided for all types of electrolytes. Comparison among the values provides insight into the transport mechanisms occurring in polymer electrolytes. It is desirable to decouple the mechanical properties of polymer electrolyte membranes from the ionic conductivity. One way to accomplish this is through the development of microphase-separated polymers, wherein one of the microphases conducts ions while the other enhances the mechanical rigidity of the heterogeneous polymer electrolyte. We cover all three types of conducting polymer electrolyte phases (types III, IV, and V). We present a simple framework that relates the transport parameters of heterogeneous electrolytes to homogeneous analogs. We conclude by discussing electrochemical stability of electrolytes and the effects of water contamination because of their relevance to applications such as lithium ion batteries.

  15. Polymer Chemistry

    NASA Technical Reports Server (NTRS)

    Williams, Martha; Roberson, Luke; Caraccio, Anne

    2010-01-01

    This viewgraph presentation describes new technologies in polymer and material chemistry that benefits NASA programs and missions. The topics include: 1) What are Polymers?; 2) History of Polymer Chemistry; 3) Composites/Materials Development at KSC; 4) Why Wiring; 5) Next Generation Wiring Materials; 6) Wire System Materials and Integration; 7) Self-Healing Wire Repair; 8) Smart Wiring Summary; 9) Fire and Polymers; 10) Aerogel Technology; 11) Aerogel Composites; 12) Aerogels for Oil Remediation; 13) KSC's Solution; 14) Chemochromic Hydrogen Sensors; 15) STS-130 and 131 Operations; 16) HyperPigment; 17) Antimicrobial Materials; 18) Conductive Inks Formulations for Multiple Applications; and 19) Testing and Processing Equipment.

  16. Ferroelectric polymers

    SciTech Connect

    Lovinger, A.J.

    1983-06-10

    Piezoelectricity and pyroelectricity, traditionally encountered in certain single crystals and ceramics, have now also been documented in a number of polymers. Recently, one such polymer - poly(vinylidene fluoride) - and some of its copolymers have been shown to be ferroelectric as well. The extraordinary molecular and supermolecular structural requirements for ferroelectric behavior in polymers are discussed in detail, with particular emphasis on poly(vinylidene fluoride). Piezoelectric, pyroelectric, and ferroelectric properties are also briefly reviewed, as are some promising applications of such polymers. 8 figures, 1 table.

  17. Fullerene Embedded Shape Memory Nanolens Array

    PubMed Central

    Jeon, Sohee; Jang, Jun Young; Youn, Jae Ryoun; Jeong, Jun-ho; Brenner, Howard; Song, Young Seok

    2013-01-01

    Securing fragile nanostructures against external impact is indispensable for offering sufficiently long lifetime in service to nanoengineering products, especially when coming in contact with other substances. Indeed, this problem still remains a challenging task, which may be resolved with the help of smart materials such as shape memory and self-healing materials. Here, we demonstrate a shape memory nanostructure that can recover its shape by absorbing electromagnetic energy. Fullerenes were embedded into the fabricated nanolens array. Beside the energy absorption, such addition enables a remarkable enhancement in mechanical properties of shape memory polymer. The shape memory nanolens was numerically modeled to impart more in-depth understanding on the physics regarding shape recovery behavior of the fabricated nanolens. We anticipate that our strategy of combining the shape memory property with the microwave irradiation feature can provide a new pathway for nanostructured systems able to ensure a long-term durability. PMID:24253423

  18. Fullerene Embedded Shape Memory Nanolens Array

    NASA Astrophysics Data System (ADS)

    Jeon, Sohee; Jang, Jun Young; Youn, Jae Ryoun; Jeong, Jun-Ho; Brenner, Howard; Song, Young Seok

    2013-11-01

    Securing fragile nanostructures against external impact is indispensable for offering sufficiently long lifetime in service to nanoengineering products, especially when coming in contact with other substances. Indeed, this problem still remains a challenging task, which may be resolved with the help of smart materials such as shape memory and self-healing materials. Here, we demonstrate a shape memory nanostructure that can recover its shape by absorbing electromagnetic energy. Fullerenes were embedded into the fabricated nanolens array. Beside the energy absorption, such addition enables a remarkable enhancement in mechanical properties of shape memory polymer. The shape memory nanolens was numerically modeled to impart more in-depth understanding on the physics regarding shape recovery behavior of the fabricated nanolens. We anticipate that our strategy of combining the shape memory property with the microwave irradiation feature can provide a new pathway for nanostructured systems able to ensure a long-term durability.

  19. Fullerene embedded shape memory nanolens array.

    PubMed

    Jeon, Sohee; Jang, Jun Young; Youn, Jae Ryoun; Jeong, Jun-Ho; Brenner, Howard; Song, Young Seok

    2013-01-01

    Securing fragile nanostructures against external impact is indispensable for offering sufficiently long lifetime in service to nanoengineering products, especially when coming in contact with other substances. Indeed, this problem still remains a challenging task, which may be resolved with the help of smart materials such as shape memory and self-healing materials. Here, we demonstrate a shape memory nanostructure that can recover its shape by absorbing electromagnetic energy. Fullerenes were embedded into the fabricated nanolens array. Beside the energy absorption, such addition enables a remarkable enhancement in mechanical properties of shape memory polymer. The shape memory nanolens was numerically modeled to impart more in-depth understanding on the physics regarding shape recovery behavior of the fabricated nanolens. We anticipate that our strategy of combining the shape memory property with the microwave irradiation feature can provide a new pathway for nanostructured systems able to ensure a long-term durability. PMID:24253423

  20. Serotonin, neural markers, and memory

    PubMed Central

    Meneses, Alfredo

    2015-01-01

    Diverse neuropsychiatric disorders present dysfunctional memory and no effective treatment exits for them; likely as result of the absence of neural markers associated to memory. Neurotransmitter systems and signaling pathways have been implicated in memory and dysfunctional memory; however, their role is poorly understood. Hence, neural markers and cerebral functions and dysfunctions are revised. To our knowledge no previous systematic works have been published addressing these issues. The interactions among behavioral tasks, control groups and molecular changes and/or pharmacological effects are mentioned. Neurotransmitter receptors and signaling pathways, during normal and abnormally functioning memory with an emphasis on the behavioral aspects of memory are revised. With focus on serotonin, since as it is a well characterized neurotransmitter, with multiple pharmacological tools, and well characterized downstream signaling in mammals' species. 5-HT1A, 5-HT4, 5-HT5, 5-HT6, and 5-HT7 receptors as well as SERT (serotonin transporter) seem to be useful neural markers and/or therapeutic targets. Certainly, if the mentioned evidence is replicated, then the translatability from preclinical and clinical studies to neural changes might be confirmed. Hypothesis and theories might provide appropriate limits and perspectives of evidence. PMID:26257650

  1. Memory consolidation.

    PubMed

    Squire, Larry R; Genzel, Lisa; Wixted, John T; Morris, Richard G

    2015-08-01

    Conscious memory for a new experience is initially dependent on information stored in both the hippocampus and neocortex. Systems consolidation is the process by which the hippocampus guides the reorganization of the information stored in the neocortex such that it eventually becomes independent of the hippocampus. Early evidence for systems consolidation was provided by studies of retrograde amnesia, which found that damage to the hippocampus-impaired memories formed in the recent past, but typically spared memories formed in the more remote past. Systems consolidation has been found to occur for both episodic and semantic memories and for both spatial and nonspatial memories, although empirical inconsistencies and theoretical disagreements remain about these issues. Recent work has begun to characterize the neural mechanisms that underlie the dialogue between the hippocampus and neocortex (e.g., "neural replay," which occurs during sharp wave ripple activity). New work has also identified variables, such as the amount of preexisting knowledge, that affect the rate of consolidation. The increasing use of molecular genetic tools (e.g., optogenetics) can be expected to further improve understanding of the neural mechanisms underlying consolidation. PMID:26238360

  2. Fear Memory.

    PubMed

    Izquierdo, Ivan; Furini, Cristiane R G; Myskiw, Jociane C

    2016-04-01

    Fear memory is the best-studied form of memory. It was thoroughly investigated in the past 60 years mostly using two classical conditioning procedures (contextual fear conditioning and fear conditioning to a tone) and one instrumental procedure (one-trial inhibitory avoidance). Fear memory is formed in the hippocampus (contextual conditioning and inhibitory avoidance), in the basolateral amygdala (inhibitory avoidance), and in the lateral amygdala (conditioning to a tone). The circuitry involves, in addition, the pre- and infralimbic ventromedial prefrontal cortex, the central amygdala subnuclei, and the dentate gyrus. Fear learning models, notably inhibitory avoidance, have also been very useful for the analysis of the biochemical mechanisms of memory consolidation as a whole. These studies have capitalized on in vitro observations on long-term potentiation and other kinds of plasticity. The effect of a very large number of drugs on fear learning has been intensively studied, often as a prelude to the investigation of effects on anxiety. The extinction of fear learning involves to an extent a reversal of the flow of information in the mentioned structures and is used in the therapy of posttraumatic stress disorder and fear memories in general. PMID:26983799

  3. Polymers & People

    ERIC Educational Resources Information Center

    Lentz, Linda; Robinson, Thomas; Martin, Elizabeth; Miller, Mary; Ashburn, Norma

    2004-01-01

    Each Tuesday during the fall of 2002, teams of high school students from three South Carolina counties conducted a four-hour polymer institute for their peers. In less than two months, over 300 students visited the Charleston County Public Library in Charleston, South Carolina, to explore DNA, nylon, rubber, gluep, and other polymers. Teams of

  4. Polymers & People

    ERIC Educational Resources Information Center

    Lentz, Linda; Robinson, Thomas; Martin, Elizabeth; Miller, Mary; Ashburn, Norma

    2004-01-01

    Each Tuesday during the fall of 2002, teams of high school students from three South Carolina counties conducted a four-hour polymer institute for their peers. In less than two months, over 300 students visited the Charleston County Public Library in Charleston, South Carolina, to explore DNA, nylon, rubber, gluep, and other polymers. Teams of…

  5. Polymers All Around You!

    ERIC Educational Resources Information Center

    Gertz, Susan

    Background information on natural polymers, synthetic polymers, and the properties of polymers is presented as an introduction to this curriculum guide. Details are provided on the use of polymer products in consumer goods, polymer recycling, polymer densities, the making of a polymer such as GLUEP, polyvinyl alcohol, dissolving plastics, polymers

  6. Self-assembling materials for therapeutic delivery?

    PubMed Central

    Branco, Monica C.; Schneider, Joel P.

    2009-01-01

    A growing number of medications must be administered through parenteral delivery, i.e., intravenous, intramuscular, or subcutaneous injection, to ensure effectiveness of the therapeutic. For some therapeutics, the use of delivery vehicles in conjunction with this delivery mechanism can improve drug efficacy and patient compliance. Macromolecular self-assembly has been exploited recently to engineer materials for the encapsulation and controlled delivery of therapeutics. Self-assembled materials offer the advantages of conventional crosslinked materials normally used for release, but also provide the ability to tailor specific bulk material properties, such as release profiles, at the molecular level via monomer design. As a result, the design of materials from the bottom up approach has generated a variety of supramolecular devices for biomedical applications. This review provides an overview of self-assembling molecules, their resultant structures, and their use in therapeutic delivery. It highlights the current progress in the design of polymer- and peptide-based self-assembled materials. PMID:19010748

  7. Hybridizing Poly(ε-caprolactone) and Plasmonic Titanium Nitride Nanoparticles for Broadband Photoresponsive Shape Memory Films.

    PubMed

    Ishii, Satoshi; Uto, Koichiro; Niiyama, Eri; Ebara, Mitsuhiro; Nagao, Tadaaki

    2016-03-01

    Plasmonic nanoparticles can confine light in nanoscale and locally heat the surrounding. Here we use titanium nitride (TiN) nanoparticles as broadband plasmonic light absorbers and synthesized a highly photoresponsive hybrid cross-linked polymer from shape memory polymer poly(ε-caprolactone) (PCL). The TiN-PCL hybrid is responsive to sunlight and the threshold irradiance was among the lowest when compared with other photoresponsive shape memory polymers studied previously. Sunlight heating with TiN NPs can be applied to other heat responsive smart polymers, thereby contributing to energy-saving smart polymers research for a sustainable society. PMID:26890263

  8. Cell memory-based therapy

    PubMed Central

    Anjamrooz, Seyed Hadi

    2015-01-01

    Current cell therapies, despite all of the progress in this field, still faces major ethical, technical and regulatory hurdles. Because these issues possibly stem from the current, restricted, stereotypical view of cell ultrastructure and function, we must think radically about the nature of the cell. In this regard, the author's theory of the cell memory disc offers memory-based therapy, which, with the help of immune system rejuvenation, nervous system control and microparticle-based biodrugs, may have substantial therapeutic potential. In addition to its potential value in the study and prevention of premature cell aging, age-related diseases and cell death, memory therapy may improve the treatment of diseases that are currently limited by genetic disorders, risk of tumour formation and the availability and immunocompatibility of tissue transplants. PMID:26256679

  9. Cell memory-based therapy.

    PubMed

    Anjamrooz, Seyed Hadi

    2015-11-01

    Current cell therapies, despite all of the progress in this field, still faces major ethical, technical and regulatory hurdles. Because these issues possibly stem from the current, restricted, stereotypical view of cell ultrastructure and function, we must think radically about the nature of the cell. In this regard, the author's theory of the cell memory disc offers 'memory-based therapy', which, with the help of immune system rejuvenation, nervous system control and microparticle-based biodrugs, may have substantial therapeutic potential. In addition to its potential value in the study and prevention of premature cell aging, age-related diseases and cell death, memory therapy may improve the treatment of diseases that are currently limited by genetic disorders, risk of tumour formation and the availability and immunocompatibility of tissue transplants. PMID:26256679

  10. Frequency of use of diagnostic and manual therapeutic procedures of the spine taught at the Canadian Memorial Chiropractic College: A preliminary survey of Ontario chiropractors. Part 1 practice characteristics and demographic profiles

    PubMed Central

    Gleberzon, Brian; Stuber, Kent

    2013-01-01

    Background: Students learn a plethora of physical examination and manual therapy procedures over the course of their chiropractic education. However, it is uncertain to what extent they continue to use these procedures in practice after graduation. Objective: The purpose of this study was to determine which diagnostic and therapeutic procedures of the spine are most commonly utilized by chiropractors practicing in Ontario. In Part 1 of this study (presented here), the demographics and practice patterns of the respondents are presented. Part 2 of this study will present the results of the utilization rates of diagnostic and therapeutic procedures used by respondents. Methods: The study consisted of a paper-based survey that was sent to 500 pseudo-randomly selected Ontario chiropractors who responded confidentially. Survey questions inquired into demographic and practice style characteristics. Results: There were 108 respondents to the survey, giving a response rate of 22.4%. Many chiropractors self-identified themselves with more than one practice style characteristic such as 72.4% of the self-described pain-based chiropractors who also described themselves as evidence-based, compared with 51.9% of subluxation-based chiropractors who also described themselves as evidence-based. Diversified technique was the most commonly employed technique used by 90.7% of respondents, followed by trigger point therapy indicated by 57.4% of respondents. Conclusions: Despite a low response rate, respondents reported practice characteristics in this study that were similar to practice characteristics previously published, particularly in terms of professional demographics and techniques employed. While Diversified was the most commonly used technique, respondents reported higher levels of use of proprietary soft tissue techniques systems and upper cervical techniques than have been previously reported. PMID:23482716

  11. Memory reconsolidation, emotional arousal, and the process of change in psychotherapy: New insights from brain science.

    PubMed

    Lane, Richard D; Ryan, Lee; Nadel, Lynn; Greenberg, Leslie

    2015-01-01

    Since Freud, clinicians have understood that disturbing memories contribute to psychopathology and that new emotional experiences contribute to therapeutic change. Yet, controversy remains about what is truly essential to bring about psychotherapeutic change. Mounting evidence from empirical studies suggests that emotional arousal is a key ingredient in therapeutic change in many modalities. In addition, memory seems to play an important role but there is a lack of consensus on the role of understanding what happened in the past in bringing about therapeutic change. The core idea of this paper is that therapeutic change in a variety of modalities, including behavioral therapy, cognitive-behavioral therapy, emotion-focused therapy, and psychodynamic psychotherapy, results from the updating of prior emotional memories through a process of reconsolidation that incorporates new emotional experiences. We present an integrated memory model with three interactive components-autobiographical (event) memories, semantic structures, and emotional responses-supported by emerging evidence from cognitive neuroscience on implicit and explicit emotion, implicit and explicit memory, emotion-memory interactions, memory reconsolidation, and the relationship between autobiographical and semantic memory. We propose that the essential ingredients of therapeutic change include: (1) reactivating old memories; (2) engaging in new emotional experiences that are incorporated into these reactivated memories via the process of reconsolidation; and (3) reinforcing the integrated memory structure by practicing a new way of behaving and experiencing the world in a variety of contexts. The implications of this new, neurobiologically grounded synthesis for research, clinical practice, and teaching are discussed. PMID:24827452

  12. Hollow memories

    NASA Astrophysics Data System (ADS)

    2014-04-01

    A hollow-core optical fibre filled with warm caesium atoms can temporarily store the properties of photons. Michael Sprague from the University of Oxford, UK, explains to Nature Photonics how this optical memory could be a useful building block for fibre-based quantum optics.

  13. Deep brain stimulation effects on memory.

    PubMed

    Laxton, A W; Sankar, T; Lozano, A M; Hamani, C

    2012-12-01

    As the population of many countries ages, disorders of cognition and memory-such as Alzheimer's Disease (AD) and dementia associated with Parkinson's Disease-will become a major societal burden. At present, few effective medical therapies against these conditions are available. Deep brain stimulation (DBS) may be a potential therapeutic option, because it can directly target and modulate the activity of structures implicated in circuits subserving memory function. In this article, we review the scientific literature to address some of the mechanisms by which DBS may impact memory and cognition. We then summarize the results of recent clinical experience with DBS in AD and Parkinsonian dementia. PMID:23111294

  14. Polymer nanolithography

    NASA Astrophysics Data System (ADS)

    Vance, Jennifer M.

    Nanolithography involves making patterns of materials with at least one dimension less than 100 nanometers. Surprisingly, writable CDs can provide polymer nanostructures for pennies a piece. Building on work previously done in the Drain lab, with an inherited home-built oven press, this research will explore the relationships between polymer chemical reactivity, polymer printing, and material surface energies. In addition, a relatively inexpensive entry point into high school and undergraduate education in nanolithography is presented. The ability to pattern cheaply at the nanoscale and microscale is necessary and attractive for many technologies towards biosensors, organic light emitting diodes, identification tags, layered devices, and transistors.

  15. Memorial Sloan-Kettering Cancer Center

    Cancer.gov

    Research at Memorial Sloan-Kettering Cancer Center is focused on cancer diagnosis and enhancing responses of tumor to treatment with a goal of curing cancer. Animal studies of novel cancer therapeutics, while imperfect as a treatment model, have utility, both in studying therapeutic efficacy and toxicity. Because tumors are heterogenous, both between individuals and within a single tumor, non-invasive imaging studies are necessary to provide information about variation in response.

  16. Semiconducting polymers

    NASA Astrophysics Data System (ADS)

    Hermann, A. M.

    A review is presented of the electrical properties of those polymers whose conductivities occupy the middle ground between polymeric insulators and polymeric superconductors. Attention is confined to polymers in which conduction occurs through electronic, rather than ionic, transport. Four classes of semiconductors are discussed: (1) highly-conjugated polymers, including those formed by pyrolysis; (2) polymeric charge-transfer complexes and radical-ion salts; (3) organometallic polymeric semiconductors; and (4) composite polymer systems containing carbon or other highly conducting media. The possible applications discussed include cathodes in solid-state metal/halogen primary batteries, cathodes in lithium/poly-p-phenylene or polyacetylene secondary batteries, conductive coatings and epoxies, and chemical sensing agents. Other applications are Peltier cooling devices, pressure transducers, photovoltaic devices, infrared radiation detectors, and switches and resistors.

  17. Organometallic Polymers.

    ERIC Educational Resources Information Center

    Carraher, Charles E., Jr.

    1981-01-01

    Reactions utilized to incorporate a metal-containing moiety into a polymer chain (addition, condensation, and coordination) are considered, emphasizing that these reactions also apply to smaller molecules. (JN)

  18. Rational design of molecularly imprinted polymers.

    PubMed

    Curk, Tine; Dobnikar, Jure; Frenkel, Daan

    2015-12-16

    Molecular imprinting is the process whereby a polymer matrix is cross-linked in the presence of molecules with surface sites that can bind selectively to certain ligands on the polymer. The cross-linking process endows the polymer matrix with a chemical 'memory', such that the target molecules can subsequently be recognized by the matrix. We present a simple model that accounts for the key features of this molecular recognition. Using a combination of analytical calculations and Monte Carlo simulations, we show that the model can account for the binding of rigid particles to an imprinted polymer matrix with valence-limited interactions. We show how the binding multivalency and the polymer material properties affect the efficiency and selectivity of molecular imprinting. Our calculations allow us to formulate design criteria for optimal molecular imprinting. PMID:26452006

  19. Polymers All Around You!

    ERIC Educational Resources Information Center

    Gertz, Susan

    Background information on natural polymers, synthetic polymers, and the properties of polymers is presented as an introduction to this curriculum guide. Details are provided on the use of polymer products in consumer goods, polymer recycling, polymer densities, the making of a polymer such as GLUEP, polyvinyl alcohol, dissolving plastics, polymers…

  20. Characterization of Therapeutic Coatings on Medical Devices

    NASA Astrophysics Data System (ADS)

    Wormuth, Klaus

    Therapeutic coatings on medical devices such as catheters, guide wires, and stents improve biocompatibility by favorably altering the chemical nature of the device/tissue or device/blood interface. Such coatings often minimize tissue damage (reduce friction), decrease chances for blood clot formation (prevent platelet adsorption), and improve the healing response (deliver drugs). Confocal Raman microscopy provides valuable information about biomedical coatings by, for example, facilitating the measurement of the thickness and swelling of frictionreducing hydrogel coatings on catheters and by determining the distribution of drug within a polymer-based drug-eluting coatings on stents. This chapter explores the application of Raman microscopy to the imaging of thin coatings of cross-linked poly(vinyl pyrrolidone) gels, parylene films, mixtures of dexamethasone with various polymethacrylates, and mixtures of rapamycin with hydrolysable (biodegradable) poly(lactide-co-glycolide) polymers. Raman microscopy measures the thickness and swelling of coatings, reveals the degree of mixing of drug and polymer, senses the hydrolysis of biodegradable polymers, and determines the polymorphic forms of drug present within thin therapeutic coatings on medical devices.

  1. Resistive Switching Memory Phenomena in PEDOT PSS: Coexistence of Switchable Diode Effect and Write Once Read Many Memory

    NASA Astrophysics Data System (ADS)

    Nguyen, Viet Cuong; Lee, Pooi See

    2016-01-01

    We study resistive switching memory phenomena in conducting polymer PEDOT PSS. In the same film, there are two types of memory behavior coexisting; namely, the switchable diode effect and write once read many memory. This is the first report on switchable diode phenomenon based on conducting organic materials. The effect was explained as charge trapping of PEDOT PSS film and movement of proton. The same PEDOT PSS device also exhibits write once read many memory (WORM) phenomenon which arises due to redox reaction that reduces PEDOT PSS and renders it non-conducting. The revelation of these two types of memory phenomena in PEDOT PSS highlights the remarkable versatility of this conducting conjugated polymer.

  2. Resistive Switching Memory Phenomena in PEDOT PSS: Coexistence of Switchable Diode Effect and Write Once Read Many Memory

    PubMed Central

    Nguyen, Viet Cuong; Lee, Pooi See

    2016-01-01

    We study resistive switching memory phenomena in conducting polymer PEDOT PSS. In the same film, there are two types of memory behavior coexisting; namely, the switchable diode effect and write once read many memory. This is the first report on switchable diode phenomenon based on conducting organic materials. The effect was explained as charge trapping of PEDOT PSS film and movement of proton. The same PEDOT PSS device also exhibits write once read many memory (WORM) phenomenon which arises due to redox reaction that reduces PEDOT PSS and renders it non-conducting. The revelation of these two types of memory phenomena in PEDOT PSS highlights the remarkable versatility of this conducting conjugated polymer. PMID:26806868

  3. Targeted delivery of therapeutics to endothelium

    PubMed Central

    Simone, Eric; Ding, Bi-Sen

    2009-01-01

    The endothelium is a target for therapeutic and diagnostic interventions in a plethora of human disease conditions including ischemia, inflammation, edema, oxidative stress, thrombosis and hemorrhage, and metabolic and oncological diseases. Unfortunately, drugs have no affinity to the endothelium, thereby limiting the localization, timing, specificity, safety, and effectiveness of therapeutic interventions. Molecular determinants on the surface of resting and pathologically altered endothelial cells, including cell adhesion molecules, peptidases, and receptors involved in endocytosis, can be used for drug delivery to the endothelial surface and into intracellular compartments. Drug delivery platforms such as protein conjugates, recombinant fusion constructs, targeted liposomes, and stealth polymer carriers have been designed to target drugs and imaging agents to these determinants. We review endothelial target determinants and drug delivery systems, describe parameters that control the binding of drug carriers to the endothelium, and provide examples of the endothelial targeting of therapeutic enzymes designed for the treatment of acute vascular disorders including ischemia, oxidative stress, inflammation, and thrombosis. PMID:18815813

  4. Antimicrobial Polymer

    DOEpatents

    McDonald, William F.; Wright, Stacy C.; Taylor, Andrew C.

    2004-09-28

    A polymeric composition having antimicrobial properties and a process for rendering the surface of a substrate antimicrobial are disclosed. The polymeric composition comprises a crosslinked chemical combination of (i) a polymer having amino group-containing side chains along a backbone forming the polymer, (ii) an antimicrobial agent selected from metals, metal alloys, metal salts, metal complexes and mixtures thereof, and (iii) a crosslinking agent containing functional groups capable of reacting with the amino groups. In one example embodiment, the polymer is a polyamide formed from a maleic anhydride or maleic acid ester monomer and alkylamines thereby producing a polyamide having amino substituted alkyl chains on one side of the polyamide backbone; the crosslinking agent is a phosphine having the general formula (A).sub.3 P wherein A is hydroxyalkyl; and the metallic antimicrobial agent is selected from chelated silver ions, silver metal, chelated copper ions, copper metal, chelated zinc ions, zinc metal and mixtures thereof.

  5. Antimocrobial Polymer

    DOEpatents

    McDonald, William F.; Huang, Zhi-Heng; Wright, Stacy C.

    2005-09-06

    A polymeric composition having antimicrobial properties and a process for rendering the surface of a substrate antimicrobial are disclosed. The composition comprises a crosslinked chemical combination of (i) a polymer having amino group-containing side chains along a backbone forming the polymer, (ii) an antimicrobial agent selected from quaternary ammonium compounds, gentian violet compounds, substituted or unsubstituted phenols, biguanide compounds, iodine compounds, and mixtures thereof, and (iii) a crosslinking agent containing functional groups capable of reacting with the amino groups. In one embodiment, the polymer is a polyamide formed from a maleic anhydride or maleic acid ester monomer and alkylamines thereby producing a polyamide having amino substituted alkyl chains on one side of the polyamide backbone; the crosslinking agent is a phosphine having the general formula (A)3P wherein A is hydroxyalkyl; and the antimicrobial agent is chlorhexidine, dimethylchlorophenol, cetyl pyridinium chloride, gentian violet, triclosan, thymol, iodine, and mixtures thereof.

  6. Turbidity study of polymer-polymer interaction

    NASA Astrophysics Data System (ADS)

    Schwartz, Jacob; Lu, Xihua; Hu, Zhibing

    2000-10-01

    The interaction between hydroxypropyl cellulose (HPC)polymer chains and poly(acrylic acid) (PAA) polymer chains has been studied using turbidity techniques. The lower critical solution temperature of the polymer mixture has been measured as a function of polymer concentration and polymer molecular weight. The phase behavior of the polymer mixture has been discussed in terms of hydrogen bonding between HPC and PAA. Studies in this area may lead to technological advances in controlled drug delivery and bioadhesives.

  7. Memory effects in turbulence

    NASA Technical Reports Server (NTRS)

    Hinze, J. O.

    1979-01-01

    Experimental investigations of the wake flow of a hemisphere and cylinder show that such memory effects can be substantial and have a significant influence on momentum transport. Memory effects are described in terms of suitable memory functions.

  8. Therapeutic suggestion has not effect on postoperative morphine requirements.

    PubMed

    van der Laan, W H; van Leeuwen, B L; Sebel, P S; Winograd, E; Baumann, P; Bonke, B

    1996-01-01

    This study was designed to confirm the effect of therapeutic intraoperative auditory suggestion on recovery from anesthesia, to establish the effect of preoperative suggestion, and to assess implicit memory for intraoperative information using an indirect memory task. Sixty consenting unpremedicated patients scheduled for elective gynecologic surgery were randomly divided into three equal groups: Group 1 received a tape of therapeutic suggestions preoperatively, and the story of Robinson Crusoe intraoperatively; Group 2 heard the story of Peter Pan preoperatively and therapeutic suggestions intraoperatively; Group 3 heard the Crusoe story preoperatively and the Peter Pan story intraoperatively. A standardized anesthetic technique was used with fentanyl, propofol, isoflurane, and nitrous oxide. After surgery, all patients received patient-controlled analgesia (PCA) with a standardized regimen. In the 24 h postsurgery, morphine use was recorded every 6 h and at 24 h an indirect memory test (free association) was used to test for memory of the stories. Anxiety scores were measured before surgery and at 6 and 24 h postsurgery. There were no significant differences between groups for postoperative morphine use, pain or nausea scores, anxiety scores, or days spent in hospital after surgery. Seven of 20 patients who heard the Pan story intraoperative gave a positive association with the word "Hook," whereas 2 of 20 who did not hear the story gave such an association. Indirect memory for the Pan story was established using confidence interval (CI) analysis. (The 95% CI for difference in proportion did not include zero). No indirect memory for the Crusoe story could be demonstrated. This study did not confirm previous work which suggested that positive therapeutic auditory suggestions, played intraoperatively, reduced PCA morphine requirements. In contrast, a positive implicit memory effect was found for a story presented intraoperatively. PMID:8712392

  9. Polymer solutions

    DOEpatents

    Krawczyk, Gerhard Erich (Bremen, DE); Miller, Kevin Michael (West Dundee, IL)

    2011-07-26

    There is provided a method of making a polymer solution comprising polymerizing one or more monomer in a solvent, wherein said monomer comprises one or more ethylenically unsaturated monomer that is a multi-functional Michael donor, and wherein said solvent comprises 40% or more by weight, based on the weight of said solvent, one or more multi-functional Michael donor.

  10. A Beginner's Guide to Memory.

    ERIC Educational Resources Information Center

    Hughes, Elizabeth M.

    1981-01-01

    This article is designed to equip the reader with the information needed to deal with questions of computer memory. Discussed are core memory; semiconductor memory; size of memory; expanding memory; charge-coupled device memories; magnetic bubble memory; and read-only and read-mostly memories. (KC)

  11. Reducing unwanted trauma memories by imaginal exposure or autobiographical memory elaboration: An analogue study of memory processes

    PubMed Central

    Ehlers, Anke; Mauchnik, Jana; Handley, Rachel

    2012-01-01

    Unwanted memories of traumatic events are a core symptom of post-traumatic stress disorder. A range of interventions including imaginal exposure and elaboration of the trauma memory in its autobiographical context are effective in reducing such unwanted memories. This study explored whether priming for stimuli that occur in the context of trauma and evaluative conditioning may play a role in the therapeutic effects of these procedures. Healthy volunteers (N=122) watched analogue traumatic and neutral picture stories. They were then randomly allocated to 20min of either imaginal exposure, autobiographical memory elaboration, or a control condition designed to prevent further processing of the picture stories. A blurred picture identification task showed that neutral objects that preceded traumatic pictures in the stories were subsequently more readily identified than those that had preceded neutral stories, indicating enhanced priming. There was also an evaluative conditioning effect in that participants disliked neutral objects that had preceded traumatic pictures more. Autobiographical memory elaboration reduced the enhanced priming effect. Both interventions reduced the evaluative conditioning effect. Imaginal exposure and autobiographical memory elaboration both reduced the frequency of subsequent unwanted memories of the picture stories. PMID:21227404

  12. Reducing unwanted trauma memories by imaginal exposure or autobiographical memory elaboration: an analogue study of memory processes.

    PubMed

    Ehlers, Anke; Mauchnik, Jana; Handley, Rachel

    2012-12-01

    Unwanted memories of traumatic events are a core symptom of post-traumatic stress disorder. A range of interventions including imaginal exposure and elaboration of the trauma memory in its autobiographical context are effective in reducing such unwanted memories. This study explored whether priming for stimuli that occur in the context of trauma and evaluative conditioning may play a role in the therapeutic effects of these procedures. Healthy volunteers (N = 122) watched analogue traumatic and neutral picture stories. They were then randomly allocated to 20 min of either imaginal exposure, autobiographical memory elaboration, or a control condition designed to prevent further processing of the picture stories. A blurred picture identification task showed that neutral objects that preceded traumatic pictures in the stories were subsequently more readily identified than those that had preceded neutral stories, indicating enhanced priming. There was also an evaluative conditioning effect in that participants disliked neutral objects that had preceded traumatic pictures more. Autobiographical memory elaboration reduced the enhanced priming effect. Both interventions reduced the evaluative conditioning effect. Imaginal exposure and autobiographical memory elaboration both reduced the frequency of subsequent unwanted memories of the picture stories. PMID:21227404

  13. Memory Retrieval and Interference: Working Memory Issues

    ERIC Educational Resources Information Center

    Radvansky, Gabriel A.; Copeland, David E.

    2006-01-01

    Working memory capacity has been suggested as a factor that is involved in long-term memory retrieval, particularly when that retrieval involves a need to overcome some sort of interference (Bunting, Conway, & Heitz, 2004; Cantor & Engle, 1993). Previous work has suggested that working memory is related to the acquisition of information during

  14. Extending the Memory of Microcomputers

    NASA Technical Reports Server (NTRS)

    Wiker, G. A.

    1984-01-01

    Memory increased while retaining real-time capabilities. Extra memory capacity added to microprocessor without increasing memory address length and special transfer instructions by dedicating block of space in main memory to hold addresses of locations in extra memory.

  15. Injectable preformed scaffolds with shape-memory properties

    PubMed Central

    Bencherif, Sidi A.; Sands, R. Warren; Bhatta, Deen; Arany, Praveen; Verbeke, Catia S.; Edwards, David A.; Mooney, David J.

    2012-01-01

    Injectable biomaterials are increasingly being explored to minimize risks and complications associated with surgical implantation. We describe a strategy for delivery via conventional needle–syringe injection of large preformed macroporous scaffolds with well-defined properties. Injectable 3D scaffolds, in the form of elastic sponge-like matrices, were prepared by environmentally friendly cryotropic gelation of a naturally sourced polymer. Cryogels with shape-memory properties may be molded to a variety of shapes and sizes, and may be optionally loaded with therapeutic agents or cells. These scaffolds have the capability to withstand reversible deformations at over 90% strain level, and a rapid volumetric recovery allows the structurally defined scaffolds to be injected through a small-bore needle with nearly complete geometric restoration once delivered. These gels demonstrated long-term release of biomolecules in vivo. Furthermore, cryogels impregnated with bioluminescent reporter cells provided enhanced survival, higher local retention, and extended engraftment of transplanted cells at the injection site compared with a standard injection technique. These injectable scaffolds show great promise for various biomedical applications, including cell therapies. PMID:23150549

  16. Optical memory

    DOEpatents

    Mao, Samuel S; Zhang, Yanfeng

    2013-07-02

    Optical memory comprising: a semiconductor wire, a first electrode, a second electrode, a light source, a means for producing a first voltage at the first electrode, a means for producing a second voltage at the second electrode, and a means for determining the presence of an electrical voltage across the first electrode and the second electrode exceeding a predefined voltage. The first voltage, preferably less than 0 volts, different from said second voltage. The semiconductor wire is optically transparent and has a bandgap less than the energy produced by the light source. The light source is optically connected to the semiconductor wire. The first electrode and the second electrode are electrically insulated from each other and said semiconductor wire.

  17. Shape-Memory PVDF Exhibiting Switchable Piezoelectricity.

    PubMed

    Hoeher, Robin; Raidt, Thomas; Novak, Nikola; Katzenberg, Frank; Tiller, Joerg C

    2015-12-01

    In this study, a material is designed which combines the properties of shape-memory and electroactive polymers. This is achieved by covalent cross-linking of polyvinylidene fluoride. The resulting polymer network exhibits excellent shape-memory properties with a storable strain of 200%, and fixity as well as recovery values of 100%. Programming upon rolling induces the transformation from the nonelectroactive α-phase to the piezoelectric β-phase. The highest β-phase content is found to be 83% for a programming strain of 200% affording a d33 value of -30 pm V(-1) . This is in good accordance with literature known values for piezoelectric properties. Thermal triggering this material does not only result in a shape change but also renders the material nonelectroactive. PMID:26332996

  18. Semi-permeable coatings fabricated from comb-polymers efficiently protect proteins in vivo.

    PubMed

    Liu, Mi; Johansen, Pl; Zabel, Franziska; Leroux, Jean-Christophe; Gauthier, Marc A

    2014-01-01

    In comparison to neutral linear polymers, functional and architecturally complex (that is, non-linear) polymers offer distinct opportunities for enhancing the properties and performance of therapeutic proteins. However, understanding how to harness these parameters is challenging, and studies that capitalize on them in vivo are scarce. Here we present an in vivo demonstration that modification of a protein with a polymer of appropriate architecture can impart low immunogenicity, with a commensurably low loss of therapeutic activity. These combined properties are inaccessible by conventional strategies using linear polymers. For the model protein L-asparaginase, a comb-polymer bio-conjugate significantly outperformed the linear polymer control in terms of lower immune response and more sustained bioactivity. The semi-permeability characteristics of the coatings are consistent with the phase diagram of the polymer, which will facilitate the application of this strategy to other proteins and with other therapeutic models. PMID:25407758

  19. Serotonin and emotion, learning and memory.

    PubMed

    Meneses, Alfredo; Liy-Salmeron, Gustavo

    2012-01-01

    Serotonin (5-hydroxytryptamien, 5-HT) has been linked to emotional and motivational aspects of human behavior, including anxiety, depression, impulsivity, etc. Several clinically effective drugs exert effects via 5-HT systems. Growing evidence suggests that those effects play an important role in learning and memory. Whether the role of serotonin is related to memory and/or behavioral or emotional aspects remains an important question. A key question that remains is whether 5-HT markers (e.g., receptors) directly or indirectly participate and/or contribute to the physiological and pharmacological basis of memory and its pathogenesis. The major aim of this paper is to re-examine some recent advances regarding mammalian 5-HT receptors and transporter in light of their physiological, pathophysiological and therapeutic implications for memory. We particularly address evidence involving 5-HT systems in behavioral, pharmacological, molecular, genetic and imaging results and memory. Finally, this paper aims to summarize a portion of the evidence about serotonin, memory and emotion from animal and human studies and provide an overview of potential tools, markers and cellular and molecular candidate mechanisms. It should be noted that there are several subjects that this paper only briefly touches upon, presenting only what may be the most salient findings in the context of memory, emotion and serotonin. PMID:23104855

  20. Order-memory and association-memory.

    PubMed

    Caplan, Jeremy B

    2015-09-01

    Two highly studied memory functions are memory for associations (items presented in pairs, such as SALT-PEPPER) and memory for order (a list of items whose order matters, such as a telephone number). Order- and association-memory are at the root of many forms of behaviour, from wayfinding, to language, to remembering people's names. Most researchers have investigated memory for order separately from memory for associations. Exceptions to this, associative-chaining models build an ordered list from associations between pairs of items, quite literally understanding association- and order-memory together. Alternatively, positional-coding models have been used to explain order-memory as a completely distinct function from association-memory. Both classes of model have found empirical support and both have faced serious challenges. I argue that models that combine both associative chaining and positional coding are needed. One such hybrid model, which relies on brain-activity rhythms, is promising, but remains to be tested rigourously. I consider two relatively understudied memory behaviours that demand a combination of order- and association-information: memory for the order of items within associations (is it William James or James William?) and judgments of relative order (who left the party earlier, Hermann or William?). Findings from these underexplored procedures are already difficult to reconcile with existing association-memory and order-memory models. Further work with such intermediate experimental paradigms has the potential to provide powerful findings to constrain and guide models into the future, with the aim of explaining a large range of memory functions, encompassing both association- and order-memory. PMID:25894964

  1. Chicanoizing the Therapeutic Community

    ERIC Educational Resources Information Center

    Aron, William S.; And Others

    1974-01-01

    Focusing on the drug addiction problem and its antecedent conditions in a Chicano population, the article examines several therapeutic interventions suggested by these conditions and indicates how they might be incorporated into a drug addiction Therapeutic Community treatment program designed to meet the needs of Chicano drug addicts. (Author/NQ)

  2. Therapeutic Recreation Practicum Manual.

    ERIC Educational Resources Information Center

    Schneegas, Kay

    This manual provides information on the practicum program offered by Moraine Valley Community College (MVCC) for students in its therapeutic recreation program. Sections I and II outline the rationale and goals for providing practical, on-the-job work experiences for therapeutic recreation students. Section III specifies MVCC's responsibilities…

  3. Advanced Polymer

    NASA Technical Reports Server (NTRS)

    1992-01-01

    In the mid-1980's, Langley developed a polyimide sulfone, combining desirable properties of two classes of polymers. Composites and other products made from polyimide sulfone can be used with solvents and corrosive fluids, are light weight, low cost and can be easily fabricated for a wide range of industrial uses. High Technology Systems, Inc. obtained a license for the polymer and was awarded a Small Business Innovation Research (SBIR) contract for development in a powder form. Although its principal use is as a matrix resin for composites, the material can also be used as a high temperature structural adhesive for aircraft structures and as a coating for protection from heat and radiation for electronic components.

  4. Phthalocyanine polymers

    NASA Technical Reports Server (NTRS)

    Achar, B. N.; Fohlen, G. M.; Parker, J. A. (Inventor)

    1985-01-01

    A method of forming 4,4',4'',4''' -tetraamino phthalocyanines involves reducing 4,4',4'',4''' -tetranitro phthalocyanines, polymerizing the metal tetraamino phthalocyanines with a tetracarboxylic dianhydride (preferably aromatic) or copolymerizing with a tetracarboxylic dianhydride and a diamine (preferably also aromatic) to produce amic acids which are then dehydrocyclized to imides. Thermally and oxidatively stable polymers result which form tough, flexible films, varnishes, adhesives, and fibers.

  5. Retraining Memory Strategies.

    ERIC Educational Resources Information Center

    Parente, Rick; Herrmann, Douglas

    1996-01-01

    A variety of memory strategies can be used to retrain an individual's ability to process information in working memory. This article provides step-by-step instructions for various memory encoding strategies. These strategies include training in perceptual grouping of number series, organization, mediation, mental imagery, and associative memory.

  6. Infant Visual Recognition Memory

    ERIC Educational Resources Information Center

    Rose, Susan A.; Feldman, Judith F.; Jankowski, Jeffery J.

    2004-01-01

    Visual recognition memory is a robust form of memory that is evident from early infancy, shows pronounced developmental change, and is influenced by many of the same factors that affect adult memory; it is surprisingly resistant to decay and interference. Infant visual recognition memory shows (a) modest reliability, (b) good discriminant

  7. Periodic Polymers

    NASA Astrophysics Data System (ADS)

    Thomas, Edwin

    2013-03-01

    Periodic polymers can be made by self assembly, directed self assembly and by photolithography. Such materials provide a versatile platform for 1, 2 and 3D periodic nano-micro scale composites with either dielectric or impedance contrast or both, and these can serve for example, as photonic and or phononic crystals for electromagnetic and elastic waves as well as mechanical frames/trusses. Compared to electromagnetic waves, elastic waves are both less complex (longitudinal modes in fluids) and more complex (longitudinal, transverse in-plane and transverse out-of-plane modes in solids). Engineering of the dispersion relation between wave frequency w and wave vector, k enables the opening of band gaps in the density of modes and detailed shaping of w(k). Band gaps can be opened by Bragg scattering, anti-crossing of bands and discrete shape resonances. Current interest is in our group focuses using design - modeling, fabrication and measurement of polymer-based periodic materials for applications as tunable optics and control of phonon flow. Several examples will be described including the design of structures for multispectral band gaps for elastic waves to alter the phonon density of states, the creation of block polymer and bicontinuous metal-carbon nanoframes for structures that are robust against ballistic projectiles and quasi-crystalline solid/fluid structures that can steer shock waves.

  8. Organic electrical bistable devices and applications as electronic digital memory

    NASA Astrophysics Data System (ADS)

    Yang, Yang

    2007-03-01

    Recently, organic electrical bistability has attracted considerable attention due to its potential applications as digital memory devices. In this presentation, we will present our recent study on organic electrical bistability phenomena and the application as nonvolatile memory devices (NVM). The bistability was discovered when a thin layer of metallic nano-particles introduced between two organic layers as the active cell, which interposed between two electrodes. We attribute this bistaility to the charge transfer and trap in the metal nano-particles. A further material engineering by dispersing metal nano-particles and organic electron donor within polymer films as the active cell, it forms the polymer-based memory devices. When the metal nanoparticles are integrated with tobacco mosaic virus as the active cell, it forms a virus-based (or bio-based) memory device. Mechanism studies on the polymer and bio-based memory device reveal that charge-storage in the metal nanoparticles plays an important role in the device operation. Details of the mechanism study and the memory device performance will be discussed in this presentation.

  9. Glutamate-based therapeutic approaches: ampakines.

    PubMed

    Lynch, Gary

    2006-02-01

    Ampakines are a structurally diverse family of small molecules that positively modulate alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors, and thereby enhance fast, excitatory transmission throughout the brain. Surprisingly, ampakines have discrete effects on brain activity and behavior. Because their excitatory synaptic targets mediate communication between cortical regions, serve as sites of memory encoding, and regulate the production of growth factors, ampakines have a broad range of potential therapeutic applications. Several of these possibilities have been tested with positive results in preclinical models; preliminary clinical work has also been encouraging. PMID:16361116

  10. Catching the engram: strategies to examine the memory trace

    PubMed Central

    2012-01-01

    Memories are stored within neuronal ensembles in the brain. Modern genetic techniques can be used to not only visualize specific neuronal ensembles that encode memories (e.g., fear, craving) but also to selectively manipulate those neurons. These techniques are now being expanded for the study of various types of memory. In this review, we will summarize the genetic methods used to visualize and manipulate neurons involved in the representation of memory engrams. The methods will help clarify how memory is encoded, stored and processed in the brain. Furthermore, these approaches may contribute to our understanding of the pathological mechanisms associated with human memory disorders and, ultimately, may aid the development of therapeutic strategies to ameliorate these diseases. PMID:22999350

  11. Systemic administration of riluzole enhances recognition memory andfacilitates extinction of fear memory in rats.

    PubMed

    Sugiyama, Azusa; Saitoh, Akiyoshi; Inagaki, Masatoshi; Oka, Jun-Ichiro; Yamada, Mitsuhiko

    2015-10-01

    Strategies to enhance recognition memory and facilitate extinction of fear memory have attracted increasing attention for enhancing the effectiveness of exposure therapy for anxiety disorders. Previously, we demonstrated that systemic administration of riluzole has clear anxiolytic-like effects, without impairing memory, in rats. In the present study, we examined whether riluzole could have therapeutic potential for anxiety disorders when combined with exposure therapy. Both riluzole and D-cycloserine enhanced recognition memory in the novel object recognition test and facilitated extinction learning in the contextual fear conditioning in rats. Interestingly, the facilitatory effect of riluzole on extinction learning was clearly observed even after a short re-exposure to the context, while D-cycloserine was ineffective at facilitating extinction when a short duration exposure session was given. In contrast, diazepam impaired both recognition memory and the extinction of fear memory. Our findings strongly suggest that systemic administration of riluzole may have therapeutic efficacy when combined with exposure therapy for treating a range of anxiety disorders. Clinical trials to examine the efficacy of riluzole in combination with exposure therapy in these patients are warranted. PMID:26116528

  12. Autobiographical memory dysfunctions in depressive disorders.

    PubMed

    Talarowska, Monika; Berk, Michael; Maes, Michael; Ga?ecki, Piotr

    2016-02-01

    Autobiographical memory (AM) is a ubiquitous human experience that belongs to long-term declarative memory. It plays interpersonal and intrapsychic functions. The main aim of this study is to present results of contemporary research on AM in recurrent depressive disorders. The available research literature suggests that AM dysfunctions are a precursor and risk factor for recurrent depressive disorders and that they also appear to be a consequence of depressive symptoms in a bidirectional and interacting manner. These data suggest that AM might be a viable therapeutic target for cognitive remediation strategies, given the impact of cognition on diverse clinical outcomes. PMID:26522618

  13. Caspases as therapeutic targets

    PubMed Central

    Howley, B; Fearnhead, HO

    2008-01-01

    Abstract The development of small molecules to modulate caspase activity offers a novel therapeutic strategy in the treatment of apoptosis-related and inflammatory diseases. Caspases are key mediators of apoptosis and inflammation; deregulation of their activation or expression can lead to the development of conditions such as neurodegenerative and autoinflammatory disorders. This review details the different caspase-associated disorders while focusing on caspase-1 inhibition as a potential therapeutic strategy. Problems facing the development of effective and safe caspase therapeutics will also be addressed. PMID:18298652

  14. Transient behaviour of a polymer dragged through a viscoelastic medium

    NASA Astrophysics Data System (ADS)

    Vandebroek, Hans; Vanderzande, Carlo

    2014-09-01

    We study the dynamics of a polymer that is pulled by a constant force through a viscoelastic medium. This is a model for a polymer being pulled through a cell by an external force, or for an active biopolymer moving due to a self-generated force. Using the Rouse model with a memory dependent drag force, we find that the center of mass of the polymer follows a subballistic motion. We determine the time evolution of the length and the shape of the polymer. Through an analysis of the velocity of the monomers, we investigate how the tension propagates through the polymer. We discuss how polymers can be used to probe the properties of a viscoelastic medium.

  15. Memory Metals

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Under contract to NASA during preparations for the space station, Memry Technologies Inc. investigated shape memory effect (SME). SME is a characteristic of certain metal alloys that can change shape in response to temperature variations. In the late 1980s and early 1990s, Memry used its NASA-acquired expertise to produce a line of home and industrial safety products, and refined the technology in the mid-1990s. Among the new products they developed are three MemrySafe units which prevent scalding from faucets. Each system contains a small valve that reacts to temperature, not pressure. When the water reaches dangerous temperatures, the unit reduces the flow to a trickle; when the scalding temperature subsides, the unit restores normal flow. Other products are the FIRECHEK 2 and 4, heat-activated shutoff valves for industrial process lines, which sense excessive heat and cut off pneumatic pressure. The newest of these products is Memry's Demand Management Water Heater which shifts the electricity requirement from peak to off-peak demands, conserving energy and money.

  16. Memory loss.

    PubMed

    Flicker, Leon A; Ford, Andrew H; Beer, Christopher D; Almeida, Osvaldo P

    2012-02-01

    Most older people with memory loss do not have dementia. Those with mild cognitive impairment are at increased risk of progressing to dementia, but no tests have been shown to enhance the accuracy of assessing this risk. Although no intervention has been convincingly shown to prevent dementia, data from cohort studies and randomised controlled trials are compelling in indicating that physical activity and treatment of hypertension decrease the risk of dementia. There is no evidence that pharmaceutical treatment will benefit people with mild cognitive impairment. In people with Alzheimer's disease, treatment with a cholinesterase inhibitor or memantine (an N-methyl- D-aspartate receptor antagonist) may provide symptomatic relief and enhance quality of life, but does not appear to alter progression of the illness. Non-pharmacological strategies are recommended as first-line treatments for behavioural and psychological symptoms of dementia, which are common in Alzheimer's disease. Atypical antipsychotics have modest benefit in reducing agitation and psychotic symptoms but increase the risk of cardiovascular events. The role of antidepressants in managing depressive symptoms in patients with mild cognitive impairment is uncertain and may increase the risk of delirium and falls. PMID:22304604

  17. Polymer Electronics: Power from Polymers

    SciTech Connect

    Venkataraman, D.; Russell, Thomas P.

    2012-06-19

    We review polymer-based electronics and photovoltaics to provide the reader with a sense of how the field has developed, where we stand at present, and what possibilities are looming in the future. Expertise in areas ranging from synthesis to morphology to device design was sought to achieve this end. While these reviews cannot be exhaustive, they do provide a snapshot of the field at present and give some sense of where the key impediments are.

  18. Examining Object Location and Object Recognition Memory in Mice

    PubMed Central

    Vogel-Ciernia, Annie; Wood, Marcelo A.

    2014-01-01

    Unit Introduction The ability to store and recall our life experiences defines a person's identity. Consequently, the loss of long-term memory is a particularly devastating part of a variety of cognitive disorders, diseases and injuries. There is a great need to develop therapeutics to treat memory disorders, and thus a variety of animal models and memory paradigms have been developed. Mouse models have been widely used both to study basic disease mechanisms and to evaluate potential drug targets for therapeutic development. The relative ease of genetic manipulation of Mus musculus has led to a wide variety of genetically altered mice that model cognitive disorders ranging from Alzheimer's disease to autism. Rodents, including mice, are particularly adept at encoding and remembering spatial relationships, and these long-term spatial memories are dependent on the medial temporal lobe of the brain. These brain regions are also some of the first and most heavily impacted in disorders of human memory including Alzheimer's disease. Consequently, some of the simplest and most commonly used tests of long-term memory in mice are those that examine memory for objects and spatial relationships. However, many of these tasks, such as Morris water maze and contextual fear conditioning, are dependent upon the encoding and retrieval of emotionally aversive and inherently stressful training events. While these types of memories are important, they do not reflect the typical day-to-day experiences or memories most commonly affected in human disease. In addition, stress hormone release alone can modulate memory and thus obscure or artificially enhance these types of tasks. To avoid these sorts of confounds, we and many others have utilized tasks testing animals memory for object location and novel object recognition. These tasks involve exploiting rodents innate preference for novelty, and are inherently not stressful. In this protocol we detail how memory for object location and object identity can be used to evaluate a wide variety of mouse models and treatments. PMID:25297693

  19. Nitric Oxide Release Part II. Therapeutic Applications

    PubMed Central

    Carpenter, Alexis W.; Schoenfisch, Mark H.

    2012-01-01

    Summary A wide range of nitric oxide (NO)-releasing materials have emerged as potential therapeutics that exploit NOs vast biological roles. Macromolecular NO-releasing scaffolds are particularly promising due to their ability to store and deliver larger NO payloads in a more controlled and effective manner compared to low molecular weight NO donors. While a variety of scaffolds (e.g., particles, dendrimers, and polymers/films) have been cleverly designed, the ultimate clinical utility of most NO-releasing macromolecules remains unrealized. Although not wholly predictive of clinical success, in vitro and in vivo investigations have enabled a preliminary evaluation of the therapeutic potential of such materials. Herein, we review the application of macromolecular NO therapies for cardiovascular disease, cancer, bacterial infections, and wound healing. PMID:22362384

  20. Therapeutic Drug Monitoring

    MedlinePLUS

    Proceeds from website advertising help sustain Lab Tests Online. AACC is a not-for-profit organization and does not endorse non-AACC products and services. Advertising & ... Therapeutic Drug Monitoring Share this page: Was this page ...

  1. Therapeutic Endoscopic Ultrasound

    PubMed Central

    Abu Dayyeh, Barham K.

    2012-01-01

    Endoscopic ultrasound (EUS) is a viable and often preferred alternative to interventional and radiologic procedures, and the therapeutic applications of EUS continue to evolve. This evolution was catalyzed by the introduction of linear echoendoscopes that provide continuous imaging and observation of needles and by therapeutic devices that pass through large-caliber working channels. In this paper, we will discuss the spectrum of EUS-guided interventions that are currently available and in development. PMID:23293554

  2. Applications of polymers in dentifrices and mouthrinses.

    PubMed

    Gaffar, Abdul; Hunter, Catherine M; Mirajkar, Yelloji-Rao K

    2002-01-01

    This review highlights the specific applications of polymers in oral hygiene products. Specific examples are provided to show how polymers can be used to improve retention and release of active agents for therapeutic effects in an oral environment where the residence time of the actives is low, owing to the continuous flow of saliva which washes them away. Polymers are uniquely suited as active therapy for intraoral applications and as replacement agents for augmenting the macromolecule's deficiency (saliva) caused in the aging mouth. It is expected that the next generation of products and delivery systems will be based on polymers derived from natural sources and will have functions such as enamel replacement agents for caries control, adhesion macromolecules for gingival tissue attachment to teeth, saliva mucin replacement, and the delivery of new active agents using biopolymers. PMID:12116724

  3. Nanoimprint lithography for functional polymer patterning

    NASA Astrophysics Data System (ADS)

    Cui, Dehu

    2011-07-01

    Organic semiconductors have generated huge interested in recent years for low-cost and flexible electronics. Current and future device applications for semiconducting polymers include light-emitting diodes, thin-film transistors, photovoltaic cells, photodetectors, lasers, and memories. The performance of conjugated polymer devices depends on two major factors: the chain conformation in polymer film and the device architecture. Highly ordered chain structure usually leads to much improved performance by enhancing interchain interaction to facilitate carrier transport. The goal of this research is to improve the performance of organic devices with the nanoimprint lithography. The work begins with the controlling of polymer chain orientation in patterned nanostructures through nanoimprint mold design and process parameter manipulation, and studying the effect of chain ordering on material properties. Then, step-and-repeat thermal nanoimprint technique for large-scale continuous manufacturing of conjugated polymer nanostructures is developed. After that, Systematic investigation of polymer chain configuration by Raman spectroscopy is carried out to understand how nanoimprint process parameters, such as mold pattern size, temperature, and polymer molecular weight, affects polymer chain configuration. The results indicate that chain orientation in nanoimprinted polymer micro- and nanostructures is highly related to the nanoimprint temperature and the dimensions of the mold structures. The ability to create nanoscale polymer micro- and nanostructures and manipulate their internal chain conformation establishes an original experimental platform that enables studying the properties of functional polymers at the micro- and nanoscale and understanding their fundamental structure-property relationships. In addition to the impact on basic research, the techniques developed in this work are important in applied research and development. Large-area conjugated polymer micro- and nanostructures can be easily fabricated by thermal step-and-repeat nanoimprint for organic flat-panel displays, organic circuits and organic solar panels. The ability to manipulate chain orientation through nanoimprint presents a new route to fine-tune the electrical and photophysical properties of conjugated polymers, which can lead to improved performance for all organic electronics. The techniques developed here also allow for easy incorporation of other micro- and nanoscale soft functional polymers in miniaturized devices and systems for new applications in electronics, photonics, sensors and bioengineering.

  4. Cell microencapsulation with synthetic polymers.

    PubMed

    Olabisi, Ronke M

    2015-02-01

    The encapsulation of cells into polymeric microspheres or microcapsules has permitted the transplantation of cells into human and animal subjects without the need for immunosuppressants. Cell-based therapies use donor cells to provide sustained release of a therapeutic product, such as insulin, and have shown promise in treating a variety of diseases. Immunoisolation of these cells via microencapsulation is a hotly investigated field, and the preferred material of choice has been alginate, a natural polymer derived from seaweed due to its gelling conditions. Although many natural polymers tend to gel in conditions favorable to mammalian cell encapsulation, there remain challenges such as batch to batch variability and residual components from the original source that can lead to an immune response when implanted into a recipient. Synthetic materials have the potential to avoid these issues; however, historically they have required harsh polymerization conditions that are not favorable to mammalian cells. As research into microencapsulation grows, more investigators are exploring methods to microencapsulate cells into synthetic polymers. This review describes a variety of synthetic polymers used to microencapsulate cells. PMID:24771675

  5. Cell microencapsulation with synthetic polymers

    PubMed Central

    Olabisi, Ronke M

    2015-01-01

    The encapsulation of cells into polymeric microspheres or microcapsules has permitted the transplantation of cells into human and animal subjects without the need for immunosuppressants. Cell-based therapies use donor cells to provide sustained release of a therapeutic product, such as insulin, and have shown promise in treating a variety of diseases. Immunoisolation of these cells via microencapsulation is a hotly investigated field, and the preferred material of choice has been alginate, a natural polymer derived from seaweed due to its gelling conditions. Although many natural polymers tend to gel in conditions favorable to mammalian cell encapsulation, there remain challenges such as batch to batch variability and residual components from the original source that can lead to an immune response when implanted into a recipient. Synthetic materials have the potential to avoid these issues; however, historically they have required harsh polymerization conditions that are not favorable to mammalian cells. As research into microencapsulation grows, more investigators are exploring methods to microencapsulate cells into synthetic polymers. This review describes a variety of synthetic polymers used to microencapsulate cells. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 846–859, 2015. PMID:24771675

  6. Memory beyond expression.

    PubMed

    Delorenzi, A; Maza, F J; Surez, L D; Barreiro, K; Molina, V A; Stehberg, J

    2014-01-01

    The idea that memories are not invariable after the consolidation process has led to new perspectives about several mnemonic processes. In this framework, we review our studies on the modulation of memory expression during reconsolidation. We propose that during both memory consolidation and reconsolidation, neuromodulators can determine the probability of the memory trace to guide behavior, i.e. they can either increase or decrease its behavioral expressibility without affecting the potential of persistent memories to be activated and become labile. Our hypothesis is based on the findings that positive modulation of memory expression during reconsolidation occurs even if memories are behaviorally unexpressed. This review discusses the original approach taken in the studies of the crab Neohelice (Chasmagnathus) granulata, which was then successfully applied to test the hypothesis in rodent fear memory. Data presented offers a new way of thinking about both weak trainings and experimental amnesia: memory retrieval can be dissociated from memory expression. Furthermore, the strategy presented here allowed us to show in human declarative memory that the periods in which long-term memory can be activated and become labile during reconsolidation exceeds the periods in which that memory is expressed, providing direct evidence that conscious access to memory is not needed for reconsolidation. Specific controls based on the constraints of reminders to trigger reconsolidation allow us to distinguish between obliterated and unexpressed but activated long-term memories after amnesic treatments, weak trainings and forgetting. In the hypothesis discussed, memory expressibility--the outcome of experience-dependent changes in the potential to behave--is considered as a flexible and modulable attribute of long-term memories. Expression seems to be just one of the possible fates of re-activated memories. PMID:25102126

  7. Amphetamine Increases Errors During Episodic Memory Retrieval

    PubMed Central

    Ballard, Michael Edward; Gallo, David A.; de Wit, Harriet

    2014-01-01

    Moderate doses of stimulant drugs are known to enhance memory encoding and consolidation, but their effects on memory retrieval have not been explored in depth. In laboratory animals, stimulants seem to improve retrieval of emotional memories, but comparable studies have not been carried out in humans. In the present study, we examined the effects of dextroamphetamine (AMP) on retrieval of emotional and unemotional stimuli in healthy young adults, using doses that enhanced memory formation when administered before encoding in our previous study. During 3 sessions, healthy volunteers (n = 31) received 2 doses of AMP (10 and 20 mg) and placebo in counter-balanced order under double-blind conditions. During each session, they first viewed emotional and unemotional pictures and words in a drug-free state, and then 2 days later their memory was tested, 1 hour after AMP or placebo administration. Dextroamphetamine did not affect the number of emotional or unemotional stimuli remembered, but both doses increased recall intrusions and false recognition. Dextroamphetamine (20 mg) also increased the number of positively rated picture descriptions and words generated during free recall. These data provide the first evidence that therapeutic range doses of stimulant drugs can increase memory retrieval errors. The ability of AMP to positively bias recollection of prior events could contribute to its potential for abuse. PMID:24135845

  8. Interpretations of Polymer-Polymer Miscibility.

    ERIC Educational Resources Information Center

    Olabisi, Olagoke

    1981-01-01

    Discusses various aspects of polymeric mixtures, mixtures of structurally different homopolymers, copolymers, terpolymers, and the like. Defines concepts of polymer-polymer miscibility from practical and theoretical viewpoints, and ways of predicting such miscibility. (JN)

  9. Shape memory rubber bands & supramolecular ionic copolymers

    NASA Astrophysics Data System (ADS)

    Brostowitz, Nicole

    The primary focus of this dissertation is to understand the thermo-mechanical properties that govern shape memory in rubber blends. An ideal shape memory polymer (SMP) has a large entropic component that drives shape recovery with a distinct transition mechanism to control the recovery conditions. Polyisoprene rubber is highly elastic and shows shape memory behavior through strain induced crystallization above its glass transition temperature. However, this transition temperature is below 0°C and not suitable for most applications. Shape memory blends can tailor the transition temperature through selection of the switching phase. Most SMP blends require complicated synthesis routes or intensive compounding which would be inhibitive for production. A facile method was developed for fabrication of a robust shape memory polymer by swelling cross-linked natural rubber with stearic acid. Thermal, microscopic studies showed that stearic acid formed a percolated network of crystalline platelets within the natural rubber. Further investigation of the material interactions was carried out with a low molecular weight polyisoprene analog, squalene, and stearic acid gel. Tensile tests on the rubber band demonstrated the thermo-mechanical effect of swelling with stearic acid. Low hysteresis was observed under cyclic loading which indicated viability for the stearic acid swollen rubber band as an SMP. The microscopic crystals and the cross-linked rubber produce a temporary network and a permanent network, respectively. These two networks allow thermal shape memory cycling with deformation and recovery above the melting point of stearic acidand fixation below that point. Under manual, strain-controlled tensile deformation, the shape memory rubber bands exhibited fixity and recovery of 100% +/- 10%. The recovery properties of the SMP were studied under various loading conditions and a model was fit to describe the potential recovery with relation to the fixation. An additional subject covered in this dissertation is supra-molecular ionic copolymers. Supramolecular interactions are non-covalent; e.g. hydrogen bonding, ionic interactions, van der Waals forces. Supramolecular interactions in polymers can be used to tailor the thermo-mechanical properties by controlling bond association and dissociation. Recent research has focused on hydrogen bonded systems due to established synthesis mechanisms. Reversibility of the supramolecular interactions can be triggered by environmental changes. Ionic interactions would provide greater bond strength and more control over operating conditions. Research has been limited on ionic copolymers due to complicated synthesis methods needed to include functionalization. Low molecular weight polymers were synthesized by atom transfer radical polymerization with post polymerization conversion to phosphonium end-groups. Both polystyrene and poly(methyl acrylate) were investigated with similar reaction conditions. Chromatography measured the molecular weight and indicated a low polydispersity consistent with controlled reactions. Copolymers were formed by interfacial mixing of the cationic polymers with multifunctional, anionic oligomers. Oligomers containing sulfonate groups were used to create linear or three-dimensional polymer networks. NMR and rheology was used to characterize the presence and effect of ionic groups when compared to the neat polymer.

  10. Materials for Diabetes Therapeutics

    PubMed Central

    Bratlie, Kaitlin M.; York, Roger L.; Invernale, Michael A.; Langer, Robert

    2013-01-01

    This review is focused on the materials and methods used to fabricate closed-loop systems for type 1 diabetes therapy. Herein, we give a brief overview of current methods used for patient care and discuss two types of possible treatments and the materials used for these therapies–(i) artificial pancreases, comprised of insulin producing cells embedded in a polymeric biomaterial, and (ii) totally synthetic pancreases formulated by integrating continuous glucose monitors with controlled insulin release through degradable polymers and glucose-responsive polymer systems. Both the artificial and the completely synthetic pancreas have two major design requirements: the device must be both biocompatible and be permeable to small molecules and proteins, such as insulin. Several polymers and fabrication methods of artificial pancreases are discussed: microencapsulation, conformal coatings, and planar sheets. We also review the two components of a completely synthetic pancreas. Several types of glucose sensing systems (including materials used for electrochemical, optical, and chemical sensing platforms) are discussed, in addition to various polymer-based release systems (including ethylene-vinyl acetate, polyanhydrides, and phenylboronic acid containing hydrogels). PMID:23184741

  11. Solid Tumor-Targeting Theranostic Polymer Nanoparticle in Nuclear Medicinal Fields

    PubMed Central

    Makino, Akira; Kimura, Shunsaku

    2014-01-01

    Polymer nanoparticles can be prepared by self-assembling of amphiphilic polymers, and various types of molecular assemblies have been reported. In particular, in medicinal fields, utilization of these polymer nanoparticles as carriers for drug delivery system (DDS) has been actively tried, and some nanoparticulate drugs are currently under preclinical evaluations. A radionuclide is an unstable nucleus and decays with emission of radioactive rays, which can be utilized as a tracer in the diagnostic imaging systems of PET and SPECT and also in therapeutic purposes. Since polymer nanoparticles can encapsulate most of diagnostic and therapeutic agents with a proper design of amphiphilic polymers, they should be effective DDS carriers of radionuclides in the nuclear medicinal field. Indeed, nanoparticles have been recently attracting much attention as common platform carriers for diagnostic and therapeutic drugs and contribute to the development of nanotheranostics. In this paper, recent developments of solid tumor-targeting polymer nanoparticles in nuclear medicinal fields are reviewed. PMID:25379530

  12. The "memory kinases": roles of PKC isoforms in signal processing and memory formation.

    PubMed

    Sun, Miao-Kun; Alkon, Daniel L

    2014-01-01

    The protein kinase C (PKC) isoforms, which play an essential role in transmembrane signal conduction, can be viewed as a family of "memory kinases." Evidence is emerging that they are critically involved in memory acquisition and maintenance, in addition to their involvement in other functions of cells. Deficits in PKC signal cascades in neurons are one of the earliest abnormalities in the brains of patients suffering from Alzheimer's disease. Their dysfunction is also involved in several other types of memory impairments, including those related to emotion, mental retardation, brain injury, and vascular dementia/ischemic stroke. Inhibition of PKC activity leads to a reduced capacity of many types of learning and memory, but may have therapeutic values in treating substance abuse or aversive memories. PKC activators, on the other hand, have been shown to possess memory-enhancing and antidementia actions. PKC pharmacology may, therefore, represent an attractive area for developing effective cognitive drugs for the treatment of many types of memory disorders and dementias. PMID:24484697

  13. Engineered therapeutic-releasing nanoporous anodic alumina-aluminum wires with extended release of therapeutics.

    PubMed

    Law, Cheryl Suwen; Santos, Abel; Kumeria, Tushar; Losic, Dusan

    2015-02-18

    In this study, we present a nanoengineered therapeutic-releasing system based on aluminum wires featuring nanoporous anodic alumina layers and chitosan coatings. Nanoporous anodic alumina layers are produced on the surface of aluminum wires by electrochemical anodization. These nanoporous layers with precisely engineered nanopore geometry are used as nanocontainers for bovine serum albumin molecules labeled with fluorescein isothiocyanate (BSA-FITC), which is selected as a model drug. The surface of these therapeutic-releasing implants is coated with a biocompatible and biodegradable polymer, chitosan, in order to achieve a sustained release of protein over extended periods of time. The performance of this therapeutic-releasing device is systematically assessed through a series of experiments under static and dynamic flow conditions. In these experiments, the effect of such parameters as the number of layers of chitosan coating and the temperature and pH of the eluting medium is established. The obtained results reveal that the proposed therapeutic-releasing system based on nanoporous aluminum wires can be engineered with sustained release performance for up to 6.5 weeks, which is a critical factor for medical treatments using sensitive therapeutics such as proteins and genes when a localized delivery is desired. PMID:25625878

  14. Polymers with integrated sensing capabilities

    NASA Astrophysics Data System (ADS)

    Kunzelman, Jill Nicole

    This dissertation is focused on the creation and characterization of new types of chromogenic polymers, which change their absorption and/or fluorescence characteristics in response to an external stimulus. These optical sensor materials rely on chromophores that display pronounced color changes upon self-assembly as a result of charge-transfer interactions and/or conformational changes. When these chromophores are incorporated into a polymer of interest, the relative amounts of dispersed and aggregated molecules (and therefore their optical appearance) can be initially tuned by controlling the extent of aggregation via the materials composition and the processing protocol employed; the phase-behavior is changed in a predefined manner upon exposure to a specific stimulus. This sensing scheme was exploited in a number of different polymer matrices, leading to a variety of sensor types including mechanochromic, thermochromic, moisture-sensing, and shape-memory materials that allow visualization of the set/release temperature. Important design fundamentals of "aggregachromic" sensor dyes are discussed and chemical structure is related to type of interactions (hydrophobic, pi-pi, charge-transfer) and self-assembly/color relationships. The knowledge is used to control behavior such as piezochromism, aggregation rate, and intramolecular-excimer-formation.

  15. Long-Term Delivery of Protein Therapeutics

    PubMed Central

    Vaishya, Ravi; Khurana, Varun; Patel, Sulabh; Mitra, Ashim K

    2015-01-01

    Introduction Proteins are effective biotherapetics with applications in diverse ailments. Despite being specific and potent, their full clinical potential has not yet been realized. This can be attributed to short half-lives, complex structures, poor in vivo stability, low permeability frequent parenteral administrations and poor adherence to treatment in chronic diseases. A sustained release system, providing controlled release of proteins, may overcome many of these limitations. Areas covered This review focuses on recent development in approaches, especially polymer-based formulations, which can provide therapeutic levels of proteins over extended periods. Advances in particulate, gel based formulations and novel approaches for extended protein delivery are discussed. Emphasis is placed on dosage form, method of preparation, mechanism of release and stability of biotherapeutics. Expert opinion Substantial advancements have been made in the field of extended protein delivery via various polymer-based formulations over last decade despite the unique delivery-related challenges posed by protein biologics. A number of injectable sustained-release formulations have reached market. However, therapeutic application of proteins is still hampered by delivery related issues. A large number of protein molecules are under clinical trials and hence there is an urgent need to develop new methods to deliver these highly potent biologics. PMID:25251334

  16. Understanding Memory Loss

    MedlinePLUS

    ... memory problems—causes and treatments Help for serious memory problems What you need to know Where can I get more information? Words to know ... of Health U.S. Department of Health & Human Services USA.gov

  17. Memory and Aging

    MedlinePLUS

    Memory and Aging Losing keys, misplacing a wallet, or forgetting someone’s name are common experiences. But for people nearing or over age 65, such memory lapses can be frightening. They wonder if they ...

  18. [Memory and cognitivism].

    PubMed

    Spinetto, M

    2001-12-01

    The goal of this article is to explore the notion of cognitive memory. For that reason we would study the implicit and explicit memory. We would also study the notion of childhood amnesia and trauma. PMID:11780154

  19. Emotional Memory Persists Longer than Event Memory

    ERIC Educational Resources Information Center

    Kuriyama, Kenichi; Soshi, Takahiro; Fujii, Takeshi; Kim, Yoshiharu

    2010-01-01

    The interaction between amygdala-driven and hippocampus-driven activities is expected to explain why emotion enhances episodic memory recognition. However, overwhelming behavioral evidence regarding the emotion-induced enhancement of immediate and delayed episodic memory recognition has not been obtained in humans. We found that the recognition

  20. Emotional Memory Persists Longer than Event Memory

    ERIC Educational Resources Information Center

    Kuriyama, Kenichi; Soshi, Takahiro; Fujii, Takeshi; Kim, Yoshiharu

    2010-01-01

    The interaction between amygdala-driven and hippocampus-driven activities is expected to explain why emotion enhances episodic memory recognition. However, overwhelming behavioral evidence regarding the emotion-induced enhancement of immediate and delayed episodic memory recognition has not been obtained in humans. We found that the recognition…

  1. Optical memory: Phase-change memory

    NASA Astrophysics Data System (ADS)

    Kuramochi, Eiichi; Notomi, Masaya

    2015-11-01

    Integrated nano-optical memories may help overcome the limitations of communication speeds and energy costs in electronic chips. Now, using nanoscale phase-change materials researchers have realized the first multi-bit all-optical non-volatile memories with a very small footprint.

  2. Unique Properties of Reversibly Associating Polymer Networks

    NASA Astrophysics Data System (ADS)

    Anthamatten, Mitchell

    2008-03-01

    Reversibly associating functional groups offer the polymer physicist with a new tool to develop stimuli-responsive polymers. Our focus has been to attach reversibly associating groups onto rubbery network polymers. Free radical copolymerization was used to synthesize a series of crosslinked poly(n-butylacrylate)s containing quadruple H-bonding ureidopyrimidinone (UPy) side-groups. Resulting elastomeric networks contain both covalent and dynamic non-covalent crosslinks, and this unique architecture is shown to affect viscoelastic behavior and mass-transport properties. Shape-memory effects are studied quantitatively using thermomechanical techniques. Experiments show how reversible interactions, such as hydrogen bonding, are capable of stabilizing mechanically strained states. Unlike conventional shape-memory polymers, these dynamic networks lack a well-defined shape recovery temperature. Instead, their shape recovery rate depends on temperature. To further study the dynamics and temperature dependence of mechanical relaxation, isothermal creep experiments and dynamic mechanical analysis were performed. Creep data, acquired at several different temperatures, are fit to a simple viscoelastic model. Fit viscosities exhibit Arrhenius-like temperature dependence with activation energies of 90 kJ/mol, which is in rough agreement with H-bond dissociation barriers. Molecular transport through dynamic networks is studied using gravimetric sorption and dye-diffusion techniques. Diffusion depends on temperature, network architecture, solute size, and the interaction between the solute and the network. Membranes with high temperature-sensitive diffusion properties may be useful in applications such as transdermal drug delivery, microfluidics, or liquid chemical separation processes.

  3. Polymer Spheulites

    NASA Astrophysics Data System (ADS)

    Lotz, Bernard

    2013-03-01

    The growth and/or structural features that determine lamellar shape in polymer spherulites and therefore their structure and properties have been debated for many years. The spectacular twisting of lamellae in optically banded spherulites has been explained by the existence of unbalanced stresses in opposite fold surfaces of the lamellae. This mechanical origin implying the folds explains also the demonstrated absence of correlation between lamellar twist sense and molecular chirality of chiral polymers. Unbalanced surface stresses may also generate spherulites made of scrolled lamellae, with the scroll axis radial. This original morphology was first observed in spherulites of poly(vinylidene fluoride) in its γ phase. It arises from a chemical disparity of folds formed on opposite fold surfaces, the volumes of which differ by 10Å*3. Similar chemical disparities have been suggested to explain the formation of highly unusual scrolled single crystals of polyamide 66 obtained from solution under specific annealing and crystallization conditions. Related thermal histories lead to the formation, in the bulk, of unusual optically negative spherulites of polyamide 66 that were first observed in the 1940s. These still poorly understood negative spherulites may well display a similar scrolled lamellar morphology. The analysis of unbalanced surface stresses requires to evaluate the interplay and mutual impact of crystal and fold structures. The stresses associated with different fold structures are locally small perturbations but are cumulative and are exerted on thin, flexible lamellae. The latter non-planar morphologies reveal these stresses and help reach sub-moleculr insights on the fold structures.

  4. [Therapeutic endoscopy in pediatrics].

    PubMed

    Méndez-Nieto, Carlos; Ramírez-Mayans, Jaime; Montijo-Barrios, Erica; Cervantes-Bustamante, Roberto; Zárate-Mondragón, Flora

    2005-07-01

    Gastrointestinal endoscopy is a procedure that appeared at the end of the seventies and beginning of the eighties in adult patients. With time, however, the instruments have become more sophisticated and have been adapted for use in children; with this the procedure has become at present not only an important diagnostic arm but also an indispensable therapeutic procedure in much pediatric pathology. The purpose of this article is to show any physician who treats children the main therapeutic advantages and indications of this procedure. PMID:17469419

  5. Therapeutics for cognitive aging

    PubMed Central

    Shineman, Diana W.; Salthouse, Timothy A.; Launer, Lenore J.; Hof, Patrick R.; Bartzokis, George; Kleiman, Robin; Luine, Victoria; Buccafusco, Jerry J.; Small, Gary W.; Aisen, Paul S.; Lowe, David A.; Fillit, Howard M.

    2011-01-01

    This review summarizes the scientific talks presented at the conference Therapeutics for Cognitive Aging, hosted by the New York Academy of Sciences and the Alzheimers Drug Discovery Foundation on May 15, 2009. Attended by scientists from industry and academia, as well as by a number of lay peopleapproximately 200 in allthe conference specifically tackled the many aspects of developing therapeutic interventions for cognitive impairment. Discussion also focused on how to define cognitive aging and whether it should be considered a treatable, tractable disease. PMID:20392284

  6. DELIVERY OF THERAPEUTIC PROTEINS

    PubMed Central

    Pisal, Dipak S.; Kosloski, Matthew P.; Balu-Iyer, Sathy V.

    2009-01-01

    The safety and efficacy of protein therapeutics are limited by three interrelated pharmaceutical issues, in vitro and in vivo instability, immunogenicity and shorter half-lives. Novel drug modifications for overcoming these issues are under investigation and include covalent attachment of poly(ethylene glycol) (PEG), polysialic acid, or glycolic acid, as well as developing new formulations containing nanoparticulate or colloidal systems (e.g. liposomes, polymeric microspheres, polymeric nanoparticles). Such strategies have the potential to develop as next generation protein therapeutics. This review includes a general discussion on these delivery approaches. PMID:20049941

  7. From Commodity Polymers to Functional Polymers

    PubMed Central

    Xiang, Tao; Wang, Ling-Ren; Ma, Lang; Han, Zhi-Yuan; Wang, Rui; Cheng, Chong; Xia, Yi; Qin, Hui; Zhao, Chang-Sheng

    2014-01-01

    Functional polymers bear specified chemical groups, and have specified physical, chemical, biological, pharmacological, or other uses. To adjust the properties while keeping material usage low, a method for direct synthesis of functional polymers is indispensable. Here we show that various functional polymers can be synthesized by in situ cross-linked polymerization/copolymerization. We demonstrate that the polymers synthesized by the facile method using different functional monomers own outstanding pH-sensitivity and pH-reversibility, antifouling property, antibacterial, and anticoagulant property. Our study opens a route for the functionalization of commodity polymers, which lead to important advances in polymeric materials applications. PMID:24710333

  8. From Commodity Polymers to Functional Polymers

    NASA Astrophysics Data System (ADS)

    Xiang, Tao; Wang, Ling-Ren; Ma, Lang; Han, Zhi-Yuan; Wang, Rui; Cheng, Chong; Xia, Yi; Qin, Hui; Zhao, Chang-Sheng

    2014-04-01

    Functional polymers bear specified chemical groups, and have specified physical, chemical, biological, pharmacological, or other uses. To adjust the properties while keeping material usage low, a method for direct synthesis of functional polymers is indispensable. Here we show that various functional polymers can be synthesized by in situ cross-linked polymerization/copolymerization. We demonstrate that the polymers synthesized by the facile method using different functional monomers own outstanding pH-sensitivity and pH-reversibility, antifouling property, antibacterial, and anticoagulant property. Our study opens a route for the functionalization of commodity polymers, which lead to important advances in polymeric materials applications.

  9. The role of NPY in learning and memory.

    PubMed

    Gtzsche, C R; Woldbye, D P D

    2016-02-01

    High levels of NPY expression in brain regions important for learning and memory together with its neuromodulatory and neurotrophic effects suggest a regulatory role for NPY in memory processes. Therefore it is not surprising that an increasing number of studies have provided evidence for NPY acting as a modulator of neuroplasticity, neurotransmission, and memory. Here these results are presented in relation to the types of memory affected by NPY and its receptors. NPY can exert both inhibitory and stimulatory effects on memory, depending on memory type and phase, dose applied, brain region, and NPY receptor subtypes. Thus NPY act as a resilience factor by impairing associative implicit memory after stressful and aversive events, as evident in models of fear conditioning, presumably via Y1 receptors in the amygdala and prefrontal cortex. In addition, NPY impairs acquisition but enhances consolidation and retention in models depending on spatial and discriminative types of associative explicit memory, presumably involving Y2 receptor-mediated regulations of hippocampal excitatory transmission. Moreover, spatial memory training leads to increased hippocampal NPY gene expression that together with Y1 receptor-mediated neurogenesis could constitute necessary steps in consolidation and long-term retention of spatial memory. Altogether, NPY-induced effects on learning and memory seem to be biphasic, anatomically and temporally differential, and in support of a modulatory role of NPY at keeping the system in balance. Obtaining further insight into memory-related effects of NPY could inspire the engineering of new therapeutics targeting diseases where impaired learning and memory are central elements. PMID:26454711

  10. The quintuple-shape memory effect in electrospun nanofiber membranes

    NASA Astrophysics Data System (ADS)

    Zhang, Fenghua; Zhang, Zhichun; Liu, Yanju; Lu, Haibao; Leng, Jinsong

    2013-08-01

    Shape memory fibrous membranes (SMFMs) are an emerging class of active polymers, which are capable of switching from a temporary shape to their permanent shape upon appropriate stimulation. Quintuple-shape memory membranes based on the thermoplastic polymer Nafion, with a stable fibrous structure, are achieved via electrospinning technology, and possess a broad transition temperature. The recovery of multiple temporary shapes of electrospun membranes can be triggered by heat in a single triple-, quadruple-, quintuple-shape memory cycle, respectively. The fiber morphology and nanometer size provide unprecedented design flexibility for the adjustable morphing effect. SMFMs enable complex deformations at need, having a wide potential application field including smart textiles, artificial intelligence robots, bio-medical engineering, aerospace technologies, etc in the future.

  11. Associative Memory Acceptors.

    ERIC Educational Resources Information Center

    Card, Roger

    The properties of an associative memory are examined in this paper from the viewpoint of automata theory. A device called an associative memory acceptor is studied under real-time operation. The family "L" of languages accepted by real-time associative memory acceptors is shown to properly contain the family of languages accepted by one-tape,

  12. Memories (Children's Books).

    ERIC Educational Resources Information Center

    McKinley, Carol; Peters, Donna; Semer, Susie; White, W. Quinn; Scharer, Patricia L.

    1998-01-01

    Presents brief annotations of 46 children's books that explore memories of childhood, memories of love, keepsakes that capture those memories, memorable tales from long ago, memorable journeys, times that are painful to remember, and heroes and heroines who have provided hope and change in a troubled world. (SR)

  13. Origins of Autobiographical Memory.

    ERIC Educational Resources Information Center

    Harley, Keryn; Reese, Elaine

    1999-01-01

    Tested predictions of infantile amnesia theory compared with social-interactionist account of autobiographical memory. Found maternal reminiscing style and self-recognition when child was 19 months old uniquely predicted children's shared memory reports across time, even with children's initial language and nonverbal memory factored out.

  14. Poly(ortho ester) biodegradable polymer systems.

    PubMed

    Heller, J; Himmelstein, K J

    1985-01-01

    1 approach to developing bioerodible drug delivery systems is to prepare hydrolytically labile polymers into which a drug can be physically dispersed under relatively mild conditions and in which release of the drug is controlled by the hydrolytic erosion of the matrix. Focus is on devices in which the hydrolytic erosion process is confined to the surface of a solid device. In such devices, and for a constant rate of polymer hydrolysis, rate of drug release is directly proportional to drug loading, and lifetime of the device is directly proportional to the physical dimensions of the device. Due to the fact that the rate of drug release is directly proportional to the total surface area of the device, as the physical dimensions of the device decrease because of the erosion process, the rate of drug release also will decrease. There are 2 possible approaches to the achievement of controlled surface erosion: the interior of the matrix is stabilized so that only the outer layers can erode; and development of a highly hydrophobic polymer that contains linkages in the polymer backbone whose rates of hydrolysis are pH dependent and to incorporate into the polymer excipients that, in contact with water, produce a pH that induces the desired polymer hydrolysis rate. 1 such polymer system is the poly(ortho esters). This chapter describes some work done on polymer synthesis and the use of various excipients to achieve controlled drug release of various therapeutic agents physically dispersed in these polymers. It contains a review of drug release studies, which covers the use of basic or neutral water-soluble excipients, the use of acidic excipients, the use of calcium lactate, and the use of anhydrides. Poly(ortho ester) bioerodible polymers are suitable materials for the topical administration of a wide variety of therapeutic agents; varying the nature and amounts of excipients physically incorporated into the polymer will vary the erosion rates from a few hours to many months. With this range of control, delivery systems for short-term applications such as oral 12-24 hour tablets, intermediate ophthalmic products lasting 1 week, or implants lasting as long as 1 year can be produced. No extensive toxicological studies have been performed as yet. In vivo release rate experiments performed over many months have not shown any adverse tissue reactions beyond the expected encapsulation. PMID:3930918

  15. Therapeutic Recombinant Monoclonal Antibodies

    ERIC Educational Resources Information Center

    Bakhtiar, Ray

    2012-01-01

    During the last two decades, the rapid growth of biotechnology-derived techniques has led to a myriad of therapeutic recombinant monoclonal antibodies with significant clinical benefits. Recombinant monoclonal antibodies can be obtained from a number of natural sources such as animal cell cultures using recombinant DNA engineering. In contrast to…

  16. Therapeutic HPV DNA vaccines

    PubMed Central

    Lin, Ken; Roosinovich, Elena; Ma, Barbara; Hung, Chien-Fu

    2010-01-01

    It is now well established that most cervical cancers are causally associated with HPV infection. This realization has led to efforts to control HPV-associated malignancy through prevention or treatment of HPV infection. Currently, commercially available HPV vaccines are not designed to control established HPV infection and associated premalignant and malignant lesions. To treat and eradicate pre-existing HPV infections and associated lesions which remain prevalent in the U.S. and worldwide, effective therapeutic HPV vaccines are needed. DNA vaccination has emerged as a particularly promising form of therapeutic HPV vaccines due to its safety, stability and ability to induce antigen-specific immunity. This review focuses on improving the potency of therapeutic HPV vaccines through modification of dendritic cells (DCs) by [1] increasing the number of antigen-expressing/antigen-loaded DCs, [2] improving HPV antigen expression, processing and presentation in DCs, and [3] enhancing DC and T cell interaction. Continued improvement in therapeutic HPV DNA vaccines may ultimately lead to an effective DNA vaccine for the treatment of HPV-associated malignancies. PMID:20066511

  17. Therapeutic Recombinant Monoclonal Antibodies

    ERIC Educational Resources Information Center

    Bakhtiar, Ray

    2012-01-01

    During the last two decades, the rapid growth of biotechnology-derived techniques has led to a myriad of therapeutic recombinant monoclonal antibodies with significant clinical benefits. Recombinant monoclonal antibodies can be obtained from a number of natural sources such as animal cell cultures using recombinant DNA engineering. In contrast to

  18. Developing Therapeutic Listening

    ERIC Educational Resources Information Center

    Lee, Billy; Prior, Seamus

    2013-01-01

    We present an experience-near account of the development of therapeutic listening in first year counselling students. A phenomenological approach was employed to articulate the trainees' lived experiences of their learning. Six students who had just completed a one-year postgraduate certificate in counselling skills were interviewed and the

  19. Developing Therapeutic Listening

    ERIC Educational Resources Information Center

    Lee, Billy; Prior, Seamus

    2013-01-01

    We present an experience-near account of the development of therapeutic listening in first year counselling students. A phenomenological approach was employed to articulate the trainees' lived experiences of their learning. Six students who had just completed a one-year postgraduate certificate in counselling skills were interviewed and the…

  20. Polymer-Conducting Polymer Composites

    NASA Astrophysics Data System (ADS)

    Monrreal, Juan; Foltz, Heinrich D.; Garcia, Elsa; Lozano, Karen; Villareal, Marcos; Tidrow, Steven C.; Dorina Chipara, Magdalena; Chipara, Mircea

    2008-03-01

    Polyaniline is a conducting polymer with high electrical conductivity, good thermal and thermo-oxidative resistance, and poor mechanical properties. To overcome these weaknesses, the conducting nanoparticles were dispersed within polymeric matrices characterized by high mechanical strength or high elasticity. Such composite materials found applications as lightweight antistatic materials (at low doping levels) and electromagnetic shielding capabilities (at high doping levels, typically above the percolation threshold for electrical conductivity) and exhibit potential applications as metamaterials. Nanosized particles of polyaniline were dispersed within polymeric matrices (polystyrene, polyvinylchloride, and polyethylene). The thermal properties were investigated by Thermal Analysis and Differential Scanning Calorimetry. FTIR/ATR, Raman spectroscopy, and Electron Spin Resonance spectroscopy provided additional information about the effect of nanofiller on the polymeric matrix. Electrical (dc) measurements confirmed the increase of the electrical conductivity as the concentration of conducting nanoparticle is increased and revealed a broad percolation behavior. The effect of the conducting nanofiller on the mechanical properties is reported.

  1. Neural and Cellular Mechanisms of Fear and Extinction Memory Formation

    PubMed Central

    Orsini, Caitlin A.; Maren, Stephen

    2012-01-01

    Over the course of natural history, countless animal species have evolved adaptive behavioral systems to cope with dangerous situations and promote survival. Emotional memories are central to these defense systems because they are rapidly acquired and prepare organisms for future threat. Unfortunately, the persistence and intrusion of memories of fearful experiences are quite common and can lead to pathogenic conditions, such as anxiety and phobias. Over the course of the last thirty years, neuroscientists and psychologists alike have attempted to understand the mechanisms by which the brain encodes and maintains these aversive memories. Of equal interest, though, is the neurobiology of extinction memory formation as this may shape current therapeutic techniques. Here we review the extant literature on the neurobiology of fear and extinction memory formation, with a strong focus on the cellular and molecular mechanisms underlying these processes. PMID:22230704

  2. Quantum Random Access Memory

    NASA Astrophysics Data System (ADS)

    Giovannetti, Vittorio; Lloyd, Seth; Maccone, Lorenzo

    2008-04-01

    A random access memory (RAM) uses n bits to randomly address N=2n distinct memory cells. A quantum random access memory (QRAM) uses n qubits to address any quantum superposition of N memory cells. We present an architecture that exponentially reduces the requirements for a memory call: O(log?N) switches need be thrown instead of the N used in conventional (classical or quantum) RAM designs. This yields a more robust QRAM algorithm, as it in general requires entanglement among exponentially less gates, and leads to an exponential decrease in the power needed for addressing. A quantum optical implementation is presented.

  3. ECT and memory loss.

    PubMed

    Squire, L R

    1977-09-01

    The author reviews several studies that clarify the nature of the memory loss associated with ECT. Bilateral ECT produced greater anterograde memory loss than right unilateral ECT and more extensive retrograde amnesia than unilateral ECT. Reactivating memories just before ECT did not produce amnesia. Capacity for new learning recovered substantially by several months after ECT, but memory complaints were common in individuals who had received bilateral ECT. Other things being equal, right unilateral ECT seems preferable to bilateral ECT because the risks to memory associated with unilateral ECT are smaller. PMID:331969

  4. The neurology of memory.

    PubMed

    Dworetzky, B A

    2001-01-01

    Remembering is an intrinsic and awesome aspect of human function. Memory loss, a common sequela of brain damage, has been studied extensively to understand how the brain encodes, stores and retrieves information. Important anatomic structures for memory have been identified from work in surgical therapy for epilepsy as well as other clinical syndromes where memory loss is a major feature. Beyond clinicoanatomic correlations, current research has focused on synaptic modifications and biochemical processes that underlie changes in neuronal connectivity. As Alzheimer's disease research expands our knowledge of memory, the treatment of other memory disorders will follow. PMID:11373070

  5. Memory-effects of magnetic nanocomposites.

    PubMed

    Razzaq, Muhammad Yasar; Behl, Marc; Lendlein, Andreas

    2012-10-21

    The thermally induced shape memory effect (SME) is the capability of a material to fix a temporary (deformed) shape and recover a 'memorized' permanent shape in response to heat. SMEs in polymers have enabled a variety of applications including deployable space structures, biomedical devices, adaptive optical devices, smart dry adhesives and fasteners. By the incorporation of magnetic nanoparticles (mNP) into shape-memory polymer (SMP), a magnetically controlled SME has been realized. Magnetic actuation of nanocomposites enables remotely controlled devices based on SMP, which might be useful in medical technology, e.g. remotely controlled catheters or drug delivery systems. Here, an overview of the recent advances in the field of magnetic actuation of SMP is presented. Special emphasis is given on the magnetically controlled recovery of SMP with one switching temperature T(sw) (dual-shape effect) or with two T(sw)s (triple-shape effect). The use of magnetic field to change the apparent switching temperature (T(sw,app)) of the dual or triple-shape nanocomposites is described. Finally, the capability of magnetic nanocomposites to remember the magnetic field strength (H) initially used to deform the sample (magnetic-memory effect) is addressed. The distinguished advantages of magnetic heating over conventional heating methods make these multifunctional nanocomposites attractive candidates for in vivo applications. PMID:22941347

  6. Memory-effects of magnetic nanocomposites

    NASA Astrophysics Data System (ADS)

    Razzaq, Muhammad Yasar; Behl, Marc; Lendlein, Andreas

    2012-09-01

    The thermally induced shape memory effect (SME) is the capability of a material to fix a temporary (deformed) shape and recover a `memorized' permanent shape in response to heat. SMEs in polymers have enabled a variety of applications including deployable space structures, biomedical devices, adaptive optical devices, smart dry adhesives and fasteners. By the incorporation of magnetic nanoparticles (mNP) into shape-memory polymer (SMP), a magnetically controlled SME has been realized. Magnetic actuation of nanocomposites enables remotely controlled devices based on SMP, which might be useful in medical technology, e.g. remotely controlled catheters or drug delivery systems. Here, an overview of the recent advances in the field of magnetic actuation of SMP is presented. Special emphasis is given on the magnetically controlled recovery of SMP with one switching temperature Tsw (dual-shape effect) or with two Tsws (triple-shape effect). The use of magnetic field to change the apparent switching temperature (Tsw,app) of the dual or triple-shape nanocomposites is described. Finally, the capability of magnetic nanocomposites to remember the magnetic field strength (H) initially used to deform the sample (magnetic-memory effect) is addressed. The distinguished advantages of magnetic heating over conventional heating methods make these multifunctional nanocomposites attractive candidates for in vivo applications.

  7. Influence of therapeutic radiation on polycaprolactone and polyurethane biomaterials.

    PubMed

    Cooke, Shelley L; Whittington, Abby R

    2016-03-01

    Biomedical polymers are exposed in vivo to ionizing radiation as implants, coatings and bystander materials. High levels of ionizing radiation (e.g. X-ray and gamma) have been reported to cause degradation and/or cross-linking in many polymers. This pilot study sought to determine causes of failure, by investigating how therapeutic radiation affects two different porous polymeric scaffolds: polycaprolactone (PCL) and polyurethane (PU). PCL is a bioresorbable material used in biomedical devices (e.g., dentistry, internal fixation devices and targeted drug delivery capsules). PU is commonly used in medical applications (e.g., coatings for pacemakers, tissue expanders, catheter tubing and wound dressings). PU was specifically fabricated to be a non-degradable polymer in this study. Porous scaffolds, fabricated using solvent casting and/or salt leeching techniques, were placed in phosphate buffered saline (PBS, pH=7.4) and exposed to typical cancer radiotherapy. A total dose of 50Gy was broken into 25 doses over an eleven-week period. Collected PBS was tested for polymer leachants and degradation products using Gas Chromatography Mass Spectroscopy (GC-MS), results revealed no analyzable leachants from either polymer. Scaffolds were characterized using Environmental Scanning Electron Microscopy, Size-exclusion chromatography (SEC), Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR). No gross visual changes were observed in either polymer, however PU exhibited microstructure changes after irradiation. Increased number average molecular weight and weight average molecular weight in PCL and PU were observed after irradiation, indicating crosslinking. PU displayed an increase in intrinsic viscosity that further confirms increased crosslinking. PCL and PU showed decreases in crystallinity after irradiation, and PU crystallinity shifted from long-range-order hard segments to short-range-order hard segments after irradiation. Results from both PCL and PU suggest changes in polymer backbones. This preliminary study suggests that therapeutic radiation doses cause both degradation and crosslinking in PCL and PU. PMID:26706509

  8. Polyphenols: Multipotent Therapeutic Agents in Neurodegenerative Diseases

    PubMed Central

    Bhullar, Khushwant S.; Rupasinghe, H. P. Vasantha

    2013-01-01

    Aging leads to numerous transitions in brain physiology including synaptic dysfunction and disturbances in cognition and memory. With a few clinically relevant drugs, a substantial portion of aging population at risk for age-related neurodegenerative disorders require nutritional intervention. Dietary intake of polyphenols is known to attenuate oxidative stress and reduce the risk for related neurodegenerative diseases such as Alzheimer's disease (AD), stroke, multiple sclerosis (MS), Parkinson's disease (PD), and Huntington's disease (HD). Polyphenols exhibit strong potential to address the etiology of neurological disorders as they attenuate their complex physiology by modulating several therapeutic targets at once. Firstly, we review the advances in the therapeutic role of polyphenols in cell and animal models of AD, PD, MS, and HD and activation of drug targets for controlling pathological manifestations. Secondly, we present principle pathways in which polyphenol intake translates into therapeutic outcomes. In particular, signaling pathways like PPAR, Nrf2, STAT, HIF, and MAPK along with modulation of immune response by polyphenols are discussed. Although current polyphenol researches have limited impact on clinical practice, they have strong evidence and testable hypothesis to contribute clinical advances and drug discovery towards age-related neurological disorders. PMID:23840922

  9. Immunological memory is associative

    SciTech Connect

    Smith, D.J.; Forrest, S.; Perelson, A.S.

    1996-12-31

    The purpose of this paper is to show that immunological memory is an associative and robust memory that belongs to the class of sparse distributed memories. This class of memories derives its associative and robust nature by sparsely sampling the input space and distributing the data among many independent agents. Other members of this class include a model of the cerebellar cortex and Sparse Distributed Memory (SDM). First we present a simplified account of the immune response and immunological memory. Next we present SDM, and then we show the correlations between immunological memory and SDM. Finally, we show how associative recall in the immune response can be both beneficial and detrimental to the fitness of an individual.

  10. Flexible non-volatile memory devices based on organic semiconductors

    NASA Astrophysics Data System (ADS)

    Cosseddu, Piero; Casula, Giulia; Lai, Stefano; Bonfiglio, Annalisa

    2015-09-01

    The possibility of developing fully organic electronic circuits is critically dependent on the ability to realize a full set of electronic functionalities based on organic devices. In order to complete the scene, a fundamental element is still missing, i.e. reliable data storage. Over the past few years, a considerable effort has been spent on the development and optimization of organic polymer based memory elements. Among several possible solutions, transistor-based memories and resistive switching-based memories are attracting a great interest in the scientific community. In this paper, a route for the fabrication of organic semiconductor-based memory devices with performances beyond the state of the art is reported. Both the families of organic memories will be considered. A flexible resistive memory based on a novel combination of materials is presented. In particular, high retention time in ambient conditions are reported. Complementary, a low voltage transistor-based memory is presented. Low voltage operation is allowed by an hybrid, nano-sized dielectric, which is also responsible for the memory effect in the device. Thanks to the possibility of reproducibly fabricating such device on ultra-thin substrates, high mechanical stability is reported.

  11. Memory access in shared virtual memory

    SciTech Connect

    Berrendorf, R. )

    1992-01-01

    Shared virtual memory (SVM) is a virtual memory layer with a single address space on top of a distributed real memory on parallel computers. We examine the behavior and performance of SVM running a parallel program with medium-grained, loop-level parallelism on top of it. A simulator for the underlying parallel architecture can be used to examine the behavior of SVM more deeply. The influence of several parameters, such as the number of processors, page size, cold or warm start, and restricted page replication, is studied.

  12. Memory access in shared virtual memory

    SciTech Connect

    Berrendorf, R.

    1992-09-01

    Shared virtual memory (SVM) is a virtual memory layer with a single address space on top of a distributed real memory on parallel computers. We examine the behavior and performance of SVM running a parallel program with medium-grained, loop-level parallelism on top of it. A simulator for the underlying parallel architecture can be used to examine the behavior of SVM more deeply. The influence of several parameters, such as the number of processors, page size, cold or warm start, and restricted page replication, is studied.

  13. Design strategies for therapeutic ultrasound phased arrays

    NASA Astrophysics Data System (ADS)

    Kluiwstra, Jan-Ulco A.; McGough, Robert J.; Hamilton, James D.; O'Donnell, Matthew; Cain, Charles A.

    1997-04-01

    High-intensity focused ultrasound is used in many therapeutic applications such as drug activation/drug delivery, hyperthermia, cancer therapy, ultrasound surgery and myocardial ablation. Various ultrasonic systems have been proposed for these therapeutic applications. While many applicators produce adequate power levels, multiple element ultrasound phased arrays adjust for phase aberrations, focus around obstructions such as bone and/or air spaces (lungs), and follow, in real time, a moving target. Since large aperture arrays with several hundred elements are required, design compromises keep the element count and fabrication cost at a reasonable level. These trade-offs, which optimize the array aperture with respect to element count, often result in a non-ideal aspect ratio (element width to thickness), leading to lateral mode vibrations which reduce the electrical to acoustical efficiency to about 10 - 20%. These vibrations are easily observed with a laser interferometer system. Piezo composite technology, which eliminates the non-ideal aspect ratio by dividing the individual array elements into long, thin rods, provides a solution to this problem. The spaces between the rods are filled with a polymer to provide structural support and allow deposition of electrode layers to interconnect individual rods and to outline array elements. Several piezo composite transducers have been tested, and initial results show a greatly improved beam pattern and increased efficiency. Power handling capability of composites has recently improved allowing outputs in excess of 10 watts/cm2 with efficiencies greater than 60%. This is sufficient for many therapeutic applications.

  14. Multilayered Polymer Coated Carbon Nanotubes to Deliver Dasatinib

    PubMed Central

    Moore, Thomas L.; Grimes, Stuart W.; Lewis, Robert L.; Alexis, Frank

    2014-01-01

    Multilayered, multifunctional polymer coatings were grafted onto carbon nanotubes (CNT) using a one-pot, ring-opening polymerization in order to control the release kinetic and therapeutic efficacy of dasatinib. Biocompatible, biodegradable multilayered coatings composed of poly(glycolide) (PGA), and poly(lactide) (PLA) were polymerized directly onto hydroxyl-functionalized CNT surfaces. Sequential addition of monomers into the reaction vessel enabled multilayered coatings of PLA-PGA, or PGA-PLA. Poly(ethylene glycol) capped the polymer chain ends, resulting in a multifunctional amphiphilic coating. Multilayer polymer coatings on CNTs enabled control of anticancer dasatinib’s release kinetics and enhanced the in vitro therapeutic efficacy against U-87 glioblastoma compared to monolayer polymer coatings. PMID:24294824

  15. Serotonergic Mechanisms in Addiction-Related Memories

    PubMed Central

    Nic Dhonnchadha, Bríd Á; Cunningham, Kathryn A.

    2008-01-01

    Drug-associated memories are a hallmark of addiction and a contributing factor in the continued use and relapse to drugs of abuse. Repeated association of drugs of abuse with conditioned stimuli leads to long-lasting behavioral responses that reflect reward-controlled learning and participate in the establishment of addiction. A greater understanding of the mechanisms underlying the formation and retrieval of drug-associated memories may shed light on potential therapeutic approaches to effectively intervene with drug use-associated memory. There is evidence to support the involvement of serotonin (5-HT) neurotransmission in learning and memory formation through the families of the 5-HT1 receptor (5-HT1R) and 5-HT2R which have also been shown to play a modulatory role in the behavioral effects induced by many psychostimulants. While there is a paucity of studies examining the effects of selective 5-HT1AR ligands, the available dataset suggests that 5-HT1BR agonists may inhibit retrieval of cocaine-associated memories. The 5-HT2AR and 5-HT2CR appear to be integral in the strong conditioned associations made between cocaine and environmental cues with 5-HT2AR antagonists and 5-HT2CR agonists possessing potency in blocking retrieval of cocaine-associated memories following cocaine self-administration procedures. The complex anatomical connectivity between 5-HT neurons and other neuronal phenotypes in limbic-corticostriatal brain structures, the heterogeneity of 5-HT receptors (5-HTXR) and the conflicting results of behavioral experiments which employ non-specific 5-HTXR ligands contribute to the complexity of interpreting the involvement of 5-HT systems in addictive-related memory processes. This review briefly traces the history of 5-HT involvement in retrieval of drug-cue associations and future targets of serotonergic manipulation that may reduce the impact that drug cues have on addictive behavior and relapse. PMID:18639587

  16. Photodegradability of polymer blends containing styrenic polymers

    SciTech Connect

    Kim, Jeong Ho

    1995-12-31

    Recently, lots of work has been made on the photochemistry of polymers in an attempt to understand the stability and photodegradability of polymers exposed to light. Irradiation of polymers in the presence of air leads to formation of various oxygen containing groups and carbonyl functions which increase the susceptibility of the polymer to UV light. In the present study, multicomponent blends of polystyrene and photodegradable polymers with vinylketone groups are prepared and the investigation is made on the effect of change in morphology on the photodegradability. SBS type block copolymers are added to change the morphology of the blend and the UV irradiated polymers are analyzed to check any changes in mechanical properties and specific bands in FTIR spectra.

  17. Polymers in small-interfering RNA delivery.

    PubMed

    Singha, Kaushik; Namgung, Ran; Kim, Won Jong

    2011-06-01

    This review will cover the current strategies that are being adopted to efficiently deliver small interfering RNA using nonviral vectors, including the use of polymers such as polyethylenimine, poly(lactic-co-glycolic acid), polypeptides, chitosan, cyclodextrin, dendrimers, and polymers-containing different nanoparticles. The article will provide a brief and concise account of underlying principle of these polymeric vectors and their structural and functional modifications which were intended to serve different purposes to affect efficient therapeutic outcome of small-interfering RNA delivery. The modifications of these polymeric vectors will be discussed with reference to stimuli-responsiveness, target specific delivery, and incorporation of nanoconstructs such as carbon nanotubes, gold nanoparticles, and silica nanoparticles. The emergence of small-interfering RNA as the potential therapeutic agent and its mode of action will also be mentioned in a nutshell. PMID:21749290

  18. Polymers in Small-Interfering RNA Delivery

    PubMed Central

    Singha, Kaushik; Namgung, Ran

    2011-01-01

    This review will cover the current strategies that are being adopted to efficiently deliver small interfering RNA using nonviral vectors, including the use of polymers such as polyethylenimine, poly(lactic-co-glycolic acid), polypeptides, chitosan, cyclodextrin, dendrimers, and polymers-containing different nanoparticles. The article will provide a brief and concise account of underlying principle of these polymeric vectors and their structural and functional modifications which were intended to serve different purposes to affect efficient therapeutic outcome of small-interfering RNA delivery. The modifications of these polymeric vectors will be discussed with reference to stimuli-responsiveness, target specific delivery, and incorporation of nanoconstructs such as carbon nanotubes, gold nanoparticles, and silica nanoparticles. The emergence of small-interfering RNA as the potential therapeutic agent and its mode of action will also be mentioned in a nutshell. PMID:21749290

  19. Platelet-delivered therapeutics.

    PubMed

    Lyde, R; Sabatino, D; Sullivan, S K; Poncz, M

    2015-06-01

    We have proposed that modified platelets could potentially be used to correct intrinsic platelet defects as well as for targeted delivery of therapeutic molecules to sights of vascular injury. Ectopic expression of proteins within ?-granules prior to platelet activation has been achieved for several proteins, including urokinase, factor (F) VIII, and partially for FIX. Potential uses of platelet-directed therapeutics will be discussed, focusing on targeted delivery of urokinase as a thromboprophylactic agent and FVIII for the treatment of hemophilia A patients with intractable inhibitors. This presentation will discuss new strategies that may be useful in the care of patients with vascular injury as well as remaining challenges and limitations of these approaches. PMID:26149015

  20. Multistage vector (MSV) therapeutics.

    PubMed

    Wolfram, Joy; Shen, Haifa; Ferrari, Mauro

    2015-12-10

    One of the greatest challenges in the field of medicine is obtaining controlled distribution of systemically administered therapeutic agents within the body. Indeed, biological barriers such as physical compartmentalization, pressure gradients, and excretion pathways adversely affect localized delivery of drugs to pathological tissue. The diverse nature of these barriers requires the use of multifunctional drug delivery vehicles that can overcome a wide range of sequential obstacles. In this review, we explore the role of multifunctionality in nanomedicine by primarily focusing on multistage vectors (MSVs). The MSV is an example of a promising therapeutic platform that incorporates several components, including a microparticle, nanoparticles, and small molecules. In particular, these components are activated in a sequential manner in order to successively address transport barriers. PMID:26264836

  1. Therapeutic cancer vaccines.

    PubMed

    Melief, Cornelis J M; van Hall, Thorbald; Arens, Ramon; Ossendorp, Ferry; van der Burg, Sjoerd H

    2015-09-01

    The clinical benefit of therapeutic cancer vaccines has been established. Whereas regression of lesions was shown for premalignant lesions caused by HPV, clinical benefit in cancer patients was mostly noted as prolonged survival. Suboptimal vaccine design and an immunosuppressive cancer microenvironment are the root causes of the lack of cancer eradication. Effective cancer vaccines deliver concentrated antigen to both HLA class I and II molecules of DCs, promoting both CD4 and CD8 T cell responses. Optimal vaccine platforms include DNA and RNA vaccines and synthetic long peptides. Antigens of choice include mutant sequences, selected cancer testis antigens, and viral antigens. Drugs or physical treatments can mitigate the immunosuppressive cancer microenvironment and include chemotherapeutics, radiation, indoleamine 2,3-dioxygenase (IDO) inhibitors, inhibitors of T cell checkpoints, agonists of selected TNF receptor family members, and inhibitors of undesirable cytokines. The specificity of therapeutic vaccination combined with such immunomodulation offers an attractive avenue for the development of future cancer therapies. PMID:26214521

  2. Therapeutic antibodies against cancer

    PubMed Central

    Adler, Mark J.; Dimitrov, Dimiter S.

    2012-01-01

    Antibody-based therapeutics against cancer are highly successful in clinic and currently enjoy unprecedented recognition of their potential; 13 monoclonal antibodies (mAbs) have been approved for clinical use in the European Union and in the United States (one, mylotarg, was withdrawn from market in 2010). Three of the mAbs (bevacizumab, rituximab, trastuzumab) are in the top six selling protein therapeutics with sales in 2010 of more than $5 bln each. Hundreds of mAbs including bispecific mAbs and multispecific fusion proteins, mAbs conjugated with small molecule drugs and mAbs with optimized pharmacokinetics are in clinical trials. However, challenges remain and it appears that deeper understanding of mechanisms is needed to overcome major problems including resistance to therapy, access to targets, complexity of biological systems and individual variations. PMID:22520975

  3. Complement-targeted therapeutics

    PubMed Central

    Ricklin, Daniel; Lambris, John D

    2010-01-01

    The complement system is a central component of innate immunity and bridges the innate to the adaptive immune response. However, it can also turn its destructive capabilities against host cells and is involved in numerous diseases and pathological conditions. Modulation of the complement system has been recognized as a promising strategy in drug discovery, and a large number of therapeutic modalities have been developed. However, successful marketing of complement-targeted drugs has proved to be more difficult than initially expected, and many strategies have been discontinued. The US Food and Drug Administrations approval of the first complement-specific drug, an antibody against complement component C5 (eculizumab; Soliris), in March 2007, was a long-awaited breakthrough in the field. Approval of eculizumab validates the complement system as therapeutic target and might facilitate clinical development of other promising drug candidates. PMID:17989689

  4. [Therapeutic adherence in elderly].

    PubMed

    Petermans, J; Suarez, A Samalea; Van Hees, T

    2010-01-01

    Therapeutic adherence can be defined as the degree of concordance between the behaviour of a person in relation with drugs prescription and medical recommendations. It represents the ability of people to follow a treatment. Bad adherence is frequent in geriatric patients. The behaviour of the patient is important but the role of the prescriptor and distributor of the drugs should also be emphasized. A bad adherence is responsible for iatrogenic consequences, which has a great impact on the functionality of the old person, but also on the cost and organization of care. Therapeutic education, a standardised method to help the patient take care of his own treatment, must be developed. The aims and means should be clearly efined. The patient himself must be involved and human or material sources of help must be sought. PMID:20684404

  5. Therapeutic Hypothermia for Neuroprotection

    PubMed Central

    Karnatovskaia, Lioudmila V.; Wartenberg, Katja E.

    2014-01-01

    The earliest recorded application of therapeutic hypothermia in medicine spans about 5000 years; however, its use has become widespread since 2002, following the demonstration of both safety and efficacy of regimens requiring only a mild (32°C-35°C) degree of cooling after cardiac arrest. We review the mechanisms by which hypothermia confers neuroprotection as well as its physiological effects by body system and its associated risks. With regard to clinical applications, we present evidence on the role of hypothermia in traumatic brain injury, intracranial pressure elevation, stroke, subarachnoid hemorrhage, spinal cord injury, hepatic encephalopathy, and neonatal peripartum encephalopathy. Based on the current knowledge and areas undergoing or in need of further exploration, we feel that therapeutic hypothermia holds promise in the treatment of patients with various forms of neurologic injury; however, additional quality studies are needed before its true role is fully known. PMID:24982721

  6. New levodopa therapeutic strategies.

    PubMed

    LeWitt, Peter A

    2016-01-01

    During its almost half-century of use for treating Parkinson's disease, levodopa therapy has permitted most patients to reverse much of this disorder's symptomatology. However, the full range of its therapeutic properties is not completely understood, as levodopa is showing itself to be more than just a metabolic intermediate for dopamine synthesis. Improving the constancy of drug delivery is the next frontier for enhancing therapeutic options with levodopa. Because conventional immediate-release carbidopa-levodopa tablets yield such variable pharmacokinetic profiles (as do other marketed products attempting to extend levodopa effect), improved formulations are greatly needed by patients experiencing motor fluctuations. Products under development or recently released in the U.S. include intestinal infusion, sustained-release microtablets, gastric-retentive formulations, a levodopa pro-drug, and methods for delivery of the drug by inhalation or subcutaneous infusion. PMID:26459662

  7. On therapeutic action.

    PubMed

    Aisenstein, Marilia

    2007-01-01

    The author presents her views on therapeutic action in the light of an examination of key Freudian works. She also discusses the work of some psychoanalytic thinkers who followed Freud, such as Klein and Green. Lacan's thinking and his influence on French psychoanalysis are summarized. A detailed clinical vignette is presented to illustrate the author's use of the psychoanalytic method to ameliorate a patient's troubled mental functioning. PMID:18286756

  8. Toxicology of antisense therapeutics.

    PubMed

    Jason, Tracey L H; Koropatnick, James; Berg, Randal W

    2004-11-15

    Targeting unique mRNA molecules using antisense approaches, based on sequence specificity of double-stranded nucleic acid interactions should, in theory, allow for design of drugs with high specificity for intended targets. Antisense-induced degradation or inhibition of translation of a target mRNA is potentially capable of inhibiting the expression of any target protein. In fact, a large number of proteins of widely varied character have been successfully downregulated using an assortment of antisense-based approaches. The most prevalent approach has been to use antisense oligonucleotides (ASOs), which have progressed through the preclinical development stages including pharmacokinetics and toxicological studies. A small number of ASOs are currently in human clinical trials. These trials have highlighted several toxicities that are attributable to the chemical structure of the ASOs, and not to the particular ASO or target mRNA sequence. These include mild thrombocytopenia and hyperglycemia, activation of the complement and coagulation cascades, and hypotension. Dose-limiting toxicities have been related to hepatocellular degeneration leading to decreased levels of albumin and cholesterol. Despite these toxicities, which are generally mild and readily treatable with available standard medications, the clinical trials have clearly shown that ASOs can be safely administered to patients. Alternative chemistries of ASOs are also being pursued by many investigators to improve specificity and antisense efficacy and to reduce toxicity. In the design of ASOs for anticancer therapeutics in particular, the goal is often to enhance the cytotoxicity of traditional drugs toward cancer cells or to reduce the toxicity to normal cells to improve the therapeutic index of existing clinically relevant cancer chemotherapy drugs. We predict that use of antisense ASOs in combination with small molecule therapeutics against the target protein encoded by the antisense-targeted mRNA, or an alternate target in the same or a connected biological pathway, will likely be the most beneficial application of this emerging class of therapeutic agent. PMID:15519609

  9. Therapeutic antibody engineering

    PubMed Central

    Parren, Paul W.H.I.; Lugovskoy, Alexey A.

    2013-01-01

    It is an important event in any knowledge area when an authority in the field decides that it is time to share all accumulated knowledge and learnings by writing a text book. This does not occur often in the biopharmaceutical industry, likely due to both the highly dynamic environment with tight timelines and policies and procedures at many pharmaceutical companies that hamper knowledge sharing. To take on a task like this successfully, a strong drive combined with a desire and talent to teach, but also an accommodating and stimulating environment is required. Luckily for those interested in therapeutic monoclonal antibodies, Dr. William R. Strohl decided about two years ago that the time was right to write a book about the past, present and future of these fascinating molecules. Dr. Strohls great expertise and passion for biotechnology is evident from his life story and his strong academic and industry track record. Dr. Strohl pioneered natural product biotechnology, first in academia as a full professor of microbiology and biochemistry at Ohio State University in Columbus, Ohio and later in industry while at Merck. Despite his notable advances in recombinant natural products, industry interest in this area waned and in 2001 Dr. Strohl sought new opportunities by entering the field of antibody therapeutics. He initiated antibody discovery through phage display at Merck, and then moved to Centocor Research and Development Inc. (now Janssen Biotech, Inc.) in 2008 to head Biologics Research, where he now directs the discovery of innovative therapeutic antibody candidates.

  10. Clinical therapeutics for phenylketonuria.

    PubMed

    Kochhar, Jaspreet Singh; Chan, Sui Yung; Ong, Pei Shi; Kang, Lifeng

    2012-08-01

    Phenylketonuria was amongst the first of the metabolic disorders to be characterised, exhibiting an inborn error in phenylalanine metabolism due to a functional deficit of the enzyme phenylalanine hydroxylase. It affects around 700,000 people around the globe. Mutations in the gene coding for hepatic phenylalanine hydroxylase cause this deficiency resulting in elevated plasma phenylalanine concentrations, leading to cognitive impairment, neuromotor disorders and related behavioural symptoms. Inception of low phenylalanine diet in the 1950s marked a revolution in the management of phenylketonuria and has since been a vital element of all therapeutic regimens. However, compliance to dietary therapy has been found difficult and newer supplement approaches are being examined. The current development of gene therapy and enzyme replacement therapeutics may offer promising alternatives for the management of phenylketonuria. This review outlines the pathological basis of phenylketonuria, various treatment regimes, their associated challenges and the future prospects of each approach. Briefly, novel drug delivery systems which can potentially deliver therapeutic strategies in phenylketonuria have been discussed. PMID:25787029

  11. Proteases as therapeutics

    PubMed Central

    Craik, Charles S.; Page, Michael J.; Madison, Edwin L.

    2015-01-01

    Proteases are an expanding class of drugs that hold great promise. The U.S. FDA (Food and Drug Administration) has approved 12 protease therapies, and a number of next generation or completely new proteases are in clinical development. Although they are a well-recognized class of targets for inhibitors, proteases themselves have not typically been considered as a drug class despite their application in the clinic over the last several decades; initially as plasma fractions and later as purified products. Although the predominant use of proteases has been in treating cardiovascular disease, they are also emerging as useful agents in the treatment of sepsis, digestive disorders, inflammation, cystic fibrosis, retinal disorders, psoriasis and other diseases. In the present review, we outline the history of proteases as therapeutics, provide an overview of their current clinical application, and describe several approaches to improve and expand their clinical application. Undoubtedly, our ability to harness proteolysis for disease treatment will increase with our understanding of protease biology and the molecular mechanisms responsible. New technologies for rationally engineering proteases, as well as improved delivery options, will expand greatly the potential applications of these enzymes. The recognition that proteases are, in fact, an established class of safe and efficacious drugs will stimulate investigation of additional therapeutic applications for these enzymes. Proteases therefore have a bright future as a distinct therapeutic class with diverse clinical applications. PMID:21406063

  12. Neuroradiology therapeutic workstation

    NASA Astrophysics Data System (ADS)

    Close, Robert A.; Duckwiler, Gary R.; Vinuela, Fernando; Dion, Jacques E.; Abramowitz, Joshua

    1990-07-01

    Two types of workstation are being developed at UCLA for neuroradiology a display workstation and a therapeutic workstation. The display station is used for review of images derived from neuroradiology examinations whereas the therapeutic station is for image analysis. The therapeutic workstation will be used to compare angiograms with CT and MR images and to calculate quantitative information from image sets. Parameters obtained by image analysis will be useful for planning and evaluation of interventional procedures. Current emphasis is on development of analysis tools for digital subtraction angiography. Digital densitometry and parametric imaging routines are being developed for analysis of DSA images of blood flow (with contrast injection) taken with a GE Digital Flouricon 5000 system. These routines include determination of vessel geometry regional blood volume flow rate and velocity. The starting point for software development is the CALIPSO (CALifornia Image Processing SOftware) package developed at UCLA for the Macintosh II. A Stellar GS2000 graphics mini-supercomputer will ultimately be used to allow rapid manipulation of images. The workstation will be connected to various imaging modalities through an Ethernet network. 1.

  13. Polycyclic peptide therapeutics.

    PubMed

    Baeriswyl, Vanessa; Heinis, Christian

    2013-03-01

    Owing to their excellent binding properties, high stability, and low off-target toxicity, polycyclic peptides are an attractive molecule format for the development of therapeutics. Currently, only a handful of polycyclic peptides are used in the clinic; examples include the antibiotic vancomycin, the anticancer drugs actinomycin D and romidepsin, and the analgesic agent ziconotide. All clinically used polycyclic peptide drugs are derived from natural sources, such as soil bacteria in the case of vancomycin, actinomycin D and romidepsin, or the venom of a fish-hunting coil snail in the case of ziconotide. Unfortunately, nature provides peptide macrocyclic ligands for only a small fraction of therapeutic targets. For the generation of ligands of targets of choice, researchers have inserted artificial binding sites into natural polycyclic peptide scaffolds, such as cystine knot proteins, using rational design or directed evolution approaches. More recently, large combinatorial libraries of genetically encoded bicyclic peptides have been generated de novo and screened by phage display. In this Minireview, the properties of existing polycyclic peptide drugs are discussed and related to their interesting molecular architectures. Furthermore, technologies that allow the development of unnatural polycyclic peptide ligands are discussed. Recent application of these technologies has generated promising results, suggesting that polycyclic peptide therapeutics could potentially be developed for a broad range of diseases. PMID:23355488

  14. Therapeutic targets for neuroblastomas

    PubMed Central

    Brodeur, Garrett M; lIyer, Radhika; Croucher, Jamie L; Zhuang, Tiangang; Higashi, Mayumi; Kolla, Venkatadri

    2014-01-01

    Introduction Neuroblastoma (NB) is the most common and deadly solid tumor in children. Despite recent improvements, the long-term outlook for high-risk NB is still < 50%. Further, there is considerable short- and long-term toxicity. More effective, less toxic therapy is needed, and the development of targeted therapies offers great promise. Areas covered Relevant literature was reviewed to identify current and future therapeutic targets that are critical to malignant transformation and progression of NB. The potential or actual NB therapeutic targets are classified into four categories: i) genes activated by amplification, mutation, translocation or autocrine overexpression; ii) genes inactivated by deletion, mutation or epigenetic silencing; iii) membrane-associated genes expressed on most NBs but few other tissues; or iv) common target genes relevant to NB as well as other tumors. Expert opinion Therapeutic approaches have been developed to some of these targets, but many remain untargeted at the present time. It is unlikely that single targeted agents will be sufficient for long-term cure, at least for high-risk NBs. The challenge will be how to integrate targeted agents with each other and with conventional therapy to enhance their efficacy, while simultaneously reducing systemic toxicity. PMID:24387342

  15. The Role of Reconsolidation and the Dynamic Process of Long-Term Memory Formation and Storage

    PubMed Central

    Alberini, Cristina M.

    2011-01-01

    It is becoming increasingly clear that the processes of memory formation and storage are exquisitely dynamic. Elucidating the nature and temporal evolution of the biological changes that accompany encoding, storage, and retrieval is key to understand memory formation. For explicit or medial temporal lobe-dependent memories that form after a discrete event and are stored for a long time, the physical changes underlying the encoding and processing of the information (memory trace or engram) remain in a fragile state for some time. However, over time, the new memory becomes increasingly resistant to disruption until it is consolidated. Retrieval or reactivation of an apparently consolidated memory can render the memory labile again, and reconsolidation is the process that occurs to mediate its restabilization. Reconsolidation also evolves with the age of the memory: Young memories are sensitive to post-reactivation disruption, but older memories are more resistant. Why does a memory become labile again if it is retrieved or reactivated? Here I suggest that the main function of reconsolidation is to contribute to the lingering consolidation process and mediate memory strengthening. I also discuss the literature and results regarding the influence of the passage of time on the reconsolidation of memory. These points have important implications for the use of reconsolidation in therapeutic settings. PMID:21436877

  16. Lipid-absorbing Polymers

    NASA Technical Reports Server (NTRS)

    Marsh, H. E., Jr.; Wallace, C. J.

    1973-01-01

    The removal of bile acids and cholesterol by polymeric absorption is discussed in terms of micelle-polymer interaction. The results obtained with a polymer composed of 75 parts PEO and 25 parts PB plus curing ingredients show an absorption of 305 to 309%, based on original polymer weight. Particle size effects on absorption rate are analyzed. It is concluded that crosslinked polyethylene oxide polymers will absorb water, crosslinked polybutadiene polymers will absorb lipids; neither polymer will absorb appreciable amounts of lipids from micellar solutions of lipids in water.

  17. Thermomechanical behavior of shape memory elastomeric composites

    NASA Astrophysics Data System (ADS)

    Ge, Qi; Luo, Xiaofan; Rodriguez, Erika D.; Zhang, Xiao; Mather, Patrick T.; Dunn, Martin L.; Qi, H. Jerry

    2012-01-01

    Shape memory polymers (SMPs) can fix a temporary shape and recover their permanent shape in response to environmental stimuli such as heat, electricity, or irradiation. Most thermally activated SMPs use the macromolecular chain mobility change around the glass transition temperature ( Tg) to achieve the shape memory (SM) effects. During this process, the stiffness of the material typically changes by three orders of magnitude. Recently, a composite materials approach was developed to achieve thermally activated shape memory effect where the material exhibits elastomeric response in both the temporary and the recovered configurations. These shape memory elastomeric composites (SMECs) consist of an elastomeric matrix reinforced by a semicrystalline polymer fiber network. The matrix provides background rubber elasticity while the fiber network can transform between solid crystals and melt phases over the operative temperature range. As such it serves as a reversible "switching phase" that enables shape fixing and recovery. Shape memory elastomeric composites provide a new paradigm for the development of a wide array of active polymer composites that utilize the melt-crystal transition to achieve the shape memory effect. This potentially allows for material systems with much simpler chemistries than most shape memory polymers and thus can facilitate more rapid material development and insertion. It is therefore important to understand the thermomechanical behavior and to develop corresponding material models. In this paper, a 3D finite-deformation constitutive modeling framework was developed to describe the thermomechanical behavior of SMEC. The model is phenomenological, although inspired by micromechanical considerations of load transfer between the matrix and fiber phases of a composite system. It treats the matrix as an elastomer and the fibers as a complex solid that itself is an aggregate of melt and crystal phases that evolve from one to the other during a temperature change. As such, the composite consists of an elastomer reinforced by a soft liquid at high temperature and a stiff solid at low temperature. The model includes a kinetic description of the non-isothermal crystallization and melting of the fibers during a temperature change. As the fibers transform from melt to crystal during cooling it is assumed that new crystals are formed in an undeformed state, which requires careful tracking of the kinematics of the evolving phases which comes at a significant computational cost. In order to improve the computational efficiency, an effective phase model (EPM) is adopted to treat the evolving crystal phases as an effective medium. A suite of careful thermomechanical experiments with a SMEC was carried out to calibrate various model parameters, and then to demonstrate the ability of the model to accurately capture the shape memory behavior of the SMEC system during complex thermomechanical loading scenarios. The model also identifies the effects of microstructural design parameters such as the fiber volume fraction.

  18. Human learning and memory.

    PubMed

    Johnson, M K; Hasher, L

    1987-01-01

    There have been several notable recent trends in the area of learning and memory. Problems with the episodic/semantic distinction have become more apparent, and new efforts have been made (exemplar models, distributed-memory models) to represent general knowledge without assuming a separate semantic system. Less emphasis is being placed on stable, prestored prototypes and more emphasis on a flexible memory system that provides the basis for a multitude of categories or frames of reference, derived on the spot as tasks demand. There is increasing acceptance of the idea that mental models are constructed and stored in memory in addition to, rather than instead of, memorial representations that are more closely tied to perceptions. This gives rise to questions concerning the conditions that permit inferences to be drawn and mental models to be constructed, and to questions concerning the similarities and differences in the nature of the representations in memory of perceived and generated information and in their functions. There has also been a swing from interest in deliberate strategies to interest in automatic, unconscious (even mechanistic!) processes, reflecting an appreciation that certain situations (e.g. recognition, frequency judgements, savings in indirect tasks, aspects of skill acquisition, etc) seem not to depend much on the products of strategic, effortful or reflective processes. There is a lively interest in relations among memory measures and attempts to characterize memory representations and/or processes that could give rise to dissociations among measures. Whether the pattern of results reflects the operation of functional subsystems of memory and, if so, what the "modules" are is far from clear. This issue has been fueled by work with amnesics and has contributed to a revival of interaction between researchers studying learning and memory in humans and those studying learning and memory in animals. Thus, neuroscience rivals computer science as a source of interdisciplinary stimulation. Research on topics such as memory for spatial location, the relation between memory and affect, and autobiographical memory reminds us that general theories of memory based on studies of verbal materials alone are limited. Investigating how people remember complex natural events should provide us with a larger set of memory phenomena to explain and consequently insight into a wider range of memory principles or a deeper understanding of the ones we already accept (e.g. the role of repetition, encoding specificity), including their functional significance for human behavior.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:3548580

  19. What is a suggestion? The neuroscience of implicit processing heuristics in therapeutic hypnosis and psychotherapy.

    PubMed

    Rossi, Ernest L; Rossi, Kathryn L

    2007-04-01

    Neuroscience and bioinformatics research on activity-dependent gene expression and brain plasticity in memory and learning are used to reconceptualize a fundamental question of therapeutic hypnosis, "What is a suggestion?" John Kihlstrom's cognitive-behavioral perspective of implicit (unconscious) and explicit (conscious) memory and Eric Kandel's Nobel Prize winning neurobiological research are integrated for a 30-year update of Milton H. Erickson's "neuro-psycho-physiology" of therapeutic hypnosis. Implicit processing heuristics are proposed as a more general framework for Erickson's concept of permissive indirect suggestions in therapeutic hypnosis and psychotherapy. These perspectives are illustrated by utilizing implicit processing heuristics to facilitate the four-stage creative process in converting implicit to explicit memory in a brain-damaged patient. PMID:17444364

  20. A generalized memory test algorithm

    NASA Technical Reports Server (NTRS)

    Milner, E. J.

    1982-01-01

    A general algorithm for testing digital computer memory is presented. The test checks that (1) every bit can be cleared and set in each memory work, and (2) bits are not erroneously cleared and/or set elsewhere in memory at the same time. The algorithm can be applied to any size memory block and any size memory word. It is concise and efficient, requiring the very few cycles through memory. For example, a test of 16-bit-word-size memory requries only 384 cycles through memory. Approximately 15 seconds were required to test a 32K block of such memory, using a microcomputer having a cycle time of 133 nanoseconds.

  1. Psychopharmacology and memory.

    PubMed

    Glannon, W

    2006-02-01

    Psychotropic and other drugs can alter brain mechanisms regulating the formation, storage, and retrieval of different types of memory. These include "off label" uses of existing drugs and new drugs designed specifically to target the neural bases of memory. This paper discusses the use of beta-adrenergic antagonists to prevent or erase non-conscious pathological emotional memories in the amygdala. It also discusses the use of novel psychopharmacological agents to enhance long term semantic and short term working memory by altering storage and retrieval mechanisms in the hippocampus and prefrontal cortex. Although intervention in the brain to alter memory as therapy or enhancement holds considerable promise, the long term effects of experimental drugs on the brain and memory are not known. More studies are needed to adequately assess the potential benefits and risks of these interventions. PMID:16446410

  2. Psychopharmacology and memory

    PubMed Central

    Glannon, W

    2006-01-01

    Psychotropic and other drugs can alter brain mechanisms regulating the formation, storage, and retrieval of different types of memory. These include off label uses of existing drugs and new drugs designed specifically to target the neural bases of memory. This paper discusses the use of beta?adrenergic antagonists to prevent or erase non?conscious pathological emotional memories in the amygdala. It also discusses the use of novel psychopharmacological agents to enhance long term semantic and short term working memory by altering storage and retrieval mechanisms in the hippocampus and prefrontal cortex. Although intervention in the brain to alter memory as therapy or enhancement holds considerable promise, the long term effects of experimental drugs on the brain and memory are not known. More studies are needed to adequately assess the potential benefits and risks of these interventions. PMID:16446410

  3. Regulatory T cell memory.

    PubMed

    Rosenblum, Michael D; Way, Sing Sing; Abbas, Abul K

    2016-02-01

    Memory for antigen is a defining feature of adaptive immunity. Antigen-specific lymphocyte populations show an increase in number and function after antigen encounter and more rapidly re-expand upon subsequent antigen exposure. Studies of immune memory have primarily focused on effector B cells and T cells with microbial specificity, using prime-challenge models of infection. However, recent work has also identified persistently expanded populations of antigen-specific regulatory T cells that protect against aberrant immune responses. In this Review, we consider the parallels between memory effector T cells and memory regulatory T cells, along with the functional implications of regulatory memory in autoimmunity, antimicrobial host defence and maternal-fetal tolerance. In addition, we discuss emerging evidence for regulatory T cell memory in humans and key unanswered questions in this rapidly evolving field. PMID:26688349

  4. Effect of Different Shape-Memory Processing Methods on the Thermomechanical Cyclic Properties of a Shape-Memory Polyurethane

    NASA Astrophysics Data System (ADS)

    Santiago, David; Ferrando, Francesc; De la Flor, Silvia

    2014-07-01

    Shape-memory polymers are materials that are capable of changing their shape when an external stimulus is applied. This effect is called the shape-memory effect (SME) and takes place by means of a thermomechanical cycle called programming. The SME depends on the thermomechanical conditions at which programming is performed, and the influence of these conditions differs depending on whether the programming is performed with a strain- or stress-controlled protocol. This study focuses on finding the thermomechanical cycling conditions in stress-controlled programming ( T prog and ?m) that stabilize the material in the fewest cycles while obtaining the best mechanical and shape-memory properties over the highest number of cycles. Using a T prog above or below, the glass transition temperature makes a big difference in terms of shape recovery and the maximum stress is a key factor in the stabilization of shape-memory properties.

  5. Smart polymers for implantable electronics

    NASA Astrophysics Data System (ADS)

    Ware, Taylor H.

    Neural interfaces have been heavily investigated due to their unique ability to tap into the communication system of the body. Substrates compatible with microelectronics processing are planar and 5-7 orders of magnitude stiffer than the tissue with which they interact. This work enables fabrication of devices by photolithography that are stiff enough to penetrate soft tissue, change in stiffness to more closely match the modulus of tissue after implantation and adopt shapes to conform to tissue. Several classes of physiologically-responsive, amorphous polymer networks with the onset of the glass transition above 37 °C are synthesized and thermomechanically characterized. These glassy networks exhibit an isothermal reduction in modulus due to plasticization in the presence of aqueous fluids. Modulus after plasticization can be tuned by the dry glass transition temperature, degree of plasticization and crosslink density. Acrylic shape memory polymer based intracortical probes, which can change in modulus from above 1 GPa to less than 1 MPa, are fabricated through a transfer process that shields the substrate from processing and enhances adhesion to the microelectronics. Substrates capable of withstanding the conditions of photolithography are fabricated "thiol-ene" and "thiol-epoxy" substrates. These materials provide processing windows that rival engineering thermoplastics, swell less than 6% in water, and exhibit a controllable reduction in modulus from above 1 GPa to between 5 and 150 MPa. Substrates, planar for processing, that subsequently recover 3D shapes are synthesized by the formation of post-gelation crosslinks either covalent or supramolecular in nature. Acrylics with varied supramolecular, based on ureidopyrimidone moieties, and covalent crosslink density demonstrate triple-shape memory behavior. Post-gelation covalent crosslinks are established to permanently fix 3D shapes in thiol-ene networks. Devices fabricated include intracortical and nerve cuff electrodes. Neuronal viability and device performance suggest these materials may be suitable for the design of chronically-viable neural interfaces.

  6. Alzheimer's disease pathogenesis and therapeutic interventions.

    PubMed

    Parihar, M S; Hemnani, Taruna

    2004-06-01

    Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system associated with progressive cognitive and memory loss. Molecular hallmarks of the disease are characterized by extracellular deposition of the amyloid beta peptide (Abeta) in senile plaques, the appearance of intracellular neurofibrillary tangles (NFT), cholinergic deficit, extensive neuronal loss and synaptic changes in the cerebral cortex and hippocampus and other areas of brain essential for cognitive and memory functions. Abeta deposition causes neuronal death via a number of possible mechanisms including oxidative stress, excitotoxicity, energy depletion, inflammation and apoptosis. Despite their multifactorial etiopathogenesis, genetics plays a primary role in progression of disease. To date genetic studies have revealed four genes that may be linked to autosomal dominant or familial early onset AD (FAD). These four genes include: amyloid precursor protein (APP), presenilin 1 (PS1), presenilin 2 (PS2) and apolipoprotein E (ApoE). Plaques are formed mostly from the deposition of Abeta, a peptide derived from APP. The main factors responsible for Abeta formation are mutation of APP or PS1 and PS2 genes or ApoE gene. All mutations associated with APP and PS proteins can lead to an increase in the production of Abeta peptides, specifically the more amyloidogenic form, Abeta42. In addition to genetic influences on amyloid plaque and intracellular tangle formation, environmental factors (e.g., cytokines, neurotoxins, etc.) may also play important role in the development and progression of AD. A direct understanding of the molecular mechanism of protein aggregation and its effects on neuronal cell death could open new therapeutic approaches. Some of the therapeutic approaches that have progressed to the clinical arena are the use of acetylcholinesterase inhibitors, nerve growth factors, nonsteroidal inflammatory drugs, estrogen and the compounds such as antioxidants, neuronal calcium channel blockers or antiapoptotic agents. Inhibition of secretase activity and blocking the formation of beta-amyloid oligomers and fibrils which may inhibit fibrilization and fibrilization-dependent neurotoxicity are the most promising therapeutic strategy against the accumulation of beta-amyloid fibrils associated with AD. Furthermore, development of immunotherapy could be an evolving promising therapeutic approach for the treatment of AD. PMID:15177383

  7. Memory Golf Clubs

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Memory Corporation's investigation of shape memory effect, stemming from Marshall Space Flight Center contracts to study materials for the space station, has aided in the development of Zeemet, a proprietary, high-damping shape memory alloy for the golf industry. The Nicklaus Golf Company has created a new line of golf clubs using Zeemet inserts. Its superelastic and high damping attributes translate into more spin on the ball, greater control, and a solid feel.

  8. Myrmics Memory Allocator

    Energy Science and Technology Software Center (ESTSC)

    2011-09-23

    MMA is a stand-alone memory management system for MPI clusters. It implements a shared Partitioned Global Address Space, where multiple MPI processes request objects from the allocator and the latter provides them with system-wide unique memory addresses for each object. It provides applications with an intuitive way of managing the memory system in a unified way, thus enabling easier writing of irregular application code.

  9. Sparse distributed memory

    SciTech Connect

    Kanerva, P.

    1988-01-01

    Theoretical models of the human brain and proposed neural-network computers are developed analytically. Chapters are devoted to the mathematical foundations, background material from computer science, the theory of idealized neurons, neurons as address decoders, and the search of memory for the best match. Consideration is given to sparse memory, distributed storage, the storage and retrieval of sequences, the construction of distributed memory, and the organization of an autonomous learning system. 63 refs.

  10. Memory Load and Dump

    NASA Astrophysics Data System (ADS)

    Welty, Alan

    2009-07-01

    This proposal is a test and verification of the STIS dump of memory capability.Areas of Control Section {CS} to dump include: EDAC RAM, EEPROM, and CS PROM {with the CS in Operate}. Areas of MIE memory to dump include: MIE RAM and MIE PROM {with the MIE in Operate}. Note that the MIE memory must first be copied to CS buffer RAM as images, which are then dumped.Supports Activity STIS-02

  11. Sparse distributed memory

    NASA Technical Reports Server (NTRS)

    Kanerva, Pentti

    1988-01-01

    Theoretical models of the human brain and proposed neural-network computers are developed analytically. Chapters are devoted to the mathematical foundations, background material from computer science, the theory of idealized neurons, neurons as address decoders, and the search of memory for the best match. Consideration is given to sparse memory, distributed storage, the storage and retrieval of sequences, the construction of distributed memory, and the organization of an autonomous learning system.

  12. The future of memory

    NASA Astrophysics Data System (ADS)

    Marinella, M.

    In the not too distant future, the traditional memory and storage hierarchy of may be replaced by a single Storage Class Memory (SCM) device integrated on or near the logic processor. Traditional magnetic hard drives, NAND flash, DRAM, and higher level caches (L2 and up) will be replaced with a single high performance memory device. The Storage Class Memory paradigm will require high speed (< 100 ns read/write), excellent endurance (> 1012), nonvolatility (retention > 10 years), and low switching energies (< 10 pJ per switch). The International Technology Roadmap for Semiconductors (ITRS) has recently evaluated several potential candidates SCM technologies, including Resistive (or Redox) RAM, Spin Torque Transfer RAM (STT-MRAM), and phase change memory (PCM). All of these devices show potential well beyond that of current flash technologies and research efforts are underway to improve the endurance, write speeds, and scalabilities to be on-par with DRAM. This progress has interesting implications for space electronics: each of these emerging device technologies show excellent resistance to the types of radiation typically found in space applications. Commercially developed, high density storage class memory-based systems may include a memory that is physically radiation hard, and suitable for space applications without major shielding efforts. This paper reviews the Storage Class Memory concept, emerging memory devices, and possible applicability to radiation hardened electronics for space.

  13. Retrieval of Emotional Memories

    PubMed Central

    Buchanan, Tony W.

    2008-01-01

    Long-term memories are influenced by the emotion experienced during learning as well as by the emotion experienced during memory retrieval. The present article reviews the literature addressing the effects of emotion on retrieval, focusing on the cognitive and neurological mechanisms that have been revealed. The reviewed research suggests that the amygdala, in combination with the hippocampus and prefrontal cortex, plays an important role in the retrieval of memories for emotional events. The neural regions necessary for online emotional processing also influence emotional memory retrieval, perhaps through the reexperience of emotion during the retrieval process. PMID:17723029

  14. Sparse distributed memory overview

    NASA Technical Reports Server (NTRS)

    Raugh, Mike

    1990-01-01

    The Sparse Distributed Memory (SDM) project is investigating the theory and applications of massively parallel computing architecture, called sparse distributed memory, that will support the storage and retrieval of sensory and motor patterns characteristic of autonomous systems. The immediate objectives of the project are centered in studies of the memory itself and in the use of the memory to solve problems in speech, vision, and robotics. Investigation of methods for encoding sensory data is an important part of the research. Examples of NASA missions that may benefit from this work are Space Station, planetary rovers, and solar exploration. Sparse distributed memory offers promising technology for systems that must learn through experience and be capable of adapting to new circumstances, and for operating any large complex system requiring automatic monitoring and control. Sparse distributed memory is a massively parallel architecture motivated by efforts to understand how the human brain works. Sparse distributed memory is an associative memory, able to retrieve information from cues that only partially match patterns stored in the memory. It is able to store long temporal sequences derived from the behavior of a complex system, such as progressive records of the system's sensory data and correlated records of the system's motor controls.

  15. Anion exchange polymer electrolytes

    DOEpatents

    Kim, Yu Seung; Kim, Dae Sik

    2015-06-02

    Anion exchange polymer electrolytes that include guanidinium functionalized polymers may be used as membranes and binders for electrocatalysts in preparation of anodes for electrochemical cells such as solid alkaline fuel cells.

  16. Polymer composites containing nanotubes

    NASA Technical Reports Server (NTRS)

    Bley, Richard A. (Inventor)

    2008-01-01

    The present invention relates to polymer composite materials containing carbon nanotubes, particularly to those containing singled-walled nanotubes. The invention provides a polymer composite comprising one or more base polymers, one or more functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers and carbon nanotubes. The invention also relates to functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers, particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having side chain functionalization, and more particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having olefin side chains and alkyl epoxy side chains. The invention further relates to methods of making polymer composites comprising carbon nanotubes.

  17. Mechanical Properties of Polymers.

    ERIC Educational Resources Information Center

    Aklonis, J. J.

    1981-01-01

    Mechanical properties (stress-strain relationships) of polymers are reviewed, taking into account both time and temperature factors. Topics include modulus-temperature behavior of polymers, time dependence, time-temperature correspondence, and mechanical models. (JN)

  18. Introduction to Polymer Chemistry.

    ERIC Educational Resources Information Center

    Harris, Frank W.

    1981-01-01

    Reviews the physical and chemical properties of polymers and the two major methods of polymer synthesis: addition (chain, chain-growth, or chain-reaction), and condensation (step-growth or step-reaction) polymerization. (JN)

  19. Polymer Fluid Dynamics.

    ERIC Educational Resources Information Center

    Bird, R. Byron

    1980-01-01

    Problems in polymer fluid dynamics are described, including development of constitutive equations, rheometry, kinetic theory, flow visualization, heat transfer studies, flows with phase change, two-phase flow, polymer unit operations, and drag reduction. (JN)

  20. Playing with Polymers.

    ERIC Educational Resources Information Center

    Chemecology, 1997

    1997-01-01

    Presents an activity that enables students to gain a better understanding of the importance of polymers. Students perform an experiment in which polymer chains of polyvinyl acetate form crosslinks. Includes background information and discussion questions. (DDR)