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1

Shape Memory Polymer Therapeutic Devices for Stroke  

SciTech Connect

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(usually optically) to take on an expanded conformation, and then used to dislodge and grip the thrombus while it is withdrawn through the catheter.

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

2005-10-11

2

Shape memory polymer nanocomposites  

Microsoft Academic Search

The paper describes the fabrication and characterization of composites with a shape memory polymer matrix and SiC nanoparticulate reinforcements. Composites based on a SMP matrix are active materials capable of recovering relatively large mechanical strains due to the application of heat. The composites were synthesized from a commercial shape memory polymer resin system and particulate SiC with an average diameter

Ken Gall; Martin L. Dunn; Yiping Liu; Dudley Finch; Mark Lake; Naseem A. Munshi

2002-01-01

3

Shape-Memory Polymers  

Microsoft Academic Search

Material scientists predict a prominent role in the future for self-repairing and intelligent materials. Throughout the last few years, this concept has found growing interest as a result of the rise of a new class of polymers. These so- called shape-memory polymers by far surpass well-known metallic shape- memory alloys in their shape-memory properties. As a consequence of the relatively

Andreas Lendlein; Steffen Kelch

2002-01-01

4

Polymer-Based Therapeutics  

PubMed Central

Polymeric materials have been applied in therapeutic applications, such as drug delivery and tissue regeneration, for decades owing to their biocompatibility and suitable mechanical properties. In addition, select polymer–drug conjugates have been used as bioactive pharmaceuticals owing to their increased drug efficacy, solubility, and target specificity compared with small-molecule drugs. Increased synthetic control of polymer properties has permitted the production of polymer assemblies for the targeted and controlled delivery of drugs, and polymeric sequestrants take advantage of their lack of solubility for the sequestration of target molecules in vivo. In more recent studies reviewed in greater detail here, the properties of polymers that distinguish them from small-molecule drugs, such as their high molecular weight and their ability to display multiple pendant moieties, have been specifically exploited for activating cellular targets or inhibiting the binding of pathogens. The elucidation of relevant structure–function relationships in investigations of this kind has relied on the combination of living polymerization methods with chemical conjugation methods, and protein engineering methods have shown increasing potential in the manipulation of architectural features of such polymer therapeutics. Garnering a detailed understanding of the various mechanisms by which multivalent polymers engage biological targets is certain to expand the role of polymers as therapeutics, by enabling highly specific activities of designed polymers in the biological environment.

Liu, Shuang; Maheshwari, Ronak; Kiick, Kristi L.

2009-01-01

5

Bioactive and Therapeutic ROMP Polymers  

Microsoft Academic Search

This review summarizes the developments in the area of ROMP?based polymer carriers as well as side?chain and main?chain polymer therapeutics during the period of 1993–2007. The promising emergence of ROMP?derived amphiphilic block copolymers containing therapeutic agents, their assembly into polymer nanoparticles, together with their modification for the targeting group attachment is outlined. Recent application of ROMP?based side?chain polymer therapeutics as

DeeDee Smith; Emily B. Pentzer; SonBinh T. Nguyen

2007-01-01

6

Porous Shape Memory Polymers.  

PubMed

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

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

2013-02-01

7

Surface shape memory in polymers  

NASA Astrophysics Data System (ADS)

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.

Mather, Patrick

2012-02-01

8

The dawning era of polymer therapeutics  

Microsoft Academic Search

As we enter the twenty-first century, research at the interface of polymer chemistry and the biomedical sciences has given rise to the first nano-sized (5–100 nm) polymer-based pharmaceuticals, the 'polymer therapeutics'. Polymer therapeutics include rationally designed macromolecular drugs, polymer–drug and polymer–protein conjugates, polymeric micelles containing covalently bound drug, and polyplexes for DNA delivery. The successful clinical application of polymer–protein conjugates,

Ruth Duncan

2003-01-01

9

TARGETING POLYMER THERAPEUTICS TO BONE  

PubMed Central

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.

Low, Stewart; Kopecek, Jindrich

2012-01-01

10

Thermomechanics of shape memory polymer nanocomposites  

Microsoft Academic Search

Shape memory polymers (SMPs) have the capacity to recover large strains when pre-deformed at an elevated temperature, cooled to a lower temperature, and reheated. The thermomechanical behavior of SMPs can be tailored by modifying the molecular structure of the polymer, or by using the polymer as a matrix for multiphase composites. Here we study the thermomechanics of a SMP polymer

Yiping Liu; Ken Gall; Martin L Dunn; Patrick McCluskey

2004-01-01

11

Reusable shape memory polymer mandrels  

NASA Astrophysics Data System (ADS)

Cornerstone Research Group, Inc. (CRG) has recently demonstrated the feasibility of filament winding complex compound-curved composite shapes on shape memory polymer (SMP) mandrels. Under thermal stimuli, SMPs can exhibit a radical change from a rigid polymer to a flexible, elastic state, and then back to a rigid state again. SMP tubes were fabricated using CRG's Veriflex, a thermoset SMP resin system. The SMP tubes were raised above the transition temperature, the temperature at which the SMP becomes pliable and rubber-like and inflated inside a clamshell master metal mold with a cavity in the shape of the desired mandrel. The SMP was then cooled; the lowering of the temperature allows the SMP to become a rigid structure again, resulting in an exact replica of the cavity without the need of air pressure. A composite part was filament wound onto the SMP mandrel and after curing of the composite, the SMP mandrel is again raised above the transition temperature. This allows the mandrel to return to its memory shape for easy extraction. This paper will demonstrate and discuss the feasibility of SMP mandrels for filament winding and fiber placement composite manufacturing techniques allowing for quick, easy, and low cost mandrels that are dimensionally accurate, autoclave-tolerant, rapidly removable, and reusable .

Everhart, Matthew C.; Stahl, Jaime

2005-05-01

12

Cationic polymers and their therapeutic potential.  

PubMed

The last decade has witnessed enormous research focused on cationic polymers. Cationic polymers are the subject of intense research as non-viral gene delivery systems, due to their flexible properties, facile synthesis, robustness and proven gene delivery efficiency. Here, we review the most recent scientific advances in cationic polymers and their derivatives not only for gene delivery purposes but also for various alternative therapeutic applications. An overview of the synthesis and preparation of cationic polymers is provided along with their inherent bioactive and intrinsic therapeutic potential. In addition, cationic polymer based biomedical materials are covered. Major progress in the fields of drug and gene delivery as well as tissue engineering applications is summarized in the present review. PMID:22885409

Samal, Sangram Keshari; Dash, Mamoni; Van Vlierberghe, Sandra; Kaplan, David L; Chiellini, Emo; van Blitterswijk, Clemens; Moroni, Lorenzo; Dubruel, Peter

2012-08-10

13

Thermomechanical Property of Epoxy Shape Memory Polymers  

NASA Astrophysics Data System (ADS)

Epoxy shape memory polymers (SMPs) were preparation and their mechanical properties are focused on. Full shape recovery is observed at 150 °C for each polymer, and the SMP with lower hardener content shows a quicker shape recovery speed. In addition to a good thermal stability, glass transition temperature of the polymers increases with increasing hardener content. Of particular attention of DMA test is that the epoxy SMPs show a high storage modulus not only in glass state but also in rubber state. The tension test indicates that both stress at break and corresponding elastic modulus vary with a peak value for the polymers.

Wu, Xuelian; Zheng, Hui; Liu, Yanju; Leng, Jinsong

14

Medical applications of shape memory polymers.  

PubMed

Shape memory polymers (SMP) are lightweight, have a high strain/shape recovery ability, are easy to process, and required properties can be tailored for variety of applications. Recently a number of medical applications have been considered and investigated, especially for polyurethane-based SMP. SMP materials were found to be biocompatible, non-toxic and non-mutagenic. The glass transition temperature (T(g)) can be tailored for shape restoration/self-deployment of clinical devices when inserted in the human body. Newly developed SMP foams, together with cold hibernated elastic memory (CHEM) processing, further broaden their potential biomedical applications. Polyurethane-based SMP are described here and major advantages are identified over other medical materials. Some SMP applications are already used in a clinical setting, whereas others are still in development. Lately, several important applications are being considered for CHEM foams as self-deployable vascular and coronary devices. One example is the endovascular treatment of aneurysms. PMID:18458416

Sokolowski, Witold; Metcalfe, Annick; Hayashi, Shunichi; Yahia, L'Hocine; Raymond, Jean

2007-03-02

15

Porous inorganic--organic shape memory polymers  

PubMed Central

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(?-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.

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

2012-01-01

16

Photopolymerized Thiol-Ene Systems as Shape Memory Polymers  

PubMed Central

In this study we introduce the use of thiol-ene photopolymers as shape memory polymer systems. The thiol-ene polymer networks are compared to a commonly utilized acrylic shape memory polymer and shown to have significantly improved properties for two different thiol-ene based polymer formulations. Using thermomechanical and mechanical analysis, we demonstrate that thiol-ene based shape memory polymer systems have comparable thermomechanical properties while also exhibiting a number of advantageous properties due to the thiol-ene polymerization mechanism which results in the formation of a homogenous polymer network with low shrinkage stress and negligible oxygen inhibition. The resulting thiol-ene shape memory polymer systems are tough and flexible as compared to the acrylic counterparts. The polymers evaluated in this study were engineered to have a glass transition temperature between 30 and 40 °C, exhibited free strain recovery of greater than 96% and constrained stress recovery of 100%. The thiol-ene polymers exhibited excellent shape fixity and a rapid and distinct shape memory actuation response.

Nair, Devatha P.; Cramer, Neil B.; Scott, Timothy F.; Bowman, Christopher N.; Shandas, Robin

2010-01-01

17

Shape Memory Polymers for Active Cell Culture  

PubMed Central

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 heat1-5. In a typical shape memory cycle, the SMP is first deformed at an elevated temperature that is higher than its transition temperature, Ttrans [either the melting temperature (Tm) or the glass transition temperature (Tg)]. 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 Ttrans 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 Ttrans 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 environment6. 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 forces7-14. 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.

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

2011-01-01

18

Shape memory polymers for active cell culture.  

PubMed

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

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

2011-07-04

19

Water-responsive programmable shape memory polymer devices  

Microsoft Academic Search

Shape memory polymers (SMPs) have a number of advantages as compared with their metal counterpart, namely shape memory alloys (SMAs), in particular for some particular medical applications. The recent finding of the influence of moisture on the glass transition temperature of polyurethane SMPs, which are typically thermo-responsive in nature, enable us to realize not only the water driven feature for

W. M. Huang; B. Yang; N. Liu; S. J. Phee

2007-01-01

20

Shape memory polymer (SMP) actuation technology  

NASA Astrophysics Data System (ADS)

Cornerstone Research Group Inc. (CRG) is developing low-cost, lightweight, shape memory polymer (SMP) actuators for use in the deployment of rigid aeroshells. The SMP actuator technology has been selected for use because of its ability to store energy, within a very small volume, and release that energy on demand with little requirement for power. During the Phase I SBIR effort, CRG demonstrated the feasibility of using a thermally activated SMP actuator for the deployment of a subscale, rigid, deployable aeroshell. The follow-on Phase II effort improved upon the Phase I actuator technology through the application of finite element analysis and testing. This work resulted in the fabrication of a full-scale actuator (0.127m long, 0.102m diameter) that was able to develop more than 40 ft-lb of torque during actuation. A conformal cartridge heater (CCH) was developed in parallel to solve the problem of efficiently transferring heat stimulus into the SMP materials. The CCH maintains surface contact with the walls of the SMP actuator throughout the actuator's range of motion to optimize the heat transfer between the heating surface and the SMP material surface. The SMP actuator also has the potential of moving or deploying mechanisms simply through environmental stimulus. Since CRG is able to custom tailor the material properties of the SMP, broad application of this technology is possible.

Auffinger, Frank; Fisher, Michael; Maddux, Michael

2010-03-01

21

Revealing triple-shape memory effect by polymer bilayers.  

PubMed

Bilayer polymers that consist of two epoxy dual-shape memory polymers of well-separated glass transition temperatures have been synthesized. These bilayer epoxy samples exhibit a triple-shape memory effect (TSME) with shape fixities tailorable by changing the ratio between the two layers. The triple-shape fixities of the bilayer epoxy polymers can be explained by the balance of stress between the two layers. Based on this work, it is believed that the following three molecular design criterions should be considered in designing triple-shape memory polymers with optimum TSME: 1) well-separated thermal transitions, 2) a strong interface, and 3) an appropriate balance of moduli and relative ratios between the layers (or microphases). PMID:21638460

Xie, Tao; Xiao, Xingcheng; Cheng, Yang-Tse

2009-08-04

22

Poly(2-oxazoline)s as Polymer Therapeutics  

PubMed Central

Poly(2-oxazoline)s (POx) are currently discussed as an upcoming platform for biomaterials design and especially for polymer therapeutics. POx meets several requirements needed for the development of next-generation polymer therapeutics such as biocompatibility, high modulation of solubility, variation of size, architecture as well as chemical functionality. Although in the early 1990s first and promising POx-based systems were presented but the field lay dormant for almost two decades. Only very recently, POx based polymer therapeutics came back into the focus of very intensive research. In this review, we give an overview on the chemistry and physicochemical properties of POx and summarize the research of POx-protein conjugates, POx-drug conjugates, POx-based polyplexes and POx micelles for drug delivery.

Luxenhofer, Robert; Han, Yingchao; Schulz, Anita; Tong, Jing; He, Zhijian; Kabanov, Alexander V.; Jordan, Rainer

2013-01-01

23

Shape memory polymer foams for endovascular therapies  

DOEpatents

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.

Wilson, Thomas S. (Castro Valley, CA); Maitland, Duncan J. (Pleasant Hill, CA)

2012-03-13

24

Shape memory polymer foams for endovascular therapies  

Microsoft Academic Search

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.

Thomas S. Wilson; Duncan J. Maitland

2012-01-01

25

Shape memory properties of ionic polymer-metal composites  

NASA Astrophysics Data System (ADS)

The shape memory properties of hydrated Nafion ionic polymer-metal composite (IPMC) actuators under combined thermal cycling and electrical shape fixing are presented and experimentally demonstrated. By exploiting these new properties the utility of such ionic actuators can be greatly enhanced to include bistability, multi-modal operation and increased actuation range. Shape memory effects were shown when the IPMC was deformed during programming by either an external force or by voltage-induced actuation. Comparison is made to the shape memory effects in hydrated raw Nafion membrane. It was observed that shape memory effects undergo slow decay, with different programming methods and subsequent electrical excitation exhibiting different decay profiles.

Rossiter, Jonathan; Takashima, Kazuto; Mukai, Toshiharu

2012-11-01

26

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

PubMed

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

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

2009-05-24

27

Recent Development in Polymer Ferroelectric Field Effect Transistor Memory  

Microsoft Academic Search

The article presents the recent research development in polymer ferroelectric non-volatile memory. A brief overview is given of the history of ferroelectric memory and device architectures based on inorganic ferroelectric materials. Particular emphasis is made on device elements such as metal\\/ferroelectric\\/metal type capacitor, metal- ferroelectric-insulator-semiconductor (MFIS) and ferroelectric field effect transistor (FeFET) with ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymers

Youn Jung Park; Hee June Jeong; Jiyoun Chang; Seok Ju Kang

2008-01-01

28

Guided Delivery of Polymer Therapeutics Using Plasmonic Photothermal Therapy.  

PubMed

In most drug delivery systems the clinician does not have control over the location of drug delivery after the therapeutic has been administered. As the location of the tumor mass is often known in many patients, a therapy system which enables the clinician to play an active role in nanomedicine localization would provide an advantage. Here, we show a new approach wherein a laser can be used to tag tumor tissue and enhance the delivery of targeted polymer therapeutics. Plasmonic gold nanorods are delivered to the cancerous tissue and heated by a laser to promote a targetable, hyperthermic response. Concurrent administration of a heat shock targeted polymer therapeutic thereby enhances site specific delivery. PMID:22737178

Gormley, Adam J; Larson, Nate; Sadekar, Shraddha; Robinson, Ryan; Ray, Abhijit; Ghandehari, Hamidreza

2012-05-24

29

Administration, distribution, metabolism and elimination of polymer therapeutics.  

PubMed

Polymer conjugation is an efficient approach to improve the delivery of drugs and biological agents, both by protecting the body from the drug (by improving biodistribution and reducing toxicity) and by protecting the drug from the body (by preventing degradation and enhancing cellular uptake). This review discusses the journey that polymer therapeutics make through the body, following the ADME (absorption, distribution, metabolism, excretion) concept. The biological factors and delivery system parameters that influence each stage of the process will be described, with examples illustrating the different solutions to the challenges of drug delivery systems in vivo. PMID:22286005

Markovsky, Ela; Baabur-Cohen, Hemda; Eldar-Boock, Anat; Omer, Liora; Tiram, Galia; Ferber, Shiran; Ofek, Paula; Polyak, Dina; Scomparin, Anna; Satchi-Fainaro, Ronit

2011-12-29

30

Biodegradable, Elastic Shape-Memory Polymers for Potential Biomedical Applications  

Microsoft Academic Search

The introduction of biodegradable implant materials as well as minimally invasive surgical procedures in medicine has substantially improved health care within the past few decades. This report describes a group of degradable thermoplastic polymers that are able to change their shape after an increase in temperature. Their shape-memory capability enables bulky implants to be placed in the body through small

Andreas Lendlein; Robert Langer

2002-01-01

31

Preliminary investigations of active disassembly using shape memory polymers  

Microsoft Academic Search

This paper reports initial results in the application of shape memory polymer (SMP) technology to the active disassembly of electronic products. The smart material SMP of polyurethane (PU) composition was employed. Created for these experiments were novel SMP releasable fasteners, with which it is possible to effectively disassemble products at specific triggering temperatures at the end of their life (EoL).

J. D. Chiodo; E. H. Billett; D. J. Harrison

1999-01-01

32

Thermomechanics of shape memory polymers: Uniaxial experiments and constitutive modeling  

Microsoft Academic Search

Shape memory polymers (SMPs) can retain a temporary shape after pre-deformation at an elevated temperature and subsequent cooling to a lower temperature. When reheated, the original shape can be recovered. Relatively little work in the literature has addressed the constitutive modeling of the unique thermomechanical coupling in SMPs. Constitutive models are critical for predicting the deformation and recovery of SMPs

Yiping Liu; Ken Gall; Martin L. Dunn; Alan R. Greenberg; Julie Diani

2006-01-01

33

Polymer Therapeutics for Cancer: Current Status and Future Challenges  

Microsoft Academic Search

Drug delivery systems for cancer therapeutics have revolutionized medicine. Delivery systems\\u000a have improved the efficacy and reduced the toxicity of current therapies and resulted in the development\\u000a of new ones. Today, millions of cancer patients have directly benefited from drug delivery systems,\\u000a and polymers have been at the frontline of these technological advances. Targeted delivery systems\\u000a of chemotherapeutics to the

Ronit Satchi-Fainaro; Ruth Duncan; Carmen Barnes

34

Responsive polymer systems for controlled delivery of therapeutics.  

PubMed

The ideal drug-delivery system should provide therapeutics in response to physiological requirements, having the capacity to 'sense' changes and alter the drug-release process accordingly. Such responsive controlled delivery systems are still at an experimental stage. This review focuses on two basic approaches: (1) externally regulated systems (utilizing triggers such as magnetism, ultrasound, temperature and electricity), and (2) self-regulated systems (utilizing pH-sensitive polymers, enzyme-substrate reactions, competitive binding, and antibody interactions). PMID:1368098

Kost, J; Langer, R

1992-04-01

35

Memory Focused Interventions (MFI) as a Therapeutic Strategy in Hypnotic Psychotherapy  

Microsoft Academic Search

The prospect of utilizing memory plasticity (the constructive and transitory nature of memory) for therapeutic purposes has not been widely recognized. However, a number of theoretical and clinical venues throughout the last century have shown its potential application. Intensive research conducted during these last decades, pointed out the possibility of influencing human memory in relation to new memories and their

Joseph Meyerson

2010-01-01

36

Modeling mechanical behavior of epoxy-shape memory polymers  

NASA Astrophysics Data System (ADS)

Smart materials and structures is an international frontier field in current development of engineering and science. Representative of soft smart materials include Electroactive polymers (EAPs) and Shape Memory Polymers (SMPs), etc..As a new kind of smart deformation material, SMPs have a wide range of applications in the field of smart material and structures due to their controllable shape memory effects. Deformation mechanism of SMP material is the basis of its applications. This paper proposed an useful thermoviscoelastic constitutive model by considering thermal expansion, structure relaxation and viscoelastic properties of Epoxy-SMP material. To verify the applicability of the model, various experiments such as isothermal uniaxial tensile tests were carried out and then be simulated. The results showed that the constitutive model could nicely predict mechanical behavior of Epoxy-SMP, the proposed constitutive model is useful for the design of SMPs structures.

Chen, Jianguo; Liu, Liwu; Fei, Fan; Wang, Yixing; Liu, Yanju; Leng, Jinsong

2013-04-01

37

Internal stress storage in shape memory polymer nanocomposites  

Microsoft Academic Search

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 25 °C, and subsequent shape recovery induced by heating to 120 °C. Under 50% compression

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

2004-01-01

38

Shape memory polymer snap-fits for active disassembly  

Microsoft Academic Search

This paper explores a means to simplify disassembly by engineering a snap-fit that automatically releases upon exposure to a heat field thus limiting manual labor or machine operation for disassembly. Shape memory polymer (SMP) snap-fits were designed and manufactured to actively release upon a thermal trigger. Snap-fits were designed with an added feature known here as a release angle that

John Carrell; Derrick Tate; Shiren Wang; Hong-Chao Zhang

2011-01-01

39

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

PubMed Central

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.

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

2009-01-01

40

Capacitance-voltage measurement in memory devices using ferroelectric polymer  

NASA Astrophysics Data System (ADS)

Application of thin polymer film as storing mean for non-volatile memory devices is investigated. Capacitance-voltage (C-V) measurement of metal-ferroelectric-metal device using ferroelectric copolymer P(VDF-TrFE) as dielectric layer shows stable 'butter-fly' curve. The two peaks in C-V measurement corresponding to the largest capacitance are coincidental at the coercive voltages that give rise to zero polarization in the polarization hysteresis measurement. By comparing data of C-V and P-E measurement, a correlation between two types of hysteresis is established in which it reveals simultaneous electrical processes occurring inside the device. These processes are caused by the response of irreversible and reversible polarization to the applied electric field that can be used to present a memory window. The memory effect of ferroelectric copolymer is further demonstrated for fabricating polymeric non-volatile memory devices using metal-ferroelectric-insulator-semiconductor structure (MFIS). By applying different sweeping voltages at the gate, bidirectional flat-band voltage shift is observed in the ferroelectric capacitor. The asymmetrical shift after negative sweeping is resulted from charge accumulation at the surface of Si substrate caused by the dipole direction in the polymer layer. The effect is reversed for positive voltage sweeping.

Nguyen, Chien A.; Lee, Pooi See

2006-12-01

41

Characterization and modeling of light activated shape memory polymer  

NASA Astrophysics Data System (ADS)

Shape memory polymers have recently become the focus of research for their unique ability to switch between two modulus states, allowing them to both recover from large amounts of strain as well as support complex loads. Part of this research involves engineering new formulas specifically designed for applications where traditional thermally activated SMPs are not ideal by tailoring the activation method used to transition the polymer. One such class of polymers is those that utilize optical energy at specific wavelengths to create and cleave crosslinks. It is the development of this new class of light activated shape memory polymers (LASMP) that is the focus of the presented work. Experimental methods are newly created for this novel class of active materials. Several candidate LASMP formulas are then subjected to this set of experiments characterizing their mechanical and optical properties. Experimentally observed variations among the formulae include virgin state modulus, percent change in modulus with stimulus, and in some instances inelastic response. To expedite the development of LASMP, a first principles multi-scale model based on the polymer's molecular structure is presented and used to predict the stress response of the candidate formulas. Rotational isomeric state (RIS) theory is used to build a molecular model of a phantom polymer chain. Assessment of the resulting conformation is then made via the Johnson family of statistical distributions and Boltzmann statistical thermodynamics. The ability of the presented model to predict material properties based on the molecular structure of the polymer reduces the time and resources required to test new candidate formulas of LASMP as well as aiding in the ability to tailor the polymer to specific application requirements. While the first principles model works well to identify promising formulas, it lacks precision. The stress contribution from the constraints on the polymer chain's junctions and neighboring chain entanglements is then added to that of the phantom network allowing Young's modulus to be calculated from the predicted stress response of the polymer. Simple extension, equi-biaxial, and shear strain states are modeled and associated predicted material properties presented. The added precision of this phenomenological extension will aid device design.

Beblo, Richard Vincent

42

Shape memory polymers based on uniform aliphatic urethane networks  

SciTech Connect

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.

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

43

High actuation properties of shape memory polymer composite actuator  

NASA Astrophysics Data System (ADS)

The shape memory polymers (SMPs) possess two shapes: permanent shape and temporary shape. This property leads to replacement of shape memory alloys by SMPs in various applications. In this work, two properties, namely structure activeness and the shape memory property of ‘controlled behavior composite material (CBCM)’ plate and its comparison with the conventional symmetrical composite plate (SYM), are studied. The SMPC plates (CBCM and SYM) are manufactured using epoxy resin with a thermal glass transition temperature (Tg) of 130?°C. The shape memory properties of these composites are investigated (under three-point bending test) and compared by deforming them to the same displacement. Three types of recoveries are conducted: unconstrained recovery, constrained recovery, and partial recovery under load. It is found that by coupling the structure activeness (due to its asymmetry) and its shape memory property, higher activated displacement is obtained during the unconstrained recovery. Also, at a lower recovery temperature (90?°C) than the fixing temperature, a recovery close to 100% is obtained for CBCM, whereas for SYM it is only 25%. During constrained recovery, CBCM produces five times larger recovery force than SYM. In addition, higher actuation properties are demonstrated by calculating recovered work and recovery percentages during partial recovery under load.

Basit, A.; L'Hostis, G.; Durand, B.

2013-02-01

44

Infrared laser-activated shape memory polymer  

NASA Astrophysics Data System (ADS)

This paper is concerned about the drive of shape memory styrene copolymer through an infrared optical fiber carrying infrared laser. The infrared laser was chosen to drive the SMP through the optical fiber embedded into the SMP. The working frequency of infrared laser was installed in 3-4?m, the working band of optical fiber was 1-6?m. An optical fiber was embedded into the SMP for delivery of 3-4?m laser light for activation. The surface of the optical fiber was etched by the aqueous solution of sodium-hydroxide in order to increase transmission efficiency of the optical fiber. We synthesized thermoset SMP based on styrene copolymer, and measured Tg of SMP is the 53.7oC by the DMA. The thermally activated SMP is possible to initiate an originally shape by a touchless and highly selective infrared laser stimulus. The infrared laser-activated SMP could be recovered its original shape by less temperature than Tg, it was proved this driving method of SMP is more effective than conventional external heaters. Therefore infrared laser-activated method was advantageous for using in the low temperature condition. The increase in temperature of SMP which was embedded treated optical fiber indicated that the infrared laser irradiated into the SMP from here and heated the SMP. The optical fiber was treated by the aqueous solution of sodium-hydroxide, transmission efficiency of the optical fiber increased, and the total contact area between SMP and the optical fiber. The infrared laser stimulation of SMP was interest for actuator systems as well as medical applications.

Zhang, Dawei; Liu, Yanju; Leng, Jinsong

2008-05-01

45

Conducting polymer memory devices based on dynamic doping.  

PubMed

Molecular electronic junctions consisting of a 20 nm thick layer of polypyrrole (PPy) and 10 nm of TiO2 between conducting layers of carbon and gold were investigated as potential nonvolatile memory devices. By making the polymer layer much thinner than conventional polymer electronic devices, it is possible to dynamically oxidize and reduce the polypyrrole layer by an applied bias. When the electrode in contact with the PPy is biased positive, oxidation of the PPy occurs to yield a conducting polaron state. The junctions exhibit a large increase in conductance in response to the positive bias, which is reversed by a subsequent negatively biased pulse. Switching between the conducting and nonconducting state can occur for pulses at least as short as 10 micros, and the conducting state persists after a positive bias pulse for at least 1 week. The read/write/read/erase cycle may be repeated for at least 1700 cycles, although with an error rate of approximately 3% due mainly to an incomplete "erase" step. The speed and retention of the PPy/TiO2 junctions are far superior to those of the analogous fluorene/TiO2 devices lacking the polymer, and the conductance changes are absent if SiO2 is substituted for TiO2. The observations are consistent with "dynamic doping" of the solid-state polymer layer, with the possible involvement of adventitious mobile ions. Although the speed of the current polymer/TiO2 junctions is slower than commercial dynamic random access memory, their retention is approximately 5 orders of magnitude longer. PMID:18646749

Barman, Sudip; Deng, Fengjun; McCreery, Richard L

2008-07-23

46

Shape memory polymer sensors for tracking cumulative environmental exposure  

NASA Astrophysics Data System (ADS)

Cornerstone Research Group Inc. (CRG) has developed environmental exposure tracking (EET) sensors using shape memory polymers (SMP) to monitor the degradation of perishable items, such as munitions, foods and beverages, or medicines, by measuring the cumulative exposure to temperature and moisture. SMPs are polymers whose qualities have been altered to give them dynamic shape "memory" properties. Under thermal or moisture stimuli, the SMP exhibits a radical change from a rigid thermoset to a highly flexible, elastomeric state. The dynamic response of the SMP can be tailored to match the degradation profile of the perishable item. SMP-based EET sensors require no digital memory or internal power supply and provide the capability of inexpensive, long-term life cycle monitoring of thermal and moisture exposure over time. This technology was developed through Phase I and Phase II SBIR efforts with the Navy. The emphasis of current research centers on transitioning SMP materials from the lab bench to a production environment. Here, CRG presents the commercialization progress of thermally-activated EET sensors, focusing on fabrication scale-up, process refinements, and quality control. In addition, progress on the development of vapor pressure-responsive SMP (VPR-SMP) will be discussed.

Snyder, Ryan; Rauscher, Michael; Vining, Ben; Havens, Ernie; Havens, Teresa; McFerran, Jace

2010-03-01

47

Memory focused interventions (MFI) as a therapeutic strategy in hypnotic psychotherapy.  

PubMed

The prospect of utilizing memory plasticity (the constructive and transitory nature of memory) for therapeutic purposes has not been widely recognized. However, a number of theoretical and clinical venues throughout the last century have shown its potential application. Intensive research conducted during these last decades, pointed out the possibility of influencing human memory in relation to new memories and their specific components. Moreover, the research showed the feasibility of planting alternative early childhood memories and thus altering memories of personal history. Additionally, researchers found that memory is naturally very fallible due to everyday phenomena of forgetfulness, distortion and intrusion of past and present information. Throughout the course of this paper, the integrative overview of these empirical findings with the aforementioned clinical and theoretical foundations serves as a substratum in an attempt to present an integrative therapeutic approach, named Memory Focused Interventions (MFI). PMID:20187338

Meyerson, Joseph

2010-01-01

48

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

NASA Astrophysics Data System (ADS)

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 ºC to 22 MPa and 22 ºC respectively. The same polymer networks can then attain glass transition temperatures that range from 5 ºC to 195 ºC 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 availab

Nair, Devatha P.

49

Phase transition of shape-memory effect in glassy shape-memory polymers  

NASA Astrophysics Data System (ADS)

Shape-memory materials (SMMs) are fascinating materials, with the potential for application as "smart materials" and also as actively moving materials, which can change their shape in a predefined way between/among shapes in presence of an appropriate stimulus. The intention of this article is to present a systematic and up-to-date account of chemoresponsive amorphous shape-memory polymers (SMPs) from basic principles in phase transition to experiments. Based on the previous work, phase transition of the chemo-responsive SMPs. of which the transition temperature is originated from the glass transition, is presented. Studies have been explored for chemo-responsive SMPs in various design principles in water/solvent induced shape-memory effect. Some examples, including are also presented.

Lu, Haibao

2013-04-01

50

High-temperature reusable shape memory polymer mandrels  

NASA Astrophysics Data System (ADS)

Cornerstone Research Group, Inc. (CRG) has demonstrated the feasibility of filament winding complex-curved composite shapes on shape memory polymer (SMP) mandrels. SMPs can exhibit a radical change from a rigid polymer to a flexible, elastic state, and then back to a rigid state under thermal stimuli. SMP mandrels for filament winding and fiber placement allow for a quick, easy, reusable, and low-cost mandrel system. CRG has recently improved the SMP mandrel technology by adding a high-strain fiber reinforcement (HSFR) that both raises the toughness of the SMP and allows the SMP to elongate up to 150 percent. The resulting material can produce mandrels durable enough to withstand multiple use in high production rate manufacturing. This paper will demonstrate and discuss the feasibility of HSFR-SMP mandrels for filament winding and fiber placement and recent developments in CRG's SMP mandrel technology, including the fabrication of larger parts.

Everhart, Matthew C.; Nickerson, David M.; Hreha, Richard D.

2006-04-01

51

Thermomechanical behavior of fiber reinforced shape memory polymer composite  

NASA Astrophysics Data System (ADS)

Carbon fiber fabric reinforced shape memory polymer composite (SMPC) is studied in this paper. The shape memory polymer (SMP) is a thermoset styrene-based resin. In order to discuss the basic thermomechanical properties of SMPC, the investigation is conducted with the following methods: dynamic mechanical analyzer (DMA), three-point bending test, shape recovery tests and scanning electron microscope (SEM). Results indicate that SMPC exhibits a higher glass transition temperature (Tg) and a higher storage modulus than pure SMP. SMPC shows high bending modulus before the glass transition in SMP, while exhibits low bending modulus within the range of glass transition in SMP. Moreover, shape recovery velocity and ratio rise remarkably with the increase of shape recovery temperature, while they increase in a weak trend with the increase of pre-deformation temperature. In addition, electrically conductive SMPC shows favorable recovery performances during the thermomechanical cycles. In the end, under the bending deformation, all the buckled fibers in inner surface break at the same time, which make it regular for the fracture section of buckled fiber tow. However, the cross sections of these buckled fibers are relatively rough and located in 45°C direction along fiber. By contrast, the tensile fibers in outer surface break unorderly, which make it irregular for the fracture section of tensile fiber tow. But the cross sections of these tensile fibers are relatively smooth and vertical to fiber.

Lan, Xin; Liu, Yanju; Leng, Jinsong; Du, Shanyi

2007-10-01

52

Variable stiffness property study on shape memory polymer composite tube  

NASA Astrophysics Data System (ADS)

As a typical smart material, shape memory polymers (SMPs) have the capability of variable stiffness in response to external stimuli, such as heat, electricity, magnetism and solvents. In this research, a shape memory polymer composite (SMPC) tube composed of multi-layered filament wound structures is investigated. The SMPC tube possesses considerable flexibility under high temperature and rigidity under low temperature. Significant changes in effective engineering modulus can be achieved through regulating the environment temperature. Based on the classical laminated-plate theory and Sun’s thick laminate analysis, a 3D theory method is used to study the effective engineering modulus and modulus ratio of the SMPC tube. The tensile test is conducted on the SMPC tube to verify the accuracy of the theoretical method. In addition, the effective engineering modulus and modulus ratio are discussed under different fiber-winding angles and fiber volume fractions of the SMPC tube. The presented analysis provides meaningful guidance to assist the design and manufacture of SMPC tubes in morphing skin applications.

Chen, Yijin; Sun, Jian; Liu, Yanju; Leng, Jinsong

2012-09-01

53

Dendronized polymers and surfaces: Strategies toward novel therapeutics and biomaterials  

Microsoft Academic Search

Combining linear polymers and dendrimers provides numerous advantages such as increased solubility, biodegradability and a large number of functionalizable peripheral moieties. In this work, novel carborane-containing dendronized polymers were designed as potential candidates for Boron Neutron Capture Therapy (BNCT). These polymers were successfully synthesized using two different approaches. The resulting carborane-functionalized polymers were dendronized using a divergent approach to introduce

Soumya Rahima Benhabbour

2008-01-01

54

Comparing techniques for drug loading of shape-memory polymer networks--effect on their functionalities.  

PubMed

A family of oligo[(epsilon-caprolactone)-co-glycolide]dimethacrylate (oCG-DMA) derived networks of different glycolide contents as well as precursor molecular weights has been synthesized by crosslinking oCG-DMA, providing matrices of different hydrophilicity, network density, and morphology at body temperature. Such networks were loaded with a hydrophilic model drug, ethacridine lactate, either before crosslinking or afterwards by swelling in drug solution. Disadvantageous alterations of the shape-memory functionality and degradation characteristics were observed only in few loaded materials. Loading by swelling generally resulted in low payloads, which slightly increased for more hydrophilic polymer networks, and a substantial burst and fast subsequent release for all investigated materials. Loading before crosslinking gave almost no burst and higher subsequent release rates over longer periods of time. Overall, depending on the needs of a specific application, a material from this polymer family with the desired mechanical properties, shape-memory functionality, and degradation pattern can be selected and combined with drugs when considering that (i) loading by swelling is best suited for applications that require high initial doses and (ii) loading before crosslinking allows easy variation of payloads and low burst release for therapeutics that are non-sensitive to chemical alterations during crosslinking. PMID:20542110

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

2010-06-11

55

Various shape memory effects of stimuli-responsive shape memory polymers  

NASA Astrophysics Data System (ADS)

One-step dual-shape memory polymers (SMPs) recover their original (permanent) shape upon small variation of environmental conditions such as temperature, electric field, light, magnetic field, and solvent/chemicals. For advanced applications such as aerospace and medical devices, complicated, multiple-step, spatially controllable, and two-way shape memory effects (SMEs) are required. In the past decade, researchers have devoted great effort to improve the versatility of the SME of SMPs to meet the needs of advanced applications. This paper is intended to review the up-to-date research endeavors on advanced SMEs. The problems facing the various SMPs are discussed. The challenges and opportunities for future research are discussed.

Meng, Harper; Mohamadian, Habib; Stubblefield, Michael; Jerro, Dwayne; Ibekwe, Samuel; Pang, Su-Seng; Li, Guoqiang

2013-09-01

56

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

SciTech Connect

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.

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

2008-10-29

57

Reconsidering therapeutic action: Loewald, cognitive neuroscience and the integration of memory's duality.  

PubMed

Both Loewald's relational theory of memory and the Self-Memory System (SMS) of cognitive neuroscience describe a dual memory system, one system that is experience-near sensory-perceptual, and the other, symbolic and conceptual. In contrast to perspectives that locate therapeutic action in either altering implicit procedural memories or interpreting explicit historical content, we argue that psychological health emerges from effective integration of both memory systems, achieved through a combination of transference dynamics and analytic insight. We support this position by elaborating four key assumptions of the loewaldian and SMS perspectives, followed by application to a clinical example. We highlight the power of certain integrative autobiographical memories called 'self-defining memories' in assisting an understanding of transference dynamics and providing metaphoric touchstones to guide subsequent treatment. PMID:22014365

Singer, Jefferson A; Conway, Martin A

2011-03-24

58

Anisotropic wrinkle formation on shape memory polymer substrates  

NASA Astrophysics Data System (ADS)

In this paper, we demonstrate an assisted self-assembly fabrication method for unidirectional patterns using pre-programmed shape memory polymer (SMP) as the substrate in an organic/inorganic bi-layer structure. By heating the hybrid structure above the SMP's shape recovery temperature, the substrate expands because of positive coefficients of thermal expansion in one direction, while in the perpendicular direction it shrinks due to shape memory effect overpowering thermal expansion. Consequently, the metal thin film coated on the substrate is subjected to an orthogonal compression-tension stress field and forms unidirectional wavy patterns. The experimentally obtained wrinkles are well-aligned with uniform wavelength ranging from about 930 nm to 5 ?m corresponding to various programming strains and film thicknesses. A parametric study was carried out to study the influence of programming strain and film thickness on wrinkle wavelength and amplitude. The results were compared with a finite deformation model and showed good agreement with theoretical predictions. A simple analytical model incorporating a progressive damage scheme and visco-elasticity is proposed to explain defect formation and post-buckling pattern evolution, respectively. The present study is expected to offer a convenient and simple path of fabricating large-scale unidirectional wavy patterns. A potential application to organic photovoltaics is discussed.

Chen, Zhongbi; Young Kim, Yun; Krishnaswamy, Sridhar

2012-12-01

59

Thermomechanical characterization of environmentally conditioned shape memory polymer using nanoindentation  

NASA Astrophysics Data System (ADS)

Shape memory polymers (SMPs) are an emerging class of active polymers that have dual-shape capability, and are therefore candidate materials for multifunctional reconfigurable structures (i.e., morphing structures). However, the SMPs have not been fully tested to work in relevant environments (variable activation temperature, fuel and water swell, UV radiation, etc.) required for Air Force missions. In this study, epoxy-based SMPs were conditioned separately in simulated service environments designed to be reflective of anticipated performance requirements, namely, (1) exposure to UV radiation for 125 cycles, (2) immersion in jet-oil at ambient temperature, (3) immersion in jet-oil at 49°C, and (4) immersion in water at 49°C. The novel high-temperature indentation method was used to evaluate the mechanical properties and shape recovery ability of the conditioned SMPs. Results show that environmentally conditioned SMPs exhibit higher moduli in comparison to an unconditioned one. During free recovery, the indentation impressions of all SMPs disappeared as temperature reached above Tg, indicating that the material's ability to regain shape remains relatively unchanged with conditioning.

Fulcher, J. T.; Lu, Y. C.; Tandon, G. P.; Foster, D. C.

2010-03-01

60

Polymer Therapeutics: Polymers as Drugs, Drug and Protein Conjugates and Gene Delivery Systems: Past, Present and Future Opportunities  

Microsoft Academic Search

As the 21st century begins we are witnessing a paradigm shift in medical practice. Whereas\\u000a the use of polymers in biomedical materials applications -- for example, as prostheses, medical devices,\\u000a contact lenses, dental materials and pharmaceutical excipients -- is long established, polymer-based\\u000a medicines have only recently entered routine clinical practice [1,\\u000a 2,3,4]. Importantly, many of the innovative polymer-based therapeutics\\u000a once dismissed as

Ruth Duncan; Helmut Ringsdorf; Ronit Satchi-Fainaro

61

Method for loading shape memory polymer gripper mechanisms  

DOEpatents

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.

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

62

Multifunctional smart material system (MSMS) using shape memory alloys and shape memory polymers  

NASA Astrophysics Data System (ADS)

A Multifunctional smart material system consists of two or more different smart material phases in the form of a hybrid system, in which every phase performs a different but necessary function. In this work, we show how thermally responsive Shape memory alloys (SMA) and Shape Memory Polymers (SMP) can be combined to form a Multifunctional Smart Material system (MSMS). The transformation temperatures Mf, Ms, As and Af of SMA and the glass transition Tg for the SMP play a critical role in designing such a MSMS. We illustrate how varying the Tg of SMP between the transformation temperatures Mf and Af of SMA results in a multi-state smart bias system with varying stiffnesses. In addition, we establish guidelines for the volume fractions of the individual constituents of such MSMSs to form "smart-bias" tools/devices. We further propose various ideas for smart devices that can operate through three temperature ranges, with one material constituent being passive and the other active at a given temperature.

Ghosh, Pritha; Rao, Ashwin; Srinivasa, A. R.

2012-03-01

63

Kinematic viscosity of therapeutic pulmonary surfactants with added polymers.  

PubMed

The addition of various polymers to pulmonary surfactants improves surface activity in experiments both in vitro and in vivo. Although the viscosity of surfactants has been investigated, the viscosity of surfactant polymer mixtures has not. In this study, we have measured the viscosities of Survanta and Infasurf with and without the addition of polyethylene glycol, dextran or hyaluronan. The measurements were carried out over a range of surfactant concentrations using two concentrations of polymers at two temperatures. Our results indicate that at lower surfactant concentrations, the addition of any polymers increased the viscosity. However, the addition of polyethylene glycol and dextran to surfactants at clinically used concentrations can substantially lower viscosity. Addition of hyaluronan at clinical surfactant concentrations slightly increased Infasurf viscosity and produced little change in Survanta viscosity. Effects of polymers on viscosity correlate with changes in size and distribution of surfactant aggregates and the apparent free volume of liquid as estimated by light microscopy. Aggregation of surfactant vesicles caused by polymers may therefore not only improve surface activity as previously shown, but may also affect viscosity in ways that could improve surfactant distribution in vivo. PMID:19366601

Lu, Karen W; Pérez-Gil, Jesús; Taeusch, H William

2009-03-01

64

Kinematic viscosity of therapeutic pulmonary surfactants with added polymers  

PubMed Central

The addition of various polymers to pulmonary surfactants improves surface activity in experiments both in vitro and in vivo. Although the viscosity of surfactants has been investigated, the viscosity of surfactant polymer mixtures has not. In this study, we have measured the viscosities of Survanta and Infasurf with and without the addition of polyethylene glycol, dextran or hyaluronan. The measurements were carried out over a range of surfactant concentrations using two concentrations of polymers at two temperatures. Our results indicate that at lower surfactant concentrations, the addition of any polymers increased the viscosity. However, the addition of polyethylene glycol and dextran to surfactants at clinically used concentrations can substantially lower viscosity. Addition of hyaluronan at clinical surfactant concentrations slightly increased Infasurf viscosity and produced little change in Survanta viscosity. Effects of polymers on viscosity correlate with changes in size and distribution of surfactant aggregates and the apparent free volume of liquid as estimated by light microscopy. Aggregation of surfactant vesicles caused by polymers may therefore not only improve surface activity as previously shown, but may also affect viscosity in ways that could improve surfactant distribution in vivo.

Lu, Karen W.; Perez-Gil, Jesus; Taeusch, H. William

2009-01-01

65

Light-triggered self-healing and shape-memory polymers.  

PubMed

In this review, we highlight the recent progress made in light-controlled self-healing and shape memory polymers. We analyse the materials design, underlying mechanisms and chemistries involved in the different methods developed for these two types of emerging photoresponsive materials. We show that these two seemingly different groups of functional materials are linked by a number of common approaches enabling their optical control, particularly the approaches based on the photothermal effect and photochemical reactions of photoswitching groups incorporated in polymer structures. Possible future developments and perspectives of using light as a unique trigger for polymer self-healing and shape-memory are also discussed. PMID:23440057

Habault, Damien; Zhang, Hongji; Zhao, Yue

2013-02-25

66

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

NASA Astrophysics Data System (ADS)

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%.

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

2012-03-01

67

Therapeutic efficacy of a systemically delivered oncolytic adenovirus - biodegradable polymer complex.  

PubMed

Despite great efforts to develop a more effective oncolytic adenovirus (Ad) for eradicating tumors, in vivo application via systemic administration is strictly limited to local injection due to host immune responses by Ad surface proteins and liver accumulation by the inherent nature of the Ad. In the last decade, numerous techniques using synthetic polymers have widely emerged to shield the exterior of therapeutic Ad vectors for systemic delivery. We developed a cationic polymer linked with polyethylene glycol for systemically delivering oncolytic Ad. The increased transduction efficiency and oncolytic effect of the Ad vectors physically coated with the polymer were evaluated, showing the optimal size (130 nm) of the Ad/polymer complex for systemic administration and prolonged stability of the Ad/polymer complex. Marked tumor growth suppression of the oncolytic Ad delivered by the polymer through systemic injection was observed in HT1080 and A549 xenograft models. The masking effect of the Ad surface by the polymer elicited evasion of innate adaptive immune responses and the tumor-to-liver ratio of the complex was significantly elevated 1229-fold greater than that of a naked Ad. These results demonstrate that the potential system of oncolytic Ad complexed with the biodegradable polymer may be useful for developing therapeutic vector systems via systemic delivery. PMID:23541109

Kim, Jaesung; Li, Yi; Kim, Sung Wan; Lee, Doo Sung; Yun, Chae-Ok

2013-03-27

68

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

PubMed

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

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

2008-04-01

69

The steric effect of aromatic pendant groups and electrical bistability in ?-stacked polymers for memory devices.  

PubMed

In order to investigate the steric effect of aromatic pendant groups and the electrical bistability in nonconjugated polymers potentially for memory device applications, two ?-stacked polymers with different steric structures are synthesized and characterized. They exhibit two conductivity states and can be switched from an initial low-conductivity (OFF) state to a high-conductivity (ON) state. Additionally, they demonstrate nonvolatile write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 10(4), and flash memory behavior with an ON/OFF current ratio of approximately 10(5). Both steady-state and time-resolved fluorescence spectroscopies are used to examine the conformational change of the polymers responding to an applied external electrical voltage. The results provide useful information on different steric effects of pendant groups in polymer chains, resulting in various electrical behaviors. The possibility in realizing an "erasable" behavior through breaking ?-stacked structures of pendant groups by a reversal of the electric field was also discussed on the basis of temperature-dependent fluorescence spectroscopy investigation. These results may thus offer a guideline for the design of practical polymer memory devices via tuning steric structure of ?-stacked polymers. PMID:22370967

Zhang, Bin; Chen, Yujie; Zhang, Yanfeng; Chen, Xudong; Chi, Zhenguo; Yang, Jin; Ou, Jiemei; Zhang, Ming Qiu; Li, Dehao; Wang, Dong; Liu, Mingkai; Zhou, Juying

2012-02-27

70

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

NASA Astrophysics Data System (ADS)

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.

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

2012-03-01

71

Thermally stable memory devices using graphene flakes sandwiched polymethyl methacrylate polymer layers  

NASA Astrophysics Data System (ADS)

Fabrication and characterization of graphene flakes sandwiched polymethyl methacrylate (PMMA) hybrid bistable devices (HBD) is reported in this paper. Graphene flakes (GFs) sandwiched polymer layers were prepared through a simple solution process. The fabricated memory devices have exhibited remarkable electrical bistable behavior even at 150°C. Bistable memory behavior of the fabricated devices have been described on the basis of current-voltage characteristics. Reasonably good ON/OFF current ratio (˜103) and retention property have been obtained from the constructed memory devices. The device showed excellent stability up to 105 switching cycles without any degradation both in ON and OFF states. The results obtained have indicated that the HBD fabricated by embedding graphene flakes in an insulating polymer matrix have potential applications in organic nonvolatile flash memory devices.

Valanarasu, S.; Kathalingam, A.; Senthilkumar, V.; Kannan, V.; Rhee, J. K.

2012-12-01

72

Constitutive modeling of shape memory polymer based self-healing syntactic foam  

Microsoft Academic Search

In a previous study, it was found that the shape memory functionality of a shape memory polymer based syntactic foam can be utilized to self-seal impact damage repeatedly, efficiently, and almost autonomously [Li G., John M., 2008. A self-healing smart syntactic foam under multiple impacts. Comp. Sci. Technol. 68(15–16), 3337–3343]. The purpose of this study is to develop a thermodynamics

We Xu; Guoqiang Li

2010-01-01

73

Multiscale Characterization of Water, Oil and UV-Conditioned Shape-Memory Polymer under Compression  

Microsoft Academic Search

\\u000a Shape memory polymers (SMPs) are an emerging class of active polymers that may be used for reconfigurable structures on air\\u000a vehicles. In this study, epoxy-based SMPs were conditioned separately in simulated service environments relevant to Air Force\\u000a missions, namely, (1) exposure to UV radiation, (2) immersion in jet-oil, and (3) immersion in water. The mechanical properties\\u000a and shape recovery abilities

J. T. Fulcher; H. E. Karaca; G. P. Tandon; D. C. Foster; Y. C. Lu

74

All organic memory devices utilizing fullerene molecules and insulating polymers  

NASA Astrophysics Data System (ADS)

The convergence of mobile technologies combined with stricter power requirements and increasing demands have strained the current memory technology. Newer technologies such as phase changing, ferroelectric, and magnetic random access memories are unsatisfactory in meeting the new requirements. We propose a new memory technology based on our initial discovery of charge storage in C60 molecules within poly (4-vinyl phenol) (PVP). To understand the memory potential, we created single-layer devices consisting of ˜30nm films of PVP+C60 sandwiched between aluminum (Al) electrodes. Current versus voltage (I-V) sweeps showed a significant hysteresis of 75nA, with distinguishable memory states. Room temperature charging of C60 was confirmed indirectly through capacitance versus voltage measurements and directly by monitoring the A1g characteristic peak of C60 during Raman measurements. We demonstrated memory operations by applying read-write-erase (RWE) pulses. The PVP+C60 devices exhibited memory retention for over 1 hour and response times of around 10ns. Characteristic hysteresis was demonstrated at the nanoscale. Conduction models were fitted at room temperature to the I-V curves. It was found that combination of direct and Fowler-Nordheim tunneling were the principle conduction mechanisms. For a more technologically viable memory device, we developed a multi-layer device structure, consisting of a polystyrene (PS) capping layer. The resulting asymmetrical I-V curve exhibited a hysteresis ratio of 103 . RWE cycles were measured with clearly distinguishable states. The memory retentions were measured over 2 hours and the response time around 10ns. The stability of the multi-layer devices was improved. I-V measurements at temperatures varying from 4.2 K to 298 K were performed to construct a theoretical model. The I-V curves were found to be temperature independent and exhibited similar tunneling behaviors as the single-layer devices. A simple model for conduction and memory operation is proposed based on the I-V fits. These devices exhibit the characteristics needed to satisfy the new demands for memory application and have the potential of becoming the first universal memory technology. They possess the high speed, non-volatility, thermal stability, and potentially high memory densities to make them ideal for use in laptops, iPhones, mp3 players, portable video players, GPS systems, and other mobile devices.

Kanwal, Alokik Paul

75

Advanced memory effects in the aging of a polymer glass  

NASA Astrophysics Data System (ADS)

A new kind of memory effect on low frequency dielectric measurements on plexiglass (PMMA) is described. These measurements show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant ?. A temporary stop of cooling produces a downward relaxation of ?. Two main features are observed (i) when cooling is resumed ? goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) (ii) upon reheating ? keeps the memory of all the cooling stops (Advanced memory). The dependence of this effect on frequency and on the cooling rate is analyzed. The memory deletion is studied too. Finally the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs.

Bellon, L.; Ciliberto, S.; Laroche, C.

2002-02-01

76

Programmable polymer thin film and non-volatile memory device  

Microsoft Academic Search

Building on the success of organic electronic devices, such as light-emitting diodes and field-effect transistors, procedures for fabricating non-volatile organic memory devices are now being explored. Here, we demonstrate a novel organic memory device fabricated by solution processing. Programmable electrical bistability was observed in a device made from a polystyrene film containing gold nanoparticles and 8-hydroxyquinoline sandwiched between two metal

Jianyong Ouyang; Chih-Wei Chu; Charles R. Szmanda; Liping Ma; Yang Yang

2004-01-01

77

Biodistribution of polymer hydrogel capsules for the delivery of therapeutics.  

PubMed

A key phase in the development of intelligently designed nanoparticle delivery vehicles for new therapeutic agents is to gain an understanding of their interaction with tissues and cells. We report a series of in vitro and in vivo experiments aimed at tracking a potential delivery vehicle for therapeutic agents, including vaccine peptides and drugs derived from poly(methacrylic acid) hydrogel capsules in certain organs and cell types. For the in vitro studies, two immortal liver-derived cell lines (Huh7 and Hepa1-6) and primary cultures of mouse hepatocytes were incubated with Alexa 647 labelled fluorescent capsules to track their internalization and intracellular distribution by confocal microscopy. Capsules, 500nm in diameter, were taken up into the cells in a time-dependent manner in all three cell lines. Capsules were observed in plasma membrane-derived vesicles within the cells. After 24h a significant proportion of the capsules was observed in lysosomes. To understand the behaviour of the capsules in vivo, Alexa 488 labelled fluorescent capsules were intravenously injected into Sprague-Dawley rats and after 24h the fate of the capsules in a number of organs was determined by flow cytometry and confocal microscopy. By flow cytometry, the majority of the capsules were detected in the spleen whilst similar numbers were found in the lung and liver. By confocal microscopy, the majority of the capsules were found in the liver and spleen with significantly less capsules in the lung, heart and kidney. Colocalization of capsules with cell-type specific markers indicated that in lung, heart and kidney, the majority of the capsules were located in endothelial cells. In the spleen ~50% of the capsules were found in CD163-positive cells, whereas in the liver, almost all capsules were located in CD163-positive cells, indicating uptake by Kupffer cells. Electron microscopy confirmed the presence of capsules within Kupffer cells. PMID:22659177

Hinton, Tracey M; Monaghan, Paul; Green, Diane; Kooijmans, Sander A A; Shi, Shuning; Breheney, Kerry; Tizard, Mark; Nicolazzo, Joseph A; Zelikin, Alexander N; Wark, Kim

2012-05-30

78

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

PubMed Central

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.

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

2009-01-01

79

Active disassembly using shape memory polymers for the mobile phone industry  

Microsoft Academic Search

This paper reports results the application of shape memory polymer (SMP) technology to the active disassembly of modern mobile phones. The smart material SMP of polyurethane (PU) composition was employed. Two different types of SMP fasteners were created for these experiments. With these smart material devices, it is possible for products to disassemble themselves at specific triggering temperatures at EoL.

J. D. Chiodo; E. H. Billett; D. J. Harrison

1999-01-01

80

Water-driven programmable polyurethane shape memory polymer: Demonstration and mechanism  

Microsoft Academic Search

We demonstrate the new features of a polyurethane shape memory polymer: water-driven actuation and recovery in sequence (i.e., programmable). Hydrogen bonding is identified as the reason behind these features. In addition, the absorbed water is quantitatively separated into two parts, namely, the free water and bound water. Their individual contribution on the glass transition temperature is identified.

W. M. Huang; B. Yang; L. An; C. Li; Y. S. Chan

2005-01-01

81

Electrical conductivity of thermoresponsive shape-memory polymer with embedded micron sized Ni powder chains  

Microsoft Academic Search

The electrical resistivity of a thermoresponsive polyurethane shape-memory polymer (SMP) filled with micron sized Ni powders is investigated in this letter. We show that, by forming conductive Ni chains under a weak static magnetic field (0.03 T), the electrical conductivity of the SMP composite in the chain direction can be improved significantly, which makes it more suitable for Joule heat

J. S. Leng; X. Lan; Y. J. Liu; S. Y. Du; W. M. Huang; N. Liu; S. J. Phee; Q. Yuan

2008-01-01

82

Inductively Heated Shape Memory Polymer for the Magnetic Actuation of Medical Devices  

Microsoft Academic Search

Presently, there is interest in making medical devices such as expandable stents and intravascular microactuators from shape memory polymer (SMP). One of the key challenges in realizing SMP medical devices is the implementation of a safe and effective method of thermally actuating various device geometries in vivo. A novel scheme of actuation by Curie-thermoregulated inductive heating is presented. Prototype medical

Patrick R. Buckley; Gareth H. McKinley; Thomas S. Wilson; Ward Small; William J. Benett; Jane P. Bearinger; Michael W. McElfresh; Duncan J. Maitland

2006-01-01

83

Modeling and Optimization of the Deposition of Shape Memory Polymers for Information Storage Applications  

Microsoft Academic Search

Shape memory polymers are of interest as high-capacity information storage media. This paper seeks to understand the effects of processing conditions on diethylene glycol dimethacrylate (DEGDMA) and bisphenol A ethoxylate dimethacrylate. Full factorial experiments are performed to characterize the impact of the following parameters: spin speed, spin time, and nitrogen flow rate. A total of ten experiments are conducted. The

Edem Wornyo; Gary S. May; Ken Gall

2009-01-01

84

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

NASA Astrophysics Data System (ADS)

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.

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

2012-02-01

85

Development and characterization of semi-crystalline polyalkenamer based shape memory polymers  

NASA Astrophysics Data System (ADS)

A series of thermo-responsive shape memory polymers were developed from commercially available polyalkenamer by balancing competitive crystallinity and elasticity via a monofunctional peroxide based crosslinking process. The main thermomechanical and shape memory properties of covalently crosslinked samples were characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamical-mechanical-thermal analysis (DMTA), flexural mode stress-strain tests and thermomechanical bending experiments. The obtained semi-crystalline polymer networks were characterized by shape memory activation temperatures from - 10 to 60 °C and shape recovery ratios from 95 to 100% by adjusting the melting temperatures and elasticity through a controlled density of covalent knots along the polymeric network from an accurate peroxide fraction.

Cuevas, J. M.; Laza, J. M.; Rubio, R.; German, L.; Vilas, J. L.; León, L. M.

2011-03-01

86

Vaccine-induced effector-memory CD8+ T cell responses predict therapeutic efficacy against tumors.  

PubMed

CD8(+) T cells have the potential to attack and eradicate cancer cells. The efficacy of therapeutic vaccines against cancer, however, lacks defined immune correlates of tumor eradication after (therapeutic) vaccination based on features of Ag-specific T cell responses. In this study, we examined CD8(+) T cell responses elicited by various peptide and TLR agonist-based vaccine formulations in nontumor settings and show that the formation of CD62L(-)KLRG1(+) effector-memory CD8(+) T cells producing the effector cytokines IFN-? and TNF predicts the degree of therapeutic efficacy of these vaccines against established s.c. tumors. Thus, characteristics of vaccine-induced CD8(+) T cell responses instill a predictive determinant for the efficacy of vaccines during tumor therapy. PMID:22914049

van Duikeren, Suzanne; Fransen, Marieke F; Redeker, Anke; Wieles, Brigitte; Platenburg, Gerard; Krebber, Willem-Jan; Ossendorp, Ferry; Melief, Cornelis J M; Arens, Ramon

2012-08-22

87

Surface Anchoring and Surface Memory in Dispersions of Polymers and Liquid Crystals.  

NASA Astrophysics Data System (ADS)

Surface anchoring of liquid crystals at interfaces created by polymerization-induced phase separation was studied. Such surfaces are created during the formation of some polymer-dispersed liquid crystal (PDLC) films. PDLC films have micron-scale drops of liquid crystal dispersed within a polymeric matrix. They can be switched with an electric field from a scattering to a transparent state, and are of interest for use in flat-panel displays. We found a temperature-induced anchoring transition in a series of polymers in contact with one liquid crystal. These surface anchoring transitions were used to demonstrate a "surface memory," where an otherwise isotropic surface is rendered anisotropic by being in contact with the liquid crystal. Surface anchoring, including surface memory, has a dramatic effect on electro-optic properties of PDLC films. The presence of surface memory depends on the chemical structure of the polymer side group. Also, it can be erased by heating the liquid crystal far above the nematic-to-isotropic temperature. Molecular mechanisms for surface memory will be discussed.

Amundson, Karl; Srinivasarao, Mohan

1998-03-01

88

AB-polymer networks based on oligo(?-caprolactone) segments showing shape-memory properties  

PubMed Central

Although shape-memory metal alloys have wide use in medicine and other areas, improved properties, particularly easy shaping, high shape stability, and adjustable transition temperature, are realizable only by polymer systems. In this paper, a polymer system of shape-memory polymer networks based on oligo(?-caprolactone) dimethacrylate as crosslinker and n-butyl acrylate as comonomer was introduced. The influence of two structural parameters, the molecular weight of oligo(?-caprolactone) dimethacrylate and the weight content of n-butyl acrylate, on macroscopic properties of polymer networks such as thermal and mechanical properties has been investigated. Tensile tests above and below melting temperature showed a decrease in the elastic modulus with increasing comonomer weight content. The crystallization behavior of the new materials has been investigated, and key parameters for the programming procedure of the temporary shape have been evaluated. Shape-memory properties have been quantified by thermocyclic experiments. All samples reached uniform deformation properties with recovery rates above 99% after 3 cycles. Whereas strain recovery increased with increasing n-butyl acrylate content, strain fixity decreased, reflecting the decreasing degree of crystallinity of the material.

Lendlein, Andreas; Schmidt, Annette M.; Langer, Robert

2001-01-01

89

Nanoscale shape-memory function in highly cross-linked polymers.  

PubMed

Topographic engraving of structures in polymer surfaces attracts widespread interest for application in imprint lithography and data storage. We study the nonlinear interaction of nanoindents written in close proximity, 20-100 nm, to one another in a highly cross-linked polystyrene matrix. The indents are created thermomechanically by applying heat and force stimuli of 10 micros duration to a tip, thereby raising the polymer temperature to 250 degrees C and exerting contact pressures of up to 1 GPa. We show that on the nanoscale plastic deformation is highly reversible providing outstanding shape-memory functionality of the material. PMID:19367970

Altebaeumer, T; Gotsmann, B; Pozidis, H; Knoll, A; Duerig, U

2008-12-01

90

Damage healing ability of a shape-memory-polymer-based particulate composite with small thermoplastic contents  

NASA Astrophysics Data System (ADS)

The purpose of this study is to investigate the potential of a shape-memory-polymer (SMP)-based particulate composite to heal structural-length scale damage with small thermoplastic additive contents through a close-then-heal (CTH) self-healing scheme that was introduced in a previous study (Li and Uppu 2010 Comput. Sci. Technol. 70 1419-27). The idea is to achieve reasonable healing efficiencies with minimal sacrifice in structural load capacity. By first closing cracks, the gap between two crack surfaces is narrowed and a lesser amount of thermoplastic particles is required to achieve healing. The particulate composite was fabricated by dispersing copolyester thermoplastic particles in a shape memory polymer matrix. It is found that, for small thermoplastic contents of less than 10%, the CTH scheme followed in this study heals structural-length scale damage in the SMP particulate composite to a meaningful extent and with less sacrifice of structural capacity.

Nji, Jones; Li, Guoqiang

2012-02-01

91

Regular arrays of highly ordered ferroelectric polymer nanostructures for non-volatile low-voltage memories  

Microsoft Academic Search

Ferroelectric nanostructures are attracting tremendous interest because they offer a promising route to novel integrated electronic devices such as non-volatile memories and probe-based mass data storage. Here, we demonstrate that high-density arrays of nanostructures of a ferroelectric polymer can be easily fabricated by a simple nano-embossing protocol, with integration densities larger than 33Gbitsinch-2. The orientation of the polarization axis, about

Zhijun Hu; Mingwen Tian; Bernard Nysten; Alain M. Jonas

2009-01-01

92

Electromagnetic interference shielding effect of nanocomposites with carbon nanotube and shape memory polymer  

Microsoft Academic Search

The nanocomposites with carbon nanotubes (CNTs) and shape memory polymer (SMP) were developed for electrical applications. The specimens with different CNTs weight fractions were prepared. Their electrical resistivities and electromagnetic interference (EMI) shielding effectiveness (SE) were investigated. The electrical resistivity was examined by four-probe method at different testing temperatures of 25,35,45,55 and 65°C around glass transfer temperature (Tg). As a

Chun-Sheng Zhang; Qing-Qing Ni; Shao-Yun Fu; Ken Kurashiki

2007-01-01

93

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

PubMed

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 (T(g)) 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 T(g) 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

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

2012-01-01

94

Design and Processing of Shape Memory Polymer (SMP)/Shape Memory Alloy (SMA) Composites.  

National Technical Information Service (NTIS)

This research was has been conducted primarily to create a thermo- responsive two-way shape change polymer. Such a material could work as a thermo- responsive actuator, a thermo-responsive valve, a thermo-responsive switch in broad range of engineering fi...

H. Tamagawa

2010-01-01

95

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

NASA Astrophysics Data System (ADS)

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.

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

2010-04-01

96

Isothermal recovery response and constitutive model of thermoset shape memory polymers  

NASA Astrophysics Data System (ADS)

Deformation recovery capability is one of the important indexes to examination shape memory effect of the shape memory polymers (SMPs). And the shape memory characteristic of SMPs is closely related to different phase states and mechanical properties above and below the glass transition temperature (Tg). In this paper, we investigated the strain recovery response of a thermoset shape memory epoxy resin modified by polyurethane (PU) through uniaxial compression experiments under various isothermal conditions and strain rates and developed a "three-phase" constitutive model based on phase transition concept, which including stationary phase, active phase and frozen phase. This model established the mutual transformation relationships between frozen phase and active phase of SMPs by introducing temperature switch function, which presents the stain storage and release process of SMPs under loading and changing temperature environment. Besides, the proposed model represents the SMPs deformation process of viscous hysteresis response by employing the rheological elements description of the three phases. The numerical results agree very well with experiment results of stress-strain response curve of isothermal compression/unloading test, which validated this model can predict the finite deformation behavior of SMPs.

Tan, Huifeng; Zhou, Tao; Liu, Yuyan; Lan, Lan

2011-11-01

97

Feasibility study of polyurethane shape-memory polymer actuators for pressure bandage application  

NASA Astrophysics Data System (ADS)

The feasibility of laboratory-synthesized polyurethane-based shape-memory polymer (SMPU) actuators has been investigated for possible application in medical pressure bandages where gradient pressure is required between the ankle and the knee for treatment of leg ulcers. In this study, using heat as the stimulant, SMPU strip actuators have been subjected to gradual and cyclic stresses; their recovery force, reproducibility and reusability have been monitored with respect to changes in temperature and circumference of a model leg, and the stress relaxation at various temperatures has been investigated. The findings suggest that SMPU actuators can be used for the development of the next generation of pressure bandages.

Ahmad, Manzoor; Luo, Jikui; Miraftab, Mohsen

2012-02-01

98

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

NASA Astrophysics Data System (ADS)

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.

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

2012-07-01

99

Inorganic-organic shape memory polymer (SMP) foams with highly tunable properties.  

PubMed

Thermoresponsive shape memory polymers (SMPs) are a class of smart materials that can return from a temporary to a permanent shape with the application of heat. Porous SMP foams exhibit unique properties versus solid, nonporous SMPs, enabling their utility in different applications, including some in the biomedical field. Reports on SMP foams have focused on those based on organic polymer systems. In this study, we have prepared inorganic-organic SMP foams comprising inorganic polydimethylsiloxane (PDMS) segments and organic poly(?-caprolactone) PCL segments. The PCL segments served as switching segments to induce shape changing behavior whereas the length of the PDMS soft segment was systematically tuned. SMP foams were formed via the photochemical cure of acrylated (AcO) macromers AcO-PCL(40)-block-PDMS(m)-block-PCL(40)-OAc (m = 0, 20, 37, 66 and 130) using a revised solvent casting/particulate leaching (SCPL) method. By varying the PDMS segment length, PDMS-PCL foams having excellent shape memory behavior were obtained that exhibited highly tunable properties, including pore size, % porosity, compressive modulus, and degradation rate. PMID:23227875

Zhang, Dawei; Petersen, Keri M; Grunlan, Melissa A

2012-12-21

100

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

PubMed Central

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.

Madigan, Nicolas N.; McMahon, Siobhan; O'Brien, Timothy; Yaszemski, Michael J.; Windebank, Anthony J.

2010-01-01

101

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

NASA Astrophysics Data System (ADS)

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.

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

2012-09-01

102

Side-chain liquid crystalline polymer networks: exploiting nanoscale smectic polymorphism to design shape-memory polymers.  

PubMed

Herein, we investigate the influence of nanoscale smectic polymorphism within end-on fixed side-chain liquid crystalline polymer networks (SCLCNs) on macroscopic shape-memory and actuation properties. We have synthesized a series of SCLC-type linear (TP-n) and cross-linked random terpolymers (XL-TP-n) with varying length of flexible methylene spacers (n = 5, 10, and 15) between polynorbornene main-chain and cholesteryl ester side-chains. Thermal and mechanical analyses by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) confirm a glass transition (T(g)), a clearing temperature (T(cl)), and a network structure in the XL-TP-n. Detailed structural investigation conducted using wide-angle and small-angle X-ray scattering (WAXS and SAXS) at room temperature proves self-assembled smectic A (SmA) polymorphism of the XL-TP-n which evolves from non-interdigitated bilayer (SmA(2)) for n = 5 to mixed layers of monolayer-like highly interdigitated layer (SmA(1)) and SmA(2) for n = 10 and to SmA(1) for n = 15. In addition, TP10 at temperatures above 60 °C interestingly shows transformation of SmA structure from mixed layer (SmA(1) + SmA(2)) to interdigitated structure (SmA(d)). The SmA polymorphism developed in TP-n during shape-memory cycles (SMCs) significantly impacts the ultimate strain responses. A mechanism for the unique interdigitation-based thermostrictive behavior is proposed. More importantly, this new actuation mechanism observed in these XL-TP-n can be exploited to develop intelligent thermal actuators. PMID:21401122

Ahn, Suk-kyun; Deshmukh, Prashant; Gopinadhan, Manesh; Osuji, Chinedum O; Kasi, Rajeswari M

2011-03-23

103

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

SciTech Connect

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.

Leng Jinsong; Yu Kai; Lan Xin [Center for Composite Materials and Structures, Harbin Institute of Technology, HeiLongJiang 150001 (China); Zhang Dawei [Center for Composite Materials and Structures, Harbin Institute of Technology, HeiLongJiang 150001 (China); Material Science and Engineering College, Northeast Forestry University, HeiLongJiang 150040 (China); Liu Yanju [Department of Astronautical Science and Mechanics, Harbin Institute of Technology, HeiLongJiang 150001 (China)

2010-03-15

104

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

SciTech Connect

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.

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

2006-08-16

105

Fabrication and characterization of cylindrical light diffusers comprised of shape memory polymer  

PubMed Central

We 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. The devices are 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 are characterized for various blasting pressures, nozzle-to-sample distances, and nozzle translation speeds. The diffusers are generally strongly forward-directed and consistently withstand over 8 W of incident IR laser light without suffering damage when immersed in water. These devices are suitable for various endoluminal and interstitial biomedical applications.

Small, Ward; Buckley, Patrick R.; Wilson, Thomas S.; Loge, Jeffrey M.; Maitland, Kristen D.; Maitland, Duncan J.

2009-01-01

106

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

SciTech Connect

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.

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

2007-01-29

107

Light polarization-controlled shape-memory polymer/gold nanorod composite.  

PubMed

It is demonstrated that light polarization can be used to control photothermal effect-based shape-memory polymers (SMPs). Gold nanorods (AuNRs) are embedded in poly(vinyl alcohol) (PVA) and aligned by stretching the composite film. By changing the polarization direction of the incident laser at 785 nm with respect to the film stretching direction, the magnitude of the longitudinal surface plasmon resonance of AuNRs can be varied continuously, which determines the amount of heat generated upon laser exposure and thus the local temperature rise in the composite relative to the glass transition of the PVA matrix. Consequently, the temporary-to-permanent shape recovery process of the composite can be made to occur to different extents by tuning the polarization of laser while keeping all other conditions unchanged. This finding enhances the toolbox for controlling light-triggered SMPs. PMID:24092559

Zhang, Hongji; Zhang, Jianming; Tong, Xia; Ma, Dongling; Zhao, Yue

2013-09-20

108

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

PubMed Central

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 37°C, 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.

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

2011-01-01

109

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

NASA Astrophysics Data System (ADS)

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.

John, Manu; Li, Guoqiang

2010-07-01

110

Photothermal Properties of Shape Memory Polymer Micro-Actuators for Treating Stroke  

SciTech Connect

Objective--In this paper the photothermal design aspects of novel shape memory polymer (SMP) microactuators for treating stroke are presented. Materials and Methods--A total of three devices will be presented: two interventional ischemic stroke devices (coil and umbrella) and one device for releasing embolic coils (microgripper). The optical properties of SMP, methods for coupling laser light into SMP, heating distributions in the SMP devices and the impact of operating the thermally activated material in a blood vessel are presented. Results--Actuating the devices requires device temperatures in the range of 65 C-85 C. Attaining these temperatures under flow conditions requires critical engineering of the SMP optical properties, optical coupling into the SMP, and device geometries. Conclusion--Laser-activated SMP devices are a unique combination of laser-tissue and biomaterial technologies. Successful deployment of the microactuator requires well-engineered coupling of the light from the diffusing fiber through the blood into the SMP.

Maitland, D J; Metzger, M F; Schumann, D; Lee, A; Wilson, T S

2001-03-05

111

Demonstration of a Nonvolatile Memory Element Based on a Ferroelectric Polymer Langmuir-Blodgett Film  

NASA Astrophysics Data System (ADS)

Ferroelectric thin films provide a basis for non-destructive, nonvolatile memory devices. The ferroelectric copolymer of vinylidene fluoride (70%) with trifluoroethylene (30%) is particularly attractive due to its chemical stability and high polarization retention. We report successful operation of a nonvolatile bistable capacitor stack consisting of a metal gate, ferroelectric polymer Langmuir-Blodgett film, Silicon Dioxide, and n-type Silicon Semiconductor. The small signal capacitance was used to determine the device state and the threshold voltage of the inversion layer. This parameter was found to depend on the voltage history of the sample. The results are in good agreement with the theory of Miller and McWhorter. (1) 1. S.L. Miller and P.J. McWhorter, J. Appl. Phys. 72, 5999 (1992).

Reece, Timothy; Sorokin, Alexander; Bai, Mengjun; Ducharme, Stephen; Fridkin, Vladimir

2002-03-01

112

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

PubMed

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

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

2013-08-06

113

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

NASA Astrophysics Data System (ADS)

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.

di Prima, Matthew Allen

114

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

PubMed Central

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.

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

2012-01-01

115

[Polymer materials for biomedical use obtained by radiation methods. IV. The therapeutic system for local release of prostaglandins].  

PubMed

The suitability of a radiation crosslinked polyvinylpyrrolidone++ as a therapeutical system for local prostaglandin monitoring has been studied. The effect of the dose and dose rate of ionizing radiation and of the time of heating the matrix on the content of gel fraction and the degree of hydrogel swelling was determined. The dimensions of a polymer network as dependent on the parameters of the process were calculated. For a chosen way of obtaining the therapeutical system, the release of prostaglandin F2 alpha in vitro was also estimated. PMID:2641404

Rosiak, J; Olejniczak, J

1989-01-01

116

Memory.  

ERIC Educational Resources Information Center

|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)|

McKean, Kevin

1983-01-01

117

Rational design of composition and activity correlations for pH-sensitive and glutathione-reactive polymer therapeutics  

Microsoft Academic Search

Limited cytoplasmic delivery of enzyme-susceptible drugs remains a significant challenge facing the development of protein and nucleic acid therapies that act in intracellular compartments. “Smart” pH-sensitive, membrane-destabilizing polymers present an attractive approach to shuttle therapeutic molecules past the endosomal membrane and into the cytoplasm of targeted cells. This report describes the use of a new functionalized monomer, pyridyl disulfide acrylate

Mohamed E. H. El-Sayed; Allan S. Hoffman; Patrick S. Stayton

2005-01-01

118

Electro-activate styrene-based shape memory polymer nanocomposite filled with multi-walled carbon nanotubes  

Microsoft Academic Search

The fabrication and characterization, especially mechanical and electrical properties, of styrene-based shape memory polymer mixed with multi-walled carbon nanotubes (MWNTs) are presented in this paper. It is found that surface-modified MWNTs incorporated very well with resin processed by royal water, and dispersion was achieved by high-energy sonication in the solution. Scanning Electron Microscope (SEM) is shown that the particulate additives

Haibao Lv; Yanju Liu; Jinsong Leng; Shanyi Du

2007-01-01

119

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

PubMed Central

The effect of moisture absorption on the glass transition temperature (Tg) and 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 our best 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 °C 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.

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

2011-01-01

120

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

PubMed Central

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 pig’s 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.

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

121

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

PubMed Central

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.

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

2007-01-01

122

In vivo tissue responses to thermal-responsive shape memory polymer nanocomposites.  

PubMed

To explore the safe use of thermal-responsive shape memory polymers (SMPs) as minimally invasive tissue scaffolds, we recently developed a class of biodegradable POSS-SMP nanocomposites exhibiting stable temporary shape fixing and facile shape recovery within a narrow window of physiological temperatures. The materials were covalently crosslinked from star-branched building blocks consisting a bioinert polyhedral oligomeric silsesquioxane (POSS) core and 8 degradable poly(D,L-lactide) (PLA) arms. Here we examine the degradation profiles and immunogenicity of POSS-SMPs as a function of the PLA arm lengths using a rat subcutaneous implantation model. We show that POSS-SMPs elicited a mild foreign body type immune response upon implantation. The degradation rates of POSS-SMPs, both in vitro and in vivo, inversely correlated with the length of the PLA chains within the crosslinked amorphous network. Upon in vivo degradation of POSS-SMPs, a second acute inflammatory response was elicited locally, and the inflammation was able to resolve over time without medical interventions. One year after the implantation of POSS-SMPs, no pathologic abnormalities were detected from the vital/scavenger organs examined. These minimally immunogenic and biodegradable SMPs are promising candidates for scaffold-assisted tissue repair where both facile surgical delivery and controlled degradation of the scaffold are desired for achieving optimal short-term and long-term clinical outcomes. PMID:21040968

Filion, Tera M; Xu, Jianwen; Prasad, Manju L; Song, Jie

2010-10-30

123

Memory  

NSDL National Science Digital Library

This is a description for a learning module from Maricopa Advanced Technology Education Center. This PDF describes the module; access may be purchased by visiting the MATEC website. PC memory is one of the most critical and rapidly advancing assemblies within modern microcomputers. The challenge of developing learners' knowledge of PC memory and keeping it current and directly applicable to today's microcomputer industry is addressed by this module. The three major topics included in this module are ROM/Flash, System Memory, and Cache Systems. Hands-on practice and final skill assessment verify learners' readiness for working with memory in an Intel-based PC system.

2012-12-07

124

Into the Fire: Using Therapeutic Enactments to Bridge Early Traumatic Memories of Childhood Sexual Abuse  

Microsoft Academic Search

While traditional forms of therapy focus heavily on a survivor's ability to tell his or her story, the very nature of traumatic\\u000a memory can present a challenge since survivors of trauma often struggle to find the verbal language to describe the terrifying\\u000a events that have occurred. In verbal therapies, survivors of childhood sexual abuse can be left in a state

Pam Hirakata; Marla J. Buchanan-Arvay

2005-01-01

125

Costimulation of Memory T-Cells by ICOS: A Potential Therapeutic Target for Autoimmunity?  

Microsoft Academic Search

Approaches that target costimulatory receptors are independent of T-cell receptor specificity and may be useful for T-cell-mediated diseases in which the antigens involved are not well defined. However, the proper costimulatory pathways need to be targeted. For example, therapies for human T-cell-mediated diseases need to be effective against previously activated memory cells. In this review, we use autoimmune demyelination as

Romeo A. Sporici; Peter J. Perrin

2001-01-01

126

Dynamic mechanical analysis for rapid assessment of the time-dependent recovery behavior of shape memory polymers  

NASA Astrophysics Data System (ADS)

Thermally activated shape memory polymers (SMPs) recover from a secondary shape induced by mechanical deformation to a primary equilibrium shape when they are heated to their actuation temperature. In certain applications, for example in the biomedical field, it may be necessary to control the rate of shape recovery under isothermal conditions, which requires knowledge of the time-dependent response of the SMP. In the present work, the time dependence of isothermal shape recovery has been investigated for polyurethane-based SMPs with two different molecular architectures. The results are discussed in terms of a linear thermo-viscoelastic model for the time and temperature dependence of the shape memory response at small strains, using data from single constant frequency dynamic mechanical analysis (DMA) temperature sweeps. This approach is based on the establishment of an approximate relationship between the storage modulus, the loss modulus and the shift factor, aT(t), usually derived from time-temperature superposition of isothermal data obtained at different temperatures. The DMA data are thus shown to provide an approximate measure of the relaxation and retardation time spectra, which may in turn be used to predict the shape memory response to a simple programming-isothermal shape recovery sequence. This procedure is argued to permit rapid quantitative comparison of the shape memory performance of different materials, with minimal experimental characterization, and is hence potentially a useful tool for designing materials for specific applications.

Azra, Charly; Plummer, Christopher J. G.; Månson, Jan-Anders E.

2013-07-01

127

Coiled coil peptides as universal linkers for the attachment of recombinant proteins to polymer therapeutics.  

PubMed

We have designed, synthesized, and characterized peptides containing four repeats of the sequences VAALEKE (peptide E) or VAALKEK (peptide K). While the peptides alone adopt in aqueous solutions a random coil conformation, their equimolar mixture forms heterodimeric coiled coils as confirmed by CD spectroscopy. 5-Azidopentanoic acid was connected to the N-terminus of peptide E via a short poly(ethylene glycol) spacer. The terminal azide group enabled conjugation of the peptide with a synthetic drug carrier based on the N-(2-hydroxypropyl)methacrylamide copolymer containing propargyl groups using "click" chemistry. When incorporated into the polymer drug carrier, peptide E formed a stable noncovalent complex with peptide K belonging to a recombinant single-chain fragment (scFv) of the M75 antibody. The complex thereby mediates a noncovalent linkage between the polymer drug carrier and the protein. The recombinant scFv antibody fragment was selected as a targeting ligand against carbonic anhydrase IX-a marker overexpressed by tumor cells of various human carcinomas. The antigen binding affinity of the polymer-scFv complex was confirmed by ELISA. This approach offers a well-defined, specific, and nondestructive universal method for the preparation of protein (antibody)-targeted polymer drug and gene carriers designed for cell-specific delivery. PMID:21863890

Pechar, Michal; Pola, Robert; Laga, Richard; Ulbrich, Karel; Bednárová, Lucie; Malo?, Petr; Sieglová, Irena; Král, Vlastimil; Fábry, Milan; Van?k, Ond?ej

2011-08-31

128

Partial erasing of temporal memory by using picosecond accumulated photon echoes in dye doped polymer film  

Microsoft Academic Search

The stimulated photon echo memory using persistent hole-burning materials has been attracting much attention as a possible candidate for high-density data storage. Most studies have been related to the writing and reading processes and little attention has been paid for a partial erasing. We demonstrate for the first time that partial erasing of photon echo memory can be accomplished by

R. Yano; N. Uesugi

1999-01-01

129

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

NASA Astrophysics Data System (ADS)

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.

Lu, Haibao; Huang, Wei Min

2013-11-01

130

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

Microsoft Academic Search

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

Sung Hye Kim

2009-01-01

131

Invading target cells: multifunctional polymer conjugates as therapeutic nucleic acid carriers  

Microsoft Academic Search

Polymer-based conjugates are an interesting option and challenge for the design of nano-sized drug-delivery systems, as they\\u000a require advanced conjugation chemistry and precise engineering. In the case of nucleic acid therapy, non-viral carriers face\\u000a several biological barriers during the delivery process, namely 1) protection of the cargo from extracellular degradation,\\u000a 2) avoidance of non-specific interactions with non-targeted tissues, 3) efficient

Ulrich Lächelt; Ernst Wagner

2011-01-01

132

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

NASA Astrophysics Data System (ADS)

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.

Seki, Kazuhiko; Tachiya, M.

2007-01-01

133

Memories.  

ERIC Educational Resources Information Center

|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,…

Brand, Judith, Ed.

1998-01-01

134

Nanoparticle-induced negative differential resistance and memory effect in polymer bistable light-emitting device  

NASA Astrophysics Data System (ADS)

Recently, electrical bistability was demonstrated in polymer thin films incorporated with metal nanoparticles [J. Ouyang, C. W. Chu, C. R. Szmanda, L. P. Ma, and Y. Yang, Nat. Mater. 3, 918 (2004)]. In this letter, we show the evidence that electrons are the dominant charge carriers in these bistable devices. Direct integration of bistable polymer layer with a light-emitting polymer layer shows a unique light-emitting property modulated by the electrical bistability. A unique negative differential resistance induced by the charged gold nanoparticles is observed due to the charge trapping effect from the nanoparticles when interfaced with the light-emitting layer.

Tseng, Ricky J.; Ouyang, Jianyong; Chu, Chih-Wei; Huang, Jinsong; Yang, Yang

2006-03-01

135

Biodegradable polymer nanocarriers for therapeutic antisense microRNA delivery in living animals  

NASA Astrophysics Data System (ADS)

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.

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

2012-02-01

136

Observation of Electrical Write/Erase Operations for a Memory-Type Polymer-Dispersed Cholesteric Liquid Crystal  

NASA Astrophysics Data System (ADS)

A polymer-dispersed cholesteric (chiral nematic) liquid crystal (PDCLC) with a memory effect is effective for color display devices. The PDCLC stably maintains both selectively reflective and transparent states without holding techniques, and the states can be changed electrically. A high-frequency electric field writes to the reflective state, and a low-frequency field erases to the transparent state. To understand the details of transition between the states, we observed the intensity of light transmitted through a PDCLC cell during operation using a digital oscilloscope. Furthermore, the frequency-dependent current in the PDCLC cell was also measured to evaluate ion movement. The results show that ion movement in the PDCLC layer plays an important role in the electrical erase operation.

Kato, Kinya; Tanaka, Keiji; Tsuru, Shinji; Sakai, Shigenobu

1995-02-01

137

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

NASA Astrophysics Data System (ADS)

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 AgOx 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 AgOx 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.

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

2009-11-01

138

Spatial profile of charge storage in organic field-effect transistor nonvolatile memory using polymer electret  

NASA Astrophysics Data System (ADS)

Spatial profile of the charge storage in the pentacene-based field-effect transistor nonvolatile memories using poly(2-vinyl naphthalene) electret is probed. The electron trapping into the electret after programming can be space dependent with more electron storage in the region closer to the contacts, and reducing the channel length is an effective approach to improve the memory performance. The deficient electron supply in pentacene is proposed to be responsible for the inhomogeneous electron storage in the electret. The hole trapping into the electret after erasing is spatially homogeneous, arising from the sufficient hole accumulation in the pentacene channel.

She, Xiao-Jian; Liu, Jie; Zhang, Jing-Yu; Gao, Xu; Wang, Sui-Dong

2013-09-01

139

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

PubMed

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

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

2011-03-23

140

Improving the electrical conductivity by forming Ni powder chains in a shape-memory polymer filled with carbon black  

NASA Astrophysics Data System (ADS)

We demonstrate a simple approach to significantly reduce the electrical resistivity of thermo-responsive shape-memory polymers (SMPs), so that they can be easily triggered for shape recovery by Joule heating at a low electrical voltage. After adding a small amount of Ni micro particles into a polyurethane SMP filled with carbon black (CB), the electrical resistivity is slightly reduced. However, if these Ni particles are aligned into chains (by applying a low magnetic field on SMP/CB/Ni solution and then drying to fix the conductive chains), the drop of electrical resistivity is significant. This kind of SMP composites is suitable for cyclic operation as only micro/nano particles are used. A sample (40×15×1mm) with 10vol% of CB and 0.5vol% of chained Ni can be heated to 80°C for shape recovery at 30 V (1.2 W) of power. This approach is generic and applicable for producing other conductive polymers.

Lan, Xin; Huang, Wei Min; Liu, Na; Phee, Sy; Leng, Jin Song; Du, Shan Yi

2008-05-01

141

Investigating siRNA delivery to chronic myeloid leukemia K562 cells with lipophilic polymers for therapeutic BCR-ABL down-regulation.  

PubMed

RNAi represents a new alternative for treatment of chronic myeloid leukemia (CML) to overcome the difficulties of current drug treatments such as the acquired resistance. However, potent carriers that can overcome delivery barriers to RNAi agents and have therapeutic efficacy especially in difficult-to-transfect CML cells are needed. Here, we explored the use of lipid-modified polyethylenimines (PEI) of low molecular weights (0.6, 1.2 and 2.0kDa) in K562 cells and showed that the delivery efficiency was dependent on the type of lipid used for polymer modification, degree of lipid substitution and polymer molecular weight. Among the lipid-substituted polymers investigated, palmitic acid (PA)-substituted 1.2kDa PEI (~2 lipids/PEI) has proven to be highly efficient in delivering siRNA and silencing of the reporter gene green fluorescent protein (GFP). The silencing efficacy achieved with this polymer was found to be higher than the 25kDa PEI and is similar to commercial reagent Lipofectamine™ 2000. Moreover, when BCR-ABL protein was targeted in K562 cells, a reduction in the corresponding mRNA levels was observed, as well as an induction of early and late stage apoptosis. The results of this study demonstrated that PA-substitutions on low MW polymers could be useful for siRNA delivery in CML cells for therapeutic purposes. PMID:23726887

Valencia-Serna, Juliana; Gul-Uluda?, Hilal; Mahdipoor, Parvin; Jiang, Xiaoyan; Uluda?, Hasan

2013-05-28

142

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

Microsoft Academic Search

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

S. de Cayeux; J. Tanguy; G. Lécayon

1996-01-01

143

Synthesis and memory performance of a conjugated polymer with an integrated fluorene, carbazole and oxadiazole backbone  

Microsoft Academic Search

A new soluble conjugated polymer, poly[{9-(4-methoxyphenyl)-9H-carbazole}(9,9-dioctylfluorene)(2,5-diphenyl-1,3,4-oxadiazole)](PCFO), was synthesized through the Suzuki coupling reaction. The absolute fluorescence quantum yield of PCFO was measured using the integrating sphere of a photoluminescence spectrofluorometer, and changed from 49.1% for a dilute tetrahydrofuran solution to 16.2% for a thin film due to the existence of a strong fluorescence quenching effect in the solid state. The

Long-Jia Zeng; Gang Liu; Bin Zhang; Junneng Chen; Yu Chen; En-Tang Kang; E-T Kang

2012-01-01

144

Femtosecond laser microfabrication in polymers towards memory devices and microfluidic applications  

NASA Astrophysics Data System (ADS)

We have investigated femtosecond laser induced microstructures, gratings, and craters in four different polymers: poly methyl methacrylate (PMMA), poly dimethyl siloxane (PDMS), polystyrene (PS) and poly vinyl alcohol (PVA) using Ti:sapphire laser delivering 800 nm, 100 femtosecond (fs) pulses at 1 kHz repetition rate with a maximum pulse energy of 1 mJ. Local chemical modifications leading to the formation of optical centers and peroxide radicals which were studied using UV-Visible absorption and emission, confocal micro-Raman and Electron Spin Resonance (ESR) spectroscopic techniques.

Deepak, K. L. N.; Venugopal Rao, S.; Narayana Rao, D.

2011-10-01

145

Vapor-phase testing of the memory-effects in benzene- and toluene-imprinted polymers conditioned at elevated temperature.  

PubMed

The preparation of polymers imprinted with common aromatic solvents such as benzene and toluene is an under-exploited subject of research. The present study was aimed at the understanding of whether true solvent memory effects can be achieved by molecular imprinting, as well as if they are stable at elevated temperature. A set of copolymers, comprising low and high cross-linking levels, was prepared from four different combinations of functional monomer and cross-linker, namely methacrylic acid (MAA)/ethylene glycol dimethacrylate (EGDMA), methyl methacrylate (MMA)/EGDMA, MAA/divinyl benzene (DVB) and MMA/DVB. Each possible combination was prepared separately in benzene, toluene and acetonitrile. The obtained materials were applied as coatings onto nickel-titanium (Ni-Ti) alloy wires which were incorporated into solid-phase microextraction devices and finally tested for their ability to competitively adsorb vapors from the headspace of an aqueous solution containing a few volatile organic compounds. Porosity analysis showed that, regardless of the solvent used, only a high cross-linking level permitted the preparation of mesoporous copolymers (BJH radius typically in the range 13-15nm), a requirement for providing accessibility to the targeted nanoscale-imprinted cavities. A noticeable exception was, however, observed for the MMA/DVB copolymers which exhibited much diminished BJH radius. The porosity data correlated well with the extraction profiles found, which suggested the presence of benzene-imprinted sites in all the highly cross-linked copolymers prepared in benzene, except for the MMA/DVB copolymers. Concerning the effect of an elevated conditioning temperature on the memory-effects created by the imprinting process, the results were clearly indicative that the tested copolymers, including the more robust highly cross-linked ones, are not suitable for high temperature applications such as solid-phase microextraction coupled to gas chromatography. PMID:24176503

Azenha, Manuel; Schillinger, Eric; Sanmartin, Esther; Regueiras, M Teresa; Silva, Fernando; Sellergren, Börje

2013-09-26

146

The role of internal structure in the anomalous switching dynamics of metal-oxide/polymer resistive random access memories  

NASA Astrophysics Data System (ADS)

The dynamic response of a non-volatile, bistable resistive memory fabricated in the form of Al2O3/polymer diodes has been probed in both the off- and on-state using triangular and step voltage profiles. The results provide insight into the wide spread in switching times reported in the literature and explain an apparently anomalous behaviour of the on-state, namely the disappearance of the negative differential resistance region at high voltage scan rates which is commonly attributed to a ``dead time'' phenomenon. The off-state response follows closely the predictions based on a classical, two-layer capacitor description of the device. As voltage scan rates increase, the model predicts that the fraction of the applied voltage, Vox, appearing across the oxide decreases. Device responses to step voltages in both the off- and on-state show that switching events are characterized by a delay time. Coupling such delays to the lower values of Vox attained during fast scan rates, the anomalous observation in the on-state that, device currents decrease with increasing voltage scan rate, is readily explained. Assuming that a critical current is required to turn off a conducting channel in the oxide, a tentative model is suggested to explain the shift in the onset of negative differential resistance to lower voltages as the voltage scan rate increases. The findings also suggest that the fundamental limitations on the speed of operation of a bilayer resistive memory are the time- and voltage-dependences of the switch-on mechanism and not the switch-off process.

Rocha, Paulo R. F.; Kiazadeh, Asal; De Leeuw, Dago M.; Meskers, Stefan C. J.; Verbakel, Frank; Taylor, David M.; Gomes, Henrique L.

2013-04-01

147

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

NASA Astrophysics Data System (ADS)

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/H2O 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.

de Cayeux, S.; Tanguy, J.; Lécayon, G.

1996-01-01

148

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

SciTech Connect

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.}

de Cayeux, S. [CEA-DSM/DRECAM/SRSIM, 91191 Gif-sur-Yvette (France)]|[IMAGO SA, 13600 La Ciotat (France); Tanguy, J.; Lecayon, G. [CEA-DSM/DRECAM/SRSIM, 91191 Gif-sur-Yvette (France)

1996-01-01

149

Polymers  

NSDL National Science Digital Library

This page contains two documents explaining ring and cross link polymers. The topic is covered at an advanced level in relation to nanotechnology and requires background knowledge in eight grade science. A powerpoint with illustrations and instructor guide (available as both a Microsoft Word Document and PDF) containing activities are included to aid in teaching this subject.

2012-10-16

150

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

NASA Astrophysics Data System (ADS)

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 capabilities—that 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 the 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 150 °C for up to 5 h or to 125 °C for up to 24 h if stabilized with 10,000 ppm BQ and could also be heated to 125 °C for up to 5 h 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.

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

2013-02-01

151

Electro-activate styrene-based shape memory polymer nanocomposite filled with multi-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

The fabrication and characterization, especially mechanical and electrical properties, of styrene-based shape memory polymer mixed with multi-walled carbon nanotubes (MWNTs) are presented in this paper. It is found that surface-modified MWNTs incorporated very well with resin processed by royal water, and dispersion was achieved by high-energy sonication in the solution. Scanning Electron Microscope (SEM) is shown that the particulate additives were dispersed homogeneously within matrix and served as local conductive paths. The glass transition temperature (Tg) of the composite containing MWNTs is lower than that of the pure SMP obtained from Differential Scanning Calorimetry (DSC). With the increasing filler content, resulting in the reduction of Tg increases. The composites have a better thermodynamic stability awarding to the results of Thermal Gravity Analyzer (TGA). The vibration of MWNTs in composite system was obtained from Raman spectrums. For the mechanical property of SMP composite with 8 wt% MWNTs, its Young's modulus increases by 12.1% and the tensile strength by 8.1% as compared with that of the pure SMP. Four-point Van De Pauw method is introduced to investigate the electrical property of composites. An electrical conductivity of 1.25×10-3 S/cm is obtained for 8 wt% MWNTs composite.

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

2007-10-01

152

Are herbal compounds the next frontier for alleviating learning and memory impairments? An integrative look at memory, dementia and the promising therapeutics of traditional chinese medicines.  

PubMed

Recent advances in neuroscience have revealed a greater, in-depth understanding of the complexities associated with memory. Contemporary theories hold that an integral relationship between memory formation, stabilization and consolidation revolve around plasticity of neuronal networks. The associated requisite receptors ?-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and N-methyl-d-aspartate (NMDA) and cellular mechanisms surrounding plasticity (posed to incite molecular functionality), also display strong correlations in the pathogenesis of dementias. When the brain is in a diseased state as a result of malignant neurotransmission (i.e. in Alzheimer's disease; AD), the homeostatic balance required for normal neuronal processes is disrupted, which leads to degeneration of neural circuitry. Present efforts to find new treatments aimed at reversing or halting neurodegeneration are immense, with increasing attention being placed on investigating various herbal medicines. A wide variety of herbal plants (i.e. Panax ginseng, Polygala tenuifolia, Acorus gramineus and Huperzia serrata, examined here within), extracts and compounds have, to date, already presented advantageous results when tested against known pathogenic markers related to AD-associated dementia. The efficaciousness of herbal medicines appears to be a modulatory effect on neurotrophins, kinases and their substrates that, in turn, initiate or take part in intracellular cascades related to memory processes. PMID:21305632

Jesky, Robert; Hailong, Chen

2011-02-09

153

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

PubMed

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

England, Richard M; Masiá, Esther; Giménez, Vanessa; Lucas, Rut; Vicent, María J

2012-08-23

154

On the origin of the Vogel-Fulcher-Tammann law in the thermo-responsive shape memory effect of amorphous polymers  

NASA Astrophysics Data System (ADS)

All amorphous shape memory polymers (SMPs) are featured by their relaxation behavior above and below the switching transition temperature (TSW). Above TSW, the glass transition and secondary transition merge together, resulting in the cooperative (?) movement in polymer macromolecules. Below TSW, movement is non-cooperative (?). In this study, three thermodynamic constitutive frameworks for the shape recovery behavior in amorphous SMPs are proposed based on the Arrhenius, Vogel-Fulcher-Tammann (VFT) and Bässler laws, respectively, and incorporated with parameters (stress, strain and relaxation time) as functions of temperature. The relaxation times of ? and ? movements satisfy the VFT and Arrhenius laws, respectively. The simulation is compared with the available experimental results reported in the literature for verification. The VFT law is found to be better than the other models, and is able to provide an accurate prediction for the temperature dependent relaxation behavior, from the Arrhenius behavior below, to the Williams-Landel-Ferry behavior above TSW.

Lu, Haibao; Huang, Wei Min

2013-10-01

155

Surface modification of medical implant materials with hydrophilic polymers for enhanced biocompatibility and delivery of therapeutic agents  

Microsoft Academic Search

In the research reported here, the surface modification of medical grade poly(dimethyl siloxane), polyetherurethane, and stainless steel through gamma-radiation grafting of hydrophilic polymers was investigated. Emphasis was placed on developing improved and simplified surface modification methods that produce more stable and more bioacceptible hydrophilic graft surfaces. As a result of this research, new surface modification techniques were developed that yield

Daniel J. Urbaniak

2004-01-01

156

Demonstrating the influence of water on shape-memory polymer networks based on poly[(rac-lactide)-co-glycolide] segments in vitro.  

PubMed

Thermally-responsive shape-memory polymers (SMP) are highly promising implant materials for applications in minimally-invasive surgery since the shape-memory effect (SME) enables the implantation of a bulky device in a compressed temporary state through a small incision. When heated to a temperature exceeding the material switching temperature (Tsw), the device recovers its original bulky shape. Therefore, SMP implants with Tsw ~ 37 °C are required for such applications because the body cannot withstand excessive applications of heat. Here, Tsw of networks based on poly[(rac-lactide)-co-glycolide] star-shaped macrotriol or macrotetrols with 19-22 wt% glycolide content, varying oligomer molecular weight (Mn = 3000-10000 g·mol-1), and netpoint functionality (f = 3 or 4) were lowered from 55-66 °C to below body temperature via the uptake of water, which also induced SME at body temperature. Programmed samples kept their temporary shape at room temperature in water as well as at 37 °C under dry conditions but recovered in 37 °C water. Water uptake/swelling studies and FTIR analysis indicated that the mechanism of solvent-induced SME involved the plasticization of water in switching domains as opposed to changes in swelling or hydrogen bonding. This indirect actuation of SME by using a combination of solvent and heat could be exploited in easy-to-handle shape-memory implant with slower degradation kinetics. PMID:21374570

Pierce, Benjamin F; Bellin, Katja; Behl, Marc; Lendlein, Andreas

2011-02-01

157

Enhancement of Cell-Based Therapeutic Angiogenesis Using a Novel Type of Injectable Scaffolds of Hydroxyapatite-Polymer Nanocomposite Microspheres  

PubMed Central

Background Clinical trials demonstrate the effectiveness of cell-based therapeutic angiogenesis in patients with severe ischemic diseases; however, their success remains limited. Maintaining transplanted cells in place are expected to augment the cell-based therapeutic angiogenesis. We have reported that nano-hydroxyapatite (HAp) coating on medical devices shows marked cell adhesiveness. Using this nanotechnology, HAp-coated poly(l-lactic acid) (PLLA) microspheres, named nano-scaffold (NS), were generated as a non-biological, biodegradable and injectable cell scaffold. We investigate the effectiveness of NS on cell-based therapeutic angiogenesis. Methods and Results Bone marrow mononuclear cells (BMNC) and NS or control PLLA microspheres (LA) were intramuscularly co-implanted into mice ischemic hindlimbs. When BMNC derived from enhanced green fluorescent protein (EGFP)-transgenic mice were injected into ischemic muscle, the muscle GFP level in NS+BMNC group was approximate fivefold higher than that in BMNC or LA+BMNC groups seven days after operation. Kaplan-Meier analysis demonstrated that NS+BMNC markedly prevented hindlimb necrosis (P<0.05 vs. BMNC or LA+BMNC). NS+BMNC revealed much higher induction of angiogenesis in ischemic tissues and collateral blood flow confirmed by three-dimensional computed tomography angiography than those of BMNC or LA+BMNC groups. NS-enhanced therapeutic angiogenesis and arteriogenesis showed good correlations with increased intramuscular levels of vascular endothelial growth factor and fibroblast growth factor-2. NS co-implantation also prevented apoptotic cell death of transplanted cells, resulting in prolonged cell retention. Conclusion A novel and feasible injectable cell scaffold potentiates cell-based therapeutic angiogenesis, which could be extremely useful for the treatment of severe ischemic disorders.

Koyama, Hidenori; Okada, Masahiro; Tanaka, Shinji; Shoji, Tetsuo; Emoto, Masanori; Furuzono, Tsutomu; Nishizawa, Yoshiki; Inaba, Masaaki

2012-01-01

158

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

Microsoft Academic Search

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

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

2007-01-01

159

A nonvolatile memory device made of a ferroelectric polymer gate nanodot and a single-walled carbon nanotube.  

PubMed

We demonstrate a field-effect nonvolatile memory device made of a ferroelectric copolymer gate nanodot and a single-walled carbon nanotube (SW-CNT). A position-controlled dip-pen nanolithography was performed to deposit a poly(vinylidene fluoride-ran-trifluoroethylene) (PVDF-TrFE) nanodot onto the SW-CNT channel with both a source and drain for field-effect transistor (FET) function. PVDF-TrFE was chosen as a gate dielectric nanodot in order to efficiently exploit its bipolar chemical nature. A piezoelectric force microscopy study confirmed the canonical ferroelectric responses of the PVDF-TrFE nanodot fabricated at the center of the SW-CNT channel. The two distinct ferroelectric polarization states with the stable current retention and fatigue-resistant characteristics make the present PVDF-TrFE-based FET suitable for nonvolatile memory applications. PMID:21050014

Son, Jong Yeog; Ryu, Sangwoo; Park, Yoon-Cheol; Lim, Yun-Tak; Shin, Yun-Sok; Shin, Young-Han; Jang, Hyun Myung

2010-11-04

160

Depression and the causal role of specific memory system degenerations: link may be supported by reported therapeutic benefits of Omega 3 fatty acids.  

PubMed

It is well documented that depressed patients, as a result of their illness, often experience some difficulties with their memory. This hypothesis suggests a vice-versa; that it is a gradual impairment and ultimate failure of specific memory systems that may underpin the onset and continuation of a depressive illness. So particular memory systems of the brain may have a greater role to play in clinical depression and associated anxiety than is generally recognised. A common feature of electroconvulsive therapy (ECT) is that it affects patients' short-term memory adversely. However, in line with the hypothesis, it is suggested that the mechanism of action of successful ECT treatment is that it facilitates the repair and reactivation of particular memory systems. One link that has some bearing on this hypothesis is that of Omega 3 fish oil. It has in some cases been observed to aid recovery of depression and possibly prevent relapse. It has been shown to improve memory. PMID:17368750

Frais, Anthony T

2007-03-26

161

Shape memory polymer foams for cerebral aneurysm reparation: effects of plasma sterilization on physical properties and cytocompatibility.  

PubMed

Shape memory polyurethanes (SMPUs) represent promising candidate materials for aneurysm embolization, since they could enable clinical problems still associated with these clinical procedures to be overcome. In this work, we report on the characterization of physicochemical, thermomechanical and in vitro interface properties of two SMPU foams (Cold Hibernated Elastic Memory, CHEM), proposed as a material for embolization devices in minimally invasive procedures. Moreover, because device sterilization is mandatory for in vivo applications, effects on the properties of the foams after plasma sterilization were also evaluated. Both foams (CHEM 3520 and CHEM 5520) showed excellent shape recovery ability (recovery rate, R(r), up to 99%) in conventional shape recovery tests, performed at constant heating rate. Transition temperatures (T(trans)), determined by tandelta peaks in dynamic mechanical analysis (DMA), were 32.2 and 45.1 degrees C, for CHEM 3520 and 5520, respectively. The value of T(trans) affects shape memory ability in the recovery test at 37 degrees C, which simulates the behavior after implantation of the device: in fact, R(r) was significantly higher for lower T(trans) foam (R(r) approximately 82% and R(r) approximately 46%, respectively, for CHEM 3520 and CHEM 5520). After plasma sterilization performed by a Sterrad sterilization system, an increase in open porosity was observed: this is probably due to the sterilization cycle; however, no effects on shape recovery behavior were observed. Furthermore, plasma treatment had no significant effect on L929 cells in in vitro cytotoxicity tests, performed on cell culture medium extracts in contact with foams for up to 7 days. Moreover, direct cytocompatibility tests showed a good colonization and growth from L929 cells on CHEM foams, suggesting the effectiveness of an in vivo healing process. All these results seem to suggest that CHEM foams could be advantageously used for manufacturing devices for mini-invasive embolization procedures of aneurysms. PMID:19136318

De Nardo, Luigi; Alberti, Rachele; Cigada, Alberto; Yahia, L'Hocine; Tanzi, Maria Cristina; Farè, Silvia

2008-12-13

162

Stronger and faster degradable biobased poly(propylene sebacate) as shape memory polymer by incorporating boehmite nanoplatelets.  

PubMed

Boehmite (BM) nanoplatelets were adopted to compound with fully biobased poly(propylene sebacate) (PPSe) to form the shape memory composites. The PPSe/BM composites kept excellent shape memory properties as previously reported PPSe. Compared to neat PPSe, the composites possess much higher mechanical properties above the melting point and faster biodegradation rate, which was demonstrated via tensile test at elevated temperature and in vitro degradation experiments in phosphate buffer saline (PBS), respectively. The obviously improved mechanical properties at elevated temperature are attributed to the uniform dispersion of the reinforcing boehmite nanoplatelets, which was facilitated by the interfacial interaction between BM and PPSe as revealed by FTIR, XPS, and XRD results. The faster degradation is correlated to accelerated hydrolysis by basic boehmite with surface aluminols. The potential biocompatibility, as substantiated by the outstanding cell viability and cell attachment, together with the realization of transformation temperature close to body temperature makes the PPSe/BM composites suitable for the biomedical applications, such as stents, in human body. PMID:22817474

Guo, Wenshan; Kang, Hailan; Chen, Yongwen; Guo, Baochun; Zhang, Liqun

2012-07-31

163

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)

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.

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

2010-05-01

164

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

NASA Astrophysics Data System (ADS)

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.

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

2007-12-01

165

Chemically cross-linked thin poly(vinylidene fluoride-co-trifluoroethylene)films for nonvolatile ferroelectric polymer memory.  

PubMed

Both chemically and electrically robust ferroelectric poly(vinylidene fluoride-co-trifluoro ethylene) (PVDF-TrFE) films were developed by spin-coating and subsequent thermal annealing with the thermal cross-linking agent 2,4,4-trimethyl-1,6-hexanediamine (THDA). Well-defined ferroelectric ? crystalline domains were developed with THDA up to approximately 50 wt %, with respect to polymer concentration, resulting in characteristic ferroelectric hysteresis polarization-voltage loops in metal/cross-linked ferroelectric layer/metal capacitors with remnant polarization of approximately 4 ?C/cm(2). Our chemically networked film allowed for facile stacking of a solution-processable organic semiconductor on top of the film, leading to a bottom-gate ferroelectric field effect transistor (FeFET). A low-voltage operating FeFET was realized with a networked PVDF-TrFE film, which had significantly reduced gate leakage current between the drain and gate electrodes. A solution-processed single crystalline tri-isopropylsilylethynyl pentacene FeFET with a chemically cross-linked PVDF-TrFE film showed reliable I-V hysteresis with source-drain ON/OFF current bistablility of 1 × 10(3) at a sweeping gate voltage of ±20 V. Furthermore, both thermal micro/nanoimprinting and transfer printing techniques were conveniently combined for micro/nanopatterning of chemically resistant cross-linked PVDF-TrFE films. PMID:21302914

Shin, Yu Jin; Kang, Seok Ju; Jung, Hee Joon; Park, Youn Jung; Bae, Insung; Choi, Dong Hoon; Park, Cheolmin

2011-02-08

166

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

A wealth of data collected in recent decades has demonstrated that ovarian sex-steroid hormones, particularly 17?-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.

Frick, Karyn M.

2012-01-01

167

Shape-memory materials and hybrid composites for smart systems: Part I Shape-memory materials  

Microsoft Academic Search

A review is presented of the current research and development of shape-memory materials, including shape-memory alloys, shape-memory ceramics and shape-memory polymers. The shape-memory materials exhibit some novel performances, such as sensoring (thermal, stress or field), large-stroke actuation, high damping, adaptive responses, shape memory and superelasticity capability, which can be utilized in various engineering approaches to smart systems. Based on an

Z. G. Wei; R. Sandstroröm; S. Miyazaki

1998-01-01

168

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

PubMed

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 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. 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

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

2013-02-15

169

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

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

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

2007-01-01

170

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

PubMed

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

Brindley, Rob; Bateman, Andrew; Gracey, Fergus

2011-06-01

171

Building a Better Hormone Therapy?: How Understanding The Rapid Effects of Sex Steroid Hormones Could Lead to New Therapeutics for Age-Related Memory Decline  

Microsoft Academic Search

A wealth of data collected in recent decades has demonstrated that ovarian sex-steroid hormones, particularly 17?-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.

Karyn M. Frick

2012-01-01

172

Memory Skill  

Microsoft Academic Search

Acquired memory skills best account for differences in memory performance. According to Chase and Ericsson's theory of skilled memory, improved memory or memory skills are due to the acquisition of more efficient storage and retrieval processes using long-term memory (LTM). Their theory specifies three principles which characterize the structure of memory skills. First, information rapidly stored in LTM is encoded

K. Anders Ericsson

1985-01-01

173

"Only Connect"--A Sexually Abused Girl's Rediscovery of Memory and Meaning as She Works towards the Transition from a Therapeutic Community to a Foster-Family  

ERIC Educational Resources Information Center

|This paper looks at the role of individual psychotherapy with a severely sexually abused girl in a therapeutic community, and the place of this work as she makes the transition into foster-care. It emphasizes the importance, not only of the individual work, but also of the drawing together of the work around the child, particularly at such a…

Cant, Diana

2005-01-01

174

Fatty Acid Based Biodegradable Polymer  

Microsoft Academic Search

Synthetic polymers have become an indispensable part of the daily?life of human beings and the biodegradable class of polymers hold immense value in therapeutics. Fatty acid incorporation in biodegradable polymers renders flexibility, low melting point, hydrophobicity, and pliability properties. At the same time, degradation into naturally occurring compounds makes them environmentally friendly besides their utility in various applications like drug

Jay Prakash Jain; Marina Sokolsky; Neeraj Kumar; A. J. Domb

2008-01-01

175

Augmentation of Therapeutic Efficacy in Drug-Resistant Tumor Models Using Ceramide Coadministration in Temporal-Controlled Polymer-Blend Nanoparticle Delivery Systems  

Microsoft Academic Search

The development of multidrug resistance (MDR) is a major hindrance to cancer eradication as it renders tumors unresponsive\\u000a to most chemotherapeutic treatments and is associated with cancer resurgence. This study describes a novel mechanism to overcome\\u000a MDR through a polymer-blend nanoparticle platform that delivers a combination therapy of C6-ceramide (CER), a synthetic analog\\u000a of an endogenously occurring apoptotic modulator, together

Lilian E. van Vlerken; Zhenfeng Duan; Steven R. Little; Michael V. Seiden; Mansoor M. Amiji

2010-01-01

176

Polymer conjugates as anticancer nanomedicines  

Microsoft Academic Search

The transfer of polymer–protein conjugates into routine clinical use, and the clinical development of polymer–anticancer-drug conjugates, both as single agents and as components of combination therapy, is establishing polymer therapeutics as one of the first classes of anticancer nanomedicines. There is growing optimism that ever more sophisticated polymer-based vectors will be a signficant addition to the armoury currently used for

Ruth Duncan

2006-01-01

177

Therapeutic Touch  

MedlinePLUS

... Ashford RL. Therapeutic touch for healing acute wounds. Cochrane Database Syst Rev. 2003;(4):CD002766. Robinson J, ... FC, Dolk H. Therapeutic touch for anxiety disorders. Cochrane Database Syst Rev. 2007 Jul 18;(3):CD006240. ...

178

Neural transdifferentiation of human bone marrow mesenchymal stem cells on hydrophobic polymer-modified surface and therapeutic effects in an animal model of ischemic stroke.  

PubMed

Human bone marrow-derived mesenchymal stem cells (MSCs) have multi-lineage differentiation potential and can become cells of mesodermal and neural lineages. These stem cells thus hold considerable clinical promise for the treatment of neurodegenerative diseases. For successful regeneration of damaged neural tissues, directed differentiation of neural or neuronal precursor cells from MSCs and integration of transplanted cells are pivotal factors. We induced MSCs into neurogenesis using a modified protocol. The therapeutic potency of the resulting neural progenitor cells in a rat model of ischemic stroke was analyzed. Using a highly hydrophobic diphenylamino-s-triazine-bridged p-phenylene (DTOPV)-coated surface and adopting a procedure for propagation of neural stem cells, we efficiently converted MSCs into neurosphere-like cellular aggregates (NS-MSCs). The spherical cells were subsequently induced to differentiate into neural cells expressing neuroectodermal markers. To determine whether these cells had neuronal fates and induced neuro-protective effects in vivo, NS-MSCs were intra-cerebrally administered to rats 48h after permanent middle cerebral artery occlusion (pMCAo). The results showed a remarkable attenuation of ischemic damage with significant functional recovery, although the cells were not fully incorporated into the damaged tissues on post-operative day 26. Improvement in the NS-MSC-transplanted rats was faster than in the MSC group and suppression of inflammation was likely the key factor. Thus, our culture system using the hydrophobic surface of a biocompatible DTOPV coating efficiently supported neural cell differentiation from MSCs. Neural-primed MSCs exhibited stronger therapeutic effects than MSCs in rat brains with pMCAo. PMID:23454369

Heo, J S; Choi, S-M; Kim, H O; Kim, E H; You, J; Park, T; Kim, E; Kim, H-S

2013-02-20

179

Temperature-dependent electron transport in highly ordered Co/Al2O3 core-shell nanocrystal memory synthesized with di-block co-polymers  

NASA Astrophysics Data System (ADS)

Di-block copolymer synthesized Co/Al2O3 core-shell nanocrystal (NC) capacitors were fabricated in order to study the temperature-dependent electron transport. The capacitance-voltage memory window is shown to increase proportionally with the substrate temperature, saturating at 3.5 V, at 175 °C. At elevated operating temperatures, the tunneling of electrons increases, resulting in large flatband voltage shift. Furthermore, the electron leakage of the NCs at high temperature is faster than the leakage at room temperature due to thermally assisted tunneling. The activation energy is determined by exponentially fitting the thermally dependent retention performance, which was then used to model the occupied energy levels and further elucidate the electron transport within the NC memory.

Zhou, Huimei; Dorman, James A.; Perng, Ya-Chuan; Chang, Jane P.; Liu, Jianlin

2012-03-01

180

Therapeutic cells via functional modification: influence of molecular properties of polymer grafts on in vivo circulation, clearance, immunogenicity, and antigen protection.  

PubMed

Modulation of cell surface properties via functional modification is of great interest in cell-based therapies, drug delivery, and in transfusion. We study the in vivo circulation, immuogenicity, and mechanism of clearance of hyperbranched polyglycerol (HPG)-modified red blood cells (RBCs) as a function of molecular properties of HPGs. The circulation half-life of modified cells can be modulated by controlling the polymer graft concentration on RBCs; low graft concentrations (0.25 and 0.5 mM) showed normal circulation as that of control RBCs. Molecular weight of HPG did not affect the circulation of modified RBCs. HPG grafting on RBCs reduced CD47 self-protein accessibility in a graft concentration-dependent fashion. HPG-grafted RBCs are not immunogenic, as is evident from their similar circulation profile upon repeated administration in mice and monitoring over 100 days. Histological examination of the spleen, liver, and kidneys of the mice injected with modified RBCs revealed distinct differences, such as elevated iron deposits and an increase in the number of CD45 expressing cells at high graft concentration of HPGs (1.5 mM); no changes were seen at low graft concentration. The absence of iron deposits in the white pulp region of the spleen and its presence in the red pulp region indicates that the clearance of functional RBCs occurs in the venous sinuses mechanical filtering system, similar to the clearance of unmodified senescent RBCs. HPG modification at grafting concentrations that yield long circulation in mice produced camouflage of a large number of minor blood group antigens on human RBCs, demonstrating its utility in chronic transfusion. The normal circulation, nonimmunogenic nature, and the potential to modulate the circulation time of modified cells without toxicity make this HPG-based cell surface modification approach attractive for drug delivery and other cell-based therapies. PMID:23713758

Chapanian, Rafi; Constantinescu, Iren; Medvedev, Nadia; Scott, Mark D; Brooks, Donald E; Kizhakkedathu, Jayachandran N

2013-05-28

181

A rapamycin-binding protein polymer nanoparticle shows potent therapeutic activity in suppressing autoimmune dacryoadenitis in a mouse model of Sjögren's syndrome.  

PubMed

Sjögren's syndrome (SjS) is a chronic autoimmune disease characterized initially by lymphocytic infiltration and destruction of exocrine glands, followed by systemic organ damage and B-cell lymphoma. Conventional treatment is based on management of symptoms and there is a shortage of therapies that address the underlying causes of inflammation at source exocrine tissue. The aim of this study was to test a novel protein polymer-based platform consisting of diblock copolymers composed from Elastin-like Polypeptides (ELPs) fused with FKBP12, to deliver a potent immunosuppressant with dose-limiting toxicity, rapamycin (Rapa) also known as Sirolimus, and evaluate its effects on the inflamed lacrimal gland (LG) of non-obese diabetic mouse (NOD), a classic mouse model of SjS. Both soluble and diblock copolymer ELPs were fused to FKBP12 and characterized with respect to purity, hydrodynamic radii, drug entrapment and release. Both formulations showed successful association with Rapa; however, the nanoparticle formulation, FSI, released drug with nearly a 5 fold longer terminal half-life of 62.5h. The strong interaction of FSI nanoparticles with Rapa was confirmed in vivo by a shift in the monoexponential pharmacokinetic profile for free drug to a biexponential profile for the nanoparticle formulation. When acutely administered by injection into NOD mice via the tail vein, this FSI formulation significantly suppressed lymphocytic infiltration in the LG relative to the control group while reducing toxicity. There was also a significant effect on inflammatory and mammalian target of Rapamycin (mTOR) pathway genes in the LG and surprisingly, our nanoparticle formulation was significantly better at decreasing a proposed tear biomarker of SjS, cathepsin S (CATS) compared to free drug. These findings suggest that FSI is a promising tool for delivering Rapa for treatment of SjS in a murine model and may be further explored to meet the unmet medical challenge of SjS. PMID:23892265

Shah, Mihir; Edman, Maria C; Janga, Srikanth R; Shi, Pu; Dhandhukia, Jugal; Liu, Siyu; Louie, Stan G; Rodgers, Kathleen; Mackay, J Andrew; Hamm-Alvarez, Sarah F

2013-07-25

182

Memory Palaces  

ERIC Educational Resources Information Center

This article presents a lesson called Memory Palaces. A memory palace is a memory tool used to remember information, usually as visual images, in a sequence that is logical to the person remembering it. In his book, "In the Palaces of Memory", George Johnson calls them "...structure(s) for arranging knowledge. Lots of connections to language arts,…

Wood, Marianne

2007-01-01

183

Memory Palaces  

ERIC Educational Resources Information Center

|This article presents a lesson called Memory Palaces. A memory palace is a memory tool used to remember information, usually as visual images, in a sequence that is logical to the person remembering it. In his book, "In the Palaces of Memory", George Johnson calls them "...structure(s) for arranging knowledge. Lots of connections to language…

Wood, Marianne

2007-01-01

184

Anomalous dynamics of polymer translocation  

NASA Astrophysics Data System (ADS)

We study the passage times of a translocating polymer of length N in three dimensions, while it passes through a narrow pore. We show that the behavior of the polymer stems from the polymer dynamics at the immediate vicinity of the pore --- in particular, the memory effects in the polymer chain tension imbalance across the pore. We take as a reaction coordinate the number s of the monomer residing in the pore. in the case of unbiased translocation, these memory effects cause the mobility of s to be anomalous diffusion for times up to the Rouse time N˜N^1+2? or Zimm time N˜N^3?, without or with hydrodynamics, respectively. Here, ? is the Flory exponent. Beyond this time, the dynamics becomes ordinary diffusion. As a consequence, the pore blockade time scales with length as ?d˜N^2+?. If a force of sufficient strength is pulling on one end, the pore blockade time scales as ?d˜N^2 in the absence of hydrodynamics. If a voltage is applied across the pore, which drives the charged polymer, the pore blockade time scales as ?d˜N^(1+2?)/(1+?) without, and ?d˜N^3?/(1+?) with hydrodynamics. In these cases, the pore blockade time decreases inversely with force and field strength, respectively. Our theoretical framework is substantiated with high-precision computer simulations. We will show that memory effects similar to those governing translocation, also play a role in the dynamics of dense polymer solutions and polymer melts.

Barkema, Gerard

2009-03-01

185

Working Memory  

Microsoft Academic Search

The term working memory refers to a brain system that provides temporary storage and manipulation of the information necessary for such complex cognitive tasks as language comprehension, learning, and reasoning. This definition has evolved from the concept of a unitary short-term memory system. Working memory has been found to require the simultaneous storage and processing of information. It can be

Alan Baddeley

1992-01-01

186

Virtual Memory  

Microsoft Academic Search

\\\\The need for automatic storage allocation arises from desires for program modularity, machine independence, and resource sharing. Virtual memory is an elegant way of achieving these objectives. In a virtual memory, the addresses a program may use to identify information are distinguished from the addresses the memory system uses to identify physical storage sites, and program-generated addresses are translated automatically

Peter J. Denning

1970-01-01

187

CLONAL MEMORY  

PubMed Central

A single clone of B cells producing anti-DNP antibody recognizable by the isoelectric-focusing spectrum has been used, in a double transfer system, to study clonal memory. Trasnsferable B memory develops between 4 and 7 days after the first transfer with antigen. B-memory cells thus proliferate before or concomitantly with antibody-forming cells.

McMichael, A. J.; Williamson, A. R.

1974-01-01

188

Therapeutic Community.  

National Technical Information Service (NTIS)

Therapeutic community programs were the subject of a 1976 conference which was intended to establish a working environment in which representatives of such programs could work towards conceptualizing the status of the field and formulating suitable respon...

G. deLeon G. M. Beschner

1977-01-01

189

New PVK-based photorefractive polymers  

NASA Astrophysics Data System (ADS)

This work describes the development, characterization and optimization of materials for optical memory storage applications. The photorefractive polymers are designed to contain second-order nonlinear optical (NLO) chromophores and charge transporting (CT) molecules embedded in a polymer matrix. The necessary electrooptic response is achieved by subjecting samples to a strong dc electric fields in order to induce a non-centrosymmetric arrangement of the NLO chromophores. This paper presents work performed on the design of a new multifunctional NLO-CT polymer.

Burzynski, Ryszard; Ghosal, Saswati; Casstevens, Martin K.; Kumar, Deepak N.; Weibel, John F.

1998-12-01

190

Quantum memory Quantum memory  

NASA Astrophysics Data System (ADS)

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 main—while still overlapping—classes. 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.

Le Gouët, Jean-Louis; Moiseev, Sergey

2012-06-01

191

Poor working memory predicts false memories  

Microsoft Academic Search

Two studies investigated whether individual differences in simple span verbal working memory and complex working memory capacity are related to memory accuracy and susceptibility to false memory development. In Study 1, undergraduate students (N=60) were given two simple span working memory tests: forward and backward digit span. They also underwent a memory task that is known to elicit false memories

Maarten J. V. Peters; Marko Jelicic; Hilde Verbeek; Harald Merckelbach

2007-01-01

192

Therapeutic Nanodevices  

NASA Astrophysics Data System (ADS)

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'être 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.

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

193

Therapeutic Nanodevices  

NASA Astrophysics Data System (ADS)

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.

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

194

Therapeutic proteins.  

PubMed

Protein-based therapeutics are highly successful in clinic and currently enjoy unprecedented recognition of their potential. More than 100 genuine and similar number of modified therapeutic proteins are approved for clinical use in the European Union and the USA with 2010 sales of US$108 bln; monoclonal antibodies (mAbs) accounted for almost half (48%) of the sales. Based on their pharmacological activity, they can be divided into five groups: (a) replacing a protein that is deficient or abnormal; (b) augmenting an existing pathway; (c) providing a novel function or activity; (d) interfering with a molecule or organism; and (e) delivering other compounds or proteins, such as a radionuclide, cytotoxic drug, or effector proteins. Therapeutic proteins can also be grouped based on their molecular types that include antibody-based drugs, Fc fusion proteins, anticoagulants, blood factors, bone morphogenetic proteins, engineered protein scaffolds, enzymes, growth factors, hormones, interferons, interleukins, and thrombolytics. They can also be classified based on their molecular mechanism of activity as (a) binding non-covalently to target, e.g., mAbs; (b) affecting covalent bonds, e.g., enzymes; and (c) exerting activity without specific interactions, e.g., serum albumin. Most protein therapeutics currently on the market are recombinant and hundreds of them are in clinical trials for therapy of cancers, immune disorders, infections, and other diseases. New engineered proteins, including bispecific mAbs and multispecific fusion proteins, mAbs conjugated with small molecule drugs, and proteins with optimized pharmacokinetics, are currently under development. However, in the last several decades, there are no conceptually new methodological developments comparable, e.g., to genetic engineering leading to the development of recombinant therapeutic proteins. It appears that a paradigm change in methodologies and understanding of mechanisms is needed to overcome major challenges, including resistance to therapy, access to targets, complexity of biological systems, and individual variations. PMID:22735943

Dimitrov, Dimiter S

2012-01-01

195

What is a Suggestion? The Neuroscience of Implicit Processing Heuristics in Therapeutic Hypnosis and Psychotherapy  

Microsoft Academic Search

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, \\

Ernest L. Rossi; Kathryn L. Rossi

2007-01-01

196

Distributed Memory.  

National Technical Information Service (NTIS)

A brief account is given of how a neural network can store a distributed content addressable memory. Some of the properties of such a network as well as a possible site of storage of long and short term memory are discussed.

L. N. Cooper

1985-01-01

197

Episodic Memories  

ERIC Educational Resources Information Center

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…

Conway, Martin A.

2009-01-01

198

VLSI Memories,  

National Technical Information Service (NTIS)

The article, an update on Mitsubishi VLSI memory technology, discusses main products including dynamic RAMs, static RAMs, ROM, and application-specific memory devices. The Corporation has developed a 4Mb dynamic RAM with a submicron (0.8 micrometer) desig...

M. Yamada S. Kayano T. Yoshihara H. Harima H. Hamano

1988-01-01

199

Moseley Memorial  

Microsoft Academic Search

THE fund founded in the University of Manchester for the provision of a memorial to the late H. G. J. Moseley (killed in action at Gallipoli, 1915), and originally proposed as a private memorial from Moseley's personal friends and fellow-workers in Manchester, has now been extended in order to give other scientific bodies, both in England and abroad, an opportunity

Henry A. Miers; C. G. Darwin; H. Robinson

1920-01-01

200

Quantum memory  

Microsoft Academic Search

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

Jean-Louis Le Gouët; Sergey Moiseev

2012-01-01

201

Collaging Memories  

ERIC Educational Resources Information Center

|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…

Wallach, Michele

2011-01-01

202

Nanostructured Shape Memory Alloys: Adaptive Composite Materials and Components.  

National Technical Information Service (NTIS)

Methods for fabricating adaptive composite materials and components using shape memory alloy (SMA) constituents were investigated using a variety of fabrication techniques, including mechanical rolling methods. Both SMA- polymer and SMA-metal composites w...

A. B. Ellis J. H. Perepezko W. C. Crone

2007-01-01

203

Polymer chemistry: Proteins in a pill  

NASA Astrophysics Data System (ADS)

Protein drugs are important therapies for many different diseases, but very few can be administered orally. Now, a cationic dendronized polymer has been shown to stabilize a therapeutic protein for delivery to the gut.

Maynard, Heather D.

2013-07-01

204

COMMENTARY Episodic Memory, Semantic Memory, and Amnesia  

Microsoft Academic Search

Episodic memory and semantic memory are two types of declarative memory. There have been two principal views about how this distinction might be reflected in the organization of memory functions in the brain. One view, that episodic memory and semantic memory are both dependent on the integrity of medial temporal lobe and midline dience- phalic structures, predicts that amnesic patients

Larry R. Squire; Stuart M. Zola

205

Silicon Polymers.  

National Technical Information Service (NTIS)

Unsaturated carbosilane polymers have been prepared by anionic as well as metathesis polymerization of silacyclopent-3-enes. Of particular interest, is unsaturated carbosilane polymers with Si-H substitution have been prepared. These complementary functio...

W. P. Weber

1992-01-01

206

Piezoelectric Polymers.  

National Technical Information Service (NTIS)

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 prom...

J. S. Harrison Z. Ounaies

2001-01-01

207

Conjugated polymers: Watching polymers dance  

NASA Astrophysics Data System (ADS)

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.

Rothberg, Lewis

2011-06-01

208

Memory reconsolidation.  

PubMed

The formation, storage and use of memories is critical for normal adaptive functioning, including the execution of goal-directed behavior, thinking, problem solving and decision-making, and is at the center of a variety of cognitive, addictive, mood, anxiety, and developmental disorders. Memory also significantly contributes to the shaping of human personality and character, and to social interactions. Hence, understanding how memories are formed, stored, retrieved, modified, updated and used potentially impacts many areas in human life, including mental health. PMID:24028957

Alberini, Cristina M; Ledoux, Joseph E

2013-09-01

209

New bioerodable thermoresponsive polymers for possible radiotherapeutic applications  

Microsoft Academic Search

A new thermoresponsive system designed for local radiotherapy has been developed. In this system a radionuclide complex is entrapped in a thermoresponsive polymer locally precipitated at body temperature after injection of a polymer–complex solution into the tissue where a therapeutic effect is required. The lifetime of the system is controlled by the rate of polymer hydrolysis, its dissolution and elimination

Martin Hruby; Jan Kucka; Ondrej Lebeda; Hana Mackova; Michal Babic; Cestmir Konak; Martin Studenovsky; Antonin Sikora; Jan Kozempel; Karel Ulbrich

2007-01-01

210

Memory Matters  

MedlinePLUS

... without even being knocked out (like in some concussions). Car accidents, bike accidents, and falls can cause ... an injury, which is not unusual with a concussion. Sometimes, these memories come back. More significant problems ...

211

Memory Metals.  

National Technical Information Service (NTIS)

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 1980...

1995-01-01

212

Memory loss  

MedlinePLUS

... alcohol abuse Migraine headache Mild head injury or concussion Nutritional problems (vitamin deficiencies such as low vitamin ... person suffering from low moods that impair concentration? Time pattern Has the memory loss been getting worse ...

213

Memory Grows.  

National Technical Information Service (NTIS)

The thesis is reaffirmed that form memory (recognition) resides in the morphology of neuronal arborescences, the latter constituting physiological counterparts of local phase portraits of the infinitesimal transformation groups involved. At birth the brai...

W. C. Hoffman

1970-01-01

214

Ferroelectric memories  

Microsoft Academic Search

In the past year it has become possible to fabricate ferroelectric thin-film memories onto standard silicon integrated circuits that combine very high speed (30-nanosecond read\\/erase\\/rewrite operation), 5-volt standard silicon logic levels, very high density (2 by 2 micrometer cell size), complete nonvolatility (no standby power required), and extreme radiation hardness. These ferroelectric random-access memories are expected to replace magnetic core

J. F. Scott; C. A. Paz de Araujo

1989-01-01

215

Simulations of Polymer Translocation  

NASA Astrophysics Data System (ADS)

Transport of molecules across membranes is an essential mechanism for life processes. These molecules are often long, and the pores in the membranes are too narrow for the molecules to pass through as a single unit. In such circumstances, the molecules have to squeeze -- i.e., translocate -- themselves through the pores. DNA, RNA and proteins are such naturally occuring long molecules in a variety of biological processes. Understandably, the process of translocation has been an active topic of current research: not only because it is a cornerstone of many biological processes, but also due to its relevance for practical applications. Translocation is a complicated process in living organisms -- the presence of chaperone molecules, pH, chemical potential gradients, and assisting molecular motors strongly influence its dynamics. Consequently, the translocation process has been empirically studied in great variety in biological literature. Study of translocation as a biophysical process is more recent. Herein, the polymer is simplified to a sequentially connected string of N monomers as it passes through a narrow pore on a membrane. The quantities of interest are the typical time scale for the polymer to leave a confining cell (the ``escape of a polymer from a vesicle'' time scale), and the typical time scale the polymer spends in the pore (the ``dwell'' time scale) as a function of N and other parameters like membrane thickness, membrane adsorption, electrochemical potential gradient, etc. Our research is focused on computer simulations of translocation. Since our main interest is in the scaling properties, we use a highly simplified description of the translocation process. The polymer is described as a self-avoiding walk on a lattice, and its dynamics consists of single-monomer jumps from one lattice site to another neighboring one. Since we have a very efficient program to simulate such polymer dynamics, which we decribe in Chapter 2, we can perform long simulations in which long polymers creep through tiny pores. In Chapter 3 we study pore blockage times for a translocating polymer of length N, driven by a field E across te pore. In three dimensions we find that the typical time the pore remains blocked during a translocation event scales as N^{1.37}/E We show that the scaling behavior stems from the polymer dynamics at the immediate vicinity of the pore -- in particular, the memory effects in the polymer chain tension imbalance across the pore. Chapter 4 studies the unbiased translocation of a polymer with length N, surrounded by equally long polymers, through a narrow pore in a membrane. We show that in dense polymeric systems a relaxation time exists that scales as N^{2.65}, much longer than the Rouse time N^2. If the polymers are well entangled, we find that the mean dwell times scales as N^{3.3}, while for shorter, less entangled polymers, we measure dwell times scaling as N^{2.7}. In Chapter 5 we study the translocation of an RNA molecule, pulled through a nanopore by an optical tweezer, as a method to determine its secondary structure. The resolution with which the elements of the secondary structure can be determined is limited by thermal fluctuations, ruling out single-nucleotide resolution under normal experimental conditions.

Vocks, H.

2008-07-01

216

Electrochemical Sensors Based on Organic Conjugated Polymers  

PubMed Central

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).

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

2008-01-01

217

Polymer adsorption  

NASA Astrophysics Data System (ADS)

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.

Joanny, Jean-Francois

2008-03-01

218

Natural Polymers  

NSDL National Science Digital Library

Polymers that exist in nature, called biopolymers , include a large and diverse range of compounds. This chapter discusses the most important types of natural polymers--their chemical makeup, key properties, and where they are found. The focus will be more on the chemical and physical properties of natural polymers and less on their biological synthesis or physiological function. The references at the end of the chapter provide additional information.

Teegarden, David

2004-01-01

219

Polymer Electrolytes  

NASA Astrophysics Data System (ADS)

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.

Hallinan, Daniel T.; Balsara, Nitash P.

2013-07-01

220

Episodic memory, semantic memory, and amnesia  

Microsoft Academic Search

ABSTRACT: Episodic memory,and semantic memory,are two types of declarative memory. There have been two principal views about how this distinction might be reflected in the organization of memory,functions in the brain. One view, that episodic memory and semantic memory are both dependent on the integrity of medial temporal lobe and midline dience- phalic structures, predicts that amnesic patients with medial

Larry R. Squire; Stuart M. Zola

1998-01-01

221

Polymers All Around You!  

ERIC Educational Resources Information Center

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

Gertz, Susan

222

Polymer flooding  

Microsoft Academic Search

This book covers all aspects of polymer flooding, an enhanced oil recovery method using water soluble polymers to increase the viscosity of flood water, for the displacement of crude oil from porous reservoir rocks. Although this method is becoming increasingly important, there is very little literature available for the engineer wishing to embark on such a project. In the past,

Littmann

1988-01-01

223

Polymers & People  

ERIC Educational Resources Information Center

|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…

Lentz, Linda; Robinson, Thomas; Martin, Elizabeth; Miller, Mary; Ashburn, Norma

2004-01-01

224

Polymer Informatics  

NASA Astrophysics Data System (ADS)

Polymers are arguably the most important set of materials in common use. The increasing adoption of both combinatorial as well as high-throughput approaches, coupled with an increasing amount of interdisciplinarity, has wrought tremendous change in the field of polymer science. Yet the informatics tools required to support and further enhance these changes are almost completely absent. In the first part of the chapter, a critical analysis of the challenges facing modern polymer informatics is provided. It is argued, that most of the problems facing the field today are rooted in the current scholarly communication process and the way in which chemists and polymer scientists handle and publish data. Furthermore, the chapter reviews existing modes of representing and communicating polymer information and discusses the impact, which the emergence of semantic technologies will have on the way in which scientific and polymer data is published and transmitted. In the second part, a review of the use of informatics tools for the prediction of polymer properties and in silico design of polymers is offered.

Adams, Nico

225

Molecularly imprinted polymers.  

PubMed

Molecular imprinting is a process that allows for the synthesis of artificial receptors for a given target molecule based on synthetic polymers. The target molecule acts as a template around which interacting and cross-linking monomers are arranged and co-polymerized to form a cast-like shell. In essence, a molecular memory is imprinted in the polymer, which is now capable of selectively binding the target. Molecularly imprinted polymers (MIPs) thus possess the most important feature of biological antibodies - specific molecular recognition. They can thus be used in applications where selective binding events are of importance, such as immunoassays, affinity separation, biosensors, and directed synthesis and catalysis. Since its beginnings in the 1970s, the technique of molecular imprinting has greatly diversified during the last decade both from a materials point of view and from an application point of view. Still, there is much room for further improvement. The key challenges, in particular the binding site homogeneity and water compatibility of MIPs, and the possibility of synthesizing MIPs specific for proteins, are actively addressed by research groups over the World. Other important points are the conception of composite materials based on MIPs, in order to include additional interesting properties into the material, and the synthesis of very small and quasi-soluble MIPs, close in size to proteins. PMID:22183146

Haupt, Karsten; Linares, Ana V; Bompart, Marc; Bui, Bernadette Tse Sum

2012-01-01

226

Super Memory  

NSDL National Science Digital Library

In this activity (pages 26-29 of the PDF), learners investigate how they can develop super memories by using mnemonic devices. In the first part of the activity, learners use mnemonic devices to memorize a group of random objects. In the second part, learners use mnemonic devices to memorize a phone number.

Text, Word

2001-01-01

227

Retracing Memories  

ERIC Educational Resources Information Center

|There are plenty of paths to poetry but few are as accessible as retracing ones own memories. When students are asked to write about something they remember, they are given them the gift of choosing from events that are important enough to recall. They remember because what happened was funny or scary or embarrassing or heartbreaking or silly.…

Harrison, David L.

2005-01-01

228

Memory Loss  

ERIC Educational Resources Information Center

In four decades of teaching college English, the author has watched many good teaching jobs morph into second-class ones. Worse, she has seen the memory and then the expectation of teaching jobs with decent status, security, and salary depart along with principles and collegiality. To help reverse this downward spiral, she contends that what is…

Cassebaum, Anne

2011-01-01

229

Memory grows  

Microsoft Academic Search

The thesis is reaffirmed that form memory (recognition) resides in the morphology of neuronal arborescences, the latter constituting physiological counterparts of local phase portraits of the infinitesimal transformation groups involved. At birth the brain comes equipped with essentially its full complement of neurons. These are initially in a very primitive, almost neuroblast form, but subsequently rapidly proliferate and branch, thus

William C. Hoffman

1971-01-01

230

Deep brain stimulation effects on memory.  

PubMed

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

Laxton, A W; Sankar, T; Lozano, A M; Hamani, C

2012-12-01

231

Increase of Azimuthal Anchoring Energy and Thermal Stability at Homogeneously Orientated Liquid Crystal\\/Polymer Interface  

Microsoft Academic Search

A surface memory effect appears on isotropic polymer surfaces when the polymer surface is exposed to a homogeneously orientated nematic liquid crystal (LC), and an azimuthal anchoring energy of the surface increases with exposure time. The increase of the anchoring energy is also observed in the homogeneous LC cell with rubbed polymer substrates, but not in the twisted nematic (TN)

Rumiko Yamaguchi; Susumu Sato

2000-01-01

232

The Therapeutic School.  

ERIC Educational Resources Information Center

Contributes to the recent research on specific institutional carriers of the therapeutic culture, such as the state, the corporation, and the self- help movement, defining therapeutic discourse and discussing the therapeutic ethic, the therapeutic school, schools of education and their critics, and disappointing results of therapeutic schooling.…

Rice, John Steadman

2002-01-01

233

Milestoning with coarse memory.  

PubMed

Milestoning is a method used to calculate the kinetics of molecular processes occurring on timescales inaccessible to traditional molecular dynamics (MD) simulations. In the method, the phase space of the system is partitioned by milestones (hypersurfaces), trajectories are initialized on each milestone, and short MD simulations are performed to calculate transitions between neighboring milestones. Long trajectories of the system are then reconstructed with a semi-Markov process from the observed statistics of transition. The procedure is typically justified by the assumption that trajectories lose memory between crossing successive milestones. Here we present Milestoning with Coarse Memory (MCM), a generalization of Milestoning that relaxes the memory loss assumption of conventional Milestoning. In the method, milestones are defined and sample transitions are calculated in the standard Milestoning way. Then, after it is clear where trajectories sample milestones, the milestones are broken up into distinct neighborhoods (clusters), and each sample transition is associated with two clusters: the cluster containing the coordinates the trajectory was initialized in, and the cluster (on the terminal milestone) containing trajectory's final coordinates. Long trajectories of the system are then reconstructed with a semi-Markov process in an extended state space built from milestone and cluster indices. To test the method, we apply it to a process that is particularly ill suited for Milestoning: the dynamics of a polymer confined to a narrow cylinder. We show that Milestoning calculations of both the mean first passage time and the mean transit time of reversal-which occurs when the end-to-end vector reverses direction-are significantly improved when MCM is applied. Finally, we note the overhead of performing MCM on top of conventional Milestoning is negligible. PMID:23614410

Hawk, Alexander T

2013-04-21

234

Memorial Poems and the Poetics of Memorializing  

Microsoft Academic Search

Public war memorials are sites of intense ideological negotiation, expressing the meaning of specific wars and their losses, whilst also speaking to private grief. War poetry also memorializes the experience of warfare and its effects. In poetry about war memorials, one form confronts the other. This essay initially considers poems that either embrace the values of the memorial or strenuously

Andrew Palmer; Sally Minogue

2010-01-01

235

Memorial Poems and the Poetics of Memorializing  

Microsoft Academic Search

: Public war memorials are sites of intense ideological negotiation, expressing the meaning of specific wars and their losses, whilst also speaking to private grief. War poetry also memorializes the experience of warfare and its effects. In poetry about war memorials, one form confronts the other. This essay initially considers poems that either embrace the values of the memorial or

Andrew Palmer; Sally Minogue

2010-01-01

236

On memories of childhood abuse: a phenomenological study  

Microsoft Academic Search

Objective: To explore the phenomenon of memories and reported recovered memories of childhood abuse, and to examine ways in which clients and therapists assess the veridicality of such memories.Method: Qualitative methodology utilizing phenomenological inquiry. Within the context of a wider study exploring perceptions of helpful and unhelpful factors in the therapeutic process, a sub-sample of 36 in-depth interviews with clients,

Peter Dale; John Allen

1998-01-01

237

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.

238

New Insights in Human Memory Interference and Consolidation  

PubMed Central

Learning new facts and skills in succession can be frustrating because no sooner has new knowledge been acquired than its retention is being jeopardized by learning another set of skills or facts. Interference between memories has recently provided important new insights into the neural and psychological systems responsible for memory processing. For example, interference occurs not only between the same types of memories; but can also occur between different types of memories, which has important implications for our understanding of memory organization. Converging evidence has begun to reveal that the brain produces interference independently from other aspects of memory processing, which suggests that interference may have an important but previously overlooked function. A memory’s initial susceptibility to interference and subsequent resistance to interference after its acquisition has revealed that memories continue to be processed ‘off-line’ during consolidation. Recent work has demonstrated that off-line processing is not limited to just the stabilization of a memory, which was once the defining characteristic of consolidation; instead, off-line processing can have a rich diversity of effects, from enhancing performance, to making hidden rules explicit. Off-line processing also occurs after memory retrieval when memories are destabilized and then subsequently restabalized during reconsolidation. Studies are beginning to reveal the function of reconsolidation, its mechanistic relationship to consolidation and its potential as a therapeutic target for the modification of memories.

Robertson, Edwin M.

2012-01-01

239

Bacopa monniera leaf extract ameliorates hypobaric hypoxia induced spatial memory impairment  

Microsoft Academic Search

Hypobaric hypoxia induced memory impairment has been attributed to several factors including increased oxidative stress, depleted mitochondrial bioenergetics, altered neurotransmission and apoptosis. This multifactorial response of the brain to hypobaric hypoxia limits the use of therapeutic agents that target individual pathways for ameliorating hypobaric hypoxia induced memory impairment. The present study aimed at exploring the therapeutic potential of a bacoside

Sunil Kumar Hota; Kalpana Barhwal; Iswar Baitharu; Dipti Prasad; Shashi Bala Singh; Govindasamy Ilavazhagan

2009-01-01

240

Radio Memories  

NSDL National Science Digital Library

The "Golden Age of Radio" that arguably lasted until the early 1950s may be hard to imagine today in an era of swirling iPod playlists and other genre-bending devices and technologies, but during this time the radio reigned supreme. People tuned in every week to hear the exploits of Flash Gordon, Sam Spade, and Amos n' Andy. Thanks to the Radio Memories website, many of these memories can be relived, or just experienced for the first time. Started in May 2005, the site contains a host of compelling programs, including episodes from the Interplanetary Adventures of Flash Gordon and a number of original episodes of the fabled Radio Detective Story Hour. If those types of programs fail to pique the interest of the casual visitor, the site also contains archived shows that explore the world of radio soap operas from the 1940s and the musical worlds of such stars as Tommy Dorsey and Harry James.

241

Polymers All Around You!  

ERIC Educational Resources Information Center

|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,…

Gertz, Susan

242

Microgravity Polymers.  

National Technical Information Service (NTIS)

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...

1986-01-01

243

Organometallic Polymers.  

ERIC Educational Resources Information Center

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)

Carraher, Charles E., Jr.

1981-01-01

244

Polymer batteries  

NASA Astrophysics Data System (ADS)

This paper presents a state-of-the-art report on polymer battery development. The research and development activities related to materials of construction for battery components, i.e., anode, electrolyte, and cathode are reviewed. Major achievements have been accomplished in the last decade and the progress is very encouraging. Some potential problems have been identified and these problems may require significant development efforts before polymer batteries become a commercial reality.

Kumar, Binod; Marsh, Richard A.

1991-04-01

245

Polymer Synthesis  

NSDL National Science Digital Library

In the first four chapters, we have seen that many different kinds of polymers exist and that they have an extremely wide range of properties. Some are stiff, others are soluble, while still others are rubbery. There are plastics, and fibers, and adhesives, and foams. The structure and composition of the macromolecule dictate the ultimate properties. Structure and composition are determined when the macromolecule is synthesized. In this chapter we want to understand how monomers react together to form long polymer chains.

Teegarden, David

2004-01-01

246

Memory karaoke: using a location-aware mobile reminiscence tool to support aging in place  

Microsoft Academic Search

Episodic memory exercises such as reminiscing and storytelling have been shown to provide therapeutic benefits for older adults by prolonging their ability to lead an independent lifestyle. In this paper, we describe a mobile reminiscence tool called Memory Karaoke, which facilitates episodic memory exercise through contextualized storytelling of meaningful experiences by using contextual cues such as location, time, and photos.

Karen P. Tang; Jason I. Hong; Ian E. Smith; Annie Ha; Lalatendu Satpathy

2007-01-01

247

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

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.

Gleberzon, Brian; Stuber, Kent

2013-01-01

248

Polymer/Solvent and Polymer/Polymer Interaction Studies.  

National Technical Information Service (NTIS)

Polymer/polymer and polymer/solvent interaction information can be obtained from solution thermodyanmic studies. In this work, gas chromatography and piezoelectric sorption techniques were used to obtain experimental solution data. A brief review of exper...

J. C. Holste C. J. Glover D. T. Magnuson K. C. Dangayach T. A. Powell

1979-01-01

249

Organizational emotional memory  

Microsoft Academic Search

Purpose – As a fascinating concept, the term of organizational memory attracted many researchers from a variety of disciplines. In particular, the content of organizational memory, which involves declarative and procedural memory, found broad research interest in the management literature. Nevertheless, there is sparse research in the management literature on the emotional content aspect of organizational memory. Emotional memory is

Ali E. Akgün; Halit Keskin; John Byrne

2012-01-01

250

Mechanisms of Memory.  

ERIC Educational Resources Information Center

|Focuses on the brain processes and brain systems involved in learning and memory from a neuropsychological perspective of analysis. Reports findings related to the locus of memory storage, types of memory and knowledge, and memory consolidation. Models of animal memory are also examined. An extensive reference list is included. (ML)|

Squire, Larry R.

1986-01-01

251

Self-assembling materials for therapeutic delivery.  

PubMed

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

Branco, Monica C; Schneider, Joel P

2008-10-10

252

Self-assembling materials for therapeutic delivery?  

PubMed Central

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.

Branco, Monica C.; Schneider, Joel P.

2009-01-01

253

Memory and Mourning: An Exhibit History  

Microsoft Academic Search

Mounted by the Strong Museum in Rochester, New York, in 1993, and traveling nationally thereafter, the exhibit Memory and Mourning provided historical and contemporary perspectives to help museum guests explore their own reactions to loss and grief. In the process the exhibit's development team encountered a range of philosophical, historical, psychological, and therapeutic issues that have surrounded bereavement in America.

Scott G. Eberle

2005-01-01

254

Types of Memory  

MedlinePLUS

... can be further divided into explicit, implicit and semantic memory. Explicit memories are facts that you made ... as driving a car or riding a bicycle. Semantic memories are facts that are so deeply ingrained ...

255

Coping with Memory Loss  

MedlinePLUS

Coping With Memory Loss Search the Consumer Updates Section Cerebral Cortex Previously formed memories are thought to be stored in the cerebral ... have a role in the formation of new memories partly through their connections with the hippocampus, and ...

256

How Memory Works  

MedlinePLUS

Memory functions through three steps: acquisition, consolidation and retrieval. 347126 InteliHealth 2010-02-10 f InteliHealth/Harvard Medical Content 2012-08-24 How Memory Works Memory functions through three steps: Acquisition Consolidation ...

257

Memorial Session  

NASA Astrophysics Data System (ADS)

Memorial session to honor Heinz H. Barschall's contributions to physics, to the physics community, and to The American Physical Society. 11:00 D. Allan Bromley, Yale University and president-elect, The American Physical Society 11:15 Robert K. Adair, Yale University 11:30 Sam M. Austin, Michigan State University 11:45 Jay C. Davis, Associate Director, LLNL 12:00 Ruth H. Howes, Ball State University 12:15 Harry Lustig, APS Treasurer Emeritus 12:30 Robert G. Sachs, University of Chicago

Bromley, D. Allan; Adair, Robert K.; Austin, Sam M.; Davis, Jay C.; Howes, Ruth H.; Lustig, Harry; Sachs, Robert G.

1997-04-01

258

Mnemosyne: lightweight persistent memory  

Microsoft Academic Search

New storage-class memory (SCM) technologies, such as phase-change memory, STT-RAM, and memristors, promise user-level access to non-volatile storage through regular memory instructions. These memory devices enable fast user-mode access to persistence, allowing regular in-memory data structures to survive system crashes. In this paper, we present Mnemosyne, a simple interface for programming with persistent memory. Mnemosyne addresses two challenges: how to

Haris Volos; Andres Jaan Tack; Michael M. Swift

2011-01-01

259

[Memory and its dysfunction].  

PubMed

In the last decades interdisciplinary research of memory takes place and it connects regions as cognitive psychology and neuroscience. Learning and memory are theoretical concepts, which enable to explain the fact that personal experience influences the behavior of the particular person. Memory has neuronal representation, which enables recollection of obtained experiences and information, and subsequently enables changes in behavior. The review describes events as registration, formation of memory trace as well as memory retrieval. Memory classification is possible according to many criteria, e.g. according to the length, its conscious recollection and the character of deposited information. Main types of memories are episodic memory (for facts and events), semantic memory (for general knowledge) and procedural memory (the ability to learn behavioral and cognitive abilities and algorithms). At present it is generally accepted that memory is a complicated process, which utilizes several brain structures at the same time that are called memory systems; according to the type of memory the experiences and information are deposited in various brain regions. The present research enables many approaches for determination of the sites of memory deposition. In the present period important role in memory localization have the brain imaging techniques. Together with the study of memory under physiological conditions, in the center of interest there is the study of memory during various life periods, under pathological conditions and diseases. The review is closed by the list of most important diseases in which we observe memory dysfunctions, including the retrograde and anterograde amnesias. PMID:21254663

Klenerová, V; Hynie, S

2010-01-01

260

Kansas Memory  

NSDL National Science Digital Library

You can travel from Cheyenne County in the northwestern corner of Kansas all the way down to Cherokee County in the southeast with a just couple of clicks on the Kansas Memory site. It's a trip filled with compelling historical artifacts, photographs, and other ephemera, and it's an engaging way to learn about the Sunflower State's history. Created by the Kansas State Historical Society, Kansas Memory helps to fulfill the Society's mission "to identify collect, preserve, interpret, and disseminate materials and information pertaining to Kansas history." First-time visitors can explore the "Item of the Week" on the homepage, create their own profiles to save materials for future visits, and take a look at the "Special Exhibits" area. On the left-hand side of the homepage, visitors will find thematic headings that allow them to browse materials dealing with the subjects including the built environment, business, and agriculture. With over 17,000 items available on the site, it's safe to say that several visits will be in order for anyone with even the faintest interest in Kansas history.

2012-01-27

261

Effects of amisulpride on emotional memory using a dual-process model in healthy male volunteers  

Microsoft Academic Search

Memory dysfunction occurs in a number of neuropsychiatric disorders. Therapeutic psychopharmacological agents may exacerbate such memory impairment. Detailed characterisation of drug-induced memory impairment is therefore important. We recently showed that the D2\\/D3 antagonist amisulpride quantitatively impairs emotional memory in a randomised placebo-controlled study of 33 healthy volunteers. Current evidence suggests that two qualitatively different processes (recollection and familiarity) contribute to

AA Gibbs; KH Naudts; EP Spencer; AS David

2010-01-01

262

Glue Polymer  

NSDL National Science Digital Library

What is a polymer, and what are some of its properties? This material is part of a series of hands-on science activities designed to arouse student interest. In this discovery activity students use white glue, water, and borax to make a vinyl polymer and study its properties. The activity includes a description, a list of science process skills and complex reasoning strategies being used, and a compilation of applicable K-12 national science education standards. Also provided are content topics, a list of necessary supplies, instructions, and presentation techniques. The content of the activity is explained, and assessment suggestions are provided.

Mid-continent Research for Education and Learning (McREL); Jacobs, Steve

2004-01-01

263

Reducing unwanted trauma memories by imaginal exposure or autobiographical memory elaboration: An analogue study of memory processes  

PubMed Central

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.

Ehlers, Anke; Mauchnik, Jana; Handley, Rachel

2012-01-01

264

Characterization of Therapeutic Coatings on Medical Devices  

NASA Astrophysics Data System (ADS)

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.

Wormuth, Klaus

265

Polymer Blends  

Microsoft Academic Search

The concept of appropriately combining two or more different polymers to obtain a new material system with the desirable features of its constituents is not new. Over the years, numerous systems based on the chemical combination of different monomers through random, block, and graft copolymerization methods have been developed with this goal in mind. For similar reasons, the coatings and

D. R. Paul; J. W. Barlow

1980-01-01

266

Ferroelectric polymers  

Microsoft Academic Search

In the early 1970s it became clear that the polymer polyvinylidene fluoride is ferroelectric. There have been extensive studies of its properties and of the properties of copolymers of vinylidene fluoride with tri- or tetra-fluoroethylene. This work has led to a fairly complete understanding of the ferroelectric and related properties of these materials. The emphasis in this review is on

R. G. Kepler; R. A. Anderson

1992-01-01

267

Functional polymers  

SciTech Connect

Improving the existing polymer materials and the designing of model polymers need fundamental insights into the structure and dynamics over a large range of length and time scales. Consequently, a host of quite different methods needs to be applied to gain insights into the molecular and supramolecular structures and interactions that determine the performance of these materials. Supramolecular structures derived from shape persistent (stiff) macromolecules are used as examples to demonstrate the correlation between chemical structure, order phenomena and performance in applications concerning advanced or developing technologies: organic light emitting diodes (OLEDs) and separator membranes in lithium based batteries and fuel cells. Polymers are also important as additives in the manufacture and the processing of other materials. The design of block copolymers to control the nucleation and growth of inorganic particles precipitating from aqueous solutions (mineralization) is discussed as well as the use of block copolymers to optimize the processing of ceramic pieces and objects. Finally, the modification of surfaces by polymers including aspects of biocompatibility is discussed. Some remarks concerning the importance of recent developments and advances in synthesis of macromolecular materials are also given.

Wegner, G.

2000-01-01

268

Polymer solutions  

SciTech Connect

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.

Krawczyk, Gerhard Erich (Bremen, DE); Miller, Kevin Michael (West Dundee, IL)

2011-07-26

269

Injectable preformed scaffolds with shape-memory properties  

PubMed Central

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.

Bencherif, Sidi A.; Sands, R. Warren; Bhatta, Deen; Arany, Praveen; Verbeke, Catia S.; Edwards, David A.; Mooney, David J.

2012-01-01

270

Imprinted polymers assisting protein crystallization.  

PubMed

Molecularly imprinted polymers (MIPs) are 'smart materials' polymerised in the presence of a template molecule, of which they retain a chemical 'memory'. When the template molecule is extracted from the polymer, it leaves behind cavities that are complementary to it, thus making the material capable of rebinding that molecule with high affinity and selectivity. Such materials, imprinted both with small molecule and with protein templates, have been used in chromatographic, chemical, and biological sensing applications. Here, we review a variety of uses for MIPs, focusing on their recently discovered role as nucleation inducing substances for protein crystals. This discovery makes them useful tailor-made 'nucleants' to be used both for optimisation of protein crystal growth and for discovering new crystallization conditions. PMID:23764007

Saridakis, Emmanuel; Chayen, Naomi E

2013-06-11

271

Memory for pain  

Microsoft Academic Search

This review summarizes some of the recent advances in the neurobiology of memory. Current research helps us to understand how memories are created and, conversely, how our memories can be influenced by stress, drugs, and aging. An understanding of how memories are encoded by the brain may also lead to new ideas about how to maximize the long-term retention of

Jason W. Brown

1979-01-01

272

Error tolerant associative memory  

Microsoft Academic Search

.   We present a new approach to enlarging the basin of attraction of associative memory, including auto-associative memory and\\u000a temporal associative memory. The memory trained by means of this method can tolerate and recover from seriously noisy patterns.\\u000a Simulations show that this approach will greatly reduce the number of limit cycles.

Cheng-Yuan Liou; Shao-Kuo Yuan

1999-01-01

273

Memories of Things Unseen  

Microsoft Academic Search

New findings reveal more about the malleability of memory. Not only is it possible to change details of memories for previously experienced events, but one can sometimes also plant entirely false memories into the minds of unsuspecting individuals, even if the events would be highly implausible or even impossible. False memories might differ statistically from true ones, in terms of

Elizabeth F. Loftus

2004-01-01

274

Errors in autobiographical memory  

Microsoft Academic Search

Memory is always constructive. People create the past based on the information that remains in memory, their general knowledge, and the social demands of the retrieval situation. Thus, memories will often contain some small errors and occasionally some large errors. In this article, we describe several different types of memory errors and consider how these errors may influence therapy.

Ira E. Hyman; Elizabeth F. Loftus

1998-01-01

275

Infant Visual Recognition Memory  

ERIC Educational Resources Information Center

|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…

Rose, Susan A.; Feldman, Judith F.; Jankowski, Jeffery J.

2004-01-01

276

Therapeutic Area Standards Table  

Center for Drug Evaluation (CDER)

Text Version... Group5 51 Diabetic Nephropathy 13 Tier 2 ... therapeutic The term “therapeutic area” also includes diagnostic and preventive areas. Some ... More results from www.fda.gov/downloads/drugs/developmentapprovalprocess

277

Nanoscale memory devices.  

PubMed

This article reviews the current status and future prospects for the use of nanomaterials and devices in memory technology. First, the status and continuing scaling trends of the flash memory are discussed. Then, a detailed discussion on technologies trying to replace flash in the near-term is provided. This includes phase change random access memory, Fe random access memory and magnetic random access memory. The long-term nanotechnology prospects for memory devices include carbon-nanotube-based memory, molecular electronics and memristors based on resistive materials such as TiO(2). PMID:20852352

Chung, Andy; Deen, Jamal; Lee, Jeong-Soo; Meyyappan, M

2010-09-17

278

Nonlinear Viscoelastic Approach to Durability Predictions for Polymer Based Composite Structures.  

National Technical Information Service (NTIS)

Current industry approaches for the durability assessment of metallic structures are briefly reviewed. For polymer based composite structures, it is suggested that new approaches must be adopted to include memory or viscoelastic effects which could lead t...

H. F. Brinson C. C. Hiel

1990-01-01

279

Catching the engram: strategies to examine the memory trace  

PubMed Central

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.

2012-01-01

280

A Comparison of Three Types of Autobiographical Memories in Old-Old Age: First Memories, Pivotal Memories and Traumatic Memories  

Microsoft Academic Search

Background: Autobiographical memory enables us to construct a personal narrative through which we identify ourselves. Especially important are memories of formative events. Objective: This study describes autobiographical memories of people who have reached old-old age (85 years and above), studying 3 types of memories of particular impact on identity and adaptation: first memories, pivotal memories and traumatic memories. In this

Jiska Cohen-Mansfield; Dov Shmotkin; Nitza Eyal; Yael Reichental; Haim Hazan

2010-01-01

281

Memory effects in classical and quantum mean-field disordered models  

NASA Astrophysics Data System (ADS)

We apply the Kovacs experimental protocol to classical and quantum p-spin models. We show that these models have memory effects as those observed experimentally in super-cooled polymer melts. We discuss our results in connection to other classical models that capture memory effects. We propose that a similar protocol applied to quantum glassy systems might be useful to understand their dynamics.

Cugliandolo, L. F.; Lozano, G.; Lozza, H.

2004-09-01

282

Linkage effect on the memory behavior of sulfonyl-containing aromatic polyether, polyester, polyamide, and polyimide.  

PubMed

Sulfonyl-containing aromatic polymers DSPE, DSPET, DSPA, and DSPI consisting of a triphenylamine moiety were synthesized and the memory behavior was investigated. By choosing the suitable linkage between the electron donor and acceptor, tunable memory properties (from insulator to different retention time SRAM) could be achieved. PMID:23423191

Chen, Chih-Jung; Hu, Yi-Cheng; Liou, Guey-Sheng

2013-03-28

283

Protein-polymer nanoreactors for medical applications.  

PubMed

Major challenges that confront nanoscience in medicine today include the development of efficacious therapies with minimum side effects, diagnostic methods featuring significantly higher sensitivities and selectivities, and personalized diagnostics and therapeutics for theragnostic approaches. With these goals in mind, combining biological molecules and synthetic carriers/templates, such as polymer supramolecular assemblies, represents a very promising strategy. In this critical review, we present protein-polymer systems as reaction spaces at the nano-scale in which the enzymatic reactions take place inside polymer supramolecular assembly, at its interface with the environment or in a combination of both. The location of the protein(s) with respect to the polymer assembly generates a diversity of systems ranging from nanoreactors to active enzymatic polymer surfaces. We describe these both in terms of general modelling and addressing the specific conditions and requirements related to the medical domain. We will particularly present protein-polymer nanoreactors that provide protected spaces for enzymatic reactions. We also show how polymer supramolecular structures, such as micelles, capsules, dendrimers and vesicles, can accommodate sensitive biomolecules to mimic natural systems and functions, and to serve as avenues for new medical approaches. Even though not yet on the market, we will emphasize possible applications of protein-polymer systems that generate reaction nanospaces-as novel ways to advanced medicine (264 references). PMID:22085991

Palivan, Cornelia G; Fischer-Onaca, Ozana; Delcea, Mihaela; Itel, Fabian; Meier, Wolfgang

2011-11-15

284

Conductive Polymers  

SciTech Connect

Electroluminescent devices such as light-emitting diodes (LED) and high-energy density batteries. These new polymers offer cost savings, weight reduction, ease of processing, and inherent rugged design compared to conventional semiconductor materials. The photovoltaic industry has grown more than 30% during the past three years. Lightweight, flexible solar modules are being used by the U.S. Army and Marine Corps for field power units. LEDs historically used for indicator lights are now being investigated for general lighting to replace fluorescent and incandescent lights. These so-called solid-state lights are becoming more prevalent across the country since they produce efficient lighting with little heat generation. Conductive polymers are being sought for battery development as well. Considerable weight savings over conventional cathode materials used in secondary storage batteries make portable devices easier to carry and electric cars more efficient and nimble. Secondary battery sales represent an $8 billion industry annually. The purpose of the project was to synthesize and characterize conductive polymers. TRACE Photonics Inc. has researched critical issues which affect conductivity. Much of their work has focused on production of substituted poly(phenylenevinylene) compounds. These compounds exhibit greater solubility over the parent polyphenylenevinylene, making them easier to process. Alkoxy substituted groups evaluated during this study included: methoxy, propoxy, and heptyloxy. Synthesis routes for production of alkoxy-substituted poly phenylenevinylene were developed. Considerable emphasis was placed on final product yield and purity.

Bohnert, G.W.

2002-11-22

285

Periodic Polymers  

NASA Astrophysics Data System (ADS)

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.

Thomas, Edwin

2013-03-01

286

Aqueous polymer compositions  

US Patent & Trademark Office Database

Aqueous polymer composition suitable for coating which comprises the following components dispersed in water: (1) a combination of an acrylic polymer(s) A and an acrylic polymer(s) B where polymer(s) A has a Tg of not more than 30.degree. C. and polymer(s) B has a Tg of at least 35.degree. C., more preferably at least 45.degree. C., which is at least 25.degree. C. higher than the Tg of polymer(s) A, and wherein one or both of polymers A and B bear crosslinker functional groups capable of imparting ambient-temperature crosslinkability to component (1) in a coating formed from the composition via the formation of non-radically-formed covalent bonds; and (2) a self-dispersible, ionically stabilised polymer having olefinically unsaturated bond functionality capable of imparting radiation-curability (preferably uv-radiation curability) thereto in a coating formed from the composition.

Overbeek; Gerardus Cornelis (Waalwijk, NL); Steenwinkel; Pablo (Waalwijk, NL); Tennebroek; Ronald (Waalwijk, NL); Nabuurs; Tijs (Waalwijk, NL)

2004-05-04

287

Memory loss.  

PubMed

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

Flicker, Leon A; Ford, Andrew H; Beer, Christopher D; Almeida, Osvaldo P

2012-02-01

288

Virginia Memory  

NSDL National Science Digital Library

The Virginia Memory initiative is part of the online presence of the Library of Virginia and it represents a magnificent effort to bring together thousands of documents that tell the story of this very unique place. The sections of the site include Digital Collections, Reading Rooms, Exhibitions, and the Online Classroom. First-time visitors may wish to start with the This Day in Virginia History section. Here they can learn about key moments in the state's history via primary documents tied to each calendar date, such as May 6, 1776, when the House of Burgesses met for the last time. The Exhibitions area contains interactive exhibits like You Have No Right: Law & Justice in Virginia. There are over two dozen past exhibits to look over on the site as well. The Digital Collections area is quite a remarkable one, featuring over 50 exhibits, including the 1939 World's Fair Photograph Collection, Revolutionary War Virginia State Pensions, and the tremendous Richmond Esthetic Survey/Historic Building Survey. To complement these materials, the Online Classrooms area contains an educator's guide, a document-based activity titled "Shaping the Constitution," and other resources. [KMG

289

Polymeric memory device with dual electrical and optical reading modes  

NASA Astrophysics Data System (ADS)

We report a write-once-read-many polymeric memory device that can be read by both electrical and optical methods. The device consists of two layers of conjugated polymer blends sandwiched between a metal electrode and a transparent electrode. One of the polymer blends functions as an ion-trapping, electrochromic layer, while the other polymer blend functions as a light-emitting electrochemical cell. Recording is facilitated by applying a negative writing voltage on the device. Reading can be performed by either probing with a low positive voltage, probing with a laser beam, or by measuring the light emission intensity from the device.

Deng, Xian-Yu; Wong, King Y.

2011-04-01

290

Nanoporous organic polymer networks  

Microsoft Academic Search

Nanoporous organic polymer networks are a class of materials consisting solely of the lighter elements in the periodic table. These materials have potential uses in areas such as storage, separation, and catalysis. Here, we review the different classes of nanoporous polymer networks including covalent organic frameworks, hypercrosslinked polymers, conjugated microporous polymers, and polymers of intrinsic microporosity. The growing variety in

Robert Dawson; Andrew I. Cooper; Dave J. Adams

291

Polymer Electronics: Power from Polymers  

SciTech Connect

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.

Venkataraman, Dhandapani; Russell, Thomas P.

2012-01-01

292

Silicon-Containing Polymers.  

National Technical Information Service (NTIS)

The major categories of homopolymers and copolymers are discussed. These include linear siloxane polymers, (with various alkyl and aryl R and R' side groups); sesquisiloxane polymers possibly having a ladder structure; siloxane-silarylene polymers, (in wh...

J. E. Mark

1990-01-01

293

Noradrenergic modulation of cognition: therapeutic implications.  

PubMed

The noradrenaline (norepinephrine) system exerts profound influences on cognition via ascending projections to the forebrain, mostly originating from the locus coeruleus. This paper provides an overview of available infrahuman and healthy human studies, exploring the effects of specific noradrenergic manipulations on dissociable cognitive functions, including attention, working memory, cognitive flexibility, response inhibition and emotional memory. Remarkable parallels across species have been reported which may account for the mechanisms by which noradrenergic medications exert their beneficial effects in disorders such as depression and attention-deficit hyperactivity disorder (ADHD). The literature is discussed in relation to prevailing models of noradrenergic influences over cognition and novel therapeutic directions, including in relation to investigating the effects of noradrenergic manipulations on other disorders characterized by impulsivity, and dementias. Unanswered questions are also highlighted, along with key avenues for future research, both proof-of-concept and clinical. PMID:23518815

Chamberlain, Samuel R; Robbins, Trevor W

2013-03-21

294

Status of 3D memory storage materials  

NASA Astrophysics Data System (ADS)

The speed of modern supercomputers is primarily limited by the relatively slow speed of memory. Research over the past years has focused on developing optical memory systems that, by nature of optics, promise to achieve high speed and high memory capacity. Three- dimensional optical memory systems are well known for their storage capacity and achievable short access time. But the early attempts to exploit 3-dimensional media were limited to photorefractive crystals such as lithium niobate, due to the unavailability of any other suitable medium (alternative media are precluded by their diffraction limited storage densities and non- erasable characteristics). Although volume phase holograms can be recorded in photorefractive crystals, these materials have many obvious flaws such as strong scattering, phase distortion, self diffraction, fast decay, and low refractive index modulation. There have also been continuous efforts to develop new 3-D media (such as photon echo, photorefractive polymers, bacteriorhodusphin, memory access cache, etc., but none can be applied in real world 3-D device because these materials are still in the early stage of development.

Savant, Gajendra D.; Jannson, Tomasz; Ho, Zonh Z.

1993-04-01

295

Metal-polymer and polymer-polymer interfaces: Application to conjugated polymer electronic devices  

Microsoft Academic Search

The study of metal-polymer and polymer-polymer interfaces is applied to conjugated polymer electronic devices. Conjugated polymers are a class of organic materials which have metallic or semiconducting properties which are being investigated as alternatives to traditional semiconducting materials. When conjugated polymers are used in devices, the interfaces are found to be critical to device performance. X-ray photoelectron spectroscopy (XPS) and

Julie Anne Osladil Smallfield

2002-01-01

296

Therapeutic use exemption  

PubMed Central

Football players who have either physical symptoms or disease after injury may need to be treated with specific medicines that are on the list of prohibited substances. Therapeutic use exemption may be granted to such players, in accordance with strictly defined criteria—these are presented in this article. Procedures of how to request for an abbreviated or a standard therapeutic use exemption are explained, and data on therapeutic use exemptions (UEFA and FIFA, 2004 and 2005) are also presented.

Dvorak, J; Kirkendall, D; Vouillamoz, M

2006-01-01

297

Molecularly imprinted polymers: a new approach to the preparation of functional materials  

Microsoft Academic Search

Molecular imprinting is a method for creating specific cavitie s in synthetic polymer matrices with memory for the template molecules. To date molecularly imprinted polymers (MIPs) have obtained a strong position in materials science and technology, expanding significantly the list of functional materials. This article provides a short review of the molecular imprinting technique with special attention paid to electrosynthesized

Andres Öpik; Anna Menaker; Jekaterina Reut; Vitali Syritski

2009-01-01

298

Application of sucrose fatty acid esters in transdermal therapeutic systems  

Microsoft Academic Search

Transdermal therapeutic systems (TTSs) were studied applying different sucrose fatty acid esters (SEs) as drug delivery agents. Matrix and membrane controlled TTSs were prepared and compared. Membrane was made from a methacrylic polymer (Eudragit® NE) of pH independent permeability which can achieve diffusion controlled drug liberation. Model drug was a water soluble ?-blocker, metoprolol, which has short biological half-life, so

G. Csóka; S. Marton; R. Zelko; N. Otomo; I. Antal

2007-01-01

299

Understanding Memory Loss  

MedlinePLUS

... National Alzheimer's Project Act (NAPA) About ADEAR Understanding Memory Loss: What To Do When You Have Trouble ... I get more information? Words to know Understanding Memory Loss What To Do When You Have Trouble ...

300

Memory and Aging  

MedlinePLUS

Memory and Aging Losing keys, misplacing a wallet, or forgetting someone’s name are common experiences. But for ... from those that require medical and psychological attention. Memory and Aging What Brain Changes Are Normal for ...

301

Sparse Distributed Memory.  

National Technical Information Service (NTIS)

Sparse distributed memory was proposed be Pentti Kanerva as a realizable architecture that could store large patterns and retrieve them based on partial matches with patterns representing current sensory inputs. This memory exhibits behaviors, both in the...

P. J. Denning

1989-01-01

302

Memory System for Microcircuits.  

National Technical Information Service (NTIS)

A program to design and develop manufacturing processes for a compact, low power, modular memory is described. The memory uses electroplated magnetic film storage elements, vacuum evaporated wiring and insulation, integrated circuits ultrasonically face-d...

M. I. Weilerstein

1968-01-01

303

Memory Technology Survey.  

National Technical Information Service (NTIS)

The current status of semiconductor, magnetic, and optical memory technologies is described. Projections based on these research activities planned for the shot term are presented. Conceptual designs of specific memory buffer pplications employing bipola,...

1981-01-01

304

Sparse Distributed Memory Overview.  

National Technical Information Service (NTIS)

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 characterist...

M. Raugh

1990-01-01

305

The quintuple-shape memory effect in electrospun nanofiber membranes  

NASA Astrophysics Data System (ADS)

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.

Zhang, Fenghua; Zhang, Zhichun; Liu, Yanju; Lu, Haibao; Leng, Jinsong

2013-08-01

306

Emotional Memory Persists Longer than Event Memory  

ERIC Educational Resources Information Center

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…

Kuriyama, Kenichi; Soshi, Takahiro; Fujii, Takeshi; Kim, Yoshiharu

2010-01-01

307

Exercise and Memory  

NSDL National Science Digital Library

This activity (on page 2 of the PDF) is a full inquiry investigation into the effects of exercise on short term memory. Groups of learners will set a baseline score with an initial memory test. Then they split into two teams, one participating in physical exercise while the other remains sedentary. After ten minutes, both teams take another memory test to tabulate and graph score changes. Relates to linked video, DragonflyTV: Exercise and Memory.

Twin Cities Public Television, Inc.

2005-01-01

308

External Memory Algorithms  

Microsoft Academic Search

Data sets in large applications are often too massive to fit completely inside the computer’s internal memory. The resulting\\u000a input\\/output communication (or I\\/O) between fast internal memory and slower external memory (such as disks) can be a major\\u000a performance bottleneck. In this tutorial, we survey the state of the art in the design and analysis of external memory algorithms (also

Jerey Scott Vitter

309

Therapeutic Alliance, Negative Mood Regulation, and Treatment Outcome in Child Abuse-Related Posttraumatic Stress Disorder  

Microsoft Academic Search

This study examined the related contributions of the therapeutic alliance and negative mood regulation to the outcome of a 2-phase treatment for childhood abuse-related posttraumatic stress disorder (PTSD). Phase 1 focused on stabilization and preparatory skills building, whereas Phase 2 was comprised primarily of imaginal exposure to traumatic memories. Hierarchical regression analyses indicated the strength of the therapeutic alliance established

Marylene Cloitre; K. Chase Stovall-McClough; Regina Miranda; Claude M. Chemtob

2004-01-01

310

Enhancing the therapeutic efficacy of adenovirus in combination with biomaterials.  

PubMed

With the reason that systemically administered adenovirus (Ad) is rapidly extinguished by innate/adaptive immune responses and accumulation in liver, in vivo application of the Ad vector is strictly restricted. For achieving to develop successful Ad vector systems for cancer therapy, the chemical or physical modification of Ad vectors with polymers has been generally used as a promising strategy to overcome the obstacles. With polyethylene glycol (PEG) first in order, a variety of polymers have been developed to shield the surface of therapeutic Ad vectors and well accomplished to extend circulation time in blood and reduce liver toxicity. However, although polymer-coated Ads can successfully evacuate from a series of guarding systems in vivo and locate within tumors by enhanced permeability and retention (EPR) effect, the possibility to entering into the target cell is few and far between. To endow targeting moiety to polymer-coated Ad vectors, a diversity of ligands such as tumor-homing peptides, growth factors or antibodies, have been introduced with avoiding unwanted transduction and enhancing therapeutic efficacy. Here, we will describe and classify the characteristics of the published polymers with respect to Ad vectors. Furthermore, we will also compare the properties of variable targeting ligands, which are being utilized for addressing polymer-coated Ad vectors actively. PMID:22142769

Kim, Jaesung; Kim, Pyung-Hwan; Kim, Sung Wan; Yun, Chae-Ok

2011-12-03

311

Unique Properties of Reversibly Associating Polymer Networks  

NASA Astrophysics Data System (ADS)

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.

Anthamatten, Mitchell

2008-03-01

312

Bidirectional changes to hippocampal theta-gamma comodulation predict memory for recent spatial episodes  

PubMed Central

Episodic memory requires the hippocampus, which is thought to bind cortical inputs into conjunctive codes. Local field potentials (LFPs) reflect dendritic and synaptic oscillations whose temporal structure may coordinate cellular mechanisms of plasticity and memory. We now report that single-trial spatial memory performance in rats was predicted by the power comodulation of theta (4–10 Hz) and low gamma (30–50 Hz) rhythms in the hippocampus. Theta–gamma comodulation (TGC) was prominent during successful memory retrieval but was weak when memory failed or was unavailable during spatial exploration in sample trials. Muscimol infusion into medial septum reduced the probability of TGC and successful memory retrieval. In contrast, patterned electrical stimulation of the fimbria-fornix increased TGC in amnestic animals and partially rescued memory performance in the water maze. The results suggest that TGC accompanies memory retrieval in the hippocampus and that patterned brain stimulation may inform therapeutic strategies for cognitive disorders.

Shirvalkar, Prasad R.; Rapp, Peter R.; Shapiro, Matthew L.

2010-01-01

313

Suggesting a Memory Screening  

MedlinePLUS

Suggesting a Memory Screening... Text Size: Email This Post Print This Post Suggesting a Memory Screening By Kevin Gault It can be a ... cognitive abilities, want to suggest screening for possible memory deficit, but aren’t sure how to go ...

314

Music, memory and emotion  

PubMed Central

Because emotions enhance memory processes and music evokes strong emotions, music could be involved in forming memories, either about pieces of music or about episodes and information associated with particular music. A recent study in BMC Neuroscience has given new insights into the role of emotion in musical memory.

Jancke, Lutz

2008-01-01

315

Music, memory and emotion.  

PubMed

Because emotions enhance memory processes and music evokes strong emotions, music could be involved in forming memories, either about pieces of music or about episodes and information associated with particular music. A recent study in BMC Neuroscience has given new insights into the role of emotion in musical memory. PMID:18710596

Jäncke, Lutz

2008-08-08

316

Testing eyewitness memory  

Microsoft Academic Search

This study identifies a memory-testing procedure that is relatively resistant to the documented effects of suggestibility on eyewitness memory. Most studies on suggestibility have used averbal recognition memory test in which the alternative test items are sentences, each to be verified as true or false regarding an originally viewedvisual sequence. In this study, participants were tested with either the verbal

Kathy Pezdek; Joelle Greener

1993-01-01

317

Numerical Memory Experiment  

NSDL National Science Digital Library

This is the entry page for the Numerical Memory Experiment. This Numerical Memory experiment employs a similar format to Digit Span tasks found in assessment instruments, comparing the individual's short-term memory for digits presented in an auditory vs. visual format.

318

Numerical Memory Explanation  

NSDL National Science Digital Library

This Numerical Memory experiment employs a similar format to Digit Span tasks found in assessment instruments, comparing an individual's short-term memory for digits presented in an auditory vs. visual format. This page provides information about the memory task and how it can be used in the classroom.

319

Chicanoizing the Therapeutic Community  

ERIC Educational Resources Information Center

|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.…

Aron, William S.; And Others

1974-01-01

320

Therapeutic applications of microbubbles  

Microsoft Academic Search

Microbubbles, currently used as contrast agents have potential therapeutic applications. Microbubbles, upon insonation of sufficiently intense ultrasound will cavitate. Cavitation with microbubbles can be used to dissolve blood clots or deliver drugs. Targeting ligands and drugs can be incorporated into microbubbles to make highly specific diagnostic and therapeutic agents for activation with ultrasound. In this paper I will review some

Evan C. Unger; Terry Onichi Matsunaga; Thomas McCreery; Patricia Schumann; Robert Sweitzer; Rachel Quigley

2002-01-01

321

Hybrid polymer latexes  

Microsoft Academic Search

Hybrid polymer latexes will be defined here as colloidal dispersions in which at least two distinct polymers exist within each particle. The two polymers may form a homogenous blend within the particle or microphase separation may occur. There are two general routes for their preparation. The first involves the use of a mini-emulsion polymerization process, in which a first polymer,

Alain Guyot; Katharina Landfester; F. Joseph Schork; Chunpeng Wang

2007-01-01

322

Nanoreplication in polymers using hot embossing and injection molding  

Microsoft Academic Search

With polymer molding techniques, it is possible to fabricate nanostructures with a replication fidelity of 25 nanometers. Both hot embossing and injection molding can be used, and cycle times of down to 4 sec can be achieved in a CD injection molding process. The resolution is far below the structure size found today in compact disc memory media. The master

H. Schift; C. David; M. Gabriel; J. Gobrecht; L. J. Heyderman; W. Kaiser; S. Koeppel; L. Scandella

2000-01-01

323

Anti-Stokes femtosecond photon echo in a polymer film  

SciTech Connect

An anti-Stokes model is proposed which explains the room-temperature blue shift of the echo-signal spectrum compared to the spectrum of exciting femtosecond pulses in a polymer film doped with dye molecules. The possibility of realising the anti-Stokes regime of coherent laser cooling of such films is analysed. (fifth seminar in memory of d.n. klyshko)

Petrushkin, S V [E.K. Zavoisky Physical-Technical Institute, Kazan Scientific Center, Russian Academy of Sciences, Kazan (Russian Federation); Samartsev, V V [Kazan State University, Kazan (Russian Federation)

2007-12-31

324

Immunological memory is associative  

SciTech Connect

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.

Smith, D.J.; Forrest, S. [New Mexico Univ., Albuquerque, NM (United States). Dept. of Computer Science; Perelson, A.S. [Los Alamos National Lab., NM (United States)

1996-12-31

325

Nitric oxide release: part II. Therapeutic applications.  

PubMed

A wide range of nitric oxide (NO)-releasing materials has emerged as potential therapeutics that exploit NO's 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. In this tutorial review, we review the application of macromolecular NO therapies for cardiovascular disease, cancer, bacterial infections, and wound healing. PMID:22362384

Carpenter, Alexis W; Schoenfisch, Mark H

2012-02-24

326

Nitric Oxide Release Part II. Therapeutic Applications  

PubMed Central

Summary A wide range of nitric oxide (NO)-releasing materials have emerged as potential therapeutics that exploit NO’s 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.

Carpenter, Alexis W.; Schoenfisch, Mark H.

2012-01-01

327

Memory access in shared virtual memory  

SciTech Connect

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.

Berrendorf, R. (Zentralinstitut fuer Angewandte Mathematik Forschungszentrum Juelich, KFA (FRG))

1992-01-01

328

Memory access in shared virtual memory  

SciTech Connect

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.

Berrendorf, R. [Zentralinstitut fuer Angewandte Mathematik Forschungszentrum Juelich, KFA (FRG)

1992-09-01

329

Serotonergic Mechanisms in Addiction-Related Memories  

PubMed Central

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.

Nic Dhonnchadha, Brid A; Cunningham, Kathryn A.

2008-01-01

330

A finite element model for shape memory behavior  

NASA Astrophysics Data System (ADS)

This paper deals with a finite element implementation concerning the shape memory behavior. Shape memory behavior is usually driven by temperature changes. This model allows the simulation of problems integrating complex mechanical loading effects under random temperature variations. According to the relationship between stress and strain, the shape fixation during cooling phases and the memory effect during heating phase are modelised through a hereditary behavior needing incremental formulation developments. The step by step process introduces an additional fixed stress. Simulations request, for complex geometries including boundary conditions, a finite element approach. Thermodynamic developments are presented in order to define energetic balance and dissipations. In this paper, we propose to generalize this dependence of elastic modulus variations. A formulation for random mechanical loading and temperature variations is proposed. An experimental validation is proposed about shape memory alloy polymer DP5.

Husson, Jean Marie; Dubois, Frédéric; Sauvat, Nicolas

2011-08-01

331

Memory bistable mechanisms of organic memory devices  

NASA Astrophysics Data System (ADS)

To investigate the memory bistable mechanisms of organic memory devices, the structure of [top Au anode/9,10-di(2-naphthyl)anthracene (ADN) active layer/bottom Au cathode] was deposited using a thermal deposition system. The Au atoms migrated into the ADN active layer was observed from the secondary ion mass spectrometry. The density of 9.6×1016 cm-3 and energy level of 0.553 eV of the induced trapping centers caused by the migrated Au atoms in the ADN active layer were calculated. The induced trapping centers did not influence the carrier injection barrier height between Au and ADN active layer. Therefore, the memory bistable behaviors of the organic memory devices were attributed to the induced trapping centers. The energy diagram was established to verify the mechanisms.

Lee, Ching-Ting; Yu, Li-Zhen; Chen, Hung-Chun

2010-07-01

332

Memory Lane and Morality: How Childhood Memories Promote Prosocial Behavior  

Microsoft Academic Search

Although research has established that autobiographical memory affects one's self-concept, little is known about how it affects moral behavior. We focus on a specific type of autobiographical memory: childhood memories. Drawing on research on memory and moral psychology, we propose that childhood memories elicit moral purity, which we define as a psychological state of feeling morally clean and innocent. In

Francesca Gino; Sreedhari D. Desai

2012-01-01

333

Memory and Meaning: Individual and Social Aspects of Memory Narratives  

Microsoft Academic Search

Memory is critical to an understanding of traumatic stress, but most research has focused on individual traumatic memories and not accounted for broader social and cultural memories. The present theoretical article focuses on memory and meaning, and the clinical implications of this, demonstrating that an understanding of traumatic memory requires an understanding of the impact of both individual narrative and

Nigel Hunt; Sue McHale

2007-01-01

334

CAN EXPERIMENTAL MEMORY RESEARCH ADEQUATELY EXPLAIN MEMORY FOR TRAUMA?  

Microsoft Academic Search

In the debate on memories of traumatic events (especially childhood abuse), traumatic memories and dissociative amnesia are central topics. These phenomena are frequently described as dissociative memory problems. The aim of the present article is to assess to what extent memory mechanisms as identified in experimental research (such as encoding, storage, and retrieval factors) are adequate in explaining memories of

Philip Spinhoven; Ellert R. S. Nijenhuis; Richard Van Dyck

1999-01-01

335

Working memory predicts the rejection of false memories  

Microsoft Academic Search

The relationship between working memory capacity (WMC) and false memories in the memory conjunction paradigm was explored. Previous research using other paradigms has shown that individuals high in WMC are not as likely to experience false memories as low-WMC individuals, the explanation being that high-WMC individuals are better able to engage in source monitoring. In the memory conjunction paradigm participants

Juliana K. Leding

2012-01-01

336

Towards Therapeutic Arteriogenesis  

Cancer.gov

Arteriogenesis or the formation of arterial conduits is a promising therapeutic approach to the treatment of a number of ischemic vascular diseases. However, the molecular basis of this process remains poorly understood.

337

Therapeutic Biological Products Approvals  

Center for Drug Evaluation (CDER)

... Therapeutic Biological Products Approvals. We are no longer updating this page. The last update of this page occurred on December 12, 2003. ... More results from www.fda.gov/drugs/developmentapprovalprocess/howdrugsaredevelopedandapproved

338

Thermomechanical behavior of shape memory elastomeric composites  

NASA Astrophysics Data System (ADS)

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.

Ge, Qi; Luo, Xiaofan; Rodriguez, Erika D.; Zhang, Xiao; Mather, Patrick T.; Dunn, Martin L.; Qi, H. Jerry

2012-01-01

339

Are therapeutic communities therapeutic for women?  

PubMed Central

This paper addresses the growing phenomena of therapeutic community (TC) treatment approaches for women in correctional settings. Although rapidly increasing in number across the country, there is very little empirical research to support the effectiveness of TC treatment for women. Therefore, the literature on the efficacy and effectiveness of TC treatment for women is reviewed in relation to the literature on women's treatment issues. The literature review highlights the gaps where TC treatment ignores or exacerbates issues that are common to addicted women, or uses methods that may be contradictory to women's recovery.

Eliason, Michele J

2006-01-01

340

Polymer-Drug Conjugates: Recent Development in Clinical Oncology  

PubMed Central

Targeted drug delivery aims to increase the therapeutic index by making more drug molecules available at the diseased sites while reducing systemic drug exposure. In this update, we provide an overview of polymer-drug conjugates that have advanced into the clinical trials. These systems use synthetic water-soluble polymers as the drug carriers. The preclinical pharmacology and recent data in clinical trials with poly(L-glutamic acid)-paclitaxel (PG-TXL) are discussed first. This is followed by a summary of conjugates of a variety of polymeric conjugates with chemotherapeutic agents. Results from early clinical trials of these polymer-drug conjugates have demonstrated several advantages over the corresponding parent drugs, including fewer side effects, enhanced therapeutic efficacy, ease of drug administration, and improved patient compliance. Collectively, these data warrant further clinical development of polymer-drug conjugates as a new class of anticancer agents.

Li, Chun; Wallace, Sidney

2008-01-01

341

Multicomponent polymer materials  

SciTech Connect

Interpenetrating polymer networks are discussed, taking into account interpenetrating polymer networks based on polybutadiene and polystyrene, polyurethane-polysiloxane simultaneous interpenetrating polymer networks, extraction studies and morphology of physical-chemical interpenetrating polymer networks based on block polymer and polystyrene, twoand three-component interpenetrating polymer networks, and poly(acrylourethane)-polyepoxide semiinterpenetrating networks formed by electron-beam curing. Other topics studied are related to the characterization of polymer blends, the characterization of block copolymers, the mechanical behavior, and rheology and applications. Attention is given to a new silicone flame-retardant system for thermoplastics, recent developments in interpenetrating polymer networks and related materials, miscibility in random copolymer blends, crystallization and melting in compatible polymer blends, and fatigue in rubber-modified epoxies and other polyblends.

Paul, D.R.; Sperling, L.H.

1986-01-01

342

Practical Memory Concerns in Adulthood  

ERIC Educational Resources Information Center

In this article, we focus on practical memory concerns in adulthood. Young, middle-aged, and community-dwelling older adults responded to seven open-ended questions covering the topics of memory self-efficacy, memory management, memory remediation, and fears about memory aging in adulthood. The results revealed several similarities among the age…

Reese, Celinda M.; Cherry, Katie E.

2004-01-01

343

Memory, emotion, and REM sleep  

Microsoft Academic Search

Explored the manner in which REM sleep deprivation might affect various aspects of memory processing. A series of tests, including S. Sternberg's test of scanning of immediate memory, past personal and nonpersonal memory, and past emotional memories, was administered to 8 college students after baseline, control-awakening, and REM-deprivation nights. Results show that only past, emotionally important memories may have been

Ramon Greenberg; Chester Pearlman; Wynn R. Schwartz; Hildreth Y. Grossman

1983-01-01

344

False Memories and Persuasion Strategies  

Microsoft Academic Search

Research on false memories, which has increased drastically in the past decade, has mainly focused on the cognitive influences that lead to the creation of false memories, such as the theoretical causes of decreased memory strength and source confusion. Although there is certainly a cognitive component to false memories, in this article, I argue that false memories are more likely

Juliana K. Leding

2012-01-01

345

Ethanol Enhances Reactivated Fear Memories  

Microsoft Academic Search

Although ethanol has been shown to impair acquisition of memory, its effect on consolidated memories is not clear. Recent reports revealed that memory retrieval converted consolidated memory into a labile state and initiated the reconsolidation process. In the present study, we have demonstrated the effect of ethanol on reactivated fear memory. We used contextual fear conditioning where rats were conditioned

Hiroshi Nomura; Norio Matsuki

2008-01-01

346

Practical Memory Concerns in Adulthood  

ERIC Educational Resources Information Center

|In this article, we focus on practical memory concerns in adulthood. Young, middle-aged, and community-dwelling older adults responded to seven open-ended questions covering the topics of memory self-efficacy, memory management, memory remediation, and fears about memory aging in adulthood. The results revealed several similarities among the age…

Reese, Celinda M.; Cherry, Katie E.

2004-01-01

347

Lincoln Memorial Interactive  

NSDL National Science Digital Library

It is hard not be moved by the Lincoln Memorial in Washington, D.C., and this engaging and interactive exhibit captures the essence of this moving tribute to the nation's 16th president. The site is divided into two areas, "Reflections" and "Memorial". In the "Reflections" area, visitors can listen and watch park rangers talk about their own memories and remembrances of this august and somber place. There are seven separate profiles here, and it's a good idea to start with Kawther Elmi's thoughts on her childhood in East Africa. The "Memorial" area includes dramatic and multi-perspective views of the Lincoln statue and the Memorial grounds. Visitors may also use the "Downloads" area to download audio files of the ranger's talks, along with images of the Memorial.

348

Psychopharmacology and memory  

PubMed Central

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.

Glannon, W

2006-01-01

349

Timed-release polymer nanoparticles.  

PubMed

Triggered-release of encapsulated therapeutics from nanoparticles without remote or environmental triggers was demonstrated in this work. Disassembly of the polymer nanoparticles to unimers at precise times allowed the controlled release of oligo DNA. The polymers used in this study consisted of a hydrophilic block for stabilization and second thermoresponsive block for self-assembly and disassembly. At temperatures below the second block's LCST (i.e., below 37 °C for in vitro assays), the diblock copolymer was fully water-soluble, and when heated to 37 °C, the polymer self-assembled into a narrow size distribution of nanoparticles with an average diameter of approximately 25 nm. The thermoresponsive nature of the second block could be manipulated in situ by the self-catalyzed degradation of cationic 2-(dimethylamino)ethyl acrylate (DMAEA) units to negatively charged acrylic acid groups and when the amount of acid groups was sufficiently high to increase the LCST of the second block above 37 °C. The disassembly of the nanoparticles could be controlled from 10 to 70 h. The use of these nanoparticles as a combined therapy, in which one or more agents can be released in a predetermined way, has the potential to improve the personal point of care treatment of patients. PMID:23298322

Tran, Nguyen T D; Truong, Nghia P; Gu, Wenyi; Jia, Zhongfan; Cooper, Matthew A; Monteiro, Michael J

2013-01-16

350

HDAC2 negatively regulates memory formation and synaptic plasticity  

PubMed Central

Chromatin modifications, especially histone-tail acetylation, have been implicated in memory formation. Increased histone-tail acetylation induced by inhibitors of histone deacetylases (HDACis) facilitates learning and memory in wildtype mice as well as in mouse models of neurodegeneration. Harnessing the therapeutic potential of HDACi requires knowledge of the specific HDAC family member(s) linked to cognitive enhancement. Here we show that neuron-specific overexpression of HDAC2, but not HDAC1, reduced dendritic spine density, synapse number, synaptic plasticity, and memory formation. Conversely, HDAC2 deficiency resulted in increased synapse number and memory facilitation, similar to chronic HDACi treatment in mice. Notably, reduced synapse number and learning impairment of HDAC2-overexpressing mice were ameliorated by chronic HDACi treatment. Correspondingly, HDACi treatment failed to further facilitate memory formation in HDAC2-deficient mice. Furthermore, analysis of promoter occupancy revealed association of HDAC2 with the promoters of genes implicated in synaptic plasticity and memory formation. Together, our results suggest that HDAC2 plays a role in modulating synaptic plasticity and long-lasting changes of neural circuits, which in turn negatively regulates learning and memory. These observations encourage the development and testing of HDAC2-selective inhibitors for human diseases associated with memory impairment.

Guan, Ji-Song; Haggarty, Stephen J.; Giacometti, Emanuela; Dannenberg, Jan-Hermen; Joseph, Nadine; Gao, Jun; Nieland, Thomas J.F.; Zhou, Ying; Wang, Xinyu; Mazitschek, Ralph; Bradner, James E.; DePinho, Ronald A.; Jaenisch, Rudolf; Tsai, Li-Huei

2012-01-01

351

Quadratic Hadamard Memories I: Adaptive Stochastic Content-Addressable Memory.  

National Technical Information Service (NTIS)

A novel associative memory is discussed which overcomes the early saturation problem of Hopfield memories, without resorting to dilute state vectors or nonlocal learning rules. The memory uses a Bidirectional Linear Transformer (BLT) which transforms the ...

H. G. Loos

1989-01-01

352

Removing pathogenic memories  

Microsoft Academic Search

Experimental research examining the neural bases of nondeclarative memory has offered intriguing insight into how functional\\u000a and dysfunctional implicit learning affects the brain. Long-term modifications of synaptic transmission, in particular, are\\u000a currently considered the most plausible mechanism underlying memory trace encoding and compulsions, addiction, anxiety, and\\u000a phobias. Therefore, an effective psychotherapy must be directed to erase maladaptive implicit memories and

Diego Centonze; Alberto Siracusano; Paolo Calabresi; Giorgio Bernardi

2005-01-01

353

Silicon Nanocrystal Nonvolatile Memory  

Microsoft Academic Search

\\u000a Silicon nanocrystal memory devices [1],[2] such as shown in Fig. 4.1, offer the potential to solve the challenging problem of scaling nonvolatile memories. Scaling of floating-gate (FG) nonvolatile\\u000a memory cells has been limited to bottom oxide thicknesses in the range of 80–110 Å primarily because of the vulnerability\\u000a to charge loss from the conducting FG through isolated defects in the

R. A. Rao; M. A. Sadd; R. F. Steimle; C. T. Swift; H. Gasquet; M. Stoker

354

Sparse distributed memory  

SciTech Connect

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.

Kanerva, P.

1988-01-01

355

Development of extended memory  

Microsoft Academic Search

Memory development is described in terms of a bio-social–cultural theory of human cognition. The development from a private unshareable system of basic memory in infancy and very early childhood is framed within an experiential perspective wherein all memory is derived from experience. It is the nature of changing experience, the result of both biological and social–cultural conditions that eventuates in

Katherine Nelson

2007-01-01

356

Cortical memory dynamics  

Microsoft Academic Search

.   Biological memories have a number of unique features, including (1) hierarchical, reciprocally interacting layers, (2) lateral\\u000a inhibitory interactions within layers, and (3) Hebbian synaptic modifications. We incorporate these key features into a mathematical\\u000a and computational model in which we derive and study Hebbian learning dynamics and recall dynamics. Introducing the construct\\u000a of a feasible memory (a memory that formally

Edward W. Kairiss; Willard L. Miranker

1998-01-01

357

Polymers in small-interfering RNA delivery.  

PubMed

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

Singha, Kaushik; Namgung, Ran; Kim, Won Jong

2011-06-01

358

Re-Mendable Polymers  

NASA Astrophysics Data System (ADS)

Polymers have become an indispensable material resource, representing billions of dollars worth of material consumption every year. The rising prices and exhaust of natural resources such as petroleum, combined with rising environmental concerns, have prompted the development of recyclable and degradable polymers. Polymers that can be reverted back to their monomers or to shorter repolymerizable oligomers, hence, reversible polymers are particularly enticing in this respect because they essentially prevent any material loss with multiple recycling. While reversible polymers have been known for a long time, there has been recent renewed interest in such polymers, since their reversibility can be exploited for repair at the molecular level.

Bergman, Sheba D.; Wudl, Fred

359

Probabilistic Quantum Memories  

SciTech Connect

Typical address-oriented computer memories cannot recognize incomplete or noisy information. Associative (content-addressable) memories solve this problem but suffer from severe capacity shortages. I propose a model of a quantum memory that solves both problems. The storage capacity is exponential in the number of qbits and thus optimal. The retrieval mechanism for incomplete or noisy inputs is probabilistic, with postselection of the measurement result. The output is determined by a probability distribution on the memory which is peaked around the stored patterns closest in Hamming distance to the input.

Trugenberger, C. A.

2001-08-06

360

The future of memory  

NASA Astrophysics Data System (ADS)

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.

Marinella, M.

361

Hypnosis, memory and amnesia.  

PubMed Central

Hypnotized subjects respond to suggestions from the hypnotist for imaginative experiences involving alterations in perception and memory. Individual differences in hypnotizability are only weakly related to other forms of suggestibility. Neuropsychological speculations about hypnosis focus on the right hemisphere and/or the frontal lobes. Posthypnotic amnesia refers to subjects' difficulty in remembering, after hypnosis, the events and experiences that transpired while they were hypnotized. Posthypnotic amnesia is not an instance of state-dependent memory, but it does seem to involve a disruption of retrieval processes similar to the functional amnesias observed in clinical dissociative disorders. Implicit memory, however, is largely spared, and may underlie subjects' ability to recognize events that they cannot recall. Hypnotic hypermnesia refers to improved memory for past events. However, such improvements are illusory: hypermnesia suggestions increase false recollection, as well as subjects' confidence in both true and false memories. Hypnotic age regression can be subjectively compelling, but does not involve the ablation of adult memory, or the reinstatement of childlike modes of mental functioning, or the revivification of memory. The clinical and forensic use of hypermnesia and age regression to enhance memory in patients, victims and witnesses (e.g. recovered memory therapy for child sexual abuse) should be discouraged.

Kihlstrom, J F

1997-01-01

362

Memory on time.  

PubMed

Considerable recent work has shown that the hippocampus is critical for remembering the order of events in distinct experiences, a defining feature of episodic memory. Correspondingly, hippocampal neuronal activity can 'replay' sequential events in memories and hippocampal neuronal ensembles represent a gradually changing temporal context signal. Most strikingly, single hippocampal neurons - called time cells - encode moments in temporally structured experiences much as the well-known place cells encode locations in spatially structured experiences. These observations bridge largely disconnected literatures on the role of the hippocampus in episodic memory and spatial mapping, and suggest that the fundamental function of the hippocampus is to establish spatio-temporal frameworks for organizing memories. PMID:23318095

Eichenbaum, Howard

2013-01-12

363

Programmable bipolar and unipolar nonvolatile memory devices based on poly(2-(N-carbazolyl)ethyl methacrylate) end-capped with fullerene.  

PubMed

A novel polymer, poly(2-(N -carbazolyl)ethyl methacrylate) end-capped with fullerene (PCzMA-C(60) ), has been synthesized via living anionic polymerization. Electrically programmable flash memory devices were easily fabricated with this polymer by using solution coating and metal deposition. This polymer was found in these devices to exhibit bipolar and unipolar switching behaviors with a high ON/OFF current ratio, a long retention time, high reliability, and low power consumption. The excellent properties and easy processability of this polymer open up the possibility of the mass production of high performance nonvolatile memory devices at low cost. PMID:22279006

Hahm, Suk Gyu; Kang, Nam-Goo; Kwon, Wonsang; Kim, Kyungtae; Ko, Yong-Gi; Ahn, Seonyoung; Kang, Beom-Goo; Chang, Taihyun; Lee, Jae-Suk; Ree, Moonhor

2012-01-26

364

Is Random Access Memory Random.  

National Technical Information Service (NTIS)

Most software is contructed on the assumption that the programs and data are stored in random access memory (RAM). Physical limitations on the relative speeds of processor and memory elements lead to a variety of memory organizations that match processor ...

P. J. Denning

1986-01-01

365

Memory Reconsolidation and Computational Learning.  

National Technical Information Service (NTIS)

Memory models are central to Artificial Intelligence and Machine Learning, since memories hold knowledge and their updates are the heart of flexibility and adaptivity. Reconsolidation is a key process of human learning, modifying learned memories with new...

H. T. Siegelmann

2010-01-01

366

Long-Term Memory Improvement?  

ERIC Educational Resources Information Center

Tests Piaget's interpretation of long-term memory improvement among 82 five- and six-year-old children. Concludes that there is little evidence for long-term memory improvement or for Piaget's theory of memory. (Author/RH)

Maurer, Daphne; And Others

1979-01-01

367

Anchoring and memory of the azimuthal nematic orientation  

NASA Astrophysics Data System (ADS)

The authors show that the azimuthal anchoring properties, strength and memory, of nematic liquid crystals on glass surfaces are intrinsically weak, contrary to what is generally asserted. They are, however, largely increased when adding residual impurities that further deposit onto the substrate, the polymers being more efficient than small molecules. The gliding of the easy axis, when submitted to a torque, may thus be significantly reduced, and consequently, the quality of the orientational memory may be considerably increased. This property is interesting since it allows one to replicate nonuniform alignment patterns by means of an imprinting method.

Pires, David; Galerne, Yves

2006-10-01

368

Photo-mechanical patterning with light activated polymers.  

SciTech Connect

Light activated polymers, which are capable of mechanically responding to light, promise to offer exciting, innovative, and unique material capabilities. Such materials include: photo-radical mediated cleavage and reformation of the polymer backbone in cross-linked elastomers that results in local stress relaxation; photo-switching cross-links in shape memory polymers; and photo-isomerization of azobenzene groups contained in liquid crystal elastomers. In this paper, using our recent material model that couples multiphysical processes involved in light-activated polymers, we demonstrate that a variety of patterns can be created on light activated polymer thin films when coupling mechanical deformation with light irradiation. Here, the polymer thin film is first stretched uniaxially or biaxially. Light is then irradiated on the surface of the thin film. After light irradiation, removal external load partially recovers the initial stretching of the polymer thin film and induces patterns. The variation of the geometry of the patterns can be controlled by a variety of parameters such as initial stretching, light intensity, etc. Photo-patterning with light activated polymer therefore offers a novel way to create surface patterns.

Long, Kevin N.; Qi, H. Jerry (University of Colorado, Boulder, CO); Dunn, Martin L. (University of Colorado, Boulder, CO)

2010-11-01

369

Recent Advancement of Chitosan-Based Nanoparticles for Oral Controlled Delivery of Insulin and Other Therapeutic Agents  

Microsoft Academic Search

Nanoparticles composed of naturally occurring biodegradable polymers have emerged as potential carriers of various therapeutic\\u000a agents for controlled drug delivery through the oral route. Chitosan, a cationic polysaccharide, is one of such biodegradable\\u000a polymers, which has been extensively exploited for the preparation of nanoparticles for oral controlled delivery of several\\u000a therapeutic agents. In recent years, the area of focus has

Anumita Chaudhury; Surajit Das

2011-01-01

370

Playing with Polymers.  

ERIC Educational Resources Information Center

|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)|

Chemecology, 1997

1997-01-01

371

Polymer Fluid Dynamics.  

ERIC Educational Resources Information Center

|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)|

Bird, R. Byron

1980-01-01

372

Playing with Polymers.  

ERIC Educational Resources Information Center

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)

Chemecology, 1997

1997-01-01

373

Introduction to Polymer Chemistry.  

ERIC Educational Resources Information Center

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)

Harris, Frank W.

1981-01-01

374

Mechanical Properties of Polymers.  

ERIC Educational Resources Information Center

|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)|

Aklonis, J. J.

1981-01-01

375

Inorganic polymer engineering materials.  

National Technical Information Service (NTIS)

Phosphazene-based, inorganic-polymer composites have been produced and evaluated as potential engineering materials. The thermal, chemical, and mechanical properties of several different composites made from one polymer formulation have been measured. Mea...

M. L. Stone

1993-01-01

376

Therapeutics for cognitive aging  

PubMed Central

This review summarizes the scientific talks presented at the conference “Therapeutics for Cognitive Aging,” hosted by the New York Academy of Sciences and the Alzheimer’s Drug Discovery Foundation on May 15, 2009. Attended by scientists from industry and academia, as well as by a number of lay people—approximately 200 in all—the 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.

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

377

Therapeutic Antioxidant Medical Gas  

PubMed Central

Medical gases are pharmaceutical gaseous molecules which offer solutions to medical needs and include traditional gases, such as oxygen and nitrous oxide, as well as gases with recently discovered roles as biological messenger molecules, such as carbon monoxide, nitric oxide and hydrogen sulphide. Medical gas therapy is a relatively unexplored field of medicine; however, a recent increasing in the number of publications on medical gas therapies clearly indicate that there are significant opportunities for use of gases as therapeutic tools for a variety of disease conditions. In this article, we review the recent advances in research on medical gases with antioxidant properties and discuss their clinical applications and therapeutic properties.

Nakao, Atsunori; Sugimoto, Ryujiro; Billiar, Timothy R; McCurry, Kenneth R

2009-01-01

378

Emerging therapeutics in sleep.  

PubMed

The development of new therapeutics for sleep disorders is increasingly dependent upon understanding the basic brain circuitry that underlies sleep-wake regulation, and how it may be pharmacologically manipulated. In this review, we consider the pathophysiological basis of major sleep disorders that often are seen by neurologists, including excessive daytime sleepiness, insomnia, narcolepsy, rapid eye movement sleep behavior disorder, and restless legs syndrome, as well as circadian disorders, and we review the current and potential future therapeutic approaches. Ann Neurol 2013;74:435-440. PMID:24038193

Saper, Clifford B; Scammell, Thomas E

2013-09-01

379

Risdon Vale: Place, Memory, and Suburban Experience  

Microsoft Academic Search

The author reflects upon the notions of personal memory, collective memory, myth, and evolved memory within her lived experience of Risdon Vale. These interrelated forms of memory influence understanding of place and sense of place. Personal memories corroborate and collaborate with intersubjective memories to inform collective memory. Both personal and collective memories are held within a fusion of cultural myths.

Kate Booth

2008-01-01

380

Polymer hydrogel capsules: en route toward synthetic cellular systems  

NASA Astrophysics Data System (ADS)

Engineered synthetic cellular systems are expected to become a powerful biomedical platform for the development of next-generation therapeutic carrier vehicles. In this mini-review, we discuss the potential of polymer capsules derived by the layer-by-layer assembly as a platform system for the construction of artificial cells and organelles. We outline the characteristics of polymer capsules that make them unique for these applications, and we describe several successful examples of microencapsulated catalysis, including biologically relevant enzymatic reactions. We also provide examples of subcompartmentalized polymer capsules, which represent a major step toward the creation of synthetic cells.

Städler, Brigitte; Price, Andrew D.; Chandrawati, Rona; Hosta-Rigau, Leticia; Zelikin, Alexander N.; Caruso, Frank

2009-09-01

381

Polymer hydrogel capsules: en route toward synthetic cellular systems.  

PubMed

Engineered synthetic cellular systems are expected to become a powerful biomedical platform for the development of next-generation therapeutic carrier vehicles. In this mini-review, we discuss the potential of polymer capsules derived by the layer-by-layer assembly as a platform system for the construction of artificial cells and organelles. We outline the characteristics of polymer capsules that make them unique for these applications, and we describe several successful examples of microencapsulated catalysis, including biologically relevant enzymatic reactions. We also provide examples of subcompartmentalized polymer capsules, which represent a major step toward the creation of synthetic cells. PMID:20644862

Städler, Brigitte; Price, Andrew D; Chandrawati, Rona; Hosta-Rigau, Leticia; Zelikin, Alexander N; Caruso, Frank

2009-08-28

382

Eavesdropping without quantum memory  

SciTech Connect

In quantum cryptography the optimal eavesdropping strategy requires that the eavesdropper uses ancillas and quantum memories in order to optimize her information. What happens if the eavesdropper has no quantum memory? It is shown that in this case the eavesdropper obtains a better information/disturbance trade-off by adopting the simple intercept/resend strategy.

Bechmann-Pasquinucci, H. [Dipartimento di Fisica 'A. Volta', University of Pavia, via Bassi 6, I-27100 Pavia, Italy and UCCI.IT, via Olmo 26, I-23888 Rovagnate (Italy)

2006-04-15

383

Human Learning and Memory  

ERIC Educational Resources Information Center

This innovative textbook is the first to integrate learning and memory, behaviour, and cognition. It focuses on fascinating human research in both memory and learning (while also bringing in important animal studies) and brings the reader up to date with the latest developments in the subject. Students are encouraged to think critically: key…

Lieberman, David A.

2012-01-01

384

Working Memory and Aphasia  

Microsoft Academic Search

This study investigated the relationship between working memory capacity and reading comprehension in aphasia. A measurement of working memory capacity was obtained using a modified version of Daneman and Carpenter's (1980) Reading Span Task. Sets of sentences ranging in length from one to six words were presented to 22 aphasic subjects who were required to retain the terminal words following

Isabelle Caspari; Stanley R. Parkinson; Leonard L. LaPointe; Richard C. Katz

1998-01-01

385

Magnetic content addressable memories  

Microsoft Academic Search

Content Addressable Memories are designed with comparison circuits built into every bit cell. This parallel structure can increase the speed of searching from O(n) (as with Random Access Memories) to O(1), where n is the number of entries being searched. The high cost in hardware limits the application of CAM within situations where higher searching speed is extremely desired. Spintronics

Zhenye Jiang

2009-01-01

386

Emotional memory is perceptual  

Microsoft Academic Search

In two experiments it was investigated which aspects of memory are influenced by emotion. Using a framework proposed by Roediger (American Psychologist 45 (1990) 1043–1056), two dimensions relevant for memory were distinguished the implicit–explicit distinction, and the perceptual versus conceptual distinction. In week 1, subjects viewed a series of slides accompanied with a spoken story in either of the two

Arnoud Arntz; Corlijn de Groot; Merel Kindt

2005-01-01

387

Asymmetric bidirectional associative memories  

Microsoft Academic Search

Bidirectional associative memory (BAM) is a potentially promising model for heteroassociative memories. However, its applications are severely restricted to networks with logical symmetry of interconnections and pattern orthogonality or small pattern size. Although the restrictions on pattern orthogonality and pattern size can be relaxed to a certain extent, all previous efforts are at the cost of increase in connection complexity.

Zong-Ben Xu; Yee Leung; Xiang-Wei He

1994-01-01

388

Memory and Reality  

ERIC Educational Resources Information Center

Although it may be disconcerting to contemplate, true and false memories arise in the same way. Memories are attributions that we make about our mental experiences based on their subjective qualities, our prior knowledge and beliefs, our motives and goals, and the social context. This article describes an approach to studying the nature of these…

Johnson, Marcia K.

2006-01-01

389

Retrieval of Emotional Memories  

ERIC Educational Resources Information Center

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…

Buchanan, Tony W.

2007-01-01

390

MEMORY AND CONSCIOUSNESS  

Microsoft Academic Search

Speculations supported by empirical observations are offered concerning different memory systems (procedural, semantic, and episodic) and corresponding varieties of consciousness (anoetic, noetic, and autonoetic), with special emphasis on episodic memory and autonoetic consciousness as its necessary correlate. Evidence relevant to these speculations is derived from a case study of an amnesic patient who is conscious in some ways but not

ENDEL TULVING

1985-01-01

391

When forgetting preserves memory.  

PubMed

There has been a resurgence of interest in defining the circumstances leading to memory modifications. Studies have shown that reactivating a supposedly stable memory re-introduces a time-limited window of plasticity during which presentation of interfering material can cause long-term memory changes. The present study asks whether such memory changes can be prevented if people are instructed to forget the memory before the new material is encoded. Participants learned a set of objects. After 48?h, they were reminded of this learning episode, and learned another set of objects. Again 48?h later, they recalled the first (Exp. 1) or second set (Exp. 3). As shown previously, a reminder caused intrusions from the second set into recall of the first set. Here I show that the instruction to forget the first set significantly diminished intrusions from the second set, especially when the instruction was given before the new set was encoded in the second session. Experiment 2 suggests that the reduced intrusions were due to list segregation/isolation, rather than temporarily inhibited access to Set 1. Taken together, the study shows that the attempt to forget a memory can immunize it such that the presentation of interfering material has limited effects, and the memory can be recalled unchanged in the future. This is important when veridical memory is essential, such as in eyewitness testimonies. PMID:23382724

Hupbach, Almut

2013-02-04

392

Working Memory and Attitudes  

ERIC Educational Resources Information Center

Working memory capacity has been shown to be an important factor in controlling understanding in the sciences. Attitudes related to studies in the sciences are also known to be important in relation to success in learning. It might be argued that if working memory capacity is a rate controlling feature of learning and success in understanding…

Jung, Eun Sook; Reid, Norman

2009-01-01

393

Distributed memory. Technical report  

SciTech Connect

A brief account is given of how a neural network can store a distributed content addressable memory. Some of the properties of such a network as well as a possible site of storage of long and short-term memory are discussed.

Cooper, L.N.

1985-03-13

394

When autobiographical memory begins  

Microsoft Academic Search

The authors review competing theories concerning the emergence and early development of autobiographical memory. It is argued that the differences between these accounts, although important, may be more apparent than real. The crux of these disagreements lies not in what processes are important, but rather, the role these different processes play in the emergence of autobiographical memory and the temporal

Mark L. Howe; Mary L. Courage; Shannon C. Edisonb

2003-01-01

395

Testing Flash Memories  

Microsoft Academic Search

Flash memories can undergo three different types of disturbances, DC-programming, DC-erasure, and drain disturbance. These faults are specific to flash memories and do not occur in RAMs. In this paper, we discuss these disturbances, their causes, and develop fault models that capture the characteristics of these faults. We present optimal and near optimal algorithms to detect these faults in flash

Mohammad Gh. Mohammad; Kewal K. Saluja; Alex Yap

2000-01-01

396

Introduction to flash memory  

Microsoft Academic Search

This paper mainly focuses on the development of the NOR flash memory technology, with the aim of describing both the basic functionality of the memory cell used so far and the main cell architecture consolidated today. The NOR cell is basically a floating-gate MOS transistor, programmed by channel hot electron and erased by Fowler-Nordheim tunneling. The main reliability issues, such

ROBERTO BEZ; EMILIO CAMERLENGHI; ALBERTO MODELLI; ANGELO VISCONTI

2003-01-01

397

Dynamic Photorefractive Optical Memories.  

National Technical Information Service (NTIS)

The extremely large storage density of volume holographic memories is applicable to numeric and neural network optical computing. Such photorefractive memories, can be used to provide optical storage of binary bit-plane or gray scale images as well as wei...

1992-01-01

398

Optical quantum memory  

Microsoft Academic Search

Quantum memory is essential for the development of many devices in quantum information processing, including a synchronization tool that matches various processes within a quantum computer, an identity quantum gate that leaves any state unchanged, and a mechanism to convert heralded photons to on-demand photons. In addition to quantum computing, quantum memory will be instrumental for implementing long-distance quantum communication

Alexander I. Lvovsky; Barry C. Sanders; Wolfgang Tittel

2009-01-01

399

The Psychology of Memory  

Microsoft Academic Search

In this chapter I will try to provide a brief overview of the concepts and techniques that are most widely used in the psychology of memory. Although it may not appear to be the case from sampling the literature, there is in fact a great deal of agreement as to what constitutes the psychology of memory, much of it developed

Alan D. Baddeley

1976-01-01

400

Predicting Reasoning from Memory  

ERIC Educational Resources Information Center

In an effort to assess the relations between reasoning and memory, in 8 experiments, the authors examined how well responses on an inductive reasoning task are predicted from responses on a recognition memory task for the same picture stimuli. Across several experimental manipulations, such as varying study time, presentation frequency, and the…

Heit, Evan; Hayes, Brett K.

2011-01-01

401

Advertising and Consumer Memory  

Microsoft Academic Search

The paper explores the idea that advertising interferes with consumers' memories of product experiences. We consider a two-period model where a monopolist sells an ex- perience good to a buyer who may only imperfectly recall her first period experience. When advertising activates memory, it enables learning and may induce the buyer to try out the good initially. Moreover, while costly

Daniel Krähmer

2004-01-01

402

Memory after silent stroke  

PubMed Central

Objective: Memory decline commonly occurs among elderly individuals. This observation is often attributed to early neurodegenerative changes in the hippocampus and related brain regions. However, the contribution of vascular lesions, such as brain infarcts, to hippocampal integrity and age-associated memory decline remains unclear. Methods: We studied 658 elderly participants without dementia from a prospective, community-based study on aging and dementia who received high-resolution structural MRI. Cortical and subcortical infarcts were identified, and hippocampal and relative brain volumes were calculated following standard protocols. Summary scores reflecting performance on tasks of memory, language, processing speed, and visuospatial function were derived from a comprehensive neuropsychological battery. We used multiple regression analyses to relate cortical and subcortical infarcts, hippocampal and relative brain volume, to measures of cognitive performance in domains of memory, language, processing speed, and visuospatial ability. Results: Presence of brain infarcts was associated with a smaller hippocampus. Smaller hippocampus volume was associated with poorer memory specifically. Brain infarcts were associated with poorer memory and cognitive performance in all other domains, which was independent of hippocampus volume. Conclusions: Both hippocampal volume and brain infarcts independently contribute to memory performance in elderly individuals without dementia. Given that age-associated neurodegenerative conditions, such as Alzheimer disease, are defined primarily by impairment in memory, these findings have clinical implications for prevention and for identification of pathogenic factors associated with disease symptomatology.

Blum, S.; Luchsinger, J.A.; Manly, J.J.; Schupf, N.; Stern, Y.; Brown, T.R.; DeCarli, C.; Small, S.A.; Mayeux, R.

2012-01-01

403

THERAPEUTIC ALLIANCE: Theme and Variations  

Microsoft Academic Search

The therapeutic alliance is often misconceived, misunderstood, or ignored in conceptualizing the therapeutic process and the therapeutic relation in analysis and other forms of therapy. Conversely, I will argue that the alliance is indispensable in all forms of therapy. After briefly outlining the nature of the alliance, I discuss some of the empirical findings regarding its utility in various therapeutic

W. W. Meissner

2007-01-01

404

Dynamics of Entangled Polymers  

Microsoft Academic Search

The effect of entanglements on polymer dynamics is one of the most interesting and most challenging areas of polymer physics. In 1967 Edwards introduced the confining tube model for polymer networks in which the effect of permanent entanglements from surrounding chains on a given one was replaced by the confining tube potential. In 1971 de Gennes proposed reptation model, suggesting

Michael Rubinstein

2008-01-01

405

Polymer flooding process  

Microsoft Academic Search

An enhanced oil recovery method consisting of two aqueous polymer slugs was proposed. The first is a permeability reducing polymer solution (e.g., containing partially hydrolyzed polyacrylamide) which is followed by a viscosity increasing biopolymer solution (e.g., Kelzan MF). The first polymer is also used to satisfy the adsorption, etc., requirements of the formation rock.

J. S. Rhudy; W. B. Gogarty; B. L. Knight; J. H. Fullinwider

1974-01-01

406

Space Durable Polymer Threads  

Microsoft Academic Search

A unique polymer called TORTM is being developed for use in twisted and braided sewing threads that exhibits excellent space durability in comparison with other organic polymers. Existing organic polymer threads for applications in low Earth orbit (LEO) can suffer significant erosion from the combined effects of atomic oxygen and vacuum ultraviolet radiation which compromise their mechanical and physical properties

Peter Schuler; Ross Haghighat; Hamid Mojazza

1999-01-01

407

Flammability Characteristics of Polymers  

Microsoft Academic Search

In recent years polymers have become versatile and widely accepted materials in almost every conceivable application. Many of these applications involve the possibility of exposure to fire hazards. Upon exposure to a sufficient heat source and sufficient atmospheric oxygen, these materials catch fire and bum. However, the rate of combustion varies from polymer to polymer. The overall fire hazard is

Tejraj M. Aminabhavi; Patrick E. Cassidy

1989-01-01

408

Memory Event Clocks  

NASA Astrophysics Data System (ADS)

We introduce logics and automata based on memory event clocks. A memory clock is not really reset: instead, a new clock is created, while the old one is still accessible by indexing. We can thus constrain not only the time since the last reset (which was the main limitation in event clocks), but also since previous resets. When we introduce these clocks in the linear temporal logic of the reals, we create Recursive Memory Event Clocks Temporal Logic (RMECTL). It turns out to have the same expressiveness as the Temporal Logic with Counting (TLC) of Hirshfeld and Rabinovich. We then examine automata with recursive memory event clocks (RMECA). Recursive event clocks are reset by simpler RMECA, hence the name "recursive". In contrast, we show that for RMECA, memory clocks do not add expressiveness, but only concision. The original RECA define thus a fully decidable, robust and expressive level of real-time expressiveness.

Jerson Ortiz, James; Legay, Axel; Schobbens, Pierre-Yves

409

Graphene flash memory.  

PubMed

Graphene's single atomic layer of sp(2) carbon has recently garnered much attention for its potential use in electronic applications. Here, we report a memory application for graphene, which we call graphene flash memory (GFM). GFM has the potential to exceed the performance of current flash memory technology by utilizing the intrinsic properties of graphene, such as high density of states, high work function, and low dimensionality. To this end, we have grown large-area graphene sheets by chemical vapor deposition and integrated them into a floating gate structure. GFM displays a wide memory window of ?6 V at significantly low program/erase voltages of ±7 V. GFM also shows a long retention time of more than 10 years at room temperature. Additionally, simulations suggest that GFM suffers very little from cell-to-cell interference, potentially enabling scaling down far beyond current state-of-the-art flash memory devices. PMID:21854056

Hong, Augustin J; Song, Emil B; Yu, Hyung Suk; Allen, Matthew J; Kim, Jiyoung; Fowler, Jesse D; Wassei, Jonathan K; Park, Youngju; Wang, Yong; Zou, Jin; Kaner, Richard B; Weiller, Bruce H; Wang, Kang L

2011-08-25

410

Therapeutic HPV DNA vaccines  

PubMed Central

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.

Lin, Ken; Roosinovich, Elena; Ma, Barbara; Hung, Chien-Fu

2010-01-01

411

Therapeutic Recombinant Monoclonal Antibodies  

ERIC Educational Resources Information Center

|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…

Bakhtiar, Ray

2012-01-01

412

Therapeutic laparoscopy in trauma  

Microsoft Academic Search

Purpose: To assess the therapeutic potential of emergent laparoscopy in the trauma setting, a retrospective review was performed in a busy urban trauma center.Patients and methods: Between December 1991 and October 1993, 133 hemodynamically stable patients with suspected abdominal injury were evaluated laparoscopically. All laparoscopic procedures were performed in the operating room under general anesthesia. Mechanism of injury was stab

R. Stephen Smith; William R. Fry; Diane J. Morabito; Richard H. Koehler; Claude H. Organ

1995-01-01

413

Psychopathy and therapeutic pessimism  

Microsoft Academic Search

It is a widely held belief that psychopathic individuals are extremely difficult to treat, if not immune to treatment. This therapeutic pessimism is pervasive and undermines motivation to search for effective modes of intervention for psychopathic individuals. A review of 42 treatment studies on psychopathy revealed that there is little scientific basis for the belief that psychopathy is an untreatable

Randall T Salekin

2002-01-01

414

Controversies in therapeutic touch  

Microsoft Academic Search

One of the most puzzling areas covered under the umbrella of integrative medicine is the field of energy healing. Based on the notion of a subtle vital force which is presumed to be the source of health, many ancient healing techniques have been evolved within this paradigm, including the modern American variant called Therapeutic Touch (TT). This article reviews the

Eric Leskowitz

2003-01-01

415

Therapeutic Hand Exerciser.  

National Technical Information Service (NTIS)

An apparatus is described for cyclic therapeutic exercise of incapacitated hands. It alternately imparts a straightening and bending motion to the fingers by the use of a splint-like inflatable member attached to the top of the hand and a lower pouch in t...

D. E. Barthlome

1975-01-01

416

Therapeutic neutrality reconsidered  

Microsoft Academic Search

This paper suggests that therapists' tendency to ignore the impact of their own religious beliefs on their patients constitutes an area of potential abuse of psychotherapy. The author reviews the religious stance of the founders of psychotherapy, as well as recent criticisms of the therapeutic process, and proposes steps to safeguard against the inadvertent fostering of therapists' religious views on

Robert H. Humphries

1982-01-01

417

Medicare Therapeutic Shoe Demonstration.  

National Technical Information Service (NTIS)

Section 4072(e)(2)(B)(i) of P.L. 100-203, Omnibus Budget Reconciliation Act (OBRA) 1987, mandated a demonstration to test the cost-effectiveness of providing therapeutic shoes to Medicare beneficiaries with severe diabetic foot disease. The demonstration ...

L. W. Sullivan

1990-01-01

418

Writer's cramp: therapeutics perspectives  

Microsoft Academic Search

Writer's cramp has been recognized for at least a century, yet its treatment remains unsatisfactory because it doesn't have a specific therapeutic proposal. The use of drug therapy that act in a systemic way like GABA agonists and anticholinergics have not been found to be of reliable pharmacological benefit. The latest attempt to treat writer's cramp has employed botulinum toxin.

Flavia Quadros; Boisson Waissman; João Santos Pereira

419

Predictors of sustained therapeutic change  

Microsoft Academic Search

The authors integrate explorations by Blatt and colleagues of contributions of patient personality, therapeutic relationship, and change in mental representation to sustained therapeutic change. A pretreatment personality characteristic, self-critical perfectionism, a negative self-schema, significantly interfered with therapeutic progress in manual-directed, brief outpatient treatment for depression. The therapeutic relationship, however, facilitated changes in this negative self-representation, leading to sustained therapeutic change.

Sidney J. Blatt; David C. Zuroff; Lance L. Hawley; John S. Auerbach

2010-01-01

420

Polymer electrolytes plasticized with hyperbranched polymer for lithium polymer batteries  

Microsoft Academic Search

Hyperbranched polymers (HBPs) with different terminal groups and different ethylene oxide (EO) chain lengths were prepared,\\u000a and the influence of the HBP structures including molecular weights and molecular weight distribution on the ionic conductivity\\u000a and the mechanical property of the composite polymer electrolytes composed of poly (ethylene oxide) (PEO), HBP, BaTiO3 as a ceramic filler, and LiN(CF3SO2)2 as a lithium

Takahito Itoh; Seiji Horii; Shinya Hashimoto; Takahiro Uno; Masataka Kubo

2004-01-01

421

Fire-safe polymers and polymer composites  

NASA Astrophysics Data System (ADS)

The intrinsic relationships between polymer structure, composition and fire behavior have been explored to develop new fire-safe polymeric materials. Different experimental techniques, especially three milligram-scale methods---pyrolysis-combustion flow calorimetry (PCFC), simultaneous thermal analysis (STA) and pyrolysis GC/MS---have been combined to fully characterize the thermal decomposition and flammability of polymers and polymer composites. Thermal stability, mass loss rate, char yield and properties of decomposition volatiles were found to be the most important parameters in determining polymer flammability. Most polymers decompose by either an unzipping or a random chain scission mechanism with an endothermic decomposition of 100--900 J/g. Aromatic or heteroaromatic rings, conjugated double or triple bonds and heteroatoms such as halogens, N, O, S, P and Si are the basic structural units for fire-resistant polymers. The flammability of polymers can also be successfully estimated by combining pyrolysis GC/MS results or chemical structures with TGA results. The thermal decomposition and flammability of two groups of inherently fire-resistant polymers---poly(hydroxyamide) (PHA) and its derivatives, and bisphenol C (BPC II) polyarylates---have been systematically studied. PHA and most of its derivatives have extremely low heat release rates and very high char yields upon combustion. PHA and its halogen derivatives can completely cyclize into quasi-polybenzoxazole (PBO) structures at low temperatures. However, the methoxy and phosphate derivatives show a very different behavior during decomposition and combustion. Molecular modeling shows that the formation of an enol intermediate is the rate-determining step in the thermal cyclization of PHA. BPC II-polyarylate is another extremely flame-resistant polymer. It can be used as an efficient flame-retardant agent in copolymers and blends. From PCFC results, the total heat of combustion of these copolymers or blends changes linearly with composition, but the change of maximum heat release rates also depends on the chemical structure of the components. The flammability of various polymers and polymer composites measured by PCFC, cone calorimeter ASTM E1354 and Ohio State University (OSU) calorimeter ASTM E906 were also compared. For pure polymers, there is a relatively good correlation between different methods. However, for polymer composites with inert fillers or flame-retardant additives, OSU and cone calorimetries are more suitable evaluation methods.

Zhang, Huiqing

422

Ellipsometry study of Cu-based shape memory films in a wide spectral range  

NASA Astrophysics Data System (ADS)

Adaptive materials integrate actuating and sensing materials into a structural material. The development of polymer composites with embedded shape memory alloys can open new perspectives with respect to the development of engineering structures with adaptive shape, stiffness, damping and other properties. The development of these advanced composites with embedded shape memory alloy wires is still in an embryonic stage. Given ellipsometry measurements of optical properties copper based alloy which require further research before these adaptive composites can be used in industrial applications.

Filipov, Y. V.; Staschuk, V. S.; Poperenko, L. V.

2005-08-01

423

Prototype Fabrication and Preliminary In Vitro Testing of a Shape Memory Endovascular Thrombectomy Device  

Microsoft Academic Search

An electromechanical microactuator comprised of shape memory polymer (SMP) and shape memory nickel-titanium alloy (nitinol) was developed and used in an endovascular thrombectomy device prototype. The microactuator maintains a straight rod shape until an applied current induces electro-resistive (Joule) heating, causing the microactuator to transform into a corkscrew shape. The straight-to-corkscrew transformation geometry was chosen to permit endovascular delivery through

Ward Small; Thomas S. Wilson; Patrick R. Buckley; William J. Benett; Jeffrey M. Loge; Jonathan Hartman; Duncan J. Maitland

2007-01-01

424

Aging Memories: Differential Decay of Episodic Memory Components  

ERIC Educational Resources Information Center

Some memories about events can persist for decades, even a lifetime. However, recent memories incorporate rich sensory information, including knowledge on the spatial and temporal ordering of event features, while old memories typically lack this "filmic" quality. We suggest that this apparent change in the nature of memories may reflect a…

Talamini, Lucia M.; Gorree, Eva

2012-01-01

425

Memory Loss: 7 Tips to Improve Your Memory  

MedlinePLUS

... may be reprinted for personal, noncommercial use only. Memory loss: 7 tips to improve your memory By Mayo Clinic staff Original Article: http://www. ... not share your e-mail address Sign up Memory loss: 7 tips to improve your memory Concerned ...

426

Genuine memory deficits in age?associated memory impairment  

Microsoft Academic Search

Memory impairment in aging may seem evident from the forgetfulness of the aged and their poor performance on memory tests, but the amelioration or elimination of apparent memory deficits in the aged when they are induced to process efficiently has shown that most, if not all, of their apparent memory deficits are due to inefficient processing, reduced processing capacity, or

Herman Buschke; Ellen Grober

1986-01-01

427

Single-Item Memory, Associative Memory, and the Human Hippocampus  

ERIC Educational Resources Information Center

|We tested recognition memory for items and associations in memory-impaired patients with bilateral lesions thought to be limited to the hippocampal region. In Experiment 1 (Combined memory test), participants studied words and then took a memory test in which studied words, new words, studied word pairs, and recombined word pairs were presented…

Squire, Larry R.; Gold, Jeffrey J.; Hopkins, Ramona O.

2006-01-01

428

Working memory and the memory distortion component of hindsight bias  

Microsoft Academic Search

One component of hindsight bias is memory distortion: Individuals' recollections of their predictions are biased towards known outcomes. The present study examined the role of working memory in the memory distortion component of hindsight bias. Participants answered almanac-like questions, completed a measure of working memory capacity, were provided with the correct answers, and attempted to recollect their original judgements in

Dustin P. Calvillo

2012-01-01

429

Memory Systems in the Brain and Localization of a Memory  

Microsoft Academic Search

It is now clear that there are a number of different forms or aspects of learning and memory that involve different brain systems. Broadly, memory phenomena have been categorized as explicit or implicit. Thus, explicit memories for experience involve the hippocampus-medial temporal lobe system and implicit basic associative learning and memory involves the cerebellum, amygdala, and other systems. Under normal

Richard F. Thompson; Jeansok J. Kim

1996-01-01

430

Single-item memory, associative memory, and the human hippocampus  

Microsoft Academic Search

We tested recognition memory for items and associations in memory-impaired patients with bilateral lesions thought to be limited to the hippocampal region. In Experiment 1 (Combined memory test), participants studied words and then took a memory test in which studied words, new words, studied word pairs, and recombined word pairs were presented in a mixed order. In Experiment 2 (Separated

Jeffrey J. Gold; Ramona O. Hopkins; Larry R. Squire

2006-01-01

431

Nanoporous polymer electrolyte  

SciTech Connect

A nanoporous polymer electrolyte and methods for making the polymer electrolyte are disclosed. The polymer electrolyte comprises a crosslinked self-assembly of a polymerizable salt surfactant, wherein the crosslinked self-assembly includes nanopores and wherein the crosslinked self-assembly has a conductivity of at least 1.0.times.10.sup.-6 S/cm at 25.degree. C. The method of making a polymer electrolyte comprises providing a polymerizable salt surfactant. The method further comprises crosslinking the polymerizable salt surfactant to form a nanoporous polymer electrolyte.

Elliott, Brian (Wheat Ridge, CO); Nguyen, Vinh (Wheat Ridge, CO)

2012-04-24

432

Neural Protein Synthesis during Aging: Effects on Plasticity and Memory  

PubMed Central

During aging, many experience a decline in cognitive function that includes memory loss. The encoding of long-term memories depends on new protein synthesis, and this is also reduced during aging. Thus, it is possible that changes in the regulation of protein synthesis contribute to the memory impairments observed in older animals. Several lines of evidence support this hypothesis. For instance, protein synthesis is required for a longer period following learning to establish long-term memory in aged rodents. Also, under some conditions, synaptic activity or pharmacological activation can induce de novo protein synthesis and lasting changes in synaptic transmission in aged, but not young, rodents; the opposite results can be observed in other conditions. These changes in plasticity likely play a role in manifesting the altered place field properties observed in awake and behaving aged rats. The collective evidence suggests a link between memory loss and the regulation of protein synthesis in senescence. In fact, pharmaceuticals that target the signaling pathways required for induction of protein synthesis have improved memory, synaptic plasticity, and place cell properties in aged animals. We suggest that a better understanding of the mechanisms that lead to different protein expression patterns in the neural circuits that change as a function of age will enable the development of more effective therapeutic treatments for memory loss.

Schimanski, Lesley A.; Barnes, Carol A.

2010-01-01

433

Degradability of Polymers for Implantable Biomedical Devices  

PubMed Central

Many key components of implantable medical devices are made from polymeric materials. The functions of these materials include structural support, electrical insulation, protection of other materials from the environment of the body, and biocompatibility, as well as other things such as delivery of a therapeutic drug. In such roles, the stability and integrity of the polymer, over what can be a very long period of time, is very important. For most of these functions, stability over time is desired, but in other cases, the opposite–the degradation and disappearance of the polymer over time is required. In either case, it is important to understand both the chemistry that can lead to the degradation of polymers as well as the kinetics that controls these reactions. Hydrolysis and oxidation are the two classes of reactions that lead to the breaking down of polymers. Both are discussed in detail in the context of the environmental factors that impact the utility of various polymers for medical device applications. Understanding the chemistry and kinetics allows prediction of stability as well as explanations for observations such as porosity and the unexpected behavior of polymeric composite materials in some situations. In the last part, physical degradation such interfacial delamination in composites is discussed.

Lyu, SuPing; Untereker, Darrel

2009-01-01

434

Memories of Reading, Memories in Writing.  

ERIC Educational Resources Information Center

Discusses how literature (especially African-American) affected and shaped the author all her life. Explores how her writing drew on her own experiences and memories. Discusses her experiences writing historical fiction further exploring African-American history. Portrays a spirit of freedom that will show her readers confidence and self-esteem…

Hansen, Joyce

1999-01-01

435

Radiation dosimetry using three-dimensional optical random access memories  

Microsoft Academic Search

Three-dimensional optical random access memories (3D ORAMs) are a new generation of high-density data storage devices. Binary information is stored and retrieved via a light induced reversible transformation of an ensemble of bistable photochromic molecules embedded in a polymer matrix. This paper describes the application of 3D ORAM materials to radiation dosimetry. It is shown both theoretically and experimentally, that

Marko Moscovitch; Gary W. Phillips

2001-01-01

436

Microoptics and Photonics Polymer  

NASA Astrophysics Data System (ADS)

In this paper, the fundamental optical properties of photonics polymers are reviewed on the basis of the relationship between lightwave and polymer materials. We have proposed and demonstrated photonics polymers with new optical functions for applications in microoptics fields, such as graded-index plastic optical fibers (GI POFs), highly scattered optical transmission (HSOT) polymers, zero-birefringence optical polymers, and graded-index plastic optical fiber amplifiers (GI POFAs). In the materials we proposed, the lightwave refracts, scatters or polarizes according to the size of heterogeneities of refractive index within the polymer matrix. With these photonics polymers, we propose the concept of “fiber to the display”, which will lead us back to “face-to-face communication”.

Koike, Yasuhiro

2008-08-01

437

Polymer modified road bitumens  

SciTech Connect

The present thesis is based on six publications, including a literature review (Paper 1) and experimental studies (Papers 2--6) on polymer modified bitumens. In the literature review, basic aspects of bitumen chemistry and rheology and characteristics of the polymers used for bitumen modification are described. Test methods and specifications of polymer modified bitumens are reviewed. The present situation in this area and the need for further development are also discussed. The experimental part deals with laboratory investigations of five bitumens from four sources modified with six polymers (four types) a different polymer content. The main objective of the laboratory work is to study fundamental properties of polymer modified binders, which include rheological properties, temperature, susceptibility, compatibility (morphology), storage stability, low-temperature properties and aging behavior. The effects of bitumen source/grade and polymer type and content on these properties are evaluated.

Lu, X.

1997-12-16

438

Generation, persistence and plasticity of CD4 T-cell memories  

PubMed Central

The development of immune memory mediated by T lymphocytes is central to durable, long-lasting protective immunity. A key issue in the field is how to direct the generation and persistence of memory T cells to elicit the appropriate secondary response to provide protection to a specific pathogen. Two prevailing views have emerged; that cellular and molecular regulators control the lineage fate and functional capacities of memory T cells early after priming, or alternatively, that populations of memory T cells are inherently plastic and subject to alterations in function and/or survival at many stages during their long-term maintenance. Here, we will review current findings in CD4 T-cell memory that suggest inherent plasticity in populations of memory CD4 T cells at all stages of their development – originating with their generation from multiple types of primed CD4 T cells, during their persistence and homeostatic turnover in response to T-cell receptor signals, and also following secondary challenge. These multiple aspects of memory CD4 T-cell flexibility contrast the more defined lineages and functions ascribed to memory CD8 T cells, suggesting a dynamic nature to memory CD4 T-cell populations and responses. The flexible attributes of CD4 T-cell memory suggest opportunities and mechanisms for therapeutic manipulation at all phases of immune memory development, maintenance and recall.

Lees, Jason R; Farber, Donna L

2010-01-01

439

Covalent assembly of gold nanoparticles: an application toward transistor memory.  

PubMed

This work reports a versatile approach utilizing covalent assembly of functionalized gold nanoparticles for organic field-effect transistor (OFET) based memory devices. 11-Mercapto-1-undecanol functionalized gold nanoparticles (AuNPs) having size of 5 ± 0.5 nm were synthesized and immobilized onto SiO(2) substrate through covalent binding using a functionalized polymer as a surface modifier. The pentacene OFET-based memory devices utilizing such covalently bound gold nanoparticles with nanoparticle density of 5 × 10(11) cm(-2) exhibited a large memory window (7.7 V), high on/off ratio between memory states (10(5)), and long retention time (>10,000 s). The present synthetic route for memory devices incorporating covalently immobilized gold nanoparticles has several advantages such as solution processable, enhanced device stability, low-cost, and low-temperature process and will be a step toward realization for low-cost, lightweight, flexible, logic display driver, and flash memory applications. PMID:22816559

Gupta, Raju Kumar; Ying, Gao; Srinivasan, M P; Lee, Pooi See

2012-08-02

440

Cache-Memory Interfaces in Compressed Memory Systems  

Microsoft Academic Search

Abstract?e consider a number of cache\\/memory hierarchy design issues in systems with compressed random access memories (C-RAMs) in which compression and decompression occur automatically to and from main memory. Using a C-RAM as main memory, the bulk of main memory contents are stored in a compressed format and dynamically decompressed to handle cache misses at the next higher level of

Caroline D. Benveniste; Peter A. Franaszek; John T. Robinson

2001-01-01

441

Materials Research Society Symposium Proceedings Volume 600, Electroactive Polymers (EAP) Symposium Held in Boston, Massachusetts on November 29-December 1, 1999.  

National Technical Information Service (NTIS)

For many years, electroactive ceramic, magnetostrictive material and shape memory alloys have been the primary source of actuation materials for manipulation and mobility systems. Electroactive polymers (EAP) received relatively little attention due to th...

J. Scheinbeim Q. M. Zhang T. Furukawa Y. Bar-Cohen

1999-01-01

442

Reduced False Memory after Sleep  

ERIC Educational Resources Information Center

Several studies have shown that sleep contributes to the successful maintenance of previously encoded information. This research has focused exclusively on memory for studied events, as opposed to false memories. Here we report three experiments showing that sleep reduces false memories in the Deese-Roediger-McDermott (DRM) memory illusion. False…

Fenn, Kimberly M.; Gallo, David A.; Margoliash, Daniel; Roediger, Henry L., III; Nusbaum, Howard C.

2009-01-01

443

Combinable memory-block transactions  

Microsoft Academic Search

This paper formalizes and studies combinable memory-block transactions (MBTs). The idea is to encode short programs that operate on a single cache\\/memory block and then to specify such a program with a memory request. The code is then executed at the cache or memory controller, atomically with respect to other accesses to that block by this or other processors. The

Guy E. Blelloch; Phillip B. Gibbons; S. Harsha Vardhan

2008-01-01

444

Reduced False Memory after Sleep  

ERIC Educational Resources Information Center

|Several studies have shown that sleep contributes to the successful maintenance of previously encoded information. This research has focused exclusively on memory for studied events, as opposed to false memories. Here we report three experiments showing that sleep reduces false memories in the Deese-Roediger-McDermott (DRM) memory illusion. False…

Fenn, Kimberly M.; Gallo, David A.; Margoliash, Daniel; Roediger, Henry L., III; Nusbaum, Howard C.

2009-01-01

445

Memory Processes and Experiential Continuity  

Microsoft Academic Search

What are the memory processes that produce coherent representations of temporally discontinuous experiences? In this ar- ticle, we describe the memory process ofresonance, a process that provides renewed access to long-term memory information that is relevant to cues in working memory. Our experiments demonstrate parallel waxing and waning of information as a function of relevance to a current episode, a

Richard J. Gerrig; Gail McKoon

2001-01-01

446

Stroke and episodic memory disorders  

Microsoft Academic Search

Memory impairments are common after stroke, and the anatomical basis for impairments may be quite variable. To determine the range of stroke-related memory impairment, we identified all case reports and group studies through the Medline database and the Science Citation Index. There is no hypothesis about memory that is unique to stroke, but there are several important facets of memory

Chun Lim; Michael P. Alexander

2009-01-01

447

Molecular Mechanisms of Memory Retrieval  

Microsoft Academic Search

Memory retrieval is a fundamental component or stage of memory processing. In fact, retrieval is the only possible measure of memory. The ability to recall past events is a major determinant of survival strategies in all species and is of paramount importance in determining our uniqueness as individuals. Most biological studies of memory using brain lesion and\\/or gene manipulation techniques

German Szapiro; Julieta M. Galante; Daniela M. Barros; Miguelina Levi de Stein; Monica R. M. Vianna; Luciana A. Izquierdo; Ivan Izquierdo; Jorge H. Medina

2002-01-01

448

Toxicity of therapeutic nanoparticles.  

PubMed

A total of six nanotherapeutic formulations are already approved for medical use and more are in the approval pipeline currently. Despite the massive research effort in nanotherapeutic materials, there is relatively little information about the toxicity of these materials or the tools needed to assess this toxicity. Recently, the scientific community has begun to respond to the paucity of information by investing in the field of nanoparticle toxicology. This review is intended to provide an overview of the techniques needed to assess toxicity of these therapeutic nanoparticles and to summarize the current state of the field. We begin with background on the toxicological assessment techniques used currently as well as considerations in nanoparticle dosing. The toxicological research overview is divided into the most common applications of therapeutic nanoparticles: drug delivery, photodynamic therapy and bioimaging. We end with a perspective section discussing the current technological gaps and promising research aimed at addressing those gaps. PMID:19193187

Maurer-Jones, Melissa A; Bantz, Kyle C; Love, Sara A; Marquis, Bryce J; Haynes, Christy L

2009-02-01

449

Strategies for therapeutic hypometabothermia  

PubMed Central

Although therapeutic hypothermia and metabolic suppression have shown robust neuroprotection in experimental brain ischemia, systemic complications have limited their use in treating acute stroke patients. The core temperature and basic metabolic rate are tightly regulated and maintained in a very stable level in mammals. Simply lowering body temperature or metabolic rate is actually a brutal therapy that may cause more systemic as well as regional problems other than providing protection. These problems are commonly seen in hypothermia and barbiturate coma. The main innovative concept of this review is to propose thermogenically optimal and synergistic reduction of core temperature and metabolic rate in therapeutic hypometabothermia using novel and clinically practical approaches. When metabolism and body temperature are reduced in a systematically synergistic manner, the outcome will be maximal protection and safe recovery, which happen in natural process, such as in hibernation, daily torpor and estivation.

Liu, Shimin; Chen, Jiang-Fan

2013-01-01

450

Therapeutic use of cannabis.  

PubMed

Therapeutic cannabis use raises a number of dilemmas for nurses. This article examines the legal, political and ethical challenges raised by the use of cannabis by people with life-limiting or terminal illnesses in their own homes. (Throughout this paper, the term cannabis refers to illegal cannabis unless specified.) A literature review of databases from 1996 was conducted and internet material was also examined. Evidence on the therapeutic use of cannabis suggests it may produce improvements in quality of life, which has led to increased use among people with life-limiting illnesses. The cannabis used is usually obtained illegally, which can have consequences for both those who use it and nurses who provide treatment in the community. PMID:22479766

de Vries, Kay; Green, Anita J

451

Single-item memory, associative memory, and the human hippocampus.  

PubMed

We tested recognition memory for items and associations in memory-impaired patients with bilateral lesions thought to be limited to the hippocampal region. In Experiment 1 (Combined memory test), participants studied words and then took a memory test in which studied words, new words, studied word pairs, and recombined word pairs were presented in a mixed order. In Experiment 2 (Separated memory test), participants studied single words and then took a memory test involving studied word and new words. In a separate test, they studied word pairs and then took a memory test involving studied word pairs and recombined word pairs. In both experiments, patients were impaired at memory for single items as well as memory for associations, suggesting that the hippocampus is important for both of these memory functions. In Experiment 1, patients appeared to be more impaired at associative memory than item memory. In Experiment 2, patients were similarly impaired at associative memory and item memory. These different findings are considered, including the fact that in Experiment 1 the results depended on the fact that controls produced unexpectedly low false-alarm rates to recombined pairs. We discuss single-item and associative memory from the perspective that the hippocampus and adjacent cortex work cooperatively to signal recognition and that simple dichotomies do not adequately describe the division of labor within the medial temporal lobe. PMID:16980546

Gold, Jeffrey J; Hopkins, Ramona O; Squire, Larry R

2006-09-15

452

Single-item memory, associative memory, and the human hippocampus  

PubMed Central

We tested recognition memory for items and associations in memory-impaired patients with bilateral lesions thought to be limited to the hippocampal region. In Experiment 1 (Combined memory test), participants studied words and then took a memory test in which studied words, new words, studied word pairs, and recombined word pairs were presented in a mixed order. In Experiment 2 (Separated memory test), participants studied single words and then took a memory test involving studied word and new words. In a separate test, they studied word pairs and then took a memory test involving studied word pairs and recombined word pairs. In both experiments, patients were impaired at memory for single items as well as memory for associations, suggesting that the hippocampus is important for both of these memory functions. In Experiment 1, patients appeared to be more impaired at associative memory than item memory. In Experiment 2, patients were similarly impaired at associative memory and item memory. These different findings are considered, including the fact that in Experiment 1 the results depended on the fact that controls produced unexpectedly low false-alarm rates to recombined pairs. We discuss single-item and associative memory from the perspective that the hippocampus and adjacent cortex work cooperatively to signal recognition and that simple dichotomies do not adequately describe the division of labor within the medial temporal lobe.

Gold, Jeffrey J.; Hopkins, Ramona O.; Squire, Larry R.

2006-01-01

453

TOPICAL REVIEW Nanoscale memory devices  

NASA Astrophysics Data System (ADS)

This article reviews the current status and future prospects for the use of nanomaterials and devices in memory technology. First, the status and continuing scaling trends of the flash memory are discussed. Then, a detailed discussion on technologies trying to replace flash in the near-term is provided. This includes phase change random access memory, Fe random access memory and magnetic random access memory. The long-term nanotechnology prospects for memory devices include carbon-nanotube-based memory, molecular electronics and memristors based on resistive materials such as TiO2.

Chung, Andy; Deen, Jamal; Lee, Jeong-Soo; Meyyappan, M.

2010-10-01

454

Mitochondrial Diseases: Therapeutic Approaches  

Microsoft Academic Search

Therapy of mitochondrial encephalomyopathies (defined restrictively as defects of the mitochondrial respiratory chain) is\\u000a woefully inadequate, despite great progress in our understanding of the molecular bases of these disorders. In this review,\\u000a we consider sequentially several different therapeutic approaches. Palliative therapy is dictated by good medical practice\\u000a and includes anticonvulsant medication, control of endocrine dysfunction, and surgical procedures. Removal of

Salvatore DiMauro; Michelangelo Mancuso

2007-01-01

455

Antibody therapeutics in cancer.  

PubMed

In a relatively short period of time, monoclonal antibodies have entered the mainstream of cancer therapy. Their first use was as antagonists of oncogenic receptor tyrosine kinases, but today monoclonal antibodies have emerged as long-sought vehicles for the targeted delivery of potent chemotherapeutic agents and as powerful tools to manipulate anticancer immune responses. With ever more promising results from the clinic, the future will likely see continued growth in the discovery and development of therapeutic antibodies and their derivatives. PMID:24031011

Sliwkowski, Mark X; Mellman, Ira

2013-09-13

456

Bleomycins: towards better therapeutics  

Microsoft Academic Search

Bleomycins are a family of glycopeptide antibiotics that have potent antitumour activity against a range of lymphomas, head and neck cancers and germ-cell tumours. The therapeutic efficacy of the bleomycins is limited by development of lung fibrosis. The cytotoxic and mutagenic effects of the bleomycins are thought to be related to their ability to mediate both single-stranded and double-stranded DNA

Jingyang Chen; JoAnne Stubbe

2005-01-01

457

Race-based therapeutics  

Microsoft Academic Search

The issue of race in medicine is problematic. Race is not a physiologic grouping, and all persons of a given race do not necessarily\\u000a share the same clinical phenotype or genetic substrate. Despite clear signals that certain risk factors and diseases vary\\u000a as a function of race, translating those differences into race-based therapeutics has been awkward and has done little

Clyde W. Yancy

2007-01-01

458

Therapeutic jurisprudence in the courts.  

PubMed

Therapeutic jurisprudence is an emerging field of law and social science inquiry that explores the role of the law in fostering therapeutic or antitherapeutic outcomes. This article considers the relationship between therapeutic jurisprudence and court performance goals, examines applications of therapeutic jurisprudence in court settings, discusses the steps involved in incorporating therapeutic jurisprudence principles into the work of courts, outlines the pros and cons associated with practicing therapeutic jurisprudence primarily in specialized courts, and offers suggestions for fostering continued experimentation by courts. PMID:11018778

Casey, P; Rottman, D B

2000-01-01

459

Antioxidant therapeutics for schizophrenia.  

PubMed

Pharmaceutical treatment for millions worldwide who have schizophrenia is limited to a handful of antipsychotics. Despite the proven efficacy of these drugs, the overall outcome for schizophrenia remains suboptimal. Thus, alternative treatment options are urgently needed. One possible approach may be antioxidant therapy. The extant evidence for the role of oxidative stress in the pathophysiology of schizophrenia offers a hypothesis-derived therapeutic approach in the form of antioxidants. Vitamins C and E, for example, are suitable for human clinical trials because they are readily available, inexpensive, and relatively safe. Research into the therapeutic use of antioxidants in schizophrenia can be grouped into two main clusters: for psychopathology and for side effects. Of these studies, some have been carefully conducted, but majority are open label. Use of antioxidants for treatment-related side effects has been more extensively investigated. The totality of the evidence to date suggests that specific antioxidants, such as N-acetyl cysteine, may offer tangible benefits for the clinical syndrome of schizophrenia, and vitamin E may offer salutary effects on glycemic effects of antipsychotics. However, a great deal of fundamental clinical research remains to be done before antioxidants can be routinely used therapeutically for schizophrenia and treatment-related complications. PMID:20977337

Reddy, Ravinder; Reddy, Rajiv

2011-04-20

460

Polycyclic peptide therapeutics.  

PubMed

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

Baeriswyl, Vanessa; Heinis, Christian

2013-01-25

461

A Review of Monte Carlo Simulations of Polymers with PERM  

NASA Astrophysics Data System (ADS)

In this review, we describe applications of the pruned-enriched Rosenbluth method (PERM), a sequential Monte Carlo algorithm with resampling, to various problems in polymer physics. PERM produces samples according to any given prescribed weight distribution, by growing configurations step by step with controlled bias, and correcting "bad" configurations by "population control". The latter is implemented, in contrast to other population based algorithms like e.g. genetic algorithms, by depth-first recursion which avoids storing all members of the population at the same time in computer memory. The problems we discuss all concern single polymers (with one exception), but under various conditions: Homopolymers in good solvents and at the ? point, semi-stiff polymers, polymers in confining geometries, stretched polymers undergoing a forced globule-linear transition, star polymers, bottle brushes, lattice animals as a model for randomly branched polymers, DNA melting, and finally—as the only system at low temperatures, lattice heteropolymers as simple models for protein folding. PERM is for some of these problems the method of choice, but it can also fail. We discuss how to recognize when a result is reliable, and we discuss also some types of bias that can be crucial in guiding the growth into the right directions.

Hsu, Hsiao-Ping; Grassberger, Peter

2011-08-01