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(usually optically) to take on an expanded conformation, and then used to dislodge and grip the thrombus while it is withdrawn through the catheter.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

Microsoft Academic Search

The past several years have witnessed significant advances in the field of shape memory polymers (SMPs) with the elucidation of new compositions for property tuning, the discovery of new mechanisms for shape fixing and recovery, and the initiation of phenomenological modeling. We critically review research findings on new shape memory polymers along these lines, emphasizing exciting progress in the areas

Patrick T. Mather; Xiaofan Luo; Ingrid A. Rousseau

2009-01-01

3

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

4

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

5

Nitinol-reinforced shape-memory polymers  

E-print Network

Reinforced shape-memory polymers have been developed from an acrylate based thermoset shape-memory polymer and nitinol wires. A rectangular shape-memory polymer measuring approximately 1 by 2 by 0.1 inches has a ten fold ...

Di Leo, Claudio V

2010-01-01

6

Shape-Memory Polymer Composites  

Microsoft Academic Search

\\u000a The development of shape-memory polymer composites (SMPCs) enables high recovery stress levels as well as novel functions\\u000a such as electrical conductivity, magnetism, and biofunctionality. In this review chapter the substantial enhancement in mechanical\\u000a properties of shape-memory polymers (SMPs) by incorporating small amounts of stiff fillers will be highlighted exemplarily\\u000a for clay and polyhedral oligomeric silsesquioxanes (POSS). Three different functions resulting

Samy A. Madbouly; Andreas Lendlein

2010-01-01

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

Shape-memory polymers for microelectromechanical systems  

Microsoft Academic Search

This paper investigates the use of shape-memory polymer thin films in microelectromechanical systems (MEMS). shape-memory polymers possess the capacity to recover large-strain deformations by the application of heat and are candidates for small-scale transduction. The key advantages of shape-memory polymers are their low material\\/fabrication cost coupled with their simplicity of integration\\/operation. In the present study, shape-memory polymers are spin coated

Ken Gall; Paul Kreiner; David Turner; Michael Hulse

2004-01-01

9

Therapeutic gene delivery using bioreducible polymers.  

PubMed

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

Ryu, Kitae; Kim, Tae-Il

2014-01-01

10

Shape-Memory Polymer Composites  

NASA Astrophysics Data System (ADS)

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

Madbouly, Samy A.; Lendlein, Andreas

11

Multifunctional shape-memory polymers.  

PubMed

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

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

2010-08-17

12

Investigation of Shape Memory Polymers and Their Hybrid Composites  

Microsoft Academic Search

In this paper, a newly developed polymer, shape memory polyurethane (SMP), will be introduced. The shape memory polymer possesses the same basic shape memory effect and elasticity memory effect as shape memory alloys. Shape memory polymers can change their elastic modulus up to 500 times around their glass transition temperatures. Both the shape memory effect and the elasticity memory effect

C. Liang; C. A. Rogers; E. Malafeew

1997-01-01

13

Temperature-memory polymer actuators  

PubMed Central

Reading out the temperature-memory of polymers, which is their ability to remember the temperature where they were deformed recently, is thus far unavoidably linked to erasing this memory effect. Here temperature-memory polymer actuators (TMPAs) based on cross-linked copolymer networks exhibiting a broad melting temperature range (?Tm) are presented, which are capable of a long-term temperature-memory enabling more than 250 cyclic thermally controlled actuations with almost constant performance. The characteristic actuation temperatures Tacts of TMPAs can be adjusted by a purely physical process, guiding a directed crystallization in a temperature range of up to 40 °C by variation of the parameter Tsep in a nearly linear correlation. The temperature Tsep divides ?Tm into an upper Tm range (T > Tsep) forming a reshapeable actuation geometry that determines the skeleton and a lower Tm range (T < Tsep) that enables the temperature-controlled bidirectional actuation by crystallization-induced elongation and melting-induced contraction. The macroscopic bidirectional shape changes in TMPAs could be correlated with changes in the nanostructure of the crystallizable domains as a result of in situ X-ray investigations. Potential applications of TMPAs include heat engines with adjustable rotation rate and active building facades with self-regulating sun protectors. PMID:23836673

Behl, Marc; Kratz, Karl; Noechel, Ulrich; Sauter, Tilman; Lendlein, Andreas

2013-01-01

14

Temperature-memory polymer actuators.  

PubMed

Reading out the temperature-memory of polymers, which is their ability to remember the temperature where they were deformed recently, is thus far unavoidably linked to erasing this memory effect. Here temperature-memory polymer actuators (TMPAs) based on cross-linked copolymer networks exhibiting a broad melting temperature range (?T(m)) are presented, which are capable of a long-term temperature-memory enabling more than 250 cyclic thermally controlled actuations with almost constant performance. The characteristic actuation temperatures T(act)s of TMPAs can be adjusted by a purely physical process, guiding a directed crystallization in a temperature range of up to 40 °C by variation of the parameter T(sep) in a nearly linear correlation. The temperature T(sep) divides ?T(m) into an upper T(m) range (T > T(sep)) forming a reshapeable actuation geometry that determines the skeleton and a lower T(m) range (T < T(sep)) that enables the temperature-controlled bidirectional actuation by crystallization-induced elongation and melting-induced contraction. The macroscopic bidirectional shape changes in TMPAs could be correlated with changes in the nanostructure of the crystallizable domains as a result of in situ X-ray investigations. Potential applications of TMPAs include heat engines with adjustable rotation rate and active building facades with self-regulating sun protectors. PMID:23836673

Behl, Marc; Kratz, Karl; Noechel, Ulrich; Sauter, Tilman; Lendlein, Andreas

2013-07-30

15

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

16

Post polymerization cure shape memory polymers  

SciTech Connect

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

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

2014-11-11

17

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

Microsoft Academic Search

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

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

2009-01-01

18

Tunable polymer multi-shape memory effect  

Microsoft Academic Search

Shape memory polymers are materials that can memorize temporary shapes and revert to their permanent shape upon exposure to an external stimulus such as heat, light, moisture or magnetic field. Such properties have enabled a variety of applications including deployable space structures, biomedical devices, adaptive optical devices, smart dry adhesives and fasteners. The ultimate potential for a shape memory polymer,

Tao Xie

2010-01-01

19

Thermomechanical constitutive model of shape memory polymer  

Microsoft Academic Search

A nonlinear thermomechanical constitutive model of shape memory polymer (SMP) is developed by modifying a linear model. The coefficients in the model are expressed by the single exponential functions of temperature in order to describe the variation in mechanical properties of the material due to the glass transition. The proposed theory expresses well the thermomechanical properties of polyurethane-shape memory polymer,

Hisaaki Tobushi; Kayo Okumura; Shunichi Hayashi; Norimitsu Ito

2001-01-01

20

Shape memory polymer actuator and catheter  

DOEpatents

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

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

2007-11-06

21

Characterization Methods for Shape-Memory Polymers  

Microsoft Academic Search

\\u000a Shape-memory polymers (SMPs) are able to fix a temporary deformed shape and recover their original permanent shape upon application\\u000a of an external stimulus such as heat or light. A shape-memory functionalization can be realized for polymer based materials\\u000a with an appropriate morphology by application of a specific shape-memory creation procedure (SMCP). Specific characterization\\u000a methods have been tailored to explore the

Wolfgang Wagermaier; Karl Kratz; Matthias Heuchel; Andreas Lendlein

2010-01-01

22

Advances in shape memory polymer actuation  

Microsoft Academic Search

Shape memory materials fulfill an important role in both actuation and mechanical coupling between actuators and associated dynamic systems. The simplest techniques are thermally based and in addition to the more common shape memory alloys there are also shape memory polymers. These have similar characteristics to those of their metallic cousins, but there the relationship stops. The basic physical principles

G. J Monkman

2000-01-01

23

Release mechanism utilizing shape memory polymer material  

DOEpatents

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

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

2000-01-01

24

Tunable polymer multi-shape memory effect.  

PubMed

Shape memory polymers are materials that can memorize temporary shapes and revert to their permanent shape upon exposure to an external stimulus such as heat, light, moisture or magnetic field. Such properties have enabled a variety of applications including deployable space structures, biomedical devices, adaptive optical devices, smart dry adhesives and fasteners. The ultimate potential for a shape memory polymer, however, is limited by the number of temporary shapes it can memorize in each shape memory cycle and the ability to tune the shape memory transition temperature(s) for the targeted applications. Currently known shape memory polymers are capable of memorizing one or two temporary shapes, corresponding to dual- and triple-shape memory effects (also counting the permanent shape), respectively. At the molecular level, the maximum number of temporary shapes a shape memory polymer can memorize correlates directly to the number of discrete reversible phase transitions (shape memory transitions) in the polymer. Intuitively, one might deduce that multi-shape memory effects are achievable simply by introducing additional reversible phase transitions. The task of synthesizing a polymer with more than two distinctive and strongly bonded reversible phases, however, is extremely challenging. Tuning shape memory effects, on the other hand, is often achieved through tailoring the shape memory transition temperatures, which requires alteration in the material composition. Here I show that the perfluorosulphonic acid ionomer (PFSA), which has only one broad reversible phase transition, exhibits dual-, triple-, and at least quadruple-shape memory effects, all highly tunable without any change to the material composition. PMID:20220846

Xie, Tao

2010-03-11

25

Partial shape memory effect of polymers  

NASA Astrophysics Data System (ADS)

A blend of PLA (80%) and PBS (20%) has been prepared first by extrusion, then by injection molding. Tensile, stress-relaxation and recovery tests have been performed on the samples at 70°C and 75°C. The results indicated that the blend can regain only 24% of its initial shape. This partial shape memory effect has been improved by successive cycles of shape memory tests. After a fourth cycle, the blend is able to regain 82% of its shape. These original results indicated that a polymer without (or with partial) shape memory effect may be transformed to a shape memory polymer without any chemical modification.

Tcharkhtchi, A.; Elhirisia, S. Abdallah; Ebrahimi, K. M.; Fitoussi, J.; Shirinbayan, M.; Farzaneh, S.

2014-05-01

26

Thermomechanical Characterization of Shape Memory Polymers  

Microsoft Academic Search

Data from comprehensive thermomechanical tests of shape memory polymers are reported, with specimens tested up to 75% strain and between 30—120°C temperatures. The data is analyzed and key observations are drawn. The stress\\/strain behavior during loading at temperatures above glass transition for the Veriflex TM shape memory polymer tested was linear and did not show much variation with the actual

Bilim Atli; Farhan Gandhi; Greg Karst

2009-01-01

27

Nanoindentation of shape memory polymer networks  

Microsoft Academic Search

This work examines the small-scale deformation and thermally induced recovery behavior of shape memory polymer networks as a function of crosslinking structure. Copolymer shape memory materials based on diethylene glycol dimethacrylate and polyethylene glycol dimethacrylate with a molecular weight of 550 crosslinkers and a tert-butyl acrylate linear chain monomer were synthesized with varying weight percentages of crosslinker from 0 to

Edem Wornyo; Ken Gall; Fuzheng Yang; William King

2007-01-01

28

Light-induced shape-memory polymers  

Microsoft Academic Search

Materials are said to show a shape-memory effect if they can be deformed and fixed into a temporary shape, and recover their original, permanent shape only on exposure to an external stimulus. Shape-memory polymers have received increasing attention because of their scientific and technological significance. In principle, a thermally induced shape-memory effect can be activated by an increase in temperature

Andreas Lendlein; Hongyan Jiang; Oliver Jünger; Robert Langer

2005-01-01

29

Medical applications of shape memory polymers  

NASA Technical Reports Server (NTRS)

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

Sokolowski, Witold M.

2005-01-01

30

Bending behavior of shape memory polymer based laminates  

Microsoft Academic Search

Shape memory polymers (SMP) are smart materials was characterized by the recoverability of shape memory effect, but its mechanical property such as the strength is low. In this study, for industrial applications, a carbon fiber fabric reinforced shape memory polymer was developed. Four kinds of specimens with different laminations of carbon fiber fabric and shape memory polymer sheet were prepared.

Chun-Sheng Zhang; Qing-Qing Ni

2007-01-01

31

Shape-Memory Polymers and Shape-Changing Polymers  

Microsoft Academic Search

\\u000a The ability of polymers to respond to external stimuli is of high scientific and technological significance. In the last few\\u000a years, research activities have been intensified substantially, exploring whether stimuli-sensitive polymers can be designed\\u000a that move actively. In this review actively-moving materials were classified according to the underlying mechanisms enabling\\u000a the shape changes: shape-memory polymers and shape-changing polymers\\/shape-changing gels were

Marc Behl; Jörg Zotzmann; Andreas Lendlein

2010-01-01

32

How polymers lose memory with age.  

PubMed

Uniquely in the world of materials, polymers deformed at high temperature and subsequently quenched at low temperature, memorize the temperature at which they have been processed. Polymers can even memorize multiple temperatures. This temperature memory is reflected by a maximum of residual stress restored at the temperature of initial processing. It has been speculated that this capability could arise from the presence of dynamical heterogeneities in glassy domains of polymers. Processing the material at a given temperature would result in the selection of certain heterogeneities that participate in the storage of mechanical stress. Because dynamical heterogeneities are associated with particular relaxation times, the temperature memory of polymers should depend on the time, for example, the glass transition temperature depends on the frequency. The first experimental study of temporal effects on the temperature memory of polymers is presently reported. It is found that aging at high temperature shifts the maximum of residual stress towards greater temperatures. The corresponding loss of memory is explained by the relaxation of dynamical heterogeneities with short characteristic times. The present results clarify the origin of the temperature memory and provide insights into their efficient exploitation in applications. PMID:25294363

Grillard, Fabienne; Zakri, Cécile; Gaillard, Patrice; Korzhenko, Alexander; Néri, Wilfrid; Poulin, Philippe

2014-11-28

33

Carbon Fiber Reinforced Shape Memory Polymer Composites  

Microsoft Academic Search

In this paper we present results on the deformation of carbon fiber reinforced shape memory polymer matrix composites for deployable space structure applications. The composites were processed using resin transfer molding or a pre-impregnated (pre-preg) laminate press, with both satin and plain weave fiber architectures. The polymer matrix glass transition temperature, Tg, was approximately 95°C. Composite specimens were bent to

Ken Gall; Martin Mikulas; Naseem A. Munshi; Fred Beavers; Michael Tupper

2000-01-01

34

Shape Memory Polymer Patrick T. Mather,1,2  

E-print Network

Shape Memory Polymer Research Patrick T. Mather,1,2 Xiaofan Luo,1,2 and Ingrid A. Rousseau3 1 witnessed significant advances in the field of shape memory polymers (SMPs) with the elucidation of new, and the initiation of phenomenological modeling. We critically review research findings on new shape memory polymers

Mather, Patrick T.

35

Review of progress in shape-memory polymers  

Microsoft Academic Search

Shape-memory polymers (SMPs) have attracted significant attention from both industrial and academic researchers due to their useful and fascinating functionality. This review thoroughly examines progress in shape-memory polymers, including the very recent past, achieved by numerous groups around the world and our own research group. Considering all of the shape- memory polymers reviewed, we identify a classification scheme wherein nearly

C. Liu; H. Qin; P. T. Mather

2007-01-01

36

[Shape-memory polymers for biomedical engineering applications].  

PubMed

The latest progress in shape-memory polymer for biomedical engineering applications was summarized in this paper. The mechanism responsible for shape memory effect was analyzed in reference to the polymer structure. Also introduced and reviewed were the characteristics of some shape-memory polymers (polyurethane polycaprolactone and polylactide) and their applications in medical engineering. PMID:16294760

Zhu, Guangming; Liu, Zhongrang

2005-10-01

37

Electrically controllable deformation memory effects in ionic polymers  

Microsoft Academic Search

This paper reports a novel electric deformation memory effect in connection with ionic polymer conductor composites (IPCC) and, in particular, ionic polymer composites (IPMC). This deformation memory effect is neither thermal, as observed in shape memory alloys, nor magnetic, as observed in magnetic shape memory alloys. It is shown that an IPCC is capable of storing geometric shape and deformation

Mohsen Shahinpoor; Kwang J. Kim

2002-01-01

38

Temperature and electrical memory of polymer fibers  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

39

Temperature and electrical memory of polymer fibers  

SciTech Connect

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

Yuan, Jinkai; Zakri, Cécile; Grillard, Fabienne; Neri, Wilfrid; Poulin, Philippe [Centre de Recherche Paul Pascal - CNRS, University of Bordeaux, Avenue Schweitzer, 33600 Pessac (France)

2014-05-15

40

Laser-activated shape memory polymer intravascular thrombectomy device.  

PubMed

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

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

2005-10-01

41

Macroscopic behaviour of magnetic shape-memory polycrystals and polymer  

E-print Network

polycrystals and composites of single-crystal magnetic shape-memory particles embedded in a soft polymer matrixMacroscopic behaviour of magnetic shape-memory polycrystals and polymer composites May 16, 2006 S dimensions. Keywords: Magnetic shape-memory, composites, polycrystals, homogenization 1 Introduction

Rumpf, Martin

42

Thermoviscoelastic shape memory behavior for epoxy-shape memory polymer  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

43

Electrically conducting shape memory polymer composites for electroactive actuator  

NASA Astrophysics Data System (ADS)

We have tried to apply electroactive shape memory polymer to smart actuator. Electroactive shape memory can be achieved by applying an electric field to shape memory polymer without any thermal heating as conventional shape memory polymers. For it, electrically conducting shape memory composites were prepared by incorporating carbon nanotube into polymer matrix. A segmented polyurethane block copolymer composed of 4,4'-methylene bis (phenylisocyanate), polycaprolactone, and 1,4-butanediol was synthesized to be used as shape memory polymer, and carbon nanotube was used after surface-modification by an acid. It was found that nanotube-reinforced composites could show high electrical conductivity with increased modulus at only several weight percentages of nanotube, and electroactive shape recovery effect more than 80% could be obtained. Consequently, electric field-stimulated shape memory could be demonstrated through combined composites of polyurethane and nanotube.

Jung, Yong Chae; Goo, Nam Seo; Cho, Jae Whan

2004-07-01

44

Thermomechanical indentation of shape memory polymers.  

SciTech Connect

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

Long, Kevin N. (University of Colorado, Boulder, CO); Nguyen, Thao D.; Castro, Francisco (University of Colorado, Boulder, CO); Qi, H. Jerry (University of Colorado, Boulder, CO); Dunn, Martin L. (University of Colorado, Boulder, CO); Shandas, Robin (University of Colorado, Boulder, CO)

2007-04-01

45

Bioreducible polymers for therapeutic gene delivery.  

PubMed

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

Lee, Young Sook; Kim, Sung Wan

2014-09-28

46

Methods of Making and Using Shape Memory Polymer Composite Patches  

NASA Technical Reports Server (NTRS)

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

Hood, Patrick J.

2011-01-01

47

A constitutive theory for shape memory polymers. Part I  

Microsoft Academic Search

A constitutive theory is developed for shape memory polymers. It is to describe the thermomechanical properties of such materials under large deformations. The theory is based on the idea, which is developed in the work of Liu et al. [2006. Thermomechanics of shape memory polymers: uniaxial experiments and constitutive modeling. Int. J. Plasticity 22, 279–313], that the coexisting active and

Yi-Chao Chen; Dimitris C. Lagoudas

2008-01-01

48

Thermomechanical behavior of epoxy shape memory polymer foams  

Microsoft Academic Search

Shape memory polymer foams have significant potential in biomedical and aerospace applications, but their thermo-mechanical behavior under relevant deformation conditions is not well understood. In this paper we examine the thermo-mechanical behavior of epoxy shape memory polymer foams with an average relative density of nearly 20%. These foams are deformed under conditions of varying stress, strain, and temperature. The glass

M. A. Di Prima; M. Lesniewski; K. Gall; D. L. McDowell; T. Sanderson; D. Campbell

2007-01-01

49

A constitutive theory for shape memory polymers. Part II  

Microsoft Academic Search

A constitutive theory is developed for shape memory polymers. It is to describe the thermomechanical properties of such materials under large deformations. The theory is based on the idea, which is developed in the work of Liu et al. [2006. Thermomechanics of shape memory polymers: uniaxial experiments and constitutive modelling. Int. J. Plasticity 22, 279–313], that the coexisting active and

Yi-Chao Chen; Dimitris C. Lagoudas

2008-01-01

50

Memristive learning and memory functions in polyvinyl alcohol polymer memristors  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

51

Advances in shape-memory polymer actuation  

NASA Astrophysics Data System (ADS)

Shape memory polymer (SMP) is a promising smart material, which is able to perform a large deformation upon applying an external stimulus, such as heat, light and moisture, etc. In recent years, many investigations have been advanced in thermo-responsive SMP actuation, and several novel actuations have been applied in SMP. In this paper, the mechanism and demonstration of three types of SMP actuations (infrared laser, physical swelling effect and electricity) are presented. These novel actuation approaches may help SMP to fully reach its potential application. Firstly, for the infrared laser-activated SMP, it is concerned about the drive of SMP by infrared light. The infrared laser, transmitted through the optical fiber embedded in the SMP matrix, was chosen to drive the SMP. The working frequency of infrared laser was installed in 3-4?m. Moreover, this paper presents a study on the effects of solution on the glass transition temperature (Tg). It shows that the hydrogen bonding of SMP was aroused by the absorbed solution that significantly reduces transition temperature of polymer. In this way, the shape memory effect (SME) can undergo solution-driven shape recovery. Finally, the actuation of two types of electro-active SMP composites filled with electrically conductive powders (carbon black, nickel powers) have been carried out, and the SMP composite can be driven by applying a relatively low voltage.

Leng, Jinsong; Liu, Yanju; Lan, Xin

2009-03-01

52

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. PMID:22865555

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

2013-01-01

53

High-Temperature Shape Memory Polymers  

NASA Technical Reports Server (NTRS)

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

Yoonessi, Mitra; Weiss, Robert A.

2012-01-01

54

Aging effects of epoxy shape memory polymers  

NASA Astrophysics Data System (ADS)

In this paper, experimental results are reported to study the influence of high-temperature aging on the thermo-mechanical behavior of a commercially-available, thermo-responsive shape memory polymer (SMP), Veri ex-E™ (glass transition temperature, Tg = 90-105 °C). To achieve a shape memory effect in high Tg SMPs such as this, high temperature cycles are required that can result in macromolecular scission and/or crosslinking, which we term thermo-mechanical aging (or chemo-rheological degradation). This process results in mechanical property changes and possible permanent set of the material that can limit the useful life of SMPs in practice. We compare experimental results of shape memory recovery with and without aging. Similar to the approach originated by Tobolsky in the 1950's, a combination of uniaxial constant stress and intermittent stretch experiments are also used in high temperature creep-recovery experiments to deduce the kinetics of scission of the original macromolecular network and the generation of newly formed networks having different reference configurations. The macroscopic effects of thermo-mechanical aging, in terms of the evolution of residual strains and change in elastic response, are quantified.

Dasharathi, Kannan; Shaw, John A.

2013-04-01

55

Photopolymerized Thiol-Ene Systems as Shape Memory Polymers.  

PubMed

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. PMID:21072253

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

2010-09-01

56

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. PMID:21072253

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

2010-01-01

57

A novel type of shape memory polymer blend and the shape memory mechanism  

Microsoft Academic Search

A novel styrene–butadiene–styrene tri-block copolymer (SBS) and poly(?-caprolactone) (PCL) blend were introduced for its shape memory properties. Compared to the reported shape memory polymers (SMPs), this novel elastomer and switch polymer blend not only simplified the fabrication process but also offer a controllable approach for the study of mechanisms and the optimization of shape memory performances. Microstructures of this blend

Heng Zhang; Haitao Wang; Wei Zhong; Qiangguo Du

2009-01-01

58

Mechanical and shape memory behavior of composites with shape memory polymer  

Microsoft Academic Search

Shape memory polymers (SMPs) are playing a prominent role for biomedical, self-repairing and smart materials. Among various SMPs, shape memory polyurethanes (PUs) are receiving much attention for their easy control of glass transition temperature (Tg) around the room temperature and excellent shape memory effect even at the room temperature. In this paper, the glass fiber reinforced PUs were developed for

Takeru Ohki; Qing-Qing Ni; Norihito Ohsako; Masaharu Iwamoto

2004-01-01

59

Polyurethane Shape-Memory Polymers Demonstrate Functional Biocompatibility  

E-print Network

Polyurethane Shape-Memory Polymers Demonstrate Functional Biocompatibility In Vitro Maricel-vitro cytotoxicity of these resins to be comparable to commercial medical grade polyurethanes.[7,16] The Mitsubishi

Simon, Scott I.

60

A Shape Memory Polymer with Improved Shape Recovery  

Microsoft Academic Search

Thermally actuated shape memory polymers (SMPs) interest, both academically and industrially, due to their ability to memorize a permanent shape that is set during processing and a temporary shape that is later programmed by manipulation above a critical temperature, either Tg or Tm. However, the thermal triggering process for SMPs is usually retarded compared to that of shape memory alloys,

Changdeng Liu; Patrick T. Mather

2005-01-01

61

Thermomechanical characterization of shape memory polymers using high temperature nanoindentation  

Microsoft Academic Search

This paper investigates the thermomechanical behavior of a thermosetting shape memory polymer (SMP) by using a high temperature nanoindentation technique. The nanoindenter is equipped with a microheater and a sophisticated temperature control and monitoring system. This allows the SMP to be activated at elevated temperatures enabling proper implementation of the thermomechanical cycle typically used to quantify the shape memory behavior.

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

2010-01-01

62

Light-activated shape memory polymers and associated applications  

Microsoft Academic Search

Continuous product development and technology integration efforts using shape memory polymers (SMPs) have uncovered a need for faster response times. As with most smart materials, SMP responds to a specific stimulus. Traditionally SMP is triggered by thermal stimulus; increasing the temperature of the SMP above a Tg will transition the polymer from a glassy state to a rubbery state. The

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

2005-01-01

63

A review of shape memory polymer composites and blends  

Microsoft Academic Search

Shape memory polymers (SMPs) are a kind of very important smart polymers. In order to improve the properties or obtain new functions of SMPs, SMP composites and blends are prepared. We thoroughly examine the research in SMP composites and blends achieved by numerous research groups around the world. The preparation of SMPs composites and blends is mainly for five aims:

Qinghao Meng; Jinlian Hu

2009-01-01

64

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. PMID:21750496

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

2011-01-01

65

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

2011-01-01

66

Review of electro-active shape-memory polymer composite  

Microsoft Academic Search

Shape-memory polymers (SMPs) have been one of the most popular subjects under intensive investigation in recent years, due to their many novel properties and great potential. These so-called SMPs by far surpass shape-memory alloys and shape-memory ceramics in many properties, e.g., easy manufacture, programming, high shape recovery ratio and low cost, and so on. However, they have not fully reached

Yanju Liu; Haibao Lv; Xin Lan; Jinsong Leng; Shanyi Du

2009-01-01

67

Shape memory polymers based on uniform aliphatic urethane networks  

Microsoft Academic Search

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,Nâ²,Nâ²-tetrakis(hydroxypropyl)ethylenediamine (HPED), triethanolamine (TEA), and 1,3-butanediol (BD). The new polymers were characterized by solvent extraction,

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

2007-01-01

68

Experimental Evaluation of the Rheological Properties of Veriflex Shape Memory Polymer  

E-print Network

Experimental Evaluation of the Rheological Properties of Veriflex® Shape Memory Polymer J. Klesa1 Abstract. Shape memory polymers (SMPs) are materials with a great potential for future use in smart to the field of shape memory polymers: [1, 2, 4]. The shape memory mechanisms has been partly described

Paris-Sud XI, Université de

69

Shape-memory polymers as stimuli-sensitive implant materials.  

PubMed

Shape-memory polymers are stimuli-responsive materials. Upon exposure to an external stimulus, e.g. an increase in temperature, they have the capability of changing their shape. The shape-memory effect results from the polymer's structure and morphology in combination with a certain processing and programming technology. Stimuli-sensitive implant materials have a high potential for applications in minimally invasive surgery. A group of biodegradable implant materials with shape-memory has been developed for applications in biomedicine. These implant materials are not a single polymer but polymer systems that allow the variation of different macroscopic properties over a wide range by only small changes in the chemical structure. In this way, it is possible to implement a variety of different applications with tailor-made polymers of the same family. Two different types of degradable shape-memory polymer systems, covalently cross-linked polymer networks and thermoplastic elastomers, are presented and examples are given for each case. PMID:15764819

Lendlein, A; Kelch, S

2005-01-01

70

Resistive switching memory based on bioinspired natural solid polymer electrolytes.  

PubMed

A solution-processed, chitosan-based resistive-switching memory device is demonstrated with Pt/Ag-doped chitosan/Ag structure. The memory device shows reproducible and reliable bipolar resistive switching characteristics. A memory device based on natural organic material is a promising device toward the next generation of nonvolatile nanoelectronics. The memory device based on chitosan as a natural solid polymer electrolyte can be switched reproducibly between high and low resistance states. In addition, the data retention measurement confirmed the reliability of the chitosan-based nonvolatile memory device. The transparent Ag-embedded chitosan film showed an acceptable and comparable resistive switching behavior on the flexible plastic substrate as well. A cost-effective, environmentally benign memory device using chitosan satisfies the functional requirements of nonvolatile memory operations. PMID:25513838

Raeis Hosseini, Niloufar; Lee, Jang-Sik

2015-01-27

71

AC Electric Field Activated Shape Memory Polymer Composite  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

72

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

2009-09-15

73

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

74

Shape memory effect and mechanical properties of carbon nanotube\\/shape memory polymer nanocomposites  

Microsoft Academic Search

Carbon nanotubes (CNT) have remarkable mechanical properties with very high elastic modulus and electrical conductivity. Shape memory polymer (SMP) as one of smart materials is characterized with its remarkable recoverability and shape memory effect, but its mechanical properties such as strength and elastic modulus is not high enough. In this study, CNT\\/SMP nanocomposites were developed with the typical CNTs of

Qing-Qing Ni; Chun-sheng Zhang; Yaqin Fu; Guangze Dai; Teruo Kimura

2007-01-01

75

Recent advances in shape memory polymers and composites: a review  

Microsoft Academic Search

Shape memory polymers (SMPs) belong to a class of smart polymers, which have drawn considerable research interest in last\\u000a few years because of their applications in microelectromechanical systems, actuators, for self healing and health monitoring\\u000a purposes, and in biomedical devices. Like in other fields of applications, SMP materials have been proved to be suitable substitutes\\u000a to metallic ones because of

Debdatta Ratna; J. Karger-Kocsis

2008-01-01

76

Unique Aspects of a Shape Memory Polymer As the Substrate for Surface Wrinkling  

E-print Network

Unique Aspects of a Shape Memory Polymer As the Substrate for Surface Wrinkling Junjun Li, Yonghao wrinkle systems employ soft elastomers as the substrates. In contrast, shape memory polymers have recently emerged as attractive alternatives. Besides the shape fixing capability, shape memory polymers distinguish

Huang, Rui

77

Facile tailoring of thermal transition temperatures of epoxy shape memory polymers  

Microsoft Academic Search

A critical parameter for a shape memory polymer (SMP) lies in its shape memory transition temperature. For an amorphous SMP polymer, it is highly desirable to develop methods to tailor its Tg, which corresponds to its shape memory transition temperature. Starting with an amine cured aromatic epoxy system, epoxy polymers were synthesized by either reducing the crosslink density or introducing

Tao Xie; Ingrid A. Rousseau

2009-01-01

78

Model Development for Shape Memory Polymers Ryan D. Siskinda and Ralph C. Smithb  

E-print Network

Model Development for Shape Memory Polymers Ryan D. Siskinda and Ralph C. Smithb Department relationship in shape memory polymers (SMPs) has drawn considerable atten- tion in many fields ranging from and are susceptible to plastic, although recoverable, deformations. Keywords: shape memory polymers, smart materials 1

79

A Shape Memory Polymer with Improved Shape Recovery* Changdeng Liu1  

E-print Network

A Shape Memory Polymer with Improved Shape Recovery* Changdeng Liu1 and Patrick T. Mather2 1 ABSTRACT Thermally actuated shape memory polymers (SMPs) interest, both academically and industrially, due in the area of shape memory polymers (SMPs) have been a fast growing topic both academically and industrially

Mather, Patrick T.

80

DESIGN OF A VARIABLE STIFFNESS LEG USING SHAPE MEMORY POLYMER COMPOSITES  

E-print Network

571 DESIGN OF A VARIABLE STIFFNESS LEG USING SHAPE MEMORY POLYMER COMPOSITES DUNCAN W. HALDANE drop in modulus as they approach their glass transition temperature. By fabricating a composite using a SMP as the resin matrix, a shape memory polymer composite is formed. A shape memory polymer composite

Collins, Emmanuel

81

Mechanical properties of shape memory polymers for morphing aircraft applications  

Microsoft Academic Search

This investigation addresses basic characterization of a shape memory polymer (SMP) as a suitable structural material for morphing aircraft applications. Tests were performed for monotonic loading in high shear at constant temperature, well below, or just above the glass transition temperature. The SMP properties were time-and temperature-dependent. Recovery by the SMP to its original shape needed to be unfettered. Based

Michelle M. Keihl; Robert S. Bortolin; Brian Sanders; Shiv Joshi; Zeb Tidwell

2005-01-01

82

Thermomechanical Behavior of a Polyurethane Shape Memory Polymer Foam  

Microsoft Academic Search

Shape memory polymers (SMPs) have attracted great interest in recent years. The SMP foams are outstanding, owing to their high shape recovery ratio in compression. They can be used for, for instance, micro foldable vehicles, shape determination, and microtags. This article presents a study on the thermomechanical behavior of a polyurethane SMP foam, associated with these three applications. This includes

W. M. Huang; C. W. Lee; H. P. Teo

2006-01-01

83

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

84

Strain induced anisotropic properties of shape memory polymer  

Microsoft Academic Search

Heat activated shape memory polymers (SMPs) are increasingly being utilized in ambitious, large deformation designs. These designs may display unexpected or even undesirable performance if the evolution of the SMP's mechanical properties as a function of deformation is neglected. Yet, despite the broadening use of SMPs in complex load bearing structures, there has been little research completed to characterize how

Richard Beblo; Lisa Mauck Weiland

2008-01-01

85

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

86

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

87

Thermomechanical Constitutive Modeling in Shape Memory Polymer of Polyurethane Series  

Microsoft Academic Search

In order to describe the thermomechanical properties in shape memory polymer of polyurethane series, a thermomechanical constitutive model was developed by modifying a standard linear viscoelastic model. The model involved a slip element due to internal friction and took account of thermal expansion. In order to describe the variation in mechanical properties due to the glass transition, coefficients in the

H. Tobushi; T. Hashimoto; S. Hayashi; E. Yamada

1997-01-01

88

Toward a self-deploying shape memory polymer neuronal electrode.  

PubMed

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

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

2006-12-01

89

Macroscopic Behaviour of Magnetic Shape-Memory Polycrystals and Polymer Composites Sergio Conti1  

E-print Network

Macroscopic Behaviour of Magnetic Shape-Memory Polycrystals and Polymer Composites Sergio Conti1 in response to an applied magnetic field. For sin- gle crystals one can achieve strains of order of magnitude-proposed alternative for shape memory devices is to embed small single-crystal shape-memory particles in a soft polymer

Sminchisescu, Cristian

90

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

91

Experimental research on viscoelastic characteristics of shape memory polymers  

NASA Astrophysics Data System (ADS)

As a class of semi-crystallized polymers, shape memory polymers (SMPs) exhibit significant viscoelastic characteristics in the vicinity of the glass transition temperature Tg, which should affect their shape storage and recovery functionality. However, until now isothermal and elastic assumptions are commonly considered when studying the thermomechanical properties of this class of functionalized materials. This papers aims to present some experimental results about the viscoelastic characteristics of SMPs. Systematic thermomechanical experiments were performed on shape-memory polyurethane under uniaxial tensile loading, which includes the frozen/recovery tests under different constraint conditions, stress-strain cycles and stress relaxation at different temperatures. Based on the testing results, the viscoelastic characteristics effect on the shape frozen and recovery responses of SMPs are discussed, which is of importance in proposing suitable thermo-viscoelastic constitutions about this type of functional materials.

Li, Z. F.; Wang, Z. D.

2009-12-01

92

Experimental research on viscoelastic characteristics of shape memory polymers  

NASA Astrophysics Data System (ADS)

As a class of semi-crystallized polymers, shape memory polymers (SMPs) exhibit significant viscoelastic characteristics in the vicinity of the glass transition temperature Tg, which should affect their shape storage and recovery functionality. However, until now isothermal and elastic assumptions are commonly considered when studying the thermomechanical properties of this class of functionalized materials. This papers aims to present some experimental results about the viscoelastic characteristics of SMPs. Systematic thermomechanical experiments were performed on shape-memory polyurethane under uniaxial tensile loading, which includes the frozen/recovery tests under different constraint conditions, stress-strain cycles and stress relaxation at different temperatures. Based on the testing results, the viscoelastic characteristics effect on the shape frozen and recovery responses of SMPs are discussed, which is of importance in proposing suitable thermo-viscoelastic constitutions about this type of functional materials.

Li, Z. F.; Wang, Z. D.

2010-03-01

93

Thermomechanical Properties of Polyurethane-Shape Memory Polymer Foam  

Microsoft Academic Search

The thermomechanical properties of polyurethane-shape memory polymer foam were investigated by the compressive tests. The results are summarized as follows. (1) The material contracts uniformly in the axial direction with the ratio of lateral strain to axial strain 0.4 in the early stage, but about 0.15 thereafter. (2) The deformation resistance is large at low temperature and at high strain

H. Tobushi; K. Okumura; M. Endo; S. Hayashi

2001-01-01

94

Mechanical spectroscopy of magnetite filled polyurethane shape memory polymers  

Microsoft Academic Search

Magnetite-polyurethane (PU) shape memory polymer (SMP) composites containing 10–40vol.% magnetite have been prepared and their mechanical properties in a temperature range from 255K to 355K at vibrating frequencies of 0.1Hz, 1.0Hz and 10Hz were investigated. The damping peak at glass transition around 318K is decreased by the addition of magnetite while it becomes simultaneously broader. Also activation energies for the

Muhammad Yasar Razzaq; Mathias Anhalt; Lars Frormann; Bernd Weidenfeller

2007-01-01

95

REVIEW ARTICLE: Medical applications of shape memory polymers  

Microsoft Academic Search

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 (Tg) can be tailored for

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

2007-01-01

96

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

97

Thermomechanical recovery couplings of shape memory polymers in flexure  

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 recovery behavior of an SMP is examined in three-point flexure for various pre-deformation and recovery conditions. Results indicate that when pre-deformed well above the glass transition temperature, Tg, the stress-strain response at the pre-deformation

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

2003-01-01

98

Strong, Tailored, Biocompatible Shape-Memory Polymer Networks.  

PubMed

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

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

2008-08-22

99

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. PMID:19633727

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

2009-01-01

100

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

101

HPA axis alterations in mental disorders: impact on memory and its relevance for therapeutic interventions.  

PubMed

Dysfunctions in hypothalamic-pituitary-adrenal (HPA) axis have been reported for several mental disorders that are also often characterized by memory disturbances. It is now well established that glucocorticoids influence cognitive processes by enhancing memory consolidation and impairing memory retrieval. There is further evidence for an association between HPA axis related disturbances and memory function in mental disorders. The present selective review provides a brief overview of HPA axis dysfunction and its impact on memory function in major depressive disorder, posttraumatic stress disorder, and borderline personality disorder. Furthermore, the relevance of these findings for therapeutic intervention is discussed. PMID:21143429

Wingenfeld, Katja; Wolf, Oliver T

2011-12-01

102

The shape memory effect in crosslinked polymers: effects of polymer chemistry and network architecture  

NASA Astrophysics Data System (ADS)

The thermal shape memory effect in polymeric materials refers to the ability of a sample to retain a deformed shape when cooled below Tg, and then recover its initial shape when subsequently heated. Although these properties are thought to be related to temperature-dependent changes in network structure and polymer chain mobility, a consistent picture of the molecular mechanisms which determine shape memory behavior does not exist. This, along with large differences in the shape memory cycling response for different materials, has made model development and specific property optimization difficult. In this work we use coarse-grained molecular dynamics (MD) simulations of the thermal shape memory effect to inform micro-macro relationships and systematically identify the salient features leading to desirable shape behavior. We consider a simulation test set including chains with increasing levels of the microscopic restrictions on chain motion (the freely-jointed, freely-rotating, and rotational isomeric state chain models), each simulated with both the NPT and NVT ensembles. It is found that the NPT ensemble with attractive interactions between monomers enabled is the most appropriate for simulating the temperature-dependent mechanical behavior of a polymer using coarse-grained MD. Of the different models, the freely-jointed chain system shows the most desirable shape memory characteristics; this behavior is attributed to the ability of the particles in this system to pack closely together in an energetically favorable configuration. A comparison with experimental data demonstrates that the coarse-grained simulations display all of the relevant trends in mechanical behavior during constant strain shape memory cycling. We conclude that atomistic detail is not needed to represent a shape memory polymer, and that multi-scale modeling techniques may build on the mechanisms embodied in the simple coarse-grained model.

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

2013-04-01

103

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

Microsoft Academic Search

In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, Tswitch. If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane

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

2006-01-01

104

Pitch-tunable size reduction patterning with a temperature-memory polymer.  

PubMed

A scalable and pitch-tunable size reduction patterning method is introduced by exploiting the temperature memory effect of shape memory polymer and replica molding of UV-curable materials. PMID:22997007

Bae, Won-Gyu; Choi, Jae Hoon; Suh, Kahp Y

2013-01-28

105

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

106

Reduced time as a unified parameter determining fixity and free recovery of shape memory polymers  

NASA Astrophysics Data System (ADS)

Shape memory polymers are at the forefront of recent materials research. Although the basic concept has been known for decades, recent advances in the research of shape memory polymers demand a unified approach to predict the shape memory performance under different thermo-temporal conditions. Here we report such an approach to predict the shape fixity and free recovery of thermo-rheologically simple shape memory polymers. The results show that the influence of programming conditions to free recovery can be unified by a reduced programming time that uniquely determines shape fixity, which consequently uniquely determines the shape recovery with a reduced recovery time. Furthermore, using the time-temperature superposition principle, shape recoveries under different thermo-temporal conditions can be extracted from the shape recovery under the reduced recovery time. Finally, a shape memory performance map is constructed based on a few simple standard polymer rheology tests to characterize the shape memory performance of the polymer.

Yu, Kai; Ge, Qi; Qi, H. Jerry

2014-01-01

107

Shape memory polymer filled honeycomb model and experimental validation  

NASA Astrophysics Data System (ADS)

An analytical model predicting the in-plane Young’s and shear moduli of a shape memory polymer filled honeycomb composite is presented. By modeling the composite as a series of rigidly attached beams, the mechanical advantage of the load distributed on each beam by the infill is accounted for. The model is compared to currently available analytical models as well as experimental data. The model correlates extremely well with experimental data for empty honeycomb and when the polymer is above its glass transition temperature. Below the glass transition temperature, rule of mixtures is shown to be more accurate as bending is no longer the dominant mode of deformation. The model is also derived for directions other than the typical x and y allowing interpolation of the stiffness of the composite in any direction.

Beblo, R. V.; Puttmann, J. P.; Joo, J. J.; Reich, G. W.

2015-02-01

108

Dynamic cell behavior on shape memory polymer substrates.  

PubMed

Cell culture substrates of defined topography have emerged as powerful tools with which to investigate cell mechanobiology, but current technologies only allow passive control of substrate properties. Here we present a thermo-responsive cell culture system that uses shape memory polymer (SMP) substrates that are programmed to change surface topography during cell culture. Our hypothesis was that a shape-memory-activated change in substrate topography could be used to control cell behavior. To test this hypothesis, we embossed an initially flat SMP substrate to produce a temporary topography of parallel micron-scale grooves. After plating cells on the substrate, we triggered shape memory activation using a change in temperature tailored to be compatible with mammalian cell culture, thereby causing topographic transformation back to the original flat surface. We found that the programmed erasure of substrate topography caused a decrease in cell alignment as evidenced by an increase in angular dispersion with corresponding remodeling of the actin cytoskeleton. Cell viability remained greater than 95% before and after topography change and temperature increase. These results demonstrate control of cell behavior through shape-memory-activated topographic changes and introduce the use of active cell culture SMP substrates for investigation of mechanotransduction, cell biomechanical function, and cell soft-matter physics. PMID:21224032

Davis, Kevin A; Burke, Kelly A; Mather, Patrick T; Henderson, James H

2011-03-01

109

Microstructured shape memory polymer surfaces with reversible dry adhesion.  

PubMed

We present a shape memory polymer (SMP) surface with repeatable, very strong (>18 atm), and extremely reversible (strong to weak adhesion ratio of >1 × 10(4)) dry adhesion to a glass substrate. This was achieved by exploiting bulk material properties of SMP and surface microstructuring. Its exceptional dry adhesive performance is attributed to the SMP's rigidity change in response to temperature and its capabilities of temporary shape locking and permanent shape recovery, which when combined with a microtip surface design enables time-independent control of contact area. PMID:23945078

Eisenhaure, Jeffrey D; Xie, Tao; Varghese, Stephen; Kim, Seok

2013-08-28

110

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

111

Investigation of mechanical behavior of epoxy shape memory polymers  

NASA Astrophysics Data System (ADS)

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

Wu, Xuelian; Liu, Yanju; Leng, Jinsong

2009-03-01

112

Characterization of Nonlinear Rate Dependent Response of Shape Memory Polymers  

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

113

Shape recovery and irrecoverable strain control in polyurethane shape-memory polymer  

Microsoft Academic Search

In shape-memory polymers, large strain can be fixed at a low temperature and thereafter recovered at a high temperature. If the shape-memory polymer is held at a high temperature for a long time, the irrecoverable strain can attain a new intermediate shape between the shape under the maximum stress and the primary shape. Irrecoverable strain control can be applied to

Hisaaki Tobushi; Syunichi Hayashi; Kazumasa Hoshio; Yoshihiro Ejiri

2008-01-01

114

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

2010-09-11

115

Shape memory polymer hexachiral auxetic structures with tunable stiffness  

NASA Astrophysics Data System (ADS)

Planar auxetic structures have the potential to impact on a wide range of applications from deployable and morphing structures to space-filling composite and medical treatments. The ability to fabricate auxetics from smart materials greatly enhances this facility by building in controllable actuation and deployment. A smart auxetic device can be compressed and fixed into a storage state. When deployment is required the device can be appropriately stimulated and the stored elastic energy is released, resulting in a marked structural expansion. Instead of using a conventional external actuator to drive deployment the material is made to undergo phase transition where one stimulus (e.g. heat) initiates a mechanical response. Here we show how smart material auxetics can be realized using a thermally responsive shape memory polymer composites. We show how a shape memory polymer auxetic hexachiral structure can be tailored to provide a tunable stiffness response in its fully deployed state by varying the angle of inter-hub connections, and yet is still able to undergo thermally stimulated deployment.

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

2014-04-01

116

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

117

Post-Polymerization Crosslinked Polyurethane Shape-Memory Polymers  

PubMed Central

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

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

2011-01-01

118

IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 53, NO. 10, OCTOBER 2006 2075 Inductively Heated Shape Memory Polymer for the  

E-print Network

Shape Memory Polymer for the Magnetic Actuation of Medical Devices Patrick R. Buckley*, Gareth H. Mc stents and intravascular microactuators from shape memory polymer (SMP). One of the key challenges in re, inductive heating magnetic particle, medical device, shape memory polymer (SMP). I. INTRODUCTION SHAPE

119

Unconstrained recovery characterization of shape-memory polymer networks for cardiovascular applications  

Microsoft Academic Search

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

Christopher Michael Yakacki; Robin Shandas; Craig Lanning; Bryan Rech; Alex Eckstein; Ken Gall

2007-01-01

120

Shape memory polymers from benzoxazine-modified epoxy  

NASA Astrophysics Data System (ADS)

Novel shape memory polymers (SMPs) were prepared from benzoxazine-modified epoxy resin. Specimens consisting of aromatic epoxy (E), aliphatic epoxy (N), Jeffamine D230 (D) and BA-a benzoxazine monomer (B) were evaluated. The mole ratio of D/B was used as a mixed curing agent for an epoxy system with a fixed E/N. The effects of BA-a content on the thermal, mechanical and shape memory properties of epoxy-based shape memory polymers (SMPs) were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), flexural test and shape recovery test. The results revealed that the obtained SMPs exhibited a higher flexural strength and flexural modulus than those of the unmodified epoxy-based SMP at room temperature and at 20?° C above glass transition temperature (Tg). The presence of 1 mol BA-a as a curing agent provided the specimen with the highest Tg, i.e. about 72?° C higher than that of epoxy-based SMP cured by Jeffamine D230. All SMP samples needed only a few minutes to fully recover to their original shape. The samples exhibited high shape fixity (98-99%) and shape recovery ratio (90-100%). In addition, the recovery stress values increased with increasing BA-a mole ratio from 20 to 38 kPa, when BA-a up to 1 mol ratio was added. All of the SMP samples exhibited only minimum change in their flexural strength at the end of a 100 recovery cycles test.

Rimdusit, Sarawut; Lohwerathama, Montha; Hemvichian, Kasinee; Kasemsiri, Pornnapa; Dueramae, Isala

2013-07-01

121

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

122

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

123

Nanoscale indent formation in shape memory polymers using a heated probe tip  

Microsoft Academic Search

This paper presents experimental investigation of nanoscale indentation formation in shape memory polymers. The polymers were synthesized by photopolymerizing a tert-butyl acrylate (tBA) monomer with a poly(ethylene glycol dimethacrylate) (PEGDMA) crosslinker. The concentration and the molecular weight of the crosslinker were varied to produce five polymers with tailored properties. Nanoscale indentations were formed on the polymer surfaces by using a

F. Yang; E. Wornyo; K. Gall; W. P. King

2007-01-01

124

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

125

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

E-print Network

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 ...

Buckley, Patrick R.

2007-01-23

126

Actuation of shape memory polymer using magnetic fields for applications in medical devices  

E-print Network

A novel approach to the heating and actuation of shape memory polymer using dispersed Curie temperature thermo-regulated particles is proposed. Such a material has potential applications in medical devices which are delivered ...

Buckley, Patrick Regan, 1981-

2004-01-01

127

Thermally actuated shape-memory polymers: Experiments, theory, and numerical simulations  

Microsoft Academic Search

With the aim of developing a thermo-mechanically coupled large-deformation constitutive theory and a numerical-simulation capability for modeling the response of thermally actuated shape-memory polymers, we have (i) conducted large strain compression experiments on a representative shape-memory polymer to strains of approximately unity at strain rates of 10?3 and 10?1s?1, and at temperatures ranging from room temperature to approximately 30°C above

Vikas Srivastava; Shawn A. Chester; Lallit Anand

2010-01-01

128

Fiber reinforced shape-memory polymer composite and its application in a deployable hinge  

Microsoft Academic Search

This paper investigates the shape recovery behavior of thermoset styrene-based shape-memory polymer composite (SMPC) reinforced by carbon fiber fabrics, and demonstrates the feasibility of using an SMPC hinge as a deployable structure. The major advantages of shape-memory polymers (SMPs) are their extremely high recovery strain, low density and low cost. However, relatively low modulus and low strength are their intrinsic

Xin Lan; Yanju Liu; Haibao Lv; Xiaohua Wang; Jinsong Leng; Shanyi Du

2009-01-01

129

Vascular Dynamics of a Shape Memory Polymer Foam Aneurysm Treatment Technique  

Microsoft Academic Search

The vascular dynamics of a shape memory polymer foam aneurysm treatment technique are assessed through the simulated treatment\\u000a of a generic basilar aneurysm using coupled fluid dynamics and heat transfer calculations. The shape memory polymer foam,\\u000a which expands to fill the aneurysm when heated, is modeled at three discrete stages of the treatment procedure. To estimate\\u000a an upper bound for

Jason Ortega; Duncan Maitland; Tom Wilson; William Tsai; Ömer Sava?; David Saloner

2007-01-01

130

Thermal, electrical and magnetic studies of magnetite filled polyurethane shape memory polymers  

Microsoft Academic Search

Thermal, electrical and magnetic properties of polyurethane shape memory polymer (SMP) samples filled with 0–40vol% magnetite particles prepared by mixing and injection molding were investigated. Shape recovery in the shape memory polymer was initiated by a magnetizing field of H=4.4kA\\/m at a frequency f=50Hz. Electric resistivity was decreased by magnetite particles from ?el?1010?m to ?el?106?m. The percolation threshold is achieved

Muhammad Yasar Razzaq; Mathias Anhalt; Lars Frormann; Bernd Weidenfeller

2007-01-01

131

Critical Material Parameters for Modeling Devices Made from an Epoxy-Based Shape Memory Polymer  

E-print Network

: characterize an epoxy-based shape memory polymer using standard mechanical tests for elastomers and determine if these parameters are essential for designing SMP based devices. No prior study has characterized epoxy-based shape memory polymer made from Epon... in the rubbery region; therefore, the American Society for Testing and Materials (ASTM) test methods for elastomers provided insight into specimen design. Manufacturing process starts with designing specimen. First, Solidworks 2013 software was used to draw 3...

Erel, Veysel

2014-06-17

132

Optical memory using localized photoinduced anisotropy in a synthetic dye-polymer  

NASA Astrophysics Data System (ADS)

We present a read/write/erase all-optical memory that fully utilizes local photoinduced birefringence in a synthetic dye-polymer. Memory reading is based on an optical vector-matrix inner product. The intrinsic chromatic characteristics of the proposed memory storage medium is the key to a novel form of nonmechanical parallel memory storage. Green light at 514.5 nm writes a spatial pattern and read light at 632 nm reads it. The dynamic memory material is an improved polyvinyl-alcohol (PVA) polymer film doped with Azo dye. Unique to this material is low optical power, no significant memory degradation after the recording process, and local information erasure or rewrite at any time. The material operates at room temperature with no sealing requirements.

Kuo, Chai-Pei

1991-07-01

133

A thermoviscoelastic model for amorphous shape memory polymers: Incorporating structural and stress relaxation  

Microsoft Academic Search

A thermoviscoelastic constitutive model is developed for amorphous shape memory polymers (SMP) based on the hypothesis that structural and stress relaxation are the primary molecular mechanisms of the shape memory effect and its time-dependence. This work represents a new and fundamentally different approach to modeling amorphous SMPs. A principal feature of the constitutive model is the incorporation of the nonlinear

Thao. D. Nguyen; H. Jerry Qi; Francisco Castro; Kevin N. Long

2008-01-01

134

Durability Assessment of Styrene and Epoxy-based Shape-memory Polymer Resins  

Microsoft Academic Search

The present study is a baseline assessment of the durability of styrene- and epoxy-based shape memory polymer resin materials being considered for morphing applications when exposed to service environment. The approach for the experimental evaluation is a measurement of the shape memory properties and elastomeric response before and after separate environmental exposure to (i) water at 49°C for 4 days,

G. P. Tandon; K. Goecke; K. Cable; J. Baur

2009-01-01

135

Dynamic cell behavior on shape memory polymer substrates Kevin A. Davis a,b  

E-print Network

Dynamic cell behavior on shape memory polymer substrates Kevin A. Davis a,b , Kelly A. Burke b: Cell culture Shape memory Thermally responsive material Surface topography a b s t r a c t Cell culture substrates of defined topography have emerged as powerful tools with which to investigate cell mechanobiology

Mather, Patrick T.

136

Highly flexible silver nanowire electrodes for shape-memory polymer light-emitting diodes.  

PubMed

Shape-memory polymer light-emitting diodes (PLEDs) using a new silver nanowire/polymer electrode are reported. The electrode can be stretched by up to 16% with only a small increase in sheet resistance. Large deformation shape change and recovery of the PLEDs to various bistable curvatures result in minimal loss of electroluminescence performance. PMID:21274917

Yu, Zhibin; Zhang, Qingwu; Li, Lu; Chen, Qi; Niu, Xiaofan; Liu, Jun; Pei, Qibing

2011-02-01

137

Mechanical and Curing Properties of a Styrene-based Shape Memory Polymer  

Microsoft Academic Search

Presented is an experimental investigation into the characteristics of a particular styrene-based shape memory polymer, Veriflex®. Tensile, 3 point bend, and creep tests are conducted yielding the Young’s modulus, yield strength, flexural modulus, flexure strength, and creep modulus of the polymer both above and below the glass transition temperature. The results of the characterization may be used to populate a

Richard Beblo; Korey Gross; Lisa Mauck Weiland

2010-01-01

138

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

NASA Astrophysics Data System (ADS)

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

Panja, Debabrata

2010-06-01

139

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

2012-09-01

140

Micro devices using shape memory polymer patches for mated connections  

SciTech Connect

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

Lee, A.P.; Fitch, J.P.

2000-07-11

141

Component assembly with shape memory polymer fastener for microrobots  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

142

Virtual treatment of basilar aneurysms using shape memory polymer foam.  

PubMed

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

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

2013-04-01

143

Virtual Treatment of Basilar Aneurysms Using Shape Memory Polymer Foam  

PubMed Central

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

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

2013-01-01

144

Micro devices using shape memory polymer patches for mated connections  

DOEpatents

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

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

2000-01-01

145

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

146

Self-Deploying Trusses Containing Shape-Memory Polymers  

NASA Technical Reports Server (NTRS)

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

Schueler, Robert M.

2008-01-01

147

Therapeutic effect of mesenchymal multipotent stromal cells on memory in animals with Alzheimer-type neurodegeneration.  

PubMed

Transplantation of human mesenchymal multipotent stromal cells improved spatial memory in bulbectomized mice with Alzheimer-type neurodegeneration. The positive effect was observed in 1 month after intracerebral transplantation and in 3 months after systemic injection of mesenchymal multipotent stromal cells. No cases of malignant transformation were noted. These findings indicate prospects of using mesenchymal multipotent stromal cells for the therapy of Alzheimer disease and the possibility of their systemic administration for attaining the therapeutic effect. PMID:24319707

Bobkova, N V; Poltavtseva, R A; Samokhin, A N; Sukhikh, G T

2013-11-01

148

Bioactive factor delivery strategies from engineered polymer hydrogels for therapeutic medicine  

PubMed Central

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

Nguyen, Minh Khanh; Alsberg, Eben

2014-01-01

149

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

2012-04-01

150

A novel high mechanical strength shape memory polymer based on ethyl cellulose and polycaprolactone.  

PubMed

A novel biological friendly shape memory polymer (SMP) based on ethyl cellulose (EC) and polycaprolactone (PCL) was prepared. The network structure of the polymer was formed by linear EC backbones which were linked by grafted PCL chains, and the results showed outstanding mechanical strength and shape memory property of this polymer. The tensile modulus varied from 104.9 to 373.4 MPa while the tensile strength ranged from 155.4 to 323.6 MPa. And the elongations at break were all above 621%. The shape memory switching temperature could be modulated to 37.2°C by decreasing the chain length of graft PCL. As EC and PCL are both biodegradable and biocompatible materials, this new polymer has potential application in biomedical field, like biomedical suture, which would be further studied in the future. PMID:23768596

Bai, Yongkang; Jiang, Cheng; Wang, Qihua; Wang, Tingmei

2013-07-25

151

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

PubMed Central

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

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

2014-01-01

152

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

PubMed

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

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

2011-04-01

153

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

PubMed Central

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

2009-01-01

154

Constitutive model for a stress- and thermal-induced phase transition in a shape memory polymer  

NASA Astrophysics Data System (ADS)

Recently, increasing applications of shape memory polymers have pushed forward the development of appropriate constitutive models for smart materials such as the shape memory polymer. During the heating process, the phase transition, which is a continuous time-dependent process, happens in the shape memory polymer, and various individual phases will form at different configuration temperatures. In addition, these phases can generally be divided into two parts: the frozen and active phase (Liu Y et al 2006 Int. J. Plast. 22 279-313). During the heating or cooling process, the strain will be stored or released with the occurring phase transition between these two parts. Therefore, a shape memory effect emerges. In this paper, a new type of model was developed to characterize the variation of the volume fraction in a shape memory polymer during the phase transition. In addition to the temperature variation, the applied stress was also taken as a significant influence factor on the phase transition. Based on the experimental results, an exponential equation was proposed to describe the relationship between the stress and phase transition temperature. For the sake of describing the mechanical behaviors of the shape memory polymer, a three-dimensional constitutive model was established. Also, the storage strain, which was the key factor of the shape memory effect, was also discussed in detail. Similar to previous works, we first explored the effect of applied stress on storage strain. Through comparisons with the DMA and the creep experimental results, the rationality and accuracy of the new phase transition and constitutive model were finally verified.

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

2014-10-01

155

Tailored (meth)acrylate shape-memory polymer networks for ophthalmic applications.  

PubMed

The unique features of shape-memory polymers enables their use in minimally invasive surgical procedures with a compact starting material switching over to a voluminous structure in vivo. In this work, a series of transparent, thermoset (meth)acrylate shape-memory polymer networks with tailored thermomechanics have been synthesized and evaluated. Fundamental trends were established for the effect of the crosslinker content and crosslinker molecular weight on glass transition temperature, rubbery modulus and shape-recovery behavior, and the results are intended to help with future shape-memory device design. The prepared (meth)acrylate networks with high transparency and favorable biocompatibility are presented as a promising shape-memory ophthalmic biomaterial. PMID:20625994

Song, Li; Hu, Wang; Wang, Guojie; Niu, Guoguang; Zhang, Hongbin; Cao, Hui; Wang, Kaijie; Yang, Huai; Zhu, Siquan

2010-10-01

156

A shape memory polymer dialysis needle adapter for the reduction of hemodynamic stress within arteriovenous grafts.  

PubMed

A deployable, shape memory polymer adapter is investigated for reducing the hemodynamic stress caused by dialysis needle flow impingement 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. Preliminary in vitro flow visualization measurements are made within a graft model following delivery and actuation of a prototype shape memory polymer adapter. Both the simulations and the qualitative flow visualization measurements demonstrate that the adapter reduces the severity of the dialysis needle flow impingement on the vascular access graft. PMID:17867367

Ortega, Jason M; Small, Ward; Wilson, Thomas S; Benett, William J; Loge, Jeffrey M; Maitland, Duncan J

2007-09-01

157

Shape memory polymer stent with expandable foam: a new concept for endovascular embolization of fusiform aneurysms.  

PubMed

We demonstrate a new concept for endovascular embolization of nonnecked fusiform aneurysms. A device prototype consisting of a stent augmented with expandable foam, both made from shape memory polymer, was fabricated and deployed in an in vitro model. Visual observation indicated that the foam achieved embolization of the aneurysm while the stent maintained an open lumen in the parent artery. The shape memory polymer stent-foam device is a potential tool for treatment of nonnecked fusiform aneurysms, as well as an alternative to stent- and balloon-assisted coil embolization of wide-necked aneurysms. PMID:17549908

Small, Ward; Buckley, Patrick R; Wilson, Thomas S; Benett, William J; Hartman, Jonathan; Saloner, David; Maitland, Duncan J

2007-06-01

158

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

PubMed

In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, T(switch). If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(epsilon-caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25 degrees C resulted in temporary fixation of the mechanical deformation by 50-60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f = 258 kHz; H = 30 kA x m(-1)). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature. PMID:16537442

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

2006-03-01

159

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

PubMed Central

In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, Tswitch. If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(?-caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25°C resulted in temporary fixation of the mechanical deformation by 50–60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f = 258 kHz; H = 30 kA·m?1). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature. PMID:16537442

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

2006-01-01

160

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

161

Constitutive modeling of the mechanics associated with crystallizable shape memory polymers  

Microsoft Academic Search

.  Shape memory polymers are novel materials that can be easily formed into complex shapes, retaining memory of their original\\u000a shape even after undergoing large deformations. The temporary shape is stable and return to the original shape is triggered\\u000a by a suitable mechanism such as heating. In this paper, we develop constitutive equations to model the mechanical behavior\\u000a of crystallizable shape

G. Barot; I. J. Rao

2006-01-01

162

Magnetic memory effects in nickel ferrite/polymer nanocomposites  

NASA Astrophysics Data System (ADS)

Memory effects are reported in the field cooled (FC) magnetization of pure nickel ferrite powders and nickel ferrite nanocomposites prepared by the solution casting method. Studies carried out at different concentrations of the nanocomposite indicate that memory effects are suppressed with increasing concentration of the magnetic component in the nanocomposite. This is linked to the increase in the dipolar interaction strength in the nanocomposites, which increase with increasing concentration, as confirmed by the Henkel plots. Model simulations of the FC magnetization carried out on an interacting array of monodispersed magnetic nanoparticles indicate that growing cluster sizes inhibit memory effects.

Malik, Rakesh; Sehdev, Neeru; Lamba, Subhalakshmi; Sharma, Parmanand; Makino, Akihiro; Annapoorni, Subramanian

2014-03-01

163

The dynamics of polymers in solution with hydrodynamic memory  

E-print Network

The theory of the dynamics of polymers in solution is developed coming from the hydrodynamic theory of the Brownian motion (BM) and the Rouse-Zimm (RZ) model. It is shown that the time correlation functions describing the polymer motion essentially differ from those in the previous RZ models based on the Einstein theory of BM. The MSD of the polymer coil is at short times proportional to t^2 (instead of t). At long times it contains additional (to the Einstein term) contributions, the leading of which is ~ t^{1/2}. The relaxation of the internal normal modes of the polymer differs from the traditional exponential decay. This is displayed in the tails of their correlation functions, the longest-lived being ~ t^{-3/2} in the Rouse limit and t^{-5/2} in the Zimm case when the hydrodynamic interaction is strong. It is discussed that the found peculiarities, in particular a slower diffusion of the coil, should be observable in dynamic scattering experiments. The dynamic structure factor and the first cumulant of the polymer coil are calculated. The theory is extended to the situation when the dynamics of the studied polymer is influenced by the presence of other polymers in dilute solution.

V. Lisy; J. Tothova; B. Brutovsky; A. V Zatovsky

2005-09-15

164

Deformation of epoxy shape memory polymer foam: Part II. Mesoscale modeling and simulation  

Microsoft Academic Search

The present study focuses on how the relative density of an epoxy shape memory polymer foam affects mesostructural response to deformation. The modeled foam had relative densities of 20%, 30%, and 40%, with a glass transition temperature (Tg) near 85°C as measured by dynamic mechanical analysis. Statistical analysis of the dynamic mechanical analyisis data showed that stiffness did not significantly

M. A. Di Prima; K. Gall; D. L. McDowell; R. Guldberg; A. Lin; T. Sanderson; D. Campbell; S. C. Arzberger

2010-01-01

165

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. PMID:17296222

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

2009-01-01

166

A thermodynamic framework for the modeling of crystallizable shape memory polymers  

Microsoft Academic Search

Shape memory polymers are a relatively new class of materials that have the ability to retain a temporary shape, which can be reset to the original shape with the use of a suitable trigger, typically an increase in temperature. The temporary shapes can be very complex and the deformations involved large. These materials are finding use in a large variety

G. Barot; I. J. Rao; K. R. Rajagopal

2008-01-01

167

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

Microsoft Academic Search

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

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

2007-01-01

168

a Glass Transition Model for Shape Memory Polymer and its Composite  

Microsoft Academic Search

As novel smart materials, shape memory polymer (SMP) and its composite (SMPC) have the ability to regain its original shape after undergoing significant deformation upon heating or other external stimuli such as light, chemic condition and so on. Their special behaviors much depends on the glass transitions due to the increasing of material temperature. Dynamic Mechanical Analysis (DMA) tests are

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

2009-01-01

169

On the effects of moisture in a polyurethane shape memory polymer  

Microsoft Academic Search

It was observed that the polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days. A significant indication for this change is the continuous decrease of the glass transition temperature (Tg) of polyurethane. Accompanying the decrease of Tg, the uniaxial tensile behaviour also changes. Differential scanning calorimetry (DSC)

B. Yang; W. M. Huang; C. Li; C. M. Lee; L. Li

2004-01-01

170

Unconstrained recovery characterization of shape-memory polymer networks for cardiovascular applications.  

PubMed

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 (T(g)), 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 T(g) and crosslink density. The pressurized response of the stents is also demonstrated to depend on crosslink density. This polymer system exhibits a wide range of shape-memory and thermomechanical responses to adapt and meet specific needs of minimally invasive cardiovascular devices. PMID:17296222

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

2007-05-01

171

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

172

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

173

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

Microsoft Academic Search

In addition to the fabrication of shape-memory thermoset polymer nanocomposites filled with conductive nanoparticles and fiber fillers, this paper is focused on factors which would influence the electrical property of this type of material. It is shown that the particulate additives are dispersed homogeneously within the matrix and served as interconnections between the fibers, while the fibrous additives act as

Jinsong Leng; Haibao Lv; Yanju Liu; Shanyi Du

2007-01-01

174

Shape Memory Polymer Stent With Expandable Foam: A New Concept for Endovascular Embolization of Fusiform Aneurysms  

Microsoft Academic Search

We demonstrate a new concept for endovascular embolization of nonnecked fusiform aneurysms. A device prototype consisting of a stent augmented with expandable foam, both made from shape memory polymer, was fabricated and deployed in an in vitro model. Visual observation indicated that the foam achieved embolization of the aneurysm while the stent maintained an open lumen in the parent artery.

Ward Small; Patrick R. Buckley; Thomas S. Wilson; William J. Benett; Jonathan Hartman; David Saloner; Duncan J. Maitland

2007-01-01

175

Effects of moisture on the thermomechanical properties of a polyurethane shape memory polymer  

Microsoft Academic Search

The glass transition temperature of an ether-based polyurethane shape memory polymer (SMP) has been found to decrease significantly after immersion in water. In order to get a better understanding of the mechanism behind this phenomenon, a systematic study on the effects of moisture on the glass transition temperature and thermomechanical properties of this SMP was carried out. The results reveal

B. Yang; W. M. Huang; C. Li; L. Li

2006-01-01

176

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

Microsoft Academic Search

A deployable, shape memory polymer adapter is investigated for reducing the hemodynamic stress caused by dialysis needle flow impingement 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. Preliminary in vitro flow visualization measurements are made within a graft model

Jason M. Ortega; Ward Small; Thomas S. Wilson; William J. Benett; Jeffrey M. Loge; Duncan J. Maitland

2007-01-01

177

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

178

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

179

Biodegradable Silicon-Containing Elastomers for Tissue Engineering Scaffolds and Shape Memory Polymers  

E-print Network

for the tissue engineering of soft tissues as well as for shape memory polymer (SMP) devices. Tri-block macromers of the form PCLn-block-PDMSm-block-PCLn were developed to permit systematic variations to key features including: PDMS block length, PCL block length...

Schoener, Cody A.

2010-10-12

180

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

181

RFID Tag Antenna Based Temperature Sensing Using Shape Memory Polymer Actuation  

E-print Network

RFID Tag Antenna Based Temperature Sensing Using Shape Memory Polymer Actuation Rahul Bhattacharyya sensor using the UHF RFID tag antenna as a sensing mechanism. Permanent changes are induced in the tag of UHF RFID tags to serve as ultra-low cost temperature alarm sensors which are capable of detecting

Entekhabi, Dara

182

Shape Fixity and Shape Recovery in a Film of Shape Memory Polymer of Polyurethane Series  

Microsoft Academic Search

The shape fixity and recovery in a film of shape memory polymer of polyurethane series were investigated by the thermomechanical cycling tests with loading at various temperatures. The results are summarized as follows: (1) Strain is recovered at temperatures in the vicinity of the glass transition temperature Tg for loading above Tg, but it is recovered at temperatures in the

H. Tobushi; T. Hashimoto; N. Ito; S. Hayashi; E. Yamada

1998-01-01

183

A torsion test for the study of the large deformation recovery of shape memory polymers  

E-print Network

simply heat, that the recovery of the SMP's original, permanent shape is triggered. The shape recovery1 A torsion test for the study of the large deformation recovery of shape memory polymers Julie recovery, Large deformation, Torsion test, Thermoelasticity, Image analysis ABSTRACT: A torsion device

Paris-Sud XI, Université de

184

Model Development and Simulation of the Response of Shape Memory Polymers  

E-print Network

The aim of this work is to develop and validate a continuum model for the simulation of the thermomechanical response of a shape memory polymer (SMP). Rather than integral type viscoelastic model, the approach here is based on the idea of two inter...

Ghosh, Pritha 1983-

2012-08-15

185

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

186

High performance shape memory polymer networks based on rigid nanoparticle cores  

PubMed Central

Smart materials that can respond to external stimuli are of widespread interest in biomedical science. Thermal-responsive shape memory polymers, a class of intelligent materials that can be fixed at a temporary shape below their transition temperature (Ttrans) and thermally triggered to resume their original shapes on demand, hold great potential as minimally invasive self-fitting tissue scaffolds or implants. The intrinsic mechanism for shape memory behavior of polymers is the freezing and activation of the long-range motion of polymer chain segments below and above Ttrans, respectively. Both Ttrans and the extent of polymer chain participation in effective elastic deformation and recovery are determined by the network composition and structure, which are also defining factors for their mechanical properties, degradability, and bioactivities. Such complexity has made it extremely challenging to achieve the ideal combination of a Ttrans slightly above physiological temperature, rapid and complete recovery, and suitable mechanical and biological properties for clinical applications. Here we report a shape memory polymer network constructed from a polyhedral oligomeric silsesquioxane nanoparticle core functionalized with eight polyester arms. The cross-linked networks comprising this macromer possessed a gigapascal-storage modulus at body temperature and a Ttrans between 42 and 48?°C. The materials could stably hold their temporary shapes for > 1 year at room temperature and achieve full shape recovery ? 51 °C in a matter of seconds. Their versatile structures allowed for tunable biodegradability and biofunctionalizability. These materials have tremendous promise for tissue engineering applications. PMID:20375285

Song, Jie

2010-01-01

187

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

188

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

189

Thermomechanical formation and recovery of nanoindents in a shape memory polymer studied using a heated tip.  

PubMed

This paper investigates the thermomechanical formation and recovery of nanometer-scale indents in a shape memory polymer (SMP), studied using a heated atomic force microscope (AFM) tip and hot-stage atomic force microscopy. The material tested is a tert-butyl acrylate (tBA)-based polymer, which has a glass transition temperature of 60 degrees C. The AFM tip forms indents in the polymer in the temperature range 25-250 degrees C. The shape recovery of the indents is studied while the polymer is heated up to 100 degrees C. The temperature required for complete annealing of the indents depends upon the indentation formation conditions, with higher temperature formation corresponding to higher temperature recovery. PMID:17987641

Yang, Fuzheng; Wornyo, Edem; Gall, Ken; King, William P

2008-01-01

190

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

PubMed

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

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

2012-05-01

191

Unique aspects of a shape memory polymer as the substrate for surface wrinkling.  

PubMed

Typical bilayer wrinkle systems employ soft elastomers as the substrates. In contrast, shape memory polymers have recently emerged as attractive alternatives. Besides the shape fixing capability, shape memory polymers distinguish from elastomers in that they are rigid at room temperature, but experience significant modulus drop upon heating. We hereby report unique aspects of shape memory polymers as the wrinkle substrate utilizing a metallic thin film as the top layer. The feasibility to create both reversible and irreversible wrinkles (and diffraction colors) on a single substrate is demonstrated. Experimental conditions are identified to create crack free wrinkles and the impact of various experimental parameters on the wrinkle wavelength and amplitude is investigated. The results suggest that the wrinkle mechanics deviate notably from the existing theories established with elastomers as the wrinkle substrates. Thus, a new theory will need to be developed in the future, taking into account of unique thermomechanical properties of the shape memory substrate and possible plastic deformation of the thin film. PMID:22233880

Li, Junjun; An, Yonghao; Huang, Rui; Jiang, Hanqing; Xie, Tao

2012-02-01

192

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

PubMed Central

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

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

2012-01-01

193

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. PMID:11158558

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

2001-01-01

194

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

PubMed

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(epsilon-caprolactone) dimethacrylate as crosslinker and n-butyl acrylate as comonomer was introduced. The influence of two structural parameters, the molecular weight of oligo(epsilon-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. PMID:11158558

Lendlein, A; Schmidt, A M; Langer, R

2001-01-30

195

Non-volatile ferroelectric memory with position-addressable polymer semiconducting nanowire.  

PubMed

One-dimensional nanowires (NWs) have been extensively examined for numerous potential nano-electronic device applications such as transistors, sensors, memories, and photodetectors. The ferroelectric-gate field effect transistors (Fe-FETs) with semiconducting NWs in particular in combination with ferroelectric polymers as gate insulating layers have attracted great attention because of their potential in high density memory integration. However, most of the devices still suffer from low yield of devices mainly due to the ill-control of the location of NWs on a substrate. NWs randomly deposited on a substrate from solution-dispersed droplet made it extremely difficult to fabricate arrays of NW Fe-FETs. Moreover, rigid inorganic NWs were rarely applicable for flexible non-volatile memories. Here, we present the NW Fe-FETs with position-addressable polymer semiconducting NWs. Polymer NWs precisely controlled in both location and number between source and drain electrode were achieved by direct electrohydrodynamic NW printing. The polymer NW Fe-FETs with a ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) exhibited non-volatile ON/OFF current margin at zero gate voltage of approximately 10(2) with time-dependent data retention and read/write endurance of more than 10(4) seconds and 10(2) cycles, respectively. Furthermore, our device showed characteristic bistable current hysteresis curves when being deformed with various bending radii and multiple bending cycles over 1000 times. PMID:24644019

Hwang, Sun Kak; Min, Sung-Yong; Bae, Insung; Cho, Suk Man; Kim, Kang Lib; Lee, Tae-Woo; Park, Cheolmin

2014-05-28

196

Influence of Holding Time on Shape Recovery in a Polyurethane Shape-Memory Polymer  

NASA Astrophysics Data System (ADS)

Shape-memory polymers have attracted a lot of interest in recent years. A shape-memory polymer can be deformed and fixed into a temporary shape and subsequently made to recover its original shape when a suitable stimulus is applied. This is accomplished by means of a thermomechanical cycle called programming. Programming can be performed in a stress- or strain-controlled mode. The thermomechanical conditions of the programming affect shape-memory properties differently in each programming mode. One of the parameters which significantly affects shape-memory properties in a stress-controlled procedure is stress-holding time ( t H) at high temperature. This paper studies how stress-holding time affects the most significant shape-memory properties under successive thermomechanical cycles. The experiments were conducted using two different programming temperatures in the vicinity of the T g. The shape-recovery ratio decreased dramatically with cycling even when the holding time was just a few seconds, however, the impact of the stress-holding time depends on the temperature at which it has been applied. Shape-fixity ratio and switching temperature were also studied, but stress-holding time and successive cycles do not seem to affect either of these factors.

Santiago, David; Ferrando, Francesc; De la Flor, Silvia

2014-07-01

197

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

PubMed

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

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

2009-11-18

198

Electron Beam Crosslinked Polyurethane Shape Memory Polymers with Tunable Mechanical Properties  

PubMed Central

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

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

2014-01-01

199

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

PubMed Central

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

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

2014-01-01

200

Thermoreversibly crosslinked poly(?-caprolactone) as recyclable shape-memory polymer network.  

PubMed

A new concept to build shape memory polymers (SMP) combining outstanding fixity and recovery ratios (both above 99% after only one training cycle) typical of chemically crosslinked SMPs with reprocessability restricted to physically crosslinked SMPs is demonstrated by covalently bonding, through thermoreversible Diels-Alder (DA) adducts, star-shaped poly(?-caprolactones) (PCL) end-functionalized by furan and maleimide moieties. A PCL network is easily prepared by melt-blending complementary end-functional star polymers in retro DA regime, then by curing at lower temperature to favour the DA cycloaddition. Such covalent network can be reprocessed when heated again at the retro DA temperature. The resulting SMP shows still excellent shape memory properties attesting for its good recyclability. PMID:21692124

Defize, Thomas; Riva, Raphaël; Raquez, Jean-Marie; Dubois, Philippe; Jérôme, Christine; Alexandre, Michaël

2011-08-17

201

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

202

A biomimic shape memory polymer based self-healing particulate composite  

Microsoft Academic Search

In a previous study, a biomimic two-step self-healing scheme (close-then-heal (CTH)) by mimicking human skin has been proposed for self-healing structural-length scale damage [Li and Uppu. Composites Science and Technology 2010; 70: 1419–1427]. The purpose of this study is to validate this idea by fabricating a composite with thermoplastic particles (Copolyster) dispersed in a shape memory polymer matrix (Veriflex Polystyrene).

Jones Nji; Guoqiang Li

2010-01-01

203

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

Microsoft Academic Search

In this paper, a three-dimensional (3D) woven fabric reinforced shape memory polymer composite for impact mitigation was proposed, fabricated, programmed using a three-step strain-controlled thermomechanical cycle at a pre-strain level of 5% and machined to two groups of specimens (G1 and G2) with dimensions 152.4 mm × 101.6 mm × 12.7 mm. The specimens were impact tested, transversely, centrally and

Jones Nji; Guoqiang Li

2010-01-01

204

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

205

Characterization of shear deformation and strain recovery behavior in shape memory polymers  

Microsoft Academic Search

The large strain deformation behavior of a styrene-based shape memory polymer (SMP) has been investigated in tensile- and shear-loading conditions with the aim of characterizing the mechanical properties. Of particular interest is the recovery behavior, which is critical for the development of new SMP-based applications, and the effect of filler-loading. Magnetite and iron spherical nano-particles have been used as fillers.

Fazeel Khan; Jeong-Hoi Koo; David Monk; Eric Eisbrenner

2008-01-01

206

Cytotoxicity and thermomechanical behavior of biomedical shape-memory polymer networks post-sterilization  

Microsoft Academic Search

Shape-memory polymers (SMPs) are being increasingly proposed for use in biomedical devices. This paper investigates the cytotoxicity, surface characteristics and thermomechanics of two acrylate-based SMP networks as a function of sterilization using a minimal essential media elution test, FTIR-ATR and dynamic mechanical analysis (DMA). Networks sterilized by low-temperature plasma elicited a cytotoxic response and are shown to completely destroy the

C. M. Yakacki; M. B. Lyons; B. Rech; K. Gall; R. Shandas

2008-01-01

207

Directed water shedding on high-aspect-ratio shape memory polymer micropillar arrays.  

PubMed

A reconfigurable, droplet-directing surface is developed based on high-aspect-ratio shape-memory polymer (SMP) pillars. The water droplet on the original or recovered SMP pillars can slide off the surface at a finite angle of inclination while being fully pinned on the deformed pillar array. This wettability contrast allows directed water shredding from the straight pillars to the deformed ones. PMID:24293288

Chen, Chi-Mon; Yang, Shu

2014-02-26

208

Shape memory polymer based self-healing syntactic foam: 3-D confined thermomechanical characterization  

Microsoft Academic Search

In this study, the thermomechanical behavior of a shape memory polymer (SMP) based syntactic foam under three-dimensional (3-D) confinement was investigated through strain-controlled programming and fully confined shape recovery tests. The 3-D confinement was created by encasing the foam in circular confining tubes and subjecting the foam cylinder to uniaxial compression. The parameters investigated included two programming temperatures, three types

Guoqiang Li; Naveen Uppu

2010-01-01

209

Prototype laser-activated shape memory polymer foam device for embolic treatment of aneurysms.  

PubMed

Conventional embolization of cerebral aneurysms using detachable coils is time-consuming and often requires retreatment. These drawbacks have prompted the development of new methods of aneurysm occlusion. We present the fabrication and laser deployment of a shape memory (SMP) polymer expanding foam device. Data acquired in an in vitro basilar aneurysm model with and without flow showed successful treatment, with the flow rate affecting foam expansion and the temperature at the aneurysm wall. PMID:17614707

Maitland, Duncan J; Small, Ward; Ortega, Jason M; Buckley, Patrick R; Rodriguez, Jennifer; Hartman, Jonathan; Wilson, Thomas S

2007-01-01

210

Thermomechanical properties in a thin film of shape memory polymer of polyurethane series  

Microsoft Academic Search

The thermomechanical properties of a thin film of shape memory polymer of polyurethane series were investigated experimentally. Based on the experimental results, the dynamic mechanical properties, cyclic deformation properties at high temperature, thermomechanical cycling properties, creep and stress relaxation are discussed. The shape fixity with loading above the glass transition temperature 0964-1726\\/5\\/4\\/012\\/img7 followed by unloading below 0964-1726\\/5\\/4\\/012\\/img7 does not change

Hisaaki Tobushi; Hisashi Hara; Etsuko Yamada; Shunichi Hayashi

1996-01-01

211

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

PubMed

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

Xu, Jianwen; Song, Jie

2010-04-27

212

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

PubMed Central

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

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

2012-01-01

213

Effects of moisture on the glass transition temperature of polyurethane shape memory polymer filled with nano-carbon powder  

Microsoft Academic Search

One simple approach to produce electrically conductive polymers is to fill them with conductive powders. This paper investigates the effects of moisture on the glass transition temperature of a polyurethane shape memory polymer (SMP) filled with nano-carbon powders. It is found that the SMP composites before immersion in water have a slightly lower glass transition temperature, and in the mean

Bin Yang; Wei Min Huang; Chuan Li; Jun Hoe Chor

2005-01-01

214

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

Microsoft Academic Search

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

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

2009-01-01

215

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

NASA Astrophysics Data System (ADS)

As a new class of smart material, shape memory polymer (SMP) receives more and more attention. In this paper, in addition to the fabrication of a new type of epoxy SMP, the thermo-mechanical properties of the polymer with/without gamma irradiation were investigated and compared systematically. The radiation source is Co-60 and the total dosage of radiation is 1×104Gy. Changes of network structures of the polymer were investigated by Fourier Transform Infrared (FTIR) spectroscopy. The influence of gamma irradiation on thermo and mechanical properties of the polymer were investigated by Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and tensile test, respectively. Furthermore, shape recovery behaviors of the polymer before/after the irradiation were compared too. Results show that the epoxy SMP possesses good chemical stability, glass transition temperature (Tg) determined by DSC decreased by 7°C after the irradiation. The gamma radiation has a slight influence on storage modulus, loss modulus and tan delta, respectively. No considerable change was found both in tensile strength and elongation at break after the gamma radiation. Finally, the shape recovery ratio of the polymer is near 100% with and without the gamma irradiation. Based on the above results, it can be demonstrated that the epoxy SMP prepared in the study possesses not only good thermo-mechanical properties but unique anti irradiation performance. The epoxy SMP shows potential for application of aerospace fields.

Wu, Xuelian; Liu, Yanju; Leng, Jinsong

2009-07-01

216

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

NASA Astrophysics Data System (ADS)

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

Luo, Xiaofan

217

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

NASA Astrophysics Data System (ADS)

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

Shi, Guanghui; Yang, Qingsheng; Zhang, Qiang

2012-04-01

218

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

NASA Astrophysics Data System (ADS)

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

Shi, Guanghui; Yang, Qingsheng; Zhang, Qiang

2011-11-01

219

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

DOEpatents

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

Maitland, Duncan J. (Pleasant Hill, CA); Lee, Abraham P. (Walnut Creek, CA); Schumann, Daniel L. (Concord, CA); Silva, Luiz Da (Danville, CA)

2000-01-01

220

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

NASA Astrophysics Data System (ADS)

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

Gormley, Adam Joseph

221

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

PubMed Central

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

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

2012-01-01

222

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

NASA Astrophysics Data System (ADS)

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

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

2007-04-01

223

Experimental Evaluation of the Rheological Properties of Veriflex Shape Memory Polymer  

E-print Network

Shape memory polymers (SMPs) are materials with a great potential for future use in smart materials and structures. When heated from cold state (below the transformation temperature, which can either be the glass transition temperature or the melting temperature of the polymer) to hot state (above the transformation temperature) they undergo transformation which can be compared with martensitic transformation of shape memory alloys. This process induces great changes of the mechanical properties and some shape memory phenomenon can be observed. This study is an experimental evaluation of the mechanical properties of SMP Veriflex under different test conditions. Veriflex was chosen because of its easy accessibility. Furthermore its properties are similar to epoxy resins which make it very suitable for usage in a wide variety of technical applications. Dynamic mechanical analysis (DMA) was used to determine evolution of the viscoelastic properties versus temperature and frequency under cyclic harmonic loading. The glass transition temperature clearly appears in a range from 45\\degree C to 60\\degree C depending on loading frequency. The glass transition is noticeably marked by an impressive decrease in the storage modulus of about 4 decades. The master curve of Veriflex was created and allows the time-temperature superposition to be constructed for this material. Thermo-mechanical working cycle of SMP with 100% elongation was also experimentally tested. Finally results from all these experimental investigations were used to design a demonstrator showing the possibility of application in engineering and especially for shape control.

Jan Klesa; Vincent Placet; Emmanuel Foltete; Manuel Collet

2009-09-16

224

Ordered arrays of a defect-modified ferroelectric polymer for non-volatile memory with minimized energy consumption  

NASA Astrophysics Data System (ADS)

Ferroelectric polymers are among the most promising materials for flexible electronic devices. Highly ordered arrays of the defect-modified ferroelectric polymer P(VDF-TrFE-CFE) (poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)) are fabricated by nanoimprint lithography for nonvolatile memory application. The defective CFE units reduce the coercive field to one-fifth of that of the un-modified P(VDF-TrFE), which can help minimize the energy consumption and extend the lifespan of the device. The nanoimprint process leads to preferable orientation of polymer chains and delicately controlled distribution of the defects, and thus a bi-stable polarization that makes the memory nonvolatile, as revealed by the pulsed polarization experiment.Ferroelectric polymers are among the most promising materials for flexible electronic devices. Highly ordered arrays of the defect-modified ferroelectric polymer P(VDF-TrFE-CFE) (poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)) are fabricated by nanoimprint lithography for nonvolatile memory application. The defective CFE units reduce the coercive field to one-fifth of that of the un-modified P(VDF-TrFE), which can help minimize the energy consumption and extend the lifespan of the device. The nanoimprint process leads to preferable orientation of polymer chains and delicately controlled distribution of the defects, and thus a bi-stable polarization that makes the memory nonvolatile, as revealed by the pulsed polarization experiment. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr03866e

Chen, Xiang-Zhong; Chen, Xin; Guo, Xu; Cui, Yu-Shuang; Shen, Qun-Dong; Ge, Hai-Xiong

2014-10-01

225

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

PubMed Central

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

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

2011-01-01

226

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

PubMed

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

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

2014-12-01

227

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

2012-04-01

228

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

229

Recovery torque modeling of carbon fiber reinforced shape memory polymer nanocomposites  

NASA Astrophysics Data System (ADS)

Carbon fiber and carbon nanofiber paper (CF&CNFP) can be incorporated into shape memory polymers (SMPs) to increase electrical conductivity and allow high speed electrical actuation with a low power. This paper studies the interactions among the recovery torques of CF&CNFP and SMP and the gravity torque during the shape recovery process. The proposed recovery torque model in a SMP CF&CNFP based structure is validated by experimental data obtained using a recently developed low cost, non-contact measurement testbed.

Shen, He; Xu, Yunjun; Liang, Fei; Gou, Jihua; Mabbott, Bob

2013-11-01

230

Three-Dimensional Flexible Electronics Enabled by Shape Memory Polymer Substrates for Responsive Neural Interfaces  

PubMed Central

Planar electronics processing methods have enabled neural interfaces to become more precise and deliver more information. However, this processing paradigm is inherently 2D and rigid. The resulting mechanical and geometrical mismatch at the biotic–abiotic interface can elicit an immune response that prevents effective stimulation. In this work, a thiol–ene/acrylate shape memory polymer is utilized to create 3D softening substrates for stimulation electrodes. This substrate system is shown to soften in vivo from more than 600 to 6 MPa. A nerve cuff electrode that coils around the vagus nerve in a rat and that drives neural activity is demonstrated. PMID:25530708

Ware, Taylor; Simon, Dustin; Hearon, Keith; Liu, Clive; Shah, Sagar; Reeder, Jonathan; Khodaparast, Navid; Kilgard, Michael P.; Maitland, Duncan J.; Rennaker, Robert L.; Voit, Walter E.

2014-01-01

231

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

232

Laser-Activated Shape Memory Polymer Microactuator for Thrombus Removal Following Ischemic Stroke: Preliminary In Vitro Analysis  

SciTech Connect

Due to the narrow (3-hour) treatment window for effective use of the thrombolytic drug recombinant tissue-type plasminogen activator (rt-PA), there is a need to develop alternative treatments for ischemic stroke. We are developing an intravascular device for mechanical thrombus removal using shape memory polymer (SMP). We propose to deliver the SMP microactuator in its secondary straight rod form (length = 4 cm, diameter = 350 {micro}m) through a catheter distal to the vascular occlusion. The microactuator, which is mounted on the end of an optical fiber, is then transformed into its primary corkscrew shape by laser heating (diode laser, {lambda} = 800 nm) above its soft phase glass transition temperature (T{sub gs} = 55 C). Once deployed, the microactuator is retracted and the captured thrombus is removed to restore blood flow. The SMP is doped with indocyanine green (ICG) dye to increase absorption of the laser light. Successful deployment of the microactuator depends on the optical properties of the ICG-doped SMP and the optical coupling efficiency of the interface between the optical fiber and the SMP. Spectrophotometry, thermal imaging, and computer simulation aided the initial design effort and continue to be useful tools for optimization of the dye concentration and laser power. Thermomechanical testing was performed to characterize the elastic modulus of the SMP. We have demonstrated laser-activation of the SMP microactuator in air at room temperature, suggesting this concept is a promising therapeutic alternative to rt-PA.

Small, W; Metzger, M F; Wilson, T S; Maitland, D J

2004-09-23

233

Preparation of a novel adenovirus formulation with artificial envelope of multilayer polymer-coatings: therapeutic effect on metastatic ovarian cancer.  

PubMed

Layer-by-layer deposition of the ionic polymers onto adenovirus particles afforded the multilayer-coated virus vectors. The infectivity of the virus in the presence of anti-adenovirus antibody increased as the layer number and the viruses with five or six polymer layers allowed relatively high efficiency of reporter gene expression in vitro. Therapeutic effect of the intraperitoneal injection of the oncolytic adenovirus with quintal polymer multilayers on the mice bearing intraperitoneal metastatic ovarian cancer was examined. All the control mice injected with PBS died within 21 days after the tumor inoculation. On the other hand, the mice injected with the multilayer-coated oncolytic virus lived much longer and seven eighths of them lived >60 days without apparent accumulation of ascites. These approaches would open a new way to create a novel, safe and efficient viral gene therapy. PMID:20127013

Yoshihara, Chieko; Hamada, Katsuyuki; Koyama, Yoshiyuki

2010-03-01

234

Conductive nanoparticles in electro activated shape memory polymer sensor and actuator  

NASA Astrophysics Data System (ADS)

There is a strong interest in the use of conductive shape memory polymer (SMP) for actuation by passing an electrical current. This paper presents a systematic study on the effect of multi-walled carbon nanotubes (MWCNTs) and carbon nanoparticles on the electro activate shape memory polymer (SMP). The first is the fabrication and characterization of styrene-based SMP filled with MWCNTs was investigated. Then the resistivity of 8 wt% MWNTs sample is 80 ohm•cm obtained by using four-point probe Van De Pawn method, and for 8.0×2.0×0.2 cm 3 rectangle sheet, it can be triggered by passing an electrical current with a constant voltage of 200 V. The second is focused on the effect of conductive particulate and fibrous fillers on the electrical property of composite. The electrical conductivity of the composites achieves 8.73×10 -2, 9.63×10 -2 and 1.13×10 -1 S/cm by DC measurement and 0.12, 1.05 and 3 S/cm by four-point probe Van De Pauw method. Their shape recovery can be activated by passing an electrical current of 25 V voltages. In this paper, the sensors using conducting SMP composites testified by the temperature-dependent resistance and strain-dependent resistance tests. At the same time, the shape self-recovery of SMPs and their composites when heated above transition temperature acts as actuator.

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

2008-03-01

235

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

2013-01-01

236

Vascular dynamics of a shape memory polymer foam aneurysm treatment technique.  

PubMed

The vascular dynamics of a shape memory polymer foam aneurysm treatment technique are assessed through the simulated treatment of a generic basilar aneurysm using coupled fluid dynamics and heat transfer calculations. The shape memory polymer foam, which expands to fill the aneurysm when heated, is modeled at three discrete stages of the treatment procedure. To estimate an upper bound for the maximum amount of thermal damage due to foam heating, a steady velocity is specified through the basilar artery, corresponding to a minimum physiological flow velocity over a cardiac cycle. During expansion, the foam alters the flow patterns within the aneurysm by shielding the aneurysm dome from a confined jet that issues from the basilar artery. The time scales for thermal damage to the artery walls and surrounding blood flow are computed from the temperature field. The flow through the post-treatment bifurcation is comprised of two counter-rotating vortex tubes that are located beneath the aneurysm neck and extend downstream into the outlet arteries. Beneath the aneurysm neck, a marked increase in the wall shear stress is observed due to the close proximity of the counter-rotating vortex tubes to the artery wall. PMID:17676399

Ortega, Jason; Maitland, Duncan; Wilson, Tom; Tsai, William; Sava?, Omer; Saloner, David

2007-11-01

237

Biodegradable shape-memory block co-polymers for fast self-expandable stents.  

PubMed

Block co-polymers PCTBVs (M(n) of 36,300-65,300 g/mol, T(m) of 39-40 and 142 degrees C) containing hyperbranched three-arm poly(epsilon-caprolactone) (PCL) as switching segment and microbial polyester PHBV as crystallizable hard segment were designed as biodegradable shape-memory polymer (SMP) for fast self-expandable stent and synthesized in 96% yield by the reaction of three-arm PCL-triol (M(n) of 4200 g/mol, T(m) of 47 degrees C) with methylene diphenyl 4,4'-diisocyanate isocynate (MDI) to form the hyperbrached MDI-linked PCL (PTCM; M(n) of 25,400 g/mol and a T(m) of 38 degrees C), followed by further polymerization with PHBV-diol (M(n) of 2200 g/mol, T(m) of 137 and 148 degrees C). The polymers were characterized by (1)H NMR, GPC, DSC, tensile test, and cyclic thermomechanical tensile test. PCTBVs showed desired thermal properties, mechanical properties, and ductile nature. PCTBV containing 25 wt% PHBV (PCTBV-25) demonstrated excellent shape-memory property at 40 degrees C, with R(f) of 94%, R(r) of 98%, and shape recovery within 25s. PCTBV-25 was also shown as a safe material with good biocompatibility by cytotoxicity tests and cell growth experiments. The stent made from PCTBV-25 film showed nearly complete self-expansion at 37 degrees C within only 25 s, which is much better and faster than the best known self-expandable stents. PMID:20723973

Xue, Liang; Dai, Shiyao; Li, Zhi

2010-11-01

238

A stress-induced phase transition model for semi-crystallize shape memory polymer  

NASA Astrophysics Data System (ADS)

The developments of constitutive models for shape memory polymer (SMP) have been motivated by its increasing applications. During cooling or heating process, the phase transition which is a continuous time-dependent process happens in semi-crystallize SMP and the various individual phases form at different temperature and in different configuration. Then, the transformation between these phases occurred and shape memory effect will emerge. In addition, stress applied on SMP is an important factor for crystal melting during phase transition. In this theory, an ideal phase transition model considering stress or pre-strain is the key to describe the behaviors of shape memory effect. So a normal distributed model was established in this research to characterize the volume fraction of each phase in SMP during phase transition. Generally, the experiment results are partly backward (in heating process) or forward (in cooling process) compared with the ideal situation considering delay effect during phase transition. So, a correction on the normal distributed model is needed. Furthermore, a nonlinear relationship between stress and phase transition temperature Tg is also taken into account for establishing an accurately normal distributed phase transition model. Finally, the constitutive model which taking the stress as an influence factor on phase transition was also established. Compared with the other expressions, this new-type model possesses less parameter and is more accurate. For the sake of verifying the rationality and accuracy of new phase transition and constitutive model, the comparisons between the simulated and experimental results were carried out.

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

2014-03-01

239

Biodegradable shape-memory polymers exhibiting sharp thermal transitions and controlled drug release.  

PubMed

Biodegradable shape-memory polymer networks prepared by cross-linking star shape branched oligo(?-caprolactone) (bOCL) with hexamethylene diisocyanate are introduced. The thermal and mechanical properties of these networks were investigated using differential scanning calorimetry and tensile testing, respectively, and the morphology of the phase structure was characterized by polarized optical microscopy. The shape-memory properties of the networks were quantified using thermomechanical tensile experiments and showed strain fixity rates R(f) higher than 97% and strain recovery rates R(r) as high as 100%. Of note, networks of OCL segments with a lower degree of polymerization (DP; 10) exhibited significantly improved temperature-sensitive shape recovery: 90% of the permanent shape was recovered upon heating to within a 2 °C range (37-39 °C). The networks exhibited complete shape recovery to the permanent shape within 10 s at 42 °C. Theophylline-loaded (10 and 20 wt %) shape-memory materials, prepared by cross-linking bOCL with hexamethylene diisocyanate in the presence of theophylline, are also described as a model for a controlled drug release device. The 10 wt % loaded material was sufficiently soft and flexible for complex shape transformation and also showed high R(f) (98%) and R(r) (99%). Sustained release of loaded theophylline was achieved over 1 month without initial burst-release in a phosphate buffer solution (PBS; pH 7.4) at 37 °C. PMID:19425546

Nagahama, Koji; Ueda, Yuichi; Ouchi, Tatsuro; Ohya, Yuichi

2009-07-13

240

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

PubMed

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

Wischke, Christian; Lendlein, Andreas

2014-03-18

241

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

242

Analysis of the mechanical behavior of shape memory polymer membranes by nanoindentation, bulging and point membrane deflection tests  

Microsoft Academic Search

The mechanical properties of a thin film of polyurethane shape memory polymer were investigated experimentally. Non-conventional mechanical tests such as nanoindentation, bulging and point membrane deflection are used. The quantitative results obtained by these three experimental investigations are consistent. These tests, performed at room temperature (approx. 35 K below the glass transition temperature Tg), yield a Young's modulus equal to

C. Poilane; P. Delobelle; C. Lexcellent; S. Hayashi; H. Tobushi

2000-01-01

243

Qualitative separation of the effect of the solubility parameter on the recovery behavior of shape-memory polymer  

Microsoft Academic Search

For the thermal response of shape-memory polymer (SMP) it has been experimentally demonstrated that the actuation can be achieved using interactive solvent. In this paper, the effect of the solubility parameter of the interactive solvent on the shape recovery behavior and glass transition temperature of polystyrene SMP was investigated experimentally. The effect of the solubility parameter on the activation energy

Haibao Lu; Yanju Liu; Jinsong Leng; Shanyi Du

2009-01-01

244

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

245

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

246

Ordered arrays of a defect-modified ferroelectric polymer for non-volatile memory with minimized energy consumption.  

PubMed

Ferroelectric polymers are among the most promising materials for flexible electronic devices. Highly ordered arrays of the defect-modified ferroelectric polymer P(VDF-TrFE-CFE) (poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)) are fabricated by nanoimprint lithography for nonvolatile memory application. The defective CFE units reduce the coercive field to one-fifth of that of the un-modified P(VDF-TrFE), which can help minimize the energy consumption and extend the lifespan of the device. The nanoimprint process leads to preferable orientation of polymer chains and delicately controlled distribution of the defects, and thus a bi-stable polarization that makes the memory nonvolatile, as revealed by the pulsed polarization experiment. PMID:25316324

Chen, Xiang-Zhong; Chen, Xin; Guo, Xu; Cui, Yu-Shuang; Shen, Qun-Dong; Ge, Hai-Xiong

2014-11-21

247

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

248

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

249

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

2013-10-01

250

Thermomechanical properties, collapse pressure, and expansion of shape memory polymer neurovascular stent prototypes.  

PubMed

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 degrees 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. PMID:19107804

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

2009-07-01

251

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. PMID:19107804

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

2011-01-01

252

Monitoring static shape memory polymers using a fiber Bragg grating as a vector-bending sensor  

NASA Astrophysics Data System (ADS)

We propose and demonstrate a technique for monitoring the recovery deformation of the shape-memory polymers (SMP) using a surface-attached fiber Bragg grating (FBG) as a vector-bending sensor. The proposed sensing scheme could monitor the pure bending deformation for the SMP sample. When the SMP sample undergoes concave or convex bending, the resonance wavelength of the FBG will have red-shift or blue-shift according to the tensile or compressive stress gradient along the FBG. As the results show, the bending sensitivity is around 4.07 nm/cm-1. The experimental results clearly indicate that the deformation of such an SMP sample can be effectively monitored by the attached FBG not just for the bending curvature but also the bending direction.

Li, Peng; Yan, Zhijun; Zhou, Kaiming; Zhang, Lin; Leng, Jinsong

2013-01-01

253

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

PubMed

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. PMID:18465981

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

2008-01-01

254

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. PMID:18465981

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

2009-01-01

255

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

256

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

257

Cytotoxicity and thermomechanical behavior of biomedical shape-memory polymer networks post-sterilization.  

PubMed

Shape-memory polymers (SMPs) are being increasingly proposed for use in biomedical devices. This paper investigates the cytotoxicity, surface characteristics and thermomechanics of two acrylate-based SMP networks as a function of sterilization using a minimal essential media elution test, FTIR-ATR and dynamic mechanical analysis (DMA). Networks sterilized by low-temperature plasma elicited a cytotoxic response and are shown to completely destroy the cell monolayer. FTIR-ATR analysis showed evidence of surface oxidation with an increase and broadening of the absorbance peak from approximately 3500 to 3100 cm(-1), which is associated with an increase in hydroxyl groups. DMA revealed small, but statistically significant, differences in reduction of the glass transition temperatures of both networks when sterilized with gamma irradiation. One network showed an increase in rubbery modulus, which is an indication of crosslink density, after gamma irradiation. Lastly, practical sterilization concerns of SMP devices are discussed in light of the different methods. PMID:18458497

Yakacki, C M; Lyons, M B; Rech, B; Gall, K; Shandas, R

2008-03-01

258

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

2013-11-01

259

Effects of sensitizer length on radiation crosslinked shape-memory polymers  

NASA Astrophysics Data System (ADS)

Shape-memory polymers (SMPs) are smart materials that can be designed to retain a metastable state and upon activation, recover a preprogrammed shape. In this study, poly(methyl acrylate) (PMA) is blended with poly(ethylene glycol) diacrylate (PEGDA) of various molecular weights in various concentrations and subsequently exposed to ionizing radiation. PEGDA sensitizes the radiation crosslinking of PMA, lowering the minimum absorbed dose for gelation and increasing the rubbery modulus, after crosslinking. Minimum dose for gelation, as determined by the Charlesby-Pinner equation, decreases from 25.57 kGy for unblended PMA to 2.06 kGy for PMA blended with 10.00 mole% PEGDA. Moreover, increase in the blend concentration of PEGDA increases the crosslinking density of the resulting networks. Sensitizer length, namely Mn of PEGDA, also affects crosslinking and final mechanical properties. Increase in the length of the PEGDA molecule at a constant molar ratio increases the efficacy of the molecule as a radiation sensitizer as determined by the increase in gel fraction and rubbery modulus across doses. However, at a constant weight ratio of PEGDA to PMA, shorter PEGDA chains sensitize more crosslinking because they have more reactive ends per weight fraction. Sensitized samples of PMA with PEGDA were tested for shape-memory properties and showed shape fixity of greater than 99%. Samples had a glass transition temperature near 28 °C and recovered between 97% and 99% of the induced strain when strained to 50%.

Ware, Taylor; Voit, Walter; Gall, Ken

2010-04-01

260

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. PMID:22904597

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

2012-01-01

261

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

PubMed Central

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

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

2011-01-01

262

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

NASA Astrophysics Data System (ADS)

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

Zhang, Dawei

263

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

264

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

Microsoft Academic Search

It was found in previous work on the thermomechanical properties of the polyurethane-shape memory polymer foam that the shape fixity and shape recovery become imperfect and that secondary-shape forming appears, depending on the strain-holding conditions. The main factors of the strain-holding conditions which affect the secondary-shape forming are the holding temperature, holding time and holding strain. In the present study,

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

2006-01-01

265

The influence of shape-holding conditions on shape recovery of polyurethane-shape memory polymer foams  

Microsoft Academic Search

The thermomechanical properties of polyurethane-shape memory polymer (SMP) foams and the influence of shape-holding conditions on shape recovery were investigated experimentally. The results obtained can be summarized as follows. (1) By cooling the foam down to below the glass transition temperature Tg after compressive deformation above Tg, stress decreases and the deformed shape is fixed. By heating the shape-fixed foam

H. Tobushi; R. Matsui; S. Hayashi; D. Shimada

2004-01-01

266

Laser-activated shape memory polymer microactuator for thrombus removal following ischemic stroke: preliminary in vitro analysis  

Microsoft Academic Search

Due to the narrow (3-h) treatment window for effective use of the thrombolytic drug recombinant tissue-type plasminogen activator (rt-PA), there is a need to develop alternative treatments for ischemic stroke. We are developing an intravascular device for mechanical thrombus removal using shape memory polymer (SMP). We propose to deliver the SMP microactuator in its secondary straight rod form (length=4 cm,

Melodie F. Metzger; Thomas S. Wilson; Duncan J. Maitland

2005-01-01

267

Variation of free volume size and content of shape memory polymer — Polyurethane — Upon temperature studied by positron annihilation lifetime techniques and infrared spectroscopy  

Microsoft Academic Search

Positron annihilation lifetime measurement and Fourier transform infrared spectrometry were applied to the study of temperature dependencies of free volume parameters and hydrogen bonds in segmented polyurethane, specially fabricated as a shape memory polymer. The variation of free volumes in amorphous region were correlated to that of hydrogen bonding and the shape memory mechanism of polyurethane is elucidated from a

K. Ito; K. Abe; H. L. Li; Y. Ujihira; N. Ishikawa; S. Hayashi

1996-01-01

268

Qualitative separation of the effects of carbon nano-powder and moisture on the glass transition temperature of polyurethane shape memory polymer  

Microsoft Academic Search

Based on a series of cyclic differential scanning calorimetry analyses together with thermogravimetric analyses, the effects of carbon nano-powder and moisture on the glass transition temperature of a polyurethane shape memory polymer were separated and qualitatively identified. This approach should be applicable to other polyurethane polymers and their composites.

B. Yang; W. M. Huang; C. Li; L. Li; J. H. Chor

2005-01-01

269

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

PubMed

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

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

2013-11-01

270

Polymer-Based Therapeutics: Nanoassemblies and Nanoparticles for Management of Atherosclerosis  

PubMed Central

Coronary arterial disease, one of the leading causes of adult mortality, is triggered by atherosclerosis. A disease with complex etiology, atherosclerosis results from the progressive long-term combination of atherogenesis, the accumulation of modified lipoproteins within blood vessel walls, along with vascular and systemic inflammatory processes. The management of atherosclerosis is challenged by the localized flare-up of several multipronged signaling interactions between activated monocytes, atherogenic macrophages and inflamed or dysfunctional endothelial cells. A new generation of approaches is now emerging founded on multifocal, targeted therapies that seek to reverse or ameliorate the athero-inflammatory cascade within the vascular intima. This article reviews the various classes and primary examples of bioactive configurations of nanoscale assemblies. Of specific interest are polymer-based or polymer-lipid micellar assemblies designed as multimodal receptor-targeted blockers or drug carriers whose activity can be tuned by variations in polymer hydrophobicity, charge, and architecture. Also reviewed are emerging reports on multifunctional nanoassemblies and nanoparticles for improved circulation and enhanced targeting to athero-inflammatory lesions and atherosclerotic plaques. PMID:21523920

Lewis, Daniel R.; Kamisoglu, Kubra; York, Adam; Moghe, Prabhas V.

2012-01-01

271

Thermoresponsive semicrystalline poly(?-caprolactone) networks: exploiting cross-linking with cinnamoyl moieties to design polymers with tunable shape memory.  

PubMed

The overall goal of this study was to synthesize semicrystalline poly(?-caprolactone) (PCL) copolymer networks with stimuli-responsive shape memory behavior. Herein, we investigate the influence of a cinnamoyl moiety to design shape memory polymer networks with tunable transition temperatures. The effect of various copolymer architectures (random or ABA triblock), the molecular weight of the crystalline domains, PCL diol, (M(w) 1250 or 2000 g mol(-1)) and its composition in the triblock (50 or 80 mol %) were also investigated. The polymer microstructures were confirmed by NMR, DSC, WAXS and UV-vis spectroscopic techniques. The thermal and mechanical properties and the cross-linking density of the networks were characterized by DSC, tensile testing and solvent swelling, respectively. Detailed thermomechanical investigations conducted using DMA showed that shape memory behavior was obtained only in the ABA triblock copolymers. The best shape memory fixity, R(f) of ~99% and shape recovery, R(r) of ~99% was obtained when PCL diol with M(w) 2000 g mol(-1) was incorporated in the triblock copolymer at a concentration of 50 mol %. The series of triblock copolymers with PCL at 50 mol % also showed mechanical properties with tunable shape memory transition temperatures, ranging from 54 °C to close to body temperature. Our work establishes a general design concept for inducing a shape memory effect into any semicrystalline polyester network. More specifically, it can be applied to systems which have the highest transition temperature closest to the application temperature. An advantage of our novel copolymers is their ability to be cross-linked with UV radiation without any initiator or chemical cross-linker. Possible applications are envisioned in the area of endovascular treatment of ischemic stroke and cerebrovascular aneurysms, and for femoral stents. PMID:22252722

Garle, Amit; Kong, Sany; Ojha, Umaprassana; Budhlall, Bridgette M

2012-02-01

272

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

PubMed Central

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

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

2011-01-01

273

Opacification of shape memory polymer foam designed for treatment of intracranial aneurysms.  

PubMed

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 radio-opacity 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. PMID:22101759

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

2012-04-01

274

Inductively heated shape memory polymer for the magnetic actuation of medical devices.  

PubMed

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 devices made from SMP loaded with nickel zinc ferrite ferromagnetic particles were actuated in air by applying an alternating magnetic field to induce heating. Dynamic mechanical thermal analysis was performed on both the particle-loaded and neat SMP materials to assess the impact of the ferrite particles on the mechanical properties of the samples. Calorimetry was used to quantify the rate of heat generation as a function of particle size and volumetric loading of ferrite particles in the SMP. These tests demonstrated the feasibility of SMP actuation by inductive heating. Rapid and uniform heating was achieved in complex device geometries and particle loading up to 10% volume content did not interfere with the shape recovery of the SMP. PMID:17019872

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

2006-10-01

275

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

SciTech Connect

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 devices made from SMP loaded with Nickel Zinc ferrite ferromagnetic particles were actuated in air by applying an alternating magnetic field to induce heating. Dynamic mechanical thermal analysis was performed on both the particle-loaded and neat SMP materials to assess the impact of the ferrite particles on the mechanical properties of the samples. Calorimetry was used to quantify the rate of heat generation as a function of particle size and volumetric loading of ferrite particles in the SMP. These tests demonstrated the feasibility of SMP actuation by inductive heating. Rapid and uniform heating was achieved in complex device geometries and particle loading up to 10% volume content did not interfere with the shape recovery of the SMP.

Buckley, P; Mckinley, G; Wilson, T; Small, W; Benett, W; Bearinger, J; McElfresh, M; Maitland, D

2005-09-06

276

Shape memory polymer nanocomposites for application of multiple-field active disassembly: experiment and simulation.  

PubMed

Active disassembly (AD) uses innovative materials that can perform a designed disassembly action by the application of an external field. AD provides improvements over current disassembly processes by limiting machine or manual labor and enabling batch processing for end-of-life products. With improved disassembly operations, more reuse of components and purer recycling streams may be seen. One problem with AD, however, has been with the single-field actuation because of the probability of accidental disassembly. This presentation will discuss the application of shape memory polymer (SMP) nanocomposites in a new AD process. This novel AD process requires multiple-field actuation of the SMP nanocomposite fastener. In the analysis of this AD process, thermal and magnetic field tests were performed on the SMP nanocomposite. From these tests, finite-element analysis was performed to model and simulate the multiple-field AD process. The results of the simulations provide performance variables for the AD process and show a better performance time for the SMP nanocomposite fastener than for a comparable SMP fastener. PMID:24117335

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

2013-11-19

277

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

2011-02-01

278

Modelling of loading, stress relaxation and stress recovery in a shape memory polymer.  

PubMed

A multi-element constitutive model for a lactide-based shape memory polymer has been developed that represents loading to large tensile deformations, stress relaxation and stress recovery at 60, 65 and 70°C. The model consists of parallel Maxwell arms each comprising neo-Hookean and Eyring elements. Guiu-Pratt analysis of the stress relaxation curves yields Eyring parameters. When these parameters are used to define the Eyring process in a single Maxwell arm, the resulting model yields at too low a stress, but gives good predictions for longer times. Stress dip tests show a very stiff response on unloading by a small strain decrement. This would create an unrealistically high stress on loading to large strain if it were modelled by an elastic element. Instead it is modelled by an Eyring process operating via a flow rule that introduces strain hardening after yield. When this process is incorporated into a second parallel Maxwell arm, there results a model that fully represents both stress relaxation and stress dip tests at 60°C. At higher temperatures a third arm is required for valid predictions. PMID:24878964

Sweeney, J; Bonner, M; Ward, I M

2014-09-01

279

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. PMID:18042294

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

2007-01-01

280

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. PMID:22101759

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

281

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. PMID:21949469

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

2011-01-01

282

In Vivo Tissue Responses to Thermal-responsive Shape Memory Polymer Nanocomposites  

PubMed Central

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 abnormities 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

2010-01-01

283

Development of a new transvenous patent ductus arteriosus occlusion technique using a shape memory polymer.  

PubMed

A novel percutaneous patent ductus arteriosus (PDA) occlusion technique, without the potential problems associated with conventional techniques, has been long awaited. The development of a novel transvenous PDA occlusion technique using a temperature-shape changeable occluder device, and the verification of its in vitro performance, were demonstrated in this study. The principles of this technique are: 1) the bar form device was inserted into the PDA transvenously by a guide wire and a pushing catheter, 2) the device was dashed with hot water through catheters, 3) the device was expanded by hot water in the PDA, and the PDA was occluded. The occluder device, made of a shape memory polymer (polynorbornene), was designed to have the monobloc configuration of a thin disk with a hole for a guide wire in the center and a cone. The barlike device by hot press was fully expanded within 10 sec upon immersion into 45 degrees C water. The mock-circulation test with the "great arteries" and a specially designed "PDA" showed 1) the introduction of hot water (45 degrees C) through the catheters caused expansion of the device which stayed in the "PDA" without any support, 2) the "aortic" pressure and the distal "aortic" flow increased rapidly, and the "pulmonary" flow reduced promptly. This resulted in a drastically reduced shunt ratio at the PDA from 68% to 30%. Thus, the novel PDA occlusion technique developed here functioned well to occlude the PDA in a great arteries model. PMID:2252656

Echigo, S; Matsuda, T; Kamiya, T; Tsuda, E; Suda, K; Kuroe, K; Ono, Y; Yazawa, K

1990-01-01

284

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

PubMed

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

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

2011-09-01

285

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

NASA Astrophysics Data System (ADS)

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

Gu, Jianping; Sun, Huiyu; Fang, Changqing

2015-02-01

286

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

287

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

NASA Astrophysics Data System (ADS)

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

Wang, Anqi; Li, Guoqiang; Meng, Harper

2013-08-01

288

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

289

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

290

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

PubMed

The effect of moisture absorption on the glass transition temperature (T(g)) 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 T(g) of the foam, with a maximum water uptake shifting the T(g) 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. PMID:21949469

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

2011-08-01

291

Therapeutic Vaccination Expands and Improves the Function of the HIV-Specific Memory T-Cell Repertoire  

PubMed Central

Background.?The licensing of herpes zoster vaccine has demonstrated that therapeutic vaccination can help control chronic viral infection. Unfortunately, human trials of immunodeficiency virus (HIV) vaccine have shown only marginal efficacy. Methods.?In this double-blind study, 17 HIV-infected individuals with viral loads of <50 copies/mL and CD4+ T-cell counts of >350 cells/µL were randomly assigned to the vaccine or placebo arm. Vaccine recipients received 3 intramuscular injections of HIV DNA (4 mg) coding for clade B Gag, Pol, and Nef and clade A, B, and C Env, followed by a replication-deficient adenovirus type 5 boost (1010 particle units) encoding all DNA vaccine antigens except Nef. Humoral, total T-cell, and CD8+ cytotoxic T-lymphocyte (CTL) responses were studied before and after vaccination. Single-copy viral loads and frequencies of latently infected CD4+ T cells were determined. Results.?Vaccination was safe and well tolerated. Significantly stronger HIV-specific T-cell responses against Gag, Pol, and Env, with increased polyfunctionality and a broadened epitope-specific CTL repertoire, were observed after vaccination. No changes in single-copy viral load or the frequency of latent infection were observed. Conclusions.?Vaccination of individuals with existing HIV-specific immunity improved the magnitude, breadth, and polyfunctionality of HIV-specific memory T-cell responses but did not impact markers of viral control. Clinical Trials Registration.?NCT00270465 PMID:23482645

Casazza, Joseph P.; Bowman, Kathryn A.; Adzaku, Selorm; Smith, Emily C.; Enama, Mary E.; Bailer, Robert T.; Price, David A.; Gostick, Emma; Gordon, Ingelise J.; Ambrozak, David R.; Nason, Martha C.; Roederer, Mario; Andrews, Charla A.; Maldarelli, Frank M.; Wiegand, Ann; Kearney, Mary F.; Persaud, Deborah; Ziemniak, Carrie; Gottardo, Raphael; Ledgerwood, Julie E.; Graham, Barney S.; Koup, Richard A.

2013-01-01

292

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.

2012-03-01

293

Shape Memory Mechanics of an Elastic Memory Composite Resin  

Microsoft Academic Search

Substantially more attention has been given in the past to shape memory alloys and shape memory ceramics than to shape memory polymers because unreinforced shape memory polymers have much lower stiffness and recovery force potential than shape memory alloys and shape memory ceramics. However, when incorporated into a fiber-reinforced composite, both the stiffness and the recovery force of a shape

Erik R. Abrahamson; Mark S. Lake; Naseem A. Munshi; Ken Gall

2003-01-01

294

A biocompatible oxidation-triggered carrier polymer with potential in therapeutics.  

PubMed

Dextran, a water-soluble, biocompatible polymer of glucose, was modified at its hydroxyls with arylboronic esters to make it soluble in common organic solvents, allowing for the facile preparation of oxidation-sensitive dextran (Oxi-DEX) carrier microparticles. These particles were found to release their payload with a half-life of 36 min at 1 mM H2O2, which can be compared with a half-life of greater than 1 week in the absence of H2O2. When used in a model vaccine application, Oxi-DEX particles loaded with ovalbumin (OVA) increased the presentation to CD8+ T-cells 27-fold relative to OVA encapsulated in a classical vehicle not sensitive to oxidation. No presentation was observed from cells incubated with unencapsulated OVA. Additionally, Oxi-DEX was found to be nontoxic in preliminary in vitro cytotoxicity assays. Because it is easy to prepare, sensitive to biological oxidation, and biocompatible, this material may represent an attractive new platform for selective delivery applications. PMID:21171594

Broaders, Kyle E; Grandhe, Sirisha; Fréchet, Jean M J

2011-02-01

295

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

296

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

NASA Astrophysics Data System (ADS)

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

Huang, Jinying; Ma, Dongge

2014-09-01

297

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

298

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

Microsoft Academic Search

In this paper, the effects of long-term storage in compressed cold hibernated elastic memory (CHEM) polyurethane foam, a kind of shape memory polymer, are investigated experimentally. The foams were pre-strained at a high temperature, which was above the glass transition temperature, to 80% and 93.4%, respectively, and then cooled back to room temperature. After various periods of cold hibernation (up

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

2001-01-01

299

Memory  

MedlinePLUS

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

300

Strain rate- and temperature-dependent tensile properties of an epoxy-based, thermosetting, shape memory polymer (Veriflex-E)  

NASA Astrophysics Data System (ADS)

In this study, the inelastic deformation behavior of an epoxy-based, thermally triggered shape memory polymer resin, known as Veriflex-E, was investigated. The experimental program was designed to explore the influence of strain rate on monotonic loading at various temperatures which is needed to establish the design space of SMPs in load bearing applications. Thermally actuated shape memory polymers can be thought of as having two phases separated by the glass transition temperature ( T g ). At temperatures below the T g , Veriflex-E exhibits a high elastic modulus and positive, non-linear strain rate sensitivity in monotonic loading. The Poisson's ratio at room temperature is independent of the strain rate, but dependent upon the strain magnitude. As the temperature is increased, the strain rate sensitivity in monotonic loading decreases. Well above the T g , the elastic modulus drops by several orders of magnitude. In this high temperature region, the material achieves strain levels well above 100% and Poisson's ratio is constant at 0.5 regardless of strain rate or strain magnitude.

McClung, Amber J. W.; Tandon, Gyaneshwar P.; Baur, Jeffery W.

2012-05-01

301

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

302

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

NASA Astrophysics Data System (ADS)

Hydrogel systems for controlled delivery therapeutic growth factors have been developed in a wide spectrum of strategies: these systems aim for the release of growth factors via a passive diffusion, electrostatic interaction, degradation of hydrogels, and responsiveness to external stimuli. Heparin, a highly sulfated glycosaminoglycan (GAG), was employed for a targeted delivery system of vascular endothelial growth factor (VEGF) to endothelial cells overexpressing a relevant receptor VEGFR-2. Addition of dimeric VEGF to 4-arm star-shaped poly(ethylene glycol) (PEG) immobilized with low-molecular weight heparin (LMWH) afforded a non-covalently assembled hydrogel via interaction between heparin and VEGF, with storage modulus 10 Pa. The release of VEGF and hydrogel erosion reached maximum 100 % at day 4 in the presence of VEGFR-2 overexpressing pocine aortic endothelial cell (PAE/KDR), while those of 80% were achieved via passive release at day 5 in the presence of PAE cell lacking VEGFR-2 or in the absence of cell, indicating that the release of VEGF was in targeted manner toward cell receptor. The proliferation of PAE/KDR in the presence of [PEG-LMWH/VEGF] hydrogel was greater by ca. 30% at day 4 compared to that of PAE, confirming that the release of VEGF was in response to the cellular demand. The phosphorylation fraction of VEGFR-2 on PAE/KDR was greater in the presence of [PEG-LMWH/VEGF] hydrogel, increasing from 0.568 at day 1 to 0.790 at day 4, whereas it was maintained at 0.230 at day 4 in the presence of [PEG-LMWH] hydrogel. This study has proven that this hydrogel, assembled via bio-inspired non-covalent interaction, liberating VEGFon celluar demand to target cell, eroding upon VEGF release, and triggering endothelial cell proliferation, could be used in multiple applications including targeted delivery and angiogenesis. Heparin has been widely exploited in growth factor delivery systems owing to its ability to bind many growth factors through the flexible patterns of functional groups. However, heterogeneity in the composition and in the polydispersity of heparin has been problematic in controlled delivery system and thus motivated the development of homogeneous heparin mimics. Peptides of appropriate sequence and chemical function have therefore recently emerged as potential replacements for heparin in select applications. Studied was the assessment of the binding affinities of multiple sulfated peptides (SPs) for a set of heparin-binding peptides (HBPs) and for VEGF; these binding partners have application in the selective immobilization of proteins and in hydrogel formation through non-covalent interactions. Sulfated peptides were produced via solid-phase methods, and their affinity for the HBPs and VEGF was assessed via affinity liquid chromatography (ALC), surface plasmon resonance (SPR), and in select cases, isothermal titration calorimetry (ITC). The shortest peptide, SPa, showed the highest affinity binding of HBPs and VEGF165 in both ALC and SPR measurements, with slight exceptions. Of the investigated HBPs, a peptide based on the heparin-binding domain of human platelet factor 4 showed greatest binding affinities toward all of the SPs, consistent with its stronger binding to heparin. The affinity between SPa and PF4ZIP was indicated via SPR ( KD = 5.27 muM) and confirmed via ITC (KD = 8.09 muM). The binding by SPa of both VEGF and HBPs suggests its use as a binding partner to multiple species, and the use of these interactions in assembly of materials. Given that the peptide sequences can be varied to control binding affinity and selectivity, opportunities are also suggested for the production of a wider array of matrices with selective binding and release properties useful for biomaterials applications. Hydrogel consisting of SPa was formed via a covalent Michael Addition reaction between maleimide- and thiol-terminated multi-arm PEGs and Cys-SPa. The mechanical property of hydrogel was tunable from ca. 186 to 1940 Pa. by varing the cross-linking density, suggesting its flexible applications depending

Kim, Sung Hye

303

The glass transition temperature of polyurethane shape memory polymer reinforced with treated\\/non-treated attapulgite (playgorskite) clay in dry and wet conditions  

Microsoft Academic Search

Attapulgite (playgorskite), a kind of nanosized fibrous clay mineral, may provide a simple and cheap alternative to improve the stiffness and actuation stress of shape memory polymers (SMPs). As a first step, in this paper, we investigate the glass transition temperature of a polyurethane SMP reinforced with treated\\/non-treated attapulgite in wet and dry conditions. In addition to confirming the strong

G H Pan; W M Huang; Z C Ng; N Liu; S J Phee

2008-01-01

304

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

305

Microfabricated therapeutic actuators  

DOEpatents

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

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

1999-01-01

306

Polymers.  

ERIC Educational Resources Information Center

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

Tucker, David C.

1986-01-01

307

ZnO-based nonvolatile memory thin-film transistors with polymer dielectric/ferroelectric double gate insulators  

NASA Astrophysics Data System (ADS)

The authors report on the fabrication of a top-gate ZnO thin-film transistor (TFT) with a polymer dielectric/ferroelectric double-layer gate insulator that was formed on patterned ZnO through a sequential spin-casting process of 450-nm-thick poly-4-vinylphenol (PVP) and 200-nm-thick poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)]. Compared to the single P(VDF/TrFE) layer, double layer shows remarkably reduced leakage current with the aid of the PVP buffer. TFT with the PVP/P(VDF/TrFE) double layer exhibits a field effect mobility of 0.36cm2/V and a large memory hysteresis in the transfer characteristics due to the ferroelectric P(VDF/TrFE). The retention of the device lasted over 2h.

Noh, Seok Hwan; Choi, Wonjun; Oh, Min Suk; Hwang, D. K.; Lee, Kimoon; Im, Seongil; Jang, Sungjin; Kim, Eugene

2007-06-01

308

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

309

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

2011-04-11

310

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

NASA Astrophysics Data System (ADS)

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

Basfar, A. A.; Lotfy, S.

2015-01-01

311

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

NASA Astrophysics Data System (ADS)

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

Yang, Qianxi; Li, Guoqiang

2014-10-01

312

A remote-activated shape memory polymer network employing vinyl-capped Fe3O4 nanoparticles as netpoints for durable performance  

NASA Astrophysics Data System (ADS)

A new type of shape memory polymer (SMP) employing vinyl-capped Fe3O4 nanoparticles as netpoints that determine the permanent shape for remote activation has been presented. The new design effectively prevents the nanoparticles from moving and re-aggregating in a polymer matrix and guarantees the stability of the SMP networks when a high temperature and external stress are applied. Therefore, durable shape memory performance is obtained during the programmed deformation-recovery processes. Meanwhile, a homogeneous distribution of vinyl-capped Fe3O4 nanoparticles achieves uniform heat generation and heat transfer in the alternating magnetic field. Consequently, the novel remote-activated SMP also exhibits a fast magnetic responsiveness compared to the SMPs physically dispersed with Fe3O4 nanoparticles.

Xia, Shuang; Li, Xingjian; Wang, Yaru; Pan, Yi; Zheng, Zhaohui; Ding, Xiaobin; Peng, Yuxing

2014-08-01

313

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.

314

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

PubMed Central

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 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 five hours or to 125°C for up to 24 hours if stabilized with 10,000 ppm BQ and could also be heated to 125°C for up to 5 hours if stabilized with 1000 ppm BQ without sensitizer reaction occurring. We believe this study provides significant insight into methods for manipulation of the competing mechanisms of radiation crosslinking and thermal stabilization of radiation sensitizers, thereby facilitating further development of radiation crosslinkable thermoplastic SMPs. PMID:23226930

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

2012-01-01

315

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

316

Shape-memory polymer networks from oligo[(epsilon-hydroxycaproate)-co-glycolate]dimethacrylates and butyl acrylate with adjustable hydrolytic degradation rate.  

PubMed

Degradable shape-memory polymer networks intended for biomedical applications were synthesized from oligo[(epsilon-hydroxycaproate)-co-glycolate]dimethacrylates with glycolate contents between 0 and 30 mol % using a photopolymerization process. In addition AB copolymer networks were prepared by adding 60 wt % n-butyl acrylate as comonomer. All synthesized polymer networks are semicrystalline at room temperature. A melting transition T(m) between 18 and 53 degrees C which can be used as switching transition for the shape-memory effect can be attributed to the crystalline poly(epsilon-hydroxycaproate) phase. At temperatures below T(m) the elastic properties are dominated by these physical cross-links. At temperatures higher than T(m) the E modulus of the amorphous polymer networks is lowered by up to 2 orders of magnitude, depending on the chemical cross-link density. Copolymer networks based on macrodimethacrylates with a M(n) of up to 13,500 g x mol(-1) and a maximum glycolate content of 21 mol % show quantitative strain recovery rates in stress-controlled cyclic thermomechanical experiments. Hydrolytic degradation experiments of polymer networks performed in phosphate buffer solution at 37 degrees C show that the degradation rate can be accelerated by increasing the glycolate content and decelerated by the incorporation of n-butyl acrylate. PMID:17305394

Kelch, Steffen; Steuer, Susi; Schmidt, Annette M; Lendlein, Andreas

2007-03-01

317

A bioactive "self-fitting" shape memory polymer scaffold with potential to treat cranio-maxillo facial bone defects.  

PubMed

While tissue engineering is a promising alternative for treating critical-sized cranio-maxillofacial bone defects, improvements in scaffold design are needed. In particular, scaffolds that can precisely match the irregular boundaries of bone defects as well as exhibit an interconnected pore morphology and bioactivity would enhance tissue regeneration. In this study, a shape memory polymer (SMP) scaffold was developed exhibiting an open porous structure and the capacity to conformally "self-fit" into irregular defects. The SMP scaffold was prepared via photocrosslinking of poly(?-caprolactone) (PCL) diacrylate using a SCPL method, which included a fused salt template. A bioactive polydopamine coating was applied to coat the pore walls. Following exposure to warm saline at T>T(trans) (T(trans)=T(m) of PCL), the scaffold became malleable and could be pressed into an irregular model defect. Cooling caused the scaffold to lock in its temporary shape within the defect. The polydopamine coating did not alter the physical properties of the scaffold. However, polydopamine-coated scaffolds exhibited superior bioactivity (i.e. formation of hydroxyapatite in vitro), osteoblast adhesion, proliferation, osteogenic gene expression and extracellular matrix deposition. PMID:25063999

Zhang, Dawei; George, Olivia J; Petersen, Keri M; Jimenez-Vergara, Andrea C; Hahn, Mariah S; Grunlan, Melissa A

2014-11-01

318

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

PubMed

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

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

2013-11-26

319

Conductance quantization in a Ag filament-based polymer resistive memory.  

PubMed

Resistive switching and conductance quantization are systematically studied in a Ag/poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester/indium-tin oxide sandwich structure. The observed bipolar switching behavior can be attributed to the formation and dissolution of Ag filaments during positive and negative voltage sweeps, respectively. More importantly, conductance quantization with both integer and half integer multiples of single atomic point contact can be realized by slowing down the voltage sweep speed as well as by pulse measurement. The former may reflect the formed Ag filaments with different atomic point contacts, while the latter probably originates from the interaction between the Ag filaments and the elemental hydrogen provided by the organic storage medium. With appropriate current compliances, low resistance states with desired quantized conductance values are successfully achieved, thus showing the potential for ultrahigh density memory applications. Besides, 100 successive switching cycles with densely distributed resistance values of each resistance state and extrapolated retention properties over ten years are also demonstrated. PMID:23893907

Gao, Shuang; Zeng, Fei; Chen, Chao; Tang, Guangsheng; Lin, Yisong; Zheng, Zifeng; Song, Cheng; Pan, Feng

2013-08-23

320

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

NASA Astrophysics Data System (ADS)

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

Chen, Zhongbi; Krishnaswamy, Sridhar

2014-03-01

321

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

NASA Astrophysics Data System (ADS)

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

Savalia, Krupa

322

Generation of anti-NAG-2 mAb from patients' memory B cells: implications for a novel therapeutic strategy in systemic sclerosis.  

PubMed

We have previously reported that antibodies directed against the cytomegalovirus-derived protein UL94 cross react with the cell surface tetraspanin transmembrane 4 superfamily member 7 (TM4SF7 or NAG-2) molecule inducing apoptosis of endothelial cells and activation of fibroblasts in patients with systemic sclerosis (SSc). We aimed at generating a non-functional mAb directed against NAG-2 from patients' memory B cells. Direct and competitive ELISA methods have been used to evaluate the binding of antibodies from scleroderma patients' and controls' sera to the NAG-2 peptide. IgG memory B cells were sorted, EBV transformed and cloned to obtain NAG-2-specific mAbs. Endothelial cells and fibroblasts were cultured under standard conditions and used for functional assays. Anti-NAG-2-purified antibodies obtained from patients' Ig induce endothelial cell apoptosis and fibroblast proliferation. Patients' Igs depleted of the anti-NAG-2 fraction do not exert such functional activity. Therefore, the NAG-2 molecule represents a potential novel candidate for therapeutic intervention in SSc. Here, we describe the generation of a human mAb directed against the NAG-2 molecule. Such mAb does not retain any functional property and is able to block the effect of serum pathogenetic anti-NAG-2 antibodies. The majority of SSc patients present antibodies directed against tetraspanin NAG-2 and mediate both endothelial cell apoptosis and fibroblast proliferation, features of the disease. The anti-NAG-2 human mAb we have obtained blocks signal transduction and therefore may be a potential candidate for a new treatment in SSc, a disease where the current biological therapies have little or no efficacy. PMID:20207716

Traggiai, Elisabetta; Lunardi, Claudio; Bason, Caterina; Dolcino, Marzia; Tinazzi, Elisa; Corrocher, Roberto; Puccetti, Antonio

2010-05-01

323

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

324

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

325

Shape-memory materials: shape-reprogrammable polymers: encoding, erasing, and re-encoding (adv. Mater. 48/2014).  

PubMed

Shape reprogramming in a polymer is demonstrated by R. R. Kohlmeyer, J. Chen, and co-workers on page 8114. Prescribed 3D geometric information can be encoded, decoded, erased, and re-encoded. In essence, the shape-reprogrammable polymer acts as computer hardware that can be reformatted and reprogrammed repeatedly, giving the potential for the polymer to be repurposed directly without going through material disposal and recycling. PMID:25515257

Kohlmeyer, Ryan R; Buskohl, Philip R; Deneault, James R; Durstock, Michael F; Vaia, Richard A; Chen, Jian

2014-12-01

326

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

NASA Astrophysics Data System (ADS)

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

Zimkowski, Michael M.

327

Therapeutic and Prognostic Value of Modal Number of Chromosomes at the Blastic Phase of Philadelphia-Chromosome-Positive Chronic Myeloid Leukemia: Comparison Based on the Same Criteria between Nagasaki University and Roswell Park Memorial Institute  

Microsoft Academic Search

In a comparison of 47 patients with Philadelphia-chromosome (Ph)-positive chronic myeloid leukemia (CML) in the Nagasaki University School of Medicine and 64 patients with the same disease in the Roswell Park Memorial Institute, the correlation between the modal number of chromosomes and the therapeutic response and\\/or survival after the onset of the blastic phase (BP) was evaluated. The patients were

Naoki Sadamori; Ei-ichi Yao; Mariko Mine; Seiji Tokunaga; Masako Matsunaga; Hideo Nakamura; Ippei Sasagawa; Takahiro Itoyama; Toshihisa Hayashibara; Avery A. Sandberg

1992-01-01

328

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

329

Laser-induced nondestructive patterning of a thin ferroelectric polymer film with controlled crystals using Ge8Sb2Te11 alloy layer for nonvolatile memory.  

PubMed

We present a simple but robust nondestructive process for fabricating micropatterns of thin ferroelectric polymer films with controlled crystals. Our method is based on utilization of localized heat arising from thin Ge(8)Sb(2)Te(11) (GST) alloy layer upon exposure of 650 nm laser. The heat was generated on GST layer within a few hundred of nanosecond exposure and subsequently transferred to a thin poly(vinylidene fluoride-co-trifluoroethylene) film deposited on GST layer. By controlling exposure time and power of the scanned laser, ferroelectric patterns of one or two microns in size are fabricated with various shape. In the micropatterned regions, ferroelectric polymer crystals were efficiently controlled in both degree of the crystallinity and the molecular orientations. Nonvolatile memory devices with laser scanned ferroelectric polymer layers exhibited excellent device performance of large remnant polarization, ON/OFF current ratio and data retention. The results are comparable with devices containing ferroelectric films thermally annealed at least for 2 h, making our process extremely efficient for saving time. Furthermore, our approach can be conveniently combined with a number of other functional organic materials for the future electronic applications. PMID:25127181

Bae, Insung; Kim, Richard Hahnkee; Hwang, Sun Kak; Kang, Seok Ju; Park, Cheolmin

2014-09-10

330

Polymeric Anti-HIV Therapeutics.  

PubMed

The scope of this review is to highlight the application of polymer therapeutics in an effort to curb the transmission and infection of the human immunodeficiency virus (HIV). Following a description of the HIV life cycle, the use of approved antiretroviral drugs that inhibit critical steps in the HIV infection process is highlighted. After that, a comprehensive overview of the structure and inhibitory properties of polymeric anti-HIV therapeutic agents is presented. This overview will include inhibitors based on polysaccharides, synthetic polymers, dendritic polymers, polymer conjugates as well as polymeric DC-SIGN antagonists. The review will conclude with a section that discusses the applications of polymers and polymer conjugates as systemic and topical anti-HIV therapeutics. PMID:25185484

Danial, Maarten; Klok, Harm-Anton

2014-09-01

331

Stress-induced melting of crystals in natural rubber: a new way to tailor the transition temperature of shape memory polymers.  

PubMed

Lightly cross-linked natural rubber (NR, cis-1,4-polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain-induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain-stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature T(trig) (?) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal-stabilized SMP after programming. PMID:22760997

Heuwers, Benjamin; Quitmann, Dominik; Katzenberg, Frank; Tiller, Joerg C

2012-09-26

332

Physical ageing of a PU-based shape memory polymer: Influence on their applicability to the development of medical devices  

Microsoft Academic Search

The variation in the properties of polymeric materials through ageing has considerable implications, since it affects the performance of any associated devices. Specially in the case of implantable devices with shape memory, any change in the switching temperature can give rise to problems in the thermal activation of the geometrical changes necessary to treat certain pathologies.This paper presents a study

V. Lorenzo; A. Díaz-Lantada; P. Lafont; H. Lorenzo-Yustos; C. Fonseca; J. Acosta

2009-01-01

333

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

2009-06-01

334

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

PubMed

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

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

2014-02-26

335

ZnO-based nonvolatile memory thin-film transistors with polymer dielectric\\/ferroelectric double gate insulators  

Microsoft Academic Search

The authors report on the fabrication of a top-gate ZnO thin-film transistor (TFT) with a polymer dielectric\\/ferroelectric double-layer gate insulator that was formed on patterned ZnO through a sequential spin-casting process of 450-nm-thick poly-4-vinylphenol (PVP) and 200-nm-thick poly(vinylidene fluoride\\/trifluoroethylene) [P(VDF\\/TrFE)]. Compared to the single P(VDF\\/TrFE) layer, double layer shows remarkably reduced leakage current with the aid of the PVP buffer.

Seok Hwan Noh; Wonjun Choi; Min Suk Oh; D. K. Hwang; Kimoon Lee; Seongil Im; Sungjin Jang; Eugene Kim

2007-01-01

336

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

2012-08-01

337

Evolution of microstructure during shape memory cycling of a main-chain liquid crystalline elastomer  

E-print Network

Available online 28 March 2013 Keywords: Liquid crystalline elastomer Shape memory polymer Polymer microstructure a b s t r a c t The field of shape memory polymers (SMPs) has been dominated by polymeric systems, and microfluidics. Ã? 2013 Elsevier Ltd. All rights reserved. 1. Introduction Shape memory polymers [1e3] are a class

Mather, Patrick T.

338

"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

339

Wrinkling atop Shape Memory Materials  

NASA Astrophysics Data System (ADS)

Many surface related properties, such as surface roughness, surface tension and reflection etc are heavily dependent on the surface morphology of materials. Patterned surfaces may have significant effects on these properties. In this paper, we compare wrinkles produced atop three different types of shape memory materials, namely, shape memory alloy, shape memory polymer and shape memory hybrid. We show the advantages and disadvantages of them in terms of the processing techniques and the resultant wrinkle patterns.

Sun, L.; Zhao, Y.; Huang, W. M.; Purnawali, H.; Fu, Y. Q.

2012-04-01

340

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

341

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

2013-09-01

342

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

PubMed Central

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

2014-01-01

343

Cite this: RSC Advances, 2013, 3, Water-triggered shape memory of multiblock  

E-print Network

of a water-triggered shape memory polymer (SMP) family, PCL­PEG based thermoplastic polyurethanes (TPUs, actuators, and medical devices. Introduction Shape memory polymers (SMPs) are a class of stimuli- responsive

Mather, Patrick T.

344

A Bioreducible Polymer for Efficient Delivery of Fas-Silencing siRNA into Stem Cell Spheroids and Enhanced Therapeutic Angiogenesis**  

PubMed Central

This paper describes a bioreducible polymer for efficient delivery of Fas-silencing small interfering RNA (Fas siRNA) into human mesenchymal stem cells (hMSCs). The genetically modified hMSCs could be formulated as spheroids with enlarged sizes (? 800 ?m in diameter) to enhance their angiogenic efficacy. The Fas siRNA delivered into the cytoplasm of hMSCs via the bioreducible polymer could efficiently inhibit Fas expression, leading to effective inhibition of hypoxia-induced apoptosis in the core of an enlarged spheroid of hMSCs. The enlarged spheroid not only increased the number of viable hMSCs but also significantly enhanced the secretion of bioactive angiogenic growth factors per hMSC relative to small spheroids that were not treated with Fas siRNA. Twenty-eight days after transplantation into mouse with ischemic hindlimbs, the enlarged hMSC spheroids significantly enhanced cell survival, limb salvage, blood perfusion, and vessel formation while substantially reducing muscle degeneration and tissue fibrosis. This study demonstrates a promising strategy that combines siRNA and spheroid-based stem cell therapies using a stimuli-responsive nonviral siRNA carrier for the efficient treatment of ischemic disease. PMID:23074025

Shim, Min Suk; Bhang, Suk Ho; Yoon, Kyunghwan; Choi, Kyunghee

2013-01-01

345

UTILIZING THE SHAPE MEMORY EFFECT TO ENABLE FLEXIBLE ELECTRONICS  

E-print Network

UTILIZING THE SHAPE MEMORY EFFECT TO ENABLE FLEXIBLE ELECTRONICS Abhishek Raj The University performance Accurately map electrical signals in the heart and brain E-newspaper displays under strain #12;The Shape Memory Effect Shape-memory polymer (SMP) orthopedic cast 4 #12;Polymer

Petta, Jason

346

Therapeutics 1995.  

PubMed

A joint conference on therapeutics with the Faculty of Pharmaceutical Medicine was held at the Royal College of Physicians on 28 June 1995, organised by Professor M C L'E Orme. A wide variety of topics was covered ranging from management of acute poisoning to the treatment of myocardial infarction, as well as the teaching of therapeutics in the new undergraduate medical curriculum. The aim of the conference was to provide an overview of the most recent therapeutic developments and controversies in the specific subject areas covered. PMID:8748111

Pirmohamed, M; Martin, U

1995-01-01

347

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

2013-06-10

348

Shape Memory Assisted Self-Healing Coating Xiaofan Luo  

E-print Network

approaches. The first approach utilizes pretensioned shape memory alloy (SMA) wires12-14 or shape memory polymer (SMP) fibers15,16 that, when activated, exert a contractual force that pulls the crack surfaces

Mather, Patrick T.

349

Memory loss  

MedlinePLUS

Forgetfulness; Amnesia; Impaired memory; Loss of memory; Amnestic syndrome; Dementia - memory loss ... or severe illness, including brain surgery Transient global amnesia (sudden, temporary loss of memory) of unclear cause ...

350

Mechanical memory  

DOEpatents

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

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

2006-05-16

351

Mechanical memory  

DOEpatents

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

Gilkey, Jeffrey C. (Albuquerque, NM); Duesterhaus, Michelle A. (Albuquerque, NM); Peter, Frank J. (Albuquerque, NM); Renn, Rosemarie A. (Alburquerque, NM); Baker, Michael S. (Albuquerque, NM)

2006-08-15

352

Microfabricated therapeutic actuators and release mechanisms therefor  

SciTech Connect

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

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

2000-05-09

353

Microfabricated therapeutic actuators and release mechanisms therefor  

DOEpatents

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

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

2000-01-01

354

Longevity pathways and memory aging  

PubMed Central

The aging process has been associated with numerous pathologies at the cellular, tissue, and organ level. Decline or loss of brain functions, including learning and memory, is one of the most devastating and feared aspects of aging. Learning and memory are fundamental processes by which animals adjust to environmental changes, evaluate various sensory signals based on context and experience, and make decisions to generate adaptive behaviors. Age-related memory impairment is an important phenotype of brain aging. Understanding the molecular mechanisms underlying age-related memory impairment is crucial for the development of therapeutic strategies that may eventually lead to the development of drugs to combat memory loss. Studies in invertebrate animal models have taught us much about the physiology of aging and its effects on learning and memory. In this review we survey recent progress relevant to conserved molecular pathways implicated in both aging and memory formation and consolidation. PMID:24926313

Gkikas, Ilias; Petratou, Dionysia; Tavernarakis, Nektarios

2014-01-01

355

[Therapeutic bath and Alzheimer's disease].  

PubMed

To safeguard the quality of life of people suffering from Alzheimer's by the creation of an individual care plan, by identifying pleasurable activities or fond memories of the individual, thereby restoring a sense of present well being. The therapeutic bath, an action which might be considered somewhat straightforward, in fact enables the measurement of the capability of an elderly person to respond to stimulation by medical staff. PMID:22852495

Bourzeau, Madeleine

2012-01-01

356

Cache Memories  

Microsoft Academic Search

Cache memories are used in modern, medium and high-speed CPUs to hold temporarily those portions of the contents of main memory which are {believed to be) currently in use. Since instructions and data in cache memories can usually be referenced in 10 to 25 percent of the time required to access main memory, cache memories permit the executmn rate of

Alan Jay Smith

1982-01-01

357

Cache memories  

E-print Network

Cache memories are used in modern, medium and high-speed CPUs to hold temporarily those portions of the contents of main memory which are {believed to be) currently in use. Since instructions and data in cache memories can usually be referenced in 10 to 25 percent of the time required to access main memory, cache memories permit the

Alan Jay Smith

1982-01-01

358

Polymer films  

DOEpatents

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

Granick, Steve (Champaign, IL); Sukhishvili, Svetlana A. (Maplewood, NJ)

2008-12-30

359

than 10 mol% has no further influence on the shape-memory properties. After two cycles of UV irradiation, the clear film turned  

E-print Network

% in a test with 1max ¼ 20%, and 5% for 1max ¼ 50%. Relative to thermoresponsive shape-memory polymers, the strain-recovery rate of photoresponsive shape-memory polymers is comparable, but the strain-fixity rate as in the case of thermoresponsive shape-memory polymers. The elastic contraction of the stretched chain segments

Tackley, Paul J.

360

Frontiers in Alzheimer's Disease Therapeutics  

PubMed Central

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

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

2011-01-01

361

Cognitive memory.  

PubMed

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

Widrow, Bernard; Aragon, Juan Carlos

2013-05-01

362

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

363

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

364

Microgravity Polymers  

NASA Technical Reports Server (NTRS)

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

1986-01-01

365

Polymers Presentation  

NSDL National Science Digital Library

This 15 page PowerPoint contains the presentation for the polymers module from Nano-Link. This lesson requires a background in eight grade science. Various details of polymers are discussed including molecular structures, cross-linked polymers, and ringed polymers. Lastly, an activity to explore cross-linked polymers is included. Visitors must complete a quick and free registration to access the materials.

366

Memory protection  

NASA Technical Reports Server (NTRS)

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

Denning, Peter J.

1988-01-01

367

Episodic memories in anxiety disorders: clinical implications.  

PubMed

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

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

2014-01-01

368

Frequency of use of diagnostic and manual therapeutic procedures of the spine currently taught at the Canadian Memorial Chiropractic College: A preliminary survey of Ontario chiropractors. Part 2 – procedure usage rates  

PubMed Central

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, based on a list of currently taught procedures at CMCC. In Part 1 of this study (published previously), the demographics and practice patterns of the respondents were presented. Part 2 of this study (presented here) reports on the utilization rates of spinal diagnostic and therapeutic procedures by the respondents. Methods: The study consisted of a paper-based survey that was sent to 500 randomly selected Ontario chiropractors who responded confidentially. Survey questions inquired into demographic and practice style characteristics as well as the frequency with which spinal diagnostic and therapeutic procedures were performed. Results: There were 108 respondents to the survey, giving a response rate of 22.4%. Frequency of use of diagnostic procedures fell into three broad categories: (i) those tests that are almost always performed, (ii) those tests that are almost always performed by two-thirds to one-half of patients, and (iii) those tests that are virtually never used. By comparison, respondents utilized the same therapeutic procedures for patients care less consistently. Conclusions: Despite a low response rate, respondents reported mostly relying on static and motion palpation, joint play, neurological tests, and ranges of motion when assessing their patients. Due to a low response rate, the results of this study may not be generalizable to all Ontario chiropractors. PMID:23754862

Gleberzon, Brian; Stuber, Kent

2013-01-01

369

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

370

Epigenetic memory: the Lamarckian brain.  

PubMed

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

Fischer, Andre

2014-05-01

371

Virtual memory  

NASA Technical Reports Server (NTRS)

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

Denning, P. J.

1986-01-01

372

Tailormade Polymers  

NASA Astrophysics Data System (ADS)

The national Symposium of the Division of Macromolecular Chemistry of the GDCh (Gesellschaft Deutscher Chemiker) in March 2000 was held in Merseburg with a topic of Tailormade Polymers. The scientific program was divided in two parts: contemporary activities in polymer synthesis and the tailoring of polymer properties by suitable modification steps. An excellent insight into contemporary activities in polymer synthesis, modification and characterization was given. A selection of the contributions is presented in this volume.

Cherdron, Harald; Sandner, Barbara; Schenk, H. U.; Voit, Brigitte; Meisel, I.; Kniep, C. S.; Spiegel, S.

2001-05-01

373

Piezoelectric Polymers  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

374

Consolidating memories.  

PubMed

Our own experiences, as well as the findings of many studies, suggest that emotionally arousing experiences can create lasting memories. This autobiographical article provides a brief summary of the author's research investigating neurobiological systems responsible for the influence of emotional arousal on the consolidation of lasting memories. The research began with the finding that stimulant drugs enhanced memory in rats when administered shortly after training. Those findings suggested the possibility that endogenous systems activated by arousal might influence neural processes underlying memory consolidation. Subsequent findings that adrenal stress hormones activated by learning experiences enhance memory consolidation provided strong evidence supporting this hypothesis. Other findings suggest that the enhancement is induced by stress hormone activation of the amygdala. The findings also suggest that the basolateral amygdala modulates memory consolidation via its projections to brain regions involved in processing different aspects and forms of memory. This emotional-arousal-activated neurobiological system thus seems to play an important adaptive role in insuring that the strength of our memories will reflect their emotional significance. PMID:25559113

McGaugh, James L

2015-01-01

375

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

376

Flipping the switch: mechanisms that regulate memory consolidation.  

PubMed

Memories can follow different processing routes. For example, some memories are enhanced during wakefulness while the enhancement of others is delayed until sleep. Converging evidence suggests that inhibitory mechanisms can 'switch off' a processing route, thereby preventing the consolidation of select memories during wakefulness. This switch arises due to an actively imposed 'bottleneck' generated by the brain. Transcranial magnetic stimulation (TMS) can interfere with this bottleneck, allowing multiple memories to be consolidated simultaneously during wakefulness. This bottleneck restricts memory processing, perhaps allowing for the selection of only rewarded, or relevant memories. Overall, this bottleneck makes it necessary to select memories for consolidation, and the state of a switch ('on' or 'off') determines whether or not a memory is subsequently consolidated. Understanding how memory consolidation is regulated may provide novel therapeutic strategies. PMID:25240672

Breton, Jocelyn; Robertson, Edwin M

2014-12-01

377

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

378

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

379

Nonvolatile memory device based on Ag nanoparticle: Characteristics improvement  

Microsoft Academic Search

A single layer memory device based on silver nanoparticles has been fabricated. The device exhibits electrical bistability and nonvolatile memory phenomenon. The performance of the device improved (in terms of On\\/Off ratio, switching cycles, and retention time) when an additional polymer (PMMA) layer was deposited prior to nanoparticles deposition. The retention time and switching cycles of the device improved a

Biswanath Mukherjee; Moumita Mukherjee

2009-01-01

380

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

381

Learning, Memory, & Attention Instructor  

E-print Network

1 COGS 101B: Learning, Memory, & Attention · Welcome! · Instructor ­ Dr. Coulson ­ Email: coulson Attention ­ Divided Attention ­ Automaticity ­ Attentional Capture · Immediate Memory ­ Sensory Memory ­ Short-Term Memory ­ Working Memory · Long-Term Memory ­ Levels of Processing ­ Memory Systems

Coulson, Seana

382

POW Memory  

NSDL National Science Digital Library

Most people think eyewitness testimony is the best possible evidence against an alleged criminal -- especially when that testimony comes from the victim. But people who survive terrifying situations may actually have surprisingly unreliable memories of who or what caused them.

Science Update;

2004-07-12

383

Fullerene embedded shape memory nanolens array.  

PubMed

Securing fragile nanostructures against external impact is indispensable for offering sufficiently long lifetime in service to nanoengineering products, especially when coming in contact with other substances. Indeed, this problem still remains a challenging task, which may be resolved with the help of smart materials such as shape memory and self-healing materials. Here, we demonstrate a shape memory nanostructure that can recover its shape by absorbing electromagnetic energy. Fullerenes were embedded into the fabricated nanolens array. Beside the energy absorption, such addition enables a remarkable enhancement in mechanical properties of shape memory polymer. The shape memory nanolens was numerically modeled to impart more in-depth understanding on the physics regarding shape recovery behavior of the fabricated nanolens. We anticipate that our strategy of combining the shape memory property with the microwave irradiation feature can provide a new pathway for nanostructured systems able to ensure a long-term durability. PMID:24253423

Jeon, Sohee; Jang, Jun Young; Youn, Jae Ryoun; Jeong, Jun-Ho; Brenner, Howard; Song, Young Seok

2013-01-01

384

Fullerene Embedded Shape Memory Nanolens Array  

NASA Astrophysics Data System (ADS)

Securing fragile nanostructures against external impact is indispensable for offering sufficiently long lifetime in service to nanoengineering products, especially when coming in contact with other substances. Indeed, this problem still remains a challenging task, which may be resolved with the help of smart materials such as shape memory and self-healing materials. Here, we demonstrate a shape memory nanostructure that can recover its shape by absorbing electromagnetic energy. Fullerenes were embedded into the fabricated nanolens array. Beside the energy absorption, such addition enables a remarkable enhancement in mechanical properties of shape memory polymer. The shape memory nanolens was numerically modeled to impart more in-depth understanding on the physics regarding shape recovery behavior of the fabricated nanolens. We anticipate that our strategy of combining the shape memory property with the microwave irradiation feature can provide a new pathway for nanostructured systems able to ensure a long-term durability.

Jeon, Sohee; Jang, Jun Young; Youn, Jae Ryoun; Jeong, Jun-Ho; Brenner, Howard; Song, Young Seok

2013-11-01

385

Fullerene Embedded Shape Memory Nanolens Array  

PubMed Central

Securing fragile nanostructures against external impact is indispensable for offering sufficiently long lifetime in service to nanoengineering products, especially when coming in contact with other substances. Indeed, this problem still remains a challenging task, which may be resolved with the help of smart materials such as shape memory and self-healing materials. Here, we demonstrate a shape memory nanostructure that can recover its shape by absorbing electromagnetic energy. Fullerenes were embedded into the fabricated nanolens array. Beside the energy absorption, such addition enables a remarkable enhancement in mechanical properties of shape memory polymer. The shape memory nanolens was numerically modeled to impart more in-depth understanding on the physics regarding shape recovery behavior of the fabricated nanolens. We anticipate that our strategy of combining the shape memory property with the microwave irradiation feature can provide a new pathway for nanostructured systems able to ensure a long-term durability. PMID:24253423

Jeon, Sohee; Jang, Jun Young; Youn, Jae Ryoun; Jeong, Jun-ho; Brenner, Howard; Song, Young Seok

2013-01-01

386

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

387

Thermomechanical modeling of a shape memory polymer  

E-print Network

-dashpot type analogy and the resulting equations are classified as state-equations and suitable kinetic equations for the recoverable-energy elements and the dissipative elements in the model respectively. These elements have mechanical properties which vary...

Ghosh, Pritha B.

2009-05-15

388

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.

David Teegarden

2004-01-01

389

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

390

Nonvolatile memory device based on Ag nanoparticle: Characteristics improvement  

NASA Astrophysics Data System (ADS)

A single layer memory device based on silver nanoparticles has been fabricated. The device exhibits electrical bistability and nonvolatile memory phenomenon. The performance of the device improved (in terms of On/Off ratio, switching cycles, and retention time) when an additional polymer (PMMA) layer was deposited prior to nanoparticles deposition. The retention time and switching cycles of the device improved a lot and on/off current ratio of the device increased by more than three orders of magnitude. The ability to write, erase, read, and refresh the electrical states of the polymer-nanoparticle composite fulfills the functionality of a dynamic random access memory.

Mukherjee, Biswanath; Mukherjee, Moumita

2009-04-01

391

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

392

Reversible recovery of nanoimprinted polymer structures.  

PubMed

A shape memory polymer, Nafion, has its shape memory simultaneously programmed and patterned with micro- and nanometer-scale surface textures using a nanoimprint process. Highly ordered and well-defined micro- and nanometer surface textures, for example, high aspect ratio (~5) micropillars, form the permanent shape memory of the Nafion films. When damaged, these permanently shaped micro- and nanostructures possess repair ability through a heat treatment. Reversible recoveries of the damages caused by mechanical and irradiation exposure have been demonstrated. The recovery retains above 90% of the structural fidelity, which is comparable to the shape recovery in bulk film. PMID:23841687

Kustandi, Tanu Suryadi; Loh, Wei Wei; Shen, Lu; Low, Hong Yee

2013-08-20

393

Therapeutic use exemption.  

PubMed

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. PMID:16799102

Dvorak, J; Kirkendall, D; Vouillamoz, M

2006-07-01

394

Polymers Guide  

NSDL National Science Digital Library

This 21 page document contains an instructor guide for the polymers module from Nano-Link. The activity requires a background in eight grade science. The document includes background information on polymers, a hands-on learning activity, questions to check understanding, links to multimedia resources, and further readings. Visitors must complete a quick and free registration to access the materials.

395

A coarse grained model of polymer networks focusing on the intermediate length scales  

E-print Network

We propose a coarse-grained model for polymer chains and polymer networks based on the meso-scale dynamics. The model takes the internal degrees of freedom of the constituent polymer chains into account using memory functions and colored noises. We apply our model to dilute polymer solutions and polymer networks. A numerical simulation on a dilute polymer solution demonstrates the validity of the assumptions on the dynamics of our model. By applying this model to polymer networks, we find a transition in the dynamical behavior from an isolated chain state to a network state.

Takashi Shibata; Hidemitsu Furukawa; Toshihiro Kawakatsu

2008-03-29

396

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

397

Therapeutic Crisis Intervention.  

ERIC Educational Resources Information Center

Describes Therapeutic Crisis Intervention (TCI) program as providing staff with skills, knowledge, and confidence to manage child in crisis to bring about a "maximum amount of lasting response." Contends that, by applying principles of TCI training, direct care worker can attain therapeutic control and maintain dignity of both adult and child…

Holden, Martha J.; Powers, Jane Levine

1993-01-01

398

Polymer nanolithography  

NASA Astrophysics Data System (ADS)

Nanolithography involves making patterns of materials with at least one dimension less than 100 nanometers. Surprisingly, writable CDs can provide polymer nanostructures for pennies a piece. Building on work previously done in the Drain lab, with an inherited home-built oven press, this research will explore the relationships between polymer chemical reactivity, polymer printing, and material surface energies. In addition, a relatively inexpensive entry point into high school and undergraduate education in nanolithography is presented. The ability to pattern cheaply at the nanoscale and microscale is necessary and attractive for many technologies towards biosensors, organic light emitting diodes, identification tags, layered devices, and transistors.

Vance, Jennifer M.

399

Painting memory  

Microsoft Academic Search

This article develops the Victorian fascination with the ways in which one visualizes, in the mind's eye, what is in fact invisible.†† In particular, it explores what happens when one exercises the faculty of memory.†† It argues that developments in painting during the period – especially the shift from an emphasis on realism to styles which invoke a spectator's subjective

Kate Flint

2003-01-01

400

Memory Loss  

Microsoft Academic Search

In the wake of the current storm over what constitutes truth – non-fiction – and what is “made up” – fictional – my fascination with the flexibility of memory is suddenly more than a little apropos. Current literary events notwithstanding, I grew up under a dark veil of depression, which seemingly “erased” my childhood. It wasn’t until I delved into

Anne M. McDermott

2006-01-01

401

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

402

Spatial memory, recognition memory, and the hippocampus  

E-print Network

Spatial memory, recognition memory, and the hippocampus Nicola J. Broadbent*, Larry R. Squire. Squire, August 27, 2004 There is wide agreement that spatial memory is dependent on the integrity recognition memory is not as clear. We examined the relationship between hippocampal lesion size and both

Squire, Larry R.

403

Memory Technologies Vivek Asthana  

E-print Network

Memory Technologies Vivek Asthana 13th Mar 2013 #12;13-Mar-13 2 Memory Usage (2025) #12;13-Mar-13 3 Outline What is a Memory Current Memory technologies · SRAM · DRAM · Flash Upcoming Memory technologies · MRAM · PCRAM · FeRAM · ... #12;13-Mar-13 4 What is a Memory Memory cell: Binary data storage element

Kumar, M. Jagadesh

404

Therapeutics for Bowel Disorders  

Cancer.gov

The National Cancer Institute''s Laboratory of Metabolism is seeking statements of capability or interest from parties interested in collaborative research to further develop, evaluate, or commercialize therapeutics that ameliorate bowel disorders.

405

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.

406

Memory on the move  

Microsoft Academic Search

The author describes how, competing for the US $ 11 billion portable electronic device memory market are several venerable but revitalized memory systems as well as new storage technologies: flash memory cards; PC memory cards; and small disk drives. Flashers, a relatively young technology contain one or more nonvolatile solid-state memory chips. They have no moving parts and retain data

R. M. Sherwin

2001-01-01

407

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

408

Memory Systems Doug Burger  

E-print Network

Memory Systems Doug Burger University of Wisconsin-Madison A computer's memory system and produces. A perfect memory system is one that can supply immediately any datum that the CPU requests. This ideal memory is not practically implementable, however, as the three factors of memory capacity, speed

Burger, Doug

409

Antimocrobial Polymer  

DOEpatents

A polymeric composition having antimicrobial properties and a process for rendering the surface of a substrate antimicrobial are disclosed. The composition comprises a crosslinked chemical combination of (i) a polymer having amino group-containing side chains along a backbone forming the polymer, (ii) an antimicrobial agent selected from quaternary ammonium compounds, gentian violet compounds, substituted or unsubstituted phenols, biguanide compounds, iodine compounds, and mixtures thereof, and (iii) a crosslinking agent containing functional groups capable of reacting with the amino groups. In one embodiment, the polymer is a polyamide formed from a maleic anhydride or maleic acid ester monomer and alkylamines thereby producing a polyamide having amino substituted alkyl chains on one side of the polyamide backbone; the crosslinking agent is a phosphine having the general formula (A)3P wherein A is hydroxyalkyl; and the antimicrobial agent is chlorhexidine, dimethylchlorophenol, cetyl pyridinium chloride, gentian violet, triclosan, thymol, iodine, and mixtures thereof.

McDonald, William F. (Utica, OH); Huang, Zhi-Heng (Walnut Creek, CA); Wright, Stacy C. (Columbus, GA)

2005-09-06

410

Memory Coalescing Techniques 1 Accessing Global and Shared Memory  

E-print Network

Memory Coalescing Techniques 1 Accessing Global and Shared Memory memory coalescing to global memory avoiding bank conflicts in shared memory 2 Memory Coalescing Techniques accessing global memory for a matrix using shared memory for coalescing 3 Avoiding Bank Conflicts computing consecutive powers MCS 572

Verschelde, Jan

411

Engineered therapeutic-releasing nanoporous anodic alumina-aluminum wires with extended release of therapeutics.  

PubMed

In this study, we present a nanoengineered therapeutic-releasing system based on aluminum wires featuring nanoporous anodic alumina layers and chitosan coatings. Nanoporous anodic alumina layers are produced on the surface of aluminum wires by electrochemical anodization. These nanoporous layers with precisely engineered nanopore geometry are used as nanocontainers for bovine serum albumin molecules labeled with fluorescein isothiocyanate (BSA-FITC), which is selected as a model drug. The surface of these therapeutic-releasing implants is coated with a biocompatible and biodegradable polymer, chitosan, in order to achieve a sustained release of protein over extended periods of time. The performance of this therapeutic-releasing device is systematically assessed through a series of experiments under static and dynamic flow conditions. In these experiments, the effect of such parameters as the number of layers of chitosan coating and the temperature and pH of the eluting medium is established. The obtained results reveal that the proposed therapeutic-releasing system based on nanoporous aluminum wires can be engineered with sustained release performance for up to 6.5 weeks, which is a critical factor for medical treatments using sensitive therapeutics such as proteins and genes when a localized delivery is desired. PMID:25625878

Law, Cheryl Suwen; Santos, Abel; Kumeria, Tushar; Losic, Dusan

2015-02-18

412

In vitro cytotoxicity testing of AB-polymer networks based on oligo(epsilon-caprolactone) segments after different sterilization techniques.  

PubMed

Recently developed versatile biodegradable polymeric biomaterial offer new therapeutic options in numerous medical fields. Biocompatibility is a crucial requirement for the biomedical application of biomaterials, including the sterilization of these materials with the use of accepted protocols. Ethylene-oxide (EO) and low-temperature plasma (LTP) sterilization are frequently used low-temperature sterilization technologies for heat-sensitive materials. The agarose diffusion assay is a recommended cell-screening test to assess the cytotoxicity of biomaterials in vitro. The sensitivity of the agarose assay can be increased by using a modified computer-based image-analysis system. The influence of EO and LTP sterilization on the cytotoxicity of a versatile polymer system of shape-memory polymer networks based on oligo (epsilon-caprolactone) dimethacrylate and n-butyl acrylate was investigated. Statistically significant differences in the rate of cell lysis after EO and LTP sterilization of the polymer samples were detected by using this modified quantification system. The influence of the different sterilization techniques on the cytotoxicity of the polymeric material, as well as the clinical relevance of the described differences, are discussed. PMID:14598399

Rickert, Dorothee; Lendlein, A; Schmidt, A M; Kelch, S; Roehlke, W; Fuhrmann, R; Franke, R P

2003-11-15

413

Self-Folding Origami: Shape Memory Composites Activated by Uniform Heating  

E-print Network

materials and tools. The folding mechanism based on the in-plane contraction of a sheet of shape memory polymer is modeled, and parameters for the design of composites that self-fold into target shapes

Wood, Robert

414

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 ...

415

Materials for Diabetes Therapeutics  

PubMed Central

This review is focused on the materials and methods used to fabricate closed-loop systems for type 1 diabetes therapy. Herein, we give a brief overview of current methods used for patient care and discuss two types of possible treatments and the materials used for these therapies–(i) artificial pancreases, comprised of insulin producing cells embedded in a polymeric biomaterial, and (ii) totally synthetic pancreases formulated by integrating continuous glucose monitors with controlled insulin release through degradable polymers and glucose-responsive polymer systems. Both the artificial and the completely synthetic pancreas have two major design requirements: the device must be both biocompatible and be permeable to small molecules and proteins, such as insulin. Several polymers and fabrication methods of artificial pancreases are discussed: microencapsulation, conformal coatings, and planar sheets. We also review the two components of a completely synthetic pancreas. Several types of glucose sensing systems (including materials used for electrochemical, optical, and chemical sensing platforms) are discussed, in addition to various polymer-based release systems (including ethylene-vinyl acetate, polyanhydrides, and phenylboronic acid containing hydrogels). PMID:23184741

Bratlie, Kaitlin M.; York, Roger L.; Invernale, Michael A.; Langer, Robert

2013-01-01

416

Polymer solutions  

DOEpatents

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

417

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. PMID:19177183

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

2009-01-01

418

DELIVERY OF THERAPEUTIC PROTEINS  

PubMed Central

The safety and efficacy of protein therapeutics are limited by three interrelated pharmaceutical issues, in vitro and in vivo instability, immunogenicity and shorter half-lives. Novel drug modifications for overcoming these issues are under investigation and include covalent attachment of poly(ethylene glycol) (PEG), polysialic acid, or glycolic acid, as well as developing new formulations containing nanoparticulate or colloidal systems (e.g. liposomes, polymeric microspheres, polymeric nanoparticles). Such strategies have the potential to develop as next generation protein therapeutics. This review includes a general discussion on these delivery approaches. PMID:20049941

Pisal, Dipak S.; Kosloski, Matthew P.; Balu-Iyer, Sathy V.

2009-01-01

419

Memory formation and memory alterations: 5-HT6 and 5-HT7 receptors, novel alternative.  

PubMed

Agonists and antagonists of the 5-hydroxytryptamine (serotonin) receptor6 (5-HT6) or receptor7 (5-HT7) might improve memory and/or reverse amnesia, although the mechanisms involved are poorly understood. Hence, the current work summarizes recent reviews and findings involving these receptors. Evidence indicates that diverse 5-HT6 receptor antagonists produce promnesic and/or antiamnesic effect in conditions, such as memory formation, age-related cognitive impairments and memory deficit in preclinical studies, as well as in diseases such as schizophrenia, Parkinson's, and Alzheimer's disease (AD). Memory, aging, and AD modify 5-HT6 receptors and signaling cascades; likewise, the modulation of 5-HT6 drugs on memory seems to be accompanied with neural changes. Moreover, 5-HT7 receptors are localized in brain areas mediating memory, including the cortex, hippocampus (e.g., Zola-Morgan and Squire, 1993) and raphe nuclei; however, the role of these receptors on memory has yet to be fully explored. Hence, findings and reviews are summarized in this work. Evidence suggests that both 5-HT7 receptor agonists and antagonists might have promnesic and anti-amnesic effects. These effects seem to be dependent on the basal level of performance, i.e., normal or impaired. Available evidence suggests that a potential utility of 5-HT6 and 5-HT7 receptor in mild-to-moderate AD patients and other memory dysfunctions as therapeutic targets. PMID:24698823

Meneses, Alfredo

2014-01-01

420

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

421

Solid Tumor-Targeting Theranostic Polymer Nanoparticle in Nuclear Medicinal Fields  

PubMed Central

Polymer nanoparticles can be prepared by self-assembling of amphiphilic polymers, and various types of molecular assemblies have been reported. In particular, in medicinal fields, utilization of these polymer nanoparticles as carriers for drug delivery system (DDS) has been actively tried, and some nanoparticulate drugs are currently under preclinical evaluations. A radionuclide is an unstable nucleus and decays with emission of radioactive rays, which can be utilized as a tracer in the diagnostic imaging systems of PET and SPECT and also in therapeutic purposes. Since polymer nanoparticles can encapsulate most of diagnostic and therapeutic agents with a proper design of amphiphilic polymers, they should be effective DDS carriers of radionuclides in the nuclear medicinal field. Indeed, nanoparticles have been recently attracting much attention as common platform carriers for diagnostic and therapeutic drugs and contribute to the development of nanotheranostics. In this paper, recent developments of solid tumor-targeting polymer nanoparticles in nuclear medicinal fields are reviewed. PMID:25379530

Makino, Akira; Kimura, Shunsaku

2014-01-01

422

Deformation rate-, hold time-, and cycle-dependent shape-memory performance of Veriflex-E resin  

NASA Astrophysics Data System (ADS)

Shape-memory polymers have attracted great interest in recent years for application in reconfigurable structures (for instance morphing aircraft, micro air vehicles, and deployable space structures). However, before such applications can be attempted, the mechanical behavior of the shape-memory polymers must be thoroughly understood. The present study represents an assessment of viscous effects during multiple shape-memory cycles of Veriflex-E, an epoxy-based, thermally triggered shape-memory polymer resin. The experimental program is designed to explore the influence of multiple thermomechanical cycles on the shape-memory performance of Veriflex-E. The effects of the deformation rate and hold times at elevated temperature on the shape-memory behavior are also investigated.

McClung, Amber J. W.; Tandon, Gyaneshwar P.; Baur, Jeffery W.

2013-02-01

423

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

424

Memory Training in the Community Aged: Effects on Depression, Memory Complaint, and Memory Performance.  

ERIC Educational Resources Information Center

Compared the effects of memory and growth training groups on memory complaints, memory performance, and affective status in the community elderly. Results indicated that both training groups significantly reduced concerns about memory and resulted in improved memory performance. (Author)

Zarit, Steven H.; And Others

1981-01-01

425

Polyphenols: Multipotent Therapeutic Agents in Neurodegenerative Diseases  

PubMed Central

Aging leads to numerous transitions in brain physiology including synaptic dysfunction and disturbances in cognition and memory. With a few clinically relevant drugs, a substantial portion of aging population at risk for age-related neurodegenerative disorders require nutritional intervention. Dietary intake of polyphenols is known to attenuate oxidative stress and reduce the risk for related neurodegenerative diseases such as Alzheimer's disease (AD), stroke, multiple sclerosis (MS), Parkinson's disease (PD), and Huntington's disease (HD). Polyphenols exhibit strong potential to address the etiology of neurological disorders as they attenuate their complex physiology by modulating several therapeutic targets at once. Firstly, we review the advances in the therapeutic role of polyphenols in cell and animal models of AD, PD, MS, and HD and activation of drug targets for controlling pathological manifestations. Secondly, we present principle pathways in which polyphenol intake translates into therapeutic outcomes. In particular, signaling pathways like PPAR, Nrf2, STAT, HIF, and MAPK along with modulation of immune response by polyphenols are discussed. Although current polyphenol researches have limited impact on clinical practice, they have strong evidence and testable hypothesis to contribute clinical advances and drug discovery towards age-related neurological disorders. PMID:23840922

Bhullar, Khushwant S.; Rupasinghe, H. P. Vasantha

2013-01-01

426

In vitro wrinkle formation via shape memory dynamically aligns adherent cells  

E-print Network

In vitro wrinkle formation via shape memory dynamically aligns adherent cells Pine Yang, Richard M elegant approach to fabricating cell culture substrates with highly ordered topographies for investigating cell mechanobiology. In this study we present a tunable shape memory polymer (SMP) bilayer system

Mather, Patrick T.

427

Immunological Memory is Associative  

Microsoft Academic Search

This paper argues that immunological memory is in the same class of associative memories as Kanerva's Sparse Distributed Memory , Albus's Cerebellar Model Arithmetic Computer , and Marr's Theory of the Cerebellar Cortex . This class of memories derives its associative and robust nature from a sparse sampling of a huge input space by recognition units (B and T cells

Derek J. Smith; Stephanie Forrest; Alan S. Perelson

1998-01-01

428

Memory Hard Drive Peripherals  

E-print Network

1! CSI3131 Topics CPU Memory Hard Drive Peripherals Computing Systems OS Overview StructureDeadlocks M em ory M anagem ent Basic Memory Managermtn Virtual Memory Storage and I/O File Systems Hard Drive Management Swap I/O Management 2 Module 7: Memory Management Reading: Chapter 8 § To provide a detailed

Stojmenovic, Ivan

429

Cell microencapsulation with synthetic polymers  

PubMed Central

The encapsulation of cells into polymeric microspheres or microcapsules has permitted the transplantation of cells into human and animal subjects without the need for immunosuppressants. Cell-based therapies use donor cells to provide sustained release of a therapeutic product, such as insulin, and have shown promise in treating a variety of diseases. Immunoisolation of these cells via microencapsulation is a hotly investigated field, and the preferred material of choice has been alginate, a natural polymer derived from seaweed due to its gelling conditions. Although many natural polymers tend to gel in conditions favorable to mammalian cell encapsulation, there remain challenges such as batch to batch variability and residual components from the original source that can lead to an immune response when implanted into a recipient. Synthetic materials have the potential to avoid these issues; however, historically they have required harsh polymerization conditions that are not favorable to mammalian cells. As research into microencapsulation grows, more investigators are exploring methods to microencapsulate cells into synthetic polymers. This review describes a variety of synthetic polymers used to microencapsulate cells. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 846–859, 2015. PMID:24771675

Olabisi, Ronke M

2015-01-01

430

Novel biomimetic polymersomes as polymer therapeutics for drug delivery  

Microsoft Academic Search

Novel amphiphilic diblock copolymers, cholesterol-end-capped poly(2-methacryloyloxyethyl phosphorylcholine) (CMPC), which have poly(2-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) as hydrophilic segment and cholesterol as hydrophobic segment, was specially designed as drug delivery systems. Fluorescence probe technique and transmission electron microscope (TEM) characterizations indicated that this novel amphiphilic copolymer formed micelles structure in water and the critical micelle concentration (CMC) was determined to be 1.57×10?7 mol\\/l.

Jian-Ping Xu; Jian Ji; Wei-Dong Chen; Jia-Cong Shen

2005-01-01

431

High-throughput gene expression profiling of memory differentiation in primary human T cells  

E-print Network

Background: The differentiation of naive T and B cells into memory lymphocytes is essential for immunity to pathogens. Therapeutic manipulation of this cellular differentiation program could improve vaccine efficacy and ...

Angelosanto, Jill

432

Amphetamine Increases Errors During Episodic Memory Retrieval  

PubMed Central

Moderate doses of stimulant drugs are known to enhance memory encoding and consolidation, but their effects on memory retrieval have not been explored in depth. In laboratory animals, stimulants seem to improve retrieval of emotional memories, but comparable studies have not been carried out in humans. In the present study, we examined the effects of dextroamphetamine (AMP) on retrieval of emotional and unemotional stimuli in healthy young adults, using doses that enhanced memory formation when administered before encoding in our previous study. During 3 sessions, healthy volunteers (n = 31) received 2 doses of AMP (10 and 20 mg) and placebo in counter-balanced order under double-blind conditions. During each session, they first viewed emotional and unemotional pictures and words in a drug-free state, and then 2 days later their memory was tested, 1 hour after AMP or placebo administration. Dextroamphetamine did not affect the number of emotional or unemotional stimuli remembered, but both doses increased recall intrusions and false recognition. Dextroamphetamine (20 mg) also increased the number of positively rated picture descriptions and words generated during free recall. These data provide the first evidence that therapeutic range doses of stimulant drugs can increase memory retrieval errors. The ability of AMP to positively bias recollection of prior events could contribute to its potential for abuse. PMID:24135845

Ballard, Michael Edward; Gallo, David A.; de Wit, Harriet

2014-01-01

433

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

434

Therapeutic antibodies against cancer  

PubMed Central

Antibody-based therapeutics against cancer are highly successful in clinic and currently enjoy unprecedented recognition of their potential; 13 monoclonal antibodies (mAbs) have been approved for clinical use in the European Union and in the United States (one, mylotarg, was withdrawn from market in 2010). Three of the mAbs (bevacizumab, rituximab, trastuzumab) are in the top six selling protein therapeutics with sales in 2010 of more than $5 bln each. Hundreds of mAbs including bispecific mAbs and multispecific fusion proteins, mAbs conjugated with small molecule drugs and mAbs with optimized pharmacokinetics are in clinical trials. However, challenges remain and it appears that deeper understanding of mechanisms is needed to overcome major problems including resistance to therapy, access to targets, complexity of biological systems and individual variations. PMID:22520975

Adler, Mark J.; Dimitrov, Dimiter S.

2012-01-01

435

[Therapeutic effectiveness of Crataegus].  

PubMed

Hawthorn (crataegus) has been used since antiquity for medicinal purposes. More recent research suggests it to be useful in congestive heart failure. Rigorous clinical trials show benefit concerning objective signs and subjective symptoms of congestive heart failure stage NYHA-II. No adverse drug reactions have been reported. It is therefore concluded that crataegus is an effective and safe therapeutic alternative for this indication. PMID:8647566

Weihmayr, T; Ernst, E

1996-01-20

436

Therapeutic Recreation Directory  

NSDL National Science Digital Library

The Therapeutic Recreation Directory has an abundance of information for the therapeutic recreation specialist, or those who study and teach in the field. There is an extensive collection of activity ideas, ranging from sports and cookery, for educators to experiment with in the classroom or for professionals to use on the job. This site also hosts inTeRlink, a long-running and constantly updated newsletter about developments in recreational therapy, found by clicking on the �News� link on the left hand side of the home page. All articles from the last ten years are available in the archive. A bulletin board, chat room, and forum keep professionals and students informed about current TR issues, and surveys help to gather and disseminate information and ideas about new developments in TR services. Visitors will also find the �Forms� link very helpful in nearly every aspect of providing recreational therapy to clients, including forms to help assess and treat patients, and guidelines on planning and implementing new therapeutic programs.

Dixon, Charles C.

2007-02-05

437

The "memory kinases": roles of PKC isoforms in signal processing and memory formation.  

PubMed

The protein kinase C (PKC) isoforms, which play an essential role in transmembrane signal conduction, can be viewed as a family of "memory kinases." Evidence is emerging that they are critically involved in memory acquisition and maintenance, in addition to their involvement in other functions of cells. Deficits in PKC signal cascades in neurons are one of the earliest abnormalities in the brains of patients suffering from Alzheimer's disease. Their dysfunction is also involved in several other types of memory impairments, including those related to emotion, mental retardation, brain injury, and vascular dementia/ischemic stroke. Inhibition of PKC activity leads to a reduced capacity of many types of learning and memory, but may have therapeutic values in treating substance abuse or aversive memories. PKC activators, on the other hand, have been shown to possess memory-enhancing and antidementia actions. PKC pharmacology may, therefore, represent an attractive area for developing effective cognitive drugs for the treatment of many types of memory disorders and dementias. PMID:24484697

Sun, Miao-Kun; Alkon, Daniel L

2014-01-01

438

Dielectric Actuation of Polymers  

E-print Network

cross-linked polymer networks II. Swelling, The Journal ofswelling ratio is determined by the chemical crosslinking density of the polymer andinto the polymer network. Overall, the swelling ratio with

Niu, Xiaofan

2013-01-01

439

Cotinine: a potential new therapeutic agent against Alzheimer's disease.  

PubMed

Tobacco smoking has been correlated with a lower incidence of Alzheimer's disease (AD). This negative correlation has been attributed to nicotine's properties. However, the undesired side-effects of nicotine and the absence of clear evidence of positive effects of this drug on the cognitive abilities of AD patients have decreased the enthusiasm for its therapeutic use. In this review, we discuss evidence showing that cotinine, the main metabolite of nicotine, has many of the beneficial effects but none of the negative side-effects of its precursor. Cotinine has been shown to be neuroprotective, to improve memory in primates as well as to prevent memory loss, and to lower amyloid-beta (A?)) burden in AD mice. In AD, cotinine's positive effect on memory is associated with the inhibition of A? aggregation, the stimulation of pro-survival factors such as Akt, and the inhibition of pro-apoptotic factors such as glycogen synthase kinase 3 beta (GSK3?). Because stimulation of the ?7 nicotinic acetylcholine receptors (?7nAChRs) positively modulates these factors and memory, the involvement of these receptors in cotinine's effects are discussed. Because of its beneficial effects on brain function, good safety profile, and nonaddictive properties, cotinine may represent a new therapeutic agent against AD. PMID:22530628

Echeverria, Valentina; Zeitlin, Ross

2012-07-01

440

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

441

Shrinking polymer lasers  

NASA Astrophysics Data System (ADS)

Semiconducting polymers are a rapidly advancing class of optoelectronic materials. They give efficient light emission under optical or electrical stimulation, and offer promise as compact, lightweight and simple to fabricate lasers. The development of such active polymer components complements developments in polymer fibre and planar lightwave circuits opening new directions in polymer integrated optics. In this article progress towards making compact practical polymer lasers is described. The potential for polymer lasers to operate in the space radiation environment is also discussed.

Samuel, I. D. W.; Vasdekis, A. E.; Tsiminis, G.; Turnbull, G. A.; Taylor, E. W.

2007-09-01

442

Memory Metals  

NASA Technical Reports Server (NTRS)

Under contract to NASA during preparations for the space station, Memry Technologies Inc. investigated shape memory effect (SME). SME is a characteristic of certain metal alloys that can change shape in response to temperature variations. In the late 1980s and early 1990s, Memry used its NASA-acquired expertise to produce a line of home and industrial safety products, and refined the technology in the mid-1990s. Among the new products they developed are three MemrySafe units which prevent scalding from faucets. Each system contains a small valve that reacts to temperature, not pressure. When the water reaches dangerous temperatures, the unit reduces the flow to a trickle; when the scalding temperature subsides, the unit restores normal flow. Other products are the FIRECHEK 2 and 4, heat-activated shutoff valves for industrial process lines, which sense excessive heat and cut off pneumatic pressure. The newest of these products is Memry's Demand Management Water Heater which shifts the electricity requirement from peak to off-peak demands, conserving energy and money.

1995-01-01

443

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

444

Probing Polarization Dynamics and Energy Dissipation in Ferroelectric Polymers on the Nanoscale  

Microsoft Academic Search

Ferroelectric polymers are emerging as prominent materials for ultrasonic actuators, gate materials for non-volatile ferroelectric memories, and energy storage. The nature of ferroelectricity in polymers is significantly different from that in inorganic perovskites, resulting in significant interest to elementary mechanism of switching and the role of local microstructure. In this talk, I briefly delineate Piezoresponse Force Microscopy and Spectroscopy as

Sergei V. Kalinin

2007-01-01

445

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

446

Episodic memory and executive functioning in currently depressed patients compared to healthy controls.  

PubMed

At present, little is still known about the link between depression, memory and executive functioning. This study examined whether there are memory-related impairments in depressed patients and whether the size of such deficits depends on the age group and on specific types of cognitive measures. Memory performances of 215 clinically depressed patients were compared to the data of a matched control sample. Regression analyses were performed to determine the extent to which executive dysfunctions contributed to episodic memory impairments. When compared with healthy controls, significantly lower episodic memory and executive functioning performances were found for depressed patients of all age groups. Effect sizes appeared to vary across different memory and executive functioning measures. The extent to which executive dysfunctions could explain episodic memory impairments varied depending on the type of measure examined. These findings emphasise the need to consider memory-related functioning of depressed patients in the context of therapeutic treatments. PMID:24828417

Pauls, Franz; Petermann, Franz; Lepach, Anja Christina

2015-04-01

447

POLYANILINE MODIFIED NANOCELLULOSE AS REINFORCEMENT OF A SHAPE MEMORY POLYURETHANE  

E-print Network

Shape memory polymers (SMPs) are smart materials capable of “remembering ” and autonomously recovering their original shape after being deformed, as a response to a stimulus [1,2]. Segmented polyurethanes (PU) that present a two-phase microstructure consisting on hard and soft segments, can show this type of behavior.

M. I. Aranguren; M. L. Auad; T. Richardson; S. Adanur; W. J. Orts; E. S. Medeiros; M. A. Mosiewicki; N. E. Marcovich; Instrumentaçao Agropecuaria

448

[Memory disturbances in schizophrenia].  

PubMed

The recent literature on memory disorders in schizophrenic persons is reanalysed. The present interest in memory disorders as a core symptom of cognitive changes in schizophrenia derives from the fact that brain imaging methods have revealed a reduction of substance in the regions surrounding the lateral ventricles. Given this localisation, schizophrenics should suffer from pronounced memory deficits. The paper addresses (1) the role of memory disorders in an overall view of cognitive losses, (2) the pattern of memory losses (verbal vs non-verbal, short-term memory vs long-term memory, implicit vs explicit memory etc.) and (3) recent investigations based on simultaneous use of imaging procedures (fNMR, PET) and cortical activation during memory tasks. A survey of the literature renders it likely that frontal functions play an essential role in the type of memory deficits found among schizophrenics. Thus, a purely temporal localisation is unlikely. The reduced learning efficiency which accounts for most of the schizophrenics' cognitive problems points to a working memory disturbance. On the basis of these results, a model for the memory disorders of schizophrenics is developed. The model covers recent literature on working memory as well as neural network models of schizophrenic disorders. However, a differential psychopathological symptom and syndrome analysis remains a prerequisite for reducing the great variance of the schizophrenics' performance in memory tasks. The importance of cognitive rehabilitation for sociopsychiatric efforts aimed at re-integrating mentally ill persons should not be underestimated. PMID:8851379

Brand, A; Hildebrandt, H; Scheerer, E

1996-02-01

449

Shared Memory Parallel Programming with Entry Consistency for Distributed Memory  

E-print Network

Midway: Shared Memory Parallel Programming with Entry Consistency for Distributed Memory memory multiprocessing offers a cost­effective and scalable solution for a large class of scientific and numeric applications. Unfortunately, the performance of current distributed memory programming

450

Interpretations of Polymer-Polymer Miscibility.  

ERIC Educational Resources Information Center

Discusses various aspects of polymeric mixtures, mixtures of structurally different homopolymers, copolymers, terpolymers, and the like. Defines concepts of polymer-polymer miscibility from practical and theoretical viewpoints, and ways of predicting such miscibility. (JN)

Olabisi, Olagoke

1981-01-01

451

Therapeutic HPV DNA vaccines  

PubMed Central

Human papillomavirus (HPV) has been associated with several human cancers, including cervical cancer, vulvar cancer, vaginal and anal cancer, and a subset of head and neck cancers. The identification of HPV as an etiological factor for HPV-associated malignancies creates the opportunity for the control of these cancers through vaccination. Currently, the preventive HPV vaccine using HPV virus-like particles has been proven to be safe and highly effective. However, this preventive vaccine does not have therapeutic effects, and a significant number of people have established HPV infection and HPV-associated lesions. Therefore, it is necessary to develop therapeutic HPV vaccines to facilitate the control of HPV-associated malignancies and their precursor lesions. Among the various forms of therapeutic HPV vaccines, DNA vaccines have emerged as a potentially promising approach for vaccine development due to their safety profile, ease of preparation and stability. However, since DNA does not have the intrinsic ability to amplify or spread in transfected cells like viral vectors, DNA vaccines can have limited immunogenicity. Therefore, it is important to develop innovative strategies to improve DNA vaccine potency. Since dendritic cells (DCs) are key players in the generation of antigen-specific immune responses, it is important to develop innovative strategies to modify the properties of the DNA-transfected DCs. These strategies include increasing the number of antigen-expressing/antigen-loaded DCs, improving antigen processing and presentation in DCs, and enhancing the interaction between DCs and T cells. Many of the studies on DNA vaccines have been performed on preclinical models. Encouraging results from impressive preclinical studies have led to several clinical trials. PMID:19722895

Monie, Archana; Tsen, Shaw-Wei D; Hung, Chien-Fu; Wu, T-C

2009-01-01

452

Neural and Cellular Mechanisms of Fear and Extinction Memory Formation  

PubMed Central

Over the course of natural history, countless animal species have evolved adaptive behavioral systems to cope with dangerous situations and promote survival. Emotional memories are central to these defense systems because they are rapidly acquired and prepare organisms for future threat. Unfortunately, the persistence and intrusion of memories of fearful experiences are quite common and can lead to pathogenic conditions, such as anxiety and phobias. Over the course of the last thirty years, neuroscientists and psychologists alike have attempted to understand the mechanisms by which the brain encodes and maintains these aversive memories. Of equal interest, though, is the neurobiology of extinction memory formation as this may shape current therapeutic techniques. Here we review the extant literature on the neurobiology of fear and extinction memory formation, with a strong focus on the cellular and molecular mechanisms underlying these processes. PMID:22230704

Orsini, Caitlin A.; Maren, Stephen

2012-01-01

453

[Achievement of therapeutic objectives].  

PubMed

Therapeutic objectives for patients with atherogenic dyslipidemia are achieved by improving patient compliance and adherence. Clinical practice guidelines address the importance of treatment compliance for achieving objectives. The combination of a fixed dose of pravastatin and fenofibrate increases the adherence by simplifying the drug regimen and reducing the number of daily doses. The good tolerance, the cost of the combination and the possibility of adjusting the administration to the patient's lifestyle helps achieve the objectives for these patients with high cardiovascular risk. PMID:25043543

Mantilla, Teresa

2014-07-01

454

New therapeutic approaches.  

PubMed

Clinicians have witnessed an evolution from sulfasalazine and hydrocortisone to alternative aminosalicylates and steroids. Revolutionary changes beyond these, however,