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Sample records for memory polymer stents

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

    PubMed Central

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

    2011-01-01

    Shape memory polymer stent prototypes were fabricated from thermoplastic polyurethane. Commercial stents are generally made of stainless steel or other alloys. These alloys are too stiff and prevent most stent designs from being able to navigate small and tortuous vessels to reach intracranial lesions. A solid tubular model and a high flexibility laser etched model are presented. The stents were tested for collapse in a pressure chamber. At 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

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

    SciTech Connect

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

    2007-04-25

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

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

    PubMed Central

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

    2007-01-01

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

  4. Development of a polymer stent with shape memory effect as a drug delivery system.

    PubMed

    Wache, H M; Tartakowska, D J; Hentrich, A; Wagner, M H

    2003-02-01

    The article presents a new concept for vascular endoprothesis (stent). Almost all commercially available stents are made of metallic materials. A common after effect of stent implantation is restenosis. Several studies on metal stents coated with drug show, that the use of a drug delivery system may reduce restenosis. The purpose of this work is to develop a new stent for the drug delivery application. The shape memory properties of thermoplastic polyurethane allow to design a new fully polymeric self-expandable stent. The possibility to use the stent as a drug delivery system is described. PMID:15348481

  5. Shape memory polymers

    DOEpatents

    Wilson, Thomas S.; Bearinger, Jane P.

    2015-06-09

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

  6. Shape memory polymer foams

    NASA Astrophysics Data System (ADS)

    Santo, Loredana

    2016-02-01

    Recent advances in shape memory polymer (SMP) foam research are reviewed. The SMPs belong to a new class of smart polymers which can have interesting applications in microelectromechanical systems, actuators and biomedical devices. They can respond to specific external stimulus changing their configuration and then remember the original shape. In the form of foams, the shape memory behaviour can be enhanced because they generally have higher compressibility. Considering also the low weight, and recovery force, the SMP foams are expected to have great potential applications primarily in aerospace. This review highlights the recent progress in characterization, evaluation, and proposed applications of SMP foams mainly for aerospace applications.

  7. Shape memory polymer medical device

    DOEpatents

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

    2010-06-29

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

  8. Vessel healings after stenting with different polymers in STEMI patients

    PubMed Central

    Jin, Qin-Hua; Chen, Yun-Dai; Tian, Feng; Guo, Jun; Jing, Jing; Sun, Zhi-Jun

    2016-01-01

    Background Different stents implantation in ST-segment elevation myocardial infarction (STEMI) patients may influence the long term prognosis by affecting vessel healings after stenting. The aim of this study was to evaluate the vessel healings after implantation of drug eluting stents (DES) with biodegradable or durable polymer or of bare-metal stents (BMS) in patients with acute STEMI. Methods This study included 50 patients, who underwent follow up angiogram and optical coherence tomography (OCT) assessment about one year after percutaneous coronary intervention (PCI) for STEMI. According to the initial stents types, these patients were classified to durable (n = 19) or biodegradable polymer sirolimus-eluting stents (n = 15), or BMS (n = 16) groups. The conditions of stent struts coverage and malapposition were analyzed with OCT technique. Results A total of 9003 struts were analyzed: 3299, 3202 and 2502 from durable or biodegradable polymer DES, or BMS, respectively. Strut coverage rate (89.0%, 94.9% and 99.3%, respectively), malapposition presence (1.7%, 0.03% and 0 of struts, respectively) and average intimal thickness over struts (76 ± 12 µm, 161 ± 30 µm and 292 ± 29 µm, respectively) were significantly different among different stent groups (all P < 0.001). Conclusions Vessel healing status in STEMI patients is superior after implantation of biodegradable polymer DES than durable polymer DES, while both are inferior to BMS. PMID:27403139

  9. Porous Shape Memory Polymers

    PubMed Central

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

    2013-01-01

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

  10. Shape memory alloy/shape memory polymer tools

    DOEpatents

    Seward, Kirk P.; Krulevitch, Peter A.

    2005-03-29

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

  11. Surface shape memory in polymers

    NASA Astrophysics Data System (ADS)

    Mather, Patrick

    2012-02-01

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

  12. Intense Inflammatory Reaction to Heparin Polymer Coated Intravascular Palmaz Stents in Porcine Arteries Compared to Uncoated Palmaz Stents

    SciTech Connect

    Goodwin, Scott C.; Yoon, Hyo-Chun; Chen, Gary; Abdel-Sayed, Peter; Costantino, Mary M.; Bonilla, Sheila M.; Nishimura, Earl

    2003-04-15

    The objective of this study was to evaluate the efficacy of heparin-polymer-coated intravascular stents in the reduction of vessel stenosis. Three types of coatings for Palmaz stents were tested: 1) heparin covalently bound to a polyethylene oxide(Hp-PEO) tether; 2) heparin copolymerized with ethylene vinyl acetate(Hp-Elvax) and 3) Elvax alone. Polymer-coated stents and uncoated controls were deployed in the external iliac arteries following endothelial injury in 18 swine. The animals were maintained on anatherogenic diet and examined by angiography at 6 and 12 weeks. The stented segments were then harvested for histopathologic analysis. Both types of heparin-coated stents resulted in increased luminal narrowing as compared to the contralateral uncoated stents. At 6 weeks, average luminal stenosis was 48% for Hp-PEO stents vs 35% for uncoated stents (p < 0.05). At 12 weeks, average luminal stenosis was 36% for Hp-PEO stents vs 26% for uncoated stents(p = NS). For Hp-Elvax stents, the average stenosis was 58% vs 33% for uncoated controls (p <0.05) at 6 weeks and 47% vs 19% for uncoated controls(p < 0.05) at 12 weeks. There was no significant difference between Hp-Elvax stents and Elvax stents(p = NS). Increased luminal narrowing in coated stents was primarily secondary to a marked inflammatory response.Heparin-polyethylene oxide and heparin-ethylene vinyl acetate-coated stents resulted in increased luminal narrowing as compared with uncoated stents, due to a marked inflammatory response.

  13. Applications of memory alloy stent in vertebral fractures

    PubMed Central

    Yimin, Yang; Zhi, Zhang; ZhiWei, Ren; Wei, Ma; Jha, Rajiv Kumar

    2014-01-01

    Background The aim of this study was to evaluate the feasibility of treating vertebral compression fractures using an autonomously developed nitinol memory alloy vertebral stent. Material/Methods Thoracolumbar vertebral specimens from adult human cadavers were made into models of compression fractures. The models were divided into group A, which received percutaneous kyphoplasty (PKP), balloon dilation, and nitinol memory alloy vertebral stent implantation (PKP + nitinol stent group); group B, which received percutaneous vertebroplasty (PVP) and direct implantation of a nitinol memory alloy vertebral stent (PVP + nitinol stent group); and group C, which received PKP, balloon dilation, and bone cement vertebroplasty (PKP + polymethylmethacrylate (PMMA) group). Vertebral heights were measured before and after the surgery and the water bath incubation to compare the impact of the 3 different surgical approaches on reducing vertebral compression. Results The 3 surgical groups could all significantly restore the heights of compressed vertebral bodies. The vertebral heights of the PKP + nitinol stent group, PVP + nitinol stent group, and PKP + PMMA group were changed from the preoperative levels of (1.59±0.08) cm, (1.68±0.08) cm, and (1.66±0.11) cm to the postoperative levels of (2.00±0.09) cm, (1.87±0.04) cm, and (1.99±0.09) cm, respectively. After the water bath, the vertebral heights of each group were changed to (2.10±0.07) cm, (1.98±0.09) cm, and (2.00±0.10) cm, respectively. Pairwise comparison of the differences between the preoperative and postoperative vertebral heights showed that group A and group B differed significantly (P=0.000); group B and group C differed significantly (P=0.003); and group A and group C had no significant difference (P=0.172). Pairwise comparison of the differences in the vertebral heights before and after the water bath showed that group A and group C differed significantly (P=0.000); group B and group C differed significantly

  14. Biodegradable-Polymer Biolimus-Eluting Stents versus Durable-Polymer Everolimus-Eluting Stents at One-Year Follow-Up: A Registry-Based Cohort Study.

    PubMed

    Parsa, Ehsan; Saroukhani, Sepideh; Majlessi, Fereshteh; Poorhosseini, Hamidreza; Lofti-Tokaldany, Masoumeh; Jalali, Arash; Salarifar, Mojtaba; Nematipour, Ebrahim; Alidoosti, Mohammad; Aghajani, Hassan; Amirzadegan, Alireza; Kassaian, Seyed Ebrahim

    2016-04-01

    We compared outcomes of percutaneous coronary intervention patients who received biodegradable-polymer biolimus-eluting stents with those who received durable-polymer everolimus-eluting stents. At Tehran Heart Center, we performed a retrospective analysis of the data from January 2007 through December 2011 on 3,270 consecutive patients with coronary artery disease who underwent percutaneous coronary intervention with the biodegradable-polymer biolimus-eluting stent or the durable-polymer everolimus-eluting stent. We excluded patients with histories of coronary artery bypass grafting or percutaneous coronary intervention, acute ST-segment-elevation myocardial infarction, or the implantation of 2 different stent types. Patients were monitored for 12 months. The primary endpoint was a major adverse cardiac event, defined as a composite of death, nonfatal myocardial infarction, and target-vessel and target-lesion revascularization. Durable-polymer everolimus-eluting stents were implanted in 2,648 (81%) and biodegradable-polymer biolimus-eluting stents in 622 (19%) of the study population. There was no significant difference between the 2 groups (2.7% vs 2.7%; P=0.984) in the incidence of major adverse cardiac events. The cumulative adjusted probability of major adverse cardiac events in the biodegradable-polymer biolimus-eluting stent group did not differ from that of such events in the durable-polymer everolimus-eluting stent group (hazard ratio=0.768; 95% confidence interval, 0.421-1.44; P=0.388). We conclude that in our patients the biodegradable-polymer biolimus-eluting stent was as effective and safe, during the 12-month follow-up period, as was the durable-polymer everolimus-eluting stent. PMID:27127426

  15. Biodegradable-Polymer Biolimus-Eluting Stents versus Durable-Polymer Everolimus-Eluting Stents at One-Year Follow-Up: A Registry-Based Cohort Study

    PubMed Central

    Parsa, Ehsan; Saroukhani, Sepideh; Majlessi, Fereshteh; Poorhosseini, Hamidreza; Lofti-Tokaldany, Masoumeh; Jalali, Arash; Salarifar, Mojtaba; Nematipour, Ebrahim; Alidoosti, Mohammad; Aghajani, Hassan; Amirzadegan, Alireza

    2016-01-01

    We compared outcomes of percutaneous coronary intervention patients who received biodegradable-polymer biolimus-eluting stents with those who received durable-polymer everolimus-eluting stents. At Tehran Heart Center, we performed a retrospective analysis of the data from January 2007 through December 2011 on 3,270 consecutive patients with coronary artery disease who underwent percutaneous coronary intervention with the biodegradable-polymer biolimus-eluting stent or the durable-polymer everolimus-eluting stent. We excluded patients with histories of coronary artery bypass grafting or percutaneous coronary intervention, acute ST-segment-elevation myocardial infarction, or the implantation of 2 different stent types. Patients were monitored for 12 months. The primary endpoint was a major adverse cardiac event, defined as a composite of death, nonfatal myocardial infarction, and target-vessel and target-lesion revascularization. Durable-polymer everolimus-eluting stents were implanted in 2,648 (81%) and biodegradable-polymer biolimus-eluting stents in 622 (19%) of the study population. There was no significant difference between the 2 groups (2.7% vs 2.7%; P=0.984) in the incidence of major adverse cardiac events. The cumulative adjusted probability of major adverse cardiac events in the biodegradable-polymer biolimus-eluting stent group did not differ from that of such events in the durable-polymer everolimus-eluting stent group (hazard ratio=0.768; 95% confidence interval, 0.421–1.44; P=0.388). We conclude that in our patients the biodegradable-polymer biolimus-eluting stent was as effective and safe, during the 12-month follow-up period, as was the durable-polymer everolimus-eluting stent. PMID:27127426

  16. A new polymer-free drug-eluting stent with nanocarriers eluting sirolimus from stent-plus-balloon compared with bare-metal stent and with biolimus A9 eluting stent in porcine coronary arteries

    PubMed Central

    Galon, Micheli Z.; Gutierrez, Paulo S.; Sojitra, Prakash; Vyas, Ashwin; Doshi, Manish; Lemos, Pedro A.

    2015-01-01

    Background Permanent polymers in first generation drug-eluting stent (DES) have been imputed to be a possible cause of persistent inflammation, remodeling, malapposition and late stent thrombosis. We aim to describe the in vivo experimental result of a new polymer-free DES eluting sirolimus from stent-plus-balloon (Focus np stent, Envision Scientific) compared with a bare-metal stent (BMS) (Amazonia CroCo, Minvasys) and with a biolimus A9 eluting stent (Biomatrix, Biosensors). Methods In 10 juvenile pigs, 23 coronary stents were implanted in the coronary arteries (8 Amazonia CroCo, 8 Focus np, and 7 Biomatrix). At 28-day follow-up, optical coherence tomography (OCT) and histology were used to evaluate neointimal hyperplasia and healing response. Results According to OCT analysis, Focus np stents had a greater lumen area and less neointimal hyperplasia response than BMS and Biomatrix had. Histomorphometry results showed less neointimal hyperplasia in Focus np than in BMS. Histology showed a higher fibrin deposition in Biomatrix stent compared to Focus np and BMS. Conclusions The new polymer-free DES with sirolimus eluted from stent-plus-balloon demonstrated safety and reduced neointimal proliferation compared with the BMS and Biomatrix stents at 28-day follow-up in this porcine coronary model. This new polymer-free DES is promising and warrants further clinical studies. PMID:25984451

  17. Temperature-memory polymer actuators

    PubMed Central

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

    2013-01-01

    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 (ΔTm) 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 ΔTm 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

  18. Polyurethane shape-memory polymers demonstrate functional biocompatibility in vitro.

    PubMed

    Cabanlit, Maricel; Maitland, Duncan; Wilson, Thomas; Simon, Scott; Wun, Theodore; Gershwin, M Eric; Van de Water, Judy

    2007-01-01

    Shape memory polymers (SMPs) are a class of polymeric materials used in various medical interventions such as vascular stents. In this work, two SMPs, thermoplastic (TP) and thermoset (TS), have been measured in vitro for the degree of cellular and protein adhesion, their ability to stimulate inflammatory cytokine production, as well as the effects of the SMPs on the haemostatic system. The stimulatory properties of SMPs on neutrophils have also been directly addressed. Based on the studies of SMP biocompatibility as defined by inflammation, thrombogenesis, and the activation of both platelets and neutrophils, the TS and TP SMP materials are unlikely to stimulate an inflammatory response in vivo. [figure: see text] PMID:17238230

  19. Post polymerization cure shape memory polymers

    DOEpatents

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

    2014-11-11

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

  20. Shape memory polymer actuator and catheter

    DOEpatents

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

    2007-11-06

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

  1. Shape memory polymer actuator and catheter

    DOEpatents

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

    2004-05-25

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

  2. Advances with polymer-free amphilimus-eluting stents.

    PubMed

    CARRIé, Didier

    2016-06-01

    Despite the improved clinical outcomes following the availability of second generation drug eluting stents (DES), percutaneous coronary intervention (PCI) is associated with worse clinical and angiographic outcomes among the patients with diabetes mellitus (DM) than among non-diabetics. The Cre8 Amphilimus-eluting DES is polymer-free, resulting in a reduced inflammatory response and lower risk of stent thrombosis. In a clinical study, it showed equivalent efficacy and safety in diabetic and non-diabetic populations, a unique finding among DES studies. These findings were confirmed in a real-world study, Investig8, and another real-world study, Particip8, is ongoing. The RESERVOIR Clinical Trial recruited patients with DM and showed noninferiority of the Cre8 DES compared to an everolimus eluting DES (EES) in the overall group but showed a statistical superiority of Cre8 in diabetic patients with higher metabolic dysfunctions. The Cre8 DES is therefore a valuable option for this important patient population. PMID:26934663

  3. Application of memory metallic stents to urinary tract disorders in pediatric patients.

    PubMed

    Kamata, Shinkichi; Usui, Noriaki; Kamiyama, Masafumi; Yoneda, Akihiro; Tazuke, Yuko; Ooue, Takaharu

    2005-03-01

    The use of memory metallic stents for the urinary tract in pediatric patients has not been reported. The authors report on 2 patients with urinary tract disorders who were successfully treated with a memory metallic stent. A thermoexpandable, nickel-titanium alloy stent was placed at the urethroureteral junction of a 4-year-old boy with ureteral stenosis associated with cloacal exstrophy for 18 months and at the urethra of a 2-year-old girl with ischuria after a repair of cloacal anomaly for 6 months. Temporary insertion of a memory metallic stent is a safe and effective alternative for organic stricture or functional obstruction of the urinary tract in pediatric patients. PMID:15793713

  4. Prognostic Significance of Polymer Coatings in Zotarolimus-Eluting Stents.

    PubMed

    Iqbal, M Bilal; Nadra, Imad J; Din, Jehangir N; Hendry, Cara; Ding, Lillian; Fung, Anthony; Aymong, Eve; Chan, Albert W; Hodge, Steven; Robinson, Simon D; Della Siega, Anthony

    2016-03-01

    Polymer coatings on drug-eluting stents (DES) serve as a vehicle for delivery of antirestenotic drugs. Whether they influence outcomes for contemporary DES is unknown. The evolution of polymer coatings for zotarolimus-eluting stents (ZES) provides a natural experiment that facilitates such analysis. The Resolute ZES (R-ZES) uses the same antirestenotic drug as the Endeavor ZES (E-ZES) but has a more biocompatible polymer with enhanced drug release kinetics. However, there are limited data on the real-world comparative efficacy of R-ZES and the preceding E-ZES. Thus, we analyzed 17,643 patients who received either E-ZES or R-ZES from 2008 to 2014 from the British Columbia Cardiac Registry. A total of 9,869 patients (56%) received E-ZES and 7,774 patients (44%) received R-ZES. Compared with E-ZES, R-ZES was associated with lower 2-year mortality (4.1% vs 6.4%, p <0.001) and 2-year target vessel revascularization (TVR; 6.8% vs 10.7%, p <0.001). R-ZES use was an independent predictor of lower mortality rate and TVR. This was confirmed in propensity-matched analyses for 2-year mortality (hazard ratio [HR] 0.59, 95% CI 0.49 to 0.71, p <0.001) and 2-year TVR (HR 0.86, 95% CI 0.75 to 0.98, p = 0.032). Instrumental variable analyses demonstrated R-ZES to be associated with lower 2-year mortality (Δ = -2.2%, 95% CI -4.3% to -0.2%, p = 0.032) and 2-year TVR (Δ = -3.3% to 95% CI -6.1% to -0.7%, p = 0.015). Acknowledging the limitations of observational analyses, this study has shown that R-ZES was associated with lower long-term TVR and mortality. These data are reassuring for the newer R-ZES and demonstrate how polymer coatings may influence the clinical performance of DES with wider implications for future DES development and design. PMID:26796194

  5. Biomedical engineering in design and application of nitinol stents with shape memory effect

    NASA Astrophysics Data System (ADS)

    Ryklina, E. P.; Khmelevskaya, I. Y.; Morozova, Tamara V.; Prokoshkin, S. D.

    1996-04-01

    Our studies in the field of endosurgery in collaboration with the physicians of the National Research Center of Surgery of the Academy of Medical Sciences are carried out beginning in 1983. These studies laid the foundation for the new direction of X-ray surgery--X-ray Nitinol stenting of vessels and tubular structures. X-ray nitinol stents are unique self-fixing shells based on the shape memory effect and superelasticity of nickel-titanium alloys self- reconstructed under human body temperature. Applied for stenting of arteries in cases of stenosis etc., bile ducts in cases of benign and malignant stenoses, digestive tract in cases of oesophageal cancer and cervical canal uterus in cases of postsurgical atresiss and strictures of uterine. The purpose of stenting is restoration of the shape of artery or tubular structure by a cylinder frame formation. The especially elaborated original method of stenting allows to avoid the traditional surgical operation, i.e. the stenting is performed without blood, narcosis and surgical knife. The stent to be implanted is transported into the affected zone through the puncture under the X-ray control. Clinical applications of X-ray endovascular stenting has been started in March 1984. During this period nearly 400 operations on stenting have been performed on femoral, iliac, brachio-cephalic, subclavian arteries, bile ducts, tracheas, digestive tract and cervical canal uterus.

  6. In vivo assessment of stent recoil of biodegradable polymer-coated cobalt–chromium sirolimus-eluting coronary stent system☆

    PubMed Central

    Abhyankar, Atul D.; Thakkar, Ashok S.

    2012-01-01

    Introduction Immediate and acute stent recoil has been observed following balloon deflation in normal and diseased coronary arteries, and the degree varies by stent design. Methods A total of 19 patients, who underwent elective stent implantation for single de novo native coronary artery lesions, were enrolled: all patients treated with the biodegradable polymer-coated sirolimus-eluting cobalt–chromium coronary stent system (Supralimus-Core®). The immediate, acute and cumulative stent recoil was assessed by quantitative coronary angiography. The cumulative stent recoil was measured at 24 h of stent implantation. Results The absolute late loss due to recoil was found 0.08 ± 0.19 mm for Immediate Stent Recoil (ISR), 0.05 ± 0.21 mm for Acute Stent Recoil (ASR) and 0.11 ± 0.25 mm for Cumulative Stent Recoil (CSR) respectively. Conclusions In vivo acute stent recoil of the Supralimus-Core® has higher radial strength compared to other available standard drug-eluting stents. PMID:23253404

  7. Stent Thrombogenicity Early in High Risk Interventional Settings is Driven by Stent Design and Deployment, and Protected by Polymer-Drug Coatings

    PubMed Central

    Kolandaivelu, Kumaran; Swaminathan, Rajesh; Gibson, William J.; Kolachalama, Vijaya B.; Nguyen-Ehrenreich, Kim-Lien; Giddings, Virginia L.; Coleman, Leslie; Wong, Gee K.; Edelman, Elazer R.

    2011-01-01

    Background Stent thrombosis is a lethal complication of endovascular intervention. Concern has been raised for the inherent risk associated with specific stent designs and drug-eluting coatings, yet clinical and animal support are equivocal. Methods and Results We examined whether drug-eluting coatings are inherently thrombogenic and if the response to these materials was determined to a greater degree by stent design and deployment using custom-built stents. Drug/polymer coatings uniformly reduce rather than increase thrombogenicity relative to matched bare-metal counterparts (0.65-fold, p=0.011). Thick-strutted (162 μm) stents were 1.5-fold more thrombogenic than otherwise identical thin-strutted (81 μm) devices in ex vivo flow loops (p<0.001), commensurate with 1.6-fold greater thrombus coverage three days after implantation in porcine coronary arteries (p=0.004). When bare-metal stents were deployed in malapposed or overlapping configurations, thrombogenicity increased compared to apposed, length-matched controls (1.58-fold, p=0.001 and 2.32-fold, p<0.001). The thrombogenicity of polymer-coated stents with thin struts was lowest in all configurations and remained insensitive to incomplete deployment. Computational modeling-based predictions of stent-induced flow derangements correlated with spatial distribution of formed clots. Conclusions Contrary to popular conception drug/polymer coatings do not inherently increase acute stent clotting – they reduce thrombosis. However, strut dimensions and positioning relative to the vessel wall are critical factors in modulating stent thrombogenicity. Optimal stent geometries and surfaces, as demonstrated with thin stent struts, help reduce the potential for thrombosis despite complex stent configurations and variability in deployment. PMID:21422389

  8. Medical applications of shape memory polymers

    NASA Technical Reports Server (NTRS)

    Sokolowski, Witold M.

    2005-01-01

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

  9. Preclinical Study of a Biodegradable Polymer-based Stent with Abluminal Sirolimus Release

    PubMed Central

    Takimura, Celso Kiyochi; Campos, Carlos Augusto Homem M.; Melo, Pedro Henrique Magualhães Craveiro; Campos, Julliana Carvalho; Gutierrez, Paulo Sampaio; Borges, Thiago Francisco Costa; Curado, Luciano; Morato, Spero Penha; Laurindo, Francisco Rafael Martins; Lemos, Pedro Alves

    2014-01-01

    Background Bioabsorbable polymer stents with drug elution only on the abluminal surface may be safer than durable polymer drug-eluting stents. Objective To report the experimental findings with the InspironTM stent - a bioabsorbable polymer-coated stent with sirolimus release from the abluminal surface only, recently approved for clinical use. Methods 45 stents were implanted in the coronary arteries of 15 pigs. On day 28 after implantation, angiographic, intracoronary ultrasonographic and histomorphological data were collected. Five groups were analyzed: Group I (nine bare-metal stents); Group II (nine coated with bioabsorbable polymer on the luminal and abluminal surfaces); Group III (eight stents coated with bioabsorbable polymer on the abluminal surface); Group IV (nine stents with bioabsorbable polymer and sirolimus on the luminal and abluminal surfaces); and Group V (ten stents with bioabsorbable polymer and sirolimus only on the abluminal surface). Results The following results were observed for Groups I, II, III, IV and V, respectively: percentage stenosis of 29 ± 20; 36 ± 14; 33 ± 19; 22 ± 13 and 26 ± 15 (p = 0.443); late lumen loss (in mm) of 1.02 ± 0.60; 1.24 ± 0.48; 1.11 ± 0.54; 0.72 ± 0.44 and 0.78 ± 0.39 (p = 0.253); neointimal area (in mm2) of 2.60 ± 1.99; 2.74 ± 1.51; 2.74 ± 1.30; 1.30 ± 1.14 and 0.97 ± 0.84 (p = 0.001; Groups IV and V versus Groups I, II and III); and percentage neointimal area of 35 ± 25; 38 ± 18; 39 ± 19; 19 ± 18 and 15 ± 12 (p = 0.001; Groups IV and V versus Groups I, II and III). Injury and inflammation scores were low and with no differences between the groups. Conclusion The InspironTM stent proved to be safe and was able to significantly inhibit the neointimal hyperplasia observed on day 28 after implantation in porcine coronary arteries. PMID:24759951

  10. Biodegradable polymer stents vs second generation drug eluting stents: A meta-analysis and systematic review of randomized controlled trials

    PubMed Central

    Pandya, Bhavi; Gaddam, Sainath; Raza, Muhammad; Asti, Deepak; Nalluri, Nikhil; Vazzana, Thomas; Kandov, Ruben; Lafferty, James

    2016-01-01

    AIM: To evaluate the premise, that biodegradable polymer drug eluting stents (BD-DES) could improve clinical outcomes compared to second generation permanent polymer drug eluting stents (PP-DES), we pooled the data from all the available randomized control trials (RCT) comparing the clinical performance of both these stents. METHODS: A systematic literature search of PubMed, Cochrane, Google scholar databases, EMBASE, MEDLINE and SCOPUS was performed during time period of January 2001 to April 2015 for RCT and comparing safety and efficacy of BD-DES vs second generation PP-DES. The primary outcomes of interest were definite stent thrombosis, target lesion revascularization, myocardial infarction, cardiac deaths and total deaths during the study period. RESULTS: A total of 11 RCT’s with a total of 12644 patients were included in the meta-analysis, with 6598 patients in BD-DES vs 6046 patients in second generation PP-DES. The mean follow up period was 16 mo. Pooled analysis showed non-inferiority of BD-DES, comparing events of stent thrombosis (OR = 1.42, 95%CI: 0.79-2.52, P = 0.24), target lesion revascularization (OR = 0.99, 95%CI: 0.84-1.17, P = 0.92), myocardial infarction (OR = 1.06, 95%CI: 0.86-1.29, P = 0.92), cardiac deaths (OR = 1.07, 95%CI 0.82-1.41, P = 0.94) and total deaths (OR = 0.96, 95%CI: 0.80-1.17, P = 0.71). CONCLUSION: BD-DES, when compared to second generation PP-DES, showed no significant advantage and the outcomes were comparable between both the groups. PMID:26981219

  11. Stent

    MedlinePlus

    ... kinds of stents. Most are made of a metal or plastic mesh-like material. However, stent grafts are made of fabric. They are used in larger arteries. An intraluminal coronary artery ... self-expanding, metal mesh tube. It is placed inside a coronary ...

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

    NASA Astrophysics Data System (ADS)

    Rossiter, Jonathan; Takashima, Kazuto; Mukai, Toshiharu

    2014-03-01

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

  13. The pre-clinical assessment of rapamycin-eluting, durable polymer-free stent coating concepts.

    PubMed

    Steigerwald, Kristin; Merl, Sabine; Kastrati, Adnan; Wieczorek, Anna; Vorpahl, Marc; Mannhold, Raimund; Vogeser, Michael; Hausleiter, Jörg; Joner, Michael; Schömig, Albert; Wessely, Rainer

    2009-02-01

    All four currently FDA-approved drug-eluting stents (DESs) contain a durable polymeric coating which can negatively impact vascular healing processes and eventually lead to adverse cardiac events. Aim of this study was the pre-clinical assessment of two novel rapamycin-eluting stent (RES) coating technologies that abstain from use of a durable polymer. Two distinctive RES coating technologies were evaluated in vitro and in the porcine coronary artery stent model. The R-poly(S) stent platform elutes rapamycin from a biodegradable polymer that is top coated with the resin shellac to minimize the amount of polymer. The R-pro(S) stent platform allows dual drug release of rapamycin and probucol, blended by shellac. HPLC-based determination of pharmacokinetics indicated drug release for more than 28 days. At 30 days, neointimal formation was found to be significantly decreased for both DESs compared to bare-metal stents. Assessment of vascular healing revealed absence of increased inflammation in both DESs, which is commonly observed in DES with non-erodible polymeric coating. In conclusion, the pre-clinical assessment of RESs with resin-based or dual drug coating indicated an adequate efficacy profile as well as a beneficial effect for vascular healing processes. These results encourage the transfer of these technologies to clinical evaluation. PMID:18990438

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

    PubMed Central

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

    2014-01-01

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

  15. Evaluation of electrospun PLLA/PEGDMA polymer coatings for vascular stent material.

    PubMed

    Boodagh, Parnaz; Guo, Dong-Jie; Nagiah, Naveen; Tan, Wei

    2016-08-01

    The field of percutaneous coronary intervention has seen a plethora of advances over the past few decades, which have allowed for its development into safe and effective treatments for patients suffering from cardiovascular diseases. However, stent thrombosis and in-stent restenosis remain clinically significant problems. Herein, we describe the synthesis and characterization of fibrous polymer coatings on stent material nitinol, in the hopes of developing a more suitable stent surface to enhance re-endothelialization. Electrospinning technique was used to fabricate polyethylene glycol dimethacrylate/poly l-lactide acid (PEGDMA/PLLA) blend fiber substrate with tunable elasticity and hydrophilicity for use as coatings. Attachment of platelets and arterial smooth muscle cells (SMC) onto the coatings as well as the secretory effect of mesenchymal stem cells cultured on the coatings on the proliferation and migration of arterial endothelial cells and SMCs were assessed. It was demonstrated that electrospun PEGDMA/PLLA coating with 1:1 ratio of the components on the nitinol stent-reduced platelet and SMC attachment and increased stem cell secretory factors that enhance endothelial proliferation. We therefore postulate that the fibrous coating surface would possess enhanced biological compatibility of nitinol stents and hold the potential in preventing stent failure through restenosis and thrombosis. PMID:27137629

  16. A Wireless Pressure Sensor Integrated with a Biodegradable Polymer Stent for Biomedical Applications.

    PubMed

    Park, Jongsung; Kim, Ji-Kwan; Patil, Swati J; Park, Jun-Kyu; Park, SuA; Lee, Dong-Weon

    2016-01-01

    This paper describes the fabrication and characterization of a wireless pressure sensor for smart stent applications. The micromachined pressure sensor has an area of 3.13 × 3.16 mm² and is fabricated with a photosensitive SU-8 polymer. The wireless pressure sensor comprises a resonant circuit and can be used without the use of an internal power source. The capacitance variations caused by changes in the intravascular pressure shift the resonance frequency of the sensor. This change can be detected using an external antenna, thus enabling the measurement of the pressure changes inside a tube with a simple external circuit. The wireless pressure sensor is capable of measuring pressure from 0 mmHg to 230 mmHg, with a sensitivity of 0.043 MHz/mmHg. The biocompatibility of the pressure sensor was evaluated using cardiac cells isolated from neonatal rat ventricular myocytes. After inserting a metal stent integrated with the pressure sensor into a cardiovascular vessel of an animal, medical systems such as X-ray were employed to consistently monitor the condition of the blood vessel. No abnormality was found in the animal blood vessel for approximately one month. Furthermore, a biodegradable polymer (polycaprolactone) stent was fabricated with a 3D printer. The polymer stent exhibits better sensitivity degradation of the pressure sensor compared to the metal stent. PMID:27271619

  17. A Wireless Pressure Sensor Integrated with a Biodegradable Polymer Stent for Biomedical Applications

    PubMed Central

    Park, Jongsung; Kim, Ji-Kwan; Patil, Swati J.; Park, Jun-Kyu; Park, SuA; Lee, Dong-Weon

    2016-01-01

    This paper describes the fabrication and characterization of a wireless pressure sensor for smart stent applications. The micromachined pressure sensor has an area of 3.13 × 3.16 mm2 and is fabricated with a photosensitive SU-8 polymer. The wireless pressure sensor comprises a resonant circuit and can be used without the use of an internal power source. The capacitance variations caused by changes in the intravascular pressure shift the resonance frequency of the sensor. This change can be detected using an external antenna, thus enabling the measurement of the pressure changes inside a tube with a simple external circuit. The wireless pressure sensor is capable of measuring pressure from 0 mmHg to 230 mmHg, with a sensitivity of 0.043 MHz/mmHg. The biocompatibility of the pressure sensor was evaluated using cardiac cells isolated from neonatal rat ventricular myocytes. After inserting a metal stent integrated with the pressure sensor into a cardiovascular vessel of an animal, medical systems such as X-ray were employed to consistently monitor the condition of the blood vessel. No abnormality was found in the animal blood vessel for approximately one month. Furthermore, a biodegradable polymer (polycaprolactone) stent was fabricated with a 3D printer. The polymer stent exhibits better sensitivity degradation of the pressure sensor compared to the metal stent. PMID:27271619

  18. Fabrication and characterization of shape memory polymers at small-scales

    NASA Astrophysics Data System (ADS)

    Wornyo, Edem

    The objective of this research is to thoroughly investigate the shape memory effect in polymers, characterize, and optimize these polymers for applications in information storage systems. Previous research effort in this field concentrated on shape memory metals for biomedical applications such as stents. Minimal work has been done on shape memory polymers; and the available work on shape memory polymers has not characterized the behaviors of this category of polymers fully. Copolymer shape memory materials based on diethylene glycol dimethacrylate (DEGDMA) crosslinker, and tert butyl acrylate (tBA) monomer are designed. The design encompasses a careful control of the backbone chemistry of the materials. Characterization methods such as dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC); and novel nanoscale techniques such as atomic force microscopy (AFM), and nanoindentation are applied to this system of materials. Designed experiments are conducted on the materials to optimize spin coating conditions for thin films. Furthermore, the recovery, a key for the use of these polymeric materials for information storage, is examined in detail with respect to temperature. In sum, the overarching objectives of the proposed research are to: (i) Design shape memory polymers based on polyethylene glycol dimethacrylate (PEGDMA) and diethylene glycol dimethacrylate (DEGDMA) crosslinkers, 2-hydroxyethyl methacrylate (HEMA) and tert-butyl acrylate monomer (tBA). (ii) Utilize dynamic mechanical analysis (DMA) to comprehend the thermomechanical properties of shape memory polymers based on DEGDMA and tBA. (iii) Utilize nanoindentation and atomic force microscopy (AFM) to understand the nanoscale behavior of these SMPs, and explore the strain storage and recovery of the polymers from a deformed state. (iv) Study spin coating conditions on thin film quality with designed experiments. (iv) Apply neural networks and genetic algorithms to optimize these systems.

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

    DOEpatents

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

    2009-11-03

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

  20. Temperature and electrical memory of polymer fibers

    SciTech Connect

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

    2014-05-15

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

  1. The Ultimaster Biodegradable-Polymer Sirolimus-Eluting Stent: An Updated Review of Clinical Evidence.

    PubMed

    Chisari, Alberto; Pistritto, Anna Maria; Piccolo, Raffaele; La Manna, Alessio; Danzi, Gian Battista

    2016-01-01

    The Ultimaster coronary stent system (Terumo Corporation, Tokyo, Japan) represents a new iteration in drug-eluting stent (DES) technology that has recently received the Conformité Européenne (CE) mark approval for clinical use. The Ultimaster is a thin-strut, cobalt chromium, biodegradable-polymer, sirolimus-eluting coronary stent. The high elasticity of the biodegradable-polymer (PDLLA-PCL) and the abluminal gradient coating technology are additional novel features of this coronary device. The Ultimaster DES has undergone extensive clinical evaluation in two studies: The CENTURY I and II trials. Results from these two landmark studies suggested an excellent efficacy and safety profile of the Ultimaster DES across several lesion and patient subsets, with similar clinical outcomes to contemporary, new-generation DES. The aim of this review is to summarize the rationale behind this novel DES technology and to provide an update of available evidence about the clinical performance of the Ultimaster DES. PMID:27608017

  2. Thermomechanical properties of polyurethane shape memory polymers

    NASA Astrophysics Data System (ADS)

    Airoldi, Graziella; Corsi, Andrea

    1998-10-01

    Segmented polyurethanes containing soft segments with low molecular weight show shape-memorizing properties. In these materials the advantages of polyurethanes are combined with the features of smart material technology. Shape memory polymers can repeatedly transform their shape and hardness. The dependence of thermal and mechanical properties of shape memory polyurethanes on temperature were investigated experimentally by means of differential scanning calorimetry and static mechanical testing. The results show that as the thermal cycles progress, the residual strain increases and the recovery strain decreases even if these changes saturate after a suitable number of thermomechanical cycles. This kind of behavior suggest a possible training procedure in order to have a reproducible mechanical behavior when the shape memory polymer is introduced into an operating device. Some possible applications in the textile machinery are also shown.

  3. Memory operation mechanism of fullerene-containing polymer memory

    SciTech Connect

    Nakajima, Anri Fujii, Daiki

    2015-03-09

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

  4. Memory operation mechanism of fullerene-containing polymer memory

    NASA Astrophysics Data System (ADS)

    Nakajima, Anri; Fujii, Daiki

    2015-03-01

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

  5. Preclinical evaluation of a novel abluminal surface coated sirolimus eluting stent with biodegradable polymer matrix

    PubMed Central

    Doshi, Manish; Galloni, Marco; Vignolini, Christina; Vyas, Ashwin; Chevli, Bhavesh; Sheiban, Imad

    2015-01-01

    Background Second generation of drug eluting stents (DES) has attempted to improve safety using abluminal sirolimus drug delivery with biodegradable polymers matrix. The present preclinical study was designed to investigate the safety and efficacy profile of Abluminus™ stents (SES). This is a new coronary stent with sirolimus and biodegradable polymer matrix coated on abluminal stent and balloon surface. Methods SES were compared with two controls: bare metal stent (BMS) and BMS + polymer coated stents (PC). All devices (40 stents) were implanted in porcine coronary arteries with primary endpoint of endothelialization at 7 days and subsequent histological and morphometric evaluations at 7, 30 and 90 days. Results Early endothelialization at seven days was complete in all stents. Histology at 30 days revealed minimum inflammation in all groups and increased at 90 days in PC group while it was absent at 180 days. Thirty day morphometry showed significantly reduction of neointimal area in Abluminus™ (SES 0.96±0.48 mm2; BMS 1.83±0.34 mm2; PC 1.76±0.55 mm2; P<0.05); after 90 days neointimal area was 1.10±0.54 mm2 for SES; 1.92±0.36 mm2 for BMS; and 1.94±0.48 mm2 for PC; P<0.05). Neointimal thickness at 30 and 90 days respectively was 0.15±0.07 and 0.18±0.10 mm for SES, 0.57±0.08 and 0.61±0.09 mm for BMS and 0.52±0.09 and 0.59±0.08 mm, P<0.001 for PC group. Conclusions The most significant experimental evidence appears to be earlier endothelialization at 7 days for SES which led to safety of the device. Efficacy of the device was also observed by a reduced neointimal thickness and minimized inflammatory score at all follow-ups. Termination of antiplatelet at 30 days has not shown any further complications. Polymer thickness was almost in negligible amount at 180 days with no inflammation. PMID:26331109

  6. A polymer-free Paclitaxel eluting coronary stent: effects of solvents, drug concentrations and coating methods.

    PubMed

    Lamichhane, Sujan; Gallo, Annemarie; Mani, Gopinath

    2014-06-01

    Some polymer coatings used in drug-eluting stents (DES) cause adverse reactions. Hence, the use of self-assembled monolayers (SAMs) as a polymer-free platform to deliver an anti-proliferative drug (paclitaxel-PAT) from 2D metal substrates was previously demonstrated. In this study, we optimized the PAT coating on SAMs coated 3D coronary stents. For the optimization process, we investigated the effects of solvents (ethanol, DMSO, and their mixtures), drug concentrations (2, 3, 4, 8, and 12 mg/mL) in the coating solution, and coating methods (dip and spray) on PAT deposition. A solvent mixture of 75:25 v/v Et-OH:DMSO was determined to be the best for obtaining smooth and homogenous PAT coating. PAT coated stents prepared using 8 mg/mL and 3 mg/mL concentrations of PAT by dip and spray coating methods, respectively, were optimal in terms of carrying adequate drug doses (0.35 µg/mm(2) for dipping and 0.76 µg/mm(2) for spraying) as well as negligible defects observed in the coating. PAT was successfully released from SAMs coated stents in a biphasic manner with an initial burst followed by a sustained release for up to 10 weeks. Thus, this study sheds light on the effects of solvents, drug concentrations, and coating methods on preparing a polymer-free DES. PMID:24705673

  7. Blood compatibility assessment of polymers used in drug eluting stent coatings.

    PubMed

    Szott, Luisa Mayorga; Irvin, Colleen A; Trollsas, Mikael; Hossainy, Syed; Ratner, Buddy D

    2016-06-01

    Differences in thrombosis rates have been observed clinically between different drug eluting stents. Such differences have been attributed to numerous factors, including stent design, injury created by the catheter delivery system, coating application technologies, and the degree of thrombogenicity of the polymer. The relative contributions of these factors are generally unknown. This work focuses on understanding the thrombogenicity of the polymer by examining mechanistic interactions with proteins, human platelets, and human monocytes of a number of polymers used in drug eluting stent coatings, in vitro. The importance for blood interactions of adsorbed albumin and the retention of albumin was suggested by the data. Microscopic imaging and immunostaining enhanced the interpretation of results from the lactate dehydrogenase cell counting assay and provided insight into platelet interactions, total quantification, and morphometry. In particular, highly spread platelets may be surface-passivating, possibly inhibiting ongoing thrombotic events. In many of the assays used here, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) showed a differentiated protein deposition pattern that may contribute to the explanation of the consistently thromboresistant blood-materials interaction for fluororpolymers cited in literature. These results are supportive of one of several possible factors contributing to the good thromboresistant clinical safety performance of PVDF-HFP coated drug eluting stents. PMID:27083991

  8. Development of multifunctional shape memory polymer foams

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  10. Polymeric coating of surface modified nitinol stent with POSS-nanocomposite polymer.

    PubMed

    Bakhshi, Raheleh; Darbyshire, Arnold; Evans, James Eaton; You, Zhong; Lu, Jian; Seifalian, Alexander M

    2011-08-01

    Stent angioplasty is a successful treatment for arterial occlusion, particularly in coronary artery disease. The clinical communities were enthusiastic about the use of drug-eluting stents; however, these stents have a tendency to be a contributory factor towards late stage thrombosis, leading to mortality in a significant number of patients per year. This work presents an innovative approach in self-expanding coronary stents preparation. We developed a new nanocomposite polymer based on polyhedral oligomeric silsesquioxanes (POSS) and poly(carbonate-urea)urethane (PCU), which is an antithrombogenic and a non-biodegradable polymer with in situ endothelialization properties. The aim of this work is to coat a NiTi stent alloy with POSS-PCU. In prolonged applications in the human body, the corrosion of the NiTi alloy can result in the release of deleterious ions which leads to unwanted biological reactions. Coating the nitinol (NiTi) surface with POSS-PCU can enhance surface resistance and improve biocompatibility. Electrohydrodynamic spraying was used as the polymer deposition process and thus a few experiments were carried out to compare this process with casting. Prior to deposition the NiTi has been surface modified. The peel strength of the deposit was studied before and after degradation of the coating. It is shown that the surface modification enhances the peel strength by 300%. It is also indicated how the adhesion strength of the POSS-PCU coating changes post-exposure to physiological solutions comprised of hydrolytic, oxidative, peroxidative and biological media. This part of the study shows that the modified NiTi presents far greater resistance to decay in peel strength compared to the non-modified NiTi. PMID:21515031

  11. Some design considerations for polymer-free drug-eluting stents: a mathematical approach.

    PubMed

    McGinty, Sean; Vo, Tuoi T N; Meere, Martin; McKee, Sean; McCormick, Christopher

    2015-05-01

    In this paper we provide the first model of drug elution from polymer-free arterial drug-eluting stents. The generalised model is capable of predicting drug release from a number of polymer-free systems including those that exhibit nanoporous, nanotubular and smooth surfaces. We derive analytical solutions which allow us to easily determine the important parameters that control drug release. Drug release profiles are provided, and we offer design recommendations so that the release profile may be tailored to achieve the desired outcome. The models presented here are not specific to drug-eluting stents and may also be applied to other biomedical implants that use nanoporous surfaces to release a drug. PMID:25712386

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

    DOEpatents

    Lee, Abraham P.; Fitch, Joseph P.

    2000-01-01

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

  13. Thermomechanical indentation of shape memory polymers.

    SciTech Connect

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

    2007-04-01

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

  14. Shape Memory Polymer Therapeutic Devices for Stroke

    SciTech Connect

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

    2005-10-11

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

  15. Shape-Memory Polymers for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Yakacki, Christopher M.; Gall, Ken

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

  16. Advances in shape-memory polymer actuation

    NASA Astrophysics Data System (ADS)

    Leng, Jinsong; Liu, Yanju; Lan, Xin

    2009-03-01

    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 3-4μm. 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.

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

    NASA Technical Reports Server (NTRS)

    Hood, Patrick J.

    2011-01-01

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

  18. High-Temperature Shape Memory Polymers

    NASA Technical Reports Server (NTRS)

    Yoonessi, Mitra; Weiss, Robert A.

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  20. Aging effects of epoxy shape memory polymers

    NASA Astrophysics Data System (ADS)

    Dasharathi, Kannan; Shaw, John A.

    2013-04-01

    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.

  1. A mechanistic model for drug release in PLGA biodegradable stent coatings coupled with polymer degradation and erosion.

    PubMed

    Zhu, Xiaoxiang; Braatz, Richard D

    2015-07-01

    Biodegradable poly(d,l-lactic-co-glycolic acid) (PLGA) coating for applications in drug-eluting stents has been receiving increasing interest as a result of its unique properties compared with biodurable polymers in delivering drug for reducing stents-related side effects. In this work, a mathematical model for describing the PLGA degradation and erosion and coupled drug release from PLGA stent coating is developed and validated. An analytical expression is derived for PLGA mass loss that predicts multiple experimental studies in the literature. An analytical model for the change of the number-average degree of polymerization [or molecular weight (MW)] is also derived. The drug transport model incorporates simultaneous drug diffusion through both the polymer solid and the liquid-filled pores in the coating, where an effective drug diffusivity model is derived taking into account factors including polymer MW change, stent coating porosity change, and drug partitioning between solid and aqueous phases. The model is used to describe in vitro sirolimus release from PLGA stent coating, and demonstrates the significance of simultaneous sirolimus release via diffusion through both polymer solid and pore space. The proposed model is compared to existing drug transport models, and the impact of model parameters, limitations and possible extensions of the model are also discussed. PMID:25345656

  2. Release mechanism utilizing shape memory polymer material

    DOEpatents

    Lee, Abraham P.; Northrup, M. Allen; Ciarlo, Dino R.; Krulevitch, Peter A.; Benett, William J.

    2000-01-01

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

  3. Metal complex modified azo polymers for multilevel organic memories

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  4. Antirestenotic Effects of a Novel Polymer-Coated D-24851 Eluting Stent. Experimental Data in a Rabbit Iliac Artery Model

    SciTech Connect

    Lysitsas, Dimitrios N.; Katsouras, Christos S.; Papakostas, John C.; Toumpoulis, Ioannis K.; Angelidis, Charalampos; Bozidis, Petros; Thomas, Christopher G.; Seferiadis, Konstantin; Psychoyios, Nikolaos; Frillingos, Stathis; Pavlidis, Nikolaos; Marinos, Euaggelos; Khaldi, Lubna; Sideris, Dimitris A.; Michalis, Lampros K.

    2007-11-15

    Experimental and clinical data suggest that stents eluting antiproliferative agents can be used for the prevention of in-stent restenosis. Here we investigate in vitro the antiproliferative and apoptotic effect of D-24851 and evaluate the safety and efficacy of D-24851-eluting polymer-coated stents in a rabbit restenosis model (n = 53). Uncoated stents (n = 6), poly (dl-lactide-co-glycolide) (PLGA)-coated stents (n = 7), and PLGA-coated stents loaded with 0.08 {+-} 0.0025 {mu}M (31 {+-} 1 {mu}g; low dose; n = 7), 0.55 {+-} 0.02 {mu}M (216 {+-} 8 {mu}g; high dose; n = 6), and 4.55 {+-} 0.1 {mu}M (1774 {+-} 39 {mu}g; extreme dose; n = 5) of D-24851 were randomly implanted in New Zealand rabbit right iliac arteries and the animals were sacrificed after 28 days for histomorphometric analysis. For the assessment of endothelial regrowth in 90 days, 12 rabbits were subjected to PLGA-coated (n = 3), low-dose (n = 3), high-dose (n = 3), and extreme-dose (n = 3) stent implantation. In vitro studies revealed that D-24851 exerts its growth inhibitory effects via inhibition of proliferation and induction of apoptosis without increasing the expression of heat shock protein-70, a cytoprotective and antiapoptotic protein. Treatment with low-dose D-24851 stents was associated with a significant reduction in neointimal area and percentage stenosis only compared with bare metal stents (38% [P = 0.029] and 35% [P = 0.003] reduction, respectively). Suboptimal healing, however, was observed in all groups of D-24851-loaded stents in 90 days in comparison with PLGA-coated stents. We conclude that low-dose D-24851-eluting polymer-coated stents significantly inhibit neointimal hyperplasia at 28 days through inhibition of proliferation and enhancement of apoptosis. In view of the suboptimal re-endothelialization, longer-term studies are needed in order to establish whether the inhibition of intimal growth is maintained.

  5. Surface characterization of polymer-drug modified vascular stents and intraocular lenses

    NASA Astrophysics Data System (ADS)

    Elachchabi, Amin

    Two of the most important medical devices in clinical use today are endoluminal stents and intraocular lenses (IOLs). In both devices, surface and interfacial properties are of basic importance in the development and clinical performance of these devices. Drug eluting stents have revolutionized the world of interventional cardiology. Research reported here was devoted to the design and development of new drug eluting stents wherein the metallic backbone is completely embedded in a polymeric matrix used also as a drug reservoir. This design, using silicone-drug compositions can lead to higher drug payloads, less tissue damage during angioplasty balloon/stent expansion, and the novel capability of delivering multiple drugs. The adhesion of the polymeric coating to the metallic stent is essential and has not been adequately reported previously. The adhesion of polydimethylsiloxane (PDMS) coatings to a stainless steel stent substrate was shown to be enhanced by the application of mixtures of tetra-n-propyl silicate, tetrabutyltitanate, tetra-2-methoxyethoxysilane, and 3-(trimethoxysilyl)propyl methacrylate coupling agents. Additionally, the effect of drug loading on the stress/strain properties of the polymeric coating is of basic importance. The tensile strength and percent elongation of dexamethasone loaded PDMS films was shown to remain satisfactory for stent coatings at low concentrations (less than 1%) but decreased as the concentrations of dexamethasone in PDMS was increased to 5%. The release of multiple therapeutic agents from PDMS coatings to reduce in-stent restenosis has not been previously reported. The release profile of Paclitaxel, dexamethasone 21-acetate, and their combination from PDMS coatings was studied using high precision liquid chromatography (HPLC). Although dexamethasone release was reduced by paclitaxel, paclitaxel release was unaffected by combination with dexamethasone. Paclitaxel release from the polymeric matrices was shown to inhibit

  6. Shape memory polymer foams for endovascular therapies

    SciTech Connect

    Wilson, Thomas S.; Maitland, Duncan J.

    2015-05-26

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

  7. Shape memory polymer foams for endovascular therapies

    DOEpatents

    Wilson, Thomas S.; Maitland, Duncan J.

    2012-03-13

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

  8. AC Electric Field Activated Shape Memory Polymer Composite

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  9. Induction of nicotinamide-adenine dinucleotide phosphate oxidase and apoptosis by biodegradable polymers in macrophages: implications for stents.

    PubMed

    Potnis, Pushya A; Tesfamariam, Belay; Wood, Steven C

    2011-06-01

    The drug-eluting stent platform has a limited surface area, and a polymer carrier matrix is coated to enable sufficient loading of drugs. The development of a suitable polymer has been challenging because it must exhibit biocompatibility with the intravascular milieu. The use of biodegradable polymers seems to be attractive because it enables drug release as it degrades and is eventually eliminated from the body leaving the permanent metallic stent polymer-free. The aim of this study was to investigate the biocompatibility of biodegradable polymers using the human monocyte cell line. Cultured monocytes differentiated into functional macrophages (THP-1) were incubated with various polymers including poly-L-lactide (PLA), polycaprolactone (PCL), or poly-D, L-lactide-co-glycolide (PLGA) for up to 5 days. Exposure of cells to the polymers resulted in macrophage-polymer adhesion and induced marked pro-oxidant species as measured by calcein AM uptake assay and flow cytometric analysis of 2',7'-dichlorofluorescin fluorescence, respectively. Real-time reverse-transcription polymerase chain reaction and Western blot analysis of expression of nicotinamide-adenine dinucleotide phosphate (NADPH) oxidases revealed enhanced expression of NADPH oxidase subunits in response to PLA and PLGA compared with that of PCL. Flow cytometric analysis of fluorescein isothiocyanate-Annexin V and propium iodide-stained PLA and PGLA polymer-exposed THP-1 cells showed early and late apoptotic changes. Similarly, exposure to the PLA and PGLA polymers, but not to the PCL polymer, resulted in enhanced staining for cleaved poly(ADP-ribose) polymerase-1, a protein fragment produced by caspase cleavage. These results indicate that biodegradable polymers are associated with cell adhesion, NADPH oxidase-induced generation of reactive oxygen species and excess apoptosis. PMID:21436724

  10. Residual stresses in injection molded shape memory polymer parts

    NASA Astrophysics Data System (ADS)

    Katmer, Sukran; Esen, Huseyin; Karatas, Cetin

    2016-03-01

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

  11. Controlled architecture for improved macromolecular memory within polymer networks.

    PubMed

    DiPasquale, Stephen A; Byrne, Mark E

    2016-08-01

    This brief review analyzes recent developments in the field of living/controlled polymerization and the potential of this technique for creating imprinted polymers with highly structured architecture with macromolecular memory. As a result, it is possible to engineer polymers at the molecular level with increased homogeneity relating to enhanced template binding and transport. Only recently has living/controlled polymerization been exploited to decrease heterogeneity and substantially improve the efficiency of the imprinting process for both highly and weakly crosslinked imprinted polymers. Living polymerization can be utilized to create imprinted networks that are vastly more efficient than similar polymers produced using conventional free radical polymerization, and these improvements increase the role that macromolecular memory can play in the design and engineering of new drug delivery and sensing platforms. PMID:27322505

  12. Improving of Mechanical and Shape-Memory Properties in Hyperbranched Epoxy Shape-Memory Polymers

    NASA Astrophysics Data System (ADS)

    Santiago, David; Fabregat-Sanjuan, Albert; Ferrando, Francesc; De la Flor, Silvia

    2016-03-01

    A series of shape-memory epoxy polymers were synthesized using an aliphatic amine and two different commercial hyperbranched poly(ethyleneimine)s with different molecular weights as crosslinking agents. Thermal, mechanical, and shape-memory properties in materials modified with different hyperbranched polymers were analyzed and compared in order to establish the effect of the structure and the molecular weight of the hyperbranched polymers used. The presence of hyperbranched polymers led to more heterogeneous networks, and the crosslinking densities of which increase as the hyperbranched polymer content increases. The transition temperatures can be tailored from 56 to 117 °C depending on the molecular weight and content of the hyperbranched polymer. The mechanical properties showed excellent values in all formulations at room temperature and, specially, at T_{g}^{{E^' with stress at break as high as 15 MPa and strain at break as high as 60 %. The shape-memory performances revealed recovery ratios around 95 %, fixity ratios around 97 %, and shape-recovery velocities as high as 22 %/min. The results obtained in this study reveal that hyperbranched polymers with different molecular weights can be used to enhance the thermal and mechanical properties of epoxy-based SMPs while keeping excellent shape-memory properties.

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

    PubMed Central

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  15. Modeling thermomechanical processes in shape memory polymers under finite deformations

    NASA Astrophysics Data System (ADS)

    Rogovoi, A. A.; Stolbova, O. S.

    2015-11-01

    A model taking into account finite deformations is constructed for the behavior of a shape memory polymer which undergoes a transition from the highly elastic to the vitreous state and back during deformation and temperature change. The obtained relations are tested on problems which have experimental support.

  16. Blocked Shape Memory Effect in Negative Poisson's Ratio Polymer Metamaterials.

    PubMed

    Boba, Katarzyna; Bianchi, Matteo; McCombe, Greg; Gatt, Ruben; Griffin, Anselm C; Richardson, Robert M; Scarpa, Fabrizio; Hamerton, Ian; Grima, Joseph N

    2016-08-10

    We describe a new class of negative Poisson's ratio (NPR) open cell PU-PE foams produced by blocking the shape memory effect in the polymer. Contrary to classical NPR open cell thermoset and thermoplastic foams that return to their auxetic phase after reheating (and therefore limit their use in technological applications), this new class of cellular solids has a permanent negative Poisson's ratio behavior, generated through multiple shape memory (mSM) treatments that lead to a fixity of the topology of the cell foam. The mSM-NPR foams have Poisson's ratio values similar to the auxetic foams prior their return to the conventional phase, but compressive stress-strain curves similar to the ones of conventional foams. The results show that by manipulating the shape memory effect in polymer microstructures it is possible to obtain new classes of materials with unusual deformation mechanisms. PMID:27377708

  17. Nanomaterial coatings applied on stent surfaces.

    PubMed

    Bagheri, Mahsa; Mohammadi, Marzieh; Steele, Terry Wj; Ramezani, Mohammad

    2016-05-01

    The advent of percutaneous coronary intervention and intravascular stents has revolutionized the field of interventional cardiology. Nonetheless, in-stent restenosis, inflammation and late-stent thrombosis are the major obstacles with currently available stents. In order to enhance the hemocompatibility of stents, advances in the field of nanotechnology allow novel designs of nanoparticles and biomaterials toward localized drug/gene carriers or stent scaffolds. The current review focuses on promising polymers used in the fabrication of newer generations of stents with a short synopsis on atherosclerosis and current commercialized stents, nanotechnology's impact on stent development and recent advancements in stent biomaterials is discussed in context. PMID:27111467

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  19. Communication: Theory of melt-memory in polymer crystallization

    NASA Astrophysics Data System (ADS)

    Muthukumar, M.

    2016-07-01

    Details of crystallization processes of a polymer at the crystallization temperature Tc from its melt kept initially at the melt temperature Tm depend profoundly on the nature of the initial melt state and often are accompanied by memory effects. This phenomenon is in contrast to small molecular systems where the supercooling (Tm0-Tc), with Tm0 being the equilibrium melting temperature, and not (Tm - Tc), determines the nature of crystallization. In addressing this five-decade old puzzle of melt-memory in polymer crystallization, we present a theory to describe melt-memory effects, by invoking an intermediate inhomogeneous melt state in the pathway between the melt and crystalline states. Using newly introduced dissolution temperature T10 for the inhomogeneous melt state and the transition temperature Tt0 for the transition between the inhomogeneous melt and crystalline states, analytical formulas are derived for the nucleation rate as a function of the melt temperature. The theory is general to address different kinds of melt-memory effects depending on whether Tm is higher or lower than Tm0. The derived results are in qualitative agreement with known experimental data, while making predictions for further experiments on melt-memory.

  20. Communication: Theory of melt-memory in polymer crystallization.

    PubMed

    Muthukumar, M

    2016-07-21

    Details of crystallization processes of a polymer at the crystallization temperature Tc from its melt kept initially at the melt temperature Tm depend profoundly on the nature of the initial melt state and often are accompanied by memory effects. This phenomenon is in contrast to small molecular systems where the supercooling (Tm (0)-Tc), with Tm (0) being the equilibrium melting temperature, and not (Tm - Tc), determines the nature of crystallization. In addressing this five-decade old puzzle of melt-memory in polymer crystallization, we present a theory to describe melt-memory effects, by invoking an intermediate inhomogeneous melt state in the pathway between the melt and crystalline states. Using newly introduced dissolution temperature T1 (0) for the inhomogeneous melt state and the transition temperature Tt (0) for the transition between the inhomogeneous melt and crystalline states, analytical formulas are derived for the nucleation rate as a function of the melt temperature. The theory is general to address different kinds of melt-memory effects depending on whether Tm is higher or lower than Tm (0). The derived results are in qualitative agreement with known experimental data, while making predictions for further experiments on melt-memory. PMID:27448866

  1. Biomedical Applications of Thermally Activated Shape Memory Polymers

    SciTech Connect

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

    2009-04-10

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

  2. Vascular response to bioresorbable polymer sirolimus-eluting stent vs. permanent polymer everolimus-eluting stent at 9-month follow-up: an optical coherence tomography sub-study from the CENTURY II trial

    PubMed Central

    Kuramitsu, Shoichi; Kazuno, Yoshio; Sonoda, Shinjo; Domei, Takenori; Jinnouchi, Hiroyuki; Yamaji, Kyohei; Soga, Yoshimitsu; Shirai, Shinichi; Ando, Kenji; Saito, Shigeru

    2016-01-01

    Aims The Ultimaster bioresorbable polymer sirolimus-eluting stent (BP-SES) is a newly developed drug-eluting stent (DES) that consists of a thin-strut, cobalt chromium with bioresorbable polymer coated only albuminally. We sought to compare tissue coverage in coronary lesions treated with BP-SES with the XIENCE permanent polymer everolimus-eluting stent (PP-EES) using optical coherence tomography (OCT). Methods and results A total of 36 patients participated in the CENTURY II trial in our institution and were randomly assigned to BP-SES (n = 15) and PP-EES (n = 21). Of these, 27 patients (13 BP-SES and 14 PP-EES) underwent OCT at 9-month follow-up. Tissue coverage and apposition were assessed on each strut, and the results in both groups were compared using multilevel logistic or linear regression models with random effects at three levels: patient, lesion, and struts. A total of 6450 struts (BP-SES, n = 2951; PP-EES, n = 3499) were analysed. Thirty and 79 uncovered struts (1.02 and 2.26%, P = 0.35), and 3 and 4 malapposed struts (0.10 and 0.11%, P = 0.94) were found in BP-SES and PP-EES groups, respectively. Mean neointimal thickness did not significantly differ between both groups (110 ± 10 vs. 93 ± 10 µm, P = 0.22). No significant differences in per cent neointimal volume obstruction (13.2 ± 4.6 vs. 10.5 ± 4.9%, P = 0.14) or other areas-volumetric parameters were detected between both groups. Conclusion BP-SES shows an excellent vascular healing response at 9-month follow-up, which is similar to PP-EES. PMID:26333375

  3. Wafer-scale arrays of nonvolatile polymer memories with microprinted semiconducting small molecule/polymer blends.

    PubMed

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

    2013-11-13

    Nonvolatile ferroelectric-gate field-effect transistors (Fe-FETs) memories with solution-processed ferroelectric polymers are of great interest because of their potential for use in low-cost flexible devices. In particular, the development of a process for patterning high-performance semiconducting channel layers with mechanical flexibility is essential not only for proper cell-to-cell isolation but also for arrays of flexible nonvolatile memories. We demonstrate a robust route for printing large-scale micropatterns of solution-processed semiconducting small molecules/insulating polymer blends for high performance arrays of nonvolatile ferroelectric polymer memory. The nonvolatile memory devices are based on top-gate/bottom-contact Fe-FET with ferroelectric polymer insulator and micropatterned semiconducting blend channels. Printed micropatterns of a thin blended semiconducting film were achieved by our selective contact evaporation printing, with which semiconducting small molecules in contact with a micropatterned elastomeric poly(dimethylsiloxane) (PDMS) mold were preferentially evaporated and absorbed into the PDMS mold while insulating polymer remained intact. Well-defined micrometer-scale patterns with various shapes and dimensions were readily developed over a very large area on a 4 in. wafer, allowing for fabrication of large-scale printed arrays of Fe-FETs with highly uniform device performance. We statistically analyzed the memory properties of Fe-FETs, including ON/OFF ratio, operation voltage, retention, and endurance, as a function of the micropattern dimensions of the semiconducting films. Furthermore, roll-up memory arrays were produced by successfully detaching large-area Fe-FETs printed on a flexible substrate with a transient adhesive layer from a hard substrate and subsequently transferring them to a nonplanar surface. PMID:24070419

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

    PubMed Central

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

    2015-01-01

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

  5. Can Platforms Affect the Safety and Efficacy of Drug-Eluting Stents in the Era of Biodegradable Polymers?: A Meta-Analysis of 34,850 Randomized Individuals

    PubMed Central

    Zhang, Ming-Duo; Li, Xin-He; Nie, Mao-Xiao; Feng, Ting-Ting; Zhao, Xin; Wang, Lu-Ya; Zhao, Quan-Ming

    2016-01-01

    Objective In the era of bare metal stents (BMSs), alloys have been considered to be better materials for stent design than stainless steel. In the era of biodegradable polymer drug-eluting stents (BP-DESs), the safety and efficacy of BP-DESs with different metal platforms (stainless steel or alloys) have not yet been reported, although their polymers are eventually absorbed, and only the metal platforms remain in the body. This study sought to determine the clinical safety and efficacy of BP-DESs with different platforms compared with other stents (other DESs and BMSs). Methods PubMed, Embase and Clinical Trials.gov were searched for randomized controlled trials (RCTs) that compared BP-DESs with other stents. After performing pooled analysis of BP-DESs and other stents, we performed a subgroup analysis using two classification methods: stent platform and follow-up time. The study characteristics, patient characteristics and clinical outcomes were abstracted. Results Forty RCTs (49 studies) comprising 34,850 patients were included. Biodegradable polymer stainless drug-eluting stents (BP-stainless DESs) were superior to the other stents [mainly stainless drug-eluting stents (DESs)] in terms of pooled definite/probable stent thrombosis (ST) (OR [95% CI] = 0.76[0.61–0.95], p = 0.02), long-term definite/probable ST (OR [95% CI] = 0.73[0.57–0.94], p = 0.01), very late definite/probable ST (OR [95% CI] = 0.56[0.33–0.93], p = 0.03) and long-term definite ST. BP-stainless DESs had lower rates of pooled, mid-term and long-term target vessel revascularization (TVR) and target lesion revascularization (TLR) than the other stainless DESs and BMSs. Furthermore, BP-stainless DESs were associated with lower rates of long-term death than other stainless DESs and lower rates of mid-term myocardial infarction than BMSs. However, only the mid-term and long-term TVR rates were superior in BP-alloy DESs compared with the other stents. Conclusion Our results indirectly suggest that

  6. Simulations of Self-Expanding Braided Stent Using Macroscopic Model of NiTi Shape Memory Alloys Covering R-Phase

    NASA Astrophysics Data System (ADS)

    Frost, M.; Sedlák, P.; Kruisová, A.; Landa, M.

    2014-07-01

    Self-expanding stents or stentgrafts made from Nitinol superelastic alloy are widely used for a less invasive treatment of disease-induced localized flow constriction in the cardiovascular system. The therapy is based on insertion of a stent into a blood vessel to maintain the inner diameter of the vessel; it provides highly effective results at minimal cost and with reduced hospital stays. However, since stent is an external mechanical healing tool implemented into human body for quite a long time, information on the mechanical performance of it is of fundamental importance with respect to patient's safety and comfort. Advantageously, computational structural analysis can provide valuable information on the response of the product in an environment where in vivo experimentation is extremely expensive or impossible. With this motivation, a numerical model of a particular braided self-expanding stent was developed. As a reasonable approximation substantially reducing computational demands, the stent was considered to be composed of a set of helical springs with specific constrains reflecting geometry of the structure. An advanced constitutive model for NiTi-based shape memory alloys including R-phase transition was employed in analysis. Comparison to measurements shows a very good match between the numerical solution and experimental results. Relation between diameter of the stent and uniform radial pressure on its surface is estimated. Information about internal phase and stress state of the material during compression loading provided by the model is used to estimate fatigue properties of the stent during cyclic loading.

  7. Shape memory polymers based on uniform aliphatic urethane networks

    SciTech Connect

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

    2007-01-19

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

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

    PubMed Central

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

    2016-01-01

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

  9. Drug-eluting stents to prevent stent thrombosis and restenosis.

    PubMed

    Im, Eui; Hong, Myeong-Ki

    2016-01-01

    Although first-generation drug-eluting stents (DES) have significantly reduced the risk of in-stent restenosis, they have also increased the long-term risk of stent thrombosis. This safety concern directly triggered the development of new generation DES, with innovations in stent platforms, polymers, and anti-proliferative drugs. Stent platform materials have evolved from stainless steel to cobalt or platinum-chromium alloys with an improved strut design. Drug-carrying polymers have become biocompatible or biodegradable and even polymer-free DES were introduced. New limus-family drugs (such as everolimus, zotarolimus or biolimus) were adopted to enhance stent performances. As a result, these new DES demonstrated superior vascular healing responses on intracoronary imaging studies and lower stent thrombotic events in actual patients. Recently, fully-bioresorbable stents (scaffolds) have been introduced, and expanding their applications. In this article, the important concepts and clinical results of new generation DES and bioresorbable scaffolds are described. PMID:26567863

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  11. Enhanced drug delivery capabilities from stents coated with absorbable polymer and crystalline drug

    PubMed Central

    Carlyle, Wenda C.; McClain, James B.; Tzafriri, Abraham R.; Bailey, Lynn; Zani, Brett G.; Markham, Peter M.; Stanley, James R.L.; Edelman, Elazer R.

    2015-01-01

    Current drug eluting stent (DES) technology is not optimized with regard to the pharmacokinetics of drug delivery. A novel, absorbable-coating sirolimus-eluting stent (AC-SES) was evaluated for its capacity to deliver drug more evenly within the intimal area rather than concentrating drug around the stent struts and for its ability to match coating erosion with drug release. The coating consisted of absorbable poly-lactide-co-glycolic acid (PLGA) and crystalline sirolimus deposited by a dry-powder electrostatic process. The AC-SES demonstrated enhanced drug stability under simulated use conditions and consistent drug delivery balanced with coating erosion in a porcine coronary implant model. The initial drug burst was eliminated and drug release was sustained after implantation. The coating was absorbed within 90 days. Following implantation into porcine coronary arteries the AC-SES coating is distributed in the surrounding intimal tissue over the course of several weeks. Computational modeling of drug delivery characteristics demonstrates how distributed coating optimizes the load of drug immediately around each stent strut and extends drug delivery between stent struts. The result was a highly efficient arterial uptake of drug with superior performance to a clinical bare metal stent (BMS). Neointimal thickness (0.17±0.07 mm vs. 0.28±0.11 mm) and area percent stenosis (22±9% vs. 35±12%) were significantly reduced (p<0.05) by the AC-SES compared to the BMS 30 days after stent implantation in an overlap configuration in porcine coronary arteries. Inflammation was significantly reduced in the AC-SES compared to the BMS at both 30 and 90 days after implantation. Biocompatible, rapidly absorbable stent coatings enable the matching of drug release with coating erosion and provide for the controlled migration of coating material into tissue to reduce vicissitudes in drug tissue levels, optimizing efficacy and reducing potential toxicity. PMID:22800575

  12. Fiber laser micromachining of thin NiTi tubes for shape memory vascular stents

    NASA Astrophysics Data System (ADS)

    Liu, Lei; Li, Dong Bo; Tong, Yi Fei; Zhu, Yu Fu

    2016-07-01

    Nickel titanium (NiTi) alloy has widely been used in the vascular stent manufacturing due to its excellent properties. Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser is commonly used for the preparation of metal vascular stents. Recently, fiber lasers have been used for stent profiling for better cutting quality. To investigate the cutting-kerf characters of NiTi vascular stents fabricated by fiber laser cutting, laser cutting experiments with thin NiTi tubes were conducted in this study, while NiTi sheets were used in other fiber laser cutting studies. Different with striation topography, new topographies such as layer topography and topography mixed with layers and striations were observed, and the underlying reason for new topographies was also discussed. Comparative research on different topographies was conducted through analyzing the surface roughness, kerf width, heat-affected zone (HAZ) and dross formation. Laser cutting process parameters have a comprehensive influence on the cutting quality; in this study, the process parameters' influences on the cutting quality were studied from the view of power density along the cutting direction. The present research provides a guideline for improving the cutting quality of NiTi vascular stents.

  13. A randomized, prospective, intercontinental evaluation of a bioresorbable polymer sirolimus-eluting coronary stent system: the CENTURY II (Clinical Evaluation of New Terumo Drug-Eluting Coronary Stent System in the Treatment of Patients with Coronary Artery Disease) trial

    PubMed Central

    Saito, Shigeru; Valdes-Chavarri, Mariano; Richardt, Gert; Moreno, Raul; Iniguez Romo, Andrés; Barbato, Emanuele; Carrie, Didier; Ando, Kenji; Merkely, Bela; Kornowski, Ran; Eltchaninoff, Hélène; James, Stefan; Wijns, William

    2014-01-01

    Aim The aim of this study was to establish safety and efficacy of a new sirolimus-eluting stent with bioresorbable polymer, Ultimaster (BP-SES). Sirolimus-eluting stent with bioresorbable polymer was compared with everolimus-eluting, permanent polymer, Xience stent (PP-EES) in the frame of a CENTURY II clinical trial designed to make global clinical data compliant with regulatory requirements in Europe and Japan. Methods and results The CENTURY II is a prospective, multicentre, randomized (1 : 1), single blind, controlled, non-inferiority clinical trial conducted at 58 study sites in Japan, Europe, and Korea. A total of 1123 patients requiring a percutaneous coronary intervention (PCI) procedure, with implantation of drug-eluting stent (DES), were enrolled [total population (TP)]. Randomization of patients was stratified for the subset of patients matching requirements for DES in Japan (Cohort JR, n = 722). Baseline patient demographic and angiographic characteristics were similar in both study arms, with minimal differences between the TP and Cohort JR. The primary endpoint, freedom from target lesion failure (TLF) at 9 months—TLF [composite of cardiac death, target-vessel-related myocardial infarction (MI) and target lesion revascularization]—was 95.6% with BP-SES and 95.1% with PP-EES (Pnon-inferiority<0.0001). Composite of cardiac death and MI rate was 2.9 and 3.8% (P = 0.40) and target vessel revascularization was 4.5% with BP-SES and 4.2% with PP-EES (P = 0.77). The stent thrombosis rate was 0.9% in both arms. In Cohort JR, freedom from TLF was 95.9 and 94.6% (Pnon-inferiority < 0.0005) with BP-SES and PP-EES, respectively. Conclusion The new bioresorbable polymer sirolimus-eluting stent showed safety and efficacy profiles similar to durable polymer everolimus-eluting stent at 9-month follow-up. Study registration number UMIN000006940. PMID:24847155

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

    PubMed

    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

    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

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

    SciTech Connect

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

    2005-09-06

    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.

  16. Shape memory polymer sensors for tracking cumulative environmental exposure

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

  17. Vitamin-C delivery from CoCr alloy surfaces using polymer-free and polymer-based platforms for cardiovascular stent applications.

    PubMed

    Thiruppathi, Eagappanath; Mani, Gopinath

    2014-06-01

    Antiproliferative drugs such as paclitaxel and sirolimus are delivered from stents to inhibit the growth of smooth muscle cells (SMCs) for preventing neointimal hyperplasia. However, these drugs delay the growth of endothelial cells (ECs) as well and cause late stent thrombosis. We recently demonstrated the use of Vitamin-C (l-ascorbic acid, l-AA) over paclitaxel and sirolimus for inhibiting SMCs growth and promoting EC growth simultaneously. In this study, we have investigated the delivery of l-AA from CoCr alloy surfaces for potential use in stents. A polymer-free phosphoric acid (PA) platform and a polymer-based poly(lactic-co-glycolic acid) (PLGA) platform were used for coating l-AA onto CoCr surfaces. For the PA platform, FTIR confirmed that the PA was coated on CoCr, while the AFM showed that the PA coating on the CoCr surface was homogeneous. The successful deposition of l-AA on PA-coated CoCr was also confirmed by FTIR. The uniform distribution of l-AA crystals on PA-coated CoCr was shown by SEM, optical profilometer, and AFM. The drug release studies showed that l-AA (276 μg/cm(2)) was burst released from the PA platform by 1 h. For the PLGA platform, SEM showed that the l-AA incorporated polymer films were smoothly and uniformly coated on CoCr. FTIR showed that l-AA was incorporated into the bulk of the PLGA film. DSC showed that the l-AA was present in an amorphous form and formed an intermolecular bonding interaction with PLGA. The drug release studies showed that l-AA was sustained released from the PLGA coated CoCr for up to 24 h. The SEM, FTIR, and DSC characterizations of samples collected post drug release shed light on the mechanism of l-AA release from PLGA coated CoCr. Thus, this study demonstrated the delivery of l-AA from biomaterial surfaces for potential applications in stents and other implantable medical devices. PMID:24832897

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

    NASA Astrophysics Data System (ADS)

    Nair, Devatha P.

    2011-12-01

    The focus of this research was to formulate, characterize and tailor the reaction methodologies and material properties of thiol-vinyl systems to develop novel polymer platforms for a range of engineering applications. Thiol-ene photopolymers were demonstrated to exhibit several advantageous characteristics for shape memory polymer systems for a range of biomedical applications. The thiol-ene shape memory polymer systems were tough and flexible as compared to the acrylic control systems with glass transition temperatures between 30 and 40 °C; ideal for actuation at body temperature. The thiol-ene polymers also exhibited excellent shape fixity and a rapid and distinct shape memory actuation response along with free strain recoveries of greater than 96% and constrained stress recoveries of 100%. Additionally, two-stage reactive thiol-acrylate systems were engineered as a polymer platform technology enabling two independent sets of polymer processing and material properties. There are distinct advantages to designing polymer systems that afford two distinct sets of material properties -- an intermediate polymer that would enable optimum handling and processing of the material (stage 1), while maintaining the ability to tune in different, final properties that enable the optimal functioning of the polymeric material (stage 2). To demonstrate the range of applicability of the two-stage reactive systems, three specific applications were demonstrated; shape memory polymers, lithographic impression materials, and optical materials. The thiol-acrylate reactions exhibit a wide range of application versatility due to the range of available thiol and acrylate monomers as well as reaction mechanisms such as Michael Addition reactions and free radical polymerizations. By designing a series of non-stoichiometeric thiol-acrylate systems, a polymer network is initially formed via a base catalyzed 'click' Michael addition reaction. This self-limiting reaction results in a Stage 1

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

    PubMed

    Kumar, Bipin; Hu, Jinlian; Pan, Ning

    2016-01-01

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

  20. Electroactive thermoset shape memory polymer nanocomposite filled with nanocarbon powders

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

    This paper concerns an electroactive thermoset styrene-based shape memory polymer (SMP) nanocomposite filled with nanosized (30 nm) carbon powders. With an increase of the incorporated nanocarbon powders of the SMP composite, its glass transition temperature (Tg) decreases and storage modulus increases. Due to the high micro-porosity and homogeneous distributions of nanocarbon powders in the SMP matrix, the SMP composite shows good electrical conductivity with a percolation of about 3.8%. This percolation threshold is slightly lower than that of many other carbon-based conductive polymer composites. Consequently, due to the relatively high electrical conductivity, a sample filled with 10 vol% nanocarbon powders shows a good electroactive shape recovery performance heating by a voltage of 30 V above a transition temperature of 56-69 °C.

  1. Thermoset shape-memory polymer nanocomposite filled with nanocarbon powders

    NASA Astrophysics Data System (ADS)

    Lan, Xin; Liu, Yanju; Leng, Jinsong

    2009-07-01

    A system of a thermoset styrene-based shape-memory polymer (SMP) filled with nanocarbon powders is investigated in this paper. The thermomechanical properties are characterized by thermal gravity analysis, differential scanning calorimetery and dynamic mechanical analysis. In addition, the distribution of CB is investigated by scanning electron microscope. To realize the electroactive stimuli of SMP, the electrical conductivity of SMP filled with various amounts of CB is characterized. The percolation threshold of electrically conductive SMP filled with CB is about 3.8 % (volume fraction of CB), which is much lower than many other electrically conductive polymers. When applying a voltage of 30V, the shape recovery process of SMP/CB (10 vol%) can be realized in about 100s.

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

    PubMed

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

    2014-01-01

    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. PMID:24423789

  3. Morphological and mechanical analysis of electrospun shape memory polymer fibers

    NASA Astrophysics Data System (ADS)

    Budun, Sinem; İşgören, Erkan; Erdem, Ramazan; Yüksek, Metin

    2016-09-01

    Shape memory block co-polymer Polyurethane (PU) fibers were fabricated by electrospinning technique. Four different solution concentrations (5 wt.%, 10 wt.%, 15 wt.% and 20 wt.%) were prepared by using Tetrahydrofuran (THF)/N,N-dimethylformamide (DMF) (50:50, v/v) as solvents, and three different voltages (30 kV, 35 kV and 38.9 kV) were determined for the electrospinning process. Solution properties were explored in terms of viscosity and electrical conductivity. It was observed that as the polymer concentration increased in the solution, the conductivity declined. Morphological characteristics of the obtained fibers were analyzed through Scanning Electron Microscopy (SEM) measurements. Findings indicated that fiber morphology varied especially with polymer concentration and applied voltage. Obtained fiber diameter ranged from 112 ± 34 nm to 2046 ± 654 nm, respectively. DSC analysis presented that chain orientation of the polymer increased after electrospinning process. Shape fixity and shape recovery calculations were realized. The best shape fixity value (92 ± 4%) was obtained for Y10K30 and the highest shape recovery measurement (130 ± 4%) was belonged to Y15K39. Mechanical properties of the electrospun webs were also investigated in both machine and transverse directions. Tensile and elongation values were also affected from fiber diameter distribution and morphological characteristics of the electrospun webs.

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

  5. Multimaterial 4D Printing with Tailorable Shape Memory Polymers

    NASA Astrophysics Data System (ADS)

    Ge, Qi; Sakhaei, Amir Hosein; Lee, Howon; Dunn, Conner K.; Fang, Nicholas X.; Dunn, Martin L.

    2016-08-01

    We present a new 4D printing approach that can create high resolution (up to a few microns), multimaterial shape memory polymer (SMP) architectures. The approach is based on high resolution projection microstereolithography (PμSL) and uses a family of photo-curable methacrylate based copolymer networks. We designed the constituents and compositions to exhibit desired thermomechanical behavior (including rubbery modulus, glass transition temperature and failure strain which is more than 300% and larger than any existing printable materials) to enable controlled shape memory behavior. We used a high resolution, high contrast digital micro display to ensure high resolution of photo-curing methacrylate based SMPs that requires higher exposure energy than more common acrylate based polymers. An automated material exchange process enables the manufacture of 3D composite architectures from multiple photo-curable SMPs. In order to understand the behavior of the 3D composite microarchitectures, we carry out high fidelity computational simulations of their complex nonlinear, time-dependent behavior and study important design considerations including local deformation, shape fixity and free recovery rate. Simulations are in good agreement with experiments for a series of single and multimaterial components and can be used to facilitate the design of SMP 3D structures.

  6. Post-Polymerization Crosslinked Polyurethane Shape-Memory Polymers

    PubMed Central

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

    2011-01-01

    Novel urethane shape-memory polymers (SMPs) of significant industrial relevance have been synthesized and characterized. Chemically crosslinked SMPs have traditionally been made in a one-step polymerization of monomers and crosslinking agents. However, these new post-polymerization crosslinked SMPs can be processed into complex shapes by thermoplastic manufacturing methods and later crosslinked by heat exposure or by electron beam irradiation. Several series of linear, olefinic urethane polymers were made from 2-butene-1,4-diol, other saturated diols, and various aliphatic diisocyanates. These thermoplastics were melt-processed into desired geometries and thermally crosslinked at 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

  7. Multimaterial 4D Printing with Tailorable Shape Memory Polymers.

    PubMed

    Ge, Qi; Sakhaei, Amir Hosein; Lee, Howon; Dunn, Conner K; Fang, Nicholas X; Dunn, Martin L

    2016-01-01

    We present a new 4D printing approach that can create high resolution (up to a few microns), multimaterial shape memory polymer (SMP) architectures. The approach is based on high resolution projection microstereolithography (PμSL) and uses a family of photo-curable methacrylate based copolymer networks. We designed the constituents and compositions to exhibit desired thermomechanical behavior (including rubbery modulus, glass transition temperature and failure strain which is more than 300% and larger than any existing printable materials) to enable controlled shape memory behavior. We used a high resolution, high contrast digital micro display to ensure high resolution of photo-curing methacrylate based SMPs that requires higher exposure energy than more common acrylate based polymers. An automated material exchange process enables the manufacture of 3D composite architectures from multiple photo-curable SMPs. In order to understand the behavior of the 3D composite microarchitectures, we carry out high fidelity computational simulations of their complex nonlinear, time-dependent behavior and study important design considerations including local deformation, shape fixity and free recovery rate. Simulations are in good agreement with experiments for a series of single and multimaterial components and can be used to facilitate the design of SMP 3D structures. PMID:27499417

  8. Thermally driven microfluidic pumping via reversible shape memory polymers

    NASA Astrophysics Data System (ADS)

    Robertson, J. M.; Rodriguez, R. X.; Holmes, L. R., Jr.; Mather, P. T.; Wetzel, E. D.

    2016-08-01

    The need exists for autonomous microfluidic pumping systems that utilize environmental cues to transport fluid within a network of channels for such purposes as heat distribution, self-healing, or optical reconfiguration. Here, we report on reversible thermally driven microfluidic pumping enabled by two-way shape memory polymers. After developing a suitable shape memory polymer (SMP) through variation in the crosslink density, thin and flexible microfluidic devices were constructed by lamination of plastic films with channels defined by laser-cutting of double-sided adhesive film. SMP blisters integrated into the devices provide thermally driven pumping, while opposing elastic blisters are used to generate backpressure for reversible operation. Thermal cycling of the device was found to drive reversible fluid flow: upon heating to 60 °C, the SMP rapidly contracted to fill the surface channels with a transparent fluid, and upon cooling to 8 °C the flow reversed and the channel re-filled with black ink. Combined with a metallized backing layer, this device results in refection of incident light at high temperatures and absorption of light (at the portions covered with channels) at low temperatures. We discuss power-free, autonomous applications ranging from thermal regulation of structures to thermal indication via color change.

  9. Multimaterial 4D Printing with Tailorable Shape Memory Polymers

    PubMed Central

    Ge, Qi; Sakhaei, Amir Hosein; Lee, Howon; Dunn, Conner K.; Fang, Nicholas X.; Dunn, Martin L.

    2016-01-01

    We present a new 4D printing approach that can create high resolution (up to a few microns), multimaterial shape memory polymer (SMP) architectures. The approach is based on high resolution projection microstereolithography (PμSL) and uses a family of photo-curable methacrylate based copolymer networks. We designed the constituents and compositions to exhibit desired thermomechanical behavior (including rubbery modulus, glass transition temperature and failure strain which is more than 300% and larger than any existing printable materials) to enable controlled shape memory behavior. We used a high resolution, high contrast digital micro display to ensure high resolution of photo-curing methacrylate based SMPs that requires higher exposure energy than more common acrylate based polymers. An automated material exchange process enables the manufacture of 3D composite architectures from multiple photo-curable SMPs. In order to understand the behavior of the 3D composite microarchitectures, we carry out high fidelity computational simulations of their complex nonlinear, time-dependent behavior and study important design considerations including local deformation, shape fixity and free recovery rate. Simulations are in good agreement with experiments for a series of single and multimaterial components and can be used to facilitate the design of SMP 3D structures. PMID:27499417

  10. Post-Polymerization Crosslinked Polyurethane Shape-Memory Polymers.

    PubMed

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

    2011-07-01

    Novel urethane shape-memory polymers (SMPs) of significant industrial relevance have been synthesized and characterized. Chemically crosslinked SMPs have traditionally been made in a one-step polymerization of monomers and crosslinking agents. However, these new post-polymerization crosslinked SMPs can be processed into complex shapes by thermoplastic manufacturing methods and later crosslinked by heat exposure or by electron beam irradiation. Several series of linear, olefinic urethane polymers were made from 2-butene-1,4-diol, other saturated diols, and various aliphatic diisocyanates. These thermoplastics were melt-processed into desired geometries and thermally crosslinked at 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 T(g), 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

  11. Variable stiffness property study on shape memory polymer composite tube

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

    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.

  12. Shape memory polymer hexachiral auxetic structures with tunable stiffness

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  13. Shape memory-based tunable resistivity of polymer composites

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  14. Nine-Months Clinical Outcome of Biodegradable Polymer Coated Sirolimus-eluting Stent System: A Multi-Centre “Real-World” Experience

    PubMed Central

    Prajapati, Jayesh; Raheem, Asif; Thakkar, Kamlesh; Kothari, Shivani; Thakkar, Ashok

    2015-01-01

    Background The main culprit in first-generation drug eluting stents is ‘durable’ polymer, whose continuous presence may impair arterial healing and ultimately have a negative impact on late outcomes. The main enigma behind the biodegradable polymer usage is its degradation after elution of drug. This reduces adverse events in unselected patients with complex coronary artery lesions treated with biodegradable polymer coated sirolimus-eluting stents. Aim The aim of the INDOLIMUS-G Registry was to evaluate safety and efficacy of the Indolimus (Sahajanand Medical Technologies Pvt. Ltd., Surat, India) sirolimus-eluting stents in large cohorts of unselected patients with complex coronary artery lesions. Materials and Methods It is a multi-centre, non-randomized retrospective registry with a clear aim of evaluating safety and efficacy of the Indolimus sirolimus-eluting stents in consecutive patients enrolled between April 2012 and May 2014. The primary end-point of the study was major adverse cardiac events (MACE), which is a composite of cardiac death, myocardial infarction (MI), target lesion revascularization (TLR), target vessel revascularization (TVR) and stent thrombosis (ST) at the end of follow-up. Clinical follow-up were scheduled at the end of 30-days, 6-months, and 9-months period. Results The mean age of enrolled patients was 52.6 ± 11.0 years. A total of 1137 lesions were intervened successfully with 1242 stents (1.09 ± 0.30 stent per lesion). The average stent length and diameter was 27.42 ± 9.01 mm and 3.12 ± 0.36 mm respectively. There were 740 (73.40%) male patients, indicating their high prevalence. Diabetes, hypertension and totally occluded lesions were found in 372 (36.90%), 408 (40.47%) and 170 (16.86%) patients, respectively. This showed that study also included high risk complex lesions and not ideal recruited lesions. The incidence of MACE at 30-days, 6-months and 9-months were 3 (0.30%), 18 (1.80%) and 22 (2.20%) respectively. At 9-months

  15. Clinical Outcomes from Unselected “Real-World” Patients with Long Coronary Lesion Receiving 40 mm Biodegradable Polymer Coated Sirolimus-Eluting Stent

    PubMed Central

    Polavarapu, Anurag; Polavarapu, Raghava Sarma; Prajapati, Jayesh; Thakkar, Kamlesh; Raheem, Asif; Mayall, Tamanpreet; Thakkar, Ashok

    2015-01-01

    Background. Long lesions being implanted with drug-eluting stents (DES) are associated with relatively high restenosis rates and higher incidences of adverse events. Objectives. We aimed to examine the safety and efficacy of the long (40 mm) biodegradable polymer coated Indolimus sirolimus-eluting stent (SES) in real-world patients with long coronary lesions. Methods. This study was observational, nonrandomized, retrospective, and carried out in real-world patients. A total of 258 patients were enrolled for the treatment of long coronary lesions, with 40 mm Indolimus. The primary endpoints in the study were incidence of major adverse cardiac events (MACE), a miscellany of cardiac death, myocardial infarction (MI), target lesion revascularization (TLR) or target vessel revascularization (TVR), and stent thrombosis (ST) up to 6-month follow-up. Results. The study population included higher proportion of males (74.4%) and average age was 53.2 ± 11.0 years. A total of 278 lesions were intervened successfully with 280 stents. The observed MACE at 6-month follow-up was 2.0%, which included 0.8% cardiac death and 1.2% MI. There were no TLR or TVR and ST observed during 6-month follow-up. Conclusions. The long (40 mm) Indolimus stent demonstrated low MACE rate and was proven to be safe and effective treatment for long lesions in “real-world” patients. PMID:26579328

  16. Clinical Outcomes from Unselected "Real-World" Patients with Long Coronary Lesion Receiving 40 mm Biodegradable Polymer Coated Sirolimus-Eluting Stent.

    PubMed

    Polavarapu, Anurag; Polavarapu, Raghava Sarma; Prajapati, Jayesh; Thakkar, Kamlesh; Raheem, Asif; Mayall, Tamanpreet; Thakkar, Ashok

    2015-01-01

    Background. Long lesions being implanted with drug-eluting stents (DES) are associated with relatively high restenosis rates and higher incidences of adverse events. Objectives. We aimed to examine the safety and efficacy of the long (40 mm) biodegradable polymer coated Indolimus sirolimus-eluting stent (SES) in real-world patients with long coronary lesions. Methods. This study was observational, nonrandomized, retrospective, and carried out in real-world patients. A total of 258 patients were enrolled for the treatment of long coronary lesions, with 40 mm Indolimus. The primary endpoints in the study were incidence of major adverse cardiac events (MACE), a miscellany of cardiac death, myocardial infarction (MI), target lesion revascularization (TLR) or target vessel revascularization (TVR), and stent thrombosis (ST) up to 6-month follow-up. Results. The study population included higher proportion of males (74.4%) and average age was 53.2 ± 11.0 years. A total of 278 lesions were intervened successfully with 280 stents. The observed MACE at 6-month follow-up was 2.0%, which included 0.8% cardiac death and 1.2% MI. There were no TLR or TVR and ST observed during 6-month follow-up. Conclusions. The long (40 mm) Indolimus stent demonstrated low MACE rate and was proven to be safe and effective treatment for long lesions in "real-world" patients. PMID:26579328

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  18. Thermo-mechanical behavior of epoxy shape memory polymer foams

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    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 transition temperature of the foam was measured to be approximately 90 °C and compression and tensile tests were performed at temperatures ranging from 25 to 125 °C. Various shape recovery tests were used to measure recovery properties under different thermo-mechanical conditions. Tensile strain to failure was measured as a function of temperature to probe the maximum recovery limits of the foam in both temperature and strain space. Compression tests were performed to examine compressibility of the material as a function of temperature; these foams can be compacted as much as 80% and still experience full strain recovery over multiple cycles. Furthermore, both tensile strain to failure tests and cyclic compression recovery tests revealed that deforming at a temperature of 80 °C maximizes macroscopic strain recovery. Deformation temperatures above or below this optimal value lead to lower failure strains in tension and the accumulation of non-recoverable strains in cyclic compression. Micro-computed tomography (micro-CT) scans of the foam at various compressed states were used to understand foam deformation mechanisms. The micro-CT studies revealed the bending, buckling, and collapse of cells with increasing compression, consistent with results from published numerical simulations.

  19. Thermomechanical characterization of environmentally conditioned shape memory polymer using nanoindentation

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

  20. The future of drug eluting stents

    PubMed Central

    Anis, R R; Karsch, K R

    2006-01-01

    In‐stent restenosis (ISR) is the major drawback of percutaneous coronary interventions, occurring in 10–40% of patients. Drug eluting stents (DES) are successful in a large majority of patients in preventing restenosis for the first year after implantation. Recently, new stents have emerged that are loaded with anti‐inflammatory, antimigratory, antiproliferative, or pro‐healing drugs. These drugs are supposed to inhibit inflammation and neointimal growth and subsequently ISR. The future of DES lies in the development of better stents with new stent designs, better polymers including biological polymers and biological biodissolvable stent coatings, and new, better drugs. PMID:16216857

  1. A clinical evaluation of the ProNOVA XR polymer-free sirolimus eluting coronary stent system in the treatment of patients with de novo coronary artery lesions (EURONOVA XR I study)☆

    PubMed Central

    Legutko, Jacek; Zasada, Wojciech; Kałuża, Grzegorz L.; Heba, Grzegorz; Rzeszutko, Lukasz; Jakala, Jacek; Dragan, Jacek; Klecha, Artur; Giszterowicz, Dawid; Dobrowolski, Wojciech; Partyka, Łukasz; Jayaraman, Swaminathan; Dudek, Dariusz

    2013-01-01

    Aims Evaluation of safety and efficacy of ProNOVA XR, a new generation of polymer-free sirolimus eluting stents (SES), utilizing a pharmaceutical excipient for timed release of sirolimus from the XR platform. Methods and results Safety and efficacy of ProNOVA XR coronary stent system was examined in EURONOVA prospective, single arm, multi-center registry of 50 patients with de novo native coronary lesions up to 28 mm in length in arteries between 2.25 and 4 mm. At 6-month, in-stent late lumen loss by QCA was 0.45 ± 0.41 mm and in-stent neointimal volume obstruction in the IVUS sub-study was 14 ± 11%. One-year clinical follow-up revealed a favorable safety profile, with 2% of in-hospital MACE and 6.4% of MACE from hospital discharge up to 12 months (including 1 cardiac death >30 days after stent implantation and 2 TLRs). According to the ARC definition, there was no definite or probable stent thrombosis and 1 possible stent thrombosis (2%) up to 12 months of clinical follow-up. Conclusions In this preliminary evaluation, ProNOVA XR polymer-free sirolimus eluting stent system appeared safe with an early promise of adequate effectiveness in the treatment of de novo coronary lesions in up to 12 months of clinical, angiographic and IVUS follow-up. PMID:23992999

  2. Digital memory versatility of fully π-conjugated donor-acceptor hybrid polymers.

    PubMed

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

    2014-06-11

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

  3. Technical overview on the MiStent coronary stent.

    PubMed

    McCLAIN, James B; Carlyle, Wenda C; Donohoe, Dennis J; Ormiston, John A

    2016-10-01

    Drug-eluting stents (DES) have dramatically improved the long-term efficacy of percutaneous coronary intervention (PCI). Over the last decade there have been numerous advances in DES platforms, however, all but one currently approved DES in the United States and many of the approved DES worldwide still have 3 common features: a metal stent platform, an anti-proliferative drug, and a permanent polymer. In this context, the polymer is critical to control drug release, but the polymer serves no purpose after the drug is eluted. While designed to be completely biocompatible, synthetic polymers have the potential to illicit an inflammatory response within the vessel including but not limited to delayed healing and hypersensitivity. Adverse vascular reactions to these polymers have been implicated as a cause of very late stent thrombosis, ongoing intimal hyperplasia and late "catch-up" in addition to neoatherosclerosis. To avoid the long-term risks associated with prolonged polymer exposure, DES with bioabsorbable polymers have been developed. The MiStent® Sirolimus-Eluting Absorbable Polymer Coronary Stent System (MiStent SES) (MiCell Technologies, Durham, NC, USA) combines crystalline sirolimus, a rapidly absorbing polylactide-co-glycolic acid (PLGA) coating and a thin-strut cobalt chromium alloy stent platform (Genius MAGIC® Stent System, EuroCor GmbH, Germany). MiCell's supercritical fluid technology allows a rigorously controlled, solvent-free drug and polymer coating to be applied to a bare-metal stent. This solvent-free application of drug uniquely allows a crystalline form of sirolimus to be used on the MiStent SES potentially providing improved clinical benefits. It avoids the uncontrolled burst of drug seen with other DES, provides uniform drug delivery around and between the stent struts, and allows the anti-inflammatory and anti-restenotic drug (sirolimus) to be present in the tissue through the entire polymer absorption period and for months after the

  4. Favorable Outcomes after Implantation of Biodegradable Polymer Coated Sirolimus-Eluting Stents in Diabetic Population: Results from INDOLIMUS-G Diabetic Registry

    PubMed Central

    Polavarapu, Anurag; Polavarapu, Raghava Sarma; Prajapati, Jayesh; Raheem, Asif; Thakkar, Kamlesh; Kothari, Shivani; Thakkar, Ashok

    2015-01-01

    Objective. The main aim is to evaluate safety, efficacy, and clinical performance of the Indolimus (Sahajanand Medical Technologies Pvt. Ltd., Surat, India) sirolimus-eluting stent in high-risk diabetic population with complex lesions. Methods. It was a multicentre, retrospective, non-randomized, single-arm study, which enrolled 372 diabetic patients treated with Indolimus. The primary endpoint of the study was major adverse cardiac events (MACE), which is a composite of cardiac death, target lesion revascularization (TLR), target vessel revascularization (TVR), myocardial infarction (MI), and stent thrombosis (ST). The clinical follow-ups were scheduled at 30 days, 6 months, and 9 months. Results. The mean age of the enrolled patients was 53.4 ± 10.2 years. A total of 437 lesions were intervened successfully with 483 stents (1.1 ± 0.3 per lesion). There were 256 (68.8%) male patients. Hypertension and totally occluded lesions were found in 202 (54.3%) and 45 (10.3%) patients, respectively. The incidence of MACE at 30 days, 6 months and 9 months was 0 (0%), 6 (1.6%), and 8 (2.2%), respectively. The event-free survival at 9-month follow-up by Kaplan Meier method was found to be 97.8%. Conclusion. The use of biodegradable polymer coated sirolimus-eluting stent is associated with favorable outcomes. The results demonstrated in our study depict its safety and efficacy in diabetic population. PMID:26421189

  5. Method for loading shape memory polymer gripper mechanisms

    DOEpatents

    Lee, Abraham P.; Benett, William J.; Schumann, Daniel L.; Krulevitch, Peter A.; Fitch, Joseph P.

    2002-01-01

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

  6. Self-Deploying Trusses Containing Shape-Memory Polymers

    NASA Technical Reports Server (NTRS)

    Schueler, Robert M.

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

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

    PubMed Central

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

    2013-01-01

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

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

    PubMed

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

    2015-06-24

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

  10. Component assembly with shape memory polymer fastener for microrobots

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Kuo, Chai-Pei

    1991-07-01

    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.

  12. 3D Printing of Shape Memory Polymers for Flexible Electronic Devices.

    PubMed

    Zarek, Matt; Layani, Michael; Cooperstein, Ido; Sachyani, Ela; Cohn, Daniel; Magdassi, Shlomo

    2016-06-01

    The formation of 3D objects composed of shape memory polymers for flexible electronics is described. Layer-by-layer photopolymerization of methacrylated semicrystalline molten macromonomers by a 3D digital light processing printer enables rapid fabrication of complex objects and imparts shape memory functionality for electrical circuits. PMID:26402320

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

    NASA Astrophysics Data System (ADS)

    Panja, Debabrata

    2010-06-01

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

  14. Surface modification of a polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU) nanocomposite polymer as a stent coating for enhanced capture of endothelial progenitor cells

    PubMed Central

    Tan, Aaron; Farhatnia, Yasmin; Goh, Debbie; G, Natasha; de Mel, Achala; Lim, Jing; Teoh, Swee-Hin; Malkovskiy, Andrey V; Chawla, Reema; Rajadas, Jayakumar; Cousins, Brian G; Hamblin, Michael R; Alavijeh, Mohammad S; Seifalian, Alexander M

    2013-01-01

    An unmet need exists for the development of next-generation multifunctional nanocomposite materials for biomedical applications, particularly in the field of cardiovascular regenerative biology. Herein, we describe the preparation and characterization of a novel polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU) nanocomposite polymer with covalently attached anti-CD34 antibodies to enhance capture of circulating endothelial progenitor cells (EPC). This material may be used as a new coating for bare metal stents used after balloon angioplasty to improve re-endothelialization. Biophysical characterization techniques were used to assess POSS-PCU and its subsequent functionalization with anti-CD34 antibodies. Results indicated successful covalent attachment of anti-CD34 antibodies on the surface of POSS-PCU leading to an increased propensity for EPC capture, whilst maintaining in vitro biocompatibility and hemocompatibility. POSS-PCU has already been used in 3 first-in-man studies, as a bypass graft, lacrimal duct and a bioartificial trachea. We therefore postulate that its superior biocompatibility and unique biophysical properties would render it an ideal candidate for coating medical devices, with stents as a prime example. Taken together, anti-CD34 functionalized POSS-PCU could form the basis of a nano-inspired polymer platform for the next generation stent coatings. PMID:24706135

  15. Surface modification of a polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU) nanocomposite polymer as a stent coating for enhanced capture of endothelial progenitor cells.

    PubMed

    Tan, Aaron; Farhatnia, Yasmin; Goh, Debbie; G, Natasha; de Mel, Achala; Lim, Jing; Teoh, Swee-Hin; Malkovskiy, Andrey V; Chawla, Reema; Rajadas, Jayakumar; Cousins, Brian G; Hamblin, Michael R; Alavijeh, Mohammad S; Seifalian, Alexander M

    2013-12-01

    An unmet need exists for the development of next-generation multifunctional nanocomposite materials for biomedical applications, particularly in the field of cardiovascular regenerative biology. Herein, we describe the preparation and characterization of a novel polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU) nanocomposite polymer with covalently attached anti-CD34 antibodies to enhance capture of circulating endothelial progenitor cells (EPC). This material may be used as a new coating for bare metal stents used after balloon angioplasty to improve re-endothelialization. Biophysical characterization techniques were used to assess POSS-PCU and its subsequent functionalization with anti-CD34 antibodies. Results indicated successful covalent attachment of anti-CD34 antibodies on the surface of POSS-PCU leading to an increased propensity for EPC capture, whilst maintaining in vitro biocompatibility and hemocompatibility. POSS-PCU has already been used in 3 first-in-man studies, as a bypass graft, lacrimal duct and a bioartificial trachea. We therefore postulate that its superior biocompatibility and unique biophysical properties would render it an ideal candidate for coating medical devices, with stents as a prime example. Taken together, anti-CD34 functionalized POSS-PCU could form the basis of a nano-inspired polymer platform for the next generation stent coatings. PMID:24706135

  16. Collapse pressures of biodegradable stents.

    PubMed

    Venkatraman, Subbu; Poh, Tan Lay; Vinalia, Tjong; Mak, Koon Hou; Boey, Freddy

    2003-05-01

    Biodegradable stent prototypes were produced from poly L-lactic acid polymers with different molecular weights. The effects of molecular weight, drug incorporation and stent design on the collapse pressure of the stents were evaluated. While molecular weights did not show a significant effect on the collapse pressure of the stents, drug incorporation at high percentage decreased the collapse pressure of the stents substantially. Cryogenic fracture surfaces showed significant drug agglomeration as the concentration increased. The design of the stent was also found to a have significant effect on the collapse pressure. The stent produced from the same material has a higher collapse pressure when the load bearing surface area is increased. PMID:12628831

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Chen, Zhongbi

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

  2. Flexible Nonvolatile Polymer Memory Array on Plastic Substrate via Initiated Chemical Vapor Deposition.

    PubMed

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

    2016-05-25

    Resistive random access memory based on polymer thin films has been developed as a promising flexible nonvolatile memory for flexible electronic systems. Memory plays an important role in all modern electronic systems for data storage, processing, and communication; thus, the development of flexible memory is essential for the realization of flexible electronics. However, the existing solution-processed, polymer-based RRAMs have exhibited serious drawbacks in terms of the uniformity, electrical stability, and long-term stability of the polymer thin films. Here, we present poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3)-based RRAM arrays fabricated via the solvent-free technique called initiated chemical vapor deposition (iCVD) process for flexible memory application. Because of the outstanding chemical stability of pV3D3 films, the pV3D3-RRAM arrays can be fabricated by a conventional photolithography process. The pV3D3-RRAM on flexible substrates showed unipolar resistive switching memory with an on/off ratio of over 10(7), stable retention time for 10(5) s, excellent cycling endurance over 10(5) cycles, and robust immunity to mechanical stress. In addition, pV3D3-RRAMs showed good uniformity in terms of device-to-device distribution. The pV3D3-RRAM will pave the way for development of next-generation flexible nonvolatile memory devices. PMID:27142537

  3. Therapies targeting inflammation after stent implantation.

    PubMed

    Okura, Hiroyuki; Takagi, Tsutomu; Yoshida, Kiyoshi

    2013-07-01

    Since the introduction of coronary vessel scaffold by metallic stent, percutaneous coronary intervention has become widely performed all over the world. Although drug-eluting stent technology has further decrease the incidence of in-stent restenosis, there still remaining issues related to stent implantation. Vessel inflammation is one of the causes that may be related to stent restenosis as well as stent thrombosis. Therefore, systemic therapies targeting inflammation emerged as adjunctive pharmacological intervention to improve outcome. Statins, corticosteroids, antiplatelets, and immunosuppresive or anti-cancer drugs are reported to favorably impact outcome after bare-metal stent implantation. In type 2 diabetic patients, pioglitazone may be the most promising drug that can lower neointimal proliferation and, as a result, lower incidence of restenosis and target lesion revascularization. On the other hand, several new stent platforms that might decrease inflammatory response after drug-eluting stent implantation have been introduced. Because durable polymer used in the first generation drug-eluting stents are recognized to be responsible for unfavorable vessel response, biocompatible or bioabsorbable polymer has been introduce and already used clinically. Furthermore, polymer-free drug-eluting stent and bioresorbable scaffold are under investigation. Although vessel inflammation may be reduced by using these new drug-eluting stents or scaffold, long-term impact needs to be investigated further. PMID:23905635

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  5. Programmable and self-demolding microstructured molds fabricated from shape-memory polymers

    NASA Astrophysics Data System (ADS)

    Meier, Tobias; Bur, Julia; Reinhard, Maximilian; Schneider, Marc; Kolew, Alexander; Worgull, Matthias; Hölscher, Hendrik

    2015-06-01

    We introduce shape memory polymers as materials to augment molds with programmable switching between different micro and nanostructures as functional features of the mold and self-demolding properties. These polymer molds can be used for hot embossing (or nanoimprinting) and casting. Furthermore, they enable the replication of nano- and microstructures on curved surfaces as well as embedded structures like on the inside walls of a microfluidic channel. The shape memory polymer molds can be replicated from master molds fabricated by conventional techniques. We tested their durability for microfabrication processes and demonstrated the advantages of shape memory molds for hot embossing and casting by replicating microstructures with high aspect ratios and optical grade surface quality.

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

    NASA Astrophysics Data System (ADS)

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

    2006-03-01

    In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, Tswitch. If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(-caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 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. nanocomposite | shape-memory polymer | stimuli-sensitive polymer


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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  8. "Grafting to" as a novel and simple approach for triple-shape memory polymers.

    PubMed

    Suchao-in, Kanitporn; Chirachanchai, Suwabun

    2013-08-14

    Maleated-polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (m-SEBS) is a block copolymer with two melting temperatures belonging to soft poly(ethylene-co-butylene) (EB) and hard polystyrene (PS) segments. As EB segments contain anhydride reactive groups, this allows grafting polybutylene succinate (PBS) as another soft segment to m-SEBS backbone to obtain triple-shape memory polymers based on two transition temperatures, i.e., Tm values of EB (at 55-65 °C) and PBS (at 105-115 °C). The present work shows a novel and simple approach of "grafting to" to develop triple-shape memory polymers. PMID:23895373

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    PubMed

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

    2006-03-01

    In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, 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

  11. All organic memory devices utilizing fullerene molecules and insulating polymers

    NASA Astrophysics Data System (ADS)

    Kanwal, Alokik Paul

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

  12. Photo-enhanced polymer memory device based on polyimide containing spiropyran

    NASA Astrophysics Data System (ADS)

    Seok, Woong Chul; Son, Seok Ho; An, Tae Kyu; Kim, Se Hyun; Lee, Seung Woo

    2016-07-01

    This paper reports the synthesis of a new polyimide (PI) containing a spiropyran moiety in the side chain and its applications to the switchable polymer memory before and after UV exposure. UV exposure allows memory using spiropyran-based PI as an active layer with a higher current and lower switching-ON voltage compared to the unexposed device due to the structural changes in the spiropyran moiety after UV exposure. In addition, this study examined the effects of UV exposure on the performance of the memory containing spiropyran-based PI using the UV-Vis absorption spectra and space-charge limited conduction (SCLC) model. [Figure not available: see fulltext.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  14. Responsive Biomaterials: Advances in Materials Based on Shape-Memory Polymers.

    PubMed

    Hardy, John G; Palma, Matteo; Wind, Shalom J; Biggs, Manus J

    2016-07-01

    Shape-memory polymers (SMPs) are morphologically responsive materials with potential for a variety of biomedical applications, particularly as devices for minimally invasive surgery and the delivery of therapeutics and cells for tissue engineering. A brief introduction to SMPs is followed by a discussion of the current progress toward the development of SMP-based biomaterials for clinically relevant biomedical applications. PMID:27120512

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

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

    PubMed

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

    2015-02-25

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    PubMed

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

    2016-03-14

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

  1. Clinical outcomes in 995 unselected real-world patients treated with an ultrathin biodegradable polymer-coated sirolimus-eluting stent: 12-month results from the FLEX Registry

    PubMed Central

    Lemos, Pedro A; Chandwani, Prakash; Saxena, Sudheer; Ramachandran, Padma Kumar; Abhyankar, Atul; Campos, Carlos M; Marchini, Julio Flavio; Galon, Micheli Zanotti; Verma, Puneet; Sandhu, Manjinder Singh; Parikh, Nikhil; Bhupali, Ashok; Jain, Sharad; Prajapati, Jayesh

    2016-01-01

    Objectives To evaluate, in the FLEX Registry, clinical outcomes of an ultrathin (60 µm) biodegradable polymer-coated Supraflex sirolimus-eluting stent (SES) for the treatment of coronary artery disease. Additionally, to determine the vascular response to the Supraflex SES through optical coherence tomography (OCT) analysis. Setting Multicentre, single-arm, all-comers, observational registry of patients who were treated with the Supraflex SES, between July 2013 and May 2014, at nine different centres in India. Participants 995 patients (1242 lesions) who were treated with the Supraflex SES, between July 2013 and May 2014, at nine different centres in India. A total of 47 participants underwent OCT analysis at 6 months’ follow-up. Interventions Percutaneous coronary intervention with Supraflex SES, Primary and secondary outcome measures The primary endpoint—the rate of major adverse cardiac events (defined as a composite of cardiac death, myocardial infarction (MI), target lesion revascularisation (TLR))—was analysed during 12 months. Results At 12 months, the primary endpoint occurred in 36 (3.7%) of 980 patients, consisting of 18 (1.8%) cardiac deaths, 16 (1.6%) MI, 7 (0.7%) TLR and 2 (0.2%) cases of non-target lesion target vessel revascularization. In a subset of 47 patients, 1227 cross-sections (9309 struts) were analysed at 6 months by OCT. Overall, a high percentage of struts was covered (98.1%), with a mean neointimal thickness of 0.13±0.06 µm. Conclusions The FLEX Registry evaluated clinical outcomes in real-world and more complex cohorts and thus provides evidence that the Supraflex SEX can be used safely and routinely in a broader percutaneous coronary intervention population. Also, the Supraflex SES showed high percentage of stent strut coverage and good stent apposition during OCT follow-up. PMID:26888727

  2. Dual Antiplatelet Therapy Over 6 Months Increases the Risk of Bleeding after Biodegradable Polymer-Coated Sirolimus Eluting Stents Implantation: Insights from the CREATE Study

    PubMed Central

    ZHANG, LEI; LI, YI; JING, QUAN-MIN; WANG, XIAO-ZENG; MA, YING-YAN; WANG, GENG; XU, BO; GAO, RUN-LIN; HAN, YA-LING

    2014-01-01

    Background The optimal duration of dual antiplatelet therapy (DAPT) after drug-eluting stent (DES) implantation remains controversial. The primary aim of our study was to evaluate the impact of optimal DAPT duration on bleeding events between 6 and 12 months after biodegradable polymer-coated DES implantation. The secondary aim is to determine the predictors and prognostic implications of bleeding. Methods This study is a post hoc analysis of the Multi-Center Registry of EXCEL Biodegradable Polymer Drug Eluting Stents (CREATE) study population. A total of 2,040 patients surviving at 6 months were studied, including 1,639 (80.3%) who had received 6-month DAPT and 401 (19.7%) who had received DAPT greater than 6 months. Bleeding events were defined according to the bleeding academic research consortium (BARC) definitions as described previously and were classified as major/minor (BARC 2–5) and minimal (BARC 1). A left censored method with a landmark at 6 months was used to determine the incidence, predictors, and impact of bleeding on clinical prognosis between 6 and 12 months. Results At 1-year follow-up, patients who received prolonged DAPT longer than 6 months had a significantly higher incidence of overall (3.0% vs. 5.5%, P = 0.021) and major/minor bleeding (1.1% vs. 2.5%, P = 0.050) compared to the patients who received 6-month DAPT. Multivariate analysis showed that being elderly (OR = 1.882, 95% CI: 1.109–3.193, P = 0.019), having diabetes (OR = 1.735, 95% CI: 1.020–2.952, P = 0.042), having a history of coronary artery disease (OR = 2.163, 95% CI: 1.097–4.266, P = 0.026), and duration of DAPT longer than 6 months (OR = 1.814, 95% CI: 1.064–3.091, P = 0.029) were independent predictors of bleeding. Patients with bleeding events had a significantly higher incidence of cardiac death, myocardial infarction, target lesion revascularization, and stent thrombosis. Conclusions Prolonged DAPT (greater than 6 months) after biodegradable polymer-coated DES

  3. Ferroelectric switching behavior in morphology controlled ferroelectric-semiconductor polymer blends for organic memory

    NASA Astrophysics Data System (ADS)

    Lim, Eunhee; Su, Gregory; Kramer, Edward; Chabinyc, Michael

    2015-03-01

    Memory is a fundamental component of all modern electronic systems. Organic ferroelectric memories are advantageous because they are thin and lightweight devices that can be made printable, foldable, and stretchable. Organic ferroelectric memories comprise a physical blend of an organic semiconducting polymer and an insulating ferroelectric polymer as the active layer in a thin film diode. Controlling the thin film morphology in these blends is important for electrical properties of the resulting device. We have found that when a semiconducting thiophene polymer with polar alkanoate side chains (P3EPT) is blended with well-studied ferroelectric polymer poly [(vinylidenefluoride-co-trifluoroethylene] P (VDF-TrFE), the resulting film has low surface roughness and more controllable domain sizes compared to the widely used poly (3-hexylthiophene). This difference allows more reliable study of the ferroelectric switching behavior in devices with domain size of about 100nm. The influence of the 3D composition measured by a combination of methods, including soft x-ray microscopy, on the electrical characteristics will be presented.

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

    PubMed

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

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  6. Characterization of origami shape memory metamaterials (SMMM) made of bio-polymer blends

    NASA Astrophysics Data System (ADS)

    Kshad, Mohamed Ali E.; Naguib, Hani E.

    2016-04-01

    Shape memory materials (SMMs) are materials that can return to their virgin state and release mechanically induced strains by external stimuli. Shape memory polymers (SMPs) are a class of SMMs that show a high shape recoverability and which have attractive potential for structural applications. In this paper, we experimentally study the shape memory effect of origami based metamaterials. The main focus is on the Muira origami metamaterials. The fabrication technique used to produce origami structure is direct molding where all the geometrical features are molded from thermally virgin polymers without post folding of flat sheets. The study shows experimental investigations of shape memory metamaterials (SMMMs) made of SMPs that can be used in different applications such as medicine, robotics, and lightweight structures. The origami structure made from SMP blends, activated with uniform heating. The effect of blend composition on the shape memory behavior was studied. Also the influence of the thermomechanical and the viscoelastic properties of origami unit cell on the activation process have been discussed, and stress relaxation and shape recovery were investigated. Activation process of the unit cell has been demonstrated.

  7. Drug-eluting stents: role of stent design, delivery vehicle, and drug selection.

    PubMed

    Rodgers, Campbell D K

    2002-01-01

    Increasing focus has recently been directed toward the different parameters of drug-eluting stents-stent design, delivery-vehicle materials, and drug properties-and the manner in which each of these elements may affect the function of the stents. Several specific characteristics of design may affect restenosis, although design optimization often presents a choice between acute procedural success and long-term biological stability. The influence of design parameters such as strut thickness and cell configuration is described. Polymer material has frequently been used to coat drug-eluting stents, although some agents, such as paclitaxel, can be attached directly to the stent's surface, obviating the need for a polymer layer. The properties of agents used in drug-eluting stents and how those properties affect delivery and long-term outcome are discussed, as is the influence of the disease state of the target vessel on stent safety and efficacy. PMID:12478230

  8. Gold nanoparticle charge trapping and relation to organic polymer memory devices.

    PubMed

    Prime, D; Paul, S; Josephs-Franks, P W

    2009-10-28

    Nanoparticle-based polymer memory devices (PMDs) are a promising technology that could replace conventional silicon-based electronic memory, offering fast operating speeds, simple device structures and low costs. Here we report on the current state of nanoparticle PMDs and review some of the problems that are still present in the field. We also present new data regarding the charging of gold nanoparticles in metal-insulator-semiconductor capacitors, showing that charging is possible under the application of an electric field with a trapped charge density due to the nanoparticles of 3.3 x 10(12) cm(-2). PMID:19770145

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

    PubMed

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

    2009-11-18

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

  10. Porous TiO₂ surface formed on nickel-titanium alloy by plasma electrolytic oxidation: a prospective polymer-free reservoir for drug eluting stent applications.

    PubMed

    Huan, Zhiguang; Fratila-Apachitei, Lidy E; Apachitei, Iulian; Duszczyk, Jurek

    2013-07-01

    In this study, a porous oxide layer was formed on the surface of nickel-titanium alloy (NiTi) by plasma electrolytic oxidation (PEO) with the aim to produce a polymer-free drug carrier for drug eluting stent (DES) applications. The oxidation was performed galvanostatically in concentrated phosphoric acid electrolyte at low temperature. It was found that the response of NiTi substrate during the PEO process was different from that of bulk Ti, since the presence of large amount of Ni delayed the initial formation of a compact oxide layer that is essential for the PEO to take place. Under optimized PEO conditions, the resultant surface showed porosity, pore density and oxide layer thickness of 14.11%, 2.40 × 10⁵ pores/mm² and 0.8 μm, respectively. It was additionally noted that surface roughness after PEO did not significantly increase as compared with that of original NiTi substrate and the EDS analyses revealed a decrease in Ni/Ti ratio on the surface after PEO. The cross-section morphology showed no discontinuity between the PEO layer and the NiTi substrate. Furthermore, wettability and surface free energy of the NiTi substrate increased significantly after PEO treatment. The PEO process could be successfully translated to NiTi stent configuration proving for the first time its feasibility for such a medical device and offering potential for development of alternative, polymer-free drug carriers for NiTi DES. PMID:23359528

  11. Ultra Low Density Shape Memory Polymer Foams With Tunable Physicochemical Properties for Treatment of intracranial Aneurysms

    SciTech Connect

    Singhal, Pooja

    2013-12-01

    Shape memory polymers (SMPs) are a rapidly emerging class of smart materials that can be stored in a deformed temporary shape, and can actively return to their original shape upon application of an external stimulus such as heat, pH or light. This behavior is particularly advantageous for minimally invasive biomedical applications comprising embolic/regenerative scaffolds, as it enables a transcatheter delivery of the device to the target site. The focus of this work was to exploit this shape memory behavior of polyurethanes, and develop an efficient embolic SMP foam device for the treatment of intracranial aneurysms.In summary, this work reports a novel family of ultra low density polymer foams which can be delivered via a minimally invasive surgery to the aneurysm site, actuated in a controlled manner to efficiently embolize the aneurysm while promoting physiological fluid/blood flow through the reticulated/open porous structure, and eventually biodegrade leading to complete healing of the vasculature.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  13. Micro-vascular shape-memory polymer actuators with complex geometries obtained by laser stereolithography

    NASA Astrophysics Data System (ADS)

    Díaz Lantada, Andrés; de Blas Romero, Adrián; Chacón Tanarro, Enrique

    2016-06-01

    In our work we present the complete development process of geometrically complex micro-vascular shape-memory polymer actuators. The complex geometries and three-dimensional networks are designed by means of computer aided design resources. Manufacture is accomplished, in a single step, by means of laser stereolithography, directly from the computer-aided design files with the three dimensional geometries of the different actuators under development. To our knowledge, laser stereolithography is applied here for the first time to the development of shape memory polymer devices with complex geometries and inner micro-vasculatures for their activation using a thermal fluid. Final testing of the developed actuators helps to validate the approach and to put forward some present challenges.

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

    PubMed Central

    Song, Jie

    2010-01-01

    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

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

    NASA Astrophysics Data System (ADS)

    Luo, Xiaofan

    Responsive polymers are "smart" materials that are capable of performing prescribed, dynamic functions under an applied stimulus. In this dissertation, we explore several novel design strategies to develop thermally responsive polymers and polymer composites for self-healing, reversible adhesion and shape memory applications. In the first case described in Chapters 2 and 3, a thermally triggered self-healing material was prepared by blending a high-temperature epoxy resin with a thermoplastic polymer, poly(epsilon-caprolactone) (PCL). The initially miscible system undergoes polymerization induced phase separation (PIPS) during the curing of epoxy and yields a variety of compositionally dependent morphologies. At a particular PCL loading, the cured blend displays a "bricks-and-mortar" morphology in which epoxy exists as interconnected spheres ("bricks") within a continuous PCL matrix ("mortar"). A heat induced "bleeding" phenomenon was observed in the form of spontaneous wetting of all free surfaces by the molten PCL, and is attributed to the volumetric thermal expansion of PCL above its melting point in excess of epoxy brick expansion, which we term differential expansive bleeding (DEB). This DEB is capable of healing damage such as cracks. In controlled self-healing experiments, heating of a cracked specimen led to PCL bleeding from the bulk that yields a liquid layer bridging the crack gap. Upon cooling, a "scar" composed of PCL crystals was formed at the site of the crack, restoring a significant portion of mechanical strength. We further utilized DEB to enable strong and thermally-reversible adhesion of the material to itself and to metallic substrates, without any requirement for macroscopic softening or flow. After that, Chapters 4--6 present a novel composite strategy for the design and fabrication of shape memory polymer composites. The basic approach involves physically combining two or more functional components into an interpenetrating fiber

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

    NASA Astrophysics Data System (ADS)

    Shi, Guanghui; Yang, Qingsheng; Zhang, Qiang

    2012-04-01

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

  17. Tunable Diffractive Optical Elements Based on Shape-Memory Polymers Fabricated via Hot Embossing.

    PubMed

    Schauer, Senta; Meier, Tobias; Reinhard, Maximilian; Röhrig, Michael; Schneider, Marc; Heilig, Markus; Kolew, Alexander; Worgull, Matthias; Hölscher, Hendrik

    2016-04-13

    We introduce actively tunable diffractive optical elements fabricated from shape-memory polymers (SMPs). By utilizing the shape-memory effect of the polymer, at least one crucial attribute of the diffractive optical element (DOE) is tunable and adjustable subsequent to the completed fabrication process. A thermoplastic, transparent, thermoresponsive polyurethane SMP was structured with diverse diffractive microstructures via hot embossing. The tunability was enabled by programming a second, temporary shape into the diffractive optical element by mechanical deformation, either by stretching or a second embossing cycle at low temperatures. Upon exposure to the stimulus heat, the structures change continuously and controllable in a predefined way. We establish the novel concept of shape-memory diffractive optical elements by illustrating their capabilities, with regard to tunability, by displaying the morphing diffractive pattern of a height tunable and a period tunable structure, respectively. A sample where an arbitrary structure is transformed to a second, disparate one is illustrated as well. To prove the applicability of our tunable shape-memory diffractive optical elements, we verified their long-term stability and demonstrated the precise adjustability with a detailed analysis of the recovery dynamics, in terms of temperature dependence and spatially resolved, time-dependent recovery. PMID:26998646

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

    NASA Astrophysics Data System (ADS)

    Izzo, Elise; Weiss, Robert

    2009-03-01

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

  19. [Absorbable coronary stents. New promising technology].

    PubMed

    Erbel, Raimund; Böse, Dirk; Haude, Michael; Kordish, Igor; Churzidze, Sofia; Malyar, Nasser; Konorza, Thomas; Sack, Stefan

    2007-06-01

    Coronary stent implantation started in Germany 20 years ago. In the beginning, the progress was very slow and accelerated 10 years later. Meanwhile, coronary stent implantation is a standard procedure in interventional cardiology. From the beginning of permanent stent implantation, research started to provide temporary stenting of coronary arteries, first with catheter-based systems, later with stent-alone technology. Stents were produced from polymers or metal. The first polymer stent implantation failed except the Igaki-Tamai stent in Japan. Newly developed absorbable polymer stents seem to be very promising, as intravascular ultrasound (IVUS) and optical coherence tomography have demonstrated. Temporary metal stents were developed based on iron and magnesium. Currently, the iron stent is tested in peripheral arteries. The absorbable magnesium stent (Biotronik, Berlin, Germany) was tested in peripheral arteries below the knee and meanwhile in the multicenter international PROGRESS-AMS (Clinical Performance and Angiographic Results of Coronary Stenting with Absorbable Metal Stents) study. The first magnesium stent implantation was performed on July 30, 2004 after extended experimental testing in Essen. The magnesium stent behaved like a bare-metal stent with low recoil of 5-7%. The stent struts were absorbed when tested with IVUS. Stent struts were not visible by fluoroscopy or computed tomography (CT) as well as magnetic resonance imaging (MRI). That means, that the magnesium stent is invisible and therefore CT and MRI can be used for imaging of interventions. Only using micro-CT the stent struts were visible. The absorption process could be demonstrated in a patient 18 days after implantation due to suspected acute coronary syndrome, which was excluded. IVUS showed a nice open lumen. Stent struts were no longer visible, but replaced by tissue indicating the previous stent location. Coronary angiography after 4 months showed an ischemia-driven target lesion

  20. A Facile Strategy to Fabricate Multishape Memory Polymers with Controllable Mechanical Properties.

    PubMed

    Zhang, Qinglong; Hua, Wenqiang; Feng, Jiachun

    2016-08-01

    A facile blending strategy to fabricate multishape memory polymers (SMPs) with only one sort of phase transition material has been reported. In this work, olefin block copolymer (OBC) and styrene-b-(ethylene-co-butylene)-b-styrene (SEBS), which are both physically crosslinked, are blended with crystalline paraffin together. Due to the different interactions between polymer matrices and paraffin, the paraffin penetrated in OBC and SEBS exhibit separated melting transitions. It is quite interesting that merely paraffin distributed in OBC also shows two distinct melting transitions with enough OBC content in composites. Therefore, excellent quadruple shape memory effect can be achieved with a maximum of three melting transitions. Furthermore, through adjusting the polymer species and content, the mechanical and rheological properties can be conveniently tuned to a great extent. Compared with the reported strategies, this simple and controllable method sheds light on rapid design of multi-SMPs using inexpensive raw materials, which greatly paves the way for multi-SMPs from laboratory to factory. PMID:27254383

  1. Fast Triggering of Shape Memory Polymers using an Embedded Carbon Nanotube Sponge Network

    PubMed Central

    Zhou, Guoxiang; Zhang, Heng; Xu, Shuping; Gui, Xuchun; Wei, Hongqiu; Leng, Jinsong; Koratkar, Nikhil; Zhong, Jing

    2016-01-01

    In this work, a 3-D porous carbon nanotube sponge (CNTS) was embedded within a shape memory polymer (SMPs) matrix. We demonstrate complete infiltration and filling of the SMPs into the CNTS by capillary force without any damage to the CNTS structure. With only ~0.2 wt% carbon nanotube loading, the glass transition temperature is increased by ~20 °C, indicating strong interaction between CNTS and the SMPs matrix. Further, we find that the uniform distribution of the carbon nanotubes in the nanocomposite results in high electrical conductivity, and thus highly effective electricity triggering capability. The carbon nanotube sponge shape memory polymer (CNTS/SMPs) nanocomposite could be triggered within ~10 seconds by the application of ~10 volts. Results from finite element simulations showed good agreement with the experimental results, and indicated that for our system the interface thermal energy loss does not have a significant effect on the heating rate of the polymer matrix. PMID:27052451

  2. Fast Triggering of Shape Memory Polymers using an Embedded Carbon Nanotube Sponge Network

    NASA Astrophysics Data System (ADS)

    Zhou, Guoxiang; Zhang, Heng; Xu, Shuping; Gui, Xuchun; Wei, Hongqiu; Leng, Jinsong; Koratkar, Nikhil; Zhong, Jing

    2016-04-01

    In this work, a 3-D porous carbon nanotube sponge (CNTS) was embedded within a shape memory polymer (SMPs) matrix. We demonstrate complete infiltration and filling of the SMPs into the CNTS by capillary force without any damage to the CNTS structure. With only ~0.2 wt% carbon nanotube loading, the glass transition temperature is increased by ~20 °C, indicating strong interaction between CNTS and the SMPs matrix. Further, we find that the uniform distribution of the carbon nanotubes in the nanocomposite results in high electrical conductivity, and thus highly effective electricity triggering capability. The carbon nanotube sponge shape memory polymer (CNTS/SMPs) nanocomposite could be triggered within ~10 seconds by the application of ~10 volts. Results from finite element simulations showed good agreement with the experimental results, and indicated that for our system the interface thermal energy loss does not have a significant effect on the heating rate of the polymer matrix.

  3. Design and verification of a shape memory polymer peripheral occlusion device.

    PubMed

    Landsman, Todd L; Bush, Ruth L; Glowczwski, Alan; Horn, John; Jessen, Staci L; Ungchusri, Ethan; Diguette, Katelin; Smith, Harrison R; Hasan, Sayyeda M; Nash, Daniel; Clubb, Fred J; Maitland, Duncan J

    2016-10-01

    Shape memory polymer foams have been previously investigated for their safety and efficacy in treating a porcine aneurysm model. Their biocompatibility, rapid thrombus formation, and ability for endovascular catheter-based delivery to a variety of vascular beds makes these foams ideal candidates for use in numerous embolic applications, particularly within the peripheral vasculature. This study sought to investigate the material properties, safety, and efficacy of a shape memory polymer peripheral embolization device in vitro. The material characteristics of the device were analyzed to show tunability of the glass transition temperature (Tg) and the expansion rate of the polymer to ensure adequate time to deliver the device through a catheter prior to excessive foam expansion. Mechanical analysis and flow migration studies were performed to ensure minimal risk of vessel perforation and undesired thromboembolism upon device deployment. The efficacy of the device was verified by performing blood flow studies that established affinity for thrombus formation and blood penetration throughout the foam and by delivery of the device in an ultrasound phantom that demonstrated flow stagnation and diversion of flow to collateral pathways. PMID:27419615

  4. Fast Triggering of Shape Memory Polymers using an Embedded Carbon Nanotube Sponge Network.

    PubMed

    Zhou, Guoxiang; Zhang, Heng; Xu, Shuping; Gui, Xuchun; Wei, Hongqiu; Leng, Jinsong; Koratkar, Nikhil; Zhong, Jing

    2016-01-01

    In this work, a 3-D porous carbon nanotube sponge (CNTS) was embedded within a shape memory polymer (SMPs) matrix. We demonstrate complete infiltration and filling of the SMPs into the CNTS by capillary force without any damage to the CNTS structure. With only ~0.2 wt% carbon nanotube loading, the glass transition temperature is increased by ~20 °C, indicating strong interaction between CNTS and the SMPs matrix. Further, we find that the uniform distribution of the carbon nanotubes in the nanocomposite results in high electrical conductivity, and thus highly effective electricity triggering capability. The carbon nanotube sponge shape memory polymer (CNTS/SMPs) nanocomposite could be triggered within ~10 seconds by the application of ~10 volts. Results from finite element simulations showed good agreement with the experimental results, and indicated that for our system the interface thermal energy loss does not have a significant effect on the heating rate of the polymer matrix. PMID:27052451

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

    SciTech Connect

    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.

    2014-08-11

    Recently, predominantly closed-cell low density shape memory polymer (SMP) foam was 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. Lastly, 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.

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

    DOE PAGESBeta

    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; et al

    2014-08-11

    Recently, predominantly closed-cell low density shape memory polymer (SMP) foam was 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.more » Lastly, 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.« less

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed

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

    2014-12-01

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

  9. Stimuli-Responsive Reversible Two-Level Adhesion from a Structurally Dynamic Shape-Memory Polymer.

    PubMed

    Michal, Brian T; Spencer, Emily J; Rowan, Stuart J

    2016-05-01

    A shape-memory adhesive has been prepared that exhibits two levels of reversible adhesion. The adhesive is a semicrystalline cross-linked polymer that contains dynamic disulfide bonds. Melting of the crystalline regions via heat causes a drop in the modulus of the material facilitating wetting of the substrate as well as enhancing the surface contact area with the substrate, which result in the formation of an adhesive bond. Exposure to higher heat or UV light results in dynamic exchange of the disulfide bonds, which yields a further drop in the modulus/viscosity that improves surface wetting/contact and strengthens the adhesive bond. This improvement in adhesion is shown to apply over different substrates, contact forces, and deformation modes. Furthermore, the adhesive acts as a thermal shape-memory material and can be used to create joints that can reposition themselves upon application of heat. PMID:27096252

  10. Field-effect memory transistors based on arrays of nanowires of a ferroelectric polymer

    NASA Astrophysics Data System (ADS)

    Cai, Ronggang; Kassa, Hailu G.; Marrani, Alessio; van Breemen, Albert J. J. M.; Gelinck, Gerwin H.; Nysten, Bernard; Hu, Zhijun; Jonas, Alain M.

    2015-09-01

    Ferroelectric poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-TrFE), is increasingly used in organic non-volatile memory devices, e.g., in ferroelectric field effect transistors (FeFETs). Here, we report on FeFETs integrating nanoimprinted arrays of P(VDF-TrFE) nanowires. Two previously-unreported architectures are tested, the first one consisting of stacked P(VDF-TrFE) nanowires placed over a continuous semiconducting polymer film; the second one consisting of a nanostriped blend layer wherein the semiconducting and ferroelectric components alternate regularly. The devices exhibit significant reversible memory effects, with operating voltages reduced compared to their continuous film equivalent, and with different possible geometries of the channels of free charge carriers accumulating in the semiconductor.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

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

    PubMed Central

    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

    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

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

    NASA Astrophysics Data System (ADS)

    Ahmad, Manzoor; Luo, Jikui; Miraftab, Mohsen

    2012-02-01

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

  15. Recovery torque modeling of carbon fiber reinforced shape memory polymer nanocomposites

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Liu, Yingtao; Rajadas, Abhishek; Chattopadhyay, Aditi

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Tadesse, Yonas

    2013-04-01

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

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

    PubMed

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

    2015-01-01

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

  20. A Thrombus Generation Model Applied to Aneurysms Treated with Shape Memory Polymer Foam and Metal Coils

    NASA Astrophysics Data System (ADS)

    Horn, John; Ortega, Jason; Hartman, Jonathan; Maitland, Duncan

    2015-11-01

    To prevent their rupture, intracranial aneurysms are often treated with endovascular metal coils which fill the aneurysm sac and isolate it from the arterial flow. Despite its widespread use, this method can result in suboptimal outcomes leading to aneurysm recurrence. Recently, shape memory polymer foam has been proposed as an alternative aneurysm filler. In this work, a computational model has been developed to predict thrombus formation in blood in response to such cardiovascular implantable devices. The model couples biofluid and biochemical phenomena present as the blood interacts with a device and stimulates thrombus formation. This model is applied to simulations of both metal coil and shape memory polymer foam treatments within an idealized 2D aneurysm geometry. Using the predicted thrombus responses, the performance of these treatments is evaluated and compared. The results suggest that foam-treated aneurysms may fill more quickly and more completely with thrombus than coil-filled aneurysms, potentially leading to improved long-term aneurysm healing. This work was performed in part under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

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

    PubMed

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

    2010-09-11

    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

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

    PubMed Central

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    PubMed

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

    2007-11-01

    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

  6. Early Clinical Experience with a Polymer-Free Biolimus A9 Drug-Coated Stent in DES-Type Patients Who Are Poor Candidates for Prolonged Dual Anti-Platelet Therapy

    PubMed Central

    Kinnaird, Tim; Butt, Mehmood; Abdul, Fairoz; Yazji, Khaled; Hailan, Ahmed; Gallagher, Sean; Ossei-Gerning, Nicholas; Chase, Alexander; Choudhury, Anirban; Smith, David; Anderson, Richard

    2016-01-01

    Introduction Prolonged dual anti-platelet therapy (DAPT) may cause excess bleeding in certain patients. The biolimus-A9 drug-coated stent (BA9-DCS) has a rapid drug-elution profile allowing shortened DAPT. Data were gathered on the early experience implanting this stent in drug-eluting stent eligible patients deemed to be at high risk of bleeding. Background and Methods The demographics, procedural data and clinical outcomes were gathered prospectively for 249 patients treated with a BA9-DCS stent at 2 UK centres, and compared to a cohort of patients treated in the same period with drug-eluting stents (PCI-DES). Results Operator-defined BA9-DCS indications included warfarin therapy, age, and anaemia. Patients receiving a BA9-DCS were older (71.6±11.8 vs. 64.8±11.6yrs, p<0.001), more often female (38.2 vs. 26.8%, P<0.001), and more likely to have comorbidity including chronic kidney disease or poor LV function than PCI-DES patients. The baseline Mehran bleed risk score was also significantly higher in the BA9-DCS group (19.4±8.7 vs. 13.1±5.8, p<0.001). Of the BA9-DCS cohort, 95.5% of patients demonstrated disease fitting NICE criteria for DES placement. The number of lesions treated (1.81±1.1 vs. 1.58±0.92, p = 0.003), total lesion length (32.1±21.7 vs. 26.1±17.6mm, p<0.001), number of stents used (1.93±1.11 vs. 1.65±1.4, p = 0.007) and total stent length (37.5±20.8 vs. 32.4±20.3, p<0.01) were greater for BA9-DCS patients. DAPT was prescribed for 3.3±3.9 months for BA9-DCS patients and 11.3±2.4 months for PCI-DES patients (p<0.001). At follow up of 392±124 days despite the abbreviated DAPT course stent related event were infrequent with ischemia-driven restenosis PCI (2.8 vs. 3.4%, p = 0.838), and stent thrombosis (1.6 vs. 2.1%, p = 0.265) rates similar between the BA9-DCS ad PCI-DES groups. After propensity scoring all clinical end-points were similar between both cohorts. Conclusions This early experience using polymer-free BA9 drug-coated stents in

  7. Coronary Stent Thrombosis: Current Insights into New Drug-Eluting Stent Designs

    PubMed Central

    Kim, Hyun Kuk

    2012-01-01

    The advances of interventional cardiology have been achieved by new device development, finding appropriate drug regimes, and understanding of pathomechanism. Drug-eluting stents (DES) implantation with dual anti-platelet therapy reduced revascularization without increasing mortality or myocardial infarction compared with bare-metal stenting. However, late-term stent thrombosis (ST) and restenosis limited its value and raised the safety concern. Main mechanisms of this phenomenon are impaired endothelialization and hypersensitivity reaction with polymer. The second generation DES further improved safety and/or efficacy by using thinner stent strut and biocompatible polymer. Recently, new concept DES with biodegradable polymer, polymer-free and bioabsorbable scaffold are under investigation in the quest to minimize the risk of ST. PMID:23323218

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

    PubMed

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

    2016-01-01

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

  9. Mechanical analysis of carbon fiber reinforced shape memory polymer composite for self-deployable structure in space environment

    NASA Astrophysics Data System (ADS)

    Hong, Seok Bin; Ahn, Yong San; Jang, Joon Hyeok; Kim, Jin-Gyun; Goo, Nam Seo; Yu, Woong-Ryeol

    2016-04-01

    Shape memory polymer (SMP) is one of smart polymers which exhibit shape memory effect upon external stimuli. Reinforcements as carbon fiber had been used for making shape memory polymer composite (CF-SMPC). This study investigated a possibility of designing self-deployable structures in harsh space condition using CF-SMPCs and analyzed their shape memory behaviors with constitutive equation model.CF-SMPCs were prepared using woven carbon fabrics and a thermoset epoxy based SMP to obtain their basic mechanical properties including actuation in harsh environment. The mechanical and shape memory properties of SMP and CF-SMPCs were characterized using dynamic mechanical analysis (DMA) and universal tensile machine (UTM) with an environmental chamber. The mechanical properties such as flexural strength and tensile strength of SMP and CF-SMPC were measured with simple tensile/bending test and time dependent shape memory behavior was characterized with designed shape memory bending test. For mechanical analysis of CF-SMPCs, a 3D constitutive equation of SMP, which had been developed using multiplicative decomposition of the deformation gradient and shape memory strains, was used with material parameters determined from CF-SMPCs. Carbon fibers in composites reinforced tensile and flexural strength of SMP and acted as strong elastic springs in rheology based equation models. The actuation behavior of SMP matrix and CF-SMPCs was then simulated as 3D shape memory bending cases. Fiber bundle property was imbued with shell model for more precise analysis and it would be used for prediction of deploying behavior in self-deployable hinge structure.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    SciTech Connect

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

    2006-08-16

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

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

    SciTech Connect

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

    2010-03-15

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

  13. Developments in coronary artery stenting: primum non nocere.

    PubMed

    Simsek, C; Serruys, P W

    2011-03-01

    The occurrence of restenosis and acute vessel closure postballoon angioplasty was the driving force for the introduction of coronary artery stenting in the 1980s. Although the first generation of coronary artery stents were highly valuable and efficient in scaffolding (non-)threatened coronary vessels, they proved to be associated with iatrogenic side effects such as in-stent neointimal hyperplasia. The efforts to tackle these side-effects eventually lead to the most significant progress within the field of interventional cardiology in the past decennium, namely drug-eluting stents (DES). Analysts estimate that the total amount of DES implantations worldwide will be more than 5 million this year. Although this worldwide increase in percutaneous coronary interventions (PCI) is impressive, some pitfalls such as the incidence of neointimal hyperplasia, stent fracture and a local hypersensitivity reaction against the polymer coating are worrisome. According to critics, the possible causal relationship with higher rates of very-late stent thrombosis could be a ticking time bomb. These concerns paved the way for the development of novel stents, ranging from DES with biodegradable polymer coating to completely biodegradable stents. Like all progress in medical interventions, it is essential to not harm the patient throughout this complex evolvement process of coronary stents. The current review not only discusses the benefits and safety issues associated with currently utilized coronary stents but in particular highlights novel coronary stents that are being investigated in (pre-)clinical trials at this moment. PMID:21346701

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

    PubMed Central

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

    2014-01-01

    Here we report for the first time a hybrid p-channel polymer ferroelectric field-effect transistor memory device with record mobility. The memory device, fabricated at 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

  15. Continuously Tunable Wettability by Using Surface Patterned Shape Memory Polymers with Giant Deformability.

    PubMed

    Zhao, Lingyu; Zhao, Jun; Liu, Yayun; Guo, Yufeng; Zhang, Liangpei; Chen, Zhuo; Zhang, Hui; Zhang, Zhong

    2016-06-01

    Designing smart surfaces with tunable wettability has drawn much attention in recent years for academic research and practical applications. Most of the previous methods to achieve such surfaces demand some particular materials that inherently have special features or complicated structures which are usually not easy to obtain. A novel strategy to achieve such smart surfaces is proposed by using the surface patterned shape memory polymers of chemically crosslinked polycyclooctene which shows a giant deformability of up to ≈730% strain. The smart surfaces possess the ability to continuously tune the wettability by controlling the recovery temperature and/or time. Coating the modified titanium dioxide nanoparticles onto such surfaces renders the surface superhydrophobicity and expands the tunable range of contact angles (CAs). Theoretical calculations of the CAs at different strains via modified Cassie model well explain the tunable wettability behaviors of such smart surfaces. PMID:27167599

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

    SciTech Connect

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

    2007-01-29

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

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

    SciTech Connect

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

    2001-03-05

    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.

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

    SciTech Connect

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

    2008-10-29

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

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

    NASA Astrophysics Data System (ADS)

    John, Manu; Li, Guoqiang

    2010-07-01

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

  1. Inflammation and impaired wound healing after zotarolimus-eluting stent implantation.

    PubMed

    Yoneda, Shuichi; Abe, Shichiro; Taguchi, Isao; Masawa, Nobuhide; Inoue, Katsumi; Inoue, Teruo

    2012-01-01

    An 86-year-old man died suddenly 5 months after implantation of a zotarolimus-eluting stent. Two zotarolimus-eluting stents were placed to treat a highly calcified diffuse lesion in the proximal-to-mid right coronary artery. The lesion was fully covered by the two stents, and intravascular ultrasound showed complete stent apposition. However, an X-ray at autopsy showed that the proximal stent was fractured. Although we thought that thrombotic occlusion at the fracture site might have caused his sudden death, no thrombus was present. In addition, in the other sites where the stents were optimally dilated, there was stent malapposition and peri-strut inflammation including macrophage infiltration, giant cells, polymer phagocytosis, and neovascularization in the neointima. Even with a second-generation drug-eluting stent, such as the zotarolimus-eluting stent, wound healing may be impaired at the stent-injured vessel site. PMID:22356902

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

    PubMed

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

    2013-11-01

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

  3. Effects of sensitizer length on radiation crosslinked shape-memory polymers

    NASA Astrophysics Data System (ADS)

    Ware, Taylor; Voit, Walter; Gall, Ken

    2010-04-01

    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%.

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

    NASA Astrophysics Data System (ADS)

    di Prima, Matthew Allen

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

  5. Thermomechanical behavior of thermoset shape memory polymer programmed by cold-compression: Testing and constitutive modeling

    NASA Astrophysics Data System (ADS)

    Li, Guoqiang; Xu, Wei

    2011-06-01

    Programming is a key process for thermally activated stress or strain recovery of shape memory polymers (SMPs). Typically, programming requires an initial heating above the glass transition temperature ( Tg), subsequent cooling below Tg and removal of the applied load, in order to fix a temporary shape. This work adopted a new approach to program thermoset SMPs directly at temperatures well below Tg, which effectively simplified the shape fixing process. 1-D compression programming below Tg and free shape recovery of a thermoset SMP were experimentally investigated. Functional stability of the shape fixity under various environmental attacks was also experimentally evaluated. A mechanism-based thermoviscoelastic-thermoviscoplastic constitutive model incorporating structural and stress relaxation was then developed to predict the nonlinear shape memory behavior of the SMP trained below Tg. Comparison between the prediction and the experiment showed good agreement. The structure dependence of the thermomechanical behavior of the SMP was further discussed through a parametric study per the validated constitutive model. This study validates that programming by cold-compression is a viable alternative for thermally responsive thermoset SMPs.

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

    PubMed

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

    2015-01-01

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

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

    PubMed

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

    2015-09-14

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

  8. Multi-shape active composites by 3D printing of digital shape memory polymers

    PubMed Central

    Wu, Jiangtao; Yuan, Chao; Ding, Zhen; Isakov, Michael; Mao, Yiqi; Wang, Tiejun; Dunn, Martin L.; Qi, H. Jerry

    2016-01-01

    Recent research using 3D printing to create active structures has added an exciting new dimension to 3D printing technology. After being printed, these active, often composite, materials can change their shape over time; this has been termed as 4D printing. In this paper, we demonstrate the design and manufacture of active composites that can take multiple shapes, depending on the environmental temperature. This is achieved by 3D printing layered composite structures with multiple families of shape memory polymer (SMP) fibers – digital SMPs - with different glass transition temperatures (Tg) to control the transformation of the structure. After a simple single-step thermomechanical programming process, the fiber families can be sequentially activated to bend when the temperature is increased. By tuning the volume fraction of the fibers, bending deformation can be controlled. We develop a theoretical model to predict the deformation behavior for better understanding the phenomena and aiding the design. We also design and print several flat 2D structures that can be programmed to fold and open themselves when subjected to heat. With the advantages of an easy fabrication process and the controllable multi-shape memory effect, the printed SMP composites have a great potential in 4D printing applications. PMID:27071543

  9. Multi-shape active composites by 3D printing of digital shape memory polymers

    NASA Astrophysics Data System (ADS)

    Wu, Jiangtao; Yuan, Chao; Ding, Zhen; Isakov, Michael; Mao, Yiqi; Wang, Tiejun; Dunn, Martin L.; Qi, H. Jerry

    2016-04-01

    Recent research using 3D printing to create active structures has added an exciting new dimension to 3D printing technology. After being printed, these active, often composite, materials can change their shape over time; this has been termed as 4D printing. In this paper, we demonstrate the design and manufacture of active composites that can take multiple shapes, depending on the environmental temperature. This is achieved by 3D printing layered composite structures with multiple families of shape memory polymer (SMP) fibers – digital SMPs - with different glass transition temperatures (Tg) to control the transformation of the structure. After a simple single-step thermomechanical programming process, the fiber families can be sequentially activated to bend when the temperature is increased. By tuning the volume fraction of the fibers, bending deformation can be controlled. We develop a theoretical model to predict the deformation behavior for better understanding the phenomena and aiding the design. We also design and print several flat 2D structures that can be programmed to fold and open themselves when subjected to heat. With the advantages of an easy fabrication process and the controllable multi-shape memory effect, the printed SMP composites have a great potential in 4D printing applications.

  10. Multi-shape active composites by 3D printing of digital shape memory polymers.

    PubMed

    Wu, Jiangtao; Yuan, Chao; Ding, Zhen; Isakov, Michael; Mao, Yiqi; Wang, Tiejun; Dunn, Martin L; Qi, H Jerry

    2016-01-01

    Recent research using 3D printing to create active structures has added an exciting new dimension to 3D printing technology. After being printed, these active, often composite, materials can change their shape over time; this has been termed as 4D printing. In this paper, we demonstrate the design and manufacture of active composites that can take multiple shapes, depending on the environmental temperature. This is achieved by 3D printing layered composite structures with multiple families of shape memory polymer (SMP) fibers - digital SMPs - with different glass transition temperatures (Tg) to control the transformation of the structure. After a simple single-step thermomechanical programming process, the fiber families can be sequentially activated to bend when the temperature is increased. By tuning the volume fraction of the fibers, bending deformation can be controlled. We develop a theoretical model to predict the deformation behavior for better understanding the phenomena and aiding the design. We also design and print several flat 2D structures that can be programmed to fold and open themselves when subjected to heat. With the advantages of an easy fabrication process and the controllable multi-shape memory effect, the printed SMP composites have a great potential in 4D printing applications. PMID:27071543

  11. Investigation of thermomechanical couplings, strain localization and shape memory properties in a shape memory polymer subjected to loading at various strain rates

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    This paper presents experimental and modeling results of the effects of thermomechanical couplings occurring in a polyurethane shape memory polymer (SMP) subjected to tension at various strain rates within large strains. The SMP mechanical curves, recorded using a testing machine, and the related temperature changes, measured in a contactless manner using an IR camera, were used to investigate the polymer deformation process at various loading stages. The effects of thermomechanical couplings allowed the determination of the material yield point in the initial loading stage, the investigation of nucleation and development of the strain localization at larger strains and the estimation of the effects of thermoelastic behavior during the unloading process. The obtained stress–strain and thermal characteristics, the results of the dynamic mechanical analysis and estimated values of the shape fixity and shape recovery parameters confirmed that the shape memory polymer (T g = 45 °C) is characterized by good mechanical and shape memory properties, as well as high sensitivity to the strain rate. The mechanical response of the SMP subjected to tension was simulated using the finite element method and applying the large strain, two-phase model. Strain localization observed in the experiment was well reproduced in simulations and the temperature spots were correlated with the accumulated viscoplastic deformation of the SMP glassy phase.

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

    PubMed Central

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

    2012-01-01

    Thermoresponsive shape memory polymers (SMPs) are stimuli-responsive materials that return to their permanent shape from a temporary shape in response to heating. The design of new SMPs which obtain a broader range of properties including mechanical behavior is critical to realize their potential in biomedical as well as industrial and aerospace applications. To tailor the properties of SMPs, “AB networks” comprised of two distinct polymer components have been investigated but are overwhelmingly limited to those in which both components are organic. In this present work, we prepared inorganic-organic SMPs comprised of inorganic polydimethyl-siloxane (PDMS) segments of varying lengths and organic poly(ε-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

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

    PubMed Central

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

    2014-01-01

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

  14. Stent thrombosis with drug-eluting stents: is the paradigm shifting?

    PubMed

    Palmerini, Tullio; Biondi-Zoccai, Giuseppe; Della Riva, Diego; Mariani, Andrea; Genereux, Philippe; Branzi, Angelo; Stone, Gregg W

    2013-11-19

    First-generation drug-eluting stents (DES), which impart the controlled release of sirolimus or paclitaxel from durable polymers to the vessel wall, have been consistently shown to reduce the risk of restenosis and target vessel revascularization compared with bare metal stents (BMS). However, stent thrombosis (ST) emerged as a major safety concern with first-generation DES early after their adoption in clinical practice, requiring prolonged dual antiplatelet therapy. Pathological studies have shown that first-generation DES are associated with delayed arterial healing and polymer hypersensitivity reactions resulting in chronic inflammation, predisposing to late and very late ST. Second-generation DES have been developed to overcome these issues with improved stent designs and construction and the use of biocompatible and bioabsorbable polymers. Meta-analyses have shown that the thin-strut, fluoropolymer-coated cobalt-chromium everolimus-eluting stent (CoCr-EES) may be associated with lower rates of definite ST than other DES and, unexpectedly, even lower than BMS. The thin-strut structure of the stent platform, the thromboresistant properties of the fluoropolymer, and the reduced polymer and drug load may contribute to the low rate of ST with CoCr-EES. The notion of DES being safer than BMS represents a paradigm shift in the evolution of percutaneous coronary intervention. The relative safety and efficacy of fluoropolymer-coated CoCr-EES, DES with bioabsorbable polymers, and fully bioresorbable scaffolds are the subject of numerous ongoing large-scale trials. PMID:24036025

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

    NASA Astrophysics Data System (ADS)

    Sakai, Takenobu; Tao, Takayuki; Somiya, Satoshi

    2015-11-01

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

  16. The Supralimus sirolimus-eluting stent.

    PubMed

    Lemos, Pedro A; Bienert, Igor

    2013-05-01

    The use of biodegradable polymeric coatings has emerged as a potential bioengineering target to improve the vascular compatibility of coronary drug-eluting stents (DESs). This review summarizes the main features and scientific facts about the Supralimus sirolimus-eluting stent (Sahajanand Medical Technologies Ltd, Surat, India), which is a biodegradable polymer-based, sirolimus-eluting metallic stent that was recently introduced for routine use in Europe. The novel stent is built on a stainless steel platform, coated with a blend of biodegradable polymers (poly-l-lactide, poly-dl-lactide-co-glycolide and polyvinyl pyrrolidone; coating thickness is 4-5 µm). The active agent is the antiproliferative sirolimus in a dose load of 1.4 µg/mm(2), which is released within 48 days. The Supralimus stent was initially evaluated in the single-arm SERIES-I study, which showed binary angiographic restenosis rates of 0% (in-stent) and 1.7% (in-segment) and an in-stent late lumen loss of 0.09 ± 0.28 mm. The multicenter randomized PAINT trial compared two DESs with identical metallic platforms and biodegradable polymer carriers, but different agents (Infinnium [Sahajanand Medical Technologies Pvt Ltd] paclitaxel-eluting stent or Supralimus sirolimus-eluting stent) against bare stents. After 3 years, the pooled DES population had similar rates of cardiac death or myocardial infarction (9 vs 7.1%; p = 0.6), but a lower risk of repeat interventions (10 vs 29.9%; p < 0.01) than controls with bare stents. The incidence of definite or probable stent thrombosis in the pooled DES group was 2.3% (1st year: 1.8%; 2nd year: 0.4% and 3rd year: 0%). These results demonstrate that the novel Supralimus stents are effective in reducing reintervention, while potentially improving the safety profile by decreasing the risk of late-term thrombosis, even though further studies would be necessary to confirm these findings. PMID:23597097

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  18. Longitudinal stent deformation during coronary bifurcation stenting.

    PubMed

    Vijayvergiya, Rajesh; Sharma, Prafull; Gupta, Ankush; Goyal, Praveg; Panda, Prashant

    2016-03-01

    A distortion of implanted coronary stent along its longitudinal axis during coronary intervention is known as longitudinal stent deformation (LSD). LSD is frequently seen with newer drug eluting stents (DES), specifically with PROMUS Element stent. It is usually caused by impact of guide catheter tip, or following passage of catheters like balloon catheter, IVUS catheter, guideliner, etc. We hereby report a case of LSD during coronary bifurcation lesion intervention, using two-stents technique. Patient had acute stent thrombosis as a complication of LSD, which was successfully managed. PMID:26811144

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

    NASA Astrophysics Data System (ADS)

    Zhang, Dawei

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

  20. Nonvolatile memory characteristics of organic thin film transistors using poly(2-hydroxyethyl methacrylate)-based polymer multilayer dielectric

    NASA Astrophysics Data System (ADS)

    Chen, Ying-Chih; Su, Yan-Kuin; Yu, Hsin-Chieh; Huang, Chun-Yuan; Huang, Tsung-Syun

    2011-10-01

    A wide hysteresis width characteristic (memory window) was observed in the organic thin film transistors (OTFTs) using poly(2-hydroxyethyl methacrylate) (PHEMA)-based polymer multilayers. In this study, a strong memory effect was also found in the pentacene-based OTFTs and the electric characteristics were improved by introducing PHEMA/poly(methyl methacrylate) (PMMA)/PHEMA trilayer to replace the conventional PHEMA monolayer or PMMA/PHEMA and PHEMA/PMMA bilayer as the dielectric layers of OTFTs. The memory effect was originated from the electron trapping and slow polarization of the dielectrics. The hydroxyl (-OH) groups inside the polymer dielectric were the main charge storage sites of the electrons. This charge-storage phenomenon could lead to a wide flat-band voltage shift (memory window, △VFB = 22 V) which is essential for the OTFTs' memory-related applications. Moreover, the fabricated transistors also exhibited significant switchable channel current due to the charge-storage and slow charge relaxation.

  1. Memory.

    ERIC Educational Resources Information Center

    McKean, Kevin

    1983-01-01

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

  2. The impact of material characteristics on the mechanical properties of a poly(L-lactide) coronary stent.

    PubMed

    Grabow, N; Martin, H; Schmitz, K P

    2002-01-01

    Biodegradable polymer stents as an alternative to metallic vascular stents have long been under discussion. However, for various reasons no such stent concept has been made available for commercial use until today. One reason may be, that still little is known about the mechanical properties of polymer stents and their dependency on the material characteristics. In this study, finite element analysis is used to investigate the mechanical properties of a balloon expandable PLLA stent under various load conditions. It is shown, how material parameters, such as elastic modulus, yield level and material hardening, influence stent recoil and collapse behavior. PMID:12451906

  3. Memory effect in the chain-collapse process in a dilute polymer solution

    NASA Astrophysics Data System (ADS)

    Maki, Yasuyuki; Sasaki, Naoki; Nakata, Mitsuo

    2004-12-01

    The effect of temperature perturbation on a single-chain-collapse process was studied for poly(methyl methacrylate) with the molecular weight Mw=1.05×107 in the mixed solvent of tert-butyl alcohol+water (2.5 vol %). In the chain-collapse process after a quench from the θ temperature to a temperature T1, the temperature was changed from T1 to T2 at the time t1 after the quench and returned to T1 at the time t1+t2. In the three stages at T1, T2, and T1, measurements of the mean-square radius of gyration of polymer chains were carried out by static light scattering and the chain-collapse process was represented by the expansion factor as a function of time. An effect of chain aggregation on the measurements was negligibly small because of the very slow phase separation. For the negative temperature perturbation (T1>T2), the chain-collapse processes observed in the first and third stages were connected smoothly and agreed with the collapse process due to a single-stage quench to T1. A memory of the chain collapse in the first stage at T1 was found to persist into the third stage at the same temperature T1 without being affected by the temperature perturbation of T2 during t2. The memory effect was observed irrespective of the time period of t2. The positive temperature perturbation (T1

  4. Everolimus-eluting bioresorbable stent vs. durable polymer everolimus-eluting metallic stent in patients with ST-segment elevation myocardial infarction: results of the randomized ABSORB ST-segment elevation myocardial infarction—TROFI II trial

    PubMed Central

    Sabaté, Manel; Windecker, Stephan; Iñiguez, Andres; Okkels-Jensen, Lisette; Cequier, Angel; Brugaletta, Salvatore; Hofma, Sjoerd H.; Räber, Lorenz; Christiansen, Evald Høi; Suttorp, Maarten; Pilgrim, Thomas; Anne van Es, Gerrit; Sotomi, Yohei; García-García, Hector M.; Onuma, Yoshinobu; Serruys, Patrick W.

    2016-01-01

    Aims Patients with ST-segment elevation myocardial infarction (STEMI) feature thrombus-rich lesions with large necrotic core, which are usually associated with delayed arterial healing and impaired stent-related outcomes. The use of bioresorbable vascular scaffolds (Absorb) has the potential to overcome these limitations owing to restoration of native vessel lumen and physiology at long term. The purpose of this randomized trial was to compare the arterial healing response at short term, as a surrogate for safety and efficacy, between the Absorb and the metallic everolimus-eluting stent (EES) in patients with STEMI. Methods and results ABSORB-STEMI TROFI II was a multicentre, single-blind, non-inferiority, randomized controlled trial. Patients with STEMI who underwent primary percutaneous coronary intervention were randomly allocated 1:1 to treatment with the Absorb or EES. The primary endpoint was the 6-month optical frequency domain imaging healing score (HS) based on the presence of uncovered and/or malapposed stent struts and intraluminal filling defects. Main secondary endpoint included the device-oriented composite endpoint (DOCE) according to the Academic Research Consortium definition. Between 06 January 2014 and 21 September 2014, 191 patients (Absorb [n = 95] or EES [n = 96]; mean age 58.6 years old; 17.8% females) were enrolled at eight centres. At 6 months, HS was lower in the Absorb arm when compared with EES arm [1.74 (2.39) vs. 2.80 (4.44); difference (90% CI) −1.06 (−1.96, −0.16); Pnon-inferiority <0.001]. Device-oriented composite endpoint was also comparably low between groups (1.1% Absorb vs. 0% EES). One case of definite subacute stent thrombosis occurred in the Absorb arm (1.1% vs. 0% EES; P = ns). Conclusion Stenting of culprit lesions with Absorb in the setting of STEMI resulted in a nearly complete arterial healing which was comparable with that of metallic EES at 6 months. These findings provide the basis for further exploration in

  5. Second generation drug-eluting stents: a review of the everolimus-eluting platform.

    PubMed

    Whitbeck, Matthew G; Applegate, Robert J

    2013-01-01

    Everolimus-eluting stents (EES) represent the next generation of drug-eluting stents (DES). Important design modifications include thin strut stent backbones, less inflammatory and more biocompatible polymers, and lower drug dosing. The cobalt chromium EES fluoropolymer XIENCE V stent has been the most extensively studied of such stents. In animal models, this stent demonstrated minimal vessel inflammation, a biologically active endothelium with strut coverage similar to a bare metal stent, and inhibition of intimal hyperplasia comparable to that seen with sirolimus-eluting stents. The SPIRIT family of clinical trials demonstrated low rates of late loss, and clinical restenosis, as well as low rates of very late stent thrombosis. These excellent clinical outcomes addressed limitations of the 1st generation DES, and substantiated widespread clinical use of the EES platform. PMID:23926441

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

    PubMed

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

    2015-04-01

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

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

    PubMed

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

    2016-01-13

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

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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