Class Of Shape Memory Polymers Research Articles

Shape fixing abilities of SEBS/Paraffin blends with different paraffins under conventional and reversible plasticity shape memory programming

Poly(styrene-b-[ethylene-co-butylene]-b-styrene) (SEBS)/paraffin system is a promising class of shape memory polymers and the transition temperature of such materials could be flexibly regulated by choosing different paraffins. However, the difference in shape memory performance of SEBS/paraffin blends containing paraffin with same content but different melting temperature (Tm) has not been comparatively studied. In this work, two series of SEBS/paraffin blends containing same content paraffin (30 and 70 wt%, respectively) with Tm of 28.5 and 61.3 °C (denoted as PL and PH, respectively) were prepared and their shape fixing ratios (Rfs) under conventional shape memory (CSM) and reversible plasticity shape memory (RPSM) programming methods were investigated. It was found that these blends with the same paraffin content showed different Rfs regardless of the programming method. For example, the 30 wt% PH-containing sample exhibited higher Rf under CSM programming, while the 70 wt% PL-containing sample showed higher Rf under RPSM programming. By investigating microstructural changes, a possible explanation for the shape memory performance of SEBS/paraffin blends containing paraffin with different Tm was proposed. This work was helpful to deepen the understanding of shape memory mechanism and broaden the application of SEBS/paraffin-based shape memory polymers.

Space-deployable device based on shape memory cyanate ester composites

Shape memory cyanate ester is a class of shape memory polymers with high thermal stability and excellent space environmental adaptability. In this study, a space-deployable device based on cyanate ester-based shape memory polymer composite (CE-SMPC) was proposed, and its thermomechanical properties and shape memory behavior were experimentally evaluated. The space-deployable device maintained a high shape fixity rate even after prolonged exposure to high or low temperatures, which ensured its locking reliability in space applications. The results of self-deployment experiments indicated that the space-deployable device exhibited good shape recovery performance in both atmospheric and vacuum environments. The SMPC-based space-deployable device presented in this study was applied to China's first Mars exploration mission to achieve autonomous locking and release of the deployable engineering measurement subsystem on the probe.

High Energy Release-high Retraction Smart Polymer Fibers used in Artificial Muscle Fabrication

Shape-memory polymers (SMPs) could remember their original shape and then, return to their initial shape upon stimulus. So far, quantities such as fixity and recovery ratio of SMPs have been broadly reported. Nevertheless, one main issue is the existence and use of an appropriate approach to quantitatively estimate the SMPs released energy. In addition, it is hypothesized that the elastic behavior of SMPs plays an underlying role when SMP fibers need to exhibit high-tension and high-elongation capacity as required in synthetic muscles. Here, we present, for first time, SMP trinary bulk and filament systems of acrylonitrile butadiene styrene (ABS)/thermoplastic polyurethane (TPU)/ethylene vinyl acetate (EVA) fabricated under calendering intense shear mixing and hot pressing. A digital blocked force load cell was used to record specimens energy released. The results exhibited high retraction from the specimens secondary shape correlated to the tensile behavior. It was shown the blended system of 50, 25 and 25% of TPU, ABS and EVA, respectively, resulted in ~640% and 3900% increase in the elastic modulus and energy release compared to EVA/TPU systems. The double SMP filaments led to a 50% increase in the energy release compared to single fibers. Nevertheless, the blended binary specimens with the TPU/ABS ratio of 50/50 exhibited 600% increase in tensile strength. It was confirmed the elastic modulus, number of fibers and elongation at break govern the SMP stored. The findings of the research lightened a new class of SMPs to be used as fiber-based artificial muscles and orthodontic products.

Thermo/hydration responsive shape memory polymers with enhanced hydrophilicity for biomedical applications

Thiol-ene/acrylate shape memory polymers (SMPs) have sufficient stiffness for facile insertion and precision placement and soften after exposure to physiological conditions to reduce the mechanical mismatch with body tissue. As a result, they have demonstrated excellent potential as substrates for various flexible bioelectronic devices, such as cochlear implants, nerve cuffs, cortical probes, plexus blankets, and spinal cord stimulators. To enhance the shape recovery properties and softening effect of SMPs under physiological conditions, we designed and implemented a new class of SMPs as bioelectronics substrates. In detail, we introduced dopamine acrylamide (DAc) as a hydrophilic monomer into a current thiol-ene polymer network. Dry and soaked dynamic mechanical analyses were performed to evaluate the thermomechanical properties, softening kinetics under wet conditions, and shape recovery properties. Modification of SMPs by DAc provided an improved softening effect and shape recovery speed under physiological conditions. Here, we report a new strategy for designing SMPs with enhanced shape recovery properties and lower moduli than previously reported SMPs under physiological conditions without sacrificing stiffness at room temperature by introducing a hydrophilic monomer.

Constitutive Modeling of multi-stimuli-responsive shape memory polymers with multi-functional capabilities

Nowadays, shape memory polymers (SMPs)-based devices are required to be much smarter to produce large shape memory recovery and recovery force with lower working temperatures in order to enable multi-functionality in them. They could play a vital role in the advancement of multi-functional soft robot manipulators, biomedical tools and wearable devices where the working temperatures is a key challenge and must be around the body temperature, or in sustainable smart systems with low energy consumption. The aim of this paper is to introduce thermo-electro-magneto-responsive fibrous SMPs (TEMFSMPs) as a new class of SMPs with highly enhanced shape recovery and recovery force and reduced working temperature. A three-dimensional constitutive model is developed to simulate thermo-electro-magneto-visco-hyperelastic behaviors of SMPs under large deformation for the first time. Constitutive relations are derived by adopting an electro-magneto-visco-hyperelasticity theory and implementing it in a thermo-mechanical cycle of SMPs. To improve the strength of thermo-electro-magneto-responsive SMPs, a bunch of fibers is also embedded into the SMP matrix. Then, the proposed model for thermo-electro-magneto-responsive fibrous shape memory polymers (TEMFSMPs) under uniaxial tension and complex loading regimes such as simultaneous torsion and extension are solved semi-analytically. In addition, the thermo-mechanical response through the proposed model is validated via available SMP experimental tests. Numerical results reveal that electro-magnetic features can significantly enhance shape memory recovery and recovery force of TEMFSMPs and lower their working temperatures. It is found that the electro-magnetic field, the orientation, and stiffness of fibers can effectively be set to tune the shape memory effect and bio-applicability of TEMFSMPs with highly enhanced stress/strain recovery and reduced working temperature.

Microgrooves Encourage Endothelial Cell Adhesion and Organization on Shape-Memory Polymer Surfaces.

Cardiovascular stents have become the mainstay for treating coronary and other vascular diseases; however, the need for long-term anti-platelet therapies continues to drive research on novel materials and strategies to promote in situ endothelialization of these devices, which should decrease local thrombotic response. Shape-memory polymers (SMPs) have shown promise as polymer stents due to their self-deployment capabilities and vascular biocompatibility. We previously demonstrated isotropic endothelial cell adhesion on the unmodified surfaces of a family of SMPs previously developed by our group. Here, we evaluate whether endothelial cells align preferentially along microgrooved versus unpatterned surfaces of these SMPs. Results show that micropatterning SMP surfaces enhances natural surface hydrophobicity, which helps promote endothelial cell attachment and alignment along the grooves. With the addition of microgrooves to the SMP surface, this class of SMPs may provide an improved surface and material for next-generation blood-contacting devices.

Shape Memory Polymers Containing Higher Acrylate Content Display Increased Endothelial Cell Attachment.

Shape Memory Polymers (SMPs) are smart materials that can recall their shape upon the application of a stimulus, which makes them appealing materials for a variety of applications, especially in biomedical devices. Most prior SMP research has focused on tuning bulk properties; studying surface effects of SMPs may extend the use of these materials to blood-contacting applications, such as cardiovascular stents, where surfaces that support rapid endothelialization have been correlated to stent success. Here, we evaluate endothelial attachment onto the surfaces of a family of SMPs previously developed in our group that have shown promise for biomedical devices. Nine SMP formulations containing varying amounts of tert-Butyl acrylate (tBA) and Poly(ethylene glycol) dimethacrylate (PEGDMA) were analyzed for endothelial cell attachment. Dynamic mechanical analysis (DMA), contact angle studies, and atomic force microscopy (AFM) were used to verify bulk and surface properties of the SMPs. Human umbilical vein endothelial cell (HUVEC) attachment and viability was verified using fluorescent methods. Endothelial cells preferentially attached to SMPs with higher tBA content, which have rougher, more hydrophobic surfaces. HUVECs also displayed an increased metabolic activity on these high tBA SMPs over the course of the study. This class of SMPs may be promising candidates for next generation blood-contacting devices.

Reconfiguration and shape memory triggered by heat and light of carbon nanotube–polyurethane vitrimer composites

ABSTRACTThermoset shape‐memory polymers (SMPs) are widely applied because of their superiority in maintaining permanent shapes. However, the inferiority of this material is also conspicuous, namely the loss of reprocessing ability owing to the chemically crosslinked structure. Fortunately, a new class of SMPs, known as “vitrimers,” was discovered, which can be reshaped or reprocessed via topological rearrangement due to the existence of dynamic covalent bonds. Thus, this new thermoset SMP could become a novel solution. In this paper, carbon nanotube–polyurethane vitrimer (CNT‐PUV) composites have been prepared, which possess the capability of thermally induced shape memory based on entropy changes and thermal reconfiguration based on transcarbamoylation reactions of carbamate bonds. In addition, the introduction of CNTs endows them with properties of near‐infrared (NIR) triggered shape memory and reconfiguration due to the photothermal conversion effect of CNTs. Besides, due to the character of the NIR laser, step‐by‐step shape recovery of CNT‐PUVs is realized from predefined temporary shapes to a permanent shape. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45784.

Effect of chemical crosslinking on the free-strain recovery characteristics of amorphous shape-memory polymers

AbstractThe goal of this study is to investigate the fundamental relationship between the extent of crosslinking and shape-memory behavior of amorphous, (meth)acrylate-based polymer networks. The polymer networks were produced by copolymerization of tert-butyl acrylate (tBA) and poly(ethylene glycol) dimethacrylates of differing molecular weights (PEGDMA). Polymer compositions were tailored via the amount (weight percent (wt%)) and molecular weight of the PEGDMA crosslinking agents added to produce four materials with varying levels of crosslinking (0, 2, 10, and 40 wt% crosslinking agent corresponding to 0, 0.6, 3.2, and 16.6 mole%) and nearly equal glass transition temperatures (Tg). The effect of crosslinking on deformation limits and free-strain recovery is evaluated. Near complete strain recovery was demonstrated by all materials; however, absolute recovery strain decreased with increasing crosslinking due to a corresponding decrease in strain-to-failure. The results provide insights regarding the link between polymer structure, deformation limits, and strain-recovery capabilities of this class of shape-memory polymers. An improved understanding of this relationship is pivotal for optimizing system response for a wide range of shape-memory applications.

Shape memory polymers based on uniform aliphatic urethane networks

AbstractAliphatic urethane polymers have been synthesized and characterized, using monomers with high molecular symmetry, 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′,N′‐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 34–153°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 Tg. We believe these materials represent a new and potentially important class of SMPs, and should be especially useful in applications such as biomedical microdevices. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007