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Abstract Mimicking the mechanical properties of native tissue is an important requirement for tissue engineering scaffolds. Blood vessels are subject to repetitive dilation and contraction and possess a special nonlinear mechanical property due to their triple-layered structure. Fabrication of vascular grafts consisting of bioresorbable materials with biomimetic mechanical properties is an urgent demand, as well as a critical challenge. Inspired by the configuration and function of collagen and elastin in native blood vessels, a new type of triple-layered vascular graft (TLVG) was developed in this study. The TLVGs were composed of braided silk as the inner layer, polyacrylamide (PAM) hydrogel as the middle layer, and electrospun thermoplastic polyurethane (TPU) as the outer layer. The woven-structured silk fibers were able to mimic the properties of the loosely distributed collagen fibers, while the highly elastic PAM hydrogel and TPU nanofibers mimicked the elasticity of elastin in the blood vessel. With this specially designed microstructure and combination of rigid and elastic materials, the TLVGs successfully mimicked the nonlinear mechanical property of native blood vessels. Moreover, TLVGs possess sufficient suture retention strength for surgical implantation. The introduction of a PAM hydrogel layer effectively solved the leaking issue for conventional porous vascular grafts and greatly enhanced the burst pressure. In addition, all materials used have high biocompatibility to human endothelial cells, which indicates that the developed TLVGs have high potential to be used as readily available vascular grafts. Highlights • Triple-layered vascular grafts with biomimetic mechanical properties were prepared. • The grafts consist of braided silk fiber inner layer, PAM hydrogel middle layer and TPU outer layer. • Woven silk fibers result to non-linear physical property which resembles blood vessel. • The hydrogel layer prevents blood leaking and greatly enhanced burst pressure. [ABSTRACT FROM AUTHOR]

Biodegradable thermoplastic polyurethanes (TPUs) with tuneable properties are of great interest in various applications. In this study, two kinds of poly(ε-caprolactone) (PCL)-based biodegradable TPUs were synthesized using either dl -dithiothreitol (DTE) or glycerol as chain extenders. The reactive side groups on the chain extenders provide uniformly spaced post-crosslinking sites that can be bridged by thiol oxidation for DTE and by diisocyanate grafting for glycerol, thus leading to lightly crosslinked TPUs that can still be easily processed. The chemical structure, thermal properties, mechanical performance, and degradation behaviour of these TPUs were studied comprehensively. Their chemical structures were verified by nuclear magnetic resonance spectroscopy ( 1 H NMR), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. The post-crosslinking hindered the crystallization of the PCL region and significantly enhanced the thermal decomposition temperature. Post-crosslinked TPUs achieved significant improvements in modulus, ultimate strength, flexibility, and tear resistance compared to their neat counterparts. The degradation rate was found to correlate with material wettability, and the formation of chemical crosslinks reduced the hydrolytic degradation rate of TPUs. In summary, by introducing functional groups via chain extenders and post-crosslinking, biodegradable TPUs with improved and tuneable properties and suitable for various applications could be obtained. [ABSTRACT FROM AUTHOR]

Triple-layered small diameter vascular scaffolds, which consisted of thermoplastic polyurethane (TPU) and silk, were fabricated in this study for the first time by combining electrospinning, braiding, and thermally induced phase separation methods. These novel vascular scaffolds, which possess three layers of different structures (nanofibrous inner layer, woven silk filament middle layer, and porous outer layer), can mimic the structure of native blood vessels. The vascular scaffolds have a desirable toe region in tensile tests and sufficient suture retention and burst pressure for vascular graft applications. Endothelial cell culture tests showed that a cell layer could form on the inner surface of the scaffold with high cell viability and favorable morphology. [ABSTRACT FROM AUTHOR]

Fabrication of small diameter vascular grafts plays an important role in vascular tissue engineering. In this study, thermoplastic polyurethane (TPU)/graphene oxide (GO) scaffolds were fabricated via electrospinning at different GO contents as potential candidates for small diameter vascular grafts. In terms of mechanical and surface properties, the tensile strength, Young's modulus, and hydrophilicity of the scaffolds increased with an increase of GO content while plasma treatment dramatically improved the scaffold hydrophilicity. Mouse fibroblast (3T3) and human umbilical vein endothelial cells (HUVECs) were cultured on the scaffolds separately to study their biocompatibility and potential to be used as vascular grafts. It was found that cell viability for both types of cells, fibroblast proliferation, and HUVEC attachment were the highest at a 0.5 wt.% GO loading whereas oxygen plasma treatment also enhanced HUVEC viability and attachment significantly. In addition, the suture retention strength and burst pressure of tubular TPU/GO scaffolds containing 0.5 wt.% GO were found to meet the requirements of human blood vessels, and endothelial cells were able to attach to the inner surface of the tubular scaffolds. Platelet adhesion tests using mice blood indicated that vascular scaffolds containing 0.5% GO had low platelet adhesion and activation. Therefore, the electrospun TPU/GO tubular scaffolds have the potential to be used in vascular tissue engineering. [ABSTRACT FROM AUTHOR]

Novel blended scaffolds combining biobased polylactic acid (PLA) and thermoplastic polyurethane (TPU) were fabricated by thermally induced phase separation (TIPS) using two different solvents. Pure PLA and TPU polymer scaffolds using 1,4-dioxane as the sole solvent exhibited typical ladder-like structures, while blended PLA/TPU scaffolds using the same solvent showed a more uniform microstructure. When de-ionized water was added to the solution as a non-solvent, scaffolds with the mixed solvent showed more open cells and greater interconnectivity. In compression tests, it was found that specimens, including pure PLA, TPU, and blended scaffolds with the mixed solvent, showed a higher compressive modulus than their counterparts that used dioxane as the single solvent. Dynamic mechanical analysis (DMA) was employed to characterize the shape memory properties of the scaffolds. DMA indicated that the shape fixing ratio was highest in the PLA scaffolds, while the shape recovery ratio of the TPU scaffolds was the greatest among the specimens. More interestingly, when the mixed solvent was used, the shape memory property of the blended scaffolds displayed a similar deformation curve to the TPU scaffold. This was due to the presence of the TPU phase and similarity in structure between PLA/TPU and TPU scaffolds when mixed solvent was used. In the degradation test, the blended scaffolds showed a balanced degradation behavior in-between the more easily degraded PLA and the more stable TPU in the phosphate-buffered saline (PBS), and the addition of water to the systems accelerated the degradation process of the specimens. Cell culture results showed that all of the scaffolds had good biocompatibility. [ABSTRACT FROM PUBLISHER]

ABSTRACT Thermoplastic polyurethane (TPU) has been widely used in many applications because of its broad range of properties. However, synthesis of TPU with desirable properties is time consuming and only produces limited quantities. In this paper, twin-screw extrusion was used to produce TPU blends of varying soft and hard segments with tunable properties. Foamed samples of TPU blends were produced by microcellular injection molding. Multiple characterization tests were performed to confirm the miscibility and tunability of the blends. It was confirmed that soft and hard TPUs were compatible at ratios of 2:1 and 1:2, but partially miscible at a ratio of 1:1. Rigidity increased while the shape-recovery rate decreased with increasing the hard TPU content. The blend ratio influenced the foaming morphology, solid skin-layer thickness, as well as mechanical properties. It was found that microcellular injection molding could reduce the injection-shot volume without sacrificing too much mechanical property and, compared with their solid counterparts, the foamed blends could retain mechanical properties better than foamed pure TPUs. Decomposition and degradation behaviors were also studied. The biocompatibility of soft and hard TPU-foamed samples, which could be potentially used as tissue engineering scaffolds, was confirmed by fibroblast cytotoxicity test. © 2013 Wiley Periodicals, Inc. Adv Polym Technol 2014, 33, 21380; View this article online at . DOI 10.1002/adv.21380 [ABSTRACT FROM AUTHOR]

Rigid thermoplastic polyurethane (TPU)/hydroxyapatite (HA) scaffolds were prepared with micro HA (mHA) and nano HA (nHA) particles, respectively, via the thermally induced phase separation method. The effects of solvent and co-solvent, addition of sodium chloride (NaCl) porogen, and HA particle size were studied together with the morphology, compressive properties, and mineralization behavior of the scaffolds. Depending on the solvent, co-solvent, or porogen used, different porous structures were produced. In particular, a ladder-like morphology was obtained when dioxane (Di) was used as the solvent, whereas an interconnected porous structure was obtained by using dioxane and deionized water (DiW) as co-solvents. Rectangular pores with interconnected channels on the pore walls were achieved by using NaCl crystals as porogens. The TPU/nHA scaffolds showed stronger compressive properties than the TPU/mHA scaffolds and the pure TPU scaffolds. The scaffolds prepared using dioxane and water as co-solvents exhibit the greatest compressive modulus. Furthermore, TPU scaffolds with nHA particles had the ability to form bone apatite when soaked in simulated body fluid (SBF). After being soaked in SBF for 3 weeks, the weight percentage of formed apatite in the TPU/nHA-DiW scaffold was 9.2 %wt of the initial TPU content. Preliminary cytotoxicity tests were conducted using NIH 3T3 fibroblast cells. The high survival rate of these cells and the mineralization behavior suggest biocompatibility and high potential of these composites being used in bone tissue engineering applications. [ABSTRACT FROM AUTHOR]

Abstract: Polylactic acid (PLA) and thermoplastic polyurethane (TPU) are two kinds of biocompatible and biodegradable polymers that can be used in biomedical applications. PLA has rigid mechanical properties while TPU possesses flexible mechanical properties. Blended TPU/PLA tissue engineering scaffolds at different ratios for tunable properties were fabricated via twin screw extrusion and microcellular injection molding techniques for the first time. Multiple test methods were used to characterize these materials. Fourier transform infrared spectroscopy (FTIR) confirmed the existence of the two components in the blends; differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) confirmed the immiscibility between the TPU and PLA. Scanning electron microscopy (SEM) images verified that, at the composition ratios studied, PLA was dispersed as spheres or islands inside the TPU matrix and that this phase morphology further influenced the scaffold's microstructure and surface roughness. The blends exhibited a large range of mechanical properties that covered several human tissue requirements. 3T3 fibroblast cell culture showed that the scaffolds supported cell proliferation and migration properly. Most importantly, this study demonstrated the feasibility of mass producing biocompatible PLA/TPU scaffolds with tunable microstructures, surface roughnesses, and mechanical properties that have the potential to be used as artificial scaffolds in multiple tissue engineering applications. [Copyright &y& Elsevier]

Thermoplastic polyurethane is a commonly used polymer in our daily lives. Microcellular injection molding (a.k.a. MuCell) is an emerging method capable of mass-producing thermoplastic polyurethane foams with tunable microstructures and properties. This study investigated the effects of four main processing parameters—namely, plasticizing temperature, carbon dioxide (CO2) content, injection volume, and injection speed—on microcellular injection molded thermoplastic polyurethane ASTM tensile test bars. Property variables of interest included the cell diameter, cell density, skin layer thickness, and Young’s modulus. Influence sequences of parameters on each variable were obtained via the orthogonal array test method. It was found that the CO2 content primarily affected the cell diameter and cell density, whereas the temperature mainly influenced the skin layer thickness and Young’s modulus. Surface fitting of each dependent variable was done by combining its two most influential parameters from the experiment data. The value of each property variable within the processing window could then be predicted from the fitted surface. In addition, microcellular injection molding of thermoplastic polyurethane was simulated by a commercial software package, and the simulated results confirmed the reliability of the cell diameter prediction. [ABSTRACT FROM PUBLISHER]

• Synthesized supramolecular elastomer contains disulfide bonds and quadruple H-bonds. • The elastomer has strain-hardening, self-standing, and self-healing properties. • Silica nanoparticles further enhanced energy absorption and hindered relaxation. • Sacrificial bonds and nanoparticles contributed to the high energy absorption. Developing protective materials with intelligent and stimuli-responsive properties is indispensable for safety protection. However, combining contradictory characteristics into a single polymer is challenging, such as high mechanical strength, impact protection, and self-healing properties. Herein, a strain-hardening supramolecular polyurethane nanocomposite (SPN) with high mechanical strength and unique impact protection characteristics is synthesized by incorporating quadruple hydrogen bonds (H-bonds), disulfide bonds, and modified silica nanoparticles into polyurethane elastomer. Benefiting from the dynamic break and re-form characteristic of quadruple H-bonds and the stress dissipation behavior of nanoparticles, SPN exhibits high energy absorption efficiency and impact protection properties. During the drop ball striking test, the impact energy absorption efficiencies reached 90%, and the buffer time of impact was significantly longer than common buffering materials. The SPN exhibited excellent stretchability and self-healing ability, ascribing to disulfide metathesis and H-bonds association. Moreover, the prepared SPN could be easily processed through a hot press and showed negligible creeping. The developed SPN could serve as a novel self-standing impact protective material that offers promising prospects in sports, transportation, and aerospace fields. [ABSTRACT FROM AUTHOR]

Forced expression of transcription factors epigenetically reprograms somatic cells harvested from routine skin biopsies into induced pluripotent stem cells (iPSCs). Human iPSCs are key resources for drug discovery, regenerative medicine and tissue engineering. Here we developed a materials approach to explore how culture substrates could impact factor-mediated reprogramming of human fibroblasts. A materials library consisting of nanofibrous substrates with randomly oriented and aligned structures was prepared by electrospinning four polymers [polylactic acid (PLA), polycaprolactone (PCL), thermoplastic polyurethane (TPU) and polypropylene carbonate (PPC)] into nanofiber orientations. Adsorbing protein to each substrate permitted robust attachment of fibroblasts to all substrates. Fibroblasts on aligned substrates had elongated nuclei, but after reprogramming factor expression, nuclei became more circular. Reprogramming factors could override the nuclear shape constraints imposed by nanofibrous substrates, and the majority of substrates supported full reprogramming. Early culture on PCL and TPU substrates promoted reprogramming, and TGF-β repressed substrate effects. Partial least squares modeling of the biochemical and biophysical cues within our reprogramming system identified TGF-β and polymer identity as important cues governing cellular reprogramming responses. We believe that our approach of using a nanofibrous materials library can be used to dissect molecular mechanisms of reprogramming and generate novel substrates that enhance epigenetic reprogramming. [ABSTRACT FROM AUTHOR]

[Display omitted] This article systematically reviewed recently advanced progress in the development of self-healing composite elastomers for flexible strain sensors. Prevalent self-healing elastomeric matrixes, including natural rubber (NR), polydimethylsiloxane (PDMS), and polyurethane (PU), as well as other novel elastomers, were comprehensively reviewed. The properties of different dynamic linkages, the choice of various conductive fillers, and critical performance parameters were summarized and discussed in detail to provide insights into the rational combination of healing mechanisms and hybrid conductive networks to control the sensing performances. We expect this review could inspire the development of novel self-healing composite elastomers for high-performance flexible strain sensors. [ABSTRACT FROM AUTHOR]