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We report a tough, semicrystalline, ternary thiol–ene polymer system containing linear dithiols, cross-linking trithiols, and spiroacetal alkene units in the main chain backbone that is synthesized by “click” ultraviolet photopolymerization in a one-step, solvent-free process. We varied the cross-link density to tune crystallinity and microstructure; in turn, thermomechanical properties such as yield strength, glass transition temperature, failure strain, and stress–strain behavior could be modified and controlled. Thiol–enes containing 7.5 and 10 thiol mol % cross-linker resulted in networks that balanced crystallinity, elasticity, and cross-linking to maximize toughness. These materials demonstrate how the presence of spiro units throughout a polymer’s backbone creates semicrystalline networks of substantial toughness from traditionally weak chemistries such as thiol–enes. This system can be synthesized in a neat, one-step photopolymerization process; as such, it illustrates the power of spirochemistry ...

Thermoplastic polycarbonate urethanes (PCUs), have promise in many biomedical applications due to their low stiffness, favorable biocompatibility, and high strength. The long-term performance of PCU implants in load-bearing applications remains to be seen, and will depend in part on the material fatigue properties. Optimizing implants for success in fatigue-prone applications depends on a strong understanding of the relationship between material structure and fatigue performance, a surprisingly understudied area. In this study, we sought to develop relationships between PCU structure and mechanical properties, including fatigue, for three soft PCUs with systematically varied ratios of hard and soft segments. In addition, we compared injection molded controls to 3D printed (fused deposition modeling, FDM) varieties to examine the effects of such processing. Results indicate that increased hard segment content leads to increased stiffness, increased shear failure stress, and improvements in tensile fatigue from a stress-based standpoint despite relatively uniform tensile strength for the tested grades. Effects of hard segment content on tensile failure strain, and strain-based fatigue performance, were more complex and largely influenced by microphase organization and interaction. FDM samples matched or exceeded injection molded controls in terms of tensile failure stress and strain, compressive properties, shear strength, and tensile fatigue. The success of FDM samples is attributed in part to favorable printing parameters and the toughness of PCU which results in lower flaw sensitivity.

Poly(ester-urethane-urea) (PEUU) is one of many synthetic biodegradable elastomers under scrutiny for biomedical and soft tissue applications. The goal of this study was to investigate the effect of the experimental parameters on mechanical properties of PEUUs following exposure to different degrading environments, similar to that of the human body, using linear regression, producing one predictive model. The model utilizes two independent variables of poly(caprolactone) (PCL) type and copolymer crystallinity to predict the dependent variable of maximum tangential modulus (MTM). Results indicate that comparisons between PCLs at different degradation states are statistically different (p < 0.0003), while the difference between experimental and predicted average MTM is statistically negligible (p < 0.02). The linear correlation between experimental and predicted MTM values is R2 = 0.75. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A: 3382–3387, 2013.

This chapter highlights the material selection process for shape-memory polymers (SMPs). When selecting SMPs, additional properties need to be considered, so two case studies are given as examples. Current SMPs are grouped based on their polymer structure or physical structure (composite, foam, fiber) to accelerate the material selection process for SMPs. The thermomechanical properties and shape-memory properties have been tabulated for acrylics, polyurethanes, epoxies, and other SMPs. For each type of SMP, their chemical structure, synthesis, properties, and performance are discussed. The properties of commercially available SMPs are also presented and discussed.

A 3D printable and highly stretchable tough hydrogel is developed by combining poly(ethylene glycol) and sodium alginate, which synergize to form a hydrogel tougher than natural cartilage. Encapsulated cells maintain high viability over a 7 d culture period and are highly deformed together with the hydrogel. By adding biocompatible nanoclay, the tough hydrogel is 3D printed in various shapes without requiring support material., National Institutes of Health (U.S.) (Grant UH3TR000505), National Institutes of Health (U.S.) (Grant R01AR48825), National Institutes of Health (U.S.) (Common Fund for the Microphysiological Systems Initiative), AOSpine Foundation, National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (DRM-1121107)

X. Zhao and co-workers develop on page 4035 a new biocompatible hydrogel system that is extremely tough and stretchable and can be 3D printed into complex structures, such as the multilayer mesh shown. Cells encapsulated in the tough and printable hydrogel maintain high viability. 3D-printed structures of the tough hydrogel can sustain high mechanical loads and deformations.