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  1. Wrinkle topographies have been studied as simple, versatile, and in some cases biomimetic surface functionalization strategies. To fabricate surface wrinkles, one material phenomenon employed is the mechanical-instability-driven wrinkling of thin films, which occurs when a deforming substrate produces sufficient compressive strain to buckle a surface thin film. Although thin-film wrinkling has been studied on shape-changing functional materials, including shape-memory polymers (SMPs), work to date has been primarily limited to simple geometries, such as flat, uniaxially-contracting substrates. Thus, there is a need for a strategy that would allow deformation of complex substrates or 3D parts to generate wrinkles on surfaces throughout that complex substrate or part. Here, 4D printing of SMPs is combined with polymeric and metallic thin films to develop and study an approach for fiber-level topographic functionalization suitable for use in printing of arbitrarily complex shape-changing substrates or parts. The effect of nozzle temperature, substrate architecture, and film thickness on wrinkles has been characterized, as well as wrinkle topography on nuclear alignment using scanning electron microscopy, atomic force microscopy, and fluorescent imaging. As nozzle temperature increased, wrinkle wavelength increased while strain trapping and nuclear alignment decreased. Moreover, with increasing film thickness, the wavelength increased as well.

     
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  2. Abstract

    Current thoroughly described biodegradable and cross‐linkable polymers mainly rely on acrylate cross‐linking. However, despite the swift cross‐linking kinetics of acrylates, the concomitant brittleness of the resulting materials limits their applicability. Here, photo‐cross‐linkable poly(ε‐caprolactone) networks through orthogonal thiol‐ene chemistry are introduced. The step‐growth polymerized networks are tunable, predictable by means of the rubber elasticity theory and it is shown that their mechanical properties are significantly improved over their acrylate cross‐linked counterparts. Tunability is introduced to the materials, by alteringMc(or the molar mass between cross‐links), and its effect on the thermal properties, mechanical strength and degradability of the materials is evaluated. Moreover, excellent volumetric printability is illustrated and the smallest features obtained via volumetric 3D‐printing to date are reported, for thiol‐ene systems. Finally, by means of in vitro and in vivo characterization of 3D‐printed constructs, it is illustrated that the volumetrically 3D‐printed materials are biocompatible. This combination of mechanical stability, tunability, biocompatibility, and rapid fabrication by volumetric 3D‐printing charts a new path toward bedside manufacturing of biodegradable patient‐specific implants.

     
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