An ex vivo heart perfusion device preserves the donor heart in a warm beating state during transfer between extraction and implantation surgeries. One of the current challenges includes the use of rigid and noncompliant plastic tubes, which causes injuries to the heart at the junction between the tissue and the tube. The compliant and rapidly strain-stiffening mechanical property that generates a “J-shaped” stress–strain behavior is necessary for producing the Windkessel effect, which ensures continuous flow of blood through the aorta. In this study, we mimic the J-shaped and anisotropic stress–strain behavior of human aorta in synthetic elastomers to replace the problematic noncompliant plastic tube. First, we assess the mechanical properties of human (n = 1) and porcine aorta (n = 14) to quantify the nonlinear and anisotropic behavior under uniaxial tensile stress from five different regions of the aorta. Second, fabric-reinforced elastomer composites were prepared by reinforcing silicone elastomers with embedded fabrics in a trilayer geometry. The knitted structures of the fabric provide strain-stiffening as well as anisotropic mechanical properties of the resulting composite in a deterministic manner. By optimizing the combination between different elastomers and fabrics, the resulting composites matched the J-shaped and anisotropic stress–strain behavior of natural human and porcine aorta. Finally, improved analytical constitutive models based on Gent’s and Mooney–Rivlin’s constitutive model (to describe the elastomer matrix) combined with Holzapfel–Gasser–Ogden’s model (to represent the stiffer fabrics) were developed to describe the J-shaped behavior of the natural aortas and the fabric-reinforced composites. We anticipate that the suggested fabric-reinforced silicone elastomer composite design concept can be used to develop complex soft biomaterials, as well as in emerging engineering fields such as soft robotics and microfluidics, where the Windkessel effect can be useful in regulating the flow of fluids.

Natural tissues possess a so-called J-shaped strain-stiffening behavior, being soft and compliant at small strains followed by a rapid stiffening at higher strains to prevent tissue damage. In addition, they have significant anisotropy and local variations of mechanical properties that are difficult to reproduce with homogeneous materials. Inspired by many biological organisms, biomimetic and soft robotics research has been focusing on composites of soft components being reinforced by structured stiff components. Especially, structures from mature textile technology and recently emerging additive manufacturing techniques are effective in achieving complex biomimetic structures in a deterministic manner. This review focuses on composites of soft elastomers and gels reinforced by woven or knitted fibers and 3D printed structures, often with conductive or magnetic functionalities for active actuation. Discussions include describing the property requirements from biomedical and soft robotics applications with examples of specific cases, followed by a summary of a few technical solutions that have been suggested. For soft matrix materials, we focus on silicone elastomers because they are the most widely used for biomedical and soft robotics applications. Among reinforcements, knitted/woven fabrics, kirigami/origami structures, and 3D printed metamaterial reinforcements are the topics of interest because their local and global structure can be designed to govern properties of the composites and direct complex motions of soft robots in a deterministic manner. Then, application examples in the fields of biomimetic materials, soft robotics, and tissue engineering are reviewed. Finally, we emphasize the importance of advancing numerical modeling and simulation tools to predict the mechanical properties and actuation behavior of the designed composite materials.

Poly(acrylic acid) (PAA) is a promising polymer host to support alkaline electrolytes in Zn‐air batteries. Herein, precursors containing different concentrations of monomers, crosslinkers and additives such as zinc oxide in alkaline solution are polymerized to fabricate gel polymer electrolytes (GPEs) via one‐pot synthesis. The compositional effects of the GPEs on battery performance are evaluated and a more efficient cell design is demonstrated. With a vertical double air electrode configuration, ZABs using PAA‐based electrolytes show unprecedented performance including high specific energy (913 Wh kgZn−1), excellent cycling stability (at least 160 cycles at 2×10 mA cm−2) and high power density output (2×135 mW cm−2). The study represents a viable option to replace aqueous electrolytes for high performing ZABs.

In rechargeable batteries, overpotential problems may occur especially when the battery is aging. An alarm system to prevent overpotential may be useful. Colloidal nanoparticles of Fe3O4@SiO2 can self-assemble into amorphous photonic crystals (APCs) with tunable interparticle distances as a function of applied voltage. Here, we fabricated a colloidal APC that changes its color from mahogany to dark blue at applied voltages from 1.0 to 4.0 V, respectively. Citrate-modified Fe3O4 was solvothermally synthesized, followed by a SiO2 shell coating by the Stöber method to achieve a stable APC dispersed in polycarbonate solution. The APC is then connected alongside a zinc–air battery to indicate operational events including discharging, charging, and overcharging by color change of the APC. We anticipate that this simple idea provides an intuitive way to monitor the status of rechargeable batteries.

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