Bioinspired hydrogels have promising prospects in applications such as wearable devices, human health monitoring equipment, and soft robots due to their multifunctional sensing properties resembling natural skin. However, the preparation of intelligent hydrogels that provide feedback on multiple electronic signals simultaneously, such as human skin receptors, when stimulated by external contact pressure remains a substantial challenge. In this study, we designed a bioinspired hydrogel with multiple conductive capabilities by incorporating carbon nanotubes into a chelate of calcium ions with polyacrylic acid and sodium alginate. The bioinspired hydrogel consolidates self-healing ability, stretchability, 3D printability, and multiple conductivities. It can be fabricated as an integrated strain sensor with simultaneous piezoresistive and piezocapacitive performances, exhibiting sensitive (gauge factor of 6.29 in resistance mode and 1.25 kPa–1 in capacitance mode) responses to subtle pressure changes in the human body, such as finger flexion, knee flexion, and respiration. Furthermore, the bioinspired strain sensor sensitively and discriminatively recognizes the signatures written on it. Hence, we expect our ideas to provide inspiration for studies exploring the use of advanced hydrogels in multifunctional skin-like smart wearable devices.

During bone formation, collagen fibrils mineralize with carbonated hydroxyapatite, leading to a hybrid material with excellent properties. Other minerals are also known to nucleate within collagen in vitro. For a series of strontium- and calcium-based minerals, we observed that their precipitation leads to a contraction of collagen fibrils, reaching stresses as large as several megapascals. The magnitude of the stress depends on the type and amount of mineral. Using in-operando synchrotron x-ray scattering, we analyzed the kinetics of mineral deposition. Whereas no contraction occurs when the mineral deposits outside fibrils only, intrafibrillar mineralization generates fibril contraction. This chemomechanical effect occurs with collagen fully immersed in water and generates a mineral-collagen composite with tensile fibers, reminiscent of the principle of reinforced concrete.

A reduction in the particle size is expected to improve the properties and increase the application potential of high-entropy alloys. Therefore, in this study, a novel sol–gel autocombustion technique was first used to synthesize high-entropy alloys. The average grain size of the prepared nanocrystalline CoCrCuNiAl high-entropy alloys showed was 14 nm with an excellent and uniform dispersion, exhibiting a distinct magnetic behavior similar to the superparamagnetic behavior. We show that the metal nitrates first form (Co,Cu,Mg,Ni,Zn)O high-entropy oxides, and then in situ reduce to CoCrCuNiAl high-entropy alloys by the reducing gases, and the chelation between citric acid and the metal ions and the in situ chemical reactions are the dominant reaction mechanisms. We demonstrate that the sol–gel autocombustion process is an efficient way to synthesize solid solution alloys eluding the restriction of a high mixing entropy.

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