Synthesis of robust yet flexible and transparent CPA hydrogels inspired by molting crab shells†

Hydrogels are promising flexible substrates, yet their applications are always limited by their inferior mechanical robustness and lack of multifunctionality. Herein, inspired by flexible and robust molting crab shells, multifunctional ChMNF–PAA–ACC (CPA) hydrogels were developed by constructing a three-dimensional chitin micro-nanofiber (ChMNF) network with a layered structure, incorporated into an amorphous inorganic-based hybrid matrix of nano-segregated minerals (amorphous calcium carbonate, ACC) and protein-like acrylic acid (PAA) polymers. This preparation process enables a green and mild synthesis, employing sustainable ChMNF and ACC as biodegradable and biocompatible raw materials, with no need of complex treatments or costly functional agents. The resulting CPA hydrogels simultaneously feature high strength (∼28.6 MPa), optical clarity (high transmittance: ∼88.1%, low haze: ∼1.86%), good drying–swelling recycling properties, and intrinsic fluorescence and electrical conductivity, surpassing performances of most chitin fiber-reinforced gel materials. Owing to these merits, these CPA hydrogels can be assembled into multifunctional sensors to detect diverse external stimuli (such as strain, pressure, and temperature). Consequently, this dual bionic strategy provides an exciting idea for designing multifunctionally robust and transparent hydrogels, showing promising and sustainable potential in the application of flexible sensors.