Bioinspired Multiphase Gels Using Spatial Confinement Strategy

ConspectusHydrogels are ideal candidates for various advanced applications, including wearable electronics, soft robots, and biomedical engineering, which benefit from their natural merits of softness, deformability, and biocompatibility. In the early stages since the emergence of hydrogels, tremendous efforts have been made to improve their mechanical performances. Despite the investigation of several mechanical strengthening strategies, including nanocomposites, noncovalent cross-linking, and topological design, single network hydrogels still grapple with the trade-off between mechanical strength and functionality. As a result, improving network complexity and functional diversification have emerged as a significant trend in gel development. Multiphase gels are developed to incorporate mechanical enhancement components and functional components, obtaining integrated exceptional performances. This Account seeks to review mechanical strength-function integrated gels fabricated by bioinspired multiphase confinement strategy, providing inspiration and guidance for multiphase gel design. The first part starts with a specific elaboration on bioinspired strategy, involving tissue structure analysis, biological mechanism imitation, and bioinspired materials fabrication. By exploring human skeletal muscle and nacre, we elucidate how to connect biological structures and artificial material design concretely. Meanwhile, we highlight the promotion effect of in-depth analysis on the biological micro structure and working mechanism. In the next part, we subsequently evaluate diverse multiphase network structures that were previously developed and showcase their exceptional performances and unique applications. Multiple gels developed by our group─phase separation ionic gels for stiffness changing materials, phase transition organohydrogels for actuation, interpenetrating organohydrogels for lubrication, etc.─are reviewed in this section. The most crucial point for the fabrication of these multiphase gels is stability, which inextricably links to their interface interactions. Therefore, we summarize the techniques employed to establish ultrastable interfaces, such as emulsion interface interaction or heterogeneous interpenetrating networks. We delve into the manifold network structures of multiphase polymers, encompassing plasticity, elasticity, hydrophilicity, and hydrophobicity. Different fabrication strategies were adopted according to their network properties, with the aim of exhibiting their unique mechanical strength and functions. In these confined multiphase structures, the independent motions of orthogonal networks are achieved. Additionally, polymers confined in space in nanometer scale or smaller can exhibit performances deviated from bulk phase, including crystallinity, alignment degree, and glass transition temperature. The discussion also covers the confinement effects on the polymer structure and mobility. Ultimately, we introduce the advanced applications of multiphase gels, spanning broad areas including lubrication, actuation, mechanical adaptation, soft robotics, sensing, etc. In order to look into the future development direction of multiphase hydrogels, we derive conclusions about their challenges and opportunities.