Spontaneous Macrophase Separation Strategy for Bridging Hydrogels from Bilayer to Double-Network Structure

Bilayer hydrogels and double-network (DN) hydrogels represent two distinct classes of soft-wet materials, each characterized by their distinctive network structures, design principles, synthesis methods, and core functions targeted for their specific applications. Bilayer hydrogels are structured in two different layers, each with their anisotropic structure and unique properties. This dual-layer configuration facilitates targeted responses or controlled actuation in response to environmental stimuli, making them ideal for applications requiring responsive material behavior. On the other hand, DN hydrogels consist of two interwoven yet independent networks: one brittle and the other elastic. This dual-network structure, featuring contrasting network properties, allows for substantial energy dissipation and mechanical enhancement, often far exceeding that of traditional single-network hydrogels. Despite the individual strengths and specialized applications of each hydrogel type, a unified fabrication strategy that addresses both types of hydrogels has been conspicuously missing due to their inherent structural differences. This gap in the hydrogel field presents significant challenges but also opens opportunities for innovation in material design and application.