Microgel double-crosslinked hydrogel with excellent mechanical properties for flexible electronics.

Hydrogels are limited in practical applications due to insufficient mechanical properties. While microgels (MGs) and active MGs enhance hydrogel toughness via sacrificial bonding and chemical crosslinking, respectively, achieving synergistic multiple physical-chemical crosslinking remains challenging. In this study, pH-responsive soft MGs (PEA-MAA-BDDA) were synthesized as physical micro-crosslinkers, while vinyl-functionalized MGs (GMGs) were used as active MGs serving as chemical micro-crosslinkers. MGs and GMGs were dispersed in acrylamide (AAm) to prepare MGs physically crosslinked hydrogels (MPC-xMG), GMGs chemically crosslinked hydrogels (MCC-yGMG), and double micro-crosslinked hydrogels (MDC-xMG-yGMG). Mechanical performance is significantly affected by the micro-crosslinker content, pH, and crosslinking strategy, which regulate hydrogen bond strength, interparticle interactions, polymer chain entanglement, and crosslinking density. The dual crosslinked MDC hydrogels (MDC-1.0MG-0.3GMG) exhibited a synergistic balance of toughness and elasticity, resulting in exceptional stretchability and fracture resistance. Furthermore, incorporating carbon nanotubes (CNTs) yielded conductive hydrogels with excellent mechanical properties and ultralow hysteresis. These conductive hydrogels are suitable for flexible electronic skin, human motion monitoring, and real-time blood pressure prediction using long short-term memory (LSTM) neural networks. This work presents a programmable approach for designing mechanically robust hydrogels via pH-responsive dual micro-crosslinkers.