Biphase Ionic Hydrogels with Ultrasoftness and High Conductivity for Bio-Ionotronics

Achieving stable bioelectronic interfaces is hindered by inherent mechanical-electrochemical mismatches, limiting long-term device functionality in dynamic tissues. Current hydrogel-based bio-ionotronic devices face a fundamental trade-off: soft hydrogels lack sufficient ionic carriers, while ionic hydrogels compromise softness due to high cross-linking density. Here, we developed a biphasic ionic hydrogel (BIH) by integrating microgel-rich ionic reservoirs (microgel phase) into a continuous hydrogel matrix (CH phase) via hydrogen bonds. The microgel phase and CH phase of BIH work synergistically, reducing cross-linking density while maintaining the ion monomer content of the hydrogel. This synergistic structure decouples ionic storage from mechanical compliance, enabling ultrasoftness (2 kPa) and high ionic conductivity (8.55 S m-1), surpassing conventional ionic hydrogels. By tuning the microgel content, we increased the polymer network's characteristic length, facilitating ion diffusion while maintaining structural integrity and reducing interfacial impedance. Demonstrations in real-time electromyography and mechanical motion sensing validated its potential for soft bioelectronics.