A Stretchable Tactile Sensor Array Based on Hydrogel Ionic Diodes

Controlled ion migration, as seen in biological systems, has inspired the development of ionic diodes—a type of iontronics capable of controlling ion flux. However, existing ionic diodes face challenges in adapting to biological systems due to the lack of device-level integration that enables monolithic and stretchable ionic diode arrays. In this work, we propose a stretchable hydrogel diode-based sensor array that overcomes these challenges by integrating multiple ionic diodes into a single monolithic array. By doping oppositely charged polyelectrolytes into the hydrogel matrix, we create a diode-like hydrogel sensor based on ion mobility, capable of producing four distinct signal outputs—resistance, capacitance, open-circuit voltage, and short-circuit current—in response to mechanical stimuli. Through the shared double-network polymers, the hydrogel diodes and insulators are interlocked at the molecular level, enabling the integrated array excellent stretchability (over 100% strain), transparency, and spatial sensing. This design not only achieves seamless integration of multiple ionic diodes but also offers self-powered, bio-inspired sensing capabilities. Furthermore, we demonstrate its potential in human-machine interactions, showcasing applications for robotics and prosthetics. This work represents the first successful integration of ionic diodes into a stretchable monolithic array, offering a new approach for the development of bio-inspired systems with enhanced adaptability and multifunctional sensing capabilities.