Robust Integration of Highly Conductive Hydrogels with Stretchable Electronics for Skin-Interfaced Bioelectronics

Skin-interfaced bioelectronics mounted on human skin has the potential to revolutionize next-generation medical diagnostics and healthcare. To achieve this goal, designing a compliant and stretchable device is highly desirable for device reliability and long-term user comfort. In the material aspect, the limitations of conventional functional device components that originate from rigid and obtrusive interfaces must be overcome by materials with intrinsic softness and stretchability. Conductive hydrogels that possess tissue-level softness owing to their water-rich nature, can be an alternative option. Generally, for the fabrication of hydrogel-based, skin-interfaced bioelectronics, a hydrogel film is cut and placed onto an electrode. However, during device operation, large amount of water inside the hydrogel film tends to form a slippery surface rather than a robust interface between human skin and electronic device. Such poor integration capability could cause the lack of reproducible device performances, difficulty to scale up, and the loss of intimate physical/electrical contacts, which leads to critical problems in signal sensing and electrical actuation from/to human tissue. Here, we suggest direct polymerization and in-situ chemical-integration of hydrogel onto stretchable electronics as a methodology for enhancing the hydrogel-device interface of skin-interfaced bioelectronics. Highly conductive functionalized hydrogels are polymerized inside stretchable wells placed on a multichannel electrode array. The hydrogels are stably immobilized to the electronic devices during fabrication, and the robust interface contributes to the reliable measurement of bio-signals and effective electrical actuation on tissues. The demonstration shows that the direct polymerization and in-situ chemical-integration of hydrogel are key steps towards the realization of practical skin-interface bioelectronics based on functionalized hydrogels.