Metal-hydrogel chelation interfaces for ultrasoft and bidirectional bioelectronics

Emerging demand in soft bioelectronic systems poses critical challenges in stiffness control and end-to-end connections due to the huge modulus difference in various components. Here, a bidirectional electrical interface of hydrogel and metal electrodes to bridge soft skin/tissue and data collection circuits is enabled by coordination interactions. The dual-mode chelation including internal chelation and surface chelation effectively configures the cross-linking structure of hydrogel, as well as enhances the binding interface of metal-hydrogel complex surfaces. Internally, strong chelation competes with esterification, yielding tissue-like softness of hydrogel with an ultra-low modulus of ∼339.9 Pa. Externally, the hydrogel passivates the combined metal surfaces, promoting the formation of interlocked structures between metal oxide nanoislands, achieving a high binding strength of ∼1.95 MPa without compromising electrical conductivity. The stable electrical interconnections via hybrid interfacial bonding enable high signal-to-noise ratio signal recordings from the skin, neural surfaces and brain, maintaining reliable performance, even under mechanical disturbances. This work provides an effective strategy for achieving mechanically and electrically robust hybrid bioelectronic interfaces, advancing their applications in capturing both in vitro and in vivo electrical signals.