Bridging the Biotic–Abiotic Divide: Design Principles of Hydrogel Interfaces for Next‐Generation Brain‐Machine Implants

Brain–machine interfaces (BMIs), recognized as transformative technologies for restoring neural function and decoding intricate brain activity, have started to come to the fore. Despite these advancements, a significant disparity persists between traditional machines—constructed from hard, dry, inanimate materials—and soft, wet, living biological tissue. This incongruity gives rise to chronic in vivo immune responses and hindered transmission at the neural interface. Hydrogels, due to their mechanical and chemical resemblance to biological tissue, along with their flexibility and adjustability in property design, have emerged as optimal candidate materials for facilitating human‐machine interaction. Recent approaches integrate hydrogels with tissue engineering to create a biologically active and/or cell‐containing living layer at the tissue–device interface, enabling seamless biointegration and novel cell‐mediated therapeutic prospects. In this review, we comprehensively summarize the functional modalities, design principles, and present and future applications of hydrogel interfaces in attaining human–machine integration.