A nerve-adhesive stretchable electrode for stable neural signal recording and stimulation

Achieving long-term stable monitoring of neural signals and on-demand feedback electrical stimulation in a closed-loop manner is essential for personalized diagnosis and treatment of neurological disorders. In addition, stiffness of tissue-interfacing electrodes utilized during bidirectional signaling operations should be mechanically adaptive to the peripheral nerves for preventing undesired tissue compression. However, challenges remain associated with absence of tissue adhesion and cyclic stretching durability of the conventional soft electrodes, leading to unstable device-tissue interactions. Here, we developed a nerve-adhesive stretchable electrode (NSE) that is capable of stably monitoring sensory neural signals and electrical modulation. The NSE consists of a tough self-healing polymer substrate, an ultrathin stretchable polyimide-Au-polyimide electrode, and a mussel-inspired wet tissue-adhesive hydrogel layer (alginate conjugated with boronic acid, Alg-BA). The Alg-BA enabled the NSE to be reliably attached to the sciatic nerve of a rat, while significantly improving its signal-to-noise ratios. In addition, the dynamic stress relaxation of the NSE was highly beneficial for mechanical adaptation to the nerve, featuring the long-term tissue safety even after implantation for eight weeks. The synergistic use of tissue-adhesive materials coupled with the stretchable electronic devices would provide a great opportunity to develop the advanced neural prostheses. Soft stretchable electrodes have been extensively developed for achieving long-term stable peripheral neural interfacing owing to their strain-insensitive bidirectional signaling performance. Although the conventional electrodes were highly effective in measuring neural signals and providing sensory feedback in patients with limb nerve damage or amputations, they were easily slipped from the original position on the nerve surface due to absence of a tissue adhesion property. The challenge has led to inaccurate interpretation of numerous sensory/motor information obtained from high-density multichannel electrodes as well as inflammation originating from occurrence of shear stress at the device-nerve interface. In this regard, the tissue adhesion is essential to provide the long-term stable neural interfacing. To address the unmet needs, wet-adhesive hydrogel materials should be integrated with the conventional stretchable electrodes. This article reports a promising strategy for realizing the chronic nerve-interfacing electrodes without causing device-tissue detachment or mechanical compression issues. The nerve-adhesive electrode consisting of a wet hydrogel, a self-healing polymeric substrate, and a stretchable Au nanomembrane was easily implanted to a sciatic nerve of a rodent model without using a conventional suturing process. The period of implantation of the nerve-adhesive electrode was almost finalized within 60 s, leading to a dramatic decrease in surgical deviations based on the surgeon's expertise as well as an alleviation of surgery complexity. It is highly expected that development of the tissue-adhesive stretchable electrode would be the key solution for achieving future human-machine interface and personalized neural prostheses.