4D Printed Soft and Stretchable Self-folding Cuff Electrodes for Small-nerve Interfacing.

Peripheral nerve interfacing (PNI) has a high clinical potential for treating various diseases, like obesity or diabetes. However, currently existing electrodes present challenges to the interfacing procedure, which limits their clinical application, in particular, when targeting small peripheral nerves (< 200 μm). To improve the electrode handling and implantation, we fabricate a nerve interface that can fold itself to a cuff around a small nerve, triggered by the body moisture during insertion. We achieve this folding by printing a bilayer of a flexible polyurethane printing resin and a highly swelling sodium acrylate hydrogel using photopolymerization. When immersed in an aqueous liquid, the hydrogel swells and folds the electrode softly around the nerve. Furthermore, the electrodes are robust, can be stretched (> 20%), and bend to facilitate the implantation due to the use of soft and stretchable printing resins as substrates and a microcracked gold film as conductive layer. We demonstrate the straightforward implantation and extraction of the electrode as well as stimulation and recording capabilities on a small peripheral nerve in vivo. We believe that such simple and robust to use self-folding electrodes will pave the way for bringing PNI to a broader clinical application. This article is protected by copyright. All rights reserved.