Ultra-flexible and Stretchable Intrafascicular Peripheral Nerve Recording Device with Axon-dimension, Cuff-less Microneedle Electrode Array

Peripheral nerve mapping tools with higher spatial resolution are needed to advance systems neuroscience, and potentially provide a closed-loop biomarker in neuromodulation applications. Two critical challenges of microscale neural interfaces are (i) how to apply them to small peripheral nerves, and (ii) how to minimize chronic reactivity. We developed a flexible microneedle nerve array (MINA), which is the first high-density penetrating electrode array made with axon-sized silicon microneedles embedded in low-modulus thin silicone. We present the design, fabrication, acute recording, and chronic reactivity to an implanted MINA. Distinctive units were identified in the rat peroneal nerve. We also demonstrate a long-term, cuff-free, and suture-free fixation manner using rose bengal as a light-activated adhesive for two timepoints. The tissue response at 1-week included a sham (N=5) and MINA-implanted (N=5) group, and the response at 6-week also included a sham (N=3) and MINA-implanted (N=4) group. These conditions were quantified in the left vagus nerve of rats using histomorphometry. Micro-CT was added to visualize and quantify tissue encapsulation around the implant. MINA demonstrated a reduction in encapsulation thickness over previously quantified interfascicular methods. Future challenges include techniques for precise insertion of the microneedle electrodes and demonstrating long-term recording.