Highly Flexible Single-Unit Resolution All Printed Neural Interface on a Bioresorbable Backbone

Abstract

Neural interfaces are the parts of the neural prosthesis that are in contact with the target tissue. The mechanical, chemical, and electrical properties of these interfaces can be a major determinant of the life of the implant and the neural tissue for chronic and even acute integrations. In this work, we developed a fully inkjet-printed, flexible neural interface on a bioresorbable backbone capable of recording high-fidelity neural activity. We utilized room temperature fabrication processes that overcome the limitations of semiconductor fabrication techniques for processing low-melting point polymers while maintaining high spatial and single-cell recording resolution. The ∼8 μm-thick devices in this study were fabricated onto two flexible polymers: (a) polyimide (PI), a biocompatible polymer commonly used for neural interfaces, and (b) polycaprolactone (PCL), a bioresorbable polyester with outstanding mechanical properties. Electrodes for neural recording were built at 30, 50, 75, and 100 μm diameter using silver nanoparticles/(3,4-ethylenedioxytiophene)-poly(styrenesulfonate) (AgNPs/PEDOT:PSS), which through our process achieved the lowest impedance reported in the literature reaching ∼200 Ω at 1 kHz for a 50 μm electrode diameter. We further enhanced the electrochemical performance of AgNPs/PEDOT:PSS by an order of magnitude by incorporating exfoliated graphene into the electrodes. The biocompatibility of the fabricated devices and their ability to record single-unit activity were confirmed by in vitro tests on both rat PC12 cells and isolated neural rat retina, respectively.

Keywords: PEDOT:PSS; biodegradable; electrodes; flexible; neural interface; single unit.