Biocompatible Ionic Conductor-Based Neural Interface for Implantable Bioelectronics

Implantable neural prostheses, such as spinal-cord stimulators, deep-brain stimulators, and vagus nerve stimulators have enormous potential to treat a variety of neurological disorder. Stimulation electrodes serve as the interface between implantable devices and neural systems. Since high levels of charge injection capacity are applied to functional tissues and electrode materials, it is important to prevent damage to the electrode materials as well as tissues from chronic stimulation. Most metal electrodes in neurostimulator use platinum or iridium oxide, which have low bulk resistance and high charge injection capability. However, such electrodes are prone to the undesirable characteristics of neural interface between solid metal and soft tissue. Recently, efforts to overcome this limitation have attracted a great deal of attention, and research into implantable neurostimulators using soft conductors based on conducting polymers and hydrogels is surging. However, both the faradaic charge injection in the conducting polymers, which results in the creation of chemical species, and ion diffusion in hydrogels, which leads to loss of biomolecule, cause neurological disorders.<br/>In this talk, we describe a novel design for biocompatible ionic conductor for neural stimulation using the capacitive charge injection mechanism. The ionic conductor serves as a neural interface and an ion-diffusion barrier; they consist of choline-derived ionic liquids and the chitosan-based biopolymer matrix, and the graphene oxide (GO) membrane layer which is coated on the surface of the ionogel respectively. Unlike the phenomenon of electron to ion charge transfer at neural interface, the GO membrane embedded ionogel is capable of separating the electron conducting materials (e.g., conducting polymers and metal electrodes) from the biological tissues. Moreover, the ion diffusion barrier effectively prevents ion exchange in the neural interface and enables relatively high charge injection capacity owing to the large surface area of the GO membrane. This allowed us to demonstrate biocompatible and soft neural interface for highly stable electrical stimulation of the sciatic nerve in live mice. We believe that our ionic conductor-based neural interface can provide a direct link between the fields of electronics and biology for the design of next-generation implantable devices.