Cuff and sieve electrode (CASE): The combination of neural electrodes for bi-directional peripheral nerve interfacing

Background: A number of peripheral nerve interfaces for nerve stimulation and recording exist for the purpose of controlling neural prostheses, each with a set of advantages and disadvantages. The ultimate goal of neural prostheses is a seamless bi-directional communication between the peripheral nervous system and the prosthesis. Here, we developed an interfacing electrode array, the “cuff and sieve electrodes” (CASE), integrating microfabricated cuff and sieve electrodes to a single unit, to decrease the weaknesses faced by these electrode designs in isolation. This paper presents the design and fabrication of CASE with ex vivo and in vivo testing towards chronic application. Methods: Electroplating on electrode sites was performed to improve electrical properties of CASE. The surface morphology and chemical compound were characterized using scanning electron microscopy and energy-dispersive spectroscopy, respectively. Electrochemical impedance spectroscopy and cyclic voltammetry were performed to evaluate the electrical properties of CASE and determine viability for in vivo applications. Terminal CASE implantations were performed in a rat sciatic transection model to test the ease of implantation and capacity to write sensory information into the biological system. Results: The modified platinum film resulted in reducing impedance magnitude (9.18 kΩ and 2.27 kΩ) and increasing phase angle (over 70°). CASE stimulation of the sciatic nerve at different amplitudes elicited significantly different cortical responses (p < 0.005) as demonstrated by somatosensory evoked potentials, recorded via micro-electrocorticography. Conclusions: The ability to elicit cortical responses from sciatic nerve stimulation demonstrates the proof of concept for both the implantation and chronic monitoring of CASE interfaces for innovative prosthetic control.