Abstract
We demonstrate a method of neurostimulation using implanted, free-floating, inter-neural diodes. They are activated by volume-conducted, high frequency, alternating current (AC) fields and address the issue of instability caused by interconnect wires in chronic nerve stimulation. The aim of this study is to optimize the set of AC electrical parameters and the diode features to achieve wireless neurostimulation. Three different packaged Schottky diodes (1.5 mm, 500 µm and 220 µm feature sizes) were tested in vivo (n = 17 rats). A careful assessment of sciatic nerve activation as a function of diode–dipole lengths and relative position of the diode was conducted. Subsequently, free-floating Schottky microdiodes were implanted in the nerve (n = 3 rats) and stimulated wirelessly. Thresholds for muscle twitch responses increased non-linearly with frequency. Currents through implanted diodes within the nerve suffer large attenuations (~100 fold) requiring 1–2 mA drive currents for thresholds at 17 µA. The muscle recruitment response using electromyograms (EMGs) is intrinsically steep for subepineurial implants and becomes steeper as diode is implanted at increasing depths away from external AC stimulating electrodes. The study demonstrates the feasibility of activating remote, untethered, implanted microscale diodes using external AC fields and achieving neurostimulation.
Highlights
Neuromodulation for peripheral nerve stimulation (PNS) applications is increasingly being used to treat and manage chronic diseases
Diodes placed in tissue rectify the fraction of high-frequency currents that pass through them relative to that passing through the tissue and can cause local neural activation, as we demonstrate in this study
The primary goal of this study was to determine the set of stimulation parameters, diode dimensions and placement that would enable microscale, implantable diodes to function as wireless neuromodulators
Summary
Neuromodulation for peripheral nerve stimulation (PNS) applications is increasingly being used to treat and manage chronic diseases (i.e., epilepsy, micturition, pain, etc. [1,2,3,4]). A major problem with chronic neurostimulation of peripheral nerve for purposes of neural interfacing is that of lead wires tugging on microelectrodes penetrating into the body of a nerve. This becomes a more severe problem when large numbers of wires are used for advanced multichannel neural interface systems needed for both sensory and motor control of prosthetics [5]. Such systems require more channels than can be provided by most nerve cuff systems and need to contact or stimulate nerves lying deeper at the fascicular and subfasicular level. The present work suggests the potential use of free-floating, stimulating, diode-electrode systems that are wholly implanted within the nerve and the use of strong electric field gradients produced by extraneural electrodes to achieve channel selection
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