American Society for Peripheral Nerve

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Hybrid Electrical-Optical Functional Stimulation System
Sahil K. Kapur, MD1, Thomas J. Richner, MS2, Sarah K. Brodnick, BS2, Justin C. Williams, PhD2 and Samuel O. Poore, MD, PhD1
1Division of Plastic & Reconstructive Surgery, University of Wisconsin, Madison, Madison, WI, 2Department of Biomedical Engineering, University of Wisconsin, Madison, Madison, WI

Objective: Conventional neuroprostheses make use of functional electrical stimulation as a modality to produce useful motion. While there have been significant advances made in electrical stimulation based control algorithms, major obstacles to the broad adoption of this technology have been the high levels of muscle fatigue and tissue damage due to extended periods of electrical stimulation. The fast emerging technology of optogenetics has allowed us to optically stimulate peripheral nerves via the expression of light sensitive microbial opsins in mammalian neurons. Optogenetic stimulation, however, is limited by the levels of ion channel expression in a peripheral nerve such that the magnitude of compound muscle action potentials generated by optical stimulation alone is significantly lower than the responses possible with electrical stimulation. Our objective is to combine both electrical and optical stimulation modalities to develop a hybrid stimulation interface that has the capability of producing both less fatigue as well as a high magnitude of muscle EMG response. Method: Transgenic mice expressing blue light sensitive channelrhodopsin ion channels were anesthetized and their sciatic nerve and gastrocnemius muscles were exposed in accordance with IACUC guidelines. Simultaneous electrical and optical stimulation of the sciatic nerve was carried out using a concentric needle electrode and a blue light emitting diode. Compound muscle action potentials were measured using needle electrodes placed in the gastrocnemius muscle. Results: Isolated electrical stimulation generated a significantly higher EMG response in the muscle and more fatigue than isolated optical stimulation. Combined electrical-optical stimulation was able to generate a comparable magnitude of EMG response with less electrical and optical stimulus than when both modalities were used in isolation. Sub-twitch threshold electrical stimulation was amplified in the presence of simultaneous optical exposure of the nerve to generate EMG response in the gastrocnemius muscle. Combined electrical-optical stimulation did not produce similar effects in control mice. Conclusion: Combined electrical-optical stimulation allows one to use the advantages of both modalities to develop an interface that has the capability of producing less fatigue as well as a high magnitude of muscle response. This hybrid model can be integrated into existing control algorithms to improve performance and longevity of functional electrical stimulation devices.


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