Development of an Infrared Nerve Stimulator

1. Greg Wigger, Chris Tedder, and Melanie Gault Advised by: Dr. Duco Jansen, Ph.D. Development of an Infrared Nerve Stimulator

2. The Problem There is a need for an implantable device that will reliably stimulate individual nerve fascicles • This requires a reliable stimulation modality to gain better control over neural signals.

3. 10 5 0 -5 0 2 4 6 8 10 12 14 16 Our Solution: Infrared Stimulation 10 5 Electrical Electrical CMAP (V) 0 Stimulator Stimulator -5 0 2 4 6 8 10 12 14 16 Infrared Stimulation Same advantages as electrical stimulation, but: • Less damaging to nerve • Artifact free • Spatially selective CMAP (V) Rat Sciatic Nerve Rat Sciatic Nerve 0.2 Fiber Coupled Fiber Coupled 0.1 Laser Laser CMAP (V) 0 Optical Fiber -0.1 0 2 4 6 8 10 12 14 16 0.2 0.1 CMAP (V) 0 Rat Sciatic Nerve -0.1 0 2 4 6 8 10 12 14 16 Electrical Stimulation Has fundamental shortcomings that create a need for an alternative Contact can cause permanent damage to nerve Stimulation artifact Hard to selectively stimulate

4. Group Objective Develop an infrared nerve stimulator containing optical fibers running parallel to the nerve fibers • Create a single fiber prototype that sends infrared signal at 90° angle • Three models will be tested Fiber polished at 45 degree angle Fiber with flat angled mirror Fiber with concave angled mirror

5. The Three Prototypes • Biocompatibility – PEGylation • Minimal Power Loss • Small Beam Size • Energy Density • Low Cost • Durability Curved Mirror Prototype Flat Mirror Prototype

6. Possible Future Uses • Implantable devices for use in victims of paralysis • Incorporation of sensors to provide brain with feedback from the external environment

7. Past Work • Completed Solidworks • Tested nylon tube for infrared break down • Determined beam size, energy density, and power loss of 45°-polished fiber and curved mirror prototype with “Knife-Edge Technique” Before After

8. Past Work cont.

9. Past Work cont. (Data collected) • Energy Density and Beam Area • 10-fold difference in energy density and order of magnitude difference in spot area of the beam

10. Past Work cont. (Data collected) • Power Loss • Coupling loss measured from the laser to the fiber • Faulty lens? • Nylon is either scattering or absorbing infrared light as seen in large loss from fiber to nylon • Future direction

11. Current Work • Determine if nylon scatters or absorbs light by flattening a piece of nylon and measure loss and spot size • Find absorption spectra of nylon • Calculations • Find theoretical spot size of concave mirror and compare it to actual measured spot size • Find maximum distance that the fiber can be from the concave mirror without any light being lost

12. Future Work • Obtain capillary tube (600 µm ID)to determine if glass is more transparent to infrared light than the nylon tubing • We will conduct an energy-loss test using the angle-polished fiber • Determine the actual distance at which the curved mirror focuses • Place 100 µm pinholes over power meter

13. Future Work cont. • Still waiting on our flat mirrors to arrive… • Optimistic about about its feasibility and effectiveness: • Unnecessary to polish the fiber, as with angle-polished model • Convergence/divergence are non-issues, as with concave model