Ultra-low-power wireless implant stimulator for prosthesis sensory feedback

DESCRIPTION (provided by applicant): It is widely recognized that the functionality and user acceptance of prosthetic limbs would be improved by providing sensory feedback. This project aims to develop tiny button-like stimulator modules (OptiStims) which can be implanted subdermally to provide electrocutaneous based sensory feedback. The mechanical characteristics of the assembly will be similar to that of the skin to ensure stability and comfort. These OptiStims will be ultra-low power (a few microwatts) single channel devices that are individually RF powered and optically controlled transcutaneously from transmitters in the prosthesis shell. The stimulator circuitry is based on a proprietary, innovative design using technology concepts previously developed over the past 15 years at InnerSea Technology for implantable EMG telemetry. Because of the modular design, the stimulators can be placed in arbitrary locations to form customized spatial arrays for feedback strategies. The control and artificial sensor systems will be readily incorporated into presently available myoelectric arms. The Phase 1 system will be fabricated using discrete components. It will consist of a stimulator package with an attached concentric ring electrode surrounded by a thin flexible silicone. During Phase 2, an integrated circuit would be developed so that the stimulator electronics platform (ca, 2x2mm) could be merged with the electrode components to achieve a tiny, soft, disk structure approximately 6 mm diameter and 2mm thick. Subcutaneous implantation will be a simple outpatient procedure. There has been extensive prior work in developing electrotactile systems for sensory substitution that demonstrated the effectiveness of this communication strategy. The envisioned feedback system represents a considerably less invasive approach than electrical interfaces to peripheral nerves. At the same time, subdermal stimulation provides several advantages over non-invasive cutaneous communication strategies that use surface electrodes or vibrotactors. These include better stimulus localization and more consistent sensation both in regard to the quality of the sensation and its perceived intensity. More consistent sensation derives from greater immunity to variations in skin surface coupling parameters associated with surface electrodes including location, degree of hydration, pores, and contact pressure. Sensory information that will initially be targeted include: grasp force, object slippage and wrist. The Specific Aim of PHASE 1 is to develop the OptiStims and show the feasibility of the approach in one below elbow amputee subject fitted with a functional two channel sensory feedback system. Under SBIR Phase II funding, an implantable EMG telemeter is being developed. Together with the Phase II OptiStim, it will be possible to fit amputees with closed loop control using stable sources of EMG, and feedback of sensation through stable skin neurostimulation. The functionality of prosthetic limbs will be enhanced to improve quality of life and employment opportunities for veteran and civilian amputees alike.