Development of a BIONic Muscle Spindle for Prosthetic Proprioception

The replacement of proprioceptive function, whether for conscious sensation or feedback control, is likely to be an important aspect of neural prosthetic restoration of limb movements. Thus far, however, it has been hampered by the absence of unobtrusive sensors. We propose a method whereby fully implanted, telemetrically operated BIONstrade monitor muscle movement, and thereby detect changes in joint angle(s) and/or limb posture without requiring the use of secondary components attached to limb segments or external reference frames. The sensor system is designed to detect variations in the electrical coupling between devices implanted in neighboring muscles that result from changes in their relative position as the muscles contract and stretch with joint motion. The goal of this study was to develop and empirically validate mathematical models of the sensing scheme and to use computer simulations to provide an early proof of concept and inform design of the overall sensor system. Results from experiments using paired dipoles in a saline bath and finite element simulations have given insight into the current distribution and potential gradients exhibited within bounded anisotropic environments similar to a human limb segment and demonstrated an anticipated signal to noise ratio of at least 8:1 for submillimeter resolution of relative implant movement over a range of implant displacements up to 15 cm