The conformal, high-density SpineWrap microelectrode array for focal stimulation and selective muscle recruitment

Epidural electrical stimulation (EES) of the spinal cord is widely applied for pain management and has garnered considerable interest as a possible route to functional restoration after spinal cord injury. Currently, EES employs bulky, non-conformal paddle arrays with low channel counts. This limits stimulation effectiveness by requiring high stimulation currents, reduces selectivity of muscle recruitment, and requires subject-specific designs to accommodate varied neuroanatomy across the patient population. Here, we report on a thin-film, high-channel count microelectrode array, termed SpineWrap, which wraps around the dorsolateral aspect of the rat spinal cord. SpineWrap delivers focal stimulation to selectively activate muscles due to its unique design features, including its thin substrate, high conformability, high channel count, on-device ground, and the material properties of its platinum nanorod contacts. Through computational and in vivo studies, we show that SpineWrap can selectively recruit muscles in the rat lower limb and identify stimulation hotspots at a submillimeter resolution, maximizing muscle recruitment selectivity. We also investigate the effect of channel count and density on muscle recruitment selectivity and show that rat spinal cord arrays require submillimeter pitches to achieve maximal selectivity. SpineWrap represents an advancement in EES technology and, when adapted to be used chronically, has the potential to improve SCI treatment by providing more refined stimulation.