Touch and Go: Capabilities, Challenges, and Opportunities for Wearable Sensing and Tactile Feedback Technologies in Neuro-Motor Rehabilitation

The sense of touch plays a critical role in coordinating movement and facilitating interaction with the physical environment. Consequently, individuals with diminished sensation in the lower limb(s) due to amputation or neurological disorders exhibit a number of sensory-related functional deficits, including various biomechanical gait abnormalities, impaired balance, and an elevated risk of falls. The term “haptic feedback” refers to the class of technology that provides augmentative sensory feedback to users of robotic, prosthetic, and virtual systems via the sense of touch, including both tactile sensation and kinesthetic “force feedback.” Despite the well-known functional impairments experienced by individuals with lower extremity sensory deficits, inadequate effort has been devoted to the development, clinical testing, and optimization of haptic feedback systems for functional gait and balance rehabilitation in affected populations. The present work details the iterative engineering development and clinical testing of a wearable tactile biofeedback system (TBS) that provides real-time tactile feedback of plantar foot pressures to sensory-impaired users through a pneumatic tactile cuff worn on the thigh(s). Since its initial development by previous researchers at UCLA and pilot clinical testing in seven unilateral trans-tibial amputees (TTAs), the TBS has received several rounds of design upgrades to improve its performance and clinical utility, and it has been clinically tested in several patient populations through different stages of its development. In a study evaluating the effects of feedback on dynamic stability in 6 unilateral TTAs over a multi-functional set of tasks (single leg stance, stairs, and gait on an incline/decline) using a wearable plantar pressure sensing system, the most significant finding was an average 67% increase in single leg balance times on the prosthetic foot with feedback active. Most recently, the TBS has been expanded to incorporate an alternative balance-specific “differential” feedback scheme, as well as to provide real-time gait analysis, telemetry, and instructive feedback for dynamic gait modification. A single leg stance study in 17 healthy subjects and 3 with peripheral neuropathy (PN) found statistically significant reductions in mean center of pressure velocities in both populations with differential but not standard biofeedback, compared to no feedback.Finally, a plantar pressure stimulation (PPS) system based on the TBS architecture has been developed and explored as a sensory neuromodulation tool for spinal cord injury (SCI) rehabilitation. With legs suspended in a gravity-neutral apparatus, a subject previously diagnosed as SCI-complete (ASIA-A) exhibited increased leg muscle EMG activity while receiving rhythmic PPS. Together, these results confirm the feasibility and potential for tactile feedback as a rehabilitative tool and provide new insights that guide the further development of wearable sensing and tactile feedback systems across a range of clinical applications