Development and Validation of Customizable, Adaptive SPring-Actuated Hand EXoskeleton (CASPHEX) Designed for Home-Based Training of Finger Movements Post-Stroke

Passive hand devices can provide a high-dose, home-based training to stroke survivors, while active robotic systems often present practical limitations for home use due to operational complexity and safety issues. Efficacy of current passive devices, however, is reduced by their limited functionality; while their assistance typically reinforces extrinsic hand muscle function, impairments in intrinsic muscle function cannot be addressed. Passive extension assistance can also interfere with grasping movements. Therefore, we developed a novel device, Customizable, Adaptive Spring-actuated Hand Exoskeleton (CASPHEX), which can provide targeted and adaptive assistance to hand muscles to counteract unique impairments of individual subjects. CASPHEX can also adapt to user intent to allow users to perform different hand movements (i.e., hand opening followed by grasping). A novel control algorithm was developed to 1) effectively counteract worsening flexor hypertonia during extension; and 2) allow users voluntarily to switch between modes (open/close) by detecting user intent. Its performance was first validated in an experiment with 5 healthy subjects, in which CASPHEX actuated different exotendons based on their intended joint movements, whose response times were $615\pm 53$ ms (proximal) and $577\pm 47$ ms (distal). In the second experiment with 11 stroke survivors, we tested if they can voluntarily control CASPHEX to perform functional tasks. CASPHEX significantly improved the range of motion of the participants during finger extension, and more importantly, their box and block test scores also significantly improved by CASPHEX assistance. CASPHEX demonstrated potential to improve efficacy of robot-assisted therapy by enabling impairment-specific, home-based training of the impaired hand.