A Soft-Robotic Thumb Orthosis Facilitating Individual Assistance of Thumb Joints

Many wearable soft robotic devices have been developed to assist with spasticity – the increased muscle tone seen in individuals with neurological conditions such as stroke or cerebral palsy. However, these devices typically lack the ability to individually assist multiple degrees of freedom (DOF), which is essential to performing a broad range of daily tasks. To address this need, we developed a soft robotic thumb orthosis to achieve movement in three DOF. We focused on the thumb as it performs the most complex movement. Our orthosis used three unfolding textile pneumatic actuators to assist with the extension of the interphalangeal joint, combined extension of the metacarpal and carpometacarpal joints, and abduction of the carpometacarpal joint. The orthosis was tested on both a 3D-printed biomimetic test bed that emulated spasticity and a healthy individual. The orthosis met the full range of motion targets for each joint, except for the abduction of the carpometacarpal joint with medium spasticity, and surpassed the range of motion threshold required for activities of daily living. The orthosis was able to: (1) assist each DOF independently, (2) move the tip of a biomimetic thumb to a pre-determined target with total error of less than 1.5 cm when actuated with open-loop control, and, (3) provide individual joint assistance to a user with no motor impairment. This research showcases the ability of a soft robotic orthosis to assist movement in simulated spasticity of individual thumb joints and provides an important step towards a platform to study whether independent joint assistance during rehabilitation improves patient outcomes.