Design and Validation of a Soft Wearable Robot to Support Elbow Movements in People with Spinal Cord Injury

Spinal Cord Injury (SCI) damages the nerves transmitting signals between the brain and body, leading to significant motor and sensory impairments. Injuries, often occurring at the cervical level, limit neuromuscular control, particularly affecting the upper limbs. Rehabilitation approaches for SCI people include assistive technologies like robotics, which offer a promising route to support daily activities and improve quality of life. Rigid robotic systems used in rehabilitation include end-effectors and exoskeletons. End-effectors assist movements from a single distal point, providing therapy within 2D or 3D environments, while exoskeletons align with the body's joints to offer targeted support. These systems, however, can be heavy and restrictive, leading to issues with portability and patient acceptability. Soft robotics, including exosuits, presents an alternative with lightweight, flexible designs that mimic natural muscle function, increasing comfort and usability. Exosuits are often pneumatically driven, and while they produce less torque, they are highly portable and adaptable, making them suitable for both clinical and at-home therapy. This theis presents a modular pneumatic soft exosuit aimed at improving motor functions in the shoulder and elbow for individuals with spinal cord injuries (SCI). The robotic device comprises two main parts: pneumatic actuators for the arm and a control box managing actuation, sensing, and control logic. The actuators, made of TPU-coated nylon, inflate to produce motion, designed to be lightweight, flexible, and conforming to body contours. The actuators attach securely to the body, allowing independent operation for either flexion or extension, with the option to support both joints simultaneously. Anchored via a custom soft brace and 3D-printed clips, the system ensures stability during movement. For construction efficiency, TPU-coated nylon was laser-cut and assembled to create airtight chambers, with thermal sealing used to prevent air leaks and ensure robust performance. The control box, connected to a computer interface, controls air pressure via an integrated pneumatic circuit and executes control algorithms based on kinematics data from Inertial Measurements Units (IMUs). Control strategies integrate two levels: low-level pressure control for actuator stability and high-level motion control based on user intent, detected by IMUs. For shoulder movement, gravity compensation control supports arm elevation by dynamically adjusting pressure based on shoulder angle. For the elbow, a triggered passive control system assists movement when initiated by the user. Both modules work in synergy to offer coordinated, intuitive support for multi-joint movements. An initial validation on 11 healthy participants assessed the robot’s transparency and assistance potential. Testing involved dynamic and static tasks targeting kinematic and muscular benefits, including overhead extension and biceps curl exercises. Kinematic transparency ensures that the device does not restrict ROM, while muscular transparency ensures that wearing the inactive device does not increase muscular effort. The main validation phase, conducted with 10 SCI patients, followed a protocol like that of healthy subjects, focusing on improvements in ROM, EMG activity reduction, and device wearability. The control box provided reliable pneumatic support, and feedback from patients on comfort and usability confirmed the robot’s acceptability. The device demonstrated the potential to assist SCI patients effectively in daily tasks, offering both rehabilitative and assistive functions. Results indicate that the device supports elbow movement effectively, promoting independence and potentially enhancing rehabilitation outcomes. Future work may focus on improving the control box’s portability, adding a rechargeable battery for wireless operation, and optimizing the actuator design for broader applicability, including pediatric use.