A Wearable Soft Actuator for Directional Tactile Stimulation: Design and Testing

This article describes the design and characterization of a wearable, shape memory alloy (SMA)-based soft actuator that provides touch-like, directional forces to enhance motor training through proprioceptive signals. The actuator's design considers functional requirements like weight, actuation speed, and stroke length, as well as human skin mechanics. It is fabricated by embedding the SMA spring in a silicone rubber matrix using 3D-printed moulds. The impact of the silicone matrix on cooling during repeated actuations was assessed using thermal imaging. Testing was repeated on bare skin and under light clothing. Usability was evaluated through a questionnaire. The actuator demonstrates mechanical performance comparable to existing literature while ensuring comfort, lightness, and versatility, and meets functional and wearability requirements. Through the fabrication and characterization of the device it is demonstrated that the principles that are applied during its design can allow to obtain SMA-based actuators capable of delivering directional feedback. The device is well received by the users, laying the foundation for future studies aimed to apply directional haptic feedback to the enhancement of motor learning in rehabilitation and sports.