Soft Wearable Body-Powered Hydraulic Actuation System for a Prosthetic Finger Design

Objective: Finger and fingertip loss is the most common form of upper-limb amputation. With a focus on amputations involving the loss of distal and/or partial middle finger segments, this paper outlines the design and development of a novel soft body-powered hydraulically-driven actuation system for a prosthetic finger, while offering an in-depth examination of its subsystems. Method: The proposed device utilises a soft wearable hydraulic mechanism to transfer pressure from the proximal interphalangeal (PIP) joint of the human finger to the distal interphalangeal (DIP) joint of the prosthetic finger, enabling movement of the soft prosthetic DIP joint. The design parameters of the soft actuator, such as its configuration, constituent material, and volume were analysed through experiments with able-bodied participants. Each participant tried 42 different actuators while flexing their index finger, repeating the task four times, yielding 168 trials per participant. The human and prosthetic finger flexion angles and resultant pressures were measured using an Aurora electromagnetic sensor and a fluid pressure transducer. All data was segmented and analysed. Result: Soft actuator designs were selected through statistical analysis of the material (Agilus 30 and Dragon Skin 30), configuration (chambers located underside or around the PIP joint), and volume. Conclusion: The study demonstrated that the selected soft wearable hydraulic mechanism transferred generated pressure from the participant's PIP joint effectively, enabling movement of the prosthetic digit. Significance: Our research contributes to current developments in versatile body-powered prosthetic devices, laying the foundations for broad applications in affordable healthcare devices.