Monitoring pressure distributions at human-socket prostheses interfaces using graphene-fabric sensors

Despite the prevalence of socket prostheses, amputees are at risk of developing pressure ulcers due to the heavy load exerted on the socket during day-to-day use. The complex distribution of soft tissues and bony parts at the residual limb, as well as volume fluctuations that occur over time, make it particularly difficult to predict the time-varying spatial stresses and pressure distribution within the socket. Thus, this research aims to develop a sensing system that is capable of monitoring the pressure distribution in the interior of socket prostheses in real-time, specifically, for characterizing pressure “hot spots” and for preventing pressure ulcers. The long-term goal is to enable amputees and users to better understand the locations of pressure hotspots and how personalized adjustments of the position and alignment of the prosthesis can improve user comfort and overall performance. In this study, a highly strain-sensitive graphene-based thin film strain sensor was developed and implemented for monitoring pressure distributions at the human-prosthesis interface. Any changes in the applied pressure would alter the local conductivity of the thin film sensor, which can be captured by measuring the voltage distribution along the boundaries of the film. This dataset could then be used for solving an electrical impedance tomography (EIT) inverse problem to reconstruct the conductivity distribution of the graphene-based fabric sensor. Since conductivity is pre-calibrated to applied contact pressures, the result is a live view of pressure distribution. Laboratory tests were conducted to quantify the accuracy of the proposed system. Various cases of controlled pressure conditions were applied at the center of the graphene-based fabric sensor, and EIT results were acquired and characterized. The results demonstrated that this approach could be used in socket prostheses for distributed pressure monitoring.