Measurement of tissue stiffness using soft eGa-in sensors and pressure application

Modern prosthetic devices continue to improve their comfort, utility, and functionality with the advent of better manufacturing methods and understandings of human biomechanics. An essential aspect of any prosthetic is the custom fit needed to interface with the residual limb of an individual. Traditionally, these custom fit devices require professional revision and fitted interfaces created from materials that complement the geometry and composition of the residual limb. Soft, elastomeric sensors have the potential to measure tissue stiffness and create 4D models to produce these custom fit prosthetics without the need for traditional methods. For this study, soft sensors comprised of cast silicone (Ecoflex-0030) and liquid eutectic Gallium-Indium were designed to measure tissue stiffness at numerous locations on the body. Using 3D printed molds, two halves of each sensor were joined and liquid metal was injected between to create a highly elastic pressure-sensitive sensor. We demonstrated that a map of tissue stiffness can be generated when several of these sensors are deployed in an array and correlated to known positions on the body. This map can then be overlaid on a 3D scan to create a model for multi-material 3D printing. This approach could be used to generate custom, unique 3D printed prosthetic interfaces. If developed further and deployed in a full array, a diagnostic pressure cuff could be a versatile tool to any prosthetist or researcher studying tissue composition.