Date of Award
Master of Science (MS)
Georges M Fadel
While using a prosthesis, transtibial amputees can experience pain and discomfort brought on by significant changes in pressure across a finite area of skin, known as pressure gradients, at the interface between the residual limb and prosthetic socket. These pressure gradients can lead to dermatological issues, deep tissue damage, and prolonged joint and muscle pain. Current prosthetic interface solutions attempt to alleviate these pressure gradients by using highly compliant homogenous liners to distribute and therefore reduce pressures. This research investigates an approach to reduce peak pressure gradients around the limb through the design of a new inlay made from artificially structured materials, termed metamaterials, with tailored mechanical properties to act as an interface between the prosthetic socket and residual limb. The inlay is fabricated from a hyperelastic base material and has a triangular patterned unit cells which can be 3D printed with walls of various slopes. By adjusting the unit cell wall slopes and thicknesses, the metamaterial hyperelastic material properties can be customized. The hyperelastic material properties of this metamaterial are modeled using a third order representation, namely a Yeoh 3rd Order Hyperelastic Model. The 3rd Order Coefficients from this model can be adjusted and optimized, then these optimal hyperelastic material property parameters can be mapped back into the physical design space as changes in the unit cell wall thickness or slope to create an inlay that can meet the unique offloading needs of an amputee. The layout of this metamaterial within the inlay can also be adjusted and optimized to better adapt to the unique limb shape of an amputee. Furthermore, the material properties and layout of the metamaterial can be optimized simultaneously to design a customizable inlay solution that can even better meet the unique performance needs of an amputee. Multiple finite element analyses simulations evaluate the pressure gradient reduction capabilities of the metamaterial inlay. A series of inlays were designed through the optimization of metamaterial properties and layout and compared to a prosthetists’ prescription for the same patients. The metamaterial inlay shows, in all cases implemented, a greater reduction in peak pressure gradients than that of a common homogeneous silicone liner. The results show the potential feasibility of implementing this metamaterial as a customizable interface solution to meet the unique performance needs of individual transtibial amputees to better increase comfort and functionality.
Brown, Nathan Kenneth, "Design of a Single Layer Metamaterial for Pressure Offloading in Transtibial Amputees" (2020). All Theses. 3292.