Design of a Single Layer Metamaterial for Pressure Offloading of Transtibial Amputees

Abstract

While using a prosthesis, transtibial amputees can experience pain and discomfort brought on by large pressure gradients at the interface between the residual limb and prosthetic socket. Current prosthetic interface solutions attempt to alleviate these pressure gradients by using soft homogenous liners to reduce and distribute pressures. This research investigates an additively manufactured metamaterial inlay with a tailored mechanical response to reduce peak pressure gradients around the limb. The inlay uses a hyperelastic behaving metamaterial (US10244818) comprised of triangular pattern unit cells which can be 3D printed with walls of various thicknesses controlled by draft angles. The hyperelastic material properties are modeled using a Yeoh 3rd order model. The 3rd order coefficients can be adjusted and optimized, which corresponds to a change in the unit cell wall thickness to create an inlay that can meet the unique offloading needs of an amputee. Finite element analysis simulations evaluated the pressure gradient reduction from: 1) a common homogenous silicone liner, 2) a prosthetist's inlay prescription that utilizes three variations of the metamaterial, and 3) a metamaterial solution with optimized Yeoh 3rd order coefficients. When compared to a traditional homogenous silicone liner for two unique limb loading scenarios, the prosthetist prescribed inlay and the optimized material inlay can achieve equal or greater pressure gradient reduction capabilities. These results show the potential feasibility of implementing this metamaterial as a method of personalized medicine for transtibial amputees by creating a customizable interface solution to meet the unique performance needs of an individual patient.

Assessment of 3D printed mechanical metamaterials for prosthetic liners

“…A truncated TT bone module model was created in accordance with surgical guidelines of TT amputations and a detailed description was reported previously by McGrath et al 30 Subsequently, a bone cavity was created within the residuum to host the truncated bone model. The solid liner was constructed by extruding the exterior surface of the residuum 18 uniformly by 5 mm in the direction normal to the residuum. This thickness is equivalent to a single layer of the unit cell (u = 5 mm) as shown in Figure 1(a).…”

“…This ensured liner/residuum and liner/ socket interfaces were flush against each other to emulate in-vivo socket interface interactions. 18 The complete 3D model for FEA is shown in Figure 4.…”

“…15,16 3D printed elastomers 17 in particular show great promise for a range of biomedical applications due to high flexibility, strength and variable stiffness for applications involving complex surface contours such as TT residua in this study. Indeed, Brown et al 18 reported an initial study involving the use of 3D printed TangoPlus 19 metamaterials as interface materials to offload pressure at the residuum/ socket interface. However, there lacks systematic studies on the design and evaluation of prosthetic liners, especially custom liners.…”