Metamaterial Design for Targeted Limb-Socket Interface Pressure Offloading in 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 adjustable mechanical response in order 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 third order representation based on Yeoh 3rd order coefficients. The 3rd order coefficients can be adjusted and optimized to represent a change in the unit cell wall thickness to create an inlay that can meet the unique offloading needs of an amputee. Finite element analyses 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 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 customizable interface solution to the meet unique performance needs of an individual patient.

Revolutionizing Prosthetic Design with Auxetic Metamaterials and Structures: A Review of Mechanical Properties and Limitations

“…A common problem concerning lower limb prosthetics usually relates to the comfort of the user [ 28 , 29 , 30 ]. There have been efforts to solve this problem, including research investigating the use of an auxetic metamaterial inlay to improve the stress distribution associated with the residual limb for transtibial prosthetics [ 9 ]. The metamaterial structure implemented in this instance is based on orthogonally patterned equal-sized triangles repeated four times spanning 180 degrees with uniform gaps.…”

“…Each study has been generally described in the reference provided in Section 2 regarding the state-of-the-art methods for auxetic implementation in a prosthetic. This section will cover more detail regarding the limitation and comparison of the described research [ 9 , 26 , 32 , 33 , 39 ]. The auxetic single-layer liner studied by Brown et al was mainly conducted using the FEA method.…”

“…( E ) Visual representation for the FEA results to analyse PS and PPG. This resulting gradient reduction capability is compared to the “no inlay” condition [ 9 ].…”

“…This event was soon followed by significant developments such as the first hydraulic knee in 1947, the SACH (solid ankle cushion heel) introduced by Anthony Staros in 1957, a computer-aided robotic arm in 1980, and a motor-powered lower limb prosthetic in 2012 [ 7 ]. Subsequently, researchers aimed to implement the unique properties of the MR (magnetorheological) effect as a brake for lower limb prosthetics [ 8 ]; by 2020, Brown et al had conducted research to improve the comfort of amputees by proposing the use of metamaterials as a liner in the socket for a transtibial prosthetic [ 9 ]. The diagram within Figure 1 illustrates the development of prosthetics.…”

The use of conformal lattice metamaterials for relieving stress in lower limb sockets: A numerical and exploratory study

“…13 In depth, metamaterials are structures made out of repeating patterns, patterns whose properties can be manipulated through design, to achieve a desired mechanical response. 14 Along with AM, these structures enable a wide use of polymer materials, thereby that allowing the fabrication of these metamaterials. This paper investigates the reduction of stresses found in transtibial lower-limb sockets.…”