Exploring Biomechanically Adaptive Prosthetic Sockets With 3D-Printed Auxetic Meta-Structures

Abstract Prosthesis helps restore biomechanical function to allow amputees to regain ambulatory independence after limb loss. The design of prosthetic sockets is crucial to acceptability and comfort of use. The discomfort brought on by uneven distribution of stress at the interface between the residual limb and the prosthesis leads to high rates of prosthesis abandonment among amputees. An ideal prosthetic socket should be lightweight, and it should securely fit the residual limb to efficiently transfer load on to the prosthetic limb. To reduce discomfort during use, the socket should be able to evenly distribute pressure across the residual limb, even with changes in residual limb volume due to both fluctuations in body weight and changes in inflammation following the amputation. Additive manufacturing offers a promising option to design custom prosthetic sockets that improve comfort of use. This research investigates the use of additively manufactured lightweight auxetic meta-structures, with the overall goal of helping design an ideal prosthetic socket that reduces discomfort. Using tubular auxetic structures between the walls of the prosthetic socket allows to create lightweight sockets with preferable properties. This research follows a three-pronged approach to evaluate and improve the effectiveness of such a socket. As tubular auxetic structures assembled from planar auxetic frames, allow for a more efficient design for manufacturing, first, the study aims to establish the auxetic behavior of tubular structures assembled by using locking mechanisms from 3D printed planar structures. Second, compare different tubular auxetic structures to identify the structure that provides the best pressure distribution along the interface between the residual limb and the prosthesis. Third, evaluate the behavior of auxetic meta-structures designed using nanocomposite materials that could enhance the design while providing added benefits, like enhanced mechanical and antibacterial properties. The tubular meta-structures were modeled in SolidWorks and compared using finite element analysis. The behavior of two tubular auxetic structures, chiral and hexagon-chiral, were compared to a similar non-auxetic honeycomb tubular structure with minimized material usage. The material properties of the nanocomposites for simulation were determined using the Mori-Tanaka model. The considered nanocomposites include polypropylene and ultra-high molecular weight polyethylene with uniformly distributed spherical inclusions of zinc oxide, titanium dioxide and graphene nanoplatelets. Our preliminary results show favorable negative Poisson’s ratio behavior in tubular chiral and hex-chiral auxetic structures created from flexing planar auxetic structures. These results indicate the potential of using tubular auxetic meta-structures in creating lightweight prosthetics that are tailored to match the dimensions of the residual limb.