Generative design of an additively manufactured passive prosthetic foot for multiple forms of ambulation

Over 2.1 million people in the United States are living with limb loss. The majority of those individuals have a loss of a lower limb (Ziegler‐Graham et al, 2008), and over 150,000 people undergo lower limb amputation per year (Dillingham et al, 2005; Owings et al, 1996). Those with transtibial or transfemoral limb loss utilize lower-limb prostheses, which commonly includes a passive prosthetic foot. Prosthetic feet can be costly, limited in their functionality, and can be difficult to integrate with the addition of a sock, prosthetic cover (i.e. shell), and shoe. This study explores the use of computer-aided generative design to create usable additively manufactured (AM) mechanically-passive prosthetic feet that are optimized for multiple forms of ambulation including level, upstairs, downstairs, and sloped walking. Using the generative design framework, the foot is not only optimized for safety during multiple forms of ambulation, but also redesigned for reduced mass and cost using AM, as well as greater ease of use – forgoing the need for a separate shell or shoe by combining the prosthetic foot and customized sole into a single integrated unit. The result of this design study is a customizable 3D-printed foot model and sole, verified for safety through compressive loads to simulate multiple ambulation tasks, as well as different phase within these tasks. The models were tested against existing carbon fiber and 3D printed passive foot models, with and without a shell and shoe, under compression to simulate different forms of ambulation. For these conditions, we evaluate stiffness profiles and failure modes experimentally, as well as examine the distributions of stress and displacement within the finite element simulations of the generative design to understand how these designs function during different phases and modes of ambulation. This creation and validation of an AM, customizable foot and shoe prosthetic could open the door for the increased accessibility and performance of foot prostheses, as well as improve the quality of life for lower-limb amputees.