Evaluation of the influence of cyclic loading on a laser sintered transtibial prosthetic socket using Digital Image Correlation (DIC)

Abstract

People with a transtibial amputation worldwide rely on their prosthetic socket to regain their mobility. Patient comfort is largely affected by the weight and strength of these prosthetic sockets. The use of additive manufacturing could give the prosthetist a range of new design possibilities when designing a prosthetic socket. These new design possibilities can in turn lead to improved socket designs and more comfortable prosthetic sockets. This new way of designing and producing prosthetic sockets radically differs from the manual traditional production process. This makes it difficult for prosthetists to understand how all these new design possibilities influence the mechanical properties of the additive manufactured prosthetic socket. Therefore there is a growing need for a method to evaluate the strength and stiffness of newly developed socket designs.We propose a method to evaluate the strength and stiffness of prosthetic sockets. A robotic gait simulator is used to apply realistic kinetics of amputee gait to the tested socket. A Digital Image Correlation (DIC) system is then used to measure the deformation of a prosthetic socket under different loading conditions. This way it is possible to check if plastic deformation will occur in the designed transtibial socket. Furthermore it is possible to assess the effect of cyclic loading on the 3D printed socket.To illustrate the proposed method, a transtibial prosthetic socket was designed using CAD software and produced with laser sintering PA12. DIC measurements were performed on this transtibial socket both before and after it was subjected to a cyclic load of 1 million cycles (mimicking realistic amputee gait).

Scoping Review of Mechanical Testing of the Structural and Material Properties of Lower-Limb Prosthetic Sockets

“…Second to static testing, cyclic load testing was also slightly more common than the remaining tests, 24,25,39 but the articles differed in terms of the properties reported. Two publications reported the strength of sockets during cyclic loading, 24,39 whereas one reported deformation of sockets during cyclic loading 25 …”

“…No mock residual limbs had the same composition, although two studies described using polyurethane 19,35 and two other studies described using body filler 36,39 . Only two articles provided a rationale for using a mock residual limb, and both focused on trying to transfer load to the socket effectively 25,36 . Four articles provided a rationale for their choice of mock residual limb materials 19,28,39,40 .…”

“…Lamination was the most common fabrication method, with 20 of the 30 test methods testing sockets or specimens prepared using lamination 19,21,23,28,34–38,41 . The second most common fabrication method involved 3D printing, with 14 test methods testing sockets or specimens prepared using fused deposition modeling and laser sintering 24,25,28,36,39,40 . Least common, used only in four articles, was testing sockets and/or specimens prepared using thermoforming techniques, such as blister-forming and drape-forming 19,21,28,36 .…”

“…26 The search string used for the above databases was developed with the guidance of a research librarian and combined terms about lower-limb prosthetic sockets with terms about mechanical properties (Table 1). Through iterative tests of the search strategy and assessment of the articles identified against those previously known to the authors, 19,21,[23][24][25] specific words and phrases were selected to increase the yield of relevant articles, while minimizing irrelevant articles (e.g., by using the Boolean operator "NOT" to eliminate unrelated topics). The PubMed search string was modified as needed to conform to the other databases.…”

Prosthetic Sockets: Tensile Behavior of Vacuum Infiltrated Fused Deposition Modeling Sandwich Structure Composites

“…In the authors' previous work [11] as well as dynamic testing experiments by Saey et al [12], it was revealed how crucial the junction between the AM socket and modular component interface is. Without careful design consideration, these interfaces can fail at much lower strengths or cycles than predicted.…”