Material Characterization of Fused Filament Fabrication for Lower-Limb Prosthetic Sockets

Abstract Additive manufacturing (AM) is a very versatile and powerful tool for fabricating lower-limb prosthetic sockets. Fused filament fabrication (FFF), a material extrusion AM technique, has the potential to greatly improve the function and comfort of prosthetic sockets with enhanced features such as in-socket pressure monitoring or spatially varied material stiffness. Fiber-reinforced polymers (FRPs) are conventionally used to manufacture sockets that have been proven to provide adequate structural durability. However, evidence is lacking to show that sockets made with FFF have the required material properties, and the field is far from establishing a standard method for manufacturing and testing FFF sockets with acceptable strength and stiffness. In this paper, material characteristics of FFF and FRP specimens obtained from ASTM D3039 standard tensile testing are compared and analyzed. Results showed that the tensile modulus of FFF specimens is not greatly affected by build orientation, and, in general, the printed layer heights tested in this study did not have an effect on modulus nor tensile strength. Longitudinal raster orientations significantly increased the tensile strength of FFF specimens built in the flat orientation, although all FFF specimens still exhibited significantly lower strength and modulus compared to the FRP composites. This paper provides a basis for the selection of FFF process parameters for designing adaptable and smart sockets, and provides suggestions for the use of material characterization data in predicting and optimizing the structural safety of future novel prosthetic socket designs.