Modeling and fabrication of prosthetic sockets using selective laser sintering
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Successful rehabilitation of transtibial amputees involves effective fitting of prosthetic components. However, conventional techniques used to produce sockets with suitable characteristics are labor intensive and expensive, and depend on the work of skilled prosthetists that are relatively scarce compared to the number of transtibial amputees. Selective Laser Sintering (SLS) is a very promising technique for producing subject-specific sockets for transtibial amputee prostheses due to its inherent ability to create complex three-dimensional objects directly from digital shape information without the need for specific tooling, molds or human labor. This dissertation presents a framework for the design, analysis, manufacture and testing of SLS sockets for transtibial prostheses, including the development of a computer-aided design model of the socket with compliant features to enhance comfort, structural analysis using a Finite Element Method (FEM) model, fabrication of a functional prototype using SLS, and experimental validation of the FEM analysis. The validation involved quantifying the failing conditions of sockets manufactured using the vii framework during destructive tests. The experimental failure loads for the sockets were within a 3% range of the FEM results and were considered satisfactory. The specific design of orthogonally compliant features for socket was also analyzed. This process included the preliminary evaluation of design alternatives using FEM with validation through experimental measurements, definition of specific design methodology for the best alternatives, incorporation of solution within the socket and refinement of design using auxiliary features obtained through topology optimization. Finally, to investigate the structural response of the SLS socket during gait, a FEM model (acquired from Computed Tomography data of a transtibial amputee) composed of a socket, liner and residual limb under quasi-static loading derived from typical ground reaction forces was employed. Three different compliant designs were evaluated to assess their ability to locally relieve local pressure during the stance phase of gait, as well as their structural integrity to ensure safety. The design with a compliant feature consisting of spiral slots within the socket wall was determined to produce a local average relief of 65.8% in the interface pressure, reducing the peak pressure from 172 kPa to 66.4 kPa.