Department of Mechanics: Seminar: Abstract Garner 2019

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Stress-inducing compliant mechanism design for total hip arthroplasty via multi-scale topology optimization

Eric Garner, Additive Manufacturing Laboratory, Department of Biomechanical Engineering, TU Delft, The Netherlands

Room B-366, Faculty of Civil Engineering, CTU in Prague

Wednesday, 25 September 2019, 14:30-15:30

Hip arthroplasty is a surgical procedure in which the hip joint is replaced by with a prosthetic. While the design of the joint itself has been the focus of much attention in both academia and industry, less attention has been paid to the design of the stem which anchors the implant into the femur. The stem is now the main cause of implant-related injury. Specifically, poor geometric and mechanical compatibility between the stem and the surrounding bone tissue leads to bone resorption and eventual aseptic loosening and peri-prosthetic fracture, limiting the work life to approximately 10 years. We propose a topology optimization-based design approach that aims to produce ideal stress conditions in the host bone tissue, taking into account application-specific constraints and requirements. We formulate a modified compliant mechanism design problem in which the objective is to find the internal topology of the implant that maximizes the minimum compressive stress in the bone tissue located at the bone-implant interface. The nonlinear nature of the problem makes single scale optimization unable to converge to an adequate solution. Instead, we use a parametrized microstructure that can achieve a wide range of mechanical properties while ensuring excellent connectivity between adjacent unit cells. The result is a lattice-like design that can be readily fabricated using selective laser melting technology.

Keywords: Topology optimization, multi-scale optimization, microstructures, compliant mechanism, auxetic, metamaterials, hip replacement, arthroplasty.