Advanced topology optimisation for porous hip Implants: Bridging in silico models and in vitro tests.

Abstract

Total joint replacement is a cost-effective surgical operation performed in orthopaedics in which a damaged joint is replaced with a medical implant. This can relieve pain, improve motion, and allow patients to return to normal daily activities. However, there are a lot of issues with regard to the conventional solid implantation, such as high potential risk of stress shielding, customised design for different purposes or patients, specific anisotropic and heterogeneous microstructures to restore biological functions. A Floating Projection Topology Optimisation (FPTO) algorithm with ersatz material model and multiple constraints is used in this paper for implants design. The algorithm develops with a global volume constraint to control total volume fraction, a local porous infill volume constraint to generate porous infill and the objective of maximising stiffness constrained by lower volume fraction for reducing stress shielding effect. The novel FPTO-finite-element-musculoskeletal modelling and analysing pipeline allows weight factors for considering multiple loading cases in accordance with varieties of postures in gait cycle. Validations and simulation-predicted testing are conduct by finite element analysis (FEA) under varieties of loading cases to investigate the performance of the porous implant design. FPTO is feasible in designing medical implants with lower stiffness for reducing stress shielding effect. Smooth boundary of implants by FPTO can be obtained directly without post-processing, and multiple constraints are allowable. Compared with conventional design, the proposed implant can approximate natural bone structure and load transmission path. Finite-element-based FPTO design provides tailored anisotropic and heterogeneous topology based on host bone and muscle conditions for better biomechanical performance and durable serviceability whilst being lightweight. This paper proposes a Floating Projection Topology Optimisation (FPTO) algorithm with ersatz material model and multiple constraints for smooth boundary implant design to reduce stress shielding effect. With FPTO technique, it is expected to shed new light on design of porous implant considering tailored biomechanical environment.