A comparative finite element study of bioinspired porous hip implant stems optimized using nTopology-based lattice architectures

Abstract

One major cause of implant loosening after total hip replacement is the mismatch in stiffness properties between the metallic prostheses and the cortical bones. This paper evaluates the structural effectiveness of four different bioinspired porous structures, specifically Honeycomb, Gyroid, Schwarz P and Voronoi, optimized using the Solid Isotropic Material with Penalization technique in nTopology and tested in ANSYS via static finite element analysis under physiological gait loadings consisting of an axial force of 2100 N and mediolateral shear forces of 300 N applied to a Ti–6Al–4V Grade 23 hip stem with 60% design porosity. The Honeycomb lattice displayed the lowest maximum Von Mises stress and total deformation with 553 MPa and 0.565 mm, giving it a safety factor of 1.59 which meets the minimum requirement of 1.5 set by ISO 7206. On the other hand, the Voronoi lattice exhibited maximum stress and total deformation values of 986 MPa and 0.591 mm, surpassing the material ultimate tensile strength value of 950 MPa. The Schwarz P lattice and the Gyroid lattice attained intermediate magnitudes of roughly 720 MPa and 840 MPa respectively. Theoretical estimations of effective modulus through the Gibson-Ashby Scaling Law gave about 4.9% agreement with results of finite element analysis for all structures. Stress shielding effect calculations revealed that only the Honeycomb and gyroid lattices stayed within the clinically acceptable value of 50%. Given these outcomes, through this static numerical screening research, the Hexagonal honeycomb lattice configuration is revealed as the leading contender for future improvement (covering fatigue analysis and experimental tests) to be used with selective laser melting process for customized hip implant stems.