Two-layered lattice structures of CoCr28Mo6 alloy for femoral component in total knee replacement

Abstract

Different two-layered Voronoi–TPMS lattice architectures of CoCr28Mo6 alloy fabricated by LPBF were proposed, which positioned a highly porous Voronoi layer at the bone interface for osteointegration and a denser TPMS zone for load bearing. Key mechanical characteristics, including elastic modulus, yield strength, fatigue resistance and stress distribution, were analyzed through FE simulations coupled with the Brown Miller criterion and Rainflow counting. Validations were conducted based on static and cyclic compression tests. Under axial, torsional and combined loads, the Voronoi/Split P (VSP) configuration exhibited the highest compressive yield stress, shear modulus and elastic-admissible strain, whereas its Voronoi layer experienced larger stress concentrations that shortened fatigue life. Though the endurance limit of 0.18·σy was reached by the combined load, the VSP model provided a 35% reduction in local stress variance by Gaussian distribution, indicating more uniform load transfer. In addition, the Split-P base structure achieved up to 55% higher surface-area-to-volume ratio and 20% higher lacunarity than other TPMS combinations, offering more structural heterogeneity and interfaces for bone ingrowth. When inserted into a femoral component, the two-layered VSP core could increase the mean stress of femoral bone, thereby mitigate stress shielding, and reduce risk of bone damage compared to other solid and single lattice core.