Microstructure and mechanical properties of open-cellular biomaterials prototypes for total knee replacement implants fabricated by electron beam melting

Total knee replacement implants consisting of a Co–29Cr–6Mo alloy femoral component and a Ti–6Al–4V tibial component are the basis for the additive manufacturing of novel solid, mesh, and foam monoliths using electron beam melting (EBM). Ti–6Al–4V solid prototype microstructures were primarily αα-phase acicular platelets while the mesh and foam structures were characterized by α′α′-martensite with some residual αα. The Co–29Cr–6Mo containing 0.22% C formed columnar (directional) Cr23C6 carbides spaced ∼2 μm in the build direction, while HIP-annealed Co–Cr alloy exhibited an intrinsic stacking fault microstructure. A log–log plot of relative stiffness versus relative density for Ti–6Al–4V and Co–29Cr–6Mo open-cellular mesh and foams resulted in a fitted line with a nearly ideal slope, n=2.1n=2.1. A stress shielding design graph constructed from these data permitted mesh and foam implant prototypes to be fabricated for compatible bone stiffness.