Choosing between commercially pure titanium and Ti-6Al-4V gyroid structures for orthopedic applications: An analysis through Timoshenko beam theory, the Gibson-Ashby model and experimental methods

Abstract

For decades, research has focused on using gyroid lattice structures to prevent stress-induced osteopenia and improve osseointegration by promoting cell adhesion and transition, particularly in cases where implant removal is not desired after complete healing. Despite these advantages, in-depth research is still needed for innovative biomedical implants to reach optimum functionality. Although commercially pure titanium (Cp-Ti) and Ti6Al4V are both popular materials for standalone bone implants, they are not likely paired within the same application due to mechanical property differences. This study proposes a case-specific workflow to support orthopedic implant design considerations, by analytically and experimentally investigating the mechanical response of additively manufactured lattice gyroid structures in both Cp-Ti and Ti6Al4V with different porosity rates. The experimental results of both materials indicate a significant decrease in the elastic modulus against two employed analytical methods, Gibson-Ashby model and Timoshenko beam theory. This is linked to inherent manufacturing-induced stress concentrations on the physical gyroids. The experimental outcome presents itself significantly closer to the predictions of Timoshenko beam theory compared to Gibson Ashby method. Both gyroid titanium structures are loyal to Timoshenko theory, displaying a combination of multi deformation behaviors instead of one-way deformation. The deformation response of Ti6Al4V showed a 45⁰ shear band while Cp-Ti exhibited smoother deformation during compression. Higher porosity rates led to an increase in ductility due to extended horizontal plateau regions in both Cp-Ti and Ti6Al4V lattice structures. The results provide valuable comparative insight and considerations on the material choice for gyroid lattice structures within bone implants.