Low elastic modulus and highly porous triply periodic minimal surfaces architectured implant for orthopedic applications

A mismatch between the implant and interacting bone Young's modulus causes stress shielding phenomena, which leads to instability of the implant and early failure. This paper focuses on the development of medical-grade titanium alloy (Ti6Al4V)-based metallic highly porous structure to mitigate the stress shielding effect. In this study, we propose an effective method to generate a highly porous implant based on triply periodic minimal surfaces (TPMS) architecture. Three-dimensional models of different TPMS architectures such as Diamond, Gyroid, I-graph-Wrapped Package graph (IWP), and Primitive were constructed with a 2 x 2 x 2 mm lattice size and unit cell size of 1 mm. Mechanical testing of the finite-element models was performed under static loading conditions to evaluate the effective elastic modulus (E-eff) of each porous architecture. It was found that the primitive structure exhibits the lowest E-eff, whereas the Gyroid exhibits the highest E-eff, results indicate that porous architecture reduces E-eff by more than 95%, thereby reducing the stress shielding effect. Moreover, pore size and surface-area-to-volume ratio (SA/V ratio) were also investigated. Findings suggested that the primitive structure has the highest pore size, which will be suitable for enhanced bone ingrowth. A high SA/V ratio in IWP offers the possibility of enhanced cell adhesion, migration, and proliferation.