Specific Yielding of Selective Laser-Melted Ti6Al4V Open-Porous Scaffolds as a Function of Unit Cell Design and Dimensions

Bone loss in the near-vicinity of implants can be a consequence of stress shielding due to stiffness mismatch. This can be avoided by reducing implant stiffness, i.e., by implementing an open-porous structure. Three open-porous designs were therefore investigated (cubic, pyramidal and a twisted design). Scaffolds were fabricated by a selective laser-melting (SLM) process and material properties were determined by conducting uniaxial compression testing. The calculated elastic modulus values for the scaffolds varied between 3.4 and 26.3 GP and the scaffold porosities between 43% and 80%. A proportional linear correlation was found between the elastic modulus and the geometrical parameters, between the elastic modulus and the compressive strengths, as well as between the strut width-to-diameter ratio(a/d) and elastic modulus. Furthermore, we found a power-law relationship between porosity and the modulus of elasticity that characterizes specific yielding. With respect to scaffold porosity, the description of specific yielding behaviour offers a simple way to characterize the mechanical properties of open-porous structures and helps generate scaffolds with properties specific to their intended application. A direct comparison with human bone parameters is also possible. We generated scaffolds with mechanical properties sufficiently close to that of human cortical bone.