Metal Additive Manufacturing Conference - MAMC 2023

Lattice structures (porous scaffolds) with interconnected pores provide better osteointegration compared to solid implants and minimize the stress shielding effect by reducing the effective elastic modulus of implants closer to the natural bones. This research focuses on developing biocompatible Orthopedic implants with reduced stress-shielding, better load-bearing and osteointegration capabilities. Lattice structures with great bio-mimicry features and mechanical properties were designed by considering optimum pore shape, pore size and porosity percentage. Based on Gibson-Ashby scaling laws for a relation between relative density, effective elastic modulus and yield strength, Gyroid lattice unit cells with porosities ranging from 65% to 85% were designed with a variation of 5% to bring the stiffness of implants close to cortical and cancellous bones. The Ti-6Al-4V alloy, with excellent mechanical properties and biocompatibility, was used for the development of porous implants. The quasi-static performance of Gyroid lattice structures was investigated computationally by performing FEA, including size-effect analysis to obtain size-independent mechanical properties. The size effect analysis indicated that 43 unit cells are sufficient to obtain bulk mechanical properties of the lattice structure.

Lattice structures were manufactured using Direct Metal Laser Sintering, a powder bed fusion technology. The microstructural evaluation of additively manufactured lattice structures was performed using Scanning Electron Microscopy, as the micro-defects generated during the additive manufacturing process affect the mechanical strength of structures. The lattice structures were tested under compressive loading conditions to assess their suitability for load-bearing orthopedic implants. The deformation behavior of lattice structures was analyzed using the DIC technique.

It was observed that the Gyroid lattice structure provides easy control over porosity, thus, scaffolds' effective elastic modulus and strength. The Gyroid lattice structures with 65% to 85% porosities provide an effective elastic modulus of 0.2 to 3 GPa and yield strength of 6 to 45 MPa; thus, they are suitable for implantation near cancellous bones but need improvement in strength for implantation near cortical bones.