Effect of micro-architectural design and polymer infiltration on mechanical properties and fatigue life of strut- and sheet-based lattice bone scaffolds

• Sheet-based Gyroid shows much higher fatigue life than strut-based Diamond and FCC. • Gyroid fatigue life-to-stiffness ratio raises with porosity, unlike Diamond and FCC. • Polymer infiltration greatly improves strength with minimal stiffness increase. • Reducing stiffness pre-infiltration yields target distribution post-infiltration. Lattice structures are widely used in biomedical engineering, primarily due to their exceptional properties which results from their unique microstructural features. The variability in geometric parameters of the lattice microstructure, enables property adjustment to meet different needs. In this paper, the mechanical properties of lattice structures are investigated with respect to unit cell type, porosity, and presence of an infiltrated resin, which simulates bone tissue within the scaffold. Digital image correlation technique was employed to assess deformation modes in in-filled structures. Three different architectures, including Diamond, FCC and Gyroid with three distinct relative densities of 15 %, 25 %, and 35 % have been designed and fabricated using Ti-6Al-4 V biomaterial. Results showed that the Gyroid lattice structures demonstrated superior mechanical properties compared to Diamond and FCC lattices under quasi-static compression tests. Distinct failure behavior was also observed across the structures. At higher relative densities, Diamond and FCC lattices formed 45° macro-cracks, whereas Gyroid samples compressed severely without macro-cracks. Furthermore, in-filled structures, demonstrated up to 1.3 times higher strength compared to their as-built counterparts. Notably, a unified master curve was developed to facilitate the prediction of fatigue lives of all geometries. These findings support the development of implants with enhanced longevity and performance.