Electron beam melted heterogeneously porous microlattices for metallic bone applications: Design and investigations of boundary and edge effects

A successful implant requires compatible mechanical properties. Herein, microlattice models with bone-like mechanical properties (compressive strengths of 169.5–250.9 MPa, Young's modulus of 14.7–25.3 GPa) and high porosity (up to ∼ 60%) are designed and investigated through finite element modelling and electron beam additive manufacturing fabrication. Microlattices are designed to be hetero-porous, with large pores for nutrients flow and small pores for cell seeding. Size and boundary effects (3 × 3×6, 4 × 4×8 to 5 × 5×10) are studied of which revealed to affect the as-built mechanical properties via geometrical defects, generally deviating from that of modelling. The high proportion of increased nodals masses for fine features is found to greatly increase mechanical properties via the redistribution of stress concentrations. The effects of bounding edge additions to the lattices are also investigated, up to a 45% and 25% increase in strength and Young's modulus are respectively observed with a minimal increase in relative density of 4%, a large increase exceeding the modelled Gibson-Ashby trends. Mechanisms result from both the reduced fabrication defects and evenly distributed stress distributions are revealed by finite element analysis. The method allows effective enhancement of build qualities with retained pore sizes and porosities, which paves a new way for designing of microlattice with enhanced properties.