Additively manufactured radially graded stainless steel lattices for structural biomedical applications

Stress shielding is a common issue affecting osseointegrative implants and scaffolds caused by the mismatch between the elastic modulus of the bone and the implant material. We additively manufactured lattice structures with radially graded wall thickness with the intention to replicate the radially graded structure of human bone. Finite element analysis of seven different lattice structures was performed to select an ideal lattice geometry in terms of strength and effective elastic modulus, and the diamond triply periodic minimal structure (D-TPMS) lattice geometry was selected. Cylindrical D-TPMS lattice samples were manufactured via laser powder bed fusion of 316L stainless steel. Wall thickness of the D-TPMS geometry varied from 1.6 mm at the sample edge to 0.5 mm at the center, producing a radially graded structure. This radially graded lattice material showed a reduction in effective elastic modulus compared to bulk 316L while maintaining an effective yield strength comparable to that of cortical bone.