Design and testing of additively manufactured lattice structures for musculoskeletal applications

Abstract

Additive manufacturing (AM) methods present a new frontier in engineering, allowing the fabrication of porous lattice structures with tailored mechanical properties. AM structures can be made using bio-inert metals, creating controlled stiffness biomaterials. As bone formation is strain dependent, these AM biomaterials can be used in implants to optimise the strain in surrounding trabecular bone for peak bone formation. However, the behaviour of AM lattices varies and is subject to manufacturing constraints. The aim of this PhD was to investigate the mechanical behaviour of AM lattices, and maximise the clinical benefits of AM for musculoskeletal applications. Lattice architecture was shown to affect the anisotropy of an AM lattice biomaterial, increasing the stiffness in directions not often tested in the literature. The mechanical and morphological properties of individual struts within powder bed fusion (PBF) lattices were also shown to vary depending on the orientation of the struts to the build direction. The ultimate tensile strength of titanium alloy (Ti6Al4V) struts more than doubled when built at a low angle versus perpendicular to the build platform, and other properties were substantially lower than for the bulk material. Geometric imperfections were found for struts built at low angles. As such, a low stiffness modified stochastic lattice was designed and tested which avoided the problems found with struts built at low angles. The resulting lattice had improved stiffness isotropy and could be used for musculoskeletal applications, tuned to match the mechanical properties in local trabecular bone and enhancing bone formation.