Design, characterization, modeling and selection of lattice structures for bone repair plates produced by additive manufacturing

Bone repair plates are crucial in orthopaedics as they provide fixation and stability that promote adequate healing and restore function in fractured or damaged bones. However conventional bone plates can lead to complications and the strategy to overcome such problems relies on the choice of materials, designs, and non-conventional fabrication methods. The current work investigates porous structures for bone plates, obtained by additive manufacturing, featuring two different materials, namely a conventional non-biodegradable (316L stainless steel) and a new possible biodegradable metal (iron). Lattice structures were designed with two different unit cell types, Rhombitruncated Cuboctahedron (RTCO) and Truncated Octahedron (TO), with relative densities of 5%, 25% and 40%. Laser powder bed fusion was used to fabricate such complex structures that would otherwise be difficult to produce. The influence of the thickness of face-sheets and the presence of one or two core layers was also addressed. The mechanical behaviour of plates was evaluated through experimental three-point bending (3PB) and finite element analysis (FEA). A performance index based on mass minimization was proposed to support decision making in parts selection. Plates with RTCO lattices were found to carry higher bending loads than TO samples. An increase in relative density, face-sheet thickness or the number of layers resulted in higher stiffness and yield load values. Deviations between numerical results and experimental data were found, which may be a consequence of the irregularities of the production process.