Computational evaluation of the compressive properties of different lattice geometries to be used as temporary implants

Abstract

Additive manufactured iron lattice structures present unprecedented capabilities for fulfilling the role of bone temporary implants. Iron structures are biodegradable, eliminating the need for removal surgeries, and can help reduce stress shielding significantly by mimicking the properties of bone locally. Although several types of lattice structures have been proposed in the literature, there is the need to evaluate the effect of the relative density on their mechanical properties, in order to resemble bone properties.In the present work, the effects of relative density on the mechanical behavior and in particular, in elastic mechanical properties, were evaluated with finite element simulations, for several types of cells.Lattices, i.e, arrays of unit cells, were designed for 5% increments of relative density, from 5% up to the maximum allowed for each specific cell, for 5 different cell types, creating a total of 63 lattice structures. Finite element models were created for each geometry simulating a compression test, obtaining stress-strain curves and thus the Young's modulus. The material data introduced in the finite element analysis was obtained experimentally from a compression test on bulk iron.The results suggest that all lattice structures evaluated were stable for high density. Cubic (C), truncated cubic (TC), and rhombicuboctahedron (RCO) cells presented instability at low densities while truncated octahedron (TO) and rhombitruncated cuboctahedron (RTCO) cells remained stable at low densities, reaching the value of the Young's modulus of very low-density trabecular bone.Two cell types, RTCO and TO, showed the ability to reproduce the whole range of mechanical properties of bone in a stable manner. The other cell types experienced instability phenomena, like buckling, at low densities.