Finite element simulations of mechanical behaviour and degradation of iron lattices

Abstract

Biodegradable metals such as iron have become appealing for usage in temporary bone implants. Although iron possesses excellent properties of biocompatibility, it shows a very slow degradation rate and presents a higher stiffness and strength when compared to human bone. Several strategies can be applied to decrease the strength of the iron, one of them being the use of porous/cellular structures. The present work aims to study the mechanical properties and the degradation behaviour of porous iron with cellular structures composed of lattice struts. Six lattice geometries, which were previously studied, and inspired by crystalline structures, were designed. The mechanical behaviour of the lattice arrangements was studied numerically using the finite element software NX Nastran. The corrosion module of the finite element software COMSOL was used to simulate the degradation behaviour of the cellular structure immersed in simulated body fluid. After the degradation process, the compressive properties of the porous cellular structures were also assessed. Under compression, the iron lattice structures showed an elastic limit stress close to the values determined for the trabecular bone yield stress. Geometries selected to simulate degradation have shown mass loss percentage and corrosion rates close to the degradation rate established for an ideal bone substitute. The present study confirms that the structural arrangement has a strong influence on the mechanical properties of iron cellular structures. The degradation behaviour of iron lattices also appears to be affected by the unit cell topology.