Selective laser melting novel biodegradable iron-based bone scaffolds for load-bearing applications

Abstract

Autologous bone grafting has long been the "gold standard" for the reconstruction and remodelling of critical maxillofacial bone defects. However, it has several disadvantages, and as such bone scaffolds have become increasingly popular. Ceramic and polymer scaffolds have been extensively researched, but due to their limited mechanical properties, these classes of materials are generally not suited for load bearing applications.Permanent metallic scaffolds have much better mechanical properties, but their permanent nature can result in long term inflammation along and rejection.To overcome these drawbacks biodegradable metallic (BDM) implants are being developed, showing great potential. An ideal BDM would retain its mechanical properties during bone growth and slowly degrade away transferring the stress to the newly formed bone without damaging it; subsequent to full healing, the implant would completely dissolve away leaving behind no residue. Fe has emerged as an enticing candidate for load-bearing scaffold application as it has high mechanical properties, and with the addition of Mn displays excellent MRI compatibility, formability, and an increased corrosion rate compared to pure Fe.Selective laser melting (SLM) can produce highly customisable implants with optimised lattice structures, interconnected porosities and controllable pore sizes, which have been shown to improve bioactivity. Research on the SLM of pure Fe and Fe-based alloys has mostly been focused on maraging steels, tools steels, and other steels used in industry.Until the end of this thesis there had been relatively limited amount of work on the selective laser melting of Fe for biomedical applications.The first part of the thesis aims to understand the SLM processability of Fe-35Mn and how SLM affects the material properties of biodegradable implants by: (i) implementing a design of experiment approach to determine the SLM processing of Fe-35Mn and pure Fe firstly for bulk structures and after for scaffolds; (ii) understanding the effect of SLM processing on the properties of pure Fe by comparing it to other manufacturing methods, specifically for biodegradable implant applications.