Synthesis of topologically-ordered porous magnesium
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Magnesium (Mg) and its alloys offer potential as a new class of degradable metallic orthopaedic biomaterials. In comparison with current metallic orthopaedic implant materials, Mg offers advantages such as, high specific strength, closer-to-bone stiffness and biodegradability, thereby eliminating the need for a second surgery to remove hardware. The use of porous metal foams as biomaterial scaffolds has been widely adopted, however, many of these porous structures are manufactured with pore architectures that are inherently random. This makes structural optimisation for a specific purpose challenging. Scaffolds containing ordered pore architectures can be fabricated to meet design criteria, such as porosity, stiffness, and volume fraction. Currently there are few methods described in the literature to manufacture ordered porous Mg. The main aim of this thesis was to determine the resolution of a novel indirect solid free-form fabrication (SFF) process for producing topologically-ordered porous Mg (TOPM) structures from pure Mg and commercial Mg alloys. The produced structures were examined for properties such as dimensional accuracy, microstructure, surface properties, mechanical properties and corrosion behaviour. The capability of the process was further examined in manufacturing structures with complex architecture for potential application as degradable metallic orthopaedic devices, namely a spinal fusion device (SFD) and screw. With the produced structures aimed at load-bearing applications in bone, the mechanical properties and behaviour of the TOPM and SFD made from Mg alloys were investigated using finite element analysis (FEA) and compression testing. The relationship between surface roughness and degradation behaviour in Mg biomaterials has received limited interest and is still a controversial issue. Therefore, it was necessary to accurately determine the effect of surface roughness on corrosion rate of Mg, especially samples manufactured from SFF and casting of molten Mg. Given the well-established need for improved corrosion resistance of Mg, two coating techniques, including biomimetic calcium phosphates and electrochemically-assisted deposition coating, were applied on Mg substrates cast via the SFF process. Corrosion testing was employed to investigate the effectiveness of the coating layers in improving corrosion resistance. In this thesis, the capability of the SFF manufacturing process and properties of the produced structures were thoroughly investigated. Results and findings contribute to the development of topology optimised, degradable Mg devices for biomedical applications.