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This dissertation, The Development of Magnesium-based Materials for Orthopaedic Applications by Hoi-man, Wong, 黃凱文, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: The currently used biomaterials for surgical implantation include stainless steel, titanium and its alloys. However, due to the non-degradability and the mismatch of the mechanical properties between these metallic implants and human bone, there maybe a long-term adverse effect of inflammation or stress shielding effect. This may lead to bone loss which brings with a higher risk of implant failure. To avoid this problem, implants made of biodegradable materials are the alternatives. Due to the poor mechanical properties of biodegradable polymer especially for load-bearing area, biodegradable metal is used instead. Magnesium is the potential candidate since it is degradable with mechanical properties similar to human bone whilst magnesium ion is an essential element to human bodies. With the advantages of using magnesium for implantations, it can be potentially used for fracture fixation implant and bone substitutes. However, its rapid degradation and release of hydrogen gas may inhibit its use. Hence, modification is required. In this project, plasma immersion ion implantation and deposition (PIII&D) using aluminium oxide as the plasma source was conducted on the magnesium alloys. The corrosion resistance properties of the plasma-treated magnesium alloy were found to display significant improvement in immersion test especially at early time points. The plasma-treated sample was compatible with osteoblasts. Cells attached and grew on the treated sample but not the untreated sample. The animal study showed consistent results with the cell study, and there was a significant increase in bone formation around the treated sample when compared to the untreated sample. The other potential application of magnesium is its usage as a bone substitute. Due to the limitations of autografts and allografts, synthetic bone substitutes are developed. The ideal bone substitutes should have similar properties to those found with autografts. However, no such bone substitutes presently exist; hence, a novel hybrid material is fabricated in this project through the addition of magnesium granules into a biodegradable polymer polycaprolactone (PCL). The immersion test showed that an apatite layer composed of magnesium, calcium, phosphate and hydroxide was formed on the hybrids but not on pure PCL, which suggested that the hybrids were osteoinductive and osteoconductive. The compression test showed that the mechanical properties were enhanced with the incorporation of magnesium granules into pure PCL and were still maintained after 2 months of immersion. Osteoblasts grew well on the PCL-Mg hybrids. The addition of smaller amounts of magnesium granules (0.1g PCL-Mg) resulted in higher ALP activity and up-regulation of different bone markers when compared to the pure PCL. Finally, the animal studies showed that more new bone formation was found around the 0.1g PCL-Mg hybrids especially at early time points, which suggested that the healing time could be shortened. In conclusion, fracture fixation implants and novel bone substitutes based on magnesium were developed in this project. The aluminium oxide coating was a

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