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In fracture management with open reduction and internal fixation with metallic implant, secondary procedure of removal of implant is often required. Such procedure causes additional surgical risks to patients, including anaesthetic risks, wound infection, bone infection, soft tissue adhesion and joint stiffness. The procedure is also costly to the patient and society. If the fixation implant is self-resorbable, the need for secondary surgery will be completely eliminated and the social resources can be saved. Making use of the corrosion process, metals can be developed into new generation of resorbable (or biocorrodible, biodegradable) implants. An ideal bioresorbable orthopaedic implant should provide adequate mechanical support that matches the bone healing process. The implant should resorb progressively as the bone heals. Many current resorbable materials are biomechanically inferior to conventional metallic implants. Magnesium based alloys are popularly studied because of their mechanical properties and biocompatibility. Implants made of magnesium based alloy are expected to resorb in the human body with no harmful effect. The major research challenge is to identify an alloy that performs satisfactorily in the following aspects: biocompatibility, degradation rate, hydrogen gas formation (gas product from the reaction between Mg and water), and mechanical strength. In addition, there is no standard evaluation method for the biodegradable alloys. It is because the interaction between the degradable implants and the physiological environment is too complicated to mimic. The in vitro and the in vivo results often mismatch. This research involved the design and the tests of three Mg based alloys. Zinc (Zn) and manganese (Mn) were chosen as the alloying elements for corrosion resistance and mechanical enhancement. Mg-1Zn-1Mn, Mg-3Zn-1Mn, Mg-5Zn-1Mn (in wt.%) were developed and compared. The study was divided into three parts: material characterization, in vitro studies, and in vivo (animal) studies. The SEM/EDX confirmed that the surface properties of the alloys were consistent after the surface treatment. From the mechanical test, the yield strengths and the densities of the alloys were found to be close to that of the natural bones. The theoretical calculation showed that the amount of Mn determined the threshold implant mass of the test alloys. The hydrogen evolution test showed that the Mg-1Zn-1Mn was the least corrodible. The elution test showed that the Mg-1Zn-1Mn was the least cytotoxic and the cytotoxicity was affected by the pH changes brought by the alloys. The live cell imaging captured the interaction between the alloys and the cells. The subcutaneous implantation showed that the Mg-3Zn-1Mn formed the smallest gas pocket. In the six-month femoral implantation study (Mg-3Zn-1Mn excluded), the Mg-1Zn-1Mn showed the least volume loss and the steadiest degradation behaviour. It was also found to associate with better bone responses. Concluding from all the results, the Mg-1Zn-1Mn demonstrated better potential to become biodegradable orthopaedic products. This work evaluated the potentials of the new alloys and proposed some suggestions for the mismatch results. Moreover, quantitative investigation of biomechanical properties, long term degradation behaviour, and toxicity are recommended to be carried out in the future. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

Thesis (Ph.D.)--City University of Hong Kong, 2010. / "Submitted to Department of Physics and Materials Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references.

Thesis (Ph. D.)--Washington State University, May 2007. / Includes bibliographical references (p. 109-117).

No description available.

Thesis (M.S.)--California Polytechnic State University, 2010. / Title from PDF title page; viewed on May 15, 2010. Major professor: Lanny V. Griffin, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Biomedical Engineering." "April 2010." Includes bibliographical references (p. 104-108).

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 able to improve the corrosion resistance properties of magnesium alloy by suppressing the release of magnesium ions. The PCL-Mg hybrids were found to be biodegradable, biocompatible, osteoconductive, osteoinductive and mechanically matched to human bone properties. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Thesis (M.Eng.). / Written for the Dept. of Chemical Engineering. Title from title page of PDF (viewed 2009/06/15). Includes bibliographical references.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 141-152).