Novel fast manufacturing approaches for biocompatible structures

<p>Additive Manufacturing exhibits many advantages over traditional manufacturing and processing approaches, such as low energy and minimal raw material consumption, simplification in manufacturing procedures and customised production. The latter is of particular significance to biomedical devices such as orthopedic implants, which can satisfy the specific requirements for individual patient. Titanium (Ti) and its alloys are the most widely used materials for load-bearing implants owning to their high biocompatibility and mechanical properties. However, the release of toxic metal ions and wear debris may incur undesirable side-effects after Ti being placed into the human body. Tantalum (Ta), a biocompatible metallic biomaterial, exhibits high in-vivo corrosion and wear resistance, and excellent osseointegration properties. Nevertheless, the high melting temperature of Ta (3017 degrees Celsius) is a critical technical challenge for manufacturing fully dense Ta implant structures through conventional processing approaches, which thus increases production costs and limits commercial applications.</p> <p>In order to achieve ideal biomedical implant materials with excellent osseointegration, mechanical properties, corrosion resistance, most importantly, to be biocompatible, new and feasible manufacturing methods for Ta-based implant materials are highly desired. Cold spray, an additive manufacturing technique provides a promising solution to deposit metallic coatings on Ti implants with a variety of benefits, including low processing-temperature and solid-state deposition for producing Ti/Ta mixtures without metallurgical phase transformation.</p> <p>In this thesis, Ti-Ta composite coatings on Ti-based substrates (Ti-6Al-4V) were developed. Chemical and physical features were examined through electron microscopy. Hardness was evaluated by micro-hardness and nano-indentation tests. Corrosion resistance was analysed by immersion studies and potentiodynamic polarisation curves. In particular, in-vitro biocompatibility was assessed using GPE86 (mouse fibroblast) cell line through live/dead assay and cytotoxicity analysis. Moreover, cell responses to cold sprayed Ti-Ta composite were further evaluated and the mechanisms of cell-materials interaction were explored. Results illustrated cold spray is able to create Ti-Ta composite coatings with sufficient hardness, corrosion resistance and no signs of cytotoxicity for biomedical uses. In-vitro biocompatibility study revealed the significantly high cellular adherence and growth on cold sprayed Ti-Ta composite coatings especially during the initial few hours of cell culture. The mechanism of high cellular adherence on Ti-Ta composite was ascribed to the intimate contact between Ti and Ta that may create the electrochemical cells to adapt cell growth. Outcomes of the thesis hold a promise for practical applications of cold spray for manufacturing of implantable medical devices.</p>