Additively Manufactured Metal Composites for Medical Applications. Diamond Implants

Advanced manufacturing is changing the way implants can be fabricated to build personalised implants that can be designed to fit the end user. A limitation of this advance is that few materials can be currently printed to form hard tissue implants. Diamond is a versatile material that has been explored for medical applications. The favourable properties of diamond, such as selective conductivity, durability, biocompatibility and antimicrobial capability, provide the opportunity to fabricate compatible and functional implants and devices. Additive manufacturing (AM) by building parts layer by layer has advanced medical device manufacturing to manufacture parts that have been designed based on the anatomy of the end user. One type, laser metal deposition (LMD) offers flexibility in manufacturing parts by depositing composite powders to form unique design-specific hybrid surfaces not easily attained with traditional subtractive techniques or other AM technologies. This research examined the durability and biocompatibility of a new titanium-diamond hybrid material. In particular, I assessed the feasibility of developing the titanium-diamond powder, the printability of the composite material and investigated the surface and microstructure of the final additively manufactured print. The mechanical, electrochemical, and surface properties of the printed parts were examined after optimising the matrix of printing parameters and optimum powder chemistry. Moreover, cell growth and attachment studies were used to assess the material's cytotoxicity and biocompatibility. As a result my research determined the best manufacturing protocol to develop optimal metallurgical integrity, structure and surface chemistry of the titanium-diamond parts. This was achieved by demonstrating that the powder properties, the laser metal deposition printer and the printing conditions influenced the final titanium-diamond printed structure. Hence, an optimised matrix of conditions was established to successfully print and reproduce diamond-titanium, which was not achieved before. Assessing the the printing conditions of the surface electrochemical and mechanical properties allowed me to clearly classify and benchmark the diamond-titanium properties compared to other traditionally used materials showing that titanium-diamond provided a superior surface compared to titanium. 2 The research thesis also established the application of the new titanium-diamond part for biomedical applications by assessing the material and its resultant surface topography using Chinese Hamster Ovarian (CHO), osteoblast and neural cells. When comparing to the more traditional medical materials such as titanium, the titanium-diamond was found to provide a superior interface with increased CHO and osteoblast activity and cell viability. Using neural cells, I further showed that titanium-diamond had a high viability and showed neural activity. Benchmarking this against industry standard materials used in bionics such as platinum, the charge injection was comparable if not superior suggesting that my titanium-diamond has significant promise in bionics as an electrode. To test this, I report the design and fabrication of a printed diamond-titanium microelectrode array. Finally, the thesis highlights that the protocol developed to print the titanium-diamond powder using laser metal deposition can be extended to other materials such as bio-glass. In collaboration with CSIRO, the additive manufacturing protocol developed to print the titanium-diamond samples was extended and tested using composite bioglass-titanium. As a result, I successfully printed the powder into composite surfaces.