Topological design of porous titanium alloy scaffolds for additive manufacturing of orthopaedic implant applications
Creators: name: YUAN, Li
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400302
subject: Biomaterials
classificationCode: 401607
subject: Metals and alloy materials

description: With the development of material science and biological technology, new biocompatible materials such as titanium alloys are gradually used more and more in the manufacturing of medical implants to replace conventional materials including stainless steel and Co-Cr alloys. These new materials showed excellent performances in the load-bearing implant applications and can be used as a replacement of bones and joints in clinical surgeries. Nowadays, with the assistance of additive manufacturing technology, medical implants with complicated topological structures and shapes which were previously not manufacturable with conventional manufacturing approaches are designed and fabricated. It not only significantly increases the feasibility of bone/joint replacement by biomedical materials but also has dramatic influences on the development of modern medicine.<br><br>
However, the design of new implants is a challenging task in order to ensure the high quality of implants to avert both biocompatible and mechanical risks. Firstly, when designing the implants, the properties of the biomaterials should be considered, including the physical properties (e.g. density, elastic modulus) and the chemical properties (e.g. biocompatibility). Secondly, the potential negative effects on bone defect treatment should be examined to avoid issues caused by any inappropriate mechanical behaviour of materials. Finally, and more importantly, due to the mismatch of elastic modulus between natural bone and the implants, stress shielding which is another major mechanical issue of metallic implants has to be minimized. A large mismatch of elastic modulus may lead to bone atrophy and implant loosening. 
A new porous titanium scaffold which exhibits an architecture mimicking that of human bones was developed in this research for the application of implants. The scaffold will be constructed by multiple unit cell sizes, which enables adjusting the elastic modulus to meet different requirements. The porous structure can provide the necessary support for cells to proliferate and maintain their differentiated functions, and their structure defines the ultimate shape of the new bone created during growth processes.<br><br>
A comprehensive literature review was conducted by summarizing the state of the art technologies and critical issues associated with the results of the biomedical porous material fabricated with different methods. Different triply periodic minimal surface (TPMS) structures and their characteristics were investigated, especially for gyroid structures. Three-dimensional modelling of gyroid structure (unit cell and small scaffold) were conducted for further analysis of the design. To address the issue of the higher elastic modulus of Ti, a 3mm Network-based gyroid unit cell and small scaled scaffolds previous designed were analysed in regard to the mechanical behaviours. Specifically, the models were optimized for evaluating the Young modules, in order to meet the certain requirement. In addition, a 3mm cubic open-cellular structure was developed as the comparison group in this simulation.