Design, manufacture and validation of biocompatible Bulk Metallic Glasses (BMGs) for bioengineering applications

Biomedical alloys are central in both research and clinical translation for the development of solutions and devices to be deployed to improve health and quality of life. Bulk metallic glasses (BMGs) offer a compelling combination of high specific strength, relatively low elastic modulus, good corrosion resistance and near-net-shape processability, making them particularly attractive for orthopaedic applications. However, a critical challenge remains in fine-tuning their multifunctional properties, including mechanical response, electrochemical stability, and cytocompatibility of alloys. This thesis investigates two types of BMGs: (1) bioresorbable (Ca-Mg-Zn) and (2) non-bioresorbable (Ti-Zr-Cu-Pd) alloys, using a comprehensive strategy integrating thermodynamic modelling, microstructural characterisation, and experimental validation approaches. The role of amorphicity-to-crystallinity ratio was also investigated. For Ca-Mg-Zn BMGs, compositions from Ca-rich and Zn-rich domains were selected using the deep-eutectic concept. Ca-rich BMGs displayed superior glass-forming ability (GFA) and bone-like stiffness in the amorphous state, while Zn-rich alloys were more corrosion-resistant. Controlled heat treatment enabled partial and full crystallisation, revealing that devitrification consistently accelerated degradation and mechanical performance of BMGs was strongly dependent on their microstructures. In the Ti-Zr-Cu-Pd system, annealing produced a nanocrystalline BMG composite (BMGC) with enhanced compressive strength and osteoblastogenesis, attributed to a thinner, ZrO2-rich oxide layer with higher surface energy and reduced CuxO content. Moreover, thermodynamic modelling using the PHSS parameter effectively predicted GFA of this quaternary system, providing a cost-effective tool for flexible exploration of new compositions. A new cost-effective Ti42Zr8Cu42Pd8 BMG was subsequently proposed, lowering raw-material costs by ~28.5% while preserving high compressive strength (~2 GPa) and biocompatibility. Overall, this thesis provides a framework for tailoring BMGs performance through controlled crystallinity and compositional design. This strategy connects thermodynamic screening with manufacturable solutions, paving the way for patient-specific, performance-optimised biomedical implants.