Engineering the “Pluripotency” of Zr-based Bulk Metallic Glasses as Biomedical Materials

Bulk metallic glasses (BMGs) are a family of novel alloys with amorphous microstructures. The combination of their excellent mechanical properties, good chemical stability, high thermal formability, and general biocompatibility has brought up new opportunities for biomaterials. Research in this dissertation was focused on exploring multiple biomedical functionalities of Zr-based BMGs over a wide spectrum, combining materials and biological characterizations, through experimental and computational approaches. Four distinct yet interconnected tasks were endeavored, involving inflammation, hard-tissue implant, soft-tissue prosthesis, and pathogenic infection.

The inflammation that can be potentially triggered by Zr-based BMGs was investigated using macrophages. Lower level or comparable macrophage activations on were observed on Zr-based BMGs in comparison to commercial bio-alloys. The environmental stimuli can induce profound effects on macrophage activation in addition to substrate stimulation. Meanwhile, microstructure of the substrate was found to affect macrophage responses.

Ion implantation was employed to engineer the surface of a Zr-Al-Ni-Cu-Y BMG to enhance bone integration. Low energy Ca-ion implantations were adopted, which altered surface materials properties and introduced enhanced bone-forming cell adhesion. With higher fluence Ar-ion implantations, nano-sized Ar-bubbles were doped in the surface region of the Zr-based BMG, causing surface softening, which can be subsequently sensed by bone-forming cells. Cells exhibited less established adhesion and actin filament formation, whereas, higher rate of proliferation on surfaces with lower stiffness.

The potential of a Zr-Al-Fe-Cu BMG as a stent material was examined for the first time. The advantageous materials properties of the Zr-based BMG were revealed, including high strength, low elastic modulus, high elastic limit, and high biostability. Cell culture assays illustrated stronger adhesion and faster coverage of endothelial cells and slower growth of smooth muscle cells on the Zr-based BMG than on 316L stainless steel, which suggested promoted re-endothelialization and potentially lower risk of restenosis on the Zr-based BMG.

The capability to fight implant infections stacked additional biomedical benefits to Zr-based BMGs. The potency of Zr-Al-Ni-Cu(-Y) and Zr-Al-Co-Ag BMGs to inhibit bacterial growth were demonstrated against Gram positive Staphylococcus aureus. The biocidal effects of these Zr-based BMGs were related to the heavy-metal-ion release and microstructure.