Study On The Biocompatibility Of Zr-based Bulk Amorphous Alloys

In this dissertation, different Zr-based bulk metallic glasses were prepared by copper mold casting. their structure was characterized by X-ray diffraction (XRD). Thermal response was investigated using differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Instron mechanical testing system was employed to evaluate their mechanical properties. The corrosion behavior of the alloys obtained was investigated in artificial body fluid by electrochemical measurements. metal ion release of different BMGs were determined in PPb (ng/ml) level with inductively coupled plasma mass spectrometry (ICP-MS) after being immersed in artificial body fluid at 37℃for 20days. The potential cytotoxicity of the BMG was evaluated through cell culture for one week followed by 3-(4,5-Dimethylthiazol-2-yl-) -2,5- diphenyltetrazo- lium bromide (MTT) assay. The fracture surface, the morphologies of the samples after corrosion, and the cell morphologies after cell culture were investigated using Scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was employed to characterize the composition and chemical states of elements in the passive film formed after potentiodynamic polarization and in the surface of the alloy samples after cell culture.The corrosion behaviors of the Zr_65-xNb_xCu_17.5Al_7.5Ni₁₀ (x=0, 2, 5%) BMGs were firstly investigated in artificial body fluid by electrochemical measurements. It was found that the Zr-based alloys with different Nb contents were spontaneously passivated and exhibited significantly low passive current density in artificial body fluid,and Nb enhanced significantly the corrosion resistance of the Zr-based BMG. On the other hand, metal ion release of different BMGs were determined in PPb (ng/ml) level with inductively coupled plasma mass spectrometry (ICP-MS) after being immersed in artificial body fluid at 37℃for 20days. It was found that the addition of Nb considerably reduced the ion release of all kinds of metals of the base system, especially Ni, Cu. This is probably attributed to the rapid formation of highly protective film because of Nb addition.The attempt to reduce or remove the cytotoxic Ni in the Zr₆₅Nb₅Cu_17.5Al_7.5Ni₁₀ BMG led to the development of a Ni-reduced BMG (Zr₆₀Nb₅Cu_17.5Ni₅Pd₅Al_7.5) and two Ni-free BMGs (Zr₆₀Nb₅Cu_22.5Pd₅Al_7.5 and Zr₆₀Nb₅Cu₂₀Fe₅Al₁₀). DSC analyses reveal that the Zr₆₀Nb₅Cu_17.5 -Ni₅Pd₅Al_7.5 and Zr₆₀Nb₅Cu₂₀Fe₅Al₁₀ BMGs exhibit high thermal stability, as indicated by the largeΔTx of 108℃and 99℃, respectively. In addition, preferential formation of quasicrystals occured in all of the three BMGs upon annealing.Studies on the compressive mechanical behavior and fracture feature revealed that the three BMGs of Zr₆₅Nb₅Cu_17.5Al_7.5Ni₁₀, Zr₆₀Nb₅Cu_22.5Pd₅Al_7.5 and Zr₆₀Nb₅Cu₂₀Fe₅Al₁₀ all exhibit superior strength with fracture strength of 1697MPa,1724 MPa and 1795MPa,and improved plasticity with plastic strain as high as 13.2%,3.58%and 9.5%, respectively. The corrosion behaviors of the BMGs obtained were investigated in artificial body fluids by electrochemical polarization. It was found the BMGs all exhibit quite low passive current density and high pitting potential, indicating excellent corrosion resistance. XPS analysis revealed that the passive films formed after anodic polarization was enriched in zirconium, niobium and aluminum oxides, which are attributed to the improvement of corrosion resistance.The potential cytotoxicity of the two Ni-free BMGs was evaluated through cell culture for one week followed by 3-(4,5-Dimethylthiazol-2-yl-)-2,5-diphenyltetrazolium bromide (MTT) assay. It was found that The Ni-free BMGs show an absorbance similar to or even higher than that of Ti-6Al-4V alloy, implying that the BMGs have higher cell viability and proliferation activity. SEM observation demonstrates that NIH/3T3 cells can closely adhere and well extend on the surfaces of the Ni-free BMGs. This indicates that the BMGs developed exhibit excellent biocompatibility. XPS analysis revealed that the surface of the alloy samples after cell culture was enriched in highly biocompatible Zr-, and Nb- oxides, which account for the reduced cytotoxicity or good biocompatibility of the Ni-free BMGs.