Biocompatibility evaluation of sputtered zirconium-based thin film metallic glass-coated steels

Abstract

Thin film metallic glasses comprised of Zr48Cu36Al8Ag8 (at.%) of approximately 1.5 μm and 3 μm in thickness were prepared using magnetron sputtering onto medical grade 316L stainless steel. Their structural and mechanical properties, in vitro corrosion, and antimicrobial activity were analyzed. The amorphous thin film metallic glasses consisted of a single glassy phase, with an absence of any detectable peaks corresponding to crystalline phases. Elemental composition close to the target alloy was noted from EDAX analysis of the thin film. The surface morphology of the film showed a smooth surface on scanning electron microscopy and atomic force microscopy. In vitro electrochemical corrosion studies indicated that the zirconium-based metallic glass could withstand body fluid, showing superior resistance to corrosion and electrochemical stability. Interactions between the coated surface and bacteria were investigated by agar diffusion, solution suspension, and wet interfacial contact methods. The results indicated a clear zone of inhibition against the growth of microorganisms such as Escherichia coli and Staphylococcus aureus, confirming the antimicrobial activity of the thin film metallic glasses. Cytotoxicity studies using L929 fibroblast cells showed these coatings to be noncytotoxic in nature.

Keywords: antimicrobial activity; biocompatibility; corrosion; sputtering; thin film metallic glasses.

Figure 1

X-ray diffraction pattern of Zr₄₈Cu₃₆Al₈Ag₈ thin film metallic glass. Abbreviation: TFMG, thin film metallic glass.

Figure 2

Surface topography of Zr₄₈Cu₃₆Al₈Ag₈ thin film metallic glass. Notes: (A) Three-dimensional view, (B) two-dimensional view.

Figure 3

Scanning electron micrograph of the surface of the Zr₄₈Cu₃₆Al₈Ag₈ thin film metallic glass.

Figure 4

XRF spectra of the Zr-Cu-Al-Ag (A) thin film metallic glass and (B) target. Abbreviations: XRF, X-ray fluorescence; TFMG, thin film metallic glass.

Figure 5

Scratch test results (A) Graph of variation of normal force, frictional force, friction coefficient and acoustic emission for a load. Scratch track on TFMG for (B) first critical load (Lc1); (C) second critical load (Lc2); (D) third critical load (Lc3).

Figure 6

Load versus displacement nanoindendation curve obtained for Zr₄₈Cu₃₆Al₈Ag₈ thin film metallic glass.

Figure 7

Tafel plots for (A) blank stainless steel substrate, (B) 1.5 μm thick thin film metallic glass-coated stainless steel, and (C) 3 μm thick thin film metallic glass-coated stainless steel in simulated body fluid.

Figure 8

AC impedance studies of (A) blank stainless steel substrate, (B) 1.5 μm thick thin film metallic glass-coated stainless steel, and (C) 3 μm thick thin film metallic glass-coated stainless steel in simulated body fluid.

Figure 9

Contact between L929 fibroblast cells, (A) blank SS (control) and (B) TFMG.

Figure 10

Zone of inhibition produced against (A) Escherichia coli and (B) Staphylococcus aureus bacteria on bare stainless steel and on thin film metallic glass-coated stainless steel. Abbreviations: TFMG, thin film metallic glass; SS, stainless steel.

Figure 11

Bacterial killing efficiency versus time for a thin film metallic glass specimen against Escherichia coli and Staphylococcus aureus.

Figure 12

Field emission scanning electron micrographs showing attachment of bacteria (Escherichia coli and Staphylococcus aureus) on (A, B) stainless steel and (C, D) thin film metallic glass-coated stainless steel at different magnifications.

Figure 13

Epifluorescent micrographs of the killing effect on Staphylococcus aureus bacteria (A) initially and at (B) 6 hours and (C) 12 hours and the killing effect on Escherichia coli bacteria (D) initially and at (E) 6 hours (F) 12 hours.