Characterization, adhesion strength and in-vitro cytotoxicity investigation of hydroxyapatite coating synthesized on Zr-based BMG by electro discharge process

Abstract

In this study, biocompatible hydroxyapatite (HA) coatings by HA mixed electro discharge coating (HA-EDC) process was synthesized on the Zr-based bulk metallic glass (BMG) surface. The aim is to promote the cells proliferation by synthesizing a strongly adhered oxide and carbide coating on the Zr-based BMG and blocking the release of Ni and Be in the BMG alloy. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD) were employed to characterize the surface morphology, elemental compositions and the phases present in the electro-discharge coated Zr-based BMG. SEM analysis presented the formation of various micro and nano-sized craters, porosities and cracks on the coated and uncoated BMG surface. The EDX and XPS results depicted the migration of HA elements (Ca, P, O and K) to the workpiece surface, which replaced the Ni and Be in the Zr-based BMG alloy. The SEM cross-section revealed the formation of the nanoporous coating of about 27.2 μm thick and a reduced recast layer thickness. The XRD characterization identified the phases like CaZrO3, ZrO2, Ca5(PO4)3OH, ZrC and TiC formed on the coated BMG surface. A strongly adhered HA coating with adhesive failure of about 132 N load was achieved during the scratch test. A cytotoxicity study using an in-vitro 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) Assay revealed a significant rise in cells viability on the coated Zr-based BMG specimen.