Electrophoretic Deposition of Nanocrystalline Calcium Phosphate Coating for Augmenting Bioactivity of Additively Manufactured Ti-6Al-4V

Abstract

Additive manufacturing (AM) is being widely explored for engineering biomedical implants. The microstructure and surface finish of additively manufactured parts are typically different from wrought parts and exhibit limited bioactivity despite the other advantages of using AM for fabrication. The aim of this study was to enhance the bioactivity of selective laser melted Ti-6Al-4V alloy by electrophoretic deposition of nanohydroxyapatite (nanoHAp) coatings. The deposition parameters were systematically investigated after the coatings were deposited on the as-manufactured surface or after polishing the surface of the additively-manufactured sample. The surfaces were coated with nanoHAp suspended in either ethanol or butanol using different voltages (10, 30, or 50 V) for varied deposition times. The formation of the nanoHAp coating was confirmed by Fourier-transform infrared spectroscopy and X-ray diffraction. Microstructural analysis revealed that several conditions of the coating led to crack formation. The coated samples were subsequently heat-treated to improve the integrity of the coating. Heat treatment led to crack formation in several conditions due to thermal shrinkages. Coatings prepared using butanol were more uniform and had minimal cracks compared with the use of ethanol. Nanoindentation confirmed good stability and integrity of the nanoHAP coatings on the as-manufactured and polished surfaces. The coating on the as-manufactured sample exhibited higher hardness and lower elastic modulus as compared with the coating on the polished sample. In vitro study revealed that the nanoHAp coating markedly enhanced the attachment, proliferation, and differentiation of preosteoblasts on the alloy. These results provide a viable route to enhancing the bioactivity through deposition of nanoHAp with important implications for engineering additively manufactured orthopedic and dental implants suitable for better clinical performance.