Two step porosification of biomimetic thin-film hydroxyapatite/alpha-tri calcium phosphate coatings by pulsed electron beam irradiation

Abstract

Here we show a new and effective methodology for rapid/controllable porosification of thin-film ceramics, which may be applied in medical devices/electronics and membrane nano-filtration. Dense hydroxyapatite applied to Ti6Al4V by plasma-assisted PVD was electron-beam irradiated to induce flash melting/boiling. Deposited coatings contained amorphous and nano-crystalline/stoichiometric hydroxyapatite (~35 nm). Irradiation (voltages 13–29 kV) led to ablation (up to 45% mass loss) and average/maximum pore areas from (0.07–1.66)/(0.69–92.53) μm², mimicking the human cortical bone. Vitrification above 1150 °C formed (~62–30 nm) crystallites of α-Tri Calcium Phosphate. Unique porosification resulted from irradiation-induced sub-surface boiling and limited thermal conductivity of hydroxyapatite, causing material to expand/explode through the more quickly solidified top surface. Commercially applicable, roughened Ti6Al4V exacerbated the heating and boiling explosion phenomenon in certain regions, producing an array of pore sizes. Scaffold-like morphologies were generated by interconnection of micron/sub-micron porosity, showing great potential for facile generation of a biomimetic surface treatment for osseointegration.