Fabrication of bioactive poly(ether ether ketone) by laser melt infiltration of poly(ether ether ketone) inside the strontium apatite coatings

A versatile method to immobilize apatite nanoparticles onto PEEK substrate by using CO2 laser was demonstrated. Various strontium apatites were synthesized and dispersed in ethanol at a low concentration of citric acid. This dispersion of strontium apatites was coated on the surface of the PEEK substrate. The apatite-coated PEEK substrate was subsequently irradiated by CO2 laser with repeated multiple scanning mode. The surface temperature was monitored in real time and controlled at approximately the melting point of PEEK. The thermally fixed apatite coatings were unified with the PEEK substrate and unable to separate off. Dissolution of apatite layer in dilute acid solution revealed highly rugged surface morphologies of the PEEK substrate hidden inside the apatite coatings. From these observations we concluded that the heat-fixed apatite layer consisted of nanocomposite of apatite and PEEK. We propose a possible mechanism for the laser bonding processes of this apatite coating, that is, when the coating surface is irradiated by a CO2 laser with rapid periodic scanning mode, this irradiation initiates periodic temperature change with thermal expansion of the air on top of the apatite layer and may induce a photoacoustic effect on them, which may generate pressure waves to hold down the apatite matrix to the PEEK substrate. The heat on the apatite matrix also initiates melting of the adjacent PEEK surface and the melted PEEK polymer intrudes into the voids of the apatite matrix by capillary forces to produce nanocomposite of them. This surface-selective formation of PEEK/apatite nanocomposites on the PEEK substrate may be seen as an alternative method to the conventional surface coatings or various PEEK composite materials.