Laser irradiation as an easy-to-apply method for Ti-based implant materials enhancement

Abstract

Hard-tissue replacements are most commonly made from the Ti-based materials, such as commercially pure titanium (CP-Ti) and Ti-6Al-4V (mass%) alloy, because of their exceptional biocompatible properties combined with the excellent corrosive and mechanical characteristics [1]. More recently, efforts have been made to additionally enhance the properties of the metallic implants through the careful selection of the alloy composition and surface modification technics [2,3]. As a result, second-generation β-type Ti alloys, containing non-toxic elements, have been developed. One of the promising β-type implant alloys is Ti-13Nb-13Zr (mass%). Even though the corrosion resistance and mechanical properties of this alloy are improved in comparison to the commonly used metallic implant materials, its biocompatible and osseointegration properties can and must be additionally enhanced. For that purpose several surface modification technics can be used, however, laser irradiation stands out as the most promising one. Because of that scope of the present research was to investigate the possibility of successful surface modification of the most commonly used implant material, i.e. CP-Ti, and the second-generation Ti-13Nb-13Zr alloy by utilizing the easy-to-apply laser irradiation method in order to obtain improved implant tribocorrosive properties and enhanced biointegration and bioactivity. Laser surface modifications were conducted using the Nd:YAG system in the air and argon atmosphere under different laser output energies. Implant materials surface morphologies after the laser irradiation treatment were investigated using the field-emission scanning electron microscopy (FE-SEM) and optical profilometry, while the impact of the laser irradiation on the implant materials surface characteristics were examined using the energy dispersive spectrometry (EDS) and microhardness measurements. Conducted research showed that utilization of the Nd:YAG laser irradiation resulted in significant alterations of the CP-Ti and Ti-13Nb-13Zr alloy surface chemistry, morphology and microhardness. Laser irradiation of both investigated materials led to the formation of visible microcracks and hydrodynamic effects in the central part of the irradiated area, while traces of melted and solidified material were observed at its periphery. More pronounced morphological changes were induced during the laser irradiation in an argon atmosphere, while a higher degree of texturing was recorded at the surface of the Ti-13Nb-13Zr alloy. At the irradiated surfaces, the formation of the oxide layer, predominantly composed of Ti-oxide particles, was detected. Surface oxides are desirable since their presence can improve the implant material bioactivity with a simultaneous increase of the tribo-corrosive properties through the formation of the hard corrosion resistance surface film. Laserinduced chemical and morphological alterations were more distinctive in the case of the Ti-13Nb- 13Zr alloy.