Direct Laser Writing (Dlw)-Based Biofunctionalization of Ti6al4v for Enhanced Osseointegration of Implants

Abstract

The long-term success of load-bearing implants heavily relies on the physicochemical properties of their surfaces, which play a pivotal role in establishing strong osseointegration. This crucial factor significantly influences the maintenance or complete replacement of implants over time. The aim of this study was to assess the effect of laser-based technologies, specifically Direct Laser Writing (DLW) and Laser Sintering (LS), on modifying the physicochemical properties of Ti6Al4V to improve its bioactivity. DLW was used to introduce surface topography changes, which in turn modify physical properties, while LS was employed to provide mechanical interlocking of HAp (Hydroxyapatite) coating onto the already modified surfaces. This synergistic approach, combining DLW and LS, ensures effective osseointegration while preventing HAp coating detachment. For the experiments, cylindrical discs (3 mm thick, 6 mm diameter) from Ti6Al4V rods were divided into five groups according to the type of surface modification: non-structured Ti6Al4V samples; laser structured Ti6Al4V samples (Ti64L0.25 and Ti64L0.8) and HAp-coated Ti6Al4V laser structured samples (Ti64L0.25HAp and Ti64L0.8HAp). The potential of the laser-structured, and HAp-coated surfaces was evaluated concerning morphology, wettability and friction performance against bovine bone to mimic the moment of implant insertion and cellular viability and proliferation. SEM analysis validates the precise deposition of the HAp coating outlining the underlying micro-textured profile, thus confirming the interlocking bond between the HAp phase and the structured surface. Surface wettability, assessed via sessile drop, reveals highly hydrophilic behaviour. The integrity of the bioactive coating was confirmed by rigorous high-energy ultrasonic cavitation tests and friction tests against bovine bone, demonstrating no transfer of HAp to the bone. Cell-surface interactions, evaluated by culturing MC3T3-E1 cells, reveal enhanced cell viability on both laser-structured and HAp coated surfaces. These findings are highly encouraging and suggest that the HAp-coated Ti6Al4V structured surfaces could be an effective solution for manufacturing implants with improved bioactivity and avoiding coating detachment during implantation, both of which are essential for successful osseointegration. Thus, the proposed solution employing laser-based technologies is expected to increase lifespan of implants, ultimately decreasing the need for maintenance and replacements.

Keywords: Direct Laser Writing, Hydroxyapatite, Laser sintering, Ti6Al4V