Implant surface modification using laser guided coatings: in vitro comparison of mechanical properties

Purpose: Plasma-sprayed hydroxyapatite (HA)-coated implants show failures along the coating–substrate interface due to poor bond strength. We analyzed HA coatings obtained by pulsed laser deposition (PLD) and compared them to commercially used plasma-sprayed coatings with respect to their bond strength to titanium alloy (Ti-6Al-4V), as well as surface roughness alterations produced by each of the two deposition methods. Materials and Methods: Twelve titanium alloy disks were plasma-sprayed under commercial implant coating conditions, and 24 titanium alloy disks were coated using PLD. All coatings were characterized by the presence of the different calcium phosphate (CaP) phases. The plasma-sprayed coatings (n = 12) were predominantly HA, and the pulsed laser-deposited coatings were hydroxydyapatite (n = 12) and HA coating with a tetra calcium phosphate (TTCP) phase (n = 12). The surface roughness was analyzed before and after the coating processes to assess roughness changes to the surface by the coatings. The adhesive bond strengths of these coatings to the substrate titanium alloy was tested and compared. Scheffe's test was used to analyze the statistical significance of the data. Results: The surface roughness alteration following PLD was a decrease of 0.2 μm, whereas following plasma spraying the decrease was 1.0 μm. Bond strengths were as follows [mean (SD) in MPa]: pulsed laser-deposited HA coatings: 68.3 (17.8); pulsed laser-deposited HA with tetra-CaP: 55.2 (21.1); plasma-sprayed HA 17.0 (2.8). The multivariate Scheffe's test revealed that HA coatings obtained by PLD had significantly increased bond strengths compared with the plasma sprayed ones (p≤ 0.05). Conclusions: HA coatings obtained by PLD showed greater adherence to titanium alloy. PLD offers an alternative method to produce thinner coatings with better adherence properties, along with precise control over the deposition process.