Suspended-Target Laser Deposition of Bioactive Glass on Laser-Textured Magnesium Alloy

Rapid corrosion and poor coating adhesion continue to limit the use of magnesium alloys as temporary orthopedic implants. The two-stage laser process was developed to separate the high-temperature melting of 45S5 bioactive glass (BG) from the low-melting-point AZ31 substrate. Femtosecond-laser grids with spacings of 100, 200, and 300 μm were first produced on AZ31 to provide anchoring sites. Then, the target 45S5 BG was suspended above the substrate, locally melted with CO2 laser, and transported onto the textured surface by gas jet. The 200 μm grid texture for Mg substrate with lowest water contact angle could give the highest tape-test adhesion rating (4B). At the selected deposition conditions of 20 W and 20 L·min−1, two coating cycles produced a continuous layer approximately 50.5 μm thick. Relative to bare Mg alloy, this double-layer coating increased polarization resistance from 1.20 × 103 to 1.39 × 105 Ω·cm2 and decreased corrosion current density from 8.70 × 10−4 to 5.33 × 10−6 A·cm−2. It also limited alkalization and mass loss during 28 days in simulated body fluid. As such, the double-layer surface coating supported apatite formation and improved MC3T3-E1 proliferation and alkaline phosphatase activity. These findings indicated that suspended-target deposition was able to form adherent, bioactive glass coatings on magnesium while limiting direct thermal damage to the substrate.