Polycaprolactone coating with varying thicknesses for controlled corrosion of magnesium

Controlled corrosion of magnesium is critical for its clinical application to orthopedic devices. For this purpose, we coated the surface of Mg with a biodegradable polymer, polycaprolactone (PCL) and attempted to control the Mg corrosion with varied coating thicknesses in a reproducible manner. As we increased the coating thickness from 0 to 13.31 ± 0.36 μm, the volume of hydrogen gas and amount of Mg ions, the indicators of Mg corrosion, decreased by almost half from 0.57 mL/cm²/day and 0.55 mg/day to 0.20 mL/cm²/day and 0.26 mg/day, respectively. However, the elemental compositions on the surface revealed possible detachment of polymer coating and rapid water absorption at the early stage of corrosion for all coating thicknesses. Therefore, the lessons learned from this study suggest pre-treatment of the Mg surface for better polymer-metal adhesion, as well as preparation of the coating with lowered porosity as a stronger water-permeation barrier, to eventually allow precise control on Mg corrosion.