Ultrasonic Atomization Spray Coating of PCL on an Mg-Based Alloy Enhanced by Plasma Electrolytic Oxidation for Improved Adhesion, Corrosion Resistance, and Biocompatibility

This study explores the impact of plasma electrolytic oxidation (PEO) on polymer adhesion and corrosion resistance of WE43 magnesium alloy, a promising candidate for biodegradable stents. Ultrasonic atomization spray coating is used to apply polycaprolactone (PCL) over WE43 substrates treated with varying PEO durations (2, 5, and 10 min). The PEO process generates a rough Mg/O transition layer that enhances mechanical interlocking with the PCL, thereby improving adhesion and corrosion resistance. Microstructural changes, including surface roughness, porosity, and oxide layer thickness, are analyzed using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. In vitro corrosion resistance is evaluated via potentiodynamic polarization (PDP) and hydrogen evolution in phosphate-buffered saline. Scratch testing is performed to quantify polymer adhesion. Results show that longer PEO treatments, particularly the 10 min duration, result in more uniform PCL coverage and significantly better corrosion protection. Hydrogen gas evolution is reduced by more than threefold, and corrosion rates are substantially lowered. Scratch test data indicate a more than threefold increase in polymer adhesion to WE43 with PEO pretreatment. Overall, PEO pretreatment significantly enhances the performance of PCL-coated WE43 by improving coating-substrate bonding and reducing corrosion, supporting its potential as a functional surface modification for next-generation biodegradable stents.