# Surface Activation Using Atmospheric Plasma to Improve PHB Coating Adhesion and Corrosion Resistance of AZ91D Magnesium Alloys

## TL;DR

This study shows that plasma treatment improves PHB coating adhesion and corrosion resistance on magnesium alloys for medical implants.

## Contribution

The novel use of atmospheric plasma treatment on both substrate and polymer to enhance coating durability and biocompatibility.

## Key findings

- A 5-minute plasma treatment on the substrate significantly improved wettability and surface free energy.
- Plasma-treated PHB coatings reduced the corrosion rate from 4.083 to 0.001 mm/year in simulated physiological conditions.
- Pull-off tests confirmed stronger adhesion between the coating and substrate after plasma treatment.

## Abstract

Polyhydroxybutyrate (PHB) is considered a coating material capable of limiting the corrosion of biodegradable metallic implants due to its biocompatibility and ability to form a physical barrier. In this study, PHB was deposited on commercial AZ91D magnesium alloy using the spin coating technique. To improve adhesion at the polymer–substrate interface, the magnesium substrates were subjected to atmospheric pressure plasma treatment for different exposure times (5, 10, or 15 min) before coating. The optimal treatment time of 5 min significantly increased substrate wettability and surface free energy, facilitating stronger PHB adhesion. In addition, the PHB coatings were subjected to atmospheric pressure plasma treatment for 5, 10, or 15 s to evaluate potential surface modifications. Corrosion behavior under simulated physiological conditions was assessed via potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in HANK’s solution at 37 °C. Pull-off tests were used to evaluate the adhesion strength between the coating and the substrate under each treatment condition. The results showed a significant decrease in the corrosion rate (Vcorr), from 4.083 mm/year for bare Mg-AZ91D to 0.001 mm/year when both the substrate and the polymer received plasma treatment. This indicates that the treatment modifies surfaces and improves interfacial bonding, enhancing polymer–metal interaction and producing durable, biocompatible coatings for medical implants.