Comparative study on the biodegradation behavior of octacalcium phosphate and hydroxyapatite coated WE43 magnesium alloys.

Abstract

Objective: This study aimed to compare the degradation behavior and protection mechanisms of biodegradable WE43 alloys coated with two different calcium phosphate (Ca-P) phases-octacalcium phosphate (OCP) and hydroxyapatite (HA)-to identify an effective surface modification strategy for biodegradable material applications.

Methods: OCP and HA coatings were deposited on WE43 substrates and characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The degradation behavior was evaluated through immersion tests in Hanks' balanced salt solution (HBSS) by monitoring surface morphology, magnesium ion release, and pH variation over time.

Results: XRD confirmed the successful formation of OCP and HA phases, while SEM revealed distinct morphologies: porous, plate-like structures for OCP and dense, compact layers for HA. Immersion testing demonstrated that both coatings reduced magnesium ion release and stabilized the solution pH compared with uncoated WE43. The HA coating exhibited superior corrosion resistance, maintaining the lowest Mg²⁺ release and most stable pH, attributed to its high crystallinity, compact structure, and self-healing apatite reprecipitation during immersion.

Conclusion: Both Ca-P coatings improved the corrosion resistance of WE43 alloy; however, the HA layer provided markedly enhanced and more stable protection. The HA-coated WE43 alloy shows great potential for biodegradable implant applications requiring controlled degradation and sustained biocompatibility.