Effect of Initial Dissolution Behavior on Cellular Response in Uncoated and Calcium Phosphate-Coated Magnesium Alloy

Biodegradable magnesium (Mg) alloys offer a promising alternative to permanent orthopedic implants due to their bone-like mechanical properties, biocompatibility, and complete degradation in vivo. However, the rapid dissolution that occurs during the early stages of immersion remains a critical challenge in their feasibility as a resorbable implant. In this work, RF magnetron-sputtered calcium phosphate (CaP) coatings of ∼0.5 μm and ∼1 μm thickness corresponding to 15- and 30-hour deposition times, respectively, were applied to a WE22 alloy. The effect on initial dissolution behavior, ion release, and cellular responses was evaluated when immersed for 1, 7, and 24 h. Uncoated WE22 exhibited rapid dissolution with substantial Mg²⁺ release (∼18 mg/L at 24 h) and raised pH levels from ∼7 to ∼8.8. While ∼0.5 μm CaP coatings reduced these effects, they showed greater mass gain and protein adhesion, suggesting potential coating inhomogeneity or nano-defects trapping corrosion constituents. The ∼1 μm coating provided notable corrosion resistance and maintained a dissolution environment most comparable to physiological conditions. U-2 OS cell viability assessments, including RR assay, DAPI staining, and SEM study, determined that cytotoxicity was concentration-dependent across all time points (p < 0.001), with 100% corrosion medium and uncoated WE22 most detrimental to viability. These findings demonstrate the potential for CaP coatings to effectively delay or control the initial corrosion of WE22 while providing enhanced biocompatibility compared to the uncoated substrate.