Fluorescence-trackable chitosan/UCNPs coatings regulate magnesium alloy corrosion and osteogenesis

Rapid corrosion and the absence of non-invasive readouts limit the clinical translation of biodegradable magnesium implants. Here, AZ31 magnesium alloy was alkali-treated and coated with chitosan (AZ31-CS) or a chitosan/upconversion nanoparticle composite (AZ31-CN; NaYF₄:Yb³⁺,Er³⁺ ) to couple corrosion control with fluorescence-guided degradation tracking. In simulated body fluid, chitosan-based coatings reduced corrosion rate, pH increase, and hydrogen evolution compared with AZ31-OH. For AZ31-CN, near-infrared excitation generated visible emission, and fluorescence intensity decreased during immersion, serving as a surrogate indicator of coating degradation. MC3T3-E1 assays demonstrated good cytocompatibility, enhanced proliferation, and increased osteogenic differentiation, evidenced by elevated ALP activity, mineralization, and upregulated ALP, OPN, and RunX2 expression. In a rat calvarial defect model, coated samples showed higher bone volume fraction and trabecular number than AZ31-OH. The chitosan/UCNPs coating provides a multifunctional biointerface integrating degradation regulation with optical monitoring for traceable magnesium-based bone implants.