Calcium phosphate–phosphoserine composite coatings enhance corrosion resistance and cytocompatibility of 3D‑printed WE43 magnesium alloy for orthopaedic applications

Biodegradable magnesium (Mg) alloys have emerged as promising implant materials; however, their clinical application remains constrained by high corrosion rates. This study addresses this limitation through surface modification of 3D–printed WE43 Mg alloy using a composite coating comprising calcium phosphate (CaP) and phosphoserine (PS) fabricated via a wet chemistry approach at varying molar ratios. Structural and chemical analyses were conducted using X–ray diffraction (XRD) and X–ray photoelectron spectroscopy (XPS) to examine the effect of PS incorporation on dicalcium phosphate dihydrate (DCPD) and octacalcium phosphate (OCP) phases. PS addition to DCPD reduced crystallinity, increased surface roughness, and decreased the contact angle, thereby enhancing wettability. The incorporation of PS into OCP slightly alters the XRD peak intensities, suggesting a modification in crystallinity. XPS analysis confirmed chemical bonding between the coating and substrate, resulting in enhanced interfacial adhesion. The DCPD–PS–WE43 (1:1) and OCP–PS–WE43 (1:2) compositions exhibited the highest adhesion strengths as measured by shear test (5.00 ± 0.41 N and 10.33 ± 0.60 N, respectively). Electrochemical analyses demonstrated that coatings with higher adhesion strength exhibited lower corrosion current densities and reduced corrosion rates. In vitro testing using MC3T3–E1 pre–osteoblasts showed improved cell morphology and proliferation on OCP–PS–WE43 (1:2) compared with uncoated alloy. These findings indicate that the OCP–PS–WE43 (1:2) composite coating enhances both corrosion resistance and biocompatibility, supporting its potential as a surface modification for next–generation biodegradable orthopaedic implants.