The corrosion resistance, biocompatibility and antibacterial properties of the silver-doped dicalcium phosphate dihydrate coating on the surface of the additively manufactured NiTi alloy

Additive manufacturing (AM) of NiTi alloys has attracted significant attention for its exceptional forming precision and suitability for processing complex medical implant structures. However, challenges such as the excessive release of Ni2+, bioinertness, and insufficient antibacterial ability have emerged as primary factors impeding the application of NiTi alloy in the medical field. To address these issues, the silver-doped dicalcium phosphate dihydrate (Ag-DCPD) coating is electrochemically deposited on the LPBF-NiTi alloy surface for the first time. The study investigates the effects of varying Ag doping content (2 %, 4 %, and 6 %) on morphology, corrosion resistance, biomineralization, and long-term stability of DCPD coating using scanning electron microscopy (SEM), electrochemical analysis, and immersion tests. Results show that the 4Ag-DCPD coating exhibits the most uniform and dense surface morphology, excellent corrosion resistance, and biomineralization. The corrosion current density (I-corr) is two orders of magnitude lower than that of the LPBF-NiTi alloy matrix (from 1.1 x 10(-6) to 1.4 x 10(-8)), and a dense hydroxyapatite (HA) layer forms after immersion testing. In vitro cell experiments indicate that the 4Ag-DCPD coating maintains high cell viability, favorable cell morphology, and excellent biocompatibility. Additionally, the 4Ag-DCPD coating demonstrates effective antibacterial activity against Escherichia coli (79.75 %) and Staphylococcus aureus (69.33 %), which reduces the risk of implantation infection. Overall, the 4Ag-DCPD coated LPBF-NiTi alloy shows promising clinical application potential as a medical implant.