Abstract: BACKGROUND: Zirconium implants are used in the field of oral implants due to good biocompatibility. Because of its biological inertness, the surface of the implant needs to be modified to improve its bioactivity. Hydroxyapatite coating is a widely used modification technique for implant surfaces.
OBJECTIVE: The phase-transition lysozyme was modified on the zirconia surface, based on which a hydroxyapatite coating was constructed to confer its bioactivity and improve the success rate of implants.
METHODS: The phase-transition lysozyme solution was dropped onto the surface of the smooth zirconia specimen for 2 hours. The phase-transition lysozyme-modified zirconia specimen was incubated in the simulated body fluid for 10 days to induce the hydroxyapatite coating. The contact angle, roughness and mechanical properties of unmodified zirconia specimens, phase-transition lysozyme-modified zirconia specimens and hydroxyapatite-coated zirconia specimens were tested. The three kinds of zirconia specimens were co-cultured with MC3T3-E1 cells, separately. The cell proliferation and alkaline phosphatase activity were detected. Unmodified zirconia specimens and hydroxyapatite-coated zirconia specimens were co-cultured with MC3T3-E1 cells, separately, and cell adhesion was observed under a scanning electron microscope.
RESULTS AND CONCLUSION: (1) The contact angle of the hydroxyapatite coating group was smaller than that of the unmodified group (P < 0.05), and the roughness was greater than that of the unmodified group (P < 0.05). There was no significant difference in the Vickers hardness and fracture strength of the three groups of specimens (P > 0.05). (2) CCK-8 assay showed that the absorbance values of cell proliferation in the hydroxyapatite coating group on 3, 5, and 7 days of culture were higher than those in the phase-transition lysozyme group and the unmodified group (P < 0.05). The alkaline phosphatase activity of the hydroxyapatite coating group was higher than that of the phase-transition lysozyme group and the unmodified group at 7 and 14 days of culture (P < 0.05). (3) Scanning electron microscope showed that MC3T3-E1 cells adhered closely to the surfaces of the two kinds of zirconia materials after 12 hours of culture. After 3 days of culture, the number of cells on the surfaces of the two materials increased, and the number of cells in the hydroxyapatite coating group was high and cell junctions appeared. (4) The results show that for zirconia all-ceramic materials, the preparation of hydroxyapatite coating on the basis of phase-transition lysozyme modification can improve its hydrophilicity and cytocompatibility without affecting the mechanical properties of the material.

Key words: bone, material, zirconium implant, surface modification, phase-transition lysozyme, hydroxyapatite, biomimetic mineralization