Mussel-inspired silica, strontium, and fluoride-doped hydroxyapatite/BMP-2 composite coating: a new strategy to enhance the bioactivity of zirconia implants

Abstract

Zirconium dioxide (ZrO₂, zirconia) is widely regarded as an ideal material for dental implants due to its superior aesthetics, biocompatibility, and mechanical performance. However, its bioinert nature limits its clinical potential, leading to poor integration between the implant and surrounding bone tissue. Inspired by mussel adhesive proteins, we constructed a composite coating of silicon, strontium, and fluoride-doped hydroxyapatite (with theoretical dopant concentrations) and bone morphogenetic protein-2 (BMP-2) on zirconia surfaces using a polydopamine-assisted immersion method. The surfaces were pre-treated using a chemical deposition method to enhance the coating adhesion. The modified surfaces were characterized using field emission scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and an optical contact angle meter. The composite coating significantly promoted the attachment and proliferation of pre-osteoblastic MC3T3-E1 cells. After 14 days, cells on the coated surfaces exhibited higher mRNA expression of runt-related transcription factor-2 (Runx2), alkaline phosphatase (ALP), and osteocalcin (OCN). In vitro ALP staining and alizarin red S staining showed enhanced ALP activity and calcium nodule formation. Surface pre-treatment significantly improved coating adhesion strength. This bioactive modification, with the dopant concentrations of Si/Sr/F in hydroxyapatite being theoretical design values, enhances zirconia implant bioactivity, offering a novel approach to improve clinical outcomes.