Effect of polyphosphoric acid pre-treatment of titanium on attachment, proliferation, and differentiation of osteoblast-like cells (MC3T3-E1)

Purpose: To evaluate the effect of polyphosphoric acid (PPA) pre-treatment of titanium (Ti) on the initial attachment, proliferation, and differentiation of mouse osteoblast-like cells (MC3T3-E1). Materials and methods: Adsorption of PPA to Ti was achieved by immersing Ti disks (15 mm in diameter) into 0, 1, and 10 wt% PPA and 10 wt% orthophosphoric acid (OPA) for 24 h. On each pre-treated Ti disk, 5.0 × 10⁴ MC3T3-E1 cells were seeded, and 1, 3, and 5 h later cell attachment was evaluated. Cell proliferation was also determined 1, 3, and 5 days after cell seed. Cell differentiation was evaluated 5, 10, and 15 days after cell seed using osteoblast marker gene expression. Total RNA was purified from each culture and Type-I collagen, alkaline phosphatase, and osteocalcin mRNA expression levels were measured by real-time reverse transcription polymerase chain reaction. Results: Adsorption of PPA or OPA to Ti significantly accelerated initial cell attachment at every time point (P<0.0001). As with cell attachment, cell proliferation was also accelerated on the PPA-treated Ti disks in a dose-dependent manner at every time point (P<0.0001). However, OPA-treated Ti disks did not enhance the cell proliferation. Regarding osteoblastic differentiation, PPA-treated Ti significantly accelerated the Type-I collagen gene expression at 5 and 10 days after cell seed. Regarding alkaline phosphatase and osteocalcin gene expression, no significant difference was found among the different Ti surface conditions. Conclusion: The accelerated cell behavior following Ti pre-treatment with PPA is a promising new strategy to fabricate bioactive Ti implants.