Effects of the immobilization of rhBMP-2 and rhPDGF-BB to implant modified by heparin on the biologic function, osseointegration and bone regeneration

Abstract

Purpose: The aim of this study was to evaluate the effect of the immobilization of rhBMP-2 and/or rhPDGF-BB to titanium implant modified by heparin on the biologic function, osseointegration and bone regeneration in the marginal portion of the peri-implant.Materials & Methods: The heparin was coated by chemical reaction on anodized titanium surface. The surface characteristics of anodized Ti(control group) and surface-modified Ti groups (heparinized-Ti(heparin group), rhPDGF-BB-immobilized Ti (PDGF group), rhBMP-2-immobilized Ti(BMP group), and rhPDGF-BB/rhBMP-2-immobilized-Ti(PDGF/BMP group)) were investigated by a scanning electron microscopy and X-ray photoelectron spectroscopy. The release kinetics of PDGF, BMP and PDGF/BMP groups were evaluated by an enzyme-linked immunosorbent assay. MG 63 osteoblast like cell was used for in vitro study. The experiments were consisted with the viability of cells, cell proliferation by crystal violet assay, ALP activity assay, mRNA expression levels of osteocalcin and osteopontin and calcium contents. For in-vivo study, 40 implants (8.0 mm long, 4.0 mm in diameter) were fabricated. The number of specimens was eight in each group. Implants of all groups were fabricated by the same methods used in in-vitro study. The implant stability quotient (ISQ) values were measured immediately and 8 weeks after implant placement. The three-dimensional μCT images were produced to analyze the bone mineral density and bone volume of the implant-surrounding open defect area. Specimens for histometric analysis were fabricated in order to evaluate the osseointegration and bone formation. Obtained data are statistically treated using ANOVA and Mann-Whitney U test and Bonferroni test was performed as a post hoc test (p < .05).Results: The coated layer with growth factors was confirmed by XPS assay. In cell adhesion and proliferation, each group did not show a statistical significance. In cell differentiation and calcium deposition, PDGF/BMP group showed higher value than other groups (p < .05). The increase in the ISQ value was significantly higher in the BMP and PDGF/BMP group than that of other groups (p < .05). In μCT analysis, the BMP and PDGF/BMP group were significantly greater than those of other groups (p < .05), but there was no significant difference between the BMP and PDGF/BMP groups (p > .05). In the histological observation of the buccal alveolar bone levels, Jaw quadrants in BMP and PDGF/BMP groups exhibited bone formation approaching microthreads and bone remodeling around the implants. The microBICs of BMP and PDGF/BMP groups were significantly greater than those of other groups (p < 0.05), but there was not significantly different between the BMP and PDGF/BMP groups (p > 0.05). The mean percentages of BIC and intra-thread bone density within macrothreads at 8 weeks after surgery were not significantly different between groups (p > 0.05).Conclusion: Anodized Ti surface was successfully fuctionalized via a chemical method involving grafting of heparin and subsequent immobilization of rhBMP-2 and rhPDGF-BB. rhBMP-2 immobilized, heparin-grafted Ti implants seems to be a suitable delivery system to enhance osteoblast fuction and new bone formation at defect area around implant. The synergetic effects of combinations of rhBMP-2 and rhPDGF-BB were detected in this in-vitro study, but there were uncertain results in this in-vivo study.