Effect of oligonucleotide mediated immobilization of bone morphogenic proteins on titanium surfaces

The aim of the present study was to test the hypothesis that oligonucleotides can be used for anchorage and slow release of osteogenic growth factors such as BMP to enhance the osteogenic activity of a titanium implant surface. Strands of 60-mer non-coding DNA oligonucleotides (ODN) were bound to an acid-etched sandblasted cp Ti-surface by nanomechanical fixation using anodic polarization. RhBMP2 that had been conjugated to complementary strands of DNA oligonucleotides was then bound to the anchored ODN strands by hybridization. Binding studies showed a higher binding capacity compared to non-conjugated BMP2. Long term release experiments demonstrated a continuous release from all surfaces that was lowest for the conjugated BMP2 bound to the ODN anchor strands. Proliferation of human bone marrow stroma cells (hBMSC) was significantly increased on these surfaces. Immunofluorescence showed that hBMSC grown on surfaces coated with specifically bound conjugated BMP2 developed significantly higher numbers of focal adhesion points and exhibited significantly higher levels of transcription of osteogenic markers alkaline phosphatase and osteopontin at early intervals. Biological activity (induction of alkaline phosphatase) of conjugated BMP2 released from the surface was comparable to released non-conjugated BMP2, indicating that conjugation did not negatively affect the activity of the released molecules. In conclusion the present study has shown that BMP2 conjugated to ODN strands and hybridized to complementary ODN strands anchored to a titanium surface has led to slow growth factor release and can enhance the osteogenic activity of the titanium surface.