Poly(dopamine)-assisted immobilization of Arg-Gly-Asp peptides, hydroxyapatite, and bone morphogenic protein-2 on titanium to improve the osteogenesis of bone marrow stem cells.

Osteointegration of titanium implants in bone defects is clinically important for long-term performance of orthopaedic implants. In this work, we developed a facile and effective "one-pot" deposition method based on dopamine polymerization for the development of cell-adhesive, osteoconductive, and osteoinductive titanium implants. Arg-Gly-Asp (RGD)-conjugated polymers, hydroxyapatite (HAp) nanoparticles, and bone morphogenic protein-2 (BMP-2) were mixed with an alkaline dopamine solution, and then, titanium substrates were immersed in the mixture for an hour. During poly(dopamine) coating, the three types of bioactive substances were immobilized on the titanium surfaces. Our results indicate that RGD conjugation enhanced the adhesion of human bone marrow stem cell line, while HAp incorporation facilitated cellular osteodifferentiation. The immobilization of BMP-2 induced the osteogenesis of the stem cells, indicated by reverse-transcriptase polymerase chain reaction (RT-PCR) analysis. The mineralization on the deposited substrates was also enhanced greatly. This functionalized layer on titanium substrate promoted mesenchymal stem cell to osteoblast and improved osteogenic differentiation and mineralization. In conclusion, the surface modification method shows a great potential for enhancement of osteointegration of orthopaedic and dental implants.