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.

Dopamine-assisted immobilization of hydroxyapatite nanoparticles and RGD peptides to improve the osteoconductivity of titanium.

Hydroxyapatite (HAp) coating on orthopedic implants is a common strategy to increase osteointegration. In this work, a facile deposition method based on dopamine polymerization was developed for preparation of HAp-coated titanium substrates for orthopedic applications. Nanostructured HAp was mixed with an alkaline dopamine solution and then deposited onto titanium to form a dopamine/HAp ad-layer. The deposition of dopamine/HAp greatly enhanced the adhesion, proliferation, and mineralization of osteoblasts. Furthermore, RGD-containing peptides were immobilized to dopamine/HAp coated titanium and further enhanced cell adhesion and osteogenic differentiation. In conclusion, this facile dopamine-assisted surface modification method shows a great potential for orthopedic and dental applications.

Dopamine-assisted immobilization of poly(ethylene imine) based polymers for control of cell-surface interactions.

Non-fouling coatings play a critical role in many biomedical applications, such as diagnostic assay materials, biosensors, blood contacting devices and other implants. In the present work we have developed a facile, one step deposition method based on dopamine polymerization for preparation of non-fouling and biotinylated surfaces for biomedical applications. Poly(ethylene imine)-graft-poly(ethylene glycol) co-polymer (PEI-g-PEG) was mixed with an alkaline dopamine solution and then deposited onto different substrates. The dopamine coatings formed by this method were characterized by X-ray photoelectron spectroscopy (XPS), and the results indicated successful deposition of PEG. The resultant dopamine coatings formed on tissue culture polystyrene by this method revealed successful deposition of PEG, as shown by XPS. PEI-g-PEG/dopamine deposition for 2h inhibited the adsorption of serum proteins and the attachment of fibroblasts, suggesting that PEG molecules were immobilized in a sufficient density on the surface of the coating. Furthermore, co-deposition of PEI-g-PEG and PEI-g-biotin in alkaline dopamine solutions provided a cell-resisting background surface, at the same time providing accessible biotin molecules. We have demonstrated that the surface can be used for the selective binding of avidin, followed by the binding of Arg-Gly-Asp-Ser-biotin and enhanced cell attachment by specific cell-ligand interactions. In conclusion, our one step immobilization method provides a simple tool to fabricate surfaces with controllable cell affinity.