BMP-2 tethered hydroxyapatite for bone tissue regeneration: coating chemistry and osteoblast attachment

The goal of this study was to determine the effectiveness of using polyethyleneimine (PEI) and a polyethylene glycol (PEG) tether to bind human recombinant bone morphogenetic protein-2 (rhBMP-2) to hydroxyapatite (HAp) to enhance rhBMP-2 loading, alter its release properties, and enhance cellular interaction with the material. By using a branched PEI that was derived to express free thiols, rhBMP-2 was coated onto dense HAp surfaces at ~43 ng/cm(2). Using this novel attachment methodology, it was observed that the PEI-SH coating did not change the morphology of the HAp surfaces and that the amount of rhBMP-2 loaded was comparable to a direct adsorption method. In addition, it was also observed that the PEI and PEG tether significantly retained the rhBMP-2 to the HAp surface, inhibiting the burst release effect. Using human fetal osteoblast cells, the PEI- and PEG-tethered BMP-2 was also observed to increase cellular attachment by 10-fold when compared with uncoated HAp and adsorbed rhBMP-2. It was concluded from this study that PEI and PEG tether significantly reduce the initial burst release effect of rhBMP-2. It was also concluded that the rhBMP-2 conjugation to PEI and PEG tether promoted an increase in cellular attachment to the HAp surface.