Immobilization of BMP-2 on a nano-hydroxyapatite-coated titanium surface using a chitosan calcium chelating agent

Abstract

We conducted experiments to determine the most effective calcium chelating agents for use in enhancing adhesion of human bone marrow mesenchymal stem cells (BM-MSCs) on nano-hydroxyapatite (nHAp)-coated titanium substrates by covalently immobilizing bone morphogenetic protein-2 (BMP-2). The quantity of amine groups on the chitosan chelated surface was 7 mu g/surface area, and it was 1.4 mu g/surface area on the alendronate chelated surface. The quantity of BMP-2 on the BMP-2 immobilized surface chelated with chitosan (4 ng/surface area) was higher than that on BMP-2 immobilized surface chelated with alendronate (2.2 ng/surface area). Contact angles of the nHAp-coated titanium, alendronate chelated, chitosan chelated, and BMP-2 immobilized surfaces chelated with alendronate were 68.8 +/- 3.6 degrees, 78.2 +/- 1.9 degrees, 74.8 +/- 5.2 degrees, and 76.0 +/- 2.5 degrees, respectively. The contact angle of the BMP-2 immobilized surface chelated with chitosan was significantly lower (56.2 +/- 2.00 degrees) than that of any of the other groups. BM-MSCs on the chitosan surface and BMP-2 immobilized on the surface chelated with chitosan appeared to be healthy and showed a spindle-like fibroblastic morphology In addition, BM-MSCs on these surfaces appeared to have the ability to differentiate into bone-forming cells. We suggest that chitosan can be used as an effective calcium chelating agent for implants.