Quantification of adhesiveness of osteoblasts to titanium surfaces in vitro by the micropipette aspiration technique

For osseointegration to occur at a biomaterial surface implanted in tissue, osteoblasts must first adhere to the surface and subsequently lay down a framework of submatrix proteins and mineral. Thus the adhesion force of an osteoblast to a surface can serve as a measure of its biocompatibility during the first hours after implantation. This study used the micropipette aspiration technique to quantify the adhesion force of individual Ost-6 neonatal rat calvarial osteoblasts interacting with smooth, rough, fibronectin (FN)-coated, and hydroxyapatite (HA)-coated commercially pure titanium surfaces. Individual cellular adhesion forces ranged from 2 to 320 mdyn and were proportional to the time allowed to adhere (seeding time, 15-120 min) and adsorbed FN coating concentration (5-20 microg/ml). For the 60 min seeding time, osteoblasts adhered 80% more strongly to 5 microg/ml FN-coated titanium than to smooth uncoated titanium, due to specific affinity of the alpha(v)beta(1) transmembrane integrin for the FN molecule. Average adhesion force on plasma sprayed HA-coated titanium was only 40% as high as the uncoated surface, indicating that the osteoconductive effects of HA were not evident in the first 60 min of adhesion. There was no difference in adhesion force between the uncoated smooth and rough titanium surfaces for the 60 min seeding time. The uncoated and FN-coated titanium surfaces had the same average cell-surface contact angle used to assess the degree of cell flattening on the titanium surface. This indicated that osteoblasts formed equal quantities of cell-substrate bonds to the two surfaces but with very different adhesion forces, thus osteoblast affinity for the titanium surfaces was expressed in higher individual cell-substrate bond forces.