Hydroxylapatite binds more serum proteins, purified integrins, and osteoblast precursor cells than titanium or steel

The implant material hydroxylapatite (HA) has been shown in numerous studie s to be highly biocompatible and to osseointegrate well with existing bone; however, the molecular mechanisms at work behind this osseointegration rem ain largely unexplored. One possibility is that the implant, exposed to the patient's blood during surgery, adsorbs known cell adhesive proteins such as fibronectin and vitronectin from the serum. Osteoblast precursors could then adhere to these proteins through integrin-mediated mechanisms, In the present study, we have used a quantitative ELISA assay to test the hypothes is that hydroxylapatite will adsorb more fibronectin and vitronectin from s erum than two commonly used hard-tissue materials, commercially pure titani um, and 316L stainless steel. We further used the ELISA, as well as a stand ard cell adhesion assay, to test the hypothesis that increased protein adso rption will lead to better binding of purified integrins alpha (5)beta (1) and alpha (v)beta (3), and osteoblast precursor cells to the HA than to the metals. Our results show that fibronectin, vitronectin, alpha (5)beta (1), alpha (v)beta (3,) and osteoblast precursor cells do indeed bind better to FIA than to the metals, suggesting that improved integrin-mediated cell bi nding may be one of the mechanisms leading to better clinical bone integrat ion with HA-coated implants. (C) 2001 John Wiley & Sons, Inc.