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

TLDR

Hydroxylapatite is a highly biocompatible implant material that osseointegrates well, but the molecular mechanisms are largely unknown; it may adsorb serum adhesive proteins such as fibronectin and vitronectin, enabling osteoblast precursor adhesion via integrins. The study tests whether hydroxylapatite adsorbs more fibronectin and vitronectin from serum than titanium or stainless steel, and whether this leads to superior binding of integrins α5β1, αvβ3 and osteoblast precursors to HA. Using quantitative ELISA and a standard cell adhesion assay, the authors measured protein adsorption and cell binding to compare HA with titanium and stainless steel. Results show that fibronectin, vitronectin, integrins α5β1, αvβ3, and osteoblast precursor cells bind better to HA than to the metals, indicating that enhanced integrin‑mediated cell binding may underlie improved bone integration. © 2001 John Wiley & Sons, Inc., J Biomed Mater Res 57: 258–267.

Abstract

The implant material hydroxylapatite (HA) has been shown in numerous studies to be highly biocompatible and to osseointegrate well with existing bone; however, the molecular mechanisms at work behind this osseointegration remain 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 hypothesis that hydroxylapatite will adsorb more fibronectin and vitronectin from serum than two commonly used hard-tissue materials, commercially pure titanium, and 316L stainless steel. We further used the ELISA, as well as a standard cell adhesion assay, to test the hypothesis that increased protein adsorption will lead to better binding of purified integrins α5β1 and αvβ3 and osteoblast precursor cells to the HA than to the metals. Our results show that fibronectin, vitronectin, α5β1, αvβ3, and osteoblast precursor cells do indeed bind better to HA than to the metals, suggesting that improved integrin-mediated cell binding may be one of the mechanisms leading to better clinical bone integration with HA-coated implants. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 57: 258–267, 2001