Hydroxyapatite-collagen composites. Part I: can the decrease of the interactions between the two components be a physicochemical component of osteoporosis in aged bone?

The interactions of Type I acid soluble collagen (Col) with both carbonate-free hydroxyapatite (HA1100) and carbonate-rich one (CHA) were investigated. The aim was to ascertain whether the increase of bone CO3 2− with ageing could relate to the disease known as osteoporosis. HA1100-Col and CHA-Col composites with various ratios were prepared and examined. Scanning electron microscopy and differential scanning calorimetry showed a stronger adhesion of the Col matrix to the granules of HA1100 than to those of CHA. FT-IR spectroscopy showed that with HA1100 both multiple hydrogen bonds of Col peptide –NH groups with HA PO4 3−, and electrochemical interactions between Col peptide –C=O groups and HA Ca2+ were present. In the presence of CO3 2−, the interactions between –NH and phosphate were diminished, and Ca2+ interacted more strongly with CO3 2− than with peptide –C=O, so causing a separation between the two components of the bone extra-cellular matrix. The results obtained strengthen the hypothesis that the substitution of PO4 3− ions by CO3 2− ions in the HA lattice might be a significant component of osteoporosis, although further investigation is needed.