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 (HA(1100)) and carbonate-rich one (CHA) were investigated. The aim was to ascertain whether the increase of bone CO(3) (2-) with ageing could relate to the disease known as osteoporosis. HA(1100)-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 HA(1100) than to those of CHA. FT-IR spectroscopy showed that with HA(1100) both multiple hydrogen bonds of Col peptide -NH groups with HA PO(4) (3-), and electrochemical interactions between Col peptide -C=O groups and HA Ca(2+) were present. In the presence of CO(3) (2-), the interactions between -NH and phosphate were diminished, and Ca(2+) interacted more strongly with CO(3) (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 PO(4) (3-) ions by CO(3) (2-) ions in the HA lattice might be a significant component of osteoporosis, although further investigation is needed.

Biomaterials for orthopedics: a roughness analysis by atomic force microscopy.

We conducted an AFM analysis of roughness on 7 materials widely used in bone reconstruction. Roughness was evaluated by measuring Root Mean Square (RMS) values and RMS/average height (AH) ratio, in different dimensional ranges, varying from 100 microns square to a few hundreds of nanometers. The results showed that Titanium presented a lower roughness than the other materials analyzed, frequently reaching statistical significance. On the contrary, bioactive materials, such as hydroxyapatite (HA) and bioactive glasses, demonstrated an overall higher roughness. In particular, this study focuses attention on AP40 and especially RKKP, which proved to have a significant higher roughness at low dimensional ranges. This determines a large increase in surface area, which is strongly connected with osteoblast adhesion and growth and to protein absorption. Therefore, the biointegration properties of bioactive glasses can also be given as answer in terms of surface structures in which chemical composition can influence directly the biological system (e.g. with chemical exchanges and development of specific surface electrical charge) and indirectly, via the properties induced on tribological behavior that expresses itself during the smoothing of the surfaces. We also test two new bioactive glasses, RBP1 and RBP2, with a chemical composition similar to AP40, but with some significant small additions and substitutions of components, in order to make preliminary considerations on their potential role in orthopedics.

The effect of pulsed electromagnetic fields on the osteointegration of hydroxyapatite implants in cancellous bone: a morphologic and microstructural in vivo study.

Effects of pulsed electromagnetic fields (PEMFs, 75 Hz. 1.6 mT) were investigated in 12 rabbits after placing hydroxyapatite (HA) implants in their femoral condyles. Six animals were stimulated with PEMFs for three consecutive weeks, 6 h/day, while the remaining animals were sham-treated (Control Group). Rabbits were sacrificed at 3 and 6 weeks (after a 3-week non-stimulation period) for histomorphometric analysis and microhardness testing (at 200, 500, 1,000, 2,000 microm from the implant) around the implants. Histomorphometric analysis did not highlight any significant changes. On the contrary, there were statistically significant differences between the effects produced by PEMFs and Control Groups (F = 149.70, p < 0.0005) on the Affinity Index results, as well as by the experimental time of 6 and 3 weeks (F = 17.12, p = 0.001) on the same results. In PEMF-stimulated animals the microhardness (HV) values measured in trabecular bone at a distance of 200 and 500 microm from the implants, were significantly higher with respect to controls. At 6 weeks, HV values at the bone-implant interface in PEMF-stimulated animals were not significantly different with respect to normal bone, while they remained significantly lower in control animals. Both morphological and structural results demonstrated a positive therapeutic effect of PEMFs in accelerating HA osteointegration in trabecular bone.

Extracorporeal hydroxyapatite-chamber for bone and biomaterial studies.

Hydroxyapatite (HA) spherules and autologous bone (AB) with a central vascular pedicle were housed inside an HA-chamber to form the skeletal segment of specific shape. Experimental chambers were then inserted in a pocket between medial thigh muscles in 13 New Zealand male rabbits for 3 months. Three graft group were scheduled: (A) HA and AB without vascular pedicle, (B) HA with vascular pedicle, (C) HA and AB with vascular pedicle. At term, histology showed tissue and cellular degeneration in group A chambers. Due to spherules coalescence, fibrous tissue is formed in group B chambers. Group C chambers contained living osteocytes in the implanted bone, several newly formed vessels in soft tissue, bone and partial hydroxyapatite erosions. New bone was formed in apposition to both autologous bone and hydroxyapatite. Our study suggests that this experimental model could be used to grow adequately sized vascularized skeletal segments.