A comparison of the physical and chemical differences between cancellous and cortical bovine bone mineral at two ages

Abstract

To assess possible differences between the mineral phases of cortical and cancellous bone, the structure and composition of isolated bovine mineral crystals from young (1-3 months) and old (4-5 years) postnatal bovine animals were analyzed by a variety of complementary techniques: chemical analyses, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and (31)P solid-state magic angle spinning nuclear magnetic resonance spectroscopy (NMR). This combination of methods represents the most complete physicochemical characterization of cancellous and cortical bone mineral completed thus far. Spectra obtained from XRD, FTIR, and (31)P NMR all confirmed that the mineral was calcium phosphate in the form of carbonated apatite; however, a crystal maturation process was evident between the young and old and between cancellous and cortical mineral crystals. Two-way analyses of variance showed larger increases of crystal size and Ca/P ratio for the cortical vs. cancellous bone of 1-3 month than the 4-5 year animals. The Ca/(P + CO(3)) remained nearly constant within a given bone type and in both bone types at 4-5 years. The carbonate and phosphate FTIR band ratios revealed a decrease of labile ions with age and in cortical, relative to cancellous, bone. Overall, the same aging or maturation trends were observed for young vs. old and cancellous vs. cortical. Based on the larger proportion of newly formed bone in cancellous bone relative to cortical bone, the major differences between the cancellous and cortical mineral crystals must be ascribed to differences in average age of the crystals.

Fig. 1

XRD spectra of isolated bone mineral from (a) 1–3 month cancellous bone, (b) 1–3 month cortical bone, (c) 4–5 year cancellous bone, and (d) 4–5 year cortical bone. The patterns are all apatitic, but a sharpening of the 002 peak (~26° 2θ) is evident of increased crystallinity of the older and cortical bone samples

Fig. 2

FTIR spectra of isolated bone mineral from (a) 1–3 month cancellous bone, (b) 1–3 month cortical bone, (c) 4–5 year cancellous bone, and (d) 4–5 year cortical bone. The patterns are all apatitic. Deconvolution and decomposition of the υ₂ carbonate and υ₄ phosphate domains is required to detect differences between the samples, shown in Table 2

Fig. 3

³¹P NMR normal CP spectra from (a) 1–3 month cancellous bone, (b) 1–3 month cortical bone, (c) 4–5 year cancellous bone, and (d) 4–5 year cortical bone. The patterns are all apatitic with an isotropic chemical shift of 3.1 ppm, identical to the chemical shift of hydroxyapatite

Fig. 4

³¹P NMR differential CP spectra from (a) 1–3 month cancellous bone, (b) 1–3 month cortical bone, (c) 4–5 year cancellous bone, and (d) 4–5 year cortical bone. The prominent inverted spinning sideband pattern is characteristic of apatitic HPO₄. The narrow positive-going spectral feature overlapping the HPO₄ center-band is the centerband of PO₄, which is not inverted at this reverse CP time. The upfield first-order sidebands are more intense than the downfield first-order sidebands, characteristic of calcium ion in close association with the phosphorus atoms