The unique strength and rigidity of bone arises from a combination of organic components (primarily collagen) and inorganic (mineral) components. Over a lifetime, bone is continuously remodeling itself. Old bone is eroded away in a tunnel-like fashion by osteoclasts and new bone is deposited layer-by-layer in the ?tunnel? by osteoblasts. From a cross-sectional view, these new layers of bone, collectively termed an osteon, appear as series of concentric circles through a microscope. A typical osteon measures ~200 ?m in diameter, where the youngest bone is at the center. In many diseased states of bone, there is an imbalance between bone production and resorption, resulting in overgrowth (osteopetrosis) or undergrowth (osteoporosis) of bone. To date, it is unclear whether the chemical composition of the bone in a diseased state is the same as normal bone. Using infrared micro-spectroscopy, we are able to visibly and chemically image individual osteons in terms of growth-, site-, and age-dependent variations in mineral content (i.e. carbonate, phosphate, acid phosphate), mineral crystallinity, and the content/nature of the organic matrix. A significant advantage of this technique over other chemical methods is that the bone does not need to be homogenized before testing; we are able to study cross-sectional samples of bone in situ at a resolution of 3-5 ?m. In this study, we present a comparison of human osteoporotic bone to osteopetrotic bone. Early results show some similarities and also significant differences between osteopetrotic and osteoporotic bone. For both diseased states Hof bone, the ratios of phosphate-to-collagen and carbonate-to-collagen Hconcentrations are similar and these ratios increases as bone matures H(from the center to the periphery of the osteon). Also for both, the Hphosphate ions (PO43-) are replaced by other anions such as carbonate H(CO32-) as bone ages, i.e. the hydroxyapatite becomes Hnon-stoichiometric. However in contrast, we observe significantly Hmore CO32- substitution in osteoporotic bone than osteopetrotic bone Has the bone matures.
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