Investigation of the mineral and collagen arrangement in bone

The mineral arrangement in bone currently has three models: (1) the staggered crystal (most widely accepted) where the minerals are thought to be mainly in the gap regions between the collagen fibrils; (2) the wrapped crystal model where the minerals are extrafibrillar in the form of curved ribbons that wrap around collagen fibrils and (3) the interpenetrating composite model, where both mineral and collagen form their own networks that are intertwined with each other. Methods to investigate these models can be through complete demineralization or deproteinization experiments to examine each component separately. Six-month old porcine femur bones were either demineralized (HCl, CH₂O₂, EDTA, ETDA) or deproteinized (NaOCl, H₂O₂, NaOH, KOH). The resulting structures were characterized by x-ray diffraction, thermogravimetric analysis, scanning electron microscopy, Raman and Fourier transform infrared spectroscopy and compared to untreated bone. For demineralization, the CH₂O₂ treatment removed the most mineral meanwhile preserving the collagen structure. For deproteinization, NaOCl removed the most protein without altering the mineral structure. Although there is a minor amount of lipid in bone, a defatting process did not alter the findings. Both demineralization and deproteinization resulted in porous materials that remained structurally intact. The findings of these studies support the hypothesis that bone is an interpenetrating composite with continuous mineral and protein phases. These and more specific results will be discussed in the presentation.