False-coloured Scanning Electron Micrograph of cortical bone (compact bone). Cortical bone forms the dense, hard outer layer of most bones and is much more compact than the open structured 'spongy bone' or 'trabecular bone', that is found within the middle of large bones. Bone is essentially a biological composite material, somewhat akin to glass fibre or carbon fibre reinforced synthetic composites; the collagen fibrils (striated fibres that can be seen in this image) form the overall structure and provide flexibility to the tissue, within a matrix of stickly non-collagenous proteins acting like a resin. Calcium hydroxyapatite nanocrstals are distributed throughout the protein matrix, giving bone its hardness. The resulting bone is both incredibly tough and relatively lightweight. The image width is 4.97 microns.
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