Hole zone

Fig. 46. Molecular overlap and hole zone in collagen fibrils (after Holding500) and Miinzen-berg354))...

Fig. 1 Microstructure of bone, showing staggered structure of collagen molecules, which creates hole zones in which HAp is nucleated (a) [1]. The lowest level of hierarchical structure of bone, showing alignment and elongation of HAp crystals as a function of underlying aligned collagen fibrils (b) [2] (Reproduced by permission of The Royal Society of Chemistry)...

Fig. 4.8. Electron micrograph of mineralized turkey leg tendon showing possible vectorial ordering of apatite crystallites on a collagenous matrix (x 50,000) arrow (2), arrangement of crystallites in lines in the hole zone arrow (2), overlapping zone free from crystallites...

There are, however, some a priori arguments which favour non-epitaxial processes as the major mechanism of oriented overgrowth of biominerals from ion precipitation at organic surfaces. Firstly, epitaxis requires a rigid two-dimensional atomic net whereas non-epitaxial deposition can be achieved from a more flexible surface on which there are specific molecular configiirations of polypeptide side chains. For example, it has been suggested that the deposition of apatite within the 640 A ( hole ) zones between colla-... 

The mineral phase is mainly formed by calcium and phosphorous, which form spindle- or plate-shaped crystals of HAp [3Ca3(P04)2.(0H)2]. HAp nanocrystals of bone locate at hole zones within the collagen fibrils. This restricts the possible primary growth of the crystals and forces them to be discrete and discontinuous. The mineral crystals grow with a specific crystalline orientation. The c-axes of the... 

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