科研之友
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摘要
Calcium phosphates as formed in-vitro in brine and simulated body fluids are nano to micron size apatites. Their nanosize is probably due to their strong interaction with water. As derived from the chemistry of calcium phosphate cements the following apatites can be formed in simulated body fluids and brine (1) potassium containing apatite KCA (2) calcium deficient hydroxyapatite CDHA (3) sodium and carbonate containing apatite and NCCA (4) heavily carbonated hydroxyapatite HCHA. Their tentative solubility isotherms have been indicated in a potential plot of the logarithm of the ion activity product of hydroxyapatite versus pH.. Bone consists largely of a collagen meshwork in which the nanoapatitic mineral particles and plates are dispersed. This meshwork contains tightly bound water. Bone also contains glucosaminoglycans (GAGs) and glycoproteins (GPs) which contain loosely bound water. Oxygen and glucose are transported to the osteocytes through this loosely bound water.. However, by aging the GAGs and GPs are hydrolyzed slowly, the loosely bound water is lost and the osteocyte dies. The toxins of the necrosis lead to breakdown of the collagen meshwork and the conglomeration of the mineral particles by interparticle precipitation of NCCA. Bone remodeling is triggered by the toxins of the cell necrosis. Osteoclasts dig a tunnel through the old bone by formation of lactic acid. This is followed by osteoblasts which first restore the collagen meshwork and then swell to fill all spaces in the tunnel with their dendrites which suck up by collection of potassium and phosphate ions during the night. By daytime the osteoblasts are squeezed by loading of the bone and the dendrites exude the cytosol. This causes mineralization of the new collagen meshwork with KCA. The rest of the day proceeds with the transformation of the KCA crystals into CDHA. In the meantime, the osteoblast has proceeded in the direction of the osteoclast and the new bone can mature. This happens by ongrowth of a layer of NCCA onto the CDHA crystals after which the collagen meshwork is really tight around the crystals and the new bone has gained its full strength and toughness. This completes the bone remodeling. The process explains Woolfs%26apos; Law according to which bone growth occurs along the direction of its stresses.
- 出版日期2012
