Mineralization calcium phosphate precipitation

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

The insoluble Ca(II) salts of weak acids, such as calcium phosphate, carbonate, and oxalate, serve as the hard structural material in bone, dentine, enamel, shells, etc. About 99% of the calcium found in the human body appears in mineral form in the bones and teeth. Calcium accounts for approximately 2% of body weight (18,19). The mineral in bones and teeth is mosdy hydroxyapatite [1306-06-5] having unit cell composition Ca10(PO4)6(OH)2. The mineralization process in bone follows prior protein matrix formation. A calcium pumping mechanism raises the concentrations of Ca(II) and phosphate within bone cells to the level of supersaturation. Granules of amorphous calcium phosphate precipitate and are released to the outside of the bone cell. There the amorphous calcium phosphate, which may make up as much as 30—40% of the mineral in adult bone, is recrystallized to crystallites of hydroxyapatite preferentially at bone collagen sites. These small crystallites do not exceed 10 nm in diameter (20). 

In general, saliva (as well as plaque fluid) is supersaturated with respect to calcium-phosphate salts, and they prevent tendency to dissolve mineral crystals of teeth. Moreover, precipitation of calcium-phosphate salts that include hydroxyapatite may also occur (remineralization) in early lesions of tooth surfaces injured by acidic bacterial products (i.e., lactic acid). Salivary fluoride facilitates calcium-phosphate precipitation, and such crystals (i.e., fluorapatite) show lower acid solubility properties that lead to an increased caries preventive effect. The increase of pFI (i.e., buffer capacity and pH of saliva, as well as ureolysis in dental plaque) also facilitates crystal precipitation and remineralization (4, 13). 

Mineral precipitation and complexation with proteins also contribute to fouling considerably. Adsorbed minerals may serve as salt bridges between the protein and the membrane, which aggravates fouling. In physicochemical conditions that promote calcium phosphate precipitation or calcium-protein complexation, membrane fouling in the filtration of nulk or whey is severe,... 

Nucleation of calcium phosphate precipitation within the matrix vesicles is mediated by phosphatidylserine, which comprises about 8% of the phospholipids of the inner cytosolic membrane surface (Fig. 9.5a). Calbindin in the vesicle (Fig. 9.5b) may also contribute. Rapid mineral growth within the vesicle keeps the concentration of dissolved calcium and inorganic phosphate ions so low that additional Ca2+ and Pi ions spontaneously enter from the extracellular fluid via their respective transporters. Attached type II and type X collagens from cartilage in the growth plate enhance calcium ion transport and calcification during endochondral ossification (Fig. 9.5b). 

Figure 9.8 outlines how matrix vesicles increase and decrease the concentration of pyrophosphate. NTP-PPi hydrolase synthesizes pyrophosphate from stromal fluid nucleotides, mostly ATP (ATP —> AMP + PPi). Many cells secrete ATP into the extracellular fluid and it passes into the blood plasma where it affects a variety of cells independently of its function in intracellular energy metabolism. In mice, a nonfunctional ANK protein or a deletion of NTP-PPi hydrolase decreases the extracellular pyrophosphate concentration and the phenotype exhibits extensive mineralization. Thus, the hydrolysis of pyrophosphate appears to be a major function of alkaline phosphatase (TNAP) after the calcium phosphate precipitate has raptured the matrix vesicles. Rapid mineralization of collagen and the rest of the osteoid matrix ensue without a need to transport any more Ca2+ or Pi to the region. 

Brown JL (1981) Calcium phosphate precipitation Effects of common and foreign ions on hydroxyapatite crystal growth. Soil Sci Soc J 45 482-486 Bulka GR, Vinokurov VM, Nizamutdinov NM, Hasanova NM (1980) Dissymmetrization of crystals Theory and experiment. Phys Chem Minerals 6 283-293 Bums RG (1970) Mineralogical Applications of Crystal Field Theory. Cambridge University Press, Cambridge... 

The plaque matrix contains high concentrations of calcium and phosphate, either as ions in solution or bound as a calcium phosphate-protein complex. This is particularly evident in areas close to the ducts of the salivary glands. The ability of the matrix to concentrate these ions from the saliva favours calcium phosphate precipitation at high pH values. A precipitate of dicalcium phosphate can, as we have seen, mature and undergo crystal growth to give a salt of a higher calcium to phosphate molar ratio so that the plaque itself tends to mineralize ... 

Hydroxyapatite, Ca2Q(PO (OH)2, may be regarded as the parent member of a whole series of stmcturaHy related calcium phosphates that can be represented by the formula M2q(ZO X2, where M is a metal or H O" Z is P, As, Si, Ga, S, or Cr and X is OH, F, Cl, Br, 1/2 CO, etc. The apatite compounds all exhibit the same type of hexagonal crystal stmcture. Included are a series of naturally occurring minerals, synthetic salts, and precipitated hydroxyapatites. Highly substituted apatites such as FrancoHte, Ca2Q(PO (C02) (F,0H)2, are the principal component of phosphate rock used for the production of both wet-process and furnace-process phosphoric acid. 

Chitosan scaffolds were reinforced with beta-tricalciiun phosphate and calcium phosphate invert glass [177]. Along the same line, composites of Loligo beta-chitin with octacalcium phosphate or hydroxyapatite were prepared by precipitation of the mineral into a chitin scaffold by means of a double diffusion system. The octacalciiun phosphate crystals with the usual form of 001 blades grew inside chitin layers preferentially oriented with the 100 faces parallel to the surface of the squid pen and were more stable to hy-... 

The polypeptide parathormone is released from the parathyroid glands when plasma Ca + level falls. It stimulates osteoclasts to increase bone resorption in the kidneys, it promotes calcium reabsorption, while phosphate excretion is enhanced. As blood phosphate concentration diminishes, the tendency of calcium to precipitate as bone mineral decreases. By stimulating the formation of vit D hormone, parathormone has an indirect effect on the enteral uptake of Ca + and phosphate. In parathormone deficiency, vitamin D can be used as a substitute that unlike parathormone, is effective orally. 

However, methane-diphosphonate could not prevent the growth of apatite crystals in vitro on prepared sinews of rats tail out of a metastable solution with calcium and phosphate ions. On the contrary, the precipitated crystalline particles were bigger and better crystallized than those from control solutions. This is in surprising contrast to most of the information from the literature. No other calcium phosphate minerals besides apatite have been found by X-ray diffraction, whereas under comparable conditions brushite and octacalcium phosphate grow on collagenous sinews549. ... 

As well as being used as a scaffold for tissue engineering, Hutchens et al. [64] described the creation of a calcium-deficient hydroxyapatite, the main mineral component of bone. Calcium phosphate particles were precipitated in BC by consecutive incubation of calcium chloride and sodium phosphate solutions. Initial tests with osteoblasts in the in vitro evaluation showed that solid fusion between the material and the bone tissue is possible. Hence, this material is a good candidate for use as a therapeutic implant to regenerate bone and heal osseous damage. 

Radin, S. R., and Ducheyne, P, The effect of calcium phosphate ceramic composition and structure on in vitro behavior. II. Precipitation. J. Bone and Mineral Res. 27, 35 45 (1993). 

Another means of assessing the nature of the medium/solution from which the mineral forms is to analyse the very first mineral deposits precipitated. These must reflect the chemistry of the medium in which they formed. In most chiton teeth a poorly crystalline ferrihydrite is the first mineral deposited and it subsequently transforms into magnetite. In the anterior layer, amorphous calcium phosphate is first deposited, and only after several weeks does it begin... 

It has been proven over the years that the effect of fouling can be lessened to some extent for the application of whey concentration by pretreating the feed streams for the ultrafilters. Whey contains many insoluble solids such as casein fines, lipoprotein complex, mineral precipitates, free fats and microorganisms. Clarification of these debris helps reduce fouling potential during ultrafiltration. In addition, it is quite evident that calcium phosphate minerals in whey are not stable and their precipitation in the membrane pores often results in flux decline. Demineralization of whey before ultrafiltration helps maintain high permeate flux considerably [Muir and Banks, 1985]. 

---