Phosphate calcium, growth

Results were obtained on the calcium phosphate growth on phosphory-lated chitin fibres using the urea/H3P04 method and subsequently soaked in saturated Ca(OH)2 solution and in simulated body fluid solution. 

Addition of compounds with appropriate functionality to serve as nucleation sites for calcium phosphate growth to polymers can potentially improve the biocompatibility of the latter and thus the long-term stability of implant devices (Drelich and Field, 2007). Zinc stearate was added to poly(ethylene) to form poly(ethylene)-stearate blends with increased surface porosity potentially able to improve mechanical stability of the implant through enhanced osseointegration, improved rates and quality of bone-implant fusion and enhanced soft tissue wound healing via stimulation of angiogenesis. While immersion of these blends in supersaturated calcium phosphate solutions triggered deposition of a porous layer, the deposition rate was very slow, around 100 nm/day. 

Varma, H.K., Sreenivasan, K., Yokogawa, Y., and Hosumi, A. (2003) In vitro calcium phosphate growth over surface modified PMMA film. Biomaterials, 24 (2), 297-303. 

Other Ceramic Calcium Phosphate Materials. Other ceramic calcium phosphate materials for repairing bony defect iaclude p-tricalcium phosphate (P-TCP) [7758-87-4], P-Ca2(PO, and biphasic calcium phosphate (BCP) ceramics which consist of both P-TCP and HA. Unlike ceramic HA, P-TCP resorbs ia the tissue (293). The in vivo dissolution of BCP ceramic implants was shown (296) to iacrease with increasing P-TCP/HA ratio ia the implants. Both P-TCP and BCP can lead to new bone growth to various extents depending on the appHcations and the type of materials used (293,296). 

PTH has a dual effect on bone cells, depending on the temporal mode of administration given intermittently, PTH stimulates osteoblast activity and leads to substantial increases in bone density. In contrast, when given (or secreted) continuously, PTH stimulates osteoclast-mediated bone resorption and suppresses osteoblast activity. Further to its direct effects on bone cells, PTH also enhances renal calcium re-absorption and phosphate clearance, as well as renal synthesis of 1,25-dihydroxy vitamin D. Both PTH and 1,25-dihydroxyvitamin D act synergistically on bone to increase serum calcium levels and are closely involved in the regulation of the calcium/phosphate balance. The anabolic effects of PTH on osteoblasts are probably both direct and indirect via growth factors such as IGF-1 and TGF 3. The multiple signal transduction... 

Sodium carboxymethyl chitin and phosphoryl chitin had most evident influences on the crystallization of calcium phosphate from supersaturated solutions. They potently inhibited the growth of hydroxyapatite and retarded the rate of spontaneous calcium phosphate precipitation. These chitin derivatives were incorporated into the precipitate and influenced both the phase and morphology of the calcium phosphate formed (flaky precipitate resembling octacalcium phosphate instead of spherical clusters in the absence of polysaccharide) [175]. 

Growth of an amorphous calcium phosphate layer by incorporation of soluble calcium and phosphates from the solution. 

Solubilities and stabilities of calcium phosphates in natural waters have been described (735), as have the nucleation and growth of calcium phosphate from solution (736). Several species have long been known to inhibit the precipitation of calcium phosphates, for example carbohydrates (646) and statherin, the tyrosine-rich peptide which occurs in saliva (737). The role of... 

Precipitation can occur if a water is supersaturated with respect to a solid phase however, if the growth of a thermodynamically stable phase is slow, a metastable phase may form. Disordered, amorphous phases such as ferric hydroxide, aluminum hydroxide, and allophane are thermodynamically unstable with respect to crystalline phases nonetheless, these disordered phases are frequently found in nature. The rates of crystallization of these phases are strongly controlled by the presence of adsorbed ions on the surfaces of precipitates (99). Zawacki et al. (Chapter 32) present evidence that adsorption of alkaline earth ions greatly influences the formation and growth of calcium phosphates. While hydroxyapatite was the thermodynamically stable phase under the conditions studied by these authors, it is shown that several different metastable phases may form, depending upon the degree of supersaturation and the initiating surface phase. 

Calcium phosphate precipitation may also be involved in the fixation of phosphate fertilizer in soils. Studies of the uptake of phosphate on calcium carbonate surfaces at low phosphate concentrations typical of those in soils, reveal that the threshold concentration for the precipitation of the calcium phosphate phases from solution is considerably increased in the pH range 8.5 -9.0 (3). It was concluded that the presence of carbonate ion from the calcite inhibits the nucleation of calcium phosphate phases under these conditions. A recent study of the seeded crystal growth of calcite from metastable supersaturated solutions of calcium carbonate, has shown that the presence of orthophosphate ion at a concentration as low as 10-6 mol L" and a pH of 8.5 has a remarkable inhibiting influence on the rate of crystallization (4). A seeded growth study of the influence of carbonate on hydroxyapatite crystallization has also shown an appreciable inhibiting influence of carbonate ion.(5). 

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