Calcium phosphate matrix

The most widely used industrial process for the manufacture of hexagonal boron(III) nitride is the reaction of boron(III) oxide with ammonia at 800 to 1200°C in a calcium phosphate matrix ... 

In water and beverages strontium can be measured directly, but food and biological materials require a pretreatment with hydrochloric acid (3 M) and lanthanum chloride [91]. In urine strontium can be determined after dry-ashing and addition of lanthanum [91] or directly after 1 2 dilution with an acidic lanthanum chloride solution [92], The determination of strontium in bone requires special attention because the bone matrix contains high amounts of calcium and phosphate, which can easily interfere with the determination of strontium. Razmilic described a method to isolate strontium from the calcium phosphate matrix by ion exchange chromatography. The pretreated samples then can be analysed by both emission and absorption spectrophotometry measurements without chemical, ionization, or bulk interferences [93,94]. 

Some effort has also been focused on the determination of other isotope ratios, particularly St/ St with TOF-ICP-MS and LA-TOF-ICP-MS [104].These efforts have not, however, yielded precision and accuracy useful for the characterization of human tooth enamel for population movement studies. Part of the problem probably arises from interferences produced by the calcium phosphate matrix [106], but there also appears to be TOF detector-related fractionation akin to but more extreme than that observed for Pb/ Pb. 

Horstwood et al. [Ill] reported results of experiments to determine strontium isotopes in archaeological tooth enamel using LA-MC-ICP-MS and pointed out the need for careful attention to interferences from the calcium phosphate matrix. In another study, Richards et al. [112] detected evidence of Neanderthal mobility via LA-MC-ICP-MS characterization of strontium isotope ratios in tooth enamel. Enamel values from a Neanderthal molar recovered from a coastal limestone environment in Greece were found to be consistent with... 

Yaszemski et al. (1995) incorporated sodium chloride as a pore forming component into a composite formulation also including /3-tricalcium phosphate (yS-TCP) or a calcium phosphate matrix. The mixture was crosslinked with VP to form a biodegradable bone cement. The mechanical properties of the composite were studied over several varying factors in a fractional factorial design. These mixtures... 

Kovacevic, D., Fox, A.J., Bedi, A., Ying, L., Deng, X.H., Warren, R.F., Rodeo, S.A., 2011. Calcium-phosphate matrix with or without TGF-P3 improves tendon-bone healing after rotator cuff repair. American Journal of Sports Medicine 39 (4), 811-819. http //dx.doi. org/10.1177/0363546511399378. 

Figure 48-12. Schematic illustration of some aspects of the role of the osteoclast in bone resorption. Lysosomal enzymes and hydrogen ions are released into the confined microenvironment created by the attachment between bone matrix and the peripheral clear zone of the osteoclast. The acidification of this confined space facilitates the dissolution of calcium phosphate from bone and is the optimal pH for the activity of lysosomal hydrolases. Bone matrix is thus removed, and the products of bone resorption are taken up into the cytoplasm of the osteoclast, probably digested further, and transferred into capillaries. The chemical equation shown in the figure refers to the action of carbonic anhydrase II, described in the text. (Reproduced, with permission, from Jun-queira LC, Carneiro J BasicHistology. Text Atlas, 10th ed. McGraw-Hill, 2003.)...

Monomeric plutonium species deposited in the liver become concentrated in the liver ferritin, the principal iron repository (191). On analysis of plutonium deposition in bone a dichotomy becomes immediately apparent. Monomeric plutonium no longer follows an iron transport/deposition mechanism, for bone contains little or no iron complexed within the bone matrix. Calcium phosphate as a chromatographic media does, of course, retain iron. 

From a theoretical point of view, the gel layer is a barrier that reduces further hydrolysis of the silicate network, and is supposed to be more stable than the glass matrix, thus reducing the overall rate of corrosion. However, gel exfoliation may momentarily re-activate corrosion, at least locally. No clear trend was observed for the presence of the crystalline secondary phases identified at the surface of the corroded HT samples. The most abundant minerals are aluminosilicates, calcium phosphates, Fe- and Mg-rich minerals, and zeolites their role in the scavenging or release of metals remains ambiguous, although many mineral phases identified bear traces of metals. 

For methylcellulose, increased matrix material concentration did not affect the release profile (Table 4). The sustained action can be directly attributed to the formation of a hydration layer by this polymer. This hydration layer, however, did not resist attrition and remain intact. Consequently, attrition becomes more important than diffusion the hydrated layer dissolves away almost as rapidly as it is formed. On the contrary, the dibasic calcium phosphate dihydrate did not diffuse outward, but rather became entrapped within the matrix and effected an increase in release of drug because its presence necessarily decreased the polymer concentration. 

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). 

Our own skin is made up of specialized cells which become filled with microfibrils of keratin as they move outward and become the relatively dry nonliving external surface (Box 8-F). Internal epithelial cells secrete protein and carbohydrate materials that form a thin basement membrane around the exposed parts of the cells. The connective tissue that lies between organs and which also includes tendons, cartilage, and bone consists of a relatively small number of cells surrounded by a "matrix" consisting of the protein fibers collagen and elastin in a "ground substance" rich in proteoglycans (Chapter 4).616 618 in bone, the calcium phosphate is deposited within this matrix. 

At the present time it is not possible to assign a precise function for any alkaline phosphatase. Undoubtedly bone phosphatase is concerned in ossification and two alternative roles have been proposed (1) Precipitation of calcium phosphate is induced by the localized production of high concentrations of Pi owing to phosphatase activity (33) (2) the enzyme permits crystal growth at nucleation sites in the matrix by ensuring the removal and continued absence of PPi which is known to be a crystal poison (60). Other factors must be involved (35) because tissues with high concentrations of alkaline phosphatase (e.g., gut, kidney, and... 

The presence of phosphate increases the ability of the mitochondria to accumulate Ca2+, partly because of the buffering effect of the phosphate on the pH of the matrix, and partly because of the precipitation of insoluble calcium phosphate within the matrix. The formation of insoluble calcium phosphate lowers the internal free [Ca2+] and favours further influx. The amorphous nature of the precipitate is of interest as the formation of crystalline hydroxyapatite would be expected. Mitochondria must contain a factor that inhibits this process. 

One of the important fields where carbohydrate polymer/inorganic hybrids may be successfully applied is bioactive materials, e.g., artificial bones expedient for surgery to accelerate the recovery of living bones. There has been increasing interest in hydroxyapatite (HAp) deposition onto the matrix surface of cellulose or related polysaccharide. HAp is a form of calcium phosphate, a main constituent of the inorganic phase of human bone. This kind of study is also a step on the way to exploitation of new biomimetic mineralization methods. 

Another interesting approach is to use nanofiber scaffolds as a crystallization matrix to mimic biological composites. Xia and coworkers were able to produce meshes with a gradient of calcium phosphate content to mimic the tendon-to-bone insertion site [206], The variation in composition led to an interesting spatial gradient in stiffness of the scaffold. This was also reflected in an activity gradient of seeded mouse preosteoblast cells. 

---