Hydroxyapatite other processes

Once fluoride ions react with bone, they are not easily dissolved out or exchanged by other elements. If bone is buried for long periods of time, the relative amount of fluorine in the bone gradually increases as a function of time the "fluoridation" process continues until the maximum amount of fluorine (necessary to convert all the hydroxyapatite to fluorapatite) is reached. The total concentration of fluor in carbonated fluorapatite can reach levels as high as above 3%. There is ample room, therefore, for an increase in the relative amount of fluorine in buried bone. Determining the relative amount of fluorine in buried bone may thus serve as a tool for dating bone. 

The bisphosphonates inhibit osteoclastic resorption of bone by binding to the hydroxyapatite crystals of bone. When osteoclasts first attach to bone in the active resorp-tive sites, the bisphosphonates are released from that bone. The release of these compounds locally prevents further osteoclastic attachment to those resorptive surfaces. The bisphosphonates also may inhibit resorption by inducing apoptosis of osteoclasts and by inhibiting release of interleukins and other compounds involved in bone resorption. The net result of actions of these compounds is inhibition of bone osteoclastic resorption. This action allows new bone formation to catch up in the remodeling process and can result in a net gain in bone density. 

In order to improve the properties and the spinnability, fibroin sometimes has been electrospun together with other natural or synthetic polymers (Jin et al., 2002 Park et al., 2004, 2006 Wang et al., 2004, 2006). For instance, Jin et al. (2002) developed an aqueous process for silk electrospinning in combination with PEO. More recently, Cao (2008) used PVA/Silk Fibroin (SF), Gelatin/SF, and Hydroxyapatite (HAP)/SF to produce double-layered (core-shell) nanofibers (mats) by coelectrospinning. 

The use of hydroxyapatite for DNA-fractionation exploits either the process of DNA denaturation or DNA reassociation. DNA denat-uration is the separation of the two complementary strands of native DNA by heat or agents like formamide or other methods. Denaturation takes place more easily the higher the A-I-T content of the DNA. Reassociation is the forming of a complementary double helix from single strands of DNA. This depends mainly on the concentrations of the complementary strands and hence on the repetition frequency of the sequence involved (Britten and Kohne 1966, 1968). 

Each form of calcium phosphate has its own uses. The dibasic form is used as a nutrient and mineral supplement in animal foods and in certain processed foods, especially cereals. In addition to its nutritional value, dibasic calcium phosphate acts as a dough conditioner, stabilizer, and thickener in foods. The compound is also used in dental products to provide replacement for hydroxyapatite lost to decay or other factors. 

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