Hydroxy carbonate apatite

A bioactive material is one that elicits a specific biological response at the interface of the material which results in the formation of a bond between the tissues and the material. A common characteristic of bioactive glasses, bioactive glass-ceramics, and bioactive ceramics is that their surface develops a biologically active hydroxy carbonate apatite (HCA) layer which bonds with collagen fibrils. The HCA phase that forms on bioactive implants is equivalent chemically and structurally to the mineral phase of bone. It is that equivalence which is responsible for interfacial bonding ". ... 

As shown in Section 2.4.6, natural hydroxy/carbonate apatite in human bones and teeth structures exhibits a needleshaped habit. It has been a longstanding objective in the development of biomaterials to reproduce these... 

Hofmann et al. [55] have created a bioactive cellulose surface where the nonwo-ven cellulose (regenerated, oxidized) fabrics were coated with hydroxy-carbonated apatite, using a procedure based on a biomimetic method (Figure 14.8). A simulated body fluid with a high degree of supersaturation was appHed to accelerate the biomimetic formation of boneUke apatite on the cellulose fabrics. These materials are under consideration as attractive candidates for scaffolds in bone tissue engineering. 

Figu re 14.8 Nonwoven cellulose (regenerated, oxidized) fabrics coated with hydroxy-carbonated apatite. Scale bar = 20 pm. 

The hydrolysis of Cap2 in solutions containing phosphates and carbonate ions results in the formation of fluor-, fluor-hydroxy- or fluor-carbonate-apatites. Fluor and fluor-hydroxy- apatites can also be formed by the hydrolysis of dicalcium phosphate (anhydrous or dihydrate), DCPAor DCPD, respectively, in solutions containing fluoride ions [121] or from the hydrolysis of any other calcium phosphate salt. 

The fluorine in fluoroapatite can be substituted by chlorine on treatment with an N02-N0C1 mixture at 1000°C,534 and the B-type carbonate apatites lose carbon dioxide on heating between 700 and 1000 °C, giving CaO and hydroxylapatite.535 X-Ray data indicate strong similarities between the structure of strontium chloroapatite and the fluoro- and hydroxy-analogues.536... 

Keeping teeth clean requires toothpaste, a mixture of detergents and abrasives, which are hard substances that help remove unwanted materials on the tooth surface. The structure of tooth enamel is essentially that of a stone composed of calcium carbonate (CaCOj) and calcium hydroxy phosphate [apatite—GajQ(PO )g(OH)2], Despite being the hardest substance in the human body, tooth enamel is readily attacked by acids. Because the decay of some food particles produces acids, it is important to keep teeth clean. 

As in the case of calcite, the activities of various dissolved species have been calculated at different pH values for other minerals using the relevant chemical equilibria and stoichiometric restrictions. The distribution of the activities of dissolved species of hydroxy apatite is given in Figs. 3.5a and 3.5b for open and closed systems, respectively. If the system is brought to equilibrium with atmospheric carbon dioxide, the distribution will follow that shown in Fig. 3.5a. For the closed system, Ca species are the most predominant... 

Research on the benthic phosphoms cycle and phosphorites formation in particular was intensified especially in the seventies to early nineties of the last century (e g. Burnet 1977 Burnett and Froelich 1988 Burnett and Riggs 1990 Nolton and Jarvis 1990 Follmi 1996 Gleim et al. 2000). All present result clearly substantiate that the process of phosphogenesis (= the authigenic formation of carbonate fluorapatite - CFA) is highly complex and not completely understood. However, hydroxy-apatite may be the primary authigenic P-... 

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