Biological calcium hydroxyapatit

PAH/P04 -PAH/PSS capsules were employed for the biomimetic synthesis of calcium hydroxyapatite, CaiQ(P04)g(0H)2, inside polyelectrolyte capsules [53]. Transmission electron microscopy (TEM) analysis established preferable formation of the hydroxyapatite nanoparticles on the iimer side of the PAH/PSS shell, and this resulted in empty hydroxyapatite spheres. The thickness of the CajQ(P04)g(0H)2 layer is 100-120 nm, and is composed of 12- to 16-nm particles. The hydroxyapatite particles formed have shape and surface morphology which is different from the particles synthesized by common methods in solution. Other special properties of hydroxyapatite composite hollow shells, including surface acidity, catalytic and biological activity, as well as bone-repairing effects, can also be expected. 

In their publication, LeGeros and LeGeros (1993) oudine the different apatites, ranging from natural apatite (minerals) to biological (human dentin, enamel, and bone) and synthetic (chemically synthesized) apatite. This publication clearly shows that apatite is a group of crystalline compounds. The most important of these compounds is calcium hydroxyapatite. All the related crystal structures, such as fluoroapatite, chloroapatite, and carbonate apatite are derived from it. 

There are other absorbable fillers, such as collagen (bovine- or porcine-derived) injections, calcium hydroxyapatite (biodegradeable microparticles), poly(L-lactic acid) (PLLA) and non-absorbable fillers such as Artefill (polymethyl methacrylate (PMMA) with collagen) and silicone injections. Table 7.1 lists the most popular dermal fillers available in the United States [18]. Compared to the above-mentioned fillers, HA has the safest biological profile, and it is fully absorbable and biodegradable [19]. Crosslinking of its macromolecular chains increases its resistance to degradation by matrix metalloproteinases and extends its life in the body [6]. 

The biologically most relevant calcium phosphates are dahllite [carbonate hydroxyapatite, (Na,Ca)10(PO4,CO3)6(OH)2] francolite [carbonate fluoroapatite] hydroxyapatite [Ca10(PO4)6(OH)2]... 

The biocompatible CBPC development has occurred only in the last few years, and the recent trend has been to evaluate them as biocompatible ceramics. After all, biological systems form bone and dentine at room temperature, and it is natural to expect that biocompatible ceramics should also be formed at ambient temperature, preferably in a biological environment when placed in a body as a paste. CBPCs allow such placement. We have discussed such calcium phosphate-based cements in Chapter 13. Calcium-based CBPCs, especially those constituting hydroxyapatite (HAP), are a natural choice. HAP is a primary mineral in bone [3], and hence calcium phosphate cements can mimic natural bone. Some of these ceramics with tailored composition and microstructure are already in use, yet there is ample room for improvement. This Chapter focuses on the most recent biocompatible CBPCs and their testing in a biological environment. To understand biocompatible material and its biological environment, it is first necessary to understand the structure of bone and how it is formed. 

Calcium is one of the most common elements on earth. Most calcium involved in biological systems occurs as hydroxyapatite. a sialic, stabilizing structure like that found in bone. The remaining calcium is ionic (Ca ). Ionic calcium functions as a biochemical regulator, more often within the cell. The importance of calcium ions to physiological functions was realiz.ed first by Ringer, who observed in 1883 the role of Ca in cardiac contracliiity. 

The first and primary protective effect of fluoride is due to its strong, spontaneous reaction with metal ions. Biologically, the most important of these ions is the calcium ion, large amounts of which interact with phosphate to form bones and teeth. Studies show that fluoride reduces apatite solubility in acids by an isomorphic replacement of hydroxide ions with fluoride ions to form fluoro-hydroxyapatite and difluoro-apatite (Fig. 16.6a). 

Reviews of hydroxyapatite and other calcium orthophosphates including their inorganic and organic occurrences in nature, structure, transformations and biological and biomedical significance have been provided by Dorozhkin (2007) and Heimann (2010a). 

Phosphorus is required not only as a component of hydroxyapatite in bone, but also as a component of nucleic acids and many other biologically important molecules. Without phosphorus we would have no energy-storage molecules, such as ATP and creatine phosphate, for the energy derived from glycolysis and the citric acid cycle. The RDA for phosphorus is the same as that for calcium. Because it is abundant in most foods, a deficiency of phosphorus in the presence of an otherwise adequate diet is virtually impossible. 

---