Inorganic phase of bone

Composites made with carbon nanostructures have demonstrated their high performance as biomaterials, basically applied in the field of tissue regeneration with excellent results. For example, P.R. Supronowicz et al. demonstrated that nanocomposites fabricated with polylactic acid and CNTs can be used to expose cells to electrical stimulation, thus promoting osteoblast functions that are responsible for the chemical composition of the organic and inorganic phases of bone [277]. MacDonald et al. prepared composites containing a collagen matrix CNTs and found that CNTs do not affect the cell viability or cell proliferation [278]. 

The inorganic phase of bones or teeth is mainly hydroxyapatite (HA), and deviation in Ca/P ratio from common HA (Ca/P = 1.667) is explained by the presence of amorphous phosphates3). The biogenetic HA resembles in size crystals of HA prepared by precipitation from aqueous solutions. The chemical composition of biominerals is similar to HA. However, crystals in bone, dentine and enamel can vary... 

The nature of mineral phases present in bone, dentin, enamel and other phosphatic tissues, and their mode of formation have been subjects of lively discussions among health scientists and crystallographers. Bioscientists most commonly accept the viewpoint that the inorganic phase of bones or teeth is principally hydroxyapatite, Caio(P04)6(OH)2, and deviation in Ca/P ratio from common hydroxyapatite (Ca/P = 1.667) observed in mineralized tissues is explained by the presence of amorphous phosphates. In contrast, many crystallographers favor the idea of carbonate apatite, i.e. dahllite, as the major crystalline phase in biophosphates and they doubt the existence of amorphous phases. The topic has been reviewed14,15,22,28, 37,44,47,348-358) no common consent has yet been reached. In the following an attempt is made to at least coordinate the controversial findings. 

Araujo et al. (2008) prepared PCL electrospun nanofiber meshes coated with a biomimetic calcium phosphate (BCP) layer that mimics the extracellular microenvironment found in the human bone structure. The deposition of a calcium phosphate layer, similar to the inorganic phase of bone, on the PCL nanofiber meshes was... 

Some but not all of the apatite present in the body can take part in physicochemical exchange and substitution reactions. The proportion of the inorganic phase of bone which can participate in such reactions decreases as the bones become more highly mineralized. In adult animals about two-thirds of the skeletal mineral has been shown to be stable and unreactive. 

The normal range for the ionic product for serum of 13-25 (mg Ca and P per 100 ml) greatly exceeds the solubility product of 8 5 (mg Ca and P per 100 ml) for biological apatite (see above). Normal serum is thus supersaturated (or metastable) with respect to the solid inorganic phase of bone, dentine and enamel, but undersaturated with respect to calcium hydrogen phosphate. 

Diagenesis of the inorganic phase of cortical bone. In Price, T.D., ed.. Bone Chemistry and Past Behaviour. Cambridge, Cambridge University Press 211-229. 

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. 

There are three distinct biological minerals in an individual tooth, viz. enamel, dentin, and cementum. The chemical composition of dentin is quite similar to that of bone, containing 70 wt% of inorganic phase, 20 wt% of organic matrix and 10 wt% of water.83 The inorganic phase of tooth... 

Garside and Wyeth [60] have used Fourier transform infrared spectroscopy to characterise cellulose fibres such as jute, sisal, and cotton. The technique has also been used to determine low levels of polyvinyl pyrrolidinone in polysulfone [61]. Weiss and co-workers [62] used Fourier transform infrared microspectroscopy in the study of organic and inorganic phases of an injectable hydroxypropylmethylcellulose-calcium phosphate composite for bone and dental surgery. 

Bone is a porous tissue composite material containing a fluid phase, a calcified bone mineral, hydroxyapatite (HA), and organic components (mainly, collagen type). The variety of cellular and noncellular components consist of approximately 69% organic and 22% inorganic material and 9% water. The principal constiments of bone tissue are calcium (Ca ), phosphate (PO ), and hydroxyl (OH ) ions and calcium carbonate. There are smaller quantities of sodium, magnesium, and fluoride. The major compound, HA, has the formula Caio(P04)g(OH)2 in its unit cell. The porosity of bone includes membrane-lined capillary blood vessels, which function to transport nutrients and ions in bone, canaliculi, and the lacunae occupied in vivo by bone cells (osteoblasts), and the micropores present in the matrix. 

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