Organic phase of bone

The most commonly employed model is the early uptake (EU) model, where U is deemed to have been taken up sufficiently shortly after burial for the bone to approximate to a closed system. Justification for the validity of early uptake seems to have stemmed from Szabo s (1979) suggestion, later elaborated on by Rae and Ivanovich (1986), that Uranium is fixed in the bone in the U oxidation state, facilitated by the reduction of U by decay products of the organic phase of bone, collagen. Since the bulk of collagen is lost rapidly from the bone (on the U-series time-scale at least), it is assumed Uranium will be taken up rapidly, and then uptake will cease. 

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]. 

It would seem that X-ray diffraction or electron microscopic studies of the bone minerals could help in describing the mineral phase of the bone. Unfortunately, specialists do not agree on a uniform description of the crystal morphology of bone. At least three different interpretations of the observations made by X-ray diffraction or by electron microscopy prevail. A brief outline of the three theories is presented. On the basis of electron microscopic examination, the mineral phase of bone is described as a honeycombed mineral framework. The organic substance is enclosed... 

Degradation and complete removal of the organic component of bone is accompanied by mass loss of about 20-29% [9, 28-30, 32], emission of carbon dioxide (identified by mass spectrometry coupled with thermogravimetric analysis [7, 31]), and the release of water, associated in some studies to the bone organic phase decomposition [7] or loss of water from the hydroxyapatite crystal structure [30, 43]. Mass loss varies depending on the place of sampling [19,43], tissue type (cortical or cancellous) [30] or tissue health state [31,43]. 

Using collagen I as the organic phase in bone-biomimetic nanocomposites comes to nature the nearest. Collagen initiates and orientates HA crystal growth and is reported to be responsible for size and distribution of HA crystals in natural bone [37]. 

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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