Calcium bone, hydroxyapatite

As well as being used as a scaffold for tissue engineering, Hutchens et al. [64] described the creation of a calcium-deficient hydroxyapatite, the main mineral component of bone. Calcium phosphate particles were precipitated in BC by consecutive incubation of calcium chloride and sodium phosphate solutions. Initial tests with osteoblasts in the in vitro evaluation showed that solid fusion between the material and the bone tissue is possible. Hence, this material is a good candidate for use as a therapeutic implant to regenerate bone and heal osseous damage. 

The spaces between the ends of the tropocollagen molecules in a collagen fiber (see Fig. 4) are the nucleation sites for the deposition of a form of calcium phosphate, hydroxyapatite, in bone formation. Further hydroxyapatite is added until the nucleation sites grow and join with one another to form the mature bone structure. 

Key Words Biomineralization, Solid-state NMR, Biominerals, Calcium phosphate, Hydroxyapatite, Bone, Dentin, Ca-43 NMR, P-31 NMR, HAp. 

Calcium oxalate is relatively insoluble and is poorly absorbed by the gut. Calcium oxalate can be dissolved to concentrations attainable by other "insoluble" nutrients, such as the long-chain fatty acids. Only about 10% of the calcium supplied as Ca oxalate is absorbed by the human gut. The calcium of spinach is only 5% absorbable. This calcium occurs largely as calcium oxalate. It is not clear why the mineral in spinach appears to be less absorbable than pure calcium oxalate. Hydroxyapatite, a pure crystal resembling that of bone, has a solubility and absorbability similar to those of Ca oxalate. 

OC contains three specific glutamyl residues at amino acid positions 17, 21, and 24, which may be converted to y-carboxyglutamyl residues by a posttranslational, vitamin K-dependent enzymatic carboxylation. This unique car-boxylated amino acid binds calcium ions and is found in various proteins involved in blood coagulation and in calcium transport, deposition, and homeostasis. Undercar-boxylated OC, which has been reported in serum in some conditions, may be related to decreased bone density and may respond to administration of vitamin K. Although OC binds calcium and hydroxyapatite, its physiological role is unknown. 

Phosphorus is part of bone hydroxyapatite [3Ca3(P04)2(0H)2]. Normally the body has sufficient phosphorus and bone resorption is not required. Insufficient intake (e.g., carbonated beverages replacing miUc) or increased phosphorous-bound calcium complexes (e.g.,... 

Strontium distributes relatively uniformly within the bone volume where it exchanges with calcium in hydroxyapatite (see Section 3.5.1), although small differences in the calcium and strontium distributions within bone have been reported. The Sr Ca concentration ratio in bone increases with age from approximately 0.3 mg strontium/g Ca at birth to a value of 0.5 in adults (Papworth and Vannart 1984 Tanaka et al. 1981). The Sr Ca ratio in bone also has been shown to vary with the bone type ratios in cortical bone were approximately 10-20% higher than in trabecular bone (Tanaka et al. 1981). 

Phosphate is present in plasma, extracellular fluid, cell membrane phospholipids, intracellular fluid, collagen, and bone. More than 80% of total body phosphate is found in bone and -15% in soft tissues. Phosphorus (P) in the body exists in both organic and inorganic forms. Organic forms include phospholipids and various organic esters. In extracellular fluid, the bulk of phosphorus exists as inorganic phosphate (Pj) in the form of NaH PO and NajHPO. The aggregate level of Pj modifies tissue concentrations of Ca + and plays a major role in renal acid excretion. Within bone, phosphate is complexed with calcium as hydroxyapatite and calcium phosphate. 

It has been suggested that the mineral portions of bone and tooth tissue are calcium-deficient hydroxyapatites (Posner and Perloff, 1957 Neuman and Neuman, 1953). The possible presence of hydrogen bonds in these materials may provide a much needed parameter for an estimation of the stoichiometry of these biological hydroxyapatites under varying conditions (Posner et al, 1960). 

Calcium-based composites rely on their similarity to the mineral component of natural bone— hydroxyapatite (HA). The theory behind their use is that the body will see these materials as tissues that need to be remodeled, allowing them to be integrated with and then replaced by bone. Tricalcium phosphate [TCP, Ca3(P04)2], calcium sulfate [plaster of paris, CaS04], and hydroxyapatite [Ca,o(P04)s(OH)2] are all currently being used to fill bony deflects and stimulate or direct bone formation. Calcium suifate has been used for over a century due to its ready availability and bio-... 

The a form can be prepared by heating a dry mix of calcium pyrophosphate and chalk (5.65), while the P form (whitlockite) is obtained from aqueous Ca(OH>2 and H3PO4 with pH > 6.0. The P form is also obtained by heating bone hydroxyapatite at 700 C. 

Intensive investigations on preparation, characterization, and application experiments of bacterial nanocellulose tubes are also reported by Helenius et al. (2006) and Bodin et al. (2007a). As part of investigations on bone repair, Hutchens et al. (2006) demonstrated by combination of hydroxyapatite and bacterial nanocellulose that bacterial nanocellulose provides a template for the ordered formation of calcium-deficient hydroxyapatite (CDHAP), the natural mineral component of bone. An... 

Kasten, R, Luginbuhl, R., van Griensven, M., Barkhausen, T., Krettek, C., Bohner, M., and Bosch, U. 2003. Comparison of human bone marrow stromal cells seeded on calcium-deficient hydroxyapatite, P-tricalcium phosphate and deminerahzed bone matrix. Biomaterials 24 2593-603. 

The skeleton acts as the storage site for calcium. Bone calcium exists primarily in the form of hydroxyapatite (Caio(P04)6(OH)2), and this mineral comprises 40% of bone weight. In the short term, the release of calcium from bone serves to maintain... 

Formation of useful materials from polyphosphazenes is an important aspect of their utility. For example, a report discussed that phosphazene mixed in a 1 1 ratio with the ethyl ester of glycylglycine and 4-phenylphenol could be electrospun as a composite with poly(lactide-co-glycolide) into fiberous materials that may promote bone regeneration. Other polymers that have shown promise for orthopaedic application include amino acid substituted materials with phenolic residues (67 and 68). These materials were used to form biodegradable phosphazene-calcium-defident hydroxyapatite composites. Microparticles, on the order of 2 pm, have been formed from poly[(glycine ethyl ester)-(phenylalanine ethyl ester)phos-phazene] (69) using electrohydrodynamic atomization. Mechanisms for formation of the particles was discussed in an associated paper. ... 

Blood Calcium Ion Level. In normal adults, the blood Ca " level is estabhshed by an equiUbrium between blood Ca " and the more soluble intercrystalline calcium salts of the bone. Additionally, a subtle and intricate feedback mechanism responsive to the Ca " concentration of the blood that involves the less soluble crystalline hydroxyapatite comes into play. The thyroid and parathyroid glands, the fiver, kidney, and intestine also participate in Ca " control. The salient features of this mechanism are summarized in Figure 2 (29—31). 

Hydroxyapatite (HA) coating on the surface of the hip stem and the acetabular cup is the most recent advancement in artificial hip joint implant technology. This substance is a form of calcium phosphate, which is sprayed onto the hip implant. It is a material found in combination with calcium carbonate in bone tissue, and bones can easily adapt to it. When bone tissue does grow into HA, the tissue then fixes the hip joint implant permanently in position. These HA coatings are only used in press-fit, noncemented implants. 

Four of the main-group cations are essential in human nutrition (Table A). Of these, the most important is Ca2+. About 90% of the calcium in the body is found in bones and teeth, largely in the form of hydroxyapatite, CatOH)2 - SCa PO. Calcium ions in bones and teeth exchange readily with those in the blood about 0.6 g of Ca2+ enters and leaves your bones every day. In a normal adult this exchange is in balance, but in elderly people, particularly women, there is sometimes a net loss of bone calcium, leading to the disease known as osteoporosis. 

---