Hydroxyapatite high crystallinity

Similarly, a composite of hydroxyapatite and a network formed via cross-linking of chitosan and gelatin with glutaraldehyde was developed by Yin et al. [ 169]. A porous material, with similar organic-inorganic constituents to that of natural bone, was made by the sol-gel method. The presence of hydroxyapatite did not retard the formation of the chitosan-gelatin network. On the other hand, the polymer matrix had hardly any influence on the high crystallinity of hydroxyapatite. 

Fig. 10.34 shows the INS spectrum of ox femur as the organic component is progressively removed [83]. Fig. 10.34a is very similar to that of the protein Staphylococcal nuclease. Fig 10.32, and emphasises one of the problems of working in this field because proteins are largely made of the same monomers (amino acids), the INS spectra of very different proteins tend to look very similar. Removal of the fat results in little change in the spectrum, Fig. 10.34b. It can be seen that elimination of the protein is highly effective, Fig. 10.34c the C-H stretching modes just below 3000 cm" and the C-H deformation modes at 1200-1500 cm have both disappeared. There is a weak, broad peak at 630 cm and its overtone near 1300 cm. For comparison, the INS spectrum of a highly crystalline reference hydroxyapatite is shown in Fig. 10.34d. The frequency match of the of the residual bone peak and that of the hydroxyapatite is exact, the width of the peak is attributed to heterogeneous broadening. The spectrum demonstrates that hydroxyl groups are still present in bone.

Fig. 10.33 Comparison of the infrared spectra of (a) highly crystalline hydroxyapatite (b) poorly crystalline hydroxyapatite and (c) defatted, deproteinated, dried bone showing the regions of the hydroxyl stretching vibration on the right and the hydroxyl libration on the left. Reproduced from [83] with permission from the PCCP Owner Societies.

Fig. 10.34 INS spectra of bone as the organic component is progressively removed [83]. (a) Dried, powdered bone, (b) after removal of fat and drying, (c) after removal of protein and drying and (d) highly crystalline hydroxyapatite.

Fig. 10.35 INS spectra of bone and model compounds in the O—H stretching region, recorded by two groups of workers. Left spectra recorded on LRMECS (IPNS) [84] (a) nanometre sized crystalline hydroxyapatite (b) micron sized crystalline hydroxyapatite, (c) bovine bone mineral, (d) bone mineral from rat. Right spectra recorded on HET (ISIS) [85] (e) highly crystalline hydroxyapatite, (f) ox femur bone mineral, and (g) brushite CaHP04.2H20. The dashed vertical lines show the position of the hydroxyapatite peaks.

Dey, A. and Mukhopadhyay, A.K. (2014) Nanoindentation study of phase-pure highly crystalline hydroxyapatite coatings deposited by microplasma spraying. Open Bioeng. /, in press. 

Figure 7.13 H-MAS NMR spectrum of as-sprayed hydroxyapatite (Hartmann ef a ., 2001). The inset shows the spectrum of a completely ordered, highly crystalline hydroxyapatite (Hartmann ef a/., 2000). L highly...

Fig. 8 Influence of geometry of the substratum on tissue induction and bone morphogenesis in highly crystalline sintered hydroxyapatites, (a and b) Intrinsic and spontaneous bone induction within the porous spaces of hydroxyapatite biomatrices implanted heterotopically in the rectus abdominis of an adult primate without the addition of exogenously applied BMPs/OPs.

These techniques are bas not only on the principle that lead-containing phosphates with the apatite structure are highly insoluble, but also that rapid reactions occur with apatite and lead ions at the sohd/aqueous solution interface [12, 13, 15, 20, 29, 48, 53, 56]. Removal of lead from aqueous solutions using synthetic hydroxyapatite gives aqueous lead concentrations below the maximum contamination level after Ih [12, 53]. Other workers [9] observed the formation of calcium-lead apatite solid-solutions after 3 mins contact between synthetic hydroxyapatite and aqueous solutions containing lead, and no lead was detected in the aqueous solution after 24 h contact. However, the efficiency of lead removal depends on the characteristics of the phosphate rock employed [15]. It has been shown that the composition and crystallinity of the phosphate influence the speed of the surface reactions [4, 44]. More highly crystalline solids have lower solubilities and dissolution rates, making the apatite less reactive [4]. The presence of fluoride in the hydroxyapatite structure decreases its solubility and dissolution rate, while the presence of carbonate decreases structural stability, and increases solubility and the dissolution rate [4, 35]. 

M. Nagano, T. Nakamura, T. Kokubo, M. Tanahashi, and M. Ogawa, Differences of bone bonding ability and degradation behaviour in vivo between amorphous calcium phosphate and highly crystalline hydroxyapatite coating. Biomaterials, 17 (18), 1771-1777,1996. 

Park, Y.-S., and Yamazaki, Y. (2005b). Novel Nafion/hydroxyapatite composite membrane with high crystallinity and low methanol crossover for DMFCs. Polym. Bull. 53, 181. 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

Raman spectroscopy is well suited for examining calcified tissues such as bones and teeth owing to its ability to probe both the inorganic and organic constituents of the tissue. The frequency and band shape of the symmetric and asymmetric phosphate stretching vibrations provide critical information on the crystallinity and orientation of the hydroxyapatite matrix. The analysis of a Raman spectrum of dental enamel provides features that are highly characteristic of the health and integrity of the tissue. 

Children are particularly vulnerable to excess strontium because the immature skeleton has a high rate of bone remodeling, and strontium adversely affects bone development in several ways, as demonstrated in animal studies. In chickens and rats, excess strontium suppresses the activation of vitamin D3 in the kidney, which severely reduces the expression of calbindin D mRNA and the translation of calbindin D protein in the duodenum (Armbrecht et al. 1979, 1998 Omdahl and DeLuca 1972). As a result, duodenal absorption of calcium is reduced. Strontium also binds directly to hydroxyapatite crystals, which may interfere with the normal crystalline structure of bone in rats (Storey 1961). In addition, excess strontium may prevent the normal maturation of chondrocytes in the epiphyseal plates of long bones of rats (Matsumoto 1976). Excess strontium apparently interferes with the mineralization of complexed acidic phospholipids that is thought to help initiate the formation of hydroxyapatite crystals in developing bone (Neufeld and Boskey 1994). As a result, affected bone contains an excess of complexed acidic... 

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