Strontium hydroxyapatite

The nonstoichiometry of CaHAP has received extensive attention in medical and solid-state science, because the CaHAP formed in the calcified tissues or synthesized is mostly non- stoichiometric. Bett et al.[8] have reported that the catalytic activity of Ca-deficient CaHAP for the dehydration of butanol can be related to the surface acidic hydrogens of HPO4" produced to maintain the electrical neutrality. Joris and Amberg [9, 10] have pointed out that the catalytic activity of cation-deficient CaHAP and strontium hydroxyapatite (abbreviated SrHAP) for the similar dehydration reaction is due to the acidic hydrogens of the H2O molecules located in OH -defects caused by the deficiency of Ca + or Sr " " ions rather than those of the surface HPO ions. 

In contrast to the aforementioned, with strontium hydroxyapatite the selectivities are essentially independent of the composition of the catalyst, as is the Hj/COj ratio of 1.5. 

Conversion of Methane and Product Selectivities for Strontium Hydroxyapatite with and without... 

Figure 7. XRD patterns of SrHAp (A) and Pbo,je SrHAp (B) previously employed in obtaining the results shown in Table 2 but after 6 h on-stream. Symbols Open circles, strontium hydroxyapatite. Open triangles, strontium chlorapatite. Closed triangles, lead chlorapatite.

Joris SJ, Amberg CH (1971) The natnre of deficiency in nonstoichiometric hydroxyapatite. 11. Spectroscopic stndies of calcium and strontium hydroxyapatite. J Phys Chem 75 3172-3178 Kato H, Nishiguchi S, Furukawa T, Neo M, Kawanabe K, Saito K, Nakamura T (2001) Bone bonding in sintered hydroxyapatite combined with a new synthesized agent, TAK-778. J Biomed Mater Res 54 619-629... 

A similar study as reported earlier was also conducted on poly(butylene succinate) (PBSu) nancomposites with strontium hydroxyapatite nanorods (SrHNRs) and silica nanotubes (SiNts). The decomposition products were studied using thermogravimetry and pyrolysis-GC-MS [62]. A decomposition mechanism via ( -scissions is postulated for these materials as shown in Scheme 6.14. 

Lazic, S. Vukovic, Z. 1991. Ion exchange of strontium on synthetic hydroxyapatite. Journal of Radioanalytical and Nuclear Chemistry, 149, 161-168. ... 

Pujari, M. Patel, P. N. 1989. Strontium-copper-calcium hydroxyapatite solid solutions preparation, infrared, and lattice constant measurements. Journal of Solid State Chemistry, 83, 100-104. 

In the mouth, mineralization is controlled partly by proteins such as statherin from the salivary gland, which maintains a supersaturation of calcium and phosphate in the mouth. The basic mineral in tooth enamel is hydroxyapatite, in which it is possible to substitute Sr(II) for Ca(II), and F for OH isomorphously, hence the use of strontium and fluoride salts in toothpastes, said to confer extra strength to the enamel and antibacterial properties. 

Smiciklas, LD. et al.. The point of zero charge and sorption of cadmium(ll) and strontium(II) ions on synthetic hydroxyapatite, Separ. Purif. Technol., 18, 185, 2000. Newcombe, G., Hayes, R., and Drikas. M., Granular activated carbon Importance of surface properties in the adsorption of naturally occurring organics. Colloids Surf. A, 78, 65, 1993. 

Strontium is a less well-known element of Group 2, but it s important, nevertheless. Because of its chemical similarity to calcium, strontium can replace calcium in the hydroxyapatite of bones and form Sr5(P04)30H. This could be a problem only if the strontium atoms are the radioactive isotope strontium-90, which is hazardous if it is incorporated into a person s bones. 

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). 

Bone Toxicity. In addition to its effect on calcium absorption, excess absorbed strontium adversely affects bone development in several ways, leading to the development of rickets in children and young animals. Strontium binds directly to hydroxyapatite crystals, which may interfere with the normal crystalline structure of bone (Storey 1961). In addition, excess strontium may prevent the normal maturation of chondrocytes in the epiphyseal plates of long bones (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 phospholipid and a significantly lower ash weight. 

Christoffersen J, Christoffersen MR, Kolthoff N, et al. 1997. Effects of strontium ions on growth and dissolution of hydroxyapatite and on bone mineral detection. Bone 20(l) 47-54. 

Schoenberg HP. 1963. Extent of strontium substitution for calcium in hydroxyapatite. Biochim Biophys Acta 75 96-103. 

Boyd, A.R., Rutledge, L., Randolph, L.D., and Meenan, B.J. (2015) Strontium-substituted hydroxyapatite coatings deposited via a co-deposition sputter technique. Mater. 

Pure magnesium substrates were chemically pretreated at 70 °C with a Ca/Na phosphate solution to obtain a porous brushite layer and subsequently PEO at a voltage of 450 V, a frequency of 1000 Hz and a duty cycle of 40% to deposit strontium-containing hydroxyapatite (Lu et al., 2014). Figure 7.59 shows that the Sr-hydroxyapatite coating provided improved corrosion resistance in HBSS to the pure Mg substrate. The characteristic corrosion parameters are presented in Table 7.6. 

Fowler, B.O. (1974) Infrared studies of apatite I. Vibrational assignment for calcium, strontium, and barium hydroxyapatites utilizing isotopic substitution. Inorg. Chem., 13, 194-207. 

K. M.C., and Lu, W.W. (2007) Preparation and cell-materials interaction of plasma sprayed strontium-containing hydroxyapatite coating. Surf. Coat. Technol., 201, 4685 -4693. 

Bigi A, Gazzano M, Ripamonti A, Foresti E, Roveri N (1986) Thermal stability of cadmium-calcium hydroxyapatite solid solutions. J Chem Soc Dalton Trans, p 241-244 Bigi A, Falini G, Gazzano M, Roveri N, Tedesco E (1998) Stmctural refinements of strontium substituted hydroxyapatites. Mater Sci Forum 278 814-819... 

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