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Abstract

Hydroxyapatite (HA), the main component of bone and teeth, can improve its structure by incorporation of traces of silicon (Si). This paper reports a synthesis of Si-substituted calcium phosphate compounds via a chemical precipitation process. The solutions of hydroxyapatite and fumed silica were homogeneously mixed before precipitation using ammonia. The resultant solutions were then filtered and the obtained powders were calcined at various temperatures. It was found that the phase of as-precipitated powders was HA with an average size of 15 nm. However, β-tricalcium phosphate (TCP) was formed at the calcined temperature of 800°C. From Fourier-transform infrared spectroscopy spectra, the Si-O peaks were observed when the as-precipitated powder was heated. It was concluded that there was a substitution of silicate ions for phosphate ions in the HA or β-TCP structure. To evaluate the effect of silicon on the bioactivity in vitro, pure HA and silicon-substituted HA (Si-HA) powders were uniaxially pressed and the samples were soaked in simulated body fluid at 37°C for various periods of time. It was found that after 2 weeks of soaking, the surface of the Si-HA sample was covered by apatite layers, whereas that of pure HA remained unchanged even after 4 weeks. These results showed that the presence of silicon can enhance the bioactivity of HA.

Structural Analysis of Strontium-Substituted Hydroxyapatites

“…However, the main limitation of this synthetic material is its brittleness and low resorption rate due to its high crystallinity [1]. Therefore, many efforts have attempted to modify the composition of synthetic HA by ionic substitutions [2][3][4]. Among them, strontium (Sr) is known to be the essential trace element for life 1 .…”

Synthesis and characterization of a new labeled gastrin ligand, 125I‐BH‐[Leu15]‐gastrin‐(5‐17), on binding to canine fundic mucosal cells and Jurkat cells

“…Some analogs were therefore synthesized by substitution of methionine in position 15 by leucine or norleucine (25,26). In the same way, labeling of gastrin-I with iodogen (27,28) seemed to give a high specificity binding (23,29) and a ligand with a good biological activity (28)(29)(30) but unable to discriminate between gastrin and CCK receptors. The major concern with the iodinated available labeled ligands is the presence of the iodine on the tyrosine residue close to the C-terminal active tetrapeptide, which might interfere with binding characteristics and specific biological activities of gastrin.…”

“…The hypothesis has been stated that chloramine T was able to oxidize the methionine and probably the tryptophan as well, leading to the alteration of the iodinated ligand. In fact, substitution of the methion-ineI5 by a leucine or a norleucine in gastrin-I led to iodinated derivatives having a good binding for gastrin binding sites and exhibiting a correct biological activity (3,15,(20)(21)(22)(23)(24). Some analogs were therefore synthesized by substitution of methionine in position 15 by leucine or norleucine (25,26).…”