Xiaolu Ge

In situ hydrothermal crystallization of hexagonal hydroxyapatite tubes from yttrium ion-doped hydroxyapatite by the Kirkendall effect.

An in situ hydrothermal crystallization method with presence of glutamic acid, urea and yttrium ions was employed to fabricate hexagonal hydroxyapatite (HAp, Ca5(PO4)3(OH)) tubes with length of 200 nm-1 μm. Firstly, yttrium ion-doped HAp (Y-HAp, Ca(5-x)Y(x)(PO4)3(OH)) was synthesized after hydrolysis of urea and HPO4(2-) ions at 100°C with a dwell time of 24h. The shift of X-ray diffraction peaks of HAp to high angle was caused the substitution of Ca(2+) ions by small-sized Y(3+) ions. At 160°C, further hydrolysis reactions of urea and HPO4(2-) ions resulted in the generation of ample OH(-) and PO4(3-) ions, which provided a high chemical potential for the dissolution of Y-HAp and recrystallization of HAp and YPO4. Finally, HAp tubes were formed in situ on Y-HAp according to the Kirkendall effect as a result of the difference of diffusion rate of cations (Ca(2+) ions, outward and slow) and anions (OH(-) and PO4(3-) ions, inward and fast). The formation process of HAp tube was simulated by the encapsulation of fluorescein molecules in precipitates. Photoluminescence properties were enhanced for HAp tubes with thick and dense walls. This novel tubular material could find wide applications as carriers of drugs, dyes and catalysts.

Release behavior of methylene blue dimers from silica-methylene blue@octacalcium phosphate powders in phosphate-buffered saline and lysosome-like buffer

Methylene blue-loaded silica (silica-MB) was coated by octacalcium phosphate (silica-MB@OCP) through a facile sol–gel method. Both MB monomers and dimers were released from silica-MB, while release of MB dimers from silica-MB@OCP was predominant in phosphate-buffered saline and lysosome-like buffer as an indicative of the influence of the molecular weight of polyethylene glycol (PEG) on the interaction density of shell network consisted of PEG, citric acid, ethylenediaminetetraacetic acid and OCP. The ratio evolution of absorbance of dimers over that of monomers was caused by the radical distribution of MB molecules in silica-MB and silica-MB@OCP. The investigation of MB dimers/carrier system would shed light on the investigation of MB dimers in photodynamic therapy for the specific treatment to outgrowing solid tumors with the disproportion between oxygen supply and consumption.Graphical Abstract

Crystallization of dicalcium phosphate dihydrate with presence of glutamic acid and arginine at 37 °C.

The formations of non-metabolic stones, bones and teeth were seriously related to the morphology, size and surface reactivity of dicalcium phosphate dihydrate (DCPD). Herein, a facile biomimetic mineralization method with presence of glutamic acid and arginine was employed to fabricate DCPD with well-defined morphology and adjustable crystallite size. In reaction solution containing more arginine, crystallization of DCPD occurred with faster rate of nucleation and higher density of stacked layers due to the generation of more OH(-) ions after hydrolysis of arginine at 37 °C. With addition of fluorescein or acetone, the consumption of OH(-) ions or desolvation reaction of Ca(2+) ions was modulated, which resulted in the fabrication of DCPD with adjustable crystallite sizes and densities of stacked layers. In comparison with fluorescein-loading DCPD, dicalcium phosphate anhydrate was prepared with enhanced photoluminescence properties due to the reduction of self-quenching effect and regular arrangement of encapsulated fluorescein molecules. With addition of more acetone, DCPD was prepared with smaller crystallite size via antisolvent crystallization. The simulated process with addition of amino acids under 37 °C would shed light on the dynamic process of biomineralization for calcium phosphate compounds.