Calcium phosphate with high specific surface area synthesized by a reverse micro-emulsion method

Abstract

ABSTRACTA reverse micro-emulsion method has been investigated to control crystal morphology in a nanometer region and to increase specific surface area for calcium phosphate. The nanocrystals with the control of its morphology is a candidate of drug delivery carriers. This study investigated the effects of mixing volume ratios of two surfactants, tween80 (T) and aliquate 336 (A) in kerosene as an oil phase, and pH values in the nano-region on crystalline phases and specific surface area of calcium phosphate synthesized by the reverse micro-emulsion method. A di-ammonium hydrogen phosphate solution including phosphoric acid at pH of 6.3 and a calcium nitrate solution at pH of 5.7 were adjusted, and both the solutions were separately added into the kerosene with the surfactants. Both the emulsions were then mixed at the same volume and the Ca/P ratio of 1.0, and stirred at room temperature for 24 hours. The crystalline phases were dependent on the T amounts; pure DCPD with the specific surface area of 6.7 to 12 m2/g was obtained at the T/A ratio of 4, the mixture of DCPD and DCPA with that of 48 to 162 m2/g was at the ratios of 5 to 8, and a low crystalline HAp with 163 m2/g was at the ratio of 9. These specific surface areas of DCPD (T/A=4) and HAp (T/A=9) were apparently higher than those prepared with a wet method, 7.8 times and 1.8 times respectively. DCPA with 43 m2/g was successfully produced to decrease the pH of phosphate solution at T/A of 9. The change of crystalline phases would be explained as follows; the increase of T amount decreased the micro-emulsion sizes to reduce bulk water to be DCPA, and increased the pH to precipitate HAp nanocrystals.