Synthesis of Hydroxyapatite by Interfacial Reaction in a Multiple Emulsion

Isao Kimura

doi:10.1155/2007/71284

Abstract

Interfacial reaction in a multiple emulsion, which is one of methods for producing inorganic microspheres, was applied to synthesize hydroxyapatite. The multiple emulsion was a W/O/W emulsion, made of dipotassium hydrogen phosphate solution as an inner aqueous phase, benzene as an oil phase, and calcium nitrate solution as an outer aqueous phase. The reaction was carried out in the multiple emulsion for 24 hours at 323 K. The crystalline phase was varied with an initial pH of the inner aqueous phase, and single phase hydroxyapatite was synthesized at an initial pH of 12. The products were composed of porous microspheres of less than 3 μm in size. The microspheres were composed of nanospheres of less than 120 nm in size. By considering the mass balance, it was suggested that each nanosphere was formed in an inner aqueous phase droplet.

Highlights

Hydroxyapatite (Ca10(PO4)6(OH)[2], HAp) is a main inorganic constituent of hard tissues in the human body such as bones and teeth
The droplets of the inner aqueous phase were so small that they could not be observed with an optical microscope (OM) immediately after the preparation of the W/O emulsion
This suggests that the initial size of the inner aqueous phase droplets was less than 1 μm, because the droplets of larger than 1 μm were observable with the OM used

Summary

INTRODUCTION

Hydroxyapatite (Ca10(PO4)6(OH)[2], HAp) is a main inorganic constituent of hard tissues in the human body such as bones and teeth. For success in composite materials, it is generally required to homogeneously mix the ingredients and to prevent them separating. Microencapsulating an active component with HAp wall is thought to be meaningful. In the most common procedure for producing microcapsules with an inorganic wall, inorganic hollow particles or porous microspheres are prepared. After that, they are impregnated with an active component, and the wall is stuffed or covered with a suitable material. Hollow particles made of various substances have been produced by means of spray pyrolysis and interfacial reaction. Interfacial reaction is carried out in a multiple emulsion [17– 20] This method has a lot of advantages. The purpose of this study is to confirm whether HAp microspheres can be prepared by this method

EXPERIMENTAL

RESULTS AND DISCUSSION

C MHAp ρHAp y

CONCLUSIONS