Production of calcium magnesium phosphate microspheres in a water-in-oil-in-water dispersion

ABSTRACT Interfacial reaction in a multiple water-in-oil-in-water dispersion, or double emulsion, was carried out to produce microspheres in a system containing calcium, magnesium and phosphate ions. The inner aqueous phase comprised dipotassium hydrogen phosphate solution. The outer aqueous phase comprised calcium chloride and magnesium chloride solution, in which polyoxyethylene(20) sorbitan monolaurate was dissolved as a stabiliser for the oil droplets. The oil phase comprised cyclohexane, in which sorbitan monooleate was dissolved as a stabiliser for the inner aqueous droplets. Hollow microspheres, were generated by this reaction, where the surface state changed from rough to smooth with increasing magnesium content in the outer aqueous phase. The morphology of the primary particles was altered from sheet-like to spherical. The crystalline phase was identified as calcium-deficient hydroxyapatite at lower magnesium contents and as magnesium-substituted β-tricalcium phosphate at higher magnesium contents by considering the lattice parameters and ionic ratio of the products. The existence of an amorphous phase was detected, irrespective of the magnesium content. The magnesium content in the product was lower than that of the reactant solution, suggesting that magnesium was eliminated through a purification process accompanied by crystallisation of the amorphous phase. The location of the reaction site and how the outer aqueous phase is transported thereto were discussed by comparison of the magnesium content of the products formed by the solution reaction with that of the product from the interfacial reaction.