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The comparison of the influence of monomeric and dimeric surfactants on the transformation of amorphous calcium phosphate

A major problem encountered in the application of bone bioimplant materials is their slower rate of resorption in comparison to the rate of new bone formation. It was shown that the rate of new bone formation coincides more closely with the resorption rate of poorly crystalline or amorphous calcium phosphate (ACP) cements and ceramics [1]. But these materials still exhibit problems of mechanical strength, injectability, and application techniques. Coating ACP with surfactants could be the solution to some of these problems. In recent years, dimeric surfactants, consisting of two single-chain ionic surfactants linked by a spacer at head level, have attracted considerable attention due to their superior properties in comparison to conventional surfactants. In this work we have compared the influence on the transformation of ACP of monomeric dodecyltrimethlyammonium bromide, DTAB, with corresponding dimeric dimethylene-1, 2-bis(dodecyldimethlyammonium bromide), 12-2-12. ACP was precipitated by mixing equimolar calcium and phosphate solutions in the absence and presence of 12-2-12 surfactant monomers or micelles. Self-assembly of surfactant under conditions conducive to ACP formation was investigated by surface tension, zeta potential and size measurements. Transformation of ACP to crystalline phase was followed by monitoring pH. Precipitate was characterized by electron microscopy, size and zeta potential measurements. Obtained data where analyzed by one-way ANOVA. It was found that in the presence of phosphate ions DTAB forms only spherical micelles. 12-2-12 forms two kinds of micelles, spherical micelles at lower concentrations and larger micelles at higher concentrations, while in the absence of phosphate small and larger micelles are present in all investigated concentration region. DTAB monomers do not have significant influence on ACP transformation, while micelles, although not significantly affecting the rate of transformation, do significantly reduce the size of ACP particles. Both 12-2-12 monomer and micelles induces ACP formation, the size of the effect increasing in the order monomer – spherical micelles – larger micelles.

bioimplant materials ; amorphous calcium phosphate ; surfactants

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