engleski

AFM and dynamic light scattering study of amorphous calcium phosphate formation in the presence of monomeric and dimeric cationic surfactants

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. It is known that the highly hydrate spherulites of ACP grow by aggregation of much smaller primary particles and are subsequently joined together by secondary aggregation into chainlike structures [2]. Therefore coating of ACP primary particles 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 of monomeric dodecyltrimethlyammonium bromide, DTAB, and corresponding dimeric dimethylene-1, 2-bis(dodecyldimethlyammonium bromide, 12-2-12, on the transformation of ACP. AFM was successfully applied to study amorphous calcium phosphate formation in each step of aggregation process. In this work 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 non spherical micelles at higher concentrations. Combination of AFM and dynamic light scattering (DLS) enables to determine the size of both, primary particles and their secondary aggregates. The largest ACP primary particles were formed in the presence of both kinds of 12- 2-12 micelles as confirmed by AFM. However, DLS measurements have shown that the smallest ACP aggregates are obtained in the presence of both DTAB and 12-2-12 micelles. These findings could be explained by zeta potential measurements which show that charge of ACP particles becomes more positive with increasing surfactants concentration resulting in inhibition of aggregation at higher surfactant concentrations. [1] P. Frayssinet, J.L. Trouilelet, N. Rouquet, E. Azimus, and A. Autefage, Osseointegration of macroporous calcium phosphate ceramics having a different chemical composition, Biomaterials, 14 (1993) 423. [2] Lj. Brečević, V. Hlady, H. Füredi-Milhofer, Influence of gelatin on the precipitation of amorphous calcium phosphate, Colloids Surf. 28 (1987) 301.

amorphous calcium phosphate; surfactants

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