INFLUENCE OF CONCENTRATION OF CALCIUM-ION ON CONTROLLED PRECIPITATIONOF CALCIUM-PHOSPHATE WITHIN UNILAMELLAR LIPID VESICLES

The controlled precipitation of calcium phosphate within large unilame llar phosphatidylcholine (PC) vesicles with diameters of 80-120 nm has been studied by transmission electron microscopy, energy dispersive X -ray analysis and selected-area electron diffraction. The vesicles wer e filled with the aqueous solution, whose Ca2+ concentration was 4 and 0.03 mM, Ca/P was 1.67 and pH was 7.0. The vesicles were prepared by ether vaporization technique. The precipitation from the 4 mM solution within the vesicles was amorphous calcium phosphate (ACp) and it rema ined stable at room temperature. The ACp was transformed into HAp crys tals after treatment in hot water bath (60 degrees C) for 24 h. As for the 0.03 mM solution, which is nearly the critical saturation concent ration of HAp, the precipitated crystals were small HAp. The role of t he vesicle membrane in the controlled precipitation of calcium phospha te is discussed in terms of kinetic and spatial restrictions inherent in the reaction environment. The influence of concentration of calcium ion is also discussed. (C) 1998 Elsevier Science B.V. All rights rese rved.