MORPHOLOGY OF SEMISOLID AQUEOUS PHOSPHATIDYLCHOLINE DISPERSIONS, A FREEZE-FRACTURE ELECTRON-MICROSCOPY STUDY

Semisolid aqueous dispersions of soy phosphatidylcholine (PC) with hig h PC mass fractions between 0.35 and 0.6 were prepared using a high-pr essure homogeniser. Their morphologies were investigated by freeze fra cture transmission electron microscopy (FF-TEM) with regard to the qua ntity of water present. With all lipid/buffer ratios studied, vesicula r structures in dense packing were seen on FF-TEM micrographs. PC rati os of up to 0.45 yielded small, unilamellar vesicles which were unifor m in size. Matrices of higher lipid/buffer-ratios (0.45-0.6) also cont ained these small unilamellar vesicles plus an increasing fraction of more heterogeneous large multivesicular or multilamellar vesicles. App arently, organisation of PC into small, homogeneous and unilamellar ve sicles is not limited to 'classical' liposome dispersions, i.e. dilute lipid dispersions (< 300 mM), but can also be achieved in more concen trated lipid dispersions of PC fractions of up to 0.45 (600 mM) when l ipid swelling is exerted under high mechanical stress conditions. (C) 1997 Elsevier Science Ireland Ltd.