Silicone-stabilized liposomes

The present work is focused on stabilization of liposomes by covering their surface with a thin silicone layer. The appropriate silicone monomer was obtained by the hydrosilylation of vinylmethyldimethoxysilane with 1,3,5,7-tetramethylcyclotetrasiloxane. The surface potential of egg yolk phosphatidylcholine vesicles was modified by incorporation of a cationic double-tailed surfactant, dimethyldioctadecylammonium bromide (DODAB), yielding cationic liposomes. The silicone material was deposited on the cationic liposomes in base-catalyzed polycondensation/polymerization processes of the monomer at the liposomal surface. In order to initialize the processes pH of the liposomal dispersion was adjusted to the values of 8.5 or 10.2. The formed structures were characterized using dynamic light scattering (DLS) and zeta potential measurements. The DLS measurements show that the size of covered liposomes decrease during the reaction and the zeta potential turned to negative value, as can be expected. The morphology of the structures was evaluated using transmission cryo-electron microscopy (cryo-TEM). The cryo-TEM micrographs revealed the presence of the covered liposomes of sizes lower than the initial liposomes, which is in line with DLS measurements. However, some disintegration of the liposomes occurred during the covering procedure, especially at high pH value. Using the surfactant lysis and calcein-release study it was shown that silicone-covered liposomes are stable.