ИСТИНА

Liposome is a spherical particle formed by a lipid bilayer in aqueous media. Due to relative ease of preparation, low toxicity and ability to carry different compounds in both aqueous core and lipid bilayer have made this system most prominent in drug delivery applications. Complexation of liposomes with mi-crogels – networks of cross-linked macromolecules, may allow adding sensitivi-ty to a certain stimulus and ability to codeliver several compounds at once. Composition of a liposome-microgel complex may be defined as the average number of liposomes adsorbed on one microgel. This parameter may be varied at will since it is simply controlled by the concentrations of liposome and microgel solutions used. However, the liposome-to-microgel ratio controls several key properties of this system. First of all, when anionic liposomes bind to the surface of positive microgel, the charge is neutralized. If a microgel solution is titrated with a liposome solu-tion then aggregation rate is close to zero at low ratios, because the particles formed are overall positively charged, speeds up at intermediate values since the total charge is not large enough to prevent association, and slows down again when the surface of microgel is fully covered with liposomes. The constructed system is temperature-sensitive: when microgel is heated to 40-60°C, it significantly shrinks and the adsorbed doxorubicin-encapsulating liposomes release all their contents. Release kinetics are defined by the composition of the complex: doxorubicin is released faster at lower liposome-to-microgel ratios since the number of adsorption sites from which leakage may be accelerated is bigger in this case. Interestingly, there is no relation between composition and the highest ionic strength at which a complex may be formed. A rather simple explanation may be given: the strength of interaction should be defined by surface charge density. The complex where either a microgel or a liposome carries more charge is expected to sustain its stability at higher ionic strengths when compared to a system where charge density is lower. Thus, the number of adsorbed liposomes has no effect on stability in water-salt media.