Stabilized liposomes

#1. Field of the Invention

#This invention relates to a stabilized liposome composition capable of conveying active agents in cosmetic or pharmaceutical compositions and delivering them to the skin or other biological target such as the nails, hair, mucous membranes or even internally. The liposomes are carriers for the actives and are sometimes described as vectors for their ability to transport the active agent. More particularly, in preferred embodiments, the invention provides stabilized liposome compositions which can encapsulate or other wise contain acidic, water-soluble active ingredients, for example AHA's in cosmetic compositions, especially emulsions, such as creams lotions and gels, adequately through formulation and storage to deliver the actives to consumers, patients, or others, with their activity retained.

#Liposomes or "lipid bodies", sometimes called "vesicles" are structures formed spontaneously by polar lipid molecules, or amphiphilic molecules, each having a polar head and a long hydrophobic tail, e.g. phospholipids such as lecithin. Structurally, liposomes comprise an outer shell of one or more membrane-like, bilayers of the molecules arranged concentrically around a hollow interior, or "vacuole" which can serve as a storage compartment for active agents. In the outer layer the polar heads of the molecules are oriented outwardly of the liposome, while the hydrophobic tail, e.g. palmitic or stearic acid, depends inwardly. If there are multiple layers, the orientation is reversed in alternate layers so that the lipid tails of one layer intermingle with the lipid tails of the next, and the polar heads of one layer abut those of a neighbor.

#One or more ways of carrying out the invention are described in detail below with reference to the single FIGURE of the accompanying drawing which illustrates a single specific embodiment of the invention and is a schematic, much simplified cross-sectional view of a stabilized liposome according to the invention.

#All parts and proportions referenced in this description, unless otherwise stated, are on a weight or weight-for-weight basis.

#In a preferred embodiment, the present invention provides stabilized liposomes by adding a quaternized cellulose to suitable liposome membrane-forming polar lipid material, notably lecithin, during formation of the liposomes, to inhibit the resultant liposomes from aggregating in the presence of solvents and surfactants or under adverse pH conditions. Referring to the drawing, a liposome particle, or vesicle, comprises a shell-like outer layer of lecithin molecules 10 arranged, in an idealized conception, on the surface of a sphere. The lecithin molecules have polar heads 12 aligned to the outside of the liposome particle, and each has twin hydrophobic, lipophilic fatty acid tails 14 shown as aligned generally radially inwardly. It may be surmised that the fatty acid tails 14, which bind weakly together, will intermingle with their neighbors lending lateral adhesion to the liposome structure. Equally, the polar character of the head 12 of a lecithin molecule has the nature of a dipole with a positive charge located in the vicinity of lecithin's distal quaternary nitrogen atom, and a negative charge in the vicinity of its neighboring phosphatidyl group. The structural formula may be depicted as follows:

#ROOCCH.sub.2.ROOCCH.CH.sub.2 P.sup.- O.sub.4 CH.sub.2 CH.sub.2 N.sup.+ (CH.sub.3).sub.3