One option for the production of liposomal active ingredient formulations involves a special extrusion process. First of all, an ethanolic solution of lipids, which are molecules that also occur naturally as the building blocks of cell membranes, are mixed with an aqueous phase in which the active pharmaceutical ingredient is present. During the mixing, tiny structures arise in which the lipids create a bilayer. Lipids are long molecules that have one hydrophilic (water-attracting) end and one hydrophobic (with little affinity to water) end. In aqueous systems, they line up parallel to one another and form a ball filled with water. The membrane that forms the outer shell of the liposome is a lipid bilayer, which is a double layer of lipids that is similar to the membrane surrounding a cell. This is one reason why researchers were fascinated by the discovery of liposomes. During the production of the formulation, medically active ingredients that are not soluble in water accumulate preferentially in the lipid bilayer, while water-soluble ingredients accumulate in the interior of the sphere.