Liposome fixation by UV polymerization

In standard dehydration and epoxy embedding of biological material, substantial portions of lipid are extracted. In addition, the mechanisms of lipid fixation by osmium tetroxide are either unknown or poorly understood. Liposomes, particles of lamellar liquid crystalline lipid in water, react immediately with osmium, but are not preserved and the bulk of the lipid is removed in subsequent processing. Several authors heve attempted to improve lipid retention by using water-soluble embedding media, various dehydration techniques, etc., with varying degrees of success. The structure and morphology of the lipid bilayers in tissue or in liposomes remains open to question. To deal with these problems, a new type of lipid which can be polymerized was developed. The synthetic lipid, N,N dimethyl, di(ethoxycarbonyl-2,4-hexadecadienyl)ammonium iodide, DDEAI, incorporates a polymerizable conjugated diene moeity in each tail of the molecule. The counterion in the head group is iodide, which provides a strong, yet localized electron scattering site which precludes the need for other stains (Fig. 1.).