LAMELLAR BIOGELS - FLUID-MEMBRANE-BASED HYDROGELS CONTAINING POLYMER LIPIDS

A class of lamellar biological hydrogels comprised of fluid membranes of lipids and surfactants with small amounts of low molecular weight p oly(ethylene glycol)-derived polymer lipids (PEG-lipids) were studied by x-ray diffraction, polarized light microscopy, and rheometry, In co ntrast to isotropic hydrogels of polymer networks, these membrane-base d birefringent liquid crystalline biogels, labeled L(alpha,g), form th e gel phase when water is added to the liquid-like lamellar L(alpha) p hase, which reenters a liquid-like mixed phase upon further dilution. Furthermore, gels with larger water content require less PEG-lipid to remain stable, Although concentrated (similar to 50 weight percent) mi xtures of free PEG (molecular weight, 5000) and water do not gel, gela tion does occur in mixtures containing as little as 0.5 weight percent PEG-lipid, A defining signature of the L(alpha,g) regime as it sets i n from the fluid lamellar L(alpha) phase is the proliferation of layer -dislocalion-type defects, which are stabilized by the segregation of PEG-lipids to the defect regions of high membrane curvature that conne ct the membranes.