Lamellar Biogels: Fluid-Membrane-Based Hydrogels Containing Polymer Lipids

• Published in: Science (American Association for the Advancement of Science) Vol. 271; no. 5251; pp. 969 - 973
• Main Authors: Warriner, Heidi E., Stefan H. J. Idziak, Slack, Nelle L., Davidson, Patrick, Safinya, Cyrus R.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for the Advancement of Science 16.02.1996; American Association for the Advancement of Science; The American Association for the Advancement of Science
• Subjects: Analysis; Artificial membranes and reconstituted systems; Biological and medical sciences; Chemical Phenomena; Chemistry, Physical; Colloids; Curvature; Dimyristoylphosphatidylcholine - chemistry; Fluids; Fundamental and applied biological sciences. Psychology; Gelation; Gels; Hydrogels; Lipid Bilayers; Lipid research; Lipids; Lipids - chemistry; Membrane Fluidity; Membrane physicochemistry; Membranes; Microscopy, Polarization; Molecular biology; Molecular biophysics; Molecular Weight; P branes; Pentanols; Pentanols - chemistry; Phosphatidylethanolamines - chemistry; Polyethylene Glycols - chemistry; Polymers; String theory; Surface-Active Agents - chemistry; Viscosity; Water; X-Ray Diffraction; Ethylene oxide polymer; Molecular structure; Phase diagram; Molecular interaction; Artificial membrane; Hydrogel; Surfactant
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.271.5251.969

A class of lamellar biological hydrogels comprised of fluid membranes of lipids and surfactants with small amounts of low molecular weight poly(ethylene glycol)-derived polymer lipids (PEG-lipids) were studied by x-ray diffraction, polarized light microscopy, and rheometry. In contrast to isotropic hydrogels of polymer networks, these membrane-based birefringent liquid crystalline biogels, labeled L$_{\alpha,g}$, form the gel phase when water is added to the liquid-like lamellar L$_\alpha$ phase, 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 (∼50 weight percent) mixtures of free PEG (molecular weight, 5000) and water do not gel, gelation 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 in from the fluid lamellar L$_\alpha$ phase is the proliferation of layer-dislocation-type defects, which are stabilized by the segregation of PEG-lipids to the defect regions of high membrane curvature that connect the membranes.