Adhesion Deformation and Fusion of Bilayer Vesicles and Other Amphiphilic Structures in Solution

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Forces between amphiphilic structures such as bilayers, vesicles, microemulsion droplets and biological membranes are accompanied by elastic deformation of the structures as they approach and come into contact. These deformations are dependent on both the inter-aggregate and intra-aggregate forces and their coupling. This project is a study of the adhesion, fusion and accompanying structure deformations using direct force measurements, freeze-fracture, and in-situ frozen hydrate electron microscopy techniques. The experimental conditions are modified to test the effects of undulation, electrostatic interactions, hydration and hydrophobic interactions on the adhesion and fusion process. This is the first systematic effort to understand the coupling between inter-and intra-aggregate interactions and the resulting structural modifications that occur when amphiphilic structures are brought into contact. A video recording system allows one to follow the fusion process in real time using a surface forces apparatus. Though a number of these apparatus exist in various laboratories, none is being deployed to study the dynamics of fusion as in this work. The combination of rapid freezing, artifact-free freeze-fracture and in-situ frozen-hydrated electron microscopy applied to amphiphilic structures is also unprecedented. The techniques present direct images of three-dimensional structural transitions with molecular resolution. This project should have a major impact on both the theory and practice of all phenomena involving interbilayer and intermembrane interactions. The expected new insights into the fundamental forces and molecular events accompanying the fusion of micelles, bilayers, vesicles, microemulsion droplets, foams, emulsions and surfactant- coated colloidal particles will be especially important as this has been the focus of much attention in the colloid and biological sciences. The stability of vesicles and their usefulness as drug carriers, the stability of colloidal dispersions, breaking and creating foams and emulsions, the effectiveness of surfactants in flotation, and the wear of boundary lubricants are all examples where understanding of basic mechanisms are still lacking. Of greatest possible importance is the ability to directly study the interactions of real biological membranes and other specific interactions involving biological macromolecules.