Intrinsic Colloidal Attraction/Repulsion between Lipid Bilayers and Strong Attraction Induced by Non-adsorbing Polymers

  • Evan Evans
  • David Needham


Surfactant bilayers in aqueous media interact non-specifically via long range electrostatic, electrodynamic, and solvation forces.1–5 Even though the magnitude of each interaction can be very large, the free energy minimum at stable contact is usually small with a progressive increase in depth as bilayer separation decreases. Addition of large, non-adsorbing polymers (e.g. dextran or polyethylene oxide) can greatly augment the weak natural attraction between bilayers to force them into closer proximity (perhaps sufficiently close to facilitate fusion). With micromechanical experiments on giant bilayer vesicles, direct measurements are made of free energy potentials for assembly of two bilayers to adhesive contact in salt solutions and in concentrated polymer solutions.6–14 Results for neutral and charged lipid bilayers in salt buffer correlate well with classical prescriptions for van der Waals attraction and electric double-layer repulsion based on structural data derived from published X-ray diffraction studies. Adhesion in concentrated solutions of non-adsorbing polymers is promoted by interaction of depletion layers due to polymer exclusion from the bilayer surfaces. For equilibrium exchange of polymer between the gap and bulk regions, the added attraction is shown to be simply the osmotic pressure difference between the bulk polymer concentration and the depreciated value at the mid-point of bilayer separation.


Virial Coefficient Adhesion Energy Free Energy Excess Bulk Region Dextran Solution 
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Copyright information

© Plenum Press, New York 1988

Authors and Affiliations

  • Evan Evans
    • 1
  • David Needham
    • 2
  1. 1.Pathology and PhysicsUniversity of British ColumbiaVancouverCanada
  2. 2.Mechanical Engineering and Material ScienceDuke UniversityDurhamUSA

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