AVS 46th International Symposium
    Biomaterial Interfaces Group Tuesday Sessions
       Session BI-TuP

Paper BI-TuP16
Kinetics of Vesicle Adhesion and Fusion

Tuesday, October 26, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: K. Glasmästar, Chalmers University of Technology and Göteborg University, Sweden
Authors: K. Glasmästar, Chalmers University of Technology and Göteborg University, Sweden
F. Höök, Chalmers University of Technology and Göteborg University, Sweden
C.A. Keller, Chalmers University of Technology and Göteborg University, Sweden
V.P. Zhdanov, Chalmers Univ. of Tech., Göteborg Univ., Sweden and Institute of Catalysis, Novosibirsk, Russia, Sweden
B. Kasemo, Chalmers University of Technology and Göteborg University, Sweden
Correspondent: Click to Email
Vesicle adhesion and fusion are essential in many cellular processes and in the formation of supported membranes. Because of their similarity to natural membranes, they play an important role in the development of biosensors and in model studies of membrane-mediated processes. We have studied the kinetics of adsorption of small unilamellar lipid vesicles on carefully prepared SiO@sub 2@ surfaces and their subsequent fusion to form a lipid bilayer, using surface plasmon resonance (SPR) and a new quartz crystal microbalance (QCM-D) technique. With the latter the energy dissipation (D) and the resonance frequency (f) of the QCM oscillator are measured. The lipid mass adsorbed at the surface and the mass of water trapped by the adsorbed layer are measured as changes in f. The SPR technique is only sensitive to the amount of lipid adsorbed. Since one of the primary differences between lipids adsorbed as vesicles or as a bilayer is the water trapped within and between the vesicles, the combination of the two techniques provides a detailed picture of how a lipid bilayer forms on the SiO@sub 2@ surface. In addition the two types of adsorption have very different viscoelastic properties, which are reflected in the D factor. The formation of a lipid bilayer on a SiO@sub 2@ surface is a two-stage process. First a layer of intact vesicles adsorbs on the surface. Then at a sufficiently high surface concentration the vesicles begin to break and form a fluid bilayer. From detailed QCM-D and SPR measurements at different vesicle concentrations in the liquid phase, we find that (i) the adsorption is irreversible, (ii) it is rate limited by bulk diffusion, (iii) vesicle to bilayer transformation starts at a critical surface coverage, after which (iv) further adsorption from the bulk phase drives the vesicle to bilayer transformation. The kinetics of these events is further elucidated by Monte Carlo simulations, employing different mechanistic models for the kinetics.