Adhesion kinetics of functionalized vesicles and mammalian cells: A comparative study.

The suitability of the quartz crystal microbalance technique (QCM) to monitor the formation and modulation of cell- substrate contacts in real time has recently been established. A more detailed analysis of the QCM response when living cells attach and spread on the resonator surfaces is, however, hampered by the chemical and mechanical complexity of cellular systems and the experimental difficulties to control one single parameter of cell-substrate contacts in a predictable way. In this study, we made use of liposomes as simple cell models and studied the interactions of these liposomes with the resonator surface. To mimic the specific interactions between cell and protein-coated substrate as given in cell culture experiments, we incorporated biotin-labeled lipids as "receptors" in the liposome shell and preadsorbed avidin on the resonator surface. The dissipational QCM (D-QCM) technology was applied to monitor the shifts in resonance frequency and energy dissipation during the adsorption of liposomes prepared with increasing amounts of biotin-labeled lipids. We also studied the adsorption kinetics of liposomes doped with biotin moieties that were attached to the lipid core by an alkyl spacer in order to increase the distance between liposome shell and resonator surface. A comparison of these data with the adhesion kinetics of mammalian cells as monitored by D-QCM is presented and discussed. Although the shifts in resonance frequency are very similar for intact liposomes and mammalian cells, the viscous energy dissipation is significantly higher when cells attach and spread on the resonator surface.