Hydrodynamic shear dissipation and transmission in lipid bilayers

Abstract

Vital biological processes, such as trafficking, sensing, and motility, are facilitated by cellular lipid membranes, which interact mechanically with surrounding fluids. Such lipid membranes are only a few nanometers thick and composed of a liquid crystalline structure known as the lipid bilayer. Here, we introduce an active, noncontact, two-point microrheology technique combining multiple optical tweezers probes with planar freestanding lipid bilayers accessible on both sides. We use the method to quantify both fluid slip close to the bilayer surface and transmission of fluid flow across the structure, and we use numerical simulations to determine the monolayer viscosity and the intermonolayer friction. We find that these physical properties are highly dependent on the molecular structure of the lipids in the bilayer. We compare ordered-phase with liquid disordered-phase lipid bilayers, and we find the ordered-phase bilayers to be 10 to 100 times more viscous but with 100 times less intermonolayer friction. When a local shear is applied by the optical tweezers, the ultralow intermonolayer friction results in full slip of the two leaflets relative to each other and as a consequence, no shear transmission across the membrane. Our study sheds light on the physical principles governing the transfer of shear forces by and through lipid membranes, which underpin cell behavior and homeostasis.

Nanomechanics of self-assembled surfactants revealed by frequency-modulation atomic force microscopy

“…In contrast, since those in the gel phase behave like a solid, the molecules are not equilibrated and remained on the surface even under the tip interaction, which causes the significantly higher P tip accompanied by an irreversible disruption process. These results are consistent with previous studies that showed viscosity 52 as well as Young's modulus 53 in a gel phase exhibits more than one order of magnitude greater than those in a fluid phase. Note that although SM-AFM is also utilized for evaluating the energy loss during the entire force profile, FM-AFM has the advantage that it can be evaluated at the moment of the hemifusion-and-dissociation processes.…”

Effect of boundaries on displacements and motion in two-dimensional fluid or elastic films and membranes

“…On the other hand, our results will support the quantification of the behavior of inclusions in real set-ups, for instance, in flat anchored or clamped biological or artificial membranes [34][35][36][37][38][39][40]. Particularly, we hope to stimulate by our work quantitative experimental investigations and confirmation of our results.…”

Protein-coated nanoparticles exhibit Lévy flights on a suspended lipid bilayer

“…However, this difference may come from the difficulty of quantifying friction between the bilayer surface and the NPs. 46–48 Considering friction for the case of NPs moving at the bilayer surface, the corrected Stokes–Einstein equation can be expressed as: 46–48 where c ( λ ) is a dimensionless parameter and η m is the membrane viscosity. There are considerable discrepancies between the reported membrane viscosity η m from the motion of particles strongly attached to a lipid bilayer.…”

“…However, this difference may come from the difficulty of quantifying friction between the bilayer surface and the NPs. [46][47][48] Considering friction for the case of NPs moving at the bilayer surface, the corrected Stokes-Einstein equation can be expressed as: [46][47][48]…”