Adhesion-induced phase behavior of two-component membranes and vesicles

Biomembrane Adhesion to Substrates Topographically Patterned with Nanopits

We examine the adhesion of biomembranes to substrates topographically patterned with concave nanopits and identify several universal features in the adhesion process. We find three distinct states, depending on whether the membrane remains flat above the nanopit, partially enters it, or completely adheres to it, and derive analytical conditions for the stability of these states valid for a very general class of nanopit shapes. Surprisingly, completely adhered states are always (meta)stable. We also show that the presence of many nanopits can increase or decrease the effective adhesiveness of a substrate, depending on the tension of the membrane and the strength of the membrane-substrate attraction. Our results have implications regarding several experimental methods, which involve the formation of supported lipid bilayers on substrates patterned with nanopits, as well as observations of decreased spreading of cells and migration of cells toward regions of lower nanopit density on topographically patterned substrates. Furthermore, our predictions can also be directly tested in experiments exploring the adhesion of micropipette-aspirated giant vesicles to such substrates.

Membrane adhesion and the formation of heterogeneities: biology, biophysics, and biotechnology

Membrane adhesion is essential to many vital biological processes. Sites of membrane adhesion are often associated with heterogeneities in the lipid and protein composition of the membrane. These heterogeneities are thought to play functional roles by facilitating interactions between proteins. However, the causal links between membrane adhesion and membrane heterogeneities are not known. Here we survey the state of the field and indicate what we think are understudied areas ripe for development.

Remodeling of membrane compartments: some consequences of membrane fluidity

Biological membranes consist of fluid bilayers with many lipid and protein components. This fluidity implies a high flexibility that allows the membranes to attain a large variety of different shapes. One important shape parameter is the spontaneous curvature, which describes the asymmetry between the two leaflets of a bilayer and can be changed by adsorption of 'particles' such as ions or proteins from the aqueous phases. Membrane fluidity also implies that the membranes can change their local composition via lateral diffusion and form intramembrane compartments. Two mechanisms for the formation of such compartments can be distinguished: membrane segmentation arising from structured environments and domain formation as a result of phase separation within the membranes. The interplay between these two mechanisms provides a simple and generic explanation for the difficulty to observe phase domains in vivo. Intramembrane domains can form new membrane compartments via budding and tubulation processes. Which of these two processes actually occurs depends on the fluid-elastic properties of the domains, on the adsorption kinetics, and on external constraints arising, e.g., from the osmotic conditions. Vesicles are predicted to unbind from adhesive surfaces via tubulation when the spontaneous curvature of their membranes exceeds a certain threshold value.

Specific adhesion of membranes simultaneously supports dual heterogeneities in lipids and proteins

Membrane adhesion mediated by one protein species simultaneously stabilizes both ordered-phase and disordered-phase heterogeneities, distinct from the non-adhered membrane.