Lipid Bilayers on Deformable Elastic Substrates

Abstract

In this thesis an experimental model for the interface between the cell membrane and the supporting cytoskeleton has been developed and analysed. The experimental platform is a novel approach to the design of supported membrane based devices and technologies.
The system consists of a single component lipid bilayer coupled to an elastic substrate, the area of which can be reversibly increased and decreased. We uncover three independent mechanisms that the membrane may use to respond to changes in substrate area.
If the elastic support is partially hydrophilic, the area of the planar portion of the membrane is strongly coupled to the substrate area. The membrane responds to increasing substrate area by absorbing lipid protrusions, and when the substrate area is decreased the excess membrane area is projected back out in the form of lipid tubes. This mechanical remodelling of the membrane occurs above the plane of the support and mimics the passive means of membrane area regulation recently uncovered in live cells.
In contrast, when the surface support is completely hydrophilic, two further mechanisms of substrate stress relaxation are uncovered. When the pH of the solu- tion is greater than 7 the membrane is able to slide over the expanding and contract- ing substrate. This membrane sliding motion occurs in the plane of the support and is dynamic. The effectiveness at which membrane tension is relaxed is dependent on the rate at which the substrate area is changed.
When the pH is reduced below pH 7, the membrane area becomes strongly coupled to that of the support and the membrane dramatically ruptures, opening large circular pores, in response to substrate deformation. The pores exhibit a dynamic area change, revealing a complex flow of membrane across the support to equilibrate stress.
This novel supported membrane behaviour reveals the rich physics possessed by
supported lipid systems, that may assist in the design of new supported lipid based technologies.