Properties and Applications of Shear-Driven Lipid Bilayers

Doctoral thesis, 2010

A supported lipid bilayer (SLB) is a lipid bilayer formed on a solid substrate. This system is currently one of the most common model systems used to imitate the properties of the cell membrane that surrounds human cells. In this work it was found that the hydrodynamic shear force from a liquid flow above an SLB can be used to move the entire SLB in the direction of the flowing liquid. This takes place in a rolling type of motion, with the lower monolayer of the SLB being essentially stationary on the support. Forming the SLB on the walls of a microfluidic channel provides a controlled and versatile method of handling and transporting the SLB and molecules associated with it. The theory behind, and some general observations, of this phenomenon are presented in this thesis. In addition of being able to drive the SLB over different types of surfaces and structures, this technique can also be used to manipulate the concentration of molecules solubilized in, or coupled to, the SLB. For example, it was found that membrane-bound proteins could be accumulated at the front of the advancing SLB, leading to a local increase in surface concentration of several orders of magnitude. This could allow the detection of membrane-associated molecules at much lower average surface coverage than previously possible. Another observation was that different types of membrane-associated molecules have a characteristic drift velocity in the lipid bilayer, under the same bulk flow in the channel. This opens up the possibility of separating membrane-associated molecules within the SLB based on differences in drift velocity, as in chromatography, but without the need of first extracting the molecules of interest from the lipid bilayer.