Probing interleaflet coupling in phase separated lipid bilayers under high shear

Lipid membranes composed of at least three lipid types can phase separate into micron-scale, coexisting liquid phases. Domains in each leaflet are never observed to move out of registration, which indicates a strong interleaflet coupling. Our group has found that this strong coupling persists in asymmetric membranes, where lipid ratios are different in each leaflet [1]. For membranes that lack transmembrane proteins or gel phases, the origin of this strong coupling is not intuitive [2]. Previously, we have found that domain registration persists in supported bilayers to shear rates of 6 seconds$^{-1}$. Here, we use microfluidic techniques to apply higher shear to supported bilayers with the goal of overcoming coupling by moving the membrane's upper leaflet with respect to the lower leaflet. We use a flow cell design by J\"{o}nsson which was previously shown to move bilayers across a substrate [3]. In this system, the leaflet proximal to the substrate flows much slower than the leaflet proximal to the solution, leading to a macroscopic spatial shift between initially apposed regions. This technique of subjecting supported bilayers to high shear allows us to probe interactions between leaflets in the monolayer.\\[4pt] [1] Collins MD, Keller SL (2008) \textit{PNAS,} 105(1):124--128\\[0pt] [2] Devaux PF , Morris R (2004) \textit{Traffic,} 5:241--246\\[0pt] [3] J\"{o}nsson P, Beech JP, Tegenfeldt JO, H\"{o}\"{o}k F (2009) \textit{JACS}, 131(14):5294-5297