BPS2026 – Disappearing domains: Modulation of supported lipid bilayer composition by vesicle fusion

Supported lipid bilayers (SLBs) are convenient model membrane systems because they mimic important biophysical characteristics of natural membranes and they can be examined with a variety of experimental techniques. Once a SLB is formed, its composition is generally fixed unless some method for delivery or extraction of lipids is employed. In one well-known example, methyl beta-cyclodextrin can be used to extract or deliver cholesterol to a SLB. In this work, we demonstrate a method to modulate the lipid composition of a SLB by the fusion of large unilamellar vesicles (LUVs) along the perimeter of SLB patches. The SLB patches are formed by the rupture of giant unilamellar vesicles (GUVs), and upon introduction of LUVs, the patches grow outward in a fractal-like pattern that incorporates the lipids contained in the LUVs. Using this approach, we show that the composition of SLB patches possessing coexisting liquid ordered (Lo) and liquid disordered (Ld) domains can be modulated by delivery of unsaturated lipids to the SLB patch perimeter. The delivery of the unsaturated lipids to the SLB patch pushes its lipid composition out of the 2-phase region of the phase diagram into the single-phase region causing the disappearance of distinct Lo and Ld domains. The kinetics of domain disappearance can be controlled by varying the LUV concentration. We also show that Lo-associated lipids like GM1 become homogeneously distributed after domain disappearance. If LUVs with compositions identical to those of the phase-separated SLB patch are delivered, the SLB patch enlarges, but the Lo and Ld domains persist. Based on the LUV composition, concentration, and exposure time, this approach offers a route to dynamic tuning of SLB lipid composition