Phase seperation of lipids in supported membranes on patterned PDMS substrate

Abstract

Abstract We studied the curvature induced phase separation of unsaturated and saturated lipids using fluorescence microscopy. In our work, 5\u202fnm thick supported lipid membranes of various compositions unsaturated and saturated lipids were prepared by vesicle fusion method. For introducing curvature we choose poly(dimethyl)siloxane (PDMS) substrates of depressed square and elevated grids patterns of sizes varying from 5\u202fµm to 150\u202fµm and height of features is\u202f∼\u202f1.5\u202fµm. When we introduced the mixed lipid vesicles above the transition temperature of both lipids resulted in forming continuous lipid bilayer membrane proved by fluorescence recovery after photobleaching studies (FRAP) on the PDMS substrate. Upon slow cooling of lipid membrane on patterned surfaces, which presents an array of curvatures gave rise to a spontaneous self sorting phenomenon. We observed with the help of DiIC18(3) dye which prefers the saturated lipids, that saturated lipids (DPPC) migrated to the depressed square patterns and the unsaturated lipids (POPC) in the reverse direction i.e., to elevated grid patterns resulting in phase separation of lipids on curvatures. This migration of lipids is due to difference in bending rigidity, mechanical bending and preferential organization of the lipid molecules.