Tuning shape transformations in light-responsive lipid vesicles: the role of domains in a binary lipid system

We investigate ways to tune the morphology and permeability of giant unilamellar vesicles (GUVs) containing a photo-isomerizing lipid, azo-PC, which has an azobenzene moiety in one of its hydrocarbon tails. UV radiation triggers a shift from the trans to cis isomer, which has a larger area per lipid. We mix the azo-PC with various fractions of either unsaturated or saturated lipids (DOPC or DPPC). In GUVs with azo-PC and gel-forming DPPC, UV irradiation can induce large membrane deformations with notable buckling and pinning. The response depends on azo-PC fraction and UV light intensity. Analysis of wide-field and confocal fluorescent micrographs points to correlations between solid domain organization and extent and character of UV-response. Comparing the azo-PC/DPPC membranes to the fully liquid azo-PC/DOPC membranes – both phase separated and single phase – we conclude that the finite yield-stress of the solid domains plays a key role in the buckling. In addition, we find a marked increase in solute permeation when the buckling response is observed but not otherwise. The results point to a new mode of response and a new route to tuning response in triggered solid membranes.