Light-controlled membrane remodeling in gel-fluid phase-separated giant vesicles using photoswitchable lipids.

Photoswitchable lipids enable optical control of membrane area, mechanics and phase behavior, offering a platform to study stimuli-responsive biomimetic systems. Here we ask how the spatial organization of coexisting membrane phases governs photoinduced mechanical responses. We incorporate the photoswitch azobenzene-phosphatidylcholine (azoPC) and dipalmitoylphosphatidylcholine (DPPC) into gel-fluid phase-separated giant unilamellar vesicles (GUVs). Using differential scanning calorimetry and temperature-controlled confocal microscopy, we quantify phase transitions and visualize domain dynamics. Dispersed domains produce global GUV crumpling upon UV-light-induced trans-to-cis isomerization of azoPC, whereas coarsened fluid domains locally confine deformation to budding regions of the GUVs; both responses are reversed by blue light. Temperature-controlled imaging reveals that the gel-fluid transition in GUVs is considerably broader than the calorimetric profile suggests, with coexisting phases detectable well above the calorimetry peak transition temperature. Well above the transition temperature, i.e. in the fully melted membrane, UV irradiation unexpectedly induces reversible nucleation of gel-like flower domains, consistent with an increased transition temperature in the cis azoPC state due to lipid packing incompatibility with DPPC. Membrane domain architecture thus dictates the spatial distribution of photoinduced remodeling. More broadly, photoswitchable lipids can reversibly switch membrane phase equilibria as well as morphology, pointing to potential implications for the design of stimuli-responsive synthetic membrane systems and soft actuators.