Photoisomerization-induced wrinkling and leakage in azobenzene-based photoswitchable solid lipid bilayer membranes

UVC-induced morphological changes were observed in giant unilamellar vesicles (GUVs) composed of lipid mixtures of dipalmitoyl-phosphocholine (DPPC) and photoswitchable azobenzene-based phospholipid (azo-PC). The morphological changes varied considerably and depended on azo-PC's molar fraction, which undergoes a reversible trans-to-cis isomerization upon ultraviolet irradiation. Notable non-spherical morphologies, including wrinkling, swelling, elongation, and budding, were induced at nominal azo-PC concentrations of 30 mol% and above, with characteristic effects present at each concentration. Bright-field and fluorescence confocal microscopy were used to determine the GUV morphology. Over a broad range of, we found phase separation into solid DPPC domains and azo-PC enriched domains. In GUVs with near 30 mol%, rapid and reversible membrane wrinkling was observed. For above 30 mol%, vesicle swelling was observed with varying degrees. The wrinkling and leakage responses were not observed in mixtures of azo-PC with lipids that form the fluid phase. The solid (gel) DPPC-rich phase's role and the implications for designing stimuli-responsive materials will be discussed.