Photoinduced Pinocytosis for Artificial Cell and Protocell Systems

A photocleavable membrane component was introduced into synthetic liposomes to achieve light-triggered pinocytosis-like behavior as a potential solution to the feeding requirement in protocell and bottom-up artificial cell systems. Light-triggered pinocytosis was observed in both elongated liposomes, prepared by lipid film hydration, and osmotically stressed spherical vesicles prepared by the pull-down method. Liposomes formed via lipid film hydration consistently underwent pinocytosis in cases of lobed structures or in prolate ellipsoidal structures with aspect ratios ≥2, suggesting that a critical volume-to-surface-area ratio is necessary to drive pinocytosis. When liposomes formed by the pull-down method were osmotically deformed prior to irradiation, an average of 44% exhibited pinocytosis. This light-driven pinocytosis behavior is hypothesized to be due to an asymmetric distribution of photocleavable lipid between the inner and outer leaflet, consistent with the observation that liposomes assembled asymmetrically with photocleavable lipid in their outer leaflet were dramatically more readily formed (by a factor of 30) as compared to liposomes with photocleavable lipids in their inner leaflet