Asymmetric Polymersomes with Photothermal Responsiveness

Photo-mediated micro/nanorobots have found widespread interest over the past decade because of their application potential in many areas, especially in nanomedicine. By converting light energy into mechanical work, micro/nanorobots can be propelled to achieve active cargo transportation into cells with enhanced therapeutic effect. Most of the current micro/nanorobots are either based on inorganic particles or hybrid particles, such as Janus nanoparticles with a hemispherical Au shell.^1-5 The construction of fully organic-based micro/nanorobots is still underexplored. Here, a new type of light propelled nanorobots is created based on biodegradable polymersomes. Photothermal agents (PA) were co-assembled with polymer building blocks to form polymersomes with an asymmetric morphology, resembling a hot-air-balloon structure. With cryogenic transmission electron microscopy (Cryo-TEM) and cryo-electron tomography (Cryo-ET), this structure was confirmed. The formation mechanism of these asymmetric polymersomes was thereafter investigated by in situ observation of the dynamic assembly process with liquid phase transmission electron microscopy (LP-TEM). In combination with the cryo-TEM data, the LP-TEM results revealed that liquid-liquid phase separation was the main leading force for the formation of asymmetric polymersomes. Upon infrared laser irradiation (808 nm), the PA nano-assemblies in the polymersome structure provided photothermal heating and propelled the polymersomes in a controllable way regarding both direction and speed. This study demonstrates the formation of a new nanomotor topology which is driven by the photothermal effect and fully composed of organic building blocks. This nanomotor is further investigated for its application in active drug delivery.