Temperature‐Controlled Assembly and Release from Polymer Vesicles of Poly(ethylene oxide)‐block‐ poly(N‐isopropylacrylamide)

Vesicles, together with spherical micelles and cylindrical micelles, are the three most common and stable morphologies of amphiphiles in water. Unlike micelles, vesicles can entrap hydrophilic molecules within the vesicle lumen and also integrate hydrophobic molecules within the membrane core. The development of vesicle-forming materials has therefore attracted wide interest for applications ranging from cosmetics to drug delivery. Biological vesicles and membranes that selfassemble from amphiphilic phospholipids are central to cell compartmentation and function; various environmental factors and even fusion can trigger release of contents. However, lipids typically have molecular weights less than 1 kDa so encapsulation, retention, and overall stability of natural vesicles are often limited. In comparison with amphiphilic block copolymers, molecular weight, composition, and chemical functionalities can be tuned for tailored polymer vesicles or “polymersomes”, [1–4] with opportunities to improve control and stability for various applications such as sensors [5] and drug delivery. [6,7] Oxidation [7] and pH [8–11] responsive polymersomes have recently been reported for controlled encapsulation and release. Thermal transitions provide another means for stimulated release. In liposomes, membrane permeability is already known to be strongly perturbed at phase transitions, [12] and this has been exploited for hypothermic delivery of anticancer drugs by coupling to local heating. [13] Thermoresponsive polymersomes have yet to be explored, and the most thoroughly studied copolymer systems are relatively temperature insensitive, possessing either very high glass transitions (e.g., polystyrene) or subzero glass transitions (e.g., polybutadiene). [2] In addi