Temperature Responsive Poly(trimethylene carbonate)-block-Poly(L-glutamic acid) copolymer: Fusion and Fission in Polymersomes

摘要

The ability of amphiphilic block copolymers to self-assemble in a selective solvent to form nanometric objects has been widely studied and turned to good account in a variety of applications. Among the accessible morphologies in solution, polymer vesicles, also called polymersomes, are increasingly studied as models for living membranes as well as for drug delivery carriers. In addition, stimuli- responsive block copolymers can respond by a change of their size or shape to variations of pH, ionic strength or temperature. Here, we described the behavior in aqueous solution of a new system composed of a poly(trimethylene carbonate) (PTMC) block and a poly(glutamic acid) (PGA) segment. PTMC is biocompatible and biodegradable, presents a relatively low molecular weight and is semi-crystalline with a melting transition close to body temperature. PGA is a pH-sensitive and biocompatible synthetic polypeptide that undergoes a reversible transition from a rod-like α-helix to a random coil conformation upon pH variation, this behavior being extensively used for the design of stimuli-responsive polymersomes. We demonstrated that such block copolymers self-assembled in water forming vesicles with a size that can be tuned by varying the preparation conditions. These polymersomes showed interesting high membrane properties and robustness, but can be rapidly disrupted by enzymatic degradation. In addition, PGA corona secondary structure can vary in response to pH or ionic strength. Finally, due to PTMC crystallization inside the vesicle membrane, an original temperature responsive behavior has been elucidated and analogies with lipidic biological membranes performed.