Biodegradable zwitterionic nanoparticles with tunable UCST-type phase separation under physiological conditions.

Thermo-responsive polymeric nanoparticles (NPs) are emerging as a powerful tool in nanomedicine for the fabrication of advanced drug delivery systems. In addition to their size and biodegradation rate, phase separation of NPs upon application of a thermal stimulus provides an additional switch to control the rate of release of active components. Among the materials currently developed for biomedical applications, NPs stabilized by zwitterionic polymers are gaining increasing interest due to their high stability and ability to escape the body immune response. Yet, biodegradable zwitterionic NPs with temperature response under physiological conditions are currently not available. Here, we develop a new class of biodegradable zwitterionic NPs that exhibit UCST phase transition in the biological temperature range (T = 30-45 °C) and in physiological solution (i.e. 0.9% w/w NaCl). We design a strategy that relies on the self-assembly of block copolymers produced via reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization. These copolymers comprise a zwitterionic portion exhibiting an upper critical solution temperature (UCST) and a biodegradable hydrophobic block consisting of oligoesters functionalized with a vinyl group. This modular macromolecular architecture allows us to independently control a variety of NP properties by modifying the individual components of the copolymer. In particular, the zwitterionic block of the copolymers controls the UCST-type phase separation behavior, while the number of the oligoester repeating units governs the size of the NPs and the length of the oligoester dictates the degradation rate. After demonstrating the synthesis of highly controlled degradable NPs, we show the potential of this new class of materials in the context of drug delivery by controlling the release of a drug-mimic molecule upon temperature variations in a broad time range from few minutes to 20 hours.