Thermo-responsiveness and biocompatibility of star-shaped poly[2-(dimethylamino)ethyl methacrylate]-b-poly(sulfobetaine methacrylate) grafted on a β-cyclodextrin core

Star-shaped thermo-responsive block copolymers were synthesized by atom transfer radical polymerization (ATRP) of a hydrophilic cationic monomer (2-(dimethylamino)ethyl methacrylate) (DMAEMA) and a zwitterionic monomer (sulfobetaine methacrylate) (SBMA) from cyclodextrin with multi-initiator sites. These star polymers with different arm lengths and arm densities were characterized by 1H NMR and GPC. Thermo-responsive behaviors of the star polymers were investigated not only at different pH values, but also at different NaCl concentrations. The size and morphology of the star polymers and their aggregates were measured by dynamic light scattering and transmission electron microscopy. The star polymers showed only upper critical solution temperature (UCST) behavior, since zwitterionic PSBMA outer blocks shielded the lower critical solution temperature (LCST) behavior of PDMAEMA midblocks. However, PDMAEMA blocks had significant influence on the thermo-induced associations of the star polymers, and resulted in a tunable critical aggregation temperature with varying arm density or pH value of solution. Moreover, enhanced thermo-responsive behavior was also obtained at NaCl concentrations up to more than 20 mM, which is much higher than those reported before. Finally, biocompatibility evaluations showed that the star polymers could effectively reduce the adsorption of BSA in PBS solution and had insignificant cytotoxicity to MCF-7 cells. These results demonstrate they are good candidates for potential applications in biomedically relevant fields.