Fabrication of thermo-responsive hydrogels from star-shaped copolymer with a biocompatible β-cyclodextrin core

A thermally reversible hydrogel composed of a three-arm star copolymer with a specific host β-cyclodextrin (β-CD) center has been developed. The synthesis of this star copolymer initiates with β-CD core, from which sequential polymerization of a temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) block and a hydrophilic poly(N,N-dimethylacrylamide) (PDMA) block as asymmetric arms (named β-CD-g-(PNIPAM-b-PDMA)3) is performed via RAFT protocol. Below the lower critical solution temperature (LCST) of PNIPAM segment, the polymer is of good water-solubility and exhibits a sol state. Upon thermal stimulus, free-standing hydrogels can be formed rapidly at sufficiently high concentrations. By comparing the sol-gel transition of the star polymer with that of its linear counterpart without this feature, we concluded that the special star-shape topology and the thermal-collapsed PNIPAM chains were responsible for this gelation behavior. The rheology measurements indicate the mechanical properties of the polymer hydrogels and the thermal reversibility of the sol-gel transition. Using Rhodamine B as a molecule to model a typical drug, we realize the favorable encapsulation and releasing process from the hydrogel, demonstrating that this star polymer has the potential to function as an injectable hydrogel for drug delivery and gene transport.