Star polymer is a kind of polymer with special topological structure, which is in connection radiate out three or more than three linear polymer chains from a single branch core by junction points. It has become one of the hottest research topics in polymer science since its unique spatial shape, clear structure, narrow molecular weight distribution, low viscosity and versatility compared with that of linear polymers with similar chemical compositions and molecular weights. Developing star polymer with stimuli-responsive segments, which can sensitively change their structure in response to external environmental variation such as pH, temperature, redox and so on, has attracted considerable attention over the past few years for its significant application value in controllable drug release. Among them, pH and temperature stimuli-responsive star polymers have been considerably investigated because they are relatively convenient and effective drug carriers in controllable drug release. Herein, we mainly focus on the recent research work related on stimuli-responsive star polymers applied in controllable drug release, and classify them according to different types of environment stimulus. Thus pH-responsive, thermo-responsive, dual or multi stimuli-responsive star polymer systems are relatively investigated. Furthermore, the synthetic methods, self-assembly behavior in aqueous solution, stimuli-responsive behavior and functionality of controlling drug release are introduced, which are necessary to develop more desirable stimuli-responsive star polymers and self-assembly aggregations, promote the mechanism of response to stimulus and expand their applications. Finally, the improvement and development of stimuli-responsive star polymer systems are also prospected.

Contents
1 Introdution
2 Overview of synthesis and controllable drug release of stimuli-responsive star polymer
2.1 pH-responsive star polymer system
2.2 Thermo-responsive star polymer system
2.3 Dual or multi stimuli-responsive star polymer system
3 Conclusion