Stimuli-responsive carriers for controlled intracellular drug release.

Stimuli-responsive carriers are a class of drug delivery systems which can change their physicochemical properties and/or structural conformations in response to specific stimuli. Although passive and active drug targeting has proved to reduce the side effects to normal cells, controlled intracellular drug release should be included in drug carriers to enhance the bioavailability of drugs at the disease site. This review focuses on several recent advances in the development of stimuli-responsive carriers for spatially and temporally controlled release of therapeutic agents in response to intracellular stimuli, such as pH, redox potential, reactive oxygen species, enzyme and temperature. Great efforts are needed to the optimization of stimuli-responsive materials, with emphasis on their molecular designs and formulations, to enable multi-functionality and multiple stimuli-responsiveness in improving the clinical drug efficacy.