Advances in transformable drug delivery systems.

These years, transformable drug delivery systems (DDSs), which hold the capability of changing formulation morphology and subsequent functionality at the desired disease site, have shown great promise in control of spatio-temporal drug delivery/release manner and enhanced treatment efficacy. Equipped with controllability and design flexibility, the transformable DDSs are being increasingly pursued for the development of precision drug delivery platforms for biomedical applications. In this review, we describe the recently developed intracelluarly and extracellularly transformable DDSs, especially associated with assembly or disassociation of the original formulation units, for achieving various functionalities, including prolonged retention time, inhibited endocytosis and enhanced cytotoxicity. Furthermore, the different stimuli, such as pH, enzyme, light, temperature, redox and mechanical force that trigger the transformation process are also introduced. The future outlook and challenges are discussed in the end.