Stimuli Responsive Drug Delivery Systems: Types, Mechanisms, and Pharmaceutical Applications

Modern exogenous and endogenous-based stimuli-responsive drug delivery systems (DDSs) for temporal and spatial drug release were examined aiming to focus on the shortcomings of traditional treatment approaches. This review addresses the mechanism of action and smart chemistry of numerous stimuli-responsive polymeric carriers, which are important in both the exogenous and endogenous domains of sick cells or tissues. Research is being conducted globally to build new stimuli-responsive DDSs, both internal and external, for biomedical, and/or pharmaceutical applications. A crucial component of designing so-called "smart" DDSs, which sophisticatedly regulates drug loading, adjusts the mechanism of drug release, controls individual variability, and offers targeted drug delivery, is the polymeric carriers' dual/multi-responsive, internal, and even external behavior. Numerous DDSs have been invented, proposed, and used thus far. These systems include electrical, photo/light, pH, magnetic, temperature, ultrasonic, redox responsive DDSs, and multi-responsive DDSs (linking two or more from any of the aforementioned). To close the research gap, several difficult issues still need to be resolved despite the tremendous advancements made in the DDSs field. The drug release mechanisms and the uses of exogenous and endogenous stimuli-responsive DDSs in therapeutic settings were therefore highlighted.