Figure 5.

External and internal stimuli for controlled drug release. External stimuli allow for time and site-specific drug release triggered by the application of physical forces, as is magnetic field, temperature, ultrasound, electromagnetic field, light etc. On the other hand, internal stimuli stem from the nature of the tumor and its microenvironment, where specific pH, redox potential or enzyme activity act as a trigger in the tumor tissue or intracellularly. Adapted from Cheng et al. ¹³⁹ with publisher´s permission (license no. 4892530661903).