Figure 4.

Schematic representation of the two strategies to control drug release from polymers in the tumor extracellular pH (pHe) environment. (A) The polymer carrier maintains its stealth function while circulating in the blood circulation. (B) Upon arrival at slightly acidic tumor sites through the EPR effect, the stealth polymer carrier is activated by pH to release its cargos. (C) Surface charge reversal to a positive charge when the stealth polymer carrier arrived at tumor vicinity, and drugs were released.