One of the most common triggers for drug delivery systems is pH. This stimulus is abundantly used in cancer therapies due to the fact that the tumor microenvironment is acidic. The development of pH triggered systems meant that drug could be introduced to the body but not be deployed until encountering the tumor microenvironment. Hence a possible and probable reason that pH triggered systems are so common. There are a few approaches to making these systems. One method is using linkages that dissolve at certain pH levels. As the system enters an acidic environment, the linkages that hold that gates onto the porous scaffold are hydrolyzed and the cargo can be released. Examples of pH linkages are imine, amides, esters, and acetals. Another method that can be used is protonation. This method relies on electrostatic interactions between the gate molecule and the porous scaffold. The two will be linked together with a certain molecule, for example, acetylated carboxymethyl. When the system reaches an acidic environment, protonation of the molecule is initiated. The protonation causes a disruption in the linkage and the cargo can be released.