Progress on Preparation of pH/Temperature-Sensitive Intelligent Hydrogels and Applications in Target Transport and Controlled Release of Drugs

Figure 3

Phase transition behavior of different types of pH-sensitive hydrogels. Adapted from [27], acidic hydrogels (red rectangle) are ionised by deprotonation in basic solutions, which have an excess of hydroxyl groups. Basic hydrogels (blue circle) swell in acidic solutions due to the ionisation of their basic groups by protonation. Amphiphilic hydrogels (green triangle) contain both acidic and basic groups. Therefore, they show two phase transitions. (reproduced from reference [27] without permissions that are required for this figure as the original publication is open access).