Fig. 2.

Schematic diagrams showing the difference between a physically and chemically cross-linked chitosan-PMAA-CdSe hybrid nanogel. Whereas the covalently cross-linked nanogels are very stable in both structure and composition upon pH variation, the hybrid nanogels based on the physical associations exhibit a significant change in the structure and composition in response to a pH increase to physiological condition. This distinction in the stability of hybrid nanogels is important for the designed multiple functions. Adapted from Reference (33). Reprinted with permission from Elsevier Publishing Group, Copyright (2010).