Fig. 1.

DOX-loaded zwitterionic polymer-based micelles change their surface properties in response to tumor extracellular pH. (1) PCL-b-P(AEP-g-TMA/DMA), an amphiphilic zwitterionic block copolymer, assembles into micelles and encapsulates DOX at pH 7.4. The micelles are of appropriate size to take advantage of tumors’ enhanced permeability and retention effect in vivo. (2) When the extracellular pH decreases to 6.8, as in the tumor extracellular environment, DMA is cleaved from the anionic component of the polymer, forming PCL-b-P(AEP-g-TMA/Cya). The resulting micelles are positively charged and are more readily taken up by tumor cells. Reproduced with permission [26]. Copyright 2012, Wiley-VCH.