Figure 2.
Several recent studies have developed polymeric nanoparticles capable of shape transformation in response to external stimuli. (A) PLGA polymer particles can transform their shape from rod-like to spherical on time scales ranging from minutes to hours in response to external triggers such as various chemicals, pH changes, and temperature changes;33 (B) Self-assembled DNA brush polymer micelles undergo shape transformation from spherical to cylindrical particles upon enzymatic cleavage of a fraction of the brush segment, which can be reversed by re-introducing a similar DNA segment through complementary base pairing;91 (reprinted with permission, ©2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) (C) Shape transformation of polymer/DNA micelles can be achieved through cleavage of a fraction of the PEG chains on the micelle surface, leading to a transition from worm-like shapes to more condensed spherical and short rod shapes.126 (Reproduced by permission of The Royal Society of Chemistry.)