a) Size changes of a PMMA-derived hydrogel (I, Scheme 1) as function of pH; calculated maximum volume change 390 %; in 0.05M phosphate buffer (circles), and in 0.5M sodium chloride (triangles).; b) pH expansion profiles at different salt concentrations; in 0.5 M (•-a), 0.05 M(D-b), and 0.025 M(Ñ-c) sodium chloride solution, respectively, and in water with very dilute HCl or NaOH (▼-d). Schneider, H. J.; Liu, T. J.; Lomadze, N. Molecular recognition in a supramolecular polymer system translated into mechanical motion. Angew. Chem.-Int. Edit. 2003, 42, 3544-3546. Copyright Wiley-VCH Verlag GmbH & Co. [39a].