Hackelbusch, S.; Rossow, T.; Becker, H.; Seiffert, S.: Multiresponsive Polymer Hydrogels by Orthogonal Supramolecular Chain Cross-Linking. Macromolecules 47 (2014), p. 4028–4036
10.1021/ma5008573

Abstract:
Supramolecular hydrogels are water-swollen networks of macromolecules interconnected by noncovalent bonds, typically established through hydrogen bonding or metal complexation. These transient cross-links are susceptible to external stimulation by variation of pH, temperature, or the presence or absence competing ligands, rendering them useful for applications in soft and sensitive gelly materials. However, most existing approaches to prepare and actuate such responsive gels rely on the use of just one of these different triggers. We present an approach to overcome this limitation. We prepare multiresponsive supramolecular hydrogels based on linear polyglycerol cross-linked by either hydrogen bonding, metal complexation, or both. This allows supramolecular hydrogels to be formed at mild conditions in water that remain stable for several weeks and that respond to different stimuli by partial or complete polymer de-cross-linking in an orthogonal fashion.