Fig. 5

Retro-Diels-Alder reaction based hydrogels formation and their dissolution. a Michael addition and Diels-Alder (DA) reaction. Figure is adapted with permission from the original articles of Koehler et al. [51] (Copyright 2013 by American Chemical Society). b Formation and degradation of poly(ethylene glycaol)-oxanorbornadiene (PEG-OND) hydrogels. Figure is adapted with permission from the original articles of Higginson et al. [53] (Copyright 2015 by American Chemical Society). c The DA reaction was investigated as a cross-linking mechanism for PEG-based hydrogels. Figure is adapted with permission from the original articles of Kirchhof et al. [54] (Copyright 2013 by Royal Society of Chemistry)