Replacing furan with methylfuran accelerates the Diels-Alder (DA) reaction. (A) Covalently cross-linked hydrogels can be fabricated using furan-maleimide DA chemistry. (B) The methylfuran-maleimide DA reaction proceeds faster than furan-maleimide at pH 7.4. Reprinted with permission from L.J. Smith, S.M. Taimoory, R.Y. Tam, A.E.G. Baker, N. Binth Mohammad, J.F. Trant, M.S. Shoichet, Biomacromolecules 19 (2018) 926–935. Copyright 2018 American Chemical Society [506].