Fig. 2: Schematic diagram of entanglements in a hydrogel.

a Polymerization-induced entanglements (PIEs) are formed in an as-prepared hydrogel: (a1) Some PIEs cannot be removed unless chain scission happens. (a2) Some PIEs can be removed by external forces. (a3) Some chains are not entangled. b Dehydration-induced entanglements (DIEs) are introduced during hydrogel dehydration: (b1-b2) Additional DIEs are introduced based on the existing PIEs. (b3) Some initially unentangled chains form DIEs. c The dehydrated hydrogel is stretched: (c1) The DIEs are disentangled but the PIEs are not removed. (c2) Both PIEs and DIEs are removed by external forces. (c3) The DIEs are removed by external forces.