Fig. 4 |.

Self-healing behaviour and functionalization of ferritin crystal-hydrogel hybrids. a, Light microscopy images of crystal-hydrogel hybrids, showing the self-healing of cracks that appear during Ca-induced contraction. b, Extensive cracks can also appear during crystal expansion or during the initial stages of NaCl-induced contraction, but eventually self-heal. The arrows point to the termini of the major crack extending through the crystal. c, Schematic of crack formation and self-healing through the interactions between polymer strands and ferritin molecules. d, Isotropic expansion and contraction of a crystal-hydrogel hybrid with an expandable core and an expandable shell. e, Swelling-induced fragmentation of the shell of a crystal-hydrogel hybrid with a fixed core and expandable shell. All scale bars, as well as the separation between the major ticks of the ruler in e, correspond to a length of 100 μm. See Supplementary Videos 3 and 4 that accompany this figure.