fig6

Figure 6. Schematic diagram and mechanism of self-healing properties of hydrogels. (A) Schematic illustration of self-healing mechanisms of self-healing gels based on CDC. (i) A cylindrical self-healing gel is cut by a knife. (ii) The gel is cut into two pieces and the functional groups stay dissociated across the damaged zone. (iii) The crack is healed by the reformed dynamic bonds after the fractured surface contacting each other. (iv) The dynamic association and dissociation of the reversible crosslinks based on CDC^[52]. (B) Digital photographs of undyed and dyed (16% PDDA/PEI)-(20% PSS/PAAc) hydrogel cuboids that were cut into two pieces (i) and the separated pieces with different colors were well healed at room temperature for 14 h (ii). The healed hydrogel with a width of 4 mm and a thickness of 1.1 mm can be stretched to a length 6.6 times longer than its original length without fracture (iii) and hold a weight of 500 g (iv)^[53]. (C) Digital photographs of (16%PDDA/PEI)-(20%PSS/PAA) hydrogel sheets that were cut into small pieces (i) and then dried in a vacuum oven at room temperature for 24 h (ii). The dried hydrogel pieces were ground into powders (iii) and then reshaped into a heart-shaped hydrogel (iv)^[53]. (D) Use of acrylic acid and poly(ethylene glycol) methacrylate to fabricate polyelectrolyte-based hydrogels with excellent self-recovery. (i) The hydrogel is cut into two parts. (ii and iii) The healed sample can withstand stretching and lift a weight of 500 g^[54]. (A) Reproduced with permission^[52]. Copyright 2014, RSC. (B and C) Reproduced with permission^[53]. Copyright 2019, ACS. (D) Reproduced with permission^[54]. Copyright 2019, ACS.