Ultrastiff, Tough, and Healable Ionic–Hydrogen Bond Cross-Linked Hydrogels and Their Uses as Building Blocks To Construct Complex Hydrogel Structures

We
report the ultrastiff and tough poly­(acrylamide-co-acrylic acid)/Na-alginate/Fe3+ (P­(AM-co-AA)/Na-alginate/Fe3+) hydrogel via the formation of hybrid
ionic–hydrogen bond cross-linking networks. The optimal P­(AM-co-AA)/Na-alginate/Fe3+ hydrogel possessed super
high elastic modulus (∼24.6 MPa), tensile strength (∼10.4
MPa), compression strength (∼44 MPa), and toughness (∼4800
J/m2). The P­(AM-co-AA)/Na-alginate/Fe3+ hydrogel was highly stable and maintained its superior mechanical
properties in 0.5–2 M NaCl solution, aqueous solution with
pH ranging from 4 to 10. The ionic cross-linking networks of the P­(AM-co-AA)/Na-alginate/Fe3+ hydrogels can be locally
and selectively dissociated by treating with aqueous NaOH solution
with pH of 13 for 1 min and reformed by locally adding the additional
Fe3+ solutions, making the hydrogels healable and cohesive.
The healed hydrogels from the cutting surfaces can bear a tensile
strength of up to 7.1 MPa. Various complex hydrogel structures can
be constructed by using
the P­(AM-co-AA)/Na-alginate/Fe3+ hydrogels
as building blocks via the adhesion of as-prepared hydrogels.