“Freezing”, morphing, and folding of stretchy tough hydrogels

Highly stretchable and tough Ca-alginate/polyacrylamide hydrogels were “frozen” and folded into program-controlled shapes by exposing them to an Fe3+ ion aqueous solution. The elastic modulus of the as-made tough gels increased either in bulk or locally up to 2.90 MPa, while the toughness remained within the range from 8.18 to 4.41 kJ m−2.