Super-tough hydrogels using ionically crosslinked networks

Alginate and polyacrylamide hydrogels were produced by a facile one-pot method with varied ionic crosslinkers in this article. These hydrogels display outstanding mechanical properties compared to the pristine polyacrylamide (PAAm) hydrogels. The alginate network is ionically crosslinked by multivalent cation, whereas N,N′-methylenebis (acrylamide) (MBAA) is used as covalent crosslinker for the PAAm network. Particularly, the obtained hydrogels by using trivalent cations (Fe³⁺ and Al³⁺) as crosslinkers are much stronger than that of using divalent cations (Ca²⁺ and Ba²⁺) as crosslinkers. In addition, with increasing concentration of cations, the compressive properties of gels are improved, whereas when the concentration is higher than 0.3 M, the compressive properties of gels are damaged due to mono-bindings. Interestingly, the hydrogels with higher chemical crosslinker concentration depicts better mechanical properties than those hydrogels with lower chemical crosslinker, which is different from that of common double network hydrogels. These hydrogels with excellent mechanical properties are promising candidates for biomedical application like load-bearing tissues.