Ionic–Covalent Hybrid Tough Hydrogels Enabled by the in Situ Release of Metal Ions from Insoluble Salts or Alkalis

The ionic–covalent hybrid cross-linked tough hydrogels have been widely applied in various fields for their superior mechanical properties, but it is challenging to fabricate the hybrid gels with a controlled ionic cross-linking distribution. Here we report a robust, one-step fabrication method for alginate/polyacrylamide hydrogels with high stretchability, toughness, and self-recovery by the glucono-delta-lactone-triggered in situ release of metal ions from premixed insoluble metal salts or alkalis. The versatility of this method is demonstrated by employing several insoluble metal salts or alkalis, including CaCO3, BaCO3, Co(OH)2, Cu(OH)2, and La2(CO3)3·xH2O. This strategy provides an alternative method to synthesize homogeneous ionic–covalent hybrid cross-linked hydrogels.