The role of hydrogen bonding in alginate/poly(acrylamide-co-dimethylacrylamide) and alginate/poly(ethylene glycol) methyl ether methacrylate-based tough hybrid hydrogelsElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ra09926a

The interpenetrating alginate-based hybrid hydrogel network is a tough yet recoverable material. This is believed to be caused by the combination of the strength of a covalent network, and the reversibility of an ionic network. However, hydrogen bonds are believed to also be responsible for the exceptional properties of these hydrogels. In this paper, the effect of varying the reactant concentrations on the mechanical properties of the hydrogels was first studied. By changing the monomer used (from polyacrylamide to polydimethylacrylamide) in the fabrication of the hydrogel, the effect of hydrogen bonding was studied. Compression test results showed that the presence of hydrogen bonds is critical for the high toughness of the hybrid hydrogel. Additionally, co-polymeric hybrid hydrogels were synthesized and shown to have improved mechanical properties over the original hybrid hydrogel, with an elastic modulus and compressive toughness of 350 kPa and 70 J m −3 , respectively. The results of this experiment can be used to optimise the mechanical properties of future hybrid hydrogels. Hybrid hydrogels, with an elastic modulus and compressive toughness of 350 kPa and 70 J m −3 , was synthesized and reported here.