Mechanical properties of poly(N‐acryloyl‐glycinamide) hydrogels dependent on initiation number of the polymerization reaction

Hydrogels with polymer networks formed through physical interactions have received attention because of their post‐moldability and self‐healing properties upon physicochemical stimulation. Although hydrogels become fragile without covalent crosslinking, poly(N‐acryloyl‐glycinamide) (PNAGA) hydrogels, which are formed through hydrogen bonding among PNAGA molecules, have recently demonstrated exceptional strain. In this study, we prepared a series of PNAGA hydrogels with different molecular weights and constant weight concentrations of PNAGA. Stress–strain tests demonstrated that higher molecular weights of PNAGA promote extensibility. The swelling ability of the hydrogel also increased with higher molecular weights of PNAGA, suggesting that high molecular weights of PNAGA significantly increase the tolerability of hydrogels to shape change, which opens up new possibilities for developing robust hydrogels without the requirement for cross‐linking. Although different behaviors were not observed with changes in the molecular weight, we achieved hydrogel re‐construction using the PNAGA powder obtained from hydrogels, which demonstrates an advantage of such polymer networks based on hydrogen bonding. Regarding the healing ability of the cut surfaces, hydrogels with a lower molecular weight exhibited higher recoveries, probably owing to the high PNAGA mobility in the hydrogels. Finally, this study elucidates the importance of controlling the molecular weight when developing functional hydrogels. A hydrogel composed of poly(N‐acryloyl‐glycinamide) (PNAGA) exhibits excellent properties as materials towards biomedical application including cell culturing scaffolds and wound dressing, wherein mechanical strength, extensibility, and self‐healing property are important parameters. Herein, we prepare the hydrogels composed of PNAGAs with different molecular weights but at the same concentration and the comparisons among them fairly visualize the molecular weight impacts on these important parameters, providing knowledge on the further design of polymer hydrogels through physical interaction.