A universal strategy for preparing tough and smart glassy hydrogels

With a large amount of water as plasticizer, most current hydrogels stay in rubbery states with low rigidity. Inspired by the robust thermoplastics, herein we propose a facile, effective, and universal strategy for preparing tough and smart “glassy hydrogels” by maintaining the hydrogels’ network in glassy states. The key point is to integrate an appropriate amount of rigid hydrophobic polymers within hydrogels’ hydrophilic networks. Based on the composition optimization, we further establish a generally applicable criterion for material preparation: the hydrogels should possess a thermo-softening temperature slightly higher than the service condition. Following this principle, various glassy hydrogels have been readily fabricated, which demonstrate excellent rigidity (∼50.5 MPa), strength (∼8.46 MPa), extensibility (∼2200%), and toughness (∼35.2 MJ.m−3). More interestingly, the hydrogels demonstrate broad-range tunable mechanical performance in response to temperature and additives. Upon heating, the hydrogels manifest evident thermo-softening performance with the stiffness dramatically dropping more than 1000 times, endowing the hydrogels with desirable shape memory properties. When encountering various small-molecules, the hydrogels show over 3 orders’ broad-range tunable stiffness. Collectively, the ease of manipulation and universality of the as-established method, we hope, can become a widely used strategy to inspire novel designs and substantially broaden the application potentials of gels.