Recent advances in 3D printing of tough hydrogels: A review

Over the past two decades, the development of hydrogels with high mechanical strength and toughness shows both fundamental and practical significances. It is challenging yet highly desired to process these tough hydrogels into structural elements with desired architectures, which are important for real applications. Three-dimensional (3D) printing, as an emerging additive manufacturing strategy, demonstrates great potentials for engineering tough hydrogels with versatile applications. This paper aims to review the recent progress on 3D printing of tough hydrogels and their relevant applications. We give an overview on the advantages and requirements of tough hydrogel systems for specific 3D printing technologies, followed by detailed summary of the network structures, mechanical performances, toughening mechanisms, and representative applications of the printed tough hydrogels. Finally, recent advances of 4D printing of tough hydrogels are discussed as a prospective direction to devise soft actuators and robots.