The design and synthesis of double network (DN) hydrogels that can mimic the properties and/or structure of natural tissue has flourished in recent years, overcoming the bottlenecks of mechanical performance of single network hydrogels and extending their potential applications in various fields. In recent years, such bioinspired DN hydrogels with extraordinary mechanical performance, excellent biocompatibility, and considerable strength have been demonstrated to be promising candidates for biomedical applications, such as tissue engineering and biomedicine. In this minireview, we provide an overview of the recent developments of bioinspired DN hydrogels defined as DN hydrogels that mimic the properties and/or structure of natural tissue, ranging from, e.g., anisotropically structured DN hydrogels, via ultratough energy dissipating DN hydrogels to dynamic, reshapable DN hydrogels. Furthermore, we discuss future perspectives of bioinspired DN hydrogels for biomedical applications.

The present study highlights a straightforward and versatile strategy for the synthesis of strong poly(2-isopropenyl-2-oxazoline) hydrogels with tunable properties by using a bifunctional macrocyclic pillar[5]arene host having two carboxylic acid groups as cross-linker. This new strategy provides access to materials with tailored properties from soft and flexible to rigid and strong. The mechanical properties and water uptake of the hydrogels could be effortlessly controlled during the synthesis step through variation of the cross-linker content and after cross-linking by guest–host interactions. The hydrogels displayed strongly enhanced mechanical properties (i.e., compression and tensile modulus, energy dissipation, stress at break and storage modulus) compared to their counterparts cross-linked with linear dicarboxylic acids. The remarkable properties of the pillar[5]arene cross-linked hydrogels were assigned to the transfer of the external stress to the rigid and bulky pillar[5]arene residues that contribute to the overall dimensional stability of the hydrogels and allow energy dissipation. Moreover, we demonstrate the applicability of these materials for water purification. The hydrogels showed high adsorption performance for phenols and dyes such as methylene blue and methyl red and they could be easily regenerated, by washing with an organic solvent for reuse.