Biomimetic jellyfish-like PVA/graphene oxide nanocomposite hydrogels with anisotropic and pH-responsive mechanical properties

Jellyfish mesogloea with a well-developed anisotropic microstructure exhibits excellent and pH-responsive mechanical properties. It remains a great challenge to fabricate hydrogels mimicking the hierarchical structures and intriguing properties of biological hydrogels. Here we report the fabrication of a biomimetic jellyfish-like polyvinyl alcohol/graphene oxide (PVA/GO) nanocomposite hydrogel through a convenient and effective directional freezing–thawing technique. The resulting hydrogels show microstructures, water contents, and mechanical properties very similar to those of jellyfish mesogloea. Free-standing PVA/GO hydrogels with extremely high water contents (97–99 wt%) are obtained. The hydrogels show anisotropic porous structures consisted of microsized fibers and lamellae. The hydrogels exhibit high tensile and compressive strengths, up to 0.17 MPa and more than 2 MPa, respectively. In addition, anisotropic tensile mechanical properties are also observed. More interestingly, the PVA/GO nanocomposite hydrogels exhibit pH-responsive mechanical properties, which become weaker when swollen in acidic and basic solutions. Jellyfish-like structure that can mimic the swimming style of jellyfish is constructed with the PVA/GO nanocomposite hydrogel. This study might provide new idea for designing and fabricating novel biological or bio-inspired hydrogels for various applications in biomedical, industrial, and soft robotics fields.