Alginate-graphene oxide hydrogels with enhanced ionic tunability and chemomechanical stability for light-directed 3D printing

Nanocomposite hydrogels that incorporate 2D carbon nanomaterials could enable augmented and responsive behaviors not observed with polymeric matrices alone. In particular, non-covalent interactions could facilitate enhanced mechanical performance that can be self-recovered with external stimuli. Here, we demonstrate alginate-graphene oxide (GO) hydrogels using a non-covalent, ionic crosslinking mechanism compatible with light-directed 3D printing. We show that alginate-GO hydrogels exhibit improved mechanical performance in shear, compression, and tension, including a two-fold increase in shear modulus, a three-fold decrease in inelastic deformation, and a nine-fold increase in fracture energy relative to alginate-only hydrogels. Moreover, alginate-GO hydrogels are stabilized by hydrogen bonding between nanosheets and remain intact after removal of ionic crosslinkers by chelation. As a consequence, the shear modulus of these nanocomposite hydrogels can be tuned by over 500-fold via external ion concentration. We demonstrate that alginate-GO can be stereolithographically printed into robust, freestanding and overhanging 3D structures. These designer material architectures exhibit outstanding stability and superoleophobicity in high salt solution, which can be used to repel and manipulate a variety of oils. Overall, such nanocomposite hydrogels with engineered non-covalent interactions could enable smart multiresponsive and multifunctional devices for aqueous and marine environments. (C) 2018 Elsevier Ltd. All rights reserved.