The significance of graphene based composite hydrogels as smart materials: A review on the fabrication, properties, and its applications

[Display omitted] •Hydrogels are three-dimensional crosslinked stable networks.•Hydrogels can be synthesized through numerous ways.•Hydrogels are stimuli sensitive.•Hydrogels have a wide range of applications. Hydrogels are unique three-dimensional cross-linked water insoluble stable network, thereby, exhibiting a remarkable ability to absorb water and biological fluids. Currently, hydrogels attained striking attention of research community in various applications namely tissue engineering, optics, imaging, diagnostics, and drug delivery. Different materials are used to synthesize hydrogels. Graphene is an emerging two-dimensional wonder material due to its unique features in remarkably enhancing the characteristics of the traditional hydrogels. The specific features of graphene such as excellent mechanical properties, optical properties, high thermal conductivity, and high electrical conductivity result the graphene to form unique hydrogel. In addition, graphene as filler to blend with small molecules and macromolecules for the fabrication of the multifunctional graphene-based hydrogels is used in numerous fields. Compared to traditional hydrogels, the graphene-based hydrogels tend to exhibit more prominent performances in biosensors, energy storage, biomedicine, and wastewater treatment. Herein, the fabrication techniques of the different types of hydrogels and the recent progress in graphene-based hydrogels have been reviewed. However, graphene containing hydrogels are still limited by several urgent issues which will be discussed in this article. Therefore, this review article aims to elucidate the basic concepts, classification, synthesis approaches, relevant mechanism of hydrogels and the performance aspects of graphene-based composite hydrogels and its wide applications along with the associated challenges and future perspectives.