The precursor material to graphene aerogels is a hydrogel formed from an aqueous solution of graphene oxide. We investigate the time evolution of the physical and chemical properties of a graphene oxide suspension as it transitions to a hydrogel. Fully formed hydrogels undergo densification during reaction, forming mechanically stable monoliths. We demonstrate that the gelation process removes oxygen functional groups, partially re-forms the sp 2 network, and creates bonds between graphene oxide sheets. Furthermore, these changes to the physical and chemical properties occur on exactly the same time scale, suggesting that they have a common origin. This discovery lends greater understanding to the formation of graphene oxide-based hydrogels, which could allow more flexibility and tunability in synthetic methods for graphene-like materials.

The pharmacological therapy for gastrointestinal (GI) diseases, such as inflammatory bowel diseases, continues to present challenges in targeting efficacy. The need for maximal local drug exposure at the inflamed regions of the GI tract has led research to focus on a disease-targeted drug delivery approach. Smart nanomaterials responsive to the reactive oxygen species (ROS) concentrated in the inflamed areas, can be formulated into nanoplatforms to selectively release the active compounds, avoiding unspecific drug delivery to healthy tissues and limiting systemic absorption. Recent developments of ROS-responsive nanoplatforms include combination with other materials to obtain multi-responsive systems and modifications/derivatization to increase the interactions with biological tissues, cell uptake and targeting. This review describes the applications of ROS-responsive nanosystems for on-demand drug delivery to the GI tract. K E Y W O R D Sgastrointestinal tract drug delivery, irritable bowel disease, oxidation-responsive materials, stimuli-responsive nanocarriers

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