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Background: Driven by the potential biological applications of graphene, many groups have studied the response of cells exposed to graphene oxide (GO). In particular, investigations of bacteria indicate that there are 2 crucial parameters, which so far have only been investigated separately: GO size and exposure methodology. Our study took into account both parameters. We carefully characterized the samples to catalog sizes and structural properties, and tested different exposure methodologies: exposure in saline solution and in the presence of growth media. Furthermore, we performed experiments with peripheral blood mononuclear cells exposed to our GO materials. Methods: Atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy were used to characterize the morphology and composition of different samples of GO: GO-H2O, GO-PBS and GO-MG. Our samples had 2D sizes of ~100 nm (GO-H2O and GOPBS) and >2 μm (GO-MG). We tested antibacterial activity and cytotoxicity toward peripheral blood mononuclear cells of 3 different GO samples. Results: A size-dependent growth inhibition of Escherichia coli (DH5 α) in suspension was found, which proved that this effect depends strongly on the protocol followed for exposure. Hemocompatibility was confirmed by exposing peripheral blood mononuclear cells to materials for 24 hours; viability and apoptosis tests were also carried out. Conclusions: Our experiments provide vital information for future applications of GO in suspension. If its antibacterial properties are to be potentiated, care should be taken to select 2D sizes in the micrometer range, and exposure should not be carried out in the presence of grow media. [ABSTRACT FROM AUTHOR]

Salivary glands are specialized structures developed as an extensively compact, arborized design through classical embryogenesis, accompanied by a cascade of events channelized by numerous growth factors and genetic regulatory pathways. Salivary secretions maintain oral homeostasis and, when diminished in certain conditions, present as xerostomia or salivary hypofunction, adversely impacting the patient's quality of life. The current available treatments primarily aim at tackling the immediate symptoms providing temporary relief to the patient. Despite scientific efforts to develop permanent and effective solutions to restore salivation, a significant permanent treatment is yet to be established. Tissue engineering has proven as a promising remedial tool in several diseases, as well as in xerostomia, and aims to restore partial loss of organ function. Recapitulating the physiological cellular microenvironment to in vitro culture conditions is constantly evolving. Replicating the dynamic multicellular interactions, genetic pathways, and cytomorphogenic forces, as displayed during salivary gland development have experienced considerable barriers. Through this review, we endeavour to provide an outlook on the evolution of in vitro salivary gland research, highlighting the key bioengineering advances and the challenges faced with the current therapeutic strategies for salivary hypofunction, with an insight into our team's scientific contributions., (©The Author(s) 2023. Open Access. This article is licensed under a Creative Commons CC-BY International License.)