Presently, many consumer products contain nano-sized materials (NMs) to improve material properties, product quality and ease of use. NMs in food additives and in cosmetic articles (e.g., tooth paste) may be taken up by the oral route. As adverse effects of environmental nanoparticles, like ultrafine particles, have been reported, consumers worry about potential risks when using products containing NMs. The review focuses on metal and metal oxide NMs as common additives in tooth paste and in food industry and exposure by the oral route. Testing of NMs for oral exposure is very complex because differences in the diet, in mucus secretion and composition, in pH, in gastrointestinal transit time and in gastrointestinal flora influence NM uptake. Acellular (mucus, saliva) and epithelial layer of the orogastrointestinal barrier are described. Expected exposure doses, interaction of the NMs with mucus and permeation through the epithelium as well as in vivo data are mentioned. The role of in vitro models for the study of parameters relevant for ingested NMs is discussed.

A continuous tubular crystallizer system with an inner diameter of 2.0 mm and an overall length of 27 m was used to generate acetylsalicylic acid seeds in situ from ethanolic solution via cooling and ultrasound irradiation and to grow the crystals in the tubing with a controlled temperature trajectory. In order to minimize the residence time distribution, air bubbles were introduced into the system to generate a segmented gas-slurry flow. The narrow residence time distribution and the tight temperature control in the small tubing due to the large surface to volume ratio resulted in relatively narrow crystal size distributions of the product. Generally, all experiments clearly demonstrated significant crystal growth for the product crystals in comparison to the seeds and yielded product masses on the g/min scale. Furthermore, it was demonstrated that the size of the product can be easily controlled via fines removal by dissolution due to rapid heating and varying the mass of seeds per mL of solution.

Intestinal epithelial cell culture models, such as Caco-2 cells, are commonly used to assess absorption of drug molecules and transcytosis of nanoparticles across the intestinal mucosa. However, it is known that mucus strongly impacts nanoparticle mobility and that specialized M cells are involved in particulate uptake. Thus, to get a clear understanding of how nanoparticles interact with the intestinal mucosa, in vitro models are necessary that integrate the main cell types. This work aimed at developing an alternative in vitro permeability model based on a triple culture: Caco-2 cells, mucus-secreting goblet cells and M cells. Therefore, Caco-2 cells and mucus-secreting goblet cells were cocultured on Transwells and Raji B cells were added to stimulate differentiation of M cells. The in vitro triple culture model was characterized regarding confluence, integrity, differentiation/expression of M cells and cell surface architecture. Permeability of model drugs and of 50 and 200 nm polystyrene nanoparticles was studied. Data from the in vitro model were compared with ex vivo permeability results (Ussing chambers and porcine intestine) and correlated well. Nanoparticle uptake was size-dependent and strongly impacted by the mucus layer. Moreover, nanoparticle permeability studies clearly demonstrated that particles were capable of penetrating the intestinal barrier mainly via specialized M cells. It can be concluded that goblet cells and M cells strongly impact nanoparticle uptake in the intestine and should thus be integrated in an in vitro permeability model. The presented model will be an efficient tool to study intestinal transcellular uptake of particulate systems.

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Highlights► A new VITROCELL – Pariboy system was evaluated for testing of aerosolized NPs. ► Deposition rates differed between marker compounds and NPs. ► The manual aerosolizer MicroSprayer was suitable for cytotoxicity testing of NPs. ► Polystyrene nanoparticles acted more cytotoxic as aerosols than as suspensions.