Using simple to more robust in vitro methods based on human pulmonary models to evaluate the acute and subacute toxicity of micro- and nanoplastics derived from 3D printing materials.

Mechanical recycling and other processes involved in the end-of-life treatment of 3D-printed plastic polymers can lead to the generation of micro- and nanoplastics (MNPs). As the use of these materials continues to grow, the mechanical degradation of plastics from 3D printing may increase human exposure to MNPs, raising concerns about potential health risks for users and environmental impacts. One of the main routes of exposure to MNPs is via inhalation. For regulatory purposes, most of inhalation studies have been performed using rodents and following the OECD TG 412, however, these models do not accurately mimic the physiology of the human pulmonary system. As alternative, New Approach Methodologies (NAMs) based on human in vitro models have been used lately, providing simple and valuable, and physiologically relevant tools for research. In this work, simple in vitro models using Calu-3 and TK6 cells were exposed for 24 h (acute) and the advanced primary human epithelial MucilAir™ model was exposed for 24 h (acute) and 28 days (sub-acute, adapting the OECD TG 412) to MNPs made of polypropylene (PP), polycarbonate (PC), PP + silver nanoparticles (PP + Ag) and PC + single wall carbon nanotubes (PC + SWCNT). The results showed no significant toxicity of MNPs in acute exposures using the Calu-3 and TK6 models. In contrast, significant effects were observed along time after acute and subacute exposure of MucilAir™ to the different MNPs. These results indicate that robust in vitro models such as MucilAir™ may represent a valuable NAM for acute and sub-acute inhalation toxicity studies.