Three-dimensional (3D) printing, also termed additive manufacturing, has advanced from a commercial industrial process to one that is now commonly used in households and schools by hobbyists and children. There are several types of 3D printing processes, one of these being fused filament fabrication. For this type of printing, a thermoplastic material in the form of a filament is fed into a heated printer extruder printer head. The heated material is then deposited on a print bed in a pattern predetermined by code to create a 3D object. Filaments consisting of polylactic acid or acrylonitrile butadiene styrene are commonly used. Metals are added to these filaments to enhance the stability, thermal and mechanical properties, and tensile strength of the 3D printed object (Tedla et al., 2022). Copper, gold, iron, and zinc are examples of metals added to 3D printer filaments.

Recent studies have shown the potential for inhalation exposure to particles and volatile organic compounds emitted during the 3D printing process (Byrley et al., 2021; Tedla et al., 2022; Vallabani et al., 2022). These and other studies have suggested there is a risk to adverse health effects by inhalation of these emissions from 3D printers. Oral exposure to the final printed objects, particularly in children, and in some cases to the filaments is possible. However, this route of exposure is not well characterized for 3D printers. Oral exposure scenarios of the printer filaments or printed objects include ingestion, mobilization by saliva during mouthing, and mobilization by sweat following dermal contact. Inhaled particles that impact the muco-ciliary lining of the conducting airways may also be cleared and swallowed (Stuart, 1984).

A variety of metals and metalloids have been found in toys, low-cost jewelry, and costume cosmetics (Akimzhanova et al., 2020; Cui et al., 2015; Guney and Zagury, 2012; Guney and Zagury, 2013; Guney et al., 2020; Perez et al., 2017). Arsenic, cadmium, copper, and lead are examples of metals and metalloids found in these products. Guney and Zagury (2013) reported that several toys and children's jewelry had concentrations of metals that exceeded the Europeon Union's total concentration migratable concentration limits. Cadmium, lead, and copper were found to be at very high levels in some of the items examined (37–71%, w/w). These high levels of metals and metalloids in toys and jewelry place people, particularly children, at a risk of poisoning. For example, in 2006, the Centers for Disease Control reported the death of a child that had ingested a metallic charm that later was found to contain high levels of lead (CDC, 2006).

Studies have shown that metals and metalloids in toys and jewelry are bioaccessible (Cui et al., 2015; Guney and Zagury, 2013; Guney et al., 2014). Bioaccessibility can be defined as the fractional amount of an ingested substance that is soluble in the gastrointestinal tract and is available for absorption (Rodrigues et al., 2022). Bioaccessibility is determined using an in vitro method, which measures the release of a chemical from another substance; for example, the release of a metal from soil or a toy. The results are used to predict oral bioavailability, which is the fractional amount of a substance ingested that reaches the systemic circulation (Rodrigues et al., 2022). Cui et al. (2015) reported the high bioaccessibility of antimony, arsenic, cadmium, chromium, and nickel from toys under saliva mobilization or gastric ingestion. Risks, calculated in terms of the hazard index (ratio of chemical daily intake to reference dose), were >1 for several toys containing these metals and metalloids. Thus, metals and metalloids in toys present a potential adverse health risk following ingestion.

A scenario exists whereby people may be exposed by the oral route to 3D printer filaments or objects printed by this process. The objective of this study was to investigate the cytotoxicity of printed objects (extruded fibers) made with 3D printer metal-fill filaments in rat and human intestinal cells following incubation in simulated gastric fluid. We also assessed the physical characteristics of the treated filaments by scanning electron microscopy and x-ray absorption spectroscopy to address the mechanism of metal ion released from the metal powder-containing polymer.