Pulmonary evaluation of whole-body inhalation exposure of polycarbonate (PC) filament 3D printer emissions in rats

Additive manufacturing (AM) is a broad manufacturing term that encompasses a range of processes that create objects by adding material through a computer-aided design model.  Three-dimensional (3D) printing is a form of AM, which builds objects layer-by-layer deposition of feedstock material using a 3D printer machine and computer software.  Fused filament fabrication (FFF, also known as Filament Freeform Fabrication) is one 3D printing process in which filaments are melted and extruded from a heated nozzle to deposit material.  FFF is an emerging technology and one of the most popular additive manufacturing processes, especially for consumers and small manufacturers.  Polycarbonate (PC) is a versatile material and PC filaments are widely used for fused filament fabrication 3D printing.  PC filaments are often loaded with additives to achieve different properties of the print objects.  These additives range from dyes, organometallic compounds, carbon nanomaterials, nanometal oxides to micrometer-scale particles such as copper, bronze, steel, tungsten, gold, and aluminum nitride (Vance et al., 2017).   Several engineered nanomaterials were infused into PC filaments, such as silicon dioxide nanoparticles, titanium nitride nanoparticles (Vidakis et al., 2021), titanium carbide nanopowder (Vidakis et al., 2022a), aluminum nitride nanoparticles (Vidakis et al., 2022b), and carbon nanotubes (Potter et al., 2021).

During heating, PC filament undergoes thermal degradation and releases fine particles (0.1 to 2.5 um) and incidental nanoparticles (d < 100 nm) as well as numerous volatile, and semi-volatile organic compounds that are likely derived from PC polymer and additives in the polymer (Azimi et al., 2016; Byrley et al., 2020; Gu et al., 2019; Stefaniak et al., 2017; Stefaniak et al., 2019; Alijagic et al., 2022; Tedla et al., 2022).   These emissions could pose a potential hazard to human health.  Currently, the potential health hazard of PC filament printing emissions has not been determined.

A NIOSH research group used a condensation nuclei counter to study PC filament emission rates, and determined that the number-based particle emission rates from an industrial-scale material extrusion AM machine were around 2.2 x1011 number/minute and the total volatile organic compound emission rates were around 1.9 x 104 µg/minute (Stefaniak et al., 2019).  The same group also found low levels of acetone, benzene, toluene, and m,p-xylene during PC filament printing processes.  Potter et al showed that PC filament emissions contained bisphenol A (BPA), phenol, chlorobenzene, DEHP, and di-tert-butylphenol (Potter et al., 2019).  In our previous studies on PC filament printer emission-induced cell toxicity (Farcas et al., 2019), emissions from a commercial PC 3D printer were generated in a chamber using a 3D printer and collected in cell culture medium.  The number-based size distribution of the particles inside the chamber was between 140-170 nm and the mean particle sizes in cell culture medium were 201±18 nm.  Analysis of elemental composition of particles collected in the cell culture medium found C, O, Ca, Na, Si, Ni, Cr, Fe, S, Al, and Cl.  The organic compounds in the emission collection cell culture medium were BPA, p-isopropenylphenol, and phenol.  At 24 h post-exposure, PC emissions were internalized in human small airway epithelial cells (SAEC) and induced a dose-dependent cytotoxicity, oxidative stress, apoptosis, necrosis, and increases in pro-inflammatory cytokine and chemokine production in SAEC (Farcas et al., 2019).  The results demonstrated that PC filament 3D printing emissions induce a cellular toxicity in SAEC.

Although cell-based in vitro toxicity analysis is increasingly applied to screen and rank chemicals for prioritizing toxicity studies, as well as to study toxic mechanisms, the toxicological significance of in vitro study-generated data in hazard and risk assessment is limited.  In comparison with animal-based in