Characterization of fugitive emissions of SLS 3D printing

This study investigated airborne emissions and potential health risks associated with selective laser sintering (SLS) 3D printing using Nylon-12 powder. Particle size characterization, in vitro cell studies, and analytical techniques were employed to examine particulate exposure during SLS 3D printing processes. Pure Nylon-12 powder, hardened nylon, sintered material, and emitted particles during 3D printing were characterized using microscopy, spectroscopy, and other techniques. Multiple methods were utilized to collect emitted particles for further analysis. Airborne particle concentrations associated with 3D printing and the work area were monitored in real-time using particle spectrometers, which measured particle number concentrations ranging from 10 nm to 10 µm in mobility sizes. During the in vitro studies, THP-1 human monocytic leukemia cells were exposed to four concentrations of Nylon-12 powder suspension (10, 100, 500, and 1,000 μg/mL) assessing cytotoxicity and inflammatory response through 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay and Tumor Necrosis Factor Alpha (TNF-Alpha) enzyme-linked immunosorbent assay (ELISA). Cell toxicity investigations revealed non-linear viability reduction patterns, with significant decreases at higher concentrations (1000 μg/mL, p = 0.0207), but not significant at the intermediate doses (100 and 500 μg/mL). The TNF-α assay results indicated a dose-dependent inflammatory response to Nylon-12 powder exposure. The highest TNF-α concentration (0.088) was observed in cells exposed to 1000 μg/mL, while the lowest concentration (0.085) was found in the 10 μg/mL treatment group. Elemental composition analysis identified silicon, aluminum, and copper as consistent elements in pure Nylon-12, sintered material, hardened nylon, and emitted particles collected during sampling, indicating the presence of nylon particles in the airborne emission. Air sampling showed variable particle dispersion during printing phases, with respirable and nanoparticles ranging from 48.97 to 194.9 µg/m³. NanoScan SMPS data indicated elevated nanoparticle concentrations, peaking at 6,848 particles/cm³ during printing. These findings underscore the importance of monitoring and controlling airborne emissions in 3D printing environments to mitigate potential biological toxicity and develop safer practices for this technology.