To Örebro University

Metal additive manufacturing (AM), also known as industrial 3D printing, has revolutionized modern industry, enabling the creation of complex, high-performance components across sectors such as aerospace, automotive, and biomedicine. While the printing process itself is often well-contained, a critical and understudied phase – post-processing – has emerged as a source of potentially hazardous airborne particulate matter. These emissions may pose health risks to workers, particularly through interaction with the immune system, which serves as the body's first line of defense and a sentinel of environmental stressors. Yet, limited data exist on the physicochemical properties and immunotoxicological impact of these particles. This study aimed to assess the immunological consequences of particle emissions released during the post-processing of metallic AM alloys, using a human macrophage model and a multi-omics framework.

Airborne particles were collected directly from an operational AM facility using a cascade impactor, separating them into five size fractions, ranging from coarse (>2.5 μm) to nanoscale (<250 nm). A comprehensive physicochemical characterization was performed using scanning electron microscopy with energy-dispersive spectroscopy and X-ray photoelectron spectroscopy. The emitted particles were highly heterogeneous, with irregular, sharp morphologies, and exhibited increased surface oxidation compared to virgin feedstock powders. Functional toxicological assessments were performed in human macrophages, including transmission electron microscopy to evaluate particle uptake. Macrophages, both resting and lipopolysaccharide-primed, displayed potent and dose-dependent inflammatory responses, as seen by elevated secretion of several cytokines (e.g., IL-1β, IL-6). RNA sequencing revealed profound alterations in macrophage gene expression, including dysregulation of NF-κB signaling, cellular senescence, and lipid metabolism pathways. Gene set enrichment analysis indicated broader perturbations in immune regulation and macrophage homeostasis. Non-targeted metabolomics demonstrated significant changes in intracellular metabolic profiles. Specifically, there was an upregulation of numerous lipids and a suppression of several metabolites involved in immunomodulation and cellular energy homeostasis, including tryptophan, NAD, and phenylalanine. Integrated multi-omics analysis revealed a coordinated crosstalk between transcriptional and metabolic responses, pointing to an acute and multifaceted inflammatory reprogramming of macrophages in response to post-processing AM particles.

In conclusion, this study provides the first integrative multi-omics characterization of human immune cell responses to airborne particulate emissions from metal AM post-processing. These results not only advance the field of nanosafety in industrial AM environments but also underscore the urgent need for targeted risk mitigation strategies during post-processing.