Hidden cytotoxicity and mitochondrial dysfunction in 3D-printing polymers: evidence from FLEX, PETG and PC

Additive manufacturing, also known as 3D printing, is a rapidly evolving technology that is profoundly impacting consumer products and biomedical applications. The persistent lack of essential toxicological data in material safety data sheets (MSDS) for additive manufacturing raises legitimate concerns regarding the biological safety of the polymers utilized in 3D printing. In this study, the cytotoxic potential of eight widely available filaments—polylactic acid (PLA), polyethylene terephthalate (PETG), chlorinated polyethylene (CPE), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), polypropylene (PP), and flexible polyurethane (FLEX)—was examined using an ISO 10993-5 compliant indirect contact assay on primary human dermal fibroblasts. Cells were exposed to leachables diffusing from 3D-printed inserts for 24 hours or 7 days, and viability, proliferation, metabolic activity, and mitochondrial respiration were assessed. The investigation revealed that FLEX (thermoplastic polyurethane), PETG, and PC induced significant cytotoxic effects, including impaired proliferation, altered morphology, and disrupted mitochondrial respiration. Conversely, PLA, ABS, and CPE demonstrated minimal impact under the tested conditions. The observed toxicity is likely associated with additives, pigments, and plasticizers, such as isocyanates or volatile organic compounds (VOCs). These compounds are released during the thermal degradation of the material during printing. Specifically, the toxicity profile aligns with the known hazards of residual isocyanates in FLEX, glycol modifications in PETG, and the known release of bisphenol A and related compounds from PC. These findings suggest that materials commonly regarded as biocompatible may exhibit hidden toxicity due to additives or degradation by-products generated during the printing process. The findings of this study underscore the imperative for a systematic toxicological evaluation and stringent regulatory oversight of 3D-printing polymers, particularly given their pervasive use in consumer contact applications—including wearables (such as customized shoes and wristbands) and items intended for vulnerable populations (such as infant and toddler toys)—where direct and long-term exposure indicates a potential, yet unrecognized, risk to public health.