Biopersistence of man-made vitreous fibres (MMVF) / synthetic vitreous fibres (SVF): advancing from animal models to acellular testing

Abstract The field of fibre toxicology highlights a significant connection between the physicochemical properties of fibres—such as diameter, length, and durability—and their toxicity when inhaled. Among these properties, durability, particularly in terms of biopersistence and retention time in the lungs, is crucial in determining chronic toxicity. This understanding of fibre biopersistence is especially relevant to the regulation and safety assessment of Man-Made Vitreous Fibres (MMVF), also referred to in North American literature as Synthetic Vitreous Fibres (SVF). Despite its importance, current practices rely heavily on in vivo testing methods for evaluating biopersistence, which conflicts with the movement towards reducing animal testing and utilising new approach methodologies (NAMs) for hazard and risk assessment. In vitro assessments of biodurability have long been employed by the research community and industry alike to investigate the persistence of fibres in the lung, offering an alternative to reduce animal testing to evaluate this critical mediator of fibre toxicity. Here, we explore recent developments in acellular in vitro biodurability approaches for assessing fibre durability in the lung, addressing the variations and key challenges associated with using these methods to determine the safety of bio-soluble MMVF.