Freshwater planarians are considered interesting alternative models to develop new approach
; methodologies (NAMs) for (neuro)developmental toxicity assessment of chemicals
; and particulate materials1−3. They possess an exceptional regenerative capacity due to
; a high amount of pluripotent stem cells, allowing them to regenerate their entire body,
; including their central nervous system, within approximately seven days4,5. Further mechanistic
; insights into (nano)particle toxicity across different stages of (neuro)regeneration
; can be gained by integrating data from multiple test methods, including scanning transmission
; electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy
; (EDX)6,7. This can provide information on (nano)particle uptake, morphology, and agglomeration
; state, while simultaneously revealing potential ultrastructural changes8. In
; this work, a stereology-based approach is presented for the ultrastructural detection of
; (nano)particles by STEM-EDX within ultra-thin sections of the planarian Schmidtea
; mediterranea. The procedure is based on the chemical fixation and embedding of specimens
; in Epon-Spurr resin, which are subsequently sectioned ultra-thin and stained with
; lead citrate for ultrastructural analysis. Image acquisition, analysis, and workflow efficiency
; are enhanced by integrating innovative software such as Velox and MAPS (ThermoFisher
; Scientific, Eindhoven, The Netherlands). These allow automated acquisition
; of large overview images by stitching smaller high-resolution tiles together, greatly facilitating
; navigation through complex samples. By combining this with the physical dissector
; principle, an unbiased estimate of the number and volume density of intracellular
; (nano)particles can be defined. This stereological method will be integrated to objectively
; quantify (nano)particle uptake and transformations in planarians, evaluating their
; potential as a NAM for assessing (neuro)developmental toxicity of particulate materials
; applied in the food chain.