Zebrafish Chorion Nanoparticle Barrier

Before a zebrafish embryo hatches, the only way anything from the outside world reaches it is through the pore canals of its chorion — an acellular shell whose pores run about 0.5 to 0.7 micrometres across. This simulator renders that chorion in 3D and streams nanoparticles toward it, checking each arrival's effective diameter (primary size scaled up by how agglomerated the particles are in the surrounding medium) against the pore-size distribution. Particles small and well-dispersed enough slip through into the perivitelline space and accumulate as internal dose; particles that are too large — often because higher ionic strength drove them to agglomerate — are physically excluded and pile up on the chorion's outer surface. It is a size-exclusion gate that decides whether a nanomaterial's cellular toxicity mechanisms ever get a chance to act at all.