"Objective: In this study we investigated whether particles can cross the placental barrier and affect the fetus.
Methods: We used the ex vivo human placental perfusion model to investigate whether nanoparticles can cross this barrier and whether this process is size dependent. Fluorescently labeled polystyrene beads with diameters of 50, 80, 240, and 500 nm were chosen as model particles.
Results: We showed that fluorescent polystyrene particles with diameter up to 240 nm were taken up by the placenta and were able to cross the placental barrier."
Note: According to this study, the "SARS-CoV-2 vaccine candidates nCoVsaRNA and ARCoV have average particle sizes of 75 nm and 89 nm, respectively":
https://www.sciencedirect.com/science/article/pii/S0378517321003914
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