"Gold nanoparticles have been reported to cross the placenta after maternal intravenous injection in rats, but structural and physiologic differences across species preclude inferences about the ability of nanoparticles to cross human placentas based on animal studies. Wick et al. (p. 432) used an ex vivo human placental perfusion model to study the transfer of fluorescent polystyrene particles (nominal diameters of 50, 80, 240, and 500 nm) across the placenta. The authors report that polystyrene particles up to 240 nm in diameter were able to cross the placental barrier without affecting the viability of the placental explant. The authors conclude that findings are consistent with size-dependent transfer of nanomaterials across human placentas, but they acknowledge that the model involved high-dose exposures over a period of a few hours and that the perfusion rate was representative of placental perfusion late in pregnancy. In addition, they suggest that transfer may also be influenced by particle composition or surface coatings, thus preventing generalization across different types of nanoparticles."

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