Pathology of dehydrated hAM (a) and cryopreserved hAM (b) with hematoxylin and eosin stain (400x). Note the monolayer epithelium in both hAM (asterisk). Dehydrated hAM is much thinner than cryopreserved hAM. The epithelial cells of dehydrated hAM (c, e, g) and cryopreserved hAM (d, f, h) under the microscope. The epithelial cells were confirmed devitalized by staining with calcein AM (e, f), which is retained within live cells and ethidium homodimer-1 (g, h), which enters cells with damaged plasma membrane and undergoes a 40-fold enhancement of fluorescence upon binding to nucleic acids in devitalized cells.