The digestive barrier:
pH effects, digestive enzymes, interactions with components of bile and digestive secretions
The mucus barrier:
Mucus has developed to resist permeation of exogenous compounds and protect the underlying epithelia and will exclude particles based on size and charge.
The epithelial barrier:
It has previously not been possible to integrate cell culture models with accurate digestive fluids due to cell death when exposed to digestive fluids.
Cell culture systems of the epithelia are not stable with ex vivo mucus, and co-culture systems produce a patchy, incomplete layer of mucin which is not an accurate model of GI mucins and cannot protect cells from digestive secretions