Multifilm Mass Transfer and Time Constants for Mass Transfer in Food Digestion: Application to Gut-on-Chip Models

Abstract

This review highlights the involvement of mass transfer in animal food-digestion processes. There may be several mass-transfer steps during the dissolution of food components, starting from the food itself, moving into the digestive juices, then moving through the walls of the gastrointestinal tract. These steps create a sequence of film resistances to mass transfer, where one film resistance often limits the overall mass-transfer process. Mass-transfer rates, mass-transfer coefficients, and the time scales and time constants for different parts of the food-digestion process are all interlinked, and the connections have been explained. In some parts of the food-digestion process, the time constants for the mass-transfer process are similar to the residence times for food digestion, emphasising the importance of mass transfer in these parts of food digestion, such as the duodenum. The mass-transfer and transport behaviour for in vivo human digestive systems and in vitro guts-on-a-chip may be very similar, suggesting that cells on the intestine walls, whether in vitro (guts-on-a-chip) or in vivo, may see similar transport behaviour for both nutrients towards the cells, and waste products away from them.