An engineering model of the human colon

The development and performance of a three-stage tubular model of the large human intestine is outlined. Each stage comprises a membrane fermenter where flow of an aqueous polyethylene glycol solution on the outside of the tubular membrane is used to control the removal of water and metabolites (principally short chain fatty acids) from, and thus the pH of, the flowing contents on the fermenter side. The three stage system gave a fair representation of conditions in the human gut. Numbers of the main bacterial groups were consistently higher than in an existing three-chemostat gut model system, suggesting the advantages of the new design in providing an environment for bacterial growth to represent the actual colonic microflora. Concentrations of short chain fatty acids and Ph levels throughout the system were similar to those associated with corresponding sections of the human colon. The model was able to achieve considerable water transfer across the membrane, although the values were not as high as those in the colon. The model thus goes some way towards a realistic simulation of the colon, although it makes no pretence to simulate the pulsating nature of the real flow. The flow conditions in each section are characterized by low Reynolds numbers: mixing due to Taylor dispersion is significant, and the implications of Taylor mixing and biofilm development for the stability, that is the ability to operate without washout, of the system are briefly analysed and discussed. It is concluded that both phenomena are important for stabilizing the model and the human colon.