Experimental characterization of the fluid dynamics in an in- vitro system simulating the peristaltic movement of the stomach wall

Abstract

The difficulty in experimentally characterizing the dynamics of gastric contents during digestion has limited the knowledge required to understand and model the kinetics of food disintegration. The goal of this work was to experimentally characterize, in a closed system, the peristaltic flow of fluids with different rheological properties. An experimental apparatus was developed to reproduce the general characteristics of gastric motility, while supporting the use of a non-intrusive flow measurement technique (Particle Image Velocimetry). The apparatus consisted of a polycarbonate chamber with one neoprene wall that was continuously deformed by vertically moving a stainless steel cylinder at a speed of 3.5mm/s. The fluid dynamics of three Newtonian fluids (water, and water solutions of 10% and 95% corn-syrup) and two shear thinning fluids (water solutions of 0.15% and 0.50% CMC) were investigated. In addition, the effect of the occlusion ratio (30, 45 and 60%) on the fluid dynamics of water within the system was analyzed. Experimental results showed that the loci of maximum velocity were present in the section corresponding to the location of the hump peak. As the viscosity of the Newtonian fluid increased, higher and more localized retropulsive velocities developed. However, these differences were not observed in the dynamics of shear thinning fluid flows. As the viscosity of the fluid increased, a more ordered flow developed, but no differences were found with respect to maximum values of shear rates or vorticity. The differences in the overall flow behaviour of the two CMC solutions were even less noticeable, but they both exhibited lower shear rates and vorticities than the Newtonian fluid. By decreasing the compression ratio of the hump, the maximum water velocity within the system decreased by 45%, while the maximum values of shear and vorticity decreased by 18% and 23%, respectively. This work showed the significant effect of the rheological properties of the flow on the fluid-dynamics within a closed system due to the peristaltic deformation of its wall. From a boarder perspective, this work demonstrated the relevance of acquiring a good characterization of the rheology of gastric contents to fully characterize the fluid- mechanical forces involved in food digestion.