Deformation, mechanical breakdown, and flow of soft solid foods in the stomach.

Mechanical changes to solid foods in the stomach are crucial aspects of processes for regulating nutrient bioavailability, satiety, and glycaemic response after a meal. However, the underlying mechanisms are poorly understood. This study uses a Smoothed Particle Hydrodynamics (SPH) model to study the deformation and mechanical breakdown of solid beads in a liquid medium within a realistic three-dimensional representation of the stomach geometry. The model incorporates peristaltic contraction waves, including Terminal Antral Contractions (TACs), which are high-amplitude and high-speed travelling occlusions observed in the distal region of the stomach. The solid beads are modelled using elastic-plastic (EP) and elastic-brittle (EB) constitutive laws. Results show that the stomach wall can induce significant compression and fragmentation in the solid beads through direct contact, and the accompanying fluid flow contributes towards further mechanical change. An originally spherical EP bead closest to the pylorus is extruded into a thin cylindrical shape, generating 15 fragments with a 5% higher surface area, before being propelled away from the TAC region. A model-parameter sensitivity analysis shows that an increase in yield stress substantially reduces the fragmentation but not the elongation. An EB bead near the pylorus deforms less but fractures into 235 small fragments and a large chunk, leading to an overall 12% higher surface area. The EB bead remains near the pylorus, fracturing further over multiple peristaltic cycles. Increased fracture strength, represented by a higher threshold strain, significantly reduces the surface area change and the number of fragments generated by the wall contractions. These results show how a coupled biomechanics-fluid-elastic-plastic-fracture model can be used to investigate the mechanical breakdown of solid foods in the stomach.