Modeling and experimental investigation on the mechanical behavior of a spiral-type capsule in the small intestine

This paper reports on the study of the behavior of the viscoelastic contact between a spiral-type capsule and the small intestine. Both 2D and 3D simulations show that the traction force, which is due to the pressure difference between the two sides of the spirals, is velocity dependent. With an increase in the sliding velocity, the traction force decreases initially due to the reduced stress relaxation. However, if the velocity reaches some certain magnitude, the reduction in the stress becomes negligibly small. The traction force starts to increase because of the higher stress coming from the higher strain rates. The experimental torque and force measurements were taken for the capsules with different cross-section profiles. The results show that the traction force can be raised by carving grooves on the spirals´ surface or using a higher and narrower spiral structure. The difference between the mechanical behaviors of a rotating-only capsule and a rotating-and-translating capsule were experimentally studied and explained in detail. The results show that a rotating-and-advancing capsule gets slightly more resistive torque than a rotating-only capsule.