Frictional resistance model for a capsule and an intestine with different central axes based on the intestinal nonlinear constitutive relationship

Resistance model of an active capsule endoscope in a peristaltic intestine

“…When there is no peristalsis in the intestine, the resistance to the capsule will theoretically be constant since the small intestine is a straight circular tube, and indeed the measured resistance fluctuates around a certain fixed value over time, which was well demonstrated in our previous study. 20 During the experiment, we noticed that there is a small deformation in the axial direction of the intestine as the capsule travels through the narrow area of the artificial intestine, which is also caused by the structural resistance. However, in the human intestine, the intestine is surrounded by other tissues, so the axial deformation of the intestine is small and can be ignored.…”

“…According to our previous work, 20 though there is the uneven deformation of the intestinal wall, the variation of the frictional resistance can be neglected in the middle zone of the capsule, so the analytical diagram as shown in Figure 2. The inner walls of the undeformed intestine are represented as the dashed circles with the point O 0 as the center, and the inner walls of the deformed intestine ( i.e ., the capsule outer walls) are represented as the solid circles with the point O 1 as the center.…”

“…Sliker et al 19 analyzed the force between the capsule and the intestine under the partial contact state, and a predictive model was developed. Huang et al 20 developed a model to predict the frictional resistance when the centerline of the capsule is different from the centerline of the intestine based on a nonlinear viscoelastic constitutive model. Wang et al 21 analyzed the force of a passive capsule in a peristaltic intestine and developed a predictive model of the frictional resistance.…”

Dynamic analysis of a soft capsule robot self-propelling in the small intestine via finite element method

“…They aimed to understand the capsule's locomotion under intestinal motility and to develop controllable capsule robots for live examinations. Recently, the intestine wall was modelled as a viscoelastic material [14,15] due to its experimentally determined stress relaxation properties when the capsule slides on the mucosal surface. According to the above, the modelling of the intestine mainly focused on its contact condition [14,16] and frictional environments [13,15] with the capsule.…”

“…Recently, the intestine wall was modelled as a viscoelastic material [14,15] due to its experimentally determined stress relaxation properties when the capsule slides on the mucosal surface. According to the above, the modelling of the intestine mainly focused on its contact condition [14,16] and frictional environments [13,15] with the capsule. Very few studies [17][18][19] have considered the real intestinal environment through experimental investigations and analysed the simplified capsule-intestine model through finite element (FE) analysis [14,16].…”