Experimental investigation of the small intestine's viscoelasticity for the motion of capsule robot

Active capsule robots are studied widely all over the world, and various prototypes have been devised, e.g. the “internal force-static friction” capsule robot. During the previous research on this capsubot, we have found that the intestine's resistance characteristic is of great importance to both the design and motion control of the capsubot, however, there are very few studies on the viscoelasticity of the small intestine, and that may make the main causality of the capsubot's motion failure. In this work, experiments are performed based on two different methods: the stress relaxation on the self-made measurement system, and the shear measurement on the dynamic mechanical analyzer (DMA). As a result, we obtain a five-element model, describing the viscoelasticity of intestines, and find that the relaxation modulus varies with the range of strain. The DMA test indicates that the storage modulus descends with the increasing shear strain, which means the hyper-elasticity of small intestine can be measured numerically. Also the strain energy density and stress-strain hysteresis loops can be obtained. This work paves the way for the modeling of intestine and the finite element analysis (FEA) in the future.