Study Of Bio-tribology Properties Of Flexible Tubular Organ

The digestive tract is the main digestion and absorption organ of human body. With the exacerbating of the severe pollution of the environment, speeding up of the industrial production, changing of the dietetic structure, digestive tract diseases such as esophageal cancer, intestinal cancer incidence increased year by year. Digestive endoscopic checking is an important means of the digestive tract disease diagnosis and treatment, interpolation endoscopic pushed into the patients’body with the aid of outside force may cause great pain to patients and even cause postoperative complications such as throat bruises, perforation of the esophageal mucosa tear and gastrointestinal perforation. Capsule endoscopy, after swallowing, moves into the body by creeping, and it exists some other problems such as shortage of power supply, unable to locate, motion out of control, and stagnation in the body. Active decay robot, if wanting to walk smoothly in the digestive tract, must have enough frictions so as to provide driving force for its movement. So, the biological tribology research on the digestive tract, in order to solve the digestive tract tissue bruise, capsule retention, endoscopic micro robot motion control and structure optimization design has very important theoretical research significance and academic value.Taking rabbit digestive tract as the research object, this paper explores the friction mechanism by adopting the boundary lubrication theory through the characterization of surface topography change within its surface microstructure and creep, rheology, mechanical performance, intestinal mucous lubricity. The paper Simplifies the bowel movements to sine wave and uses the thin shell theory, the boundary lubrication theory and five-elements viscoelastic model to establish the friction force prediction model. The paper uses Matlab to simulate the relationship between intestinal viscoelastic deformation, endoscopic intestinal mucous, size, material and the friction under the condition of intestinal peristalsis, which will lay a solid experimental foundation for the non-destructive diagnosis so as to promote the development of medical micro robots. Tribology in surface morphology is one of the important factors affecting the friction performance, this paper uses the environmental scanning electron microscope to observe the entire inner surface of the digestive tract of rabbit microstructure, the results show that surface structure between esophagus, stomach, small intestine and large intestine is greatly different. Inner surface of esophagus distributes with discontinuous ridge structure, Inner surface of small intestine distributes with fold, small intestine villi and microvilli, and different shapes of the intestine villi with different sparse degree, stomach surface distribute with fold and gastric pit, large intestine different from small intestine has no villi.In addition to surface morphology, in the tribology, the impact of the physical, chemical and mechanical properties on friction is very big also. This article uses the micro friction tester and rheometer to test the rheological properties of intestinal mucous, lubricity, and the results show that intestinal mucous for non-newtonian fluid with shear thinning, along with the increasing of the shear rate, viscosity tends to a constant and becomes into a Newtonian fluid. Analyst say that it was caused by the damage of the protein molecules in intestinal mucous; PDMS plastic film rubs under the condition of dry friction, deionized water, and intestinal mucous, then intestinal mucous will reduce friction coefficient to10-2orders of magnitude, and intestinal mucous has good lubricity. It was showed that the phospholipids layer covering on the elastic gel in intestinal mucous has the dewatering property, and can decrease the adsorption force to have the effect of sliding friction reduction.By adopting micro-electronic stretcher to the esophagus, trachea, small intestine, large intestine, axial and radial tensile, the paper get the results that the mechanical properties of the esophagus, trachea, small intestine, large intestine are different and possess the anisotropic material, and radial elongation ratio is greater than the axial elongation ratio, then it is proposed that the digestive tract mucosa of microstructure is one of the important factors affecting its mechanical performance.We design a new test method which can eliminate the effects of viscoelastic deformation and test the intestinal changes of surface morphology and the change law of friction performance. This test method produces five different semi-cylinders with different diameter which are0%,20%,40%,60%,80%, larger than the diameter of5samples to be tested. To put the inner surface of the intestinal surface on the semi-cylinder and make five bowel radial strain rate was0%,10%,20%,30%,40%, and then test the change of the friction coefficient under different conditions of strain measurement, we got the results that, when the radial strain rate is less than10%, with the increase of speed and load fluctuating smaller, friction coefficient basically remain unchanged; When the radial strain rate is more than10%, coefficient of friction, with the increase of speed and load fluctuation volatile, increases significantly. The paper puts forward the mechanism of the friction coefficient change:when the intestinal radial strain rate is less than10%, lubrication form is liquid lubrication; when the radial strain rate is more than10%, lubrication form becomes into thin film lubrication.The paper established two kinds of friction prediction models of the deformation of intestinal producing viscoelasticity and the deformation of intestinal producing no viscoelasticity respectively, and carried on the numerical simulation by using Matlab. The first model uses the thin shell theory and intestinal dynamic model of viscoelastic deformation model to establish the dynamic model of the intestinal peristalsis, and simplifies the peristaltic wave to sine wave, and uses five-elements viscoelastic model and the basic law of friction friction to deduct the calculation expressions. The second model, after endoscopic miniaturization, has taken into account that no effect by the intestinal viscoelastic deformation is only determined by the surface morphology and the chemical and physical properties, and deduced the friction calculation expression by using boundary lubrication theory and fractal theory. The simulation results show that there are more frictions when squirming than those when not squirming; the friction increases with the capsule endoscopy radius, length, speed; radius produces bigger incremental friction force than length; contact angles of the forward end and drive end produce the same amount of friction; forward end produces more frictions than drive end with the same contact angle, friction gravity produced by gravity is negligible.