The Study On The Contact Mechanism Between Biological Tissue And Mechanical Fixture During The Tissue Clamping Process

In recent years,the incidence of cancer increased year by year,and has become the first killer of national life and property safety.At present,there is no effective way to cure cancer around the world,in which case only hope will be sent to "early detection,early treatment." The most effective method of cancer detection in clinical practice is the pathological cell examination,which need to obtain the tissue samples of the organ.Puncture biopsy is a detection method to cut a small piece of tissue samples using the biopsy needle as the cutting tool and under electron microscopy pathology cytology to determine whether the cells are diseased after dyeing.Due to the small trauma and low cost,the puncture biopsy method is the preferred method for extracting tissue samples in clinical practice.However,the current efficiency and accuracy of biopsy sampling is still not high,the main reason is that the interaction force between the needle and the tissue may lead to displacement of the organ,and it is necessary to clamp the tissue during the puncture sampling process.Clinically,medical grips are usually used for mechanical clamping.Due to the characteristics of tissue viscoelasticity,the interaction between biological tissue and mechanical fixture has obvious specificity,it is difficult to clamp firmly and easily slip off.Therefore,it is necessary to study the interaction between chuck and tissue during soft clamping process especially the mechanics response of the organization,it is very important for the research and development of the new clamping tool to reduce the misuse of the clinical medical operation and improve the accuracy of the operation.In this paper,the mechanical properties of biological soft tissue was studied,including its elasticity,hyperelasticity,viscoelasticity,etc.for the mathematical description of tissue mechanical properties is the basis of theoretical analysis.The contact mechanics theory was used to analyze the contact problem between chuck and tissue under small strain.The mechanical analysis model of single tooth and multi-tooth contact were established,and the expression of clamping force was given.The general form of the constitutive equation of differential type and integral type viscoelasticity was summarized.The stress response function of the tissue clamping process with the typical Maxwell model was studied based on the corresponding displacement principle between the viscoelasticity problem under Lagrangian space and the under elasticity of line space,and the expression of the stress peak and the stability value during the clamping process were given.The stress response function was fitted to the curve in MATLAB software and the linear correlation between stress and strain was preliminary obtained.The soft tissue chucks with different cross-sectional shapes were designed in SolidWorks software and the corresponding chuck samples were prepared by 3D printing technique.The soft tissue clamping experimental platform was constructed and the fresh liver tissue was used as the experimental object.The soft tissue clamping experiment was performed and the effects of chucks with different cross-sectional shapes on the clamping force and the relationship between the clamping feed and the clamping force was studied.The experimental results show that the clamping force measured busing the sharp teeth-shaped chuck significantly higher than that of the wave tooth chuck.The clamping force especially the peak force increases obviously with the increase of the height of tooth.There is a linear relationship between the peak and steady values of the clamping force measured and the clamping feed.The dynamic simulation of the soft tissue clamping process was carried out in the commercial finite element software ABAQUS.The parameters of the Prony series describing the material of the tissue model were obtained in MATLAB using the experimental data of the clamping force.The influence of the shape of the chuck on the stress and stability of the specimen was verified by the simulation.The influence of the clamping feed rate on the stress response and the clamping force was also verified.The output results of the simulation were in good agreement with the theoretical analysis and the experimental results.The slippage force experiment platform was constructed,and the maximum slip experiment was carried out on the chuck with different cross-sectional shapes designed in the clamping experiment.The slippage force curves of the experimental process and the critical slip data under different clamping.feeds were obtained.From the security point of view,the clamping stability of the chuck under the current experimental conditions is evaluated,and the stability of the chuck clamping of the wave tooth is obviously higher than that of the sharp teeth-shaped chuck.