Study A Machine For Drawing Fixed Liver Tissue

The accuracy of detection and forensic pathology is directly determined by the quality of tissue slices. Steps of making slices: drawn, fixation, dehydration transparent, dipping wax embedding, slice and dyeing. Drawn is not only the initial stage, but also an important step. If drawn local thickness is inconsistent, then can lead to partial dehydration is complete, partial unfinished or excessive dehydration, that affect the observation, resulting in a higher rate of misdiagnosis. At present, error rate of pathological identification up to 10%. However, through research and relevant literature, the world medical and forensic workers always using simple hand tools to cut when drawing human tissue, so result are not good. Therefore, it is necessary to study human tissue drawn methods and instruments to provide a more scientific basis for pathological diagnosis and identification of the cause of death.Consider the difficulty of human tissue obtained, this paper use liver tissue as a case. A study showed that bovine liver structure and biomechanical properties is similar with human. In this study, bovine liver are used in biomechanical test to obtain stress- strain and stress relaxation characteristics. Then bring the experimental data into finite element model to obtain parameters of the model, establish cutting model, implement cutting simulation, simulate the optimal cutting parameters. Finally, the optimization parameters are applied in drawn equipment design and cutting verification, to ensure the uniformity of cutting slice. The main research contents as follows:(1) Analysis of tissue structure and composition which affect liver mechanical properties. Analysis of liver tissue fixed effects in different reagents, as well as fixed principles and time.(2) Use SHIMADZU AG-X universal testing machine to do a large number of liver tissue tensile strength, shear strength and stress relaxation tests. According to liver tissue stress – strain properties under different tensile rates, derived relationship between tensile rates and average failure stress or average failure strain. Analysis of the stress relaxation properties of liver tissue, and fitting stress relaxation function.(3) This study focus on cutting force and energy of the liver tissue. Compare with three commonly used constitutive model to choose the best one, namely Yeoh model. When the strain is less than 30%, this model can be fit tensile test curve very well. The model based on uniaxial tensile test data can be used to simulate liver tissue deformation characteristic during cutting. After the model parameters acquired, finite element model of cutting tools and liver tissues can be built to explore the optimal vertical blade feed rate. The results show that: 4mm / s of the blade feed speed is more appropriate.(4) Explore the basic principles of drawn machine design. According to the simulated optimization parameters, use software to design drawn machine. Some cutting experiments to verify the uniformity of slices with different thicknesses.This study focus on the static and cutting properties of fixed liver tissue. Through simulation analysis, stress concentration in cutting process and uneven thickness of hand-cut are solved. The results provide a scientific drawn method and machine for pathology identification.