Mechanical Constitutive Relation Of Gelatin Phantom And Puncture Parameters Optimization For Biopsy Tests

Cytopathology examination is the main method to diagnose cancer, it requires the tissue samples of the target organ at first. Biopsy is the preferred method for tissue sampling in clinical because it has some advantages such as lower cost, less invasive, fewer complications, faster healing, etc.,Biopsy is a method to take tissue samples out together with the needle which would cut and save a small amount of tissue samples in the needle core by piercing into the target soft tissue. In actual clinical, the accuracy and efficiency of biopsy sampling has always been unsatisfactory, repeated sampling is usually required in order to obtain more desirable tissue samples for cytopathology analysis. The main reason for this problem is the deformation of the biopsy needle and the tissue caused by the interaction during the piercing process. Thus, an effective mean is, by the study of soft tissue and the needle, reducing the interaction force of the biopsy needle and tissue during the piercing process, decreasing the deformation, optimizing the needle shape, biopsy piercing path and parameters, finally improve the accuracy and efficiency of biopsy sampling.This paper used gelatin phantom as the test object, conducted tests and built constitutive models of mechanical properties of gelatin phantom, then designed and conducted orthogonal puncture test to optimize puncture parameters.This paper measured the force-time curve of the phantom material under small deformation by indentation test, calculated the parameters of Neo-Hookean hyperelastic model, used the least square method to fit the data in MATLAB software, obtained the parameters of prony viscoelasitc model, then conducted finite element simulation verification; measured the stress-strain curve of the phantom material under large deformation by uniaxial tensile test, obtained the failure stress of the material, obtained the parameters of4order Ogden hyperelastic model by fitting the data in ABAQUS software. By comparing the obtained test data and parameters of the constitutive models with the results of soft tissue presented in related papers, the similarity between gelatin phantom and biological soft tissue was verified.Since the material property editor of the FEM software ABAQUS has shortcomings and defects, by writing the deduced stress constitutive relation into ABAQUS user material subroutine VUMAT, this paper developed the soft tissue mechanical constitutive model VUMAT subroutine, and then verified the accuracy of the subroutine by comparing to the ABAQUS analysis results. This model is beneficial for adding suitable failure criterion for soft tissue and simulating the whole piercing process in the near future.Using gelatin phantom which has more stable mechanical properties as the piercing target, reduced the influence of differences in the mechanical properties of biological soft tissues to the puncture test, this paper set piercing speed, piercing depth and tip angle as influencing factors, designed and conducted orthogonal puncture test, using deviation before and after the puncture as the evaluation index, determined the importance order of different factors on the effect of puncture accuracy, and obtained the optimal puncture parameters combination.