The Research Of Mechanical Behavior About Biological Tissue Growth

The growth process of biological tissue is a complex life phenomenon,and tissue growth can produce special organ form and structure to realize its specific function.So It is very important to reserch the growth and shrinkage of biological tissue from a mechanical perspective.In this way we can understand the complicated life phenomenon,reveal the pathogenesis of some diseases,promote the clinical research and treatment of the disease and the bionic structure design.The purpose of this study was to establish the constitutive relations of biological tissue growth,and developmented the user material subroutine UMAT which had the function of growth,finally the growth process of lotus leaf fold,vines curled up,and flowers open was simulated by using nonlinear finite element software ABAQUS.The details of the study were as follows:The constitutive relation of tissue growth was established according to the continuum mechanics and the finite growth theory.Firstly,we established the constitutive relationship of orthogonal anisotropic free growth.Then we also established the constitutive relation of restricted growth under the influence of stress and strain state.Finally,using the nonlinear finite element software ABAQUS,we developed the user material subroutine UMAT which had various ways of growth.For the growth of the lotus leaf fold,we established the mechanical model of the ring and the stress distribution inside the ring was solved.It was found that the hoop compressive stress was the cause of the wrinkling.Using the energy method and growth finite element simulation,the critical buckling of circular plates was researched.It was found that the smaller the growth area was,the more critical folds were.For the growth of the chiral turnover of tendrils,the growth finite element model was used to study the influence of growth volume,boundary condition and section shape on the morphology of tendrils.It is found that the elastic constraint reduces the number of tendrils chiral inversion.Simulation results showed that the tendril attached to a stiffer support could take longer to develop drag force and generate stronger drag force than one attached to a less stiff support.The growth process of free coil was simulated by orthotropic growthmodule,and the effects of growth rate,gradient,growth direction and material properties on the two-dimensional and three-dimensional helical structure were studied.Finally,the growth process of flowers was simulated,and the effects of petal geometry,material properties and growth rate on flower opening angle were studied.It was found that if the leaves were softer and the shape of the leaves was slender,the expansion and curvature reversal of the petals needed less growth strain energy,and the flowers were easier to open.