Analysis And Application Of Mechanical Response Of Skin Suture Considering Material Parameter Uncertainty

The finite element simulation technology based on the mechanical properties of skin can effectively predict the stress distribution of the skin after suturing,and has an important guiding role in the preoperative simulation and program formulation of skin transplantation surgery.However,skin materials have complex mechanical properties such as anisotropy and hyperelasticity,and material parameters are uncertain due to experimental errors and differences in body parts.How to accurately characterize the mechanical properties of skin materials and consider the influence of material parameter uncertainty on the mechanical response of skin suture in the finite element modeling process is an urgent problem to be solved.Therefore,based on the experimental study of skin mechanical response,material parameter identification and uncertainty propagation in the mechanical modeling of skin materials was studied in this thesis.The main contents are as follows:The tensile mechanical behavior of skin under large deformation was analyzed to establish a quantitative description of the uncertainty of skin mechanical property measurement.Based on the biomechanical properties of skin,the uniaxial tensile test scheme of pigskin samples was developed,and the reasonable preconditioning treatment times were determined.The influence of sampling direction,sampling position and repeated measurement on the skin mechanical response was analyzed.The sources of measurement uncertainty were summarized,and the uncertainty of test results was evaluated based on the measurement uncertainty representation guide,and the stress-strain response data of skin uniaxial tensile under a certain confidence level were obtained.The identification and optimization methods of constitutive parameters of anisotropy and hyperelasticity were explored to accurately characterize the mechanical properties of skin materials.Using Holzapfel anisotropy and hyperelastic constitutive to describe the biomechanical properties of skin,a finite element model of skin uniaxial tensile test was established to obtain the numerical mechanical response data of skin under different parameter combinations.The approximate model was constructed and verified to replace the repeated simulation process.Then,the adaptive simulated annealing optimization algorithm was used to minimize the root-mean-square error of the test curve and the numerical calculation curve,and the constitutive parameters which best matched the results of the uniaxial tensile test of the belly and back skin of ordinary domestic pigs were obtained through inversion.A method of material parameter uncertainty propagation analysis based on Monte Carlo simulation was proposed to effectively quantify the uncertainty of skin material parameters.The normal distribution function and description sampling method were used to quantify the uncertain material parameters,and a approximate model was constructed to describe the nonlinear relationship between the uncertain material parameters and the simulation results of skin mechanics modeling.Then,the Sobol sensitivity optimization was calculated and compared to adjust the uncertain material parameters.Finally,the output response statistics were obtained based on Monte Carlo simulation.The finite element simulation of skin uniaxial tensile was taken as an example to give the complete calculation process,and the uncertainty of skin material parameters was determined.The results can be used to describe the errors introduced in the test measurement of skin mechanical properties and the identification of material parameters.The stress response of skin flap suture under the influence of material parameter uncertainty was analyzed,and the preoperative skin flap design scheme was developed.The reverse modeling technique was used to construct the geometrical model of the wound surface of clinical patients,and the preliminary design contour of the flap was obtained by threedimensional wound flattening method.On this basis,a finite element model of skin flap suturing was constructed.The stress response of skin flap suturing with different fiber orientations and different design sizes was calculated and compared by using the proposed method of uncertainty propagation analysis,so as to determine the optimal cutting direction and limit design size of skin flap.The parameter identification method of skin materials studied in this thesis can quickly and accurately characterize the mechanical properties of skin materials.Applying uncertainty propagation analysis method to skin suture simulation analysis can effectively quantify the influence of material parameter uncertainty on analysis results.This will help clinicians to diagnose,evaluate and treat patients with skin tissue diseases through mechanical modeling methods.