Study On Material Parameters Identification Of Lumbar Intervertebral Disc Based On Inverse Analysis Method

The lumbar intervertebral disk cushions the load generated by human activity and absorbs energy to keep the spine moving steadily.Long-term exposure to high-intensity compressive condition is an important cause of high incidence of disk degeneration.At present,discectomy is often used to treat patients with severe disc herniation clinically.Due to the changes in the structure and material parameters of the disc after surgery,the loading mechanism and mechanical properties of the intervertebral disc are also changed.Therefore,it is significant to study the difference of the material and mechanical properties between intact and degenerative enucleated disc.Based on the inverse analysis principle of the model parameters estimation,the study combined with the inverse finite element method,response surface design,and genetic algorithm optimization,identified the material properties of the intact and degenerative enucleated disc,and studied the differences of material and mechanical properties between them.The study is mainly composed of the following aspects.According to the sitting condition of human,the creep experiments simulated the load on the disc.The experiments were performed on the intact and degenerative enucleated sheep discs under compression load.The results show that the strain of the disk exhibits an exponential relationship with time,and the strain of degenerative enucleated lumbar discs is significantly greater than that of intact discs.Through the inverse finite element analysis and the Box-Behnken design of the response surface method,different levels within the range of material parameters of the disc to be identified were combined.According to the experimental load,different groups of material parameters were substituted into the simplified model of disc to simulate.The simulation results were used as the basis for constructing the response surface model,which provided data support for the construction of the response surface model.The root mean square error of the simulation results and experimental results was taken as the objective function.Through the response surface method,a response surface model was established,and the model was tested and simplified.The optimal material parameters were obtained by response surface optimization,and they were tested in the finite element model.Taking the response surface model as the basis of the fitness function and the range of material parameters as constraints,the genetic algorithm was used to optimize it and search for material parameters that are in good agreement with the actual results.The study shows that the calculation of genetic algorithm combined with the response surface method is less than that of the simple genetic algorithm,and it has higher recognition accuracy than response surface optimization.Its search is more comprehensive and closer to the global optimum.The study proposed the material parameter identification method and realized the identification of material parameters for the intact and degenerative enucleated disc,and effectively improved the identification efficiency and accuracy.This method has important scientific significance and theoretical value for the clinical treatment and repair of lumbar disc herniation and the artificial construction of the intervertebral disc.In addition,the identification method of material parameters can be extended to the biomechanical research of cervical disc,bone and cartilage.