Analysis on constitutive models and biomechanical properties of brain / 医用生物力学

Brain injury has become the most severe injury in traffic accident due to its high incidence and high fatality rate. The brain injury model plays a critical role in researches on brain injury. The constitutive model and the material properties used in the model are key factors in determining the accuracy of injury prediction. The present paper aims to review the application of constitutive models and material properties in brain simulation so as to better understand biomechanical properties of brain and provide references for finite element researches on brain injury.

Influence from different assigned gradients of material attributes on mechanical properties of the vertebral finite element mode / 医用生物力学

Objective To study the influence from different assigned gradients of material attributes on mechanical properties of the vertebral finite element model. Methods An adult human spine (T12-L5) was CT scanned, and the 3D models of each vertebra were reconstructed in MIMICS, which were then modified in Geomagic and imported into ANSYS for meshing. The element models were imported back to MIMICS and assigned with material properties by separating into 8 kinds of gradients (2, 4, 8, 10, 50, 100, 200, 400 divisions). These models were then imported to ANSYS again for finite element analysis under the same loading condition. Results Significant differences were found in stresses from models with 2, 4, 400 gradients, but the deviations between 8, 10, 50, 100, 200 gradients were not obvious. Conclusions The material attributes of finite element model should be appropriate, and the assigned gradient of 10 divisions could be better guarantee the accuracy of calculation and enhance the calculation speed as well, which is suitable for personalized rapid finite element modeling in clinic.

Fixation for femoral neck fracture based on nonlinear materials / 医用生物力学

Objective To make a reasonable selection from internal fixation Methods for treating femoral neck fracture, namely the fixation angle of a single screw, the number of screws and the combination mode of screws, so as to obtain the optimal stability of fracture reduction. Methods Based on the DICOM data and Lindon mode, a three-dimensional finite element model of femoral neck fracture fixation was built including different angles, numbers and combination modes of the screws. The model was attributed to nonlinear material properties based on the relationship between the property parameters of bone materials and the gray value of CT images, and loaded under the simulation of physiological loads. Results Corresponding to different angles of the fracture surface, the optimal fixation angle of the single screw was 65°and 70°in clinic. The more the number of screws, the better the effect of fixation, when the surgical condition was permitted. The inverted triangle placement was better than the triangle placement in case of three-screw fixation, while the triangle placement was superior to two-screw fixation, but the decision on the placement of two-screw fixation in flat form or diagonal form depended on the angle of the fracture surface. Conclusions Different angles of the fracture surface have significant impacts on the effect of fixation, and the loading simulation process on the three-dimensional model can provide a feasible way to the study of the fixation for the femoral neck fracture.