RESUMO
Objective To study mechanical properties of the anisotropy for pig trachea and main bronchi, and determine the constitutive model of trachea deformation by finite element numerical simulation. Methods The pig tracheas were collected and cut through in their axial directions and expanded into two-dimensional planes. Then, by setting the length direction of the trachea aortas as 0°, each planar trachea was anticlockwisely cut into 6 samples with orientation of 30°,60°,90°,120°,150° and 180°, respectively. Uniaxial tensile tests were applied on the specimen in 6 angular directions by using the electronic universal test machine, to obtain stress and strain of the specimen in different directions. Nonlinear fitting to the experimental data was performed by using the Mooney-Rivilin hyperelastic model, in order to obtain the material characteristic parameters. Finite element models of the trachea and the main bronchi were established, and tensile numerical simulation was carried out.Results Samples at different angles showed different stress-strain curves. In the trachea, the stresses of samples with angle of 30°, 120° and 150° were in the range of 1.0-1.5 MPa, the stresses of samples with angle of 60° and 90° were in the range of 0.5-1.0 MPa, and the stresses of samples with angle of 180° were in the range of 2.5-3.0 MPa. In the main bronchi, the stresses of samples with angle of 30°, 120° and 150° were in the range of 0.8-1.0 MPa, the stresses of samples with angle of 90° and 180° were in the range of 1.4-1.8 MPa, and the stresses of samples with angle of 120° were in the range of 0.4-0.6 MPa. There was an obvious difference between the trachea and the main bronchi. The finite element simulation verified that the Mooney-Rivilin constitutive model was suitable for describing small deformation behavior of the trachea. Conclusions The pig trachea exhibits strong anisotropy. Meanwhile, the Mooney-Rivilin model can characterize small tracheal deformations. The results provide theoretical references for tracheal resection and reconstruction in clinical treatment and intervention with surgical instruments such as bronchoscopy.