Traumatic Aortic Rupture (TAR) is a leading cause of fatality in motor vehicle accidents. About 20 percent of fatalities in motor vehicle crashes are caused by aortic injuries. The biomechanical mechanism of TAR is yet unknown since laboratory tests to reproduce repeatable TAR in crash tests using cadavers have been unsuccessful. A better understanding of the mechanism of TAR is essential for a) evaluation of the effect of the existing injury mitigation devices such as seat belts and airbags on TAR, b) optimization of the injury mitigation systems with regard to loading conditions with higher risk of TAR, and c) predication of the likelihood or risk of TAR for a given crash scenario. In this study a combined experimental-numerical approach will be used to produce TAR in a physical model and in a computer model. The research has two specific aims which will be carried out in parallel.
In Specific Aim 1 a physical model of TAR will be developed. This model will consist of a porcine aorta-heart specimen installed in a model of thorax made from clear silicone and urethane with similar compression characteristics as a human thorax. The lungs will be represented by compressible foams and the rest of the space will be filled 10% gelatin and saline to hold the specimen in place. The main branches of aorta will be connected to clear silicone tubes and the minor branches will be ligated. The aorta will be pressurized to the physiological systolic pressure using a normal saline solution with color dye to detect rupture. The physical model will be mounted on an impact system capable of applying 55 g deceleration from a maximum velocity of 10 m/s to rest. Crash pulses representing what is experienced by aorta in motor vehicle crashes will be applied to the system. In addition to pure inertial loading, local compression, while being decelerated, will be applied to the thorax model. These local loads will simulate the chest compression caused by steering wheel and seatbelt. The aorta will be instrumented to measure local strain, and fluid pressure at several locations. In addition, the global motion of the specimen will be recorded with high speed digital camera.
In Specific Aim 2 a finite element model of the physical model will be developed. The physical model compared to an anatomical thorax consists of simpler geometries and interfaces, and fewer materials which makes it more suitable for FE modeling. The geometry of aorta will be obtained using direct external measurements from the specimens and MRI scans. The aorta material will be modeled as an isotropic hyper-viscoelastic material. The interaction between the flow and the aorta wall will be modeled using Eulerain/Lagrangian coupling. Validation of fluid modeling will be carried out by performing controlled tests on small segments of aorta cleared with the combination alcohol and methyl salicylate and visualization of the flow. The global model will be validated against the test results of Specific Aim 1. The simultaneous development of the two models, physical and numerical, gives the advantage that they will correct each other during the course of this study. The finite element model will be used as a tool to conduct a parametric study to identify the loading conditions with higher risk of TAR and to analyze the injury mitigation strategies.
Traumatic Aortic Rupture (TAR) is a leading cause of fatality in motor vehicle accidents. About 20 percent of fatalities in motor vehicle crashes are caused by aortic injuries. The biomechanical mechanism of TAR is yet unknown since laboratory tests to reproduce repeatable TAR in crash tests using cadavers have been unsuccessful. A better understanding of the mechanism of TAR is essential for a) evaluation of the effect of the existing injury mitigation devices such as seat belts and airbags on TAR, b) optimization of the injury mitigation systems with regard to loading conditions with higher risk of TAR, and c) predication of the likelihood or risk of TAR for a given crash scenario. In this study a combined experimental-numerical approach will be used to produce TAR in a physical model and in a computer model. The physical model will consist of a porcine aorta-heart specimen installed in a model of thorax made from clear silicone and urethane with similar compression characteristics as a human thorax. The computational model will be a finite element model that will be used to simulate the physical model. The simultaneous development of the two models, physical and numerical, gives the advantage that they will correct each other during the course of this study. The finite element model will be used as a tool to conduct a parametric study to identify the loading conditions with higher risk of TAR and to analyze the injury mitigation strategies.
| Kermani, Golriz; Hemmasizadeh, Ali; Assari, Soroush et al. (2017) Investigation of inhomogeneous and anisotropic material behavior of porcine thoracic aorta using nano-indentation tests. J Mech Behav Biomed Mater 69:50-56 |
| Hemmasizadeh, Ali; Tsamis, Alkiviadis; Cheheltani, Rabee et al. (2015) Correlations between transmural mechanical and morphological properties in porcine thoracic descending aorta. J Mech Behav Biomed Mater 47:12-20 |
| Hemmasizadeh, Ali; Autieri, Michael; Darvish, Kurosh (2012) Multilayer material properties of aorta determined from nanoindentation tests. J Mech Behav Biomed Mater 15:199-207 |
| Hemmasizadeh, Ali; Darvish, Kurosh; Autieri, Michael (2012) Characterization of changes to the mechanical properties of arteries due to cold storage using nanoindentation tests. Ann Biomed Eng 40:1434-42 |
