An Experimental Study For Mechanical Properties Of Regional Aortic Tissues

Cardiovascular disease is a worldwide epidemic disease.Aorta has complex geometry,microstructure and hemodynamics.Atherosclerosis,aneurysms,and dissections may occur in these areas.The occurrence,development and pathological changes of vascular diseases are closely related to the geometry and microstructure of arteries.At the same time,the region where the disease occurs also interacts with the mechanical properties and hemodynamic characteristics of the vascular wall.Therefore,systematic study on the geometric morphology and mechanical properties of aorta is a necessary condition for clinical diagnosis and treatment of aortic diseases.Arterial tissue is an anisotropic material with nonlinear characteristics.Previous studies have showed that the modulus of the aorta increases away from the heart.The thickness and diameter of the vessel wall decreased from the proximal to the distal part of the descending aorta.At present,there are few reports about systemic studies on the mechanical properties of different regions of the aorta with structural differences.This work reveals the regionally mechanical characteristics of the arterial system and investigates the corresponding reason.The main contents are as follows.（1）16 regional arterial tissues of porcine descending aorta were studied using uniaxial tensile test in circumferential and axial directions.Porcine descending aorta was divided into four regions along the axis:proximal,proximal-middle,distal-middle,and distal.Along the circumferential direction,aortic tissue was divided into four regions:anterior,posterior,left and right.Thus,the specimens were formed 16 parts.The circumferential and axial mechanical properties of the 16 regional descending aorta were obtained,including elastic fiber modulus,collagen fiber modulus and tissue stiffness under physiological stress.The results showed that the maximum axial collagen fiber modulus always appeared in the anterior region and the minimum value always appeared in the posterior region.The axial collagen modulus of the left and posterior regions of the proximal descending aorta was lower than that of the anterior and right regions.The corresponding results systematically provided the mechanical properties of circumferential region of the descending aorta,and provided a possible cause for the occurrence of aneurysm.（2）The mechanical properties of anterior and posterior tissues of porcine descending aorta were studied using biaxial tensile test.EVG staining was used to analyze the two regional tissues.The results showed that there were orthogonal anisotropy differences between the anterior and posterior regional tissues.EVG staining was used to analyze the effect of the two tissue structures on the mechanical properties,and the orthogonal anisotropy difference between the anterior and posterior vascular wall tissues was explored,which was caused by the difference in the tissue structure of the anterior and posterior parts of the outer-half media.Parameters of the Gasser-Ogden-Holzapfel type SEF of the anterior and posterior regions were also given.（2）The mechanical properties of porcine pulmonary artery,aortic arch,proximal descending aorta and distal descending aorta were studied using biaxial tensile test,and 10mm/min,20mm/min and50mm/min deformation tensile rates were conducted.The mechanical properties of the descending aorta and the aortic arch and pulmonary artery were studied using same protocol.Results showed that the difference of Gasser-Ogden-Holzapfel strain energy function parameterμof pulmonary artery was significantly lower than that of aortic tissues,while for aortic tissue the difference was performed on the parameter k₂,which increased away from the heart.Meanwhile,the biaxial mechanical properties of the arteries were insensitive to the tensile rate varying from 10-50mm/min.Using biaxial tensile test for testing healthy arterial tissue,a relative high deformation rate can be used,which can greatly reduce the measurement time.（4）The elastic mechanical properties and elastocapillarity effects of the arterial walls in four different regions（pulmonary artery,aortic arch,proximal descending aorta and distal descending aorta）were studied by micro-indentation measurement.Although these four regions have different elastic moduli,all three regions of the aorta have similar elastocapillarity effects（surface tension）.We established a model of the indentation-unloading-adhesion.Uniaxial tensile test,EVG staining and Western Blot were used to verify the similar mechanical properties and tissue components of the inner half media of the arterial wall.The compressive part of the model can be used to measure the elasticity of the arterial tissue in the direction of transmural.The unloading-adhesion part of model can be used to measure the mechanical response of the inner-media half of the arterial wall.In summary,this work systematically studied the mechanical properties of the arterial tissues in different regions of the porcine aortic system,and analyzed the effect of the tissue structure on the mechanical properties.On the basis of the previous theories,the model of the press-unloading-adhesion by micro-head relative to the arterial wall was established and verified.