Biomechanical Study Of Abdominal Aortic Aneurysm And The Novel Expanding Ring For Treating Glaucoma

The development of modern economy and technology contributes to human longevity. The research related to medical service, health care, and rehabilitation of the aged population is always in the spotlight due to the senile diseases are increased every year. Biomechanics is an interdisciplinary research area, which plays an important role not only in the exploration of various life phenomena, but also in life quality improvement of the aged population through a variety of rehabilitative treatments.Both abdominal aortic aneurysm(AAA) and glaucoma are the prevalent disease in the elderly people. AAA is a localized, permanent dilatation of the infrarenal abdominal aorta similar to a balloon, if left untreated the aneurysm would grow steadily until rupture leads to sudden unexpected death in patients. The complicated evolutionary process of AAA is the result of mutual interaction of arterial wall of organism evolution and hemodynamic factors. From the biomechanics standpoint, the blood flow in the elastic arteries should be analyzed as feedback system, and more importantly, the aneurysm once forms, the changes of its geometry would have significant effect on the blood flow patterns and the mechanical parameters of the vessel wall. Study on the influence of various geometric parameters on the related mechanical parameters, which have important significance on the clinical diagnosis and primary treatment of AAA.Glaucoma is one of the main causes of blindness worldwide only subsequent to cataract which is characterized by optic nerve damage, leading ultimately to irreversible blindness. Primary angle-closure glaucoma(PACG) is the most common type in China which is a disease of ocular anatomy that is related to angle-crowding mechanisms of the anterior chamber angle. The rise of intraocular pressure(IOP) above the normal limits is usually caused by some form of blocking of the passageways that allow aqueous humor(AH) flow. Glaucoma drainage device(GDD) implantation is becoming more frequent in the treatment of refractory glaucoma. The design and development of GDDs become a hot issue in the field of glaucoma treatment. Yu Hongquan who is the inventor of the national invention patent of China(patent application number: CN200610017024.3) “the expanding ring for treating glaucoma” propose the novel design of the expanding ring for treating glaucoma. In order to make the proposal perfectly, the related biomechanics studies are made in this paper.The paper studies the numerical simulation of 3-D models of elastic AAAs and the expanding ring for treating glaucoma implanted in the anterior chamber(AC) based on the principle of the fluid-structure interaction, the structural optimization design and biomechanical experiment of the expanding ring for treating glaucoma. The main contents and some creative conclusions in the paper are as follows:(1) Study on the influence of various geometric parameters on the related mechanical parameters of 3-D elastic AAA.Based on the numerical simulation of bidirectional fluid-structure interaction under two kinds of blood pressure impulse, three dimensional models of elastic AAA with various geometric parameters are established in order to investigate the influence of geometric parameters on the hemodynamic factors and the arterial wall stress state parameters. Meanwhile, the sensitivity of mechanical parameters to various geometric parameters is examined. At first, according to the influence of geometric parameters to the streamline, vortex, wall shear stress, velocity, the research results demonstrate that the vortex dynamics play important roles in the mechanical mechanism of the formation and development of AAA. The strength of the vortex largely depends on the geometric shape of AAA as eddies induced by vortex move along the axis of vessels. As an indirect impact effect of vortex dynamic to act on vessels, a series of alternate impulse responses of the wall shear stress is produced in AAA. Secondly, the variation of the maximum displacement and the maximum equivalent stress of the elastic vessel’s wall and the influence of geometric parameters are investigated during a pressure impulse cycle.(2) Identify the parameters in the constitutive model of hydrophobic acrylic with mixed numerical-experimental method.The experimental and numerical curve of the compressive load-deformation is provided by the axial compression test and nonlinear finite element analysis(FEA) of the cylindrical specimen of hydrophobic acrylic material, respectively. The residual error between the experimental value and the simulation value is analyzed and iterated with the nonlinear optimal method. Then get the parameters in the constitutive model of hydrophobic acrylic. These parameters ensure the precision of the material parameters which play a significant role in the structural performance of the expanding ring for treating glaucoma.(3) Study on the influence of the expanding ring for treating glaucoma on the flow field of the AC and the influence of the fluid loading on the mechanical properties of the expanding ring for treating glaucoma.The numerical simulation of unidirectional fluid-structure interaction with the different implanted expanding ring for treating glaucoma in AC is made considering the small deformation of the expanding ring for treating glaucoma. Firstly, through commercial CFD code, ANSYS-FLUENT, the resistance characteristics of the trabecular meshwork(TM) is modeled as a porous medium, and the flow field of the normal AC and implanted expanding ring in AC is simulated respectively. The results show that the more and larger of the circular hole is, the more is the features of the flow approached to real situations of the normal case, the more reasonable is the structure design, on condition that the security and durability of the expanding ring is guaranteed. Secondly, the influence of IOP and the dynamic pressure of AH on the mechanical properties of the expanding ring are investigated. The results show that the IOP in the AC plays a major role in the maximum equivalent stress of the expanding ring, the dynamic pressure of AH which has influence on the deformation of the expanding ring significantly related to the number of the circular holes, while the influence is of the same order as IOP.(4) Optimization design on the expanding ring for treating glaucoma with circular holes, and design a novel expanding ring for treating glaucoma with elliptical holes.The multi-objective genetic algorithm(MOGA) in the optimization module(Design Explorer)of the ANSYS Workbench is utilized for the optimization analysis of the expanding ring for treating glaucoma. The sensitivity of the structure is analyzed to determine the influence of the main parameters on the structural mass, equivalent stress and total deformation, and the final structure size with circular holes is determined by optimization design. The expanding ring for treating glaucoma with elliptical holes was further put forward in this paper. On the basis of finite element analysis and sensitivity analysis,the final structure size of the expanding ring for treating glaucoma with the elliptical holes is determined by optimization design. The numerical simulation demonstrates that the expanding ring for treating glaucoma between with circular holes and with elliptical holes, the remarkable optimization effect of expanding ring for treating glaucoma with elliptical holes has been obtained.(5) Experimental study on the compression test, force relaxation test and creep deformation test of the expanding ring for treating glaucoma made of hydrophobic acrylic materials.As the biomechanical performance of the expanding ring can directly affect the clinical outcomes, Shimadzu Autograph AG-X Plus universal testing machine is used for the compression test, force relaxation test and creep deformation test to evaluate the biomechanical properties of the expanding ring made of hydrophobic acrylic materials. The results show that there is the nonlinear constitutive relationship between load and deformation, the stiffness of the expanding ring is very sensitive to the loading rate, and the super-elastic and viscous-elastic behavior is occurred in the loading and unloading process under different loading rate. Through the experimental study on viscoelasticity of the expanding ring, a series of experimental data of force relaxation and creep deformation is obtained under different initial condition in the tests. The normalized force relaxation function and creep deformation function are obtained by making the experimental data normalization and then using regression analysis to obtain the coefficient.