Research On Bio-mechanical Compatibility For Urethral Valve Based On Finity Element Analysis

Urinary incontinence refers to an involuntary outflow of urine caused by urethral sphincter injury or bladder nerve dysfunction.It not only brings life troubles to patients,but also easily leads to complications such as urinary system infection,which seriously affects the quality of life of patients.For patients with severe urinary incontinence,it is difficult to be cured by drugs or surgery.In this regard,some scholars have studied various artificial urethral valves that can be implanted to replace urethral function,hoping to find an effective way to overcome severe urinary incontinence from the perspective of engineering.However,in the use of urethral valve,there is a problem of insufficient bio-mechanical compatibility.The urethral valve over clamps the urethra,resulting in ischemia and hypoxia of urethral tissue,which leads to the risk of urethral tissue atrophy and necrosis.The long-term use effect of urethral valve can not be guaranteed.In order to study and improve the bio-mechanical compatibility of urethral valve and reduce the risk of urethral tissue atrophy or necrosis,a mechanical model of urethral tissue was established based on the quasi-linear viscoelastic theory;Based on the finite element method,the deformation law and stress distribution of urethra under the clamping of urethral valve and the two-way fluid-structure coupling of urine are simulated and studied;The effects of the design parameters of urethral valve and their interaction on the pressure in the central area of urethra and the clamping force of urethral valve were discussed,and the response surface model was established to optimize the parameters;The bio-mechanical compatibility imitation experimental platform was built,and the clamping force characteristics of urethral valve were studied by simulation and imitation experiment.The main contents of this thesis are as follows:（1）Based on the understanding of human lower urinary tract physiology,the material characteristics of urethral tissue are analyzed.The normalized relaxation function and elastic response function of urethral tissue are deduced according to the quasi-linear viscoelastic theory,so as to establish the mechanical model of urethral tissue,which provides a theoretical basis for quantitatively describing the deformation and stress of urethral tissue.（2）Based on the urethral tissue mechanics model,the material parameters of urethral finite element analysis were obtained.According to the different forms of urethral valve clamping the urethra,the urethral valve is divided into four types: I,II,III and IV.Combined with the structural parameters of the urethra,the finite element model of urethral urethral valve is established and simulated.The results show that the performance of type IV urethral valve is the best in terms of sealing and bio-mechanical compatibility.The fluid-structure coupling analysis of type IV urethral valve shows that the central area of urethral compression side is the main high-pressure area,and the inner wall of urinary inflow side is the potential high-pressure area;By studying the relationship between the clamping force and the valve opening,the pressure in the central area of the urethra and the valve opening in the bladder emptying stage,the clamping force characteristics and the pressure characteristics in the central area of the urethra of type IV urethral valve are clarified,which lays a foundation for the subsequent optimal design of urethral valve.（3）According to the single factor experimental results of urethral valve,combined with the response surface method,the effects of Young’s modulus,clamping length,gasket thickness and their interaction terms on the two key indexes of the pressure in the central area of urethra and urethral valve clamping force are studied.The extremely significant,significant and insignificant terms of the effects on the pressure in the central area of urethra and urethral valve clamping force are obtained respectively.According to the results of response surface analysis,the regression prediction model of the pressure in the central area of urethra and urethral valve clamping force response is obtained.On this basis,the parameter optimization and simulation verification are carried out by setting goals.The verification results prove the accuracy and reliability of the response regression model,which can provide a reference for the further optimization of urethral valve.（4）The clamping force similarity criterion of urethral valve is derived by using the similarity theory,and the bio-mechanical compatibility imitation experimental platform of urethral valve is built.The clamping force characteristics of urethral valve are verified by simulation and experiment,which further proves the effectiveness of the mechanical model and finite element model established in this thesis,and the derived clamping force similarity criterion has good applicability.