Study On The Structural Optimization Design And Hemodynamics Of Poly(L-lactide)Coronary Stent

According to reports,the current number of patients with coronary heart disease in my country has reached 11 million,and it is showing a trend of rapid growth among young people with low age and low income.With the continuous development of medical methods,the use of biodegradable polymer coronary stents has brought a major breakthrough in the treatment of CHD,and has become a research hotspot.However,due to poor mechanical properties and excessive thickness of stent,in-stent restenosis(ISR)is likely to occur in the current stage of biodegradable polymer coronary stent.The aim of this paper is to reduce the incidence of ISR and improve the mechanical properties of coronary stents by finite element analysis.The main contributions of this paper can be summarized as followes:(1)A novel honeycomb structure coronary stent was designed to simulate the process of crimping and expanding of the stent and the traditional ring structure coronary stent.The experiments were carried out to verify the simulation results.The results showed that the maximum equivalent stress of the honeycomb stent was mainly concentrated in the peak and valley of the ring,and the connecting arm was obviously deformed.Compared with the ring stent,the deformation was more uniform.Due to the unique structural design,the mechanical properties of the honeycomb stent have been greatly improved:under the same width and thickness of the stent,the radial strength(RS)of the honeycomb stent was 1.74 times that of the ring stent(2.25 vs.1.29 N/mm);the acute recoil(AR)was only 68.71%(3.03 vs.4.41%);the foreshortening(FS)was only 16.40%(1.13 vs.6.89%).The relevant performance parameters were verified by the static experiment results(RS:2.08±0.18 N/mm vs.1:44±0.04 N/mm).AR:2.51+1.04%vs.6.18 ± 2.63%;FS:0.89 ±0.94%vs.6.32±0.43%).In addition,with the same support performance(1.27 vs.1.29 N/mm),the thickness of the honeycomb stent can be reduced to 66.67%of the ring stent(0.10 vs.0.15 mm).(2)The two-way fluid-solid coupling numerical simulation study on the hemodynamics of the honeycomb stent was carried out,and the effects of the stent geometry and the thickness of the stent rod on its hemodynamics were analyzed.The results of the study showed that during the entire pulsation period,the position of the blood flow velocity of the honeycomb stent was concentrated at the peak and valley of the ring,especially the inside of the stent rod.When the blood pressure changes from systole to diastole,the minimum flow velocity on the coupling surface was reduced from 4.732e-2 mm/s to 1.498e-5 mm/s,and the area where the wall shear stress value(WSS)was less than 0.5 Pa increased from 0.29%to 9.61%.Compared with the ring stent,its low flow velocity and low wall shear stress area made the area of the WSS value on the coupling surface of the stent less than 0.5 Pa during diastolic period reduced from 11.41%of the ring-shaped stent to 9.61%,and the chance of restenosis in the stent had decreased.When the thickness of the honeycomb stent rod was reduced by 53.33%,the proportion of WSS value below 0.5 Pa can be reduced by 56.29%,the impact on local blood flow was significantly reduced,and the risk of intra-stent restenosis was also significantly reduced.(3)The substance transport model was used to simulate the release process of the drug on the surface of the designed honeycomb stent in the blood vessel model,and the effect of different drug release rates on the drug concentration distribution inside the blood vessel was studied.The results showed that the drug on the surface of the honeycomb stent can effectively diffuse and move with the blood flow,and there was a certain concentration gradient of the drug deposited on the blood vessel wall.Analysis of the local drug distribution of the honeycomb stent found that the closer the two stent rods were,the higher the local area-weighted average drug concentration,while the volume-weighted concentration was not sensitive to the distribution distance of the stent rods,and its size was related to the axial position.At the same time,the slower the release rate of the drug,the lower the change in the concentration of the drug distributed in the blood vessel.Therefore,by optimizing the concentration distribution and release rate of the drug on the surface of the stent rod,the incidence of restenosis in the stent can be further reduced.