Research Of A New Drug-loaded Stent-graft In Aortic Dissection Endovascular Repairment And Inflammation Control

Background: With the fast developing economics and growing aged population,incidence and morbidity of chronic disease are bursting simultaneously.Aortic dissection(AD)is one of the most urgent and life threatening of acute aortic syndrome(AAS).With a sudden arise and quick progression,aortic dissection should be the most important and different disease for vascular surgeon.There is great meaning to study the pathophysiology of AD-to understand the law of progression so as to conduct the treatment strategy.Inflammation of the aortic wall played central role in development and progression of AD and in the adverse event of post endovascular treatment.To research the mechanism of aortic wall inflammation can help knowing the pathophysiology of AD better.Meanwhile,to regulate the inflammation can make endovascular treatment safer and reduce morbidity and mortality.Objective: To investigate the rule of aortic wall inflammation in AD,to study influence of different treatment strategy to the inflammation.To design a new type of drug-loaded endovascular stent-graft and implant into the developed animal AD model.To investigate the inflammation regulation effect of the new device.Methods: Part1,clinical study: with approval of the Ethical Committee and acknowledgement and consent of patients,patients of Stanford type B AD were admitted.Patients were divided into three groups according to treatment strategy: A group(TEVAR),B group(blood pressure control)and group C(TEVAR and glucocorticoid).Clinical information were collected after admission,computed tomography angiography(CTA),serum inflammation biomarkers(CRP,IL-6,TNF-?)and positron emission tomography(PET)data was collected before treatment(acute phase,2 to 7days after syndrome occurrence)and after treatment(subacute phase,2 to 7days after syndrome occurrence).Difference both in and between groups were analyzed.With combined analysis of clinical data,image data and serum factors,rule of aortic wall inflammation in AD can be investigated.Part2,instrument invention: a new type of comfortable stent-graft for aortic dissection was designed with formula in CAD(Computer Aided Design).The construction was compared with FEA(finite element analysis)and best one was selected.Objective force test conformed to the FEA results.A new conception of stent-graft radial pressure was evaluated in design.Prototype was manufactured by twining nickel-titanium wire onto a 3 dimensional typed imitation and heating it to shape.Then the stent was cover by several layers of PTFE membranes and heated to be integrated.Prototype of the new stent-grafts were tested for performance of burst pressure,water résistance,radial force,extrude and compression force,Af temperature,slit résistance force,peel résistance force and delivery-release performance.A new type of drug-loaded membrane was made by coaxial electric spinning technique.A “Sandwich technique” was used compared with typical coaxial electric spinning technique.5 different concentration of methylprednisolone were loaded in the different membrane with 2 methods.Fiber construction was study with a SEM(scanning electron microscope).In vitro drugrelease behavior was accessed with HPLC(high pressure liquid chromatograph).Data of the 2 methods was compared with 2-ways ANOVA.Part3,the animal experiments were carried out to test the inflammation-regulating faction of the drug-loaded stent-graft.40 pigs were divided into 4 groups randomly.Group A was a sham-operated group with only thoracotomy.Group B was a AD-model group with thoracotomy and Stanford B AD established.Group C was a AD-model group treated with TEVAR using non-drug-loaded stent-graft.Group D was a AD-model group treated with TEVAR using drug-loaded stent-graft.AD-model was established using a modified two-end intimal flap suturing technique.Positron emission tomography(PET),Computed tomography angiography(CTA)and serum inflammation factors(CRP,IL-6,TNF-?)were acquired.Aorta target-to-background ratio(TBR)was measure to present the level of inflammation of AD aortic wall.Morphology of AD was analysis by analyzing T/F ratio,number of intimal tears,branch artery involvement etc.Aorta was harvested and analyzed with HE stain and CD68 immunohistochemical stain to search the inflammation cells.Rules of aortic dissection wall inflammation were obtained by combined analysis of clinical,imaging and serum data.Results: Part1,clinical study: from Jan,2016 to Dec,2017,15 patients were admitted for Stanford B AD and divided into 3 groups.There was no significant difference between groups in age,sex,height,weight,blood pressure,heart rate and comorbidities such as hypertension,coronary heart disease,chronic obstructive pulmonary diseases(COPD).TBR before treatment was not significant different between groups.There was significant difference between groups in TBR(P=0.009).TBR in group A after treatment was higher than before(1.75±0.12vs1.52±0.11,P<0.05).TBR in group B after treatment was higher than before(1.75±0.16vs1.6±0.14,P>0.05).TBR in group C after treatment was higher than before(1.42±0.1vs1.67±0.17,P<0.05).TBR after treatment between groups comparison: TBR in group A was higher than group B(1.92±0.23VS1.59±0.05,P=0.019);TBR in group C was higher than group B((1.30±0.05VS1.59±0.05,P=0.0352);TBR in group A was higher than group C(1.92±0.23VS1.30±0.05,P<0.0001).Part2,instrument invention: Radial force analyses with FEA comply with objective measurement.It concluded that diameter of the wire is proportional to the radial pressure,the pitch has no effect on the pressure,the wave number and amplitude are inversely proportional to the radial pressure.In vitro testing of the stent: Membrane penetration,blast test performance qualified,the bending coefficient of the stent was1.0-1.13,The tensile compression coefficient was 0.42± 0.03 N /mm,the maximum denudation force was 13.7± 1.19 N,the tearing resistance of the Membrane was 106±9.88 N,and the Af temperature of the stent was 27.58±4.60 ?.Coaxial electrostatic spinning: 10 % PCL as core layer,the formation of Taile cone and electrospinning is very obvious and stable.Diameter of coaxial electrostatic spinning fiber was 1.52±0.26 um.In vitro releases of loaded drugs by conventional coaxial spinning were obtained using a gradient of 0.01,0.05,0.1,0.5,and 1 mg total dosage,and the effects of loaded dosage and time on releases were analyzed within two factors:(1)the release rate of loaded drugs with a dose of 0.05 mg was significantly different from the other dosage(P < 0.0001).There was no difference between the remaining dosages;(2)There was a difference between days 1 and 2 of release and other time pionts(P < 0.0001),with no difference in the 4-14 day.In vitro release of loaded drugs by "sandwich" coaxial spinning method,the dosage gradient of 0.01,0.05,0.1,0.5,and 1 mg was used to manufacture the membrane.The release rate of the loaded drugs of dosage 0.01,0.05 and 0.1 mg was significantly different between 1 and 8 days,but the 8-14 day release rate was no different.(2)There was a difference between 1-8 days for the release of samples at various dosages(P < 0.0001)and other time points(P < 0.0001),while there was no difference between 8-14 days for the release of different doses.Compared with the ordinary coaxial spinning method,the "sandwich" method performed better in controlled-release of loaded drug.Part3.Animal experiments: 100% success rate in sham surgery and AD model establishment,the mean lesion length was191.7±29.7mm mm,the mean number of distal intimal tears was4 ± 0.8,the mean number of branch arteries involved: 50% in left renal artery,20 % in right renal artery,20% in celiac trunk,30 % in mesentery artery,and the patency rate of false lumen was 83.3% in 14 day.There was no significant difference between the four groups before operation.There was no difference between group 1 and group 4 after 3 days of operation,the rest were all higher;There was no difference between group 1 and group 4 after 7 days of operation,the rest were all higher;No difference was found in group 1 and 4,group 2 and 3,and group 2 and 3 were higher than group 1 and 4.There were no significant differences in WBC,CRP,IL-6,TNF-alpha levels before operation.WBC: No difference was found in the 3rd day after operation.Day 5: No difference between Group 1 and Group 4;There were no differences between groups 2 and 3;There were differences between the other two comparisons;There was no difference between Group 1 and 4 after operation with CRP.There were differences between the other two comparisons;there was no difference between 1 and group 4 after operation with IL-6.There were differences between the other two comparisons;No difference was found between groups 1,2 and 2 and 4 on the 14 th day after operation.There was no difference between group 1 and group 4 with TNF-? after operation There were differences between the other two comparisons;No difference was found between groups 1,2 and 2 and 4 on the 14 th day of operation.Pathological section analyzed with HE stain and CD68 immunohistochemical stain found a similar change of inflammatory cells and was in accordance with PET/CT.Conclusion: PET-CT can detect inflammation of aortic dissection wall accurately and noninvasively.Combined with hematologic examination,the pathological characteristics of dissection can be assessed more effectively.In acute and subacute stage,there is inflammation of aortic wall,which can be repaired anatomically by endovascular therapy,which can induce false lumen thrombosis and can enhance inflammation at the same time.Perioperative use of glucocorticoid can significantly reduce postoperative inflammation systemically and also aortic wall.The effects of short term intravenous glucocorticoid application need to be further studied however.With formula in CAD,we can design the main body of supple laminated stent which is suitable for aortic dissection.With the computer simulation of finite element analysis,the optimal structure of the stent was further selected.Prototype of the new stent-grafts manufactured by nickel-titanium wire and covered by PTFE membranes performance good in burst pressure,water resistance,radial force,extrude and compression force,Af temperature,tear resistance force,peel résistance force and in vitro delivery-release.Coaxial electrostatics technology can be used to make controlled release drug-loaded membrane.Compared with the ordinary coaxial spinning method,the "sandwich" method perform better in controlled-release of loaded drug.