Study On The Cross-linking Mechanism Of Tannin And Bovine Jugular Vein & Animal In Vivo Experimental Study On Small-caliber Biomimetic Blood Vessels Under 6mm & Study On Hydraulic Lubrication Of Axial Flow Left Heart Assist Device Bearing

Background and AimsBovine jugular vein(BJV)have been widely used in the reconstruction of right ventricular outflow tract in patients with severe congenital heart disease in cardiovascular surgery because of their natural valve structure and easy availability.At present,the glutaraldehyde(Glut)-fixed BJV commercially available is widely used in clinical practice.However,the glutaraldehyde-fixed BJV are easily calcified in the body,which affects the therapeutic effect ultimately.Tannic acid(TA)a poly galloyl glucose(Glc),is compatible with Glut fixation,bind to the protein of the BJV,improves resistance to degradation and reduces in vivo calcification.At present,the function and mechanism of the interaction between vascular proteins and TA are still unclear,although many studies provide favorable evidence of interaction between them.In addition,TA-protein conjugates shows partial instability in long-term,which can lead to implantation failure.This paper attempts to investigate the chemical reactions in TA treated BJV,which may provide a basis for further study of the anti-calcification process of tannic acid.Methods1?Glutaraldehyde fixed BJVs were subsequently treated with TA or four substitutional compounds,which contained four characteristic chemical groups of tannic acid,i.e.phenolic hydroxyl group,carboxyl group and alcoholic hydroxyl group,respectively.2?After cross-linking,the changes of the functional groups of the BJVs were detected using Fourier transform infrared spectroscopy(FTIS).3?Thermal shrinkage temperature and resistance to degradation are used to assess the stability of proteins in BJVs.4?The mechanical properties of the BJV were tested using a uniaxial tensile test.5?The rat subcutaneous implantation model was established.The implanted BJV slices were taken out in 21 and 60 days,the calcium content was determined by Inductively coupled plasma atomic emission spectrometry and the histochemical staining was did.6?The results inferred from the molecular model experiment were verified by adding urea in the TA group.7?In the urea verification experiment,the degree of crosslinking and the anti-calcification effect were examined.Results1?FTIS results indicated that a large number of hydrogen bonds were formed in the BJV of the TA treatment group.2?In the TA-treated group,the protein had the highest thermal stability(p<0.05)and the best resistance to degradation(p<0.05),indicating the highest protein stability.3?In the uniaxial tensile test,the TA group had the highest low elastic modulus in the longitudinal and circumferential direction(p<0.001).And the TA group also had the highest high elastic modulus in the longitudinal direction(p<0.05),and there were no differences between all the groups in the circumferential direction.4?After 21 days and 60 days of implantation,the results of EVG and Masson staining showed that the structure of collagen fiber and elastic fiber remained intact at 21 days.And there only the structure of the TA group is complete,other groups were fracture at 60 days.The Von Kossa staining results were consistent with the Ca content determination:the TA group had the lowest degree of calcification.5?The results were verified by adding 0.1 M,0.3 M,0.5 M and 1 M urea in the TA group.FTIS results showed that a large number of hydrogen bonds in the BJV were destroyed after the addition of urea.The results of EVG and Masson staining and resistance to degradation showed that the stability of collagen and elastin in BJV decreased.After subcutaneous implantation,the results of Von Kossa staining and Ca content determination showed an increase in calcification.ConclusionBased on the experiments,we speculate that the poly-phenolic hydroxyl group in tannic acid solution crosslink with proteins in BJV by hydrogen bond.This may be a clue to further study of stability of TA crosslinking BJV and clinical application.Background and ObjectiveCardiovascular disease is one of the major causes of serious threats to human health currently.In the case of vascxilar grafts,more than 600,000 people worldwide need various vascular surgeries each year,most of which require various vascular substitute(artificial blood vessel)calibers.Large-caliber artificial blood vessels(inner diameter >6mm)have been successfully commercialized and widely used due to their good patency;small-caliber artificial blood vessels(inner diameter <6 mm)are commonly needed in coronary artery bypass grafting(heart bypass)and pediatric cardiovascular surgery,which are still not widely used in clinical practice because of their vulnerability to inflammation,thrombosis,intimal hyperplasia,and mismatch with host vascular compliance.The currently used vascular substitutes in the clinic include autologous blood vessels allogeneic blood vessels,and artificial polymer material blood vessels.Autologous blood vessels are mainly used in clinical,but the source is limited.Not all patients are suitable for providing transplanted blood vessels.Allogeneic blood vessels include allogeneic and xenogeneic blood vessels,but allogeneic blood vessels have disadvantages such as immune rejection,and are rarely used in clinical applications.At present,the artificial vascular materials used in clinical practice are mainly Dacron and expanded polytetrafluoroethylene(ePTFE),which have better effect on high-flow vascular replacement,but in small-caliber blood vessels,it is poor patency and easy to form thrombus.The efifect is not ideal.The ideal artificial blood vessel should have good histocompatibility,anti-infection,no thrombosis and low immunogenicity;and it also have pathological and physiological functions of normal blood vessels,good vascular mechanical properties and no hyperplasia,inflammatory reaction formation;most of all,when implantation the body is eventually completely replaced by its own tissue.Vascular tissue engineering is the best way to artificially manufacture ideal blood vessels.Research on artificial blood vessels,especially small-caliber artificial blood vessels,has been a hot spot in this field.This paper attempts to evaluate the histocompatibility and clinical feasibility of a small-caliber artificial blood vessel manufactured by tissue engineering.MethodsThe molding and research of small-diameter bionic blood vessels(artificial blood vessels)was carried out in cooperation with the Institute of Biomantxfacturing of Tsinghna University.1?Using a small-caliber bionic blood vessel made by tissue engineering method,a carotid artery replacement model was constructed in the small-tailed sheep,and the postoperative 1,3,6 and 12 months were taken as the picking time.2?Blood samples were taken for blood tests and biochemical tests to determine whether the transplanted blood vessels had any effect on the health of the sheep before surgery,one week and monthly after surgery.3?Vascular ultrasound examination of the sheep was performed to detect changes in lxunen diameter,wall thickness,and patracy one-week and monthly after surgery.4?Angiography and OCT were performed on the blood vessels of the sheep before the samples were taken out,and the patency rate of tiie graft vessels was measured.5n Tissue staining of autologous blood vessels and artificial blood vessels after the materials taken out.HE and Masson staining method was used to observe the graft structure;immunofluorescence staining was used to detect the regeneration of transplanted blood vessels.Results 1.A total of 10 small-tail sheep carotid artery replacement operations were performed.All the operations were successfiiL Two animals were sacrificed after 12 months of transplantation,and one died of vascular rapture at 6 months after surgery.2?There was no abnormaKty in blood routine and biochemical examination results,indicating that the transplanted blood vessels had no significant effect on the health of tile sheep.3?Vascular ultrasound and angiography results suggest that the vascular diameter began to thicken after 2 months,suggesting the formation of hemangiomas.4. HE and Masson staining showed that the bionic vascular implantation began to reduce after 3 months,and the scaffold material was mostly degraded after 12 months.The immunofluorescence results showed that the smooth muscle and endothelial cells appeared after 3 months.ConclusionsIn the replacement experiment of the bionic blood vessel in vivo,the suture of the bionic blood vessel was good,and flie survival time of the experimental animal was 12 months,which indicated that the idea of using blood vessel tissue engineering technology to manufacture blood vessels in this study is feasible.However,the vascular materials used in this study still need to be improved in terms of mechanical properties and histocompatibility.The main manifestations are that all bionic blood vessels have different degrees of thrombosis and vascular occlusion.Several unobstructed blood vessels have sudden rupture,indicating its mechanical properties are not sufficient to withstand the pressure of blood vessels.The above provides data guidance and support for the fabrication of bionic blood vessels by tissue engineering methods in this study.Background and Aims Cardiomyocytes lacks regenerative capacity,and cardiomyocytes damage caused by any cause such as myocardial infarction,cardiomyopathy or inflammation can cause changes in cardiomyocytes structure and function,and gradually develop into heart failure.Heart failure is a serious threat to human health,due to lack of donor heart,etc.,left ventricular assisted device(LVAD)for mechanical circulation support has become an important means of treating heart failure.The clinical application of LVAD has been effective for many years,but there are also many problems to be solved.Among them,the performance of LVAD and the safety of patients have become the focus of attention.Therefore,pump design is still an urgent need for the rapid development of LVAD.The development of ventricular assist devices has experienced three driving modes:pulsating,continuous flow and full magnetic suspension.The pulsating type mainly realizes cyclic filling and emptying through the change of the volume of the pump,and the commonly used LVAD realizes continuous flow through the rotary pump technology.The design of the bearing and the lubrication status of the bearing is crucial to the performance of LVAD.Unreasonable bearing design will cause the friction between the journal and the bearing,the accumulation of red blood cells in the gap to form a clot,etc.,which will cause the rotor to stop unexpectedly during working hours,posing a threat to the safety of the patient.The lubrication status of the bearing that supports a LVAD will take great effect on the performance of the device.In this paper,the numerical simulation analysis of the hydrodynamic pressures distribution and the flowing trajectory of red blood cells(RJBCs)in the lubrication film provides key parameters for bearing design.MethodsThe self-developed FW-3 axial flow ventricular assist device was used as an example for research.Using the numerical modeling method and the commercial software ANSYS-Fluent(ANSYS,Inc.)to carry out preliminary simulation analysis of the lubrication state of the bearing end bearing,and found that the lubrication state of the axial pump bearing is related to the minimum clearance(or the eccentricity of the shaft),the average radius clearance,the journal diameter and the rotational speed.In the case of a given bearing size and speed,the commercial software ANSYS-Fluent(ANSYS,Inc.)was used to numerically simulate the hydrodynamic pressure distribution and the RBC flow trajectory in the bearing lubrication film.On this basis,the influence of bearing parameters on the support performance and whether the RBC will enter the gap is analyzed,then the bearing parameters are optimized.ResultsThe simulation analysis of lubrication status of support end bearings found that the lubrication state of the axial pump bearing is related to the minimvim clearance(or the eccentricity of the shaft),the average radius clearance,the journal diameter and the rotational speed.The analysis of the hydrodynamic pressure distribution in the bearing lubrication film shows that the pin size is better to be larger to acquire larger hmm to avoid the contact of two rough surfaces,but there is an upper limitation on the pin size since the increasing pin size would reduce the gap in the bearing;Numerical simulation analysis of RBC flow trajectory shows that the proper pin size together with the eccentricity to avoid entrainment of RBSs in the gap can be determined.To prevent the entrainment of RBCs in the gap,a practical method is to increase which reduces botii the gap size and the eccentricity.ConclusionAccording to the calculated results of hydrodynamic pressures and the streamlines of the RBCs in tbe gap,the pin size and the minimal clearance(or the eccentricity of the shaft)are the crucial parameters to affect the performance of the bearing.Considering the effects of load capacity,rough surface contact and whether RBC is entrained,a region for the design of the pin in a given bearing is provided.This demonstration may be helpfol in the design of a LVAD to reach longer working life with better performance.