In-situ Tissue Engineering Oriented Textile Reinforced Composite Vascular Graft And Its Enhanced Anti-thrombogenic Surface Development

The long-term patency rate after vascular prostheses in clinic was low,which is the emphasis and difficulty of vascular graft research.Tissue engineering vascular graft building is an effective way to improve long-term patency rate.However,there is still a considerable gap between the laboratory and the surgical ward.Currently,cell seeding and in vitro culture,used in the tissue engineering approach,are demanding,invasive,and may result in infection or immune response.The most promising approach is a synthetic graft designed for in-situ incorporation of cells,as opposed to in vitro culture.The in-situ tissue engineering vascular graft should have a role in maintaining the blood flow after implantation.After a specific time,the graft should degrade with new vascular tissue regeneration.Finally,an entire blood vessel grows on the vascular scaffold.This idea can solve the problem caused by tissue culture in vitro.Thus,the research of in-situ tissue engineering vascular graft should be a focus on the design and development high-performance vascular scaffold with good biocompatibility.The study of in-situ tissue engineering vascular is still at the starting stage and faces many key issues such as balancing mechanical properties and biocompatibility to promote endothelialization,prevent blood clots,and reduce intimal hyperplasia.This research raises a fabric reinforced composite structure vascular graft design to solve the problem of building an in-situ tissue engineering vascular.Polylactic acid(PLA)knitted fabric was chosen to provide adequate mechanical integrity and porous structure of the vascular.Flexible and plastic polycaprolactone(PCL)was coated on the PLA fabric to form a composite vascular graft(c VG)with enhanced mechanical properties and potentially surface modification ability.The intimal of c VG was combined with heparin with an innovative method to form an antithrombosis and inhibition of hyperplasia surface.This research mainly focus on the following aspects: the mechanical properties of c VG with different PLA/PCL weight ratio,the degradation behavior of c VG with different PLA/PCL weight ratio and the gradual loss of mechanical properties,the relationship between heparin combination method and the heparin content,blood and vascular cells contact with c VG material their interreactions.The second chapter mainly descript the design and development of multilayer bionical structures vascular graft with reinforced composite structure.PLA and PCL were selected as base materials,for their biocompatibility,biodegradability,and FDA approval for implant use.Two kinds of c VGs(c VG-H and c VG-L)with different fabric structure was fabricated based on the weft knitting of PLA multifilament technology,spray-coating,and freeze-drying method.The geometric characterization illustrated the dense PLA fabric(203.72 g/cm2),and lose PLA fabric(68.42 g/cm2)can form c VG-H and c VG-L with PLA/PCL weight ratio 1.32 and 0.67,respectively.PCL coating layer uniformly coved PLA multifilament.The prostheses showed compact interface combination of the two materials and the good deformability of the vascular membrane.Size and morphology of all the prototypes and control e PTFE graft were similar.In the third chapter,the mechanical properties of c VG were comprehensively characterized in vitro with emphasis on the difference of c VG-H and c VG-L.The mechanical characterization according to standard ISO 7198:2016 including tensile properties in blood flow and radial direction,probe bursting properties,suture retention properties,and compliance.Besides,compressive pressing shape recovery and torsion properties were also studied in this chapter to simulate the mechanical environment of a vascular graft in vivo.The commercial e PTFE samples were used as references.The results showed c VG had higher strength than commercial e PTFE samples.The radial strength of c VG-H was twice as c VG-L and features better compliance.In comparison,c VG-L showed anisotropy,makes it had stronger tensile strength in blood flow direction than the other.The composition of c VG,the ratio of PLA/PCL highly effect the mechanical behavior of c VG.The shape recovery property of c VG also demonstrated the importance of PCL coating and advantage of the composite structure.In addition,the cell and hemolysis test illustrated the non-biotoxicity of c VG.In the fourth chapter,the accelerating degradation of c VG-H and c VG-L were carried out in the solution with p H 3 and p H 12,respectively.The tensile and radial compressive recovery characterization were used to analyze mechanical changing of c VG.And structures(SEM,DSC,XRD)changing analyses of PLA and PCL were also studied to illustrate the interaction of two materials and their contribution to the composite.The results demonstrated that the c VG retained the circular cross-section even through its tensile strength lost 90 % during degradation,which is critical in maintaining the patency of blood flow.The c VG-H lost their tensile strength faster,while the c VG-L lost the compressive resistance strength more quickly.The PLA fabric contributes the prostheses with excellent tensile properties,and the PCL matrix prevents the knitted PLA tubular structure from collapsing against radial compression.Besides,the different degradation rates of the PLA fabric and the PCL matrix in the prostheses lead to the different mechanical deterioration rates of the composite vascular prostheses.Therefore the compressive and tensile performance of the c VG samples during degradation could be modulated by the percentage of PLA fibers.The fifth chapter introduces a two-step surface modification method on PCL material to improve the biocompatibility of c VG.They are heparin molecules covalent coupling and electrostatic adsorption.The results showed amino-PCL obtained under the condition of 60 min and 0.43 mol/L hexamethylenediamine.Amino-PCL and active carboxyl heparin can be reacted,and finally got modified PCL with 0.60?g/cm2 heparin on its surface.After five layers of chitosan and heparin deposition immobilization added on the surface of PCL,there is 2.58 ?g/cm2 heparin on PCL in total.The roughness of PCL surface decreased after modification.But the surface wettability increased.Water contact angle declined to 27.4o from 76.1o.This combined modification method wouldn't cause hemolysis and mechanical change of PCL.In the sixth chapter,heparin release behavior was studied,as well as the blood and vascular cells interaction with modified PCL during heparin released process(4 weeks).The anticoagulation property,whole blood cells adhesion on the material were characterized.Also,endothelial/ smooth muscle cells adhesion and growth on the material were studied.The results showed the material had burst release with 58 % heparin lost.60 % of heparin released from the material within the first week.The rest of heparin remains on the material until one month.Two-step heparin-linked material had better anticoagulation behavior compare to covalent grafting heparin material,even in the condition of the heparin released for a month.Cell experiments showed that modified surfaces could resist both kinds of cells.Endothelial cells could grow on the modified material,but smooth muscle cells cannot survive.The heparin modified surface behave smooth muscle cells inhibition effect stronger than endothelial cells.In this paper,an in-situ tissue engineering oriented vascular graft was designed,developed and characterized.The vascular graft prostheses have good mechanical properties,biocompatibility,and controllable loss of mechanical properties.The material modification improves the long-term anticoagulant property and the selectivity growth of the endothelial cells on the surface of the vascular graft.This research provides reference and data-support to the development of in-situ tissue engineering vascular graft,and promote the research of small diameter vascular graft to develop.