Electrospun Protein-Polysaccharide-P(LLA-CL)Composite Nanofibrous Scaffolds For Small-diameter Vascular Tissue Engineering

Cardiovascular disease,due to its high incidence,has remained to be one of the greatest threats to human health.The increasing number of patients,especially the elders,create a huge demand for repair and regeneration of vascular tissue.Although coronary artery bypass appears as a common therapy method,it is limited by the the shortage of autologous blood vessels and high surgical expense.In this case,artificial stent grafts become an innovation.So far vascular grafts with large diameter have been successfully used for the replacement of artery and hips.However,difficultness still exist in the transplantation of small diameter vascular grafts,which is mainly because of the higher demandingness for the compliance,biomechanical property,and biocompatibility of the grafts.On that account,electrospun tissue-engineered composite nanofibrous scaffolds have emerged as a promising candidate.Electrospinning has been widely used in the field of tissue repair and regeneration.Scaffolds fabricated via electrospinning technology could mimic the structure and function of natural extracellular matrix(ECM)with its high specific surface area and large porosity.In this work,natural protein collagen and natural polysaccharide chitosan were chosen to mimic the components,structure and function of ECM,and the addition of P(LLA-CL)would contribute to the enhancement of biomechanical property and biodegradability.Various electrospinning methods were used to fabricate composite nanofibrous scaffolds,and the potential application for small-diameter vascular tissue engineering was evaluated by comparing the composite ratio of materials,the modification of electrospinning methods,and the tests of structural performance and biosecurity.To begin with,different ratios of blended P(LLA-CL)/COL/CS scaffolds were fabricated and characterized,and the optimal ratio will be chosen to fabricate core-shell nanofibers with anticoagulant heparin.The weight ratio of collagen and chitosan was set as a constant of 4:1,and then the weight ratios of P(LLA-CL)and(COL/CS)were set as 3:1,1:1.1:3,Morphology of fibers,suture retention stress,thermostability,and biocompatibility of blended scaffolds were tested.The results showed that the addition of P(LLA-CL)significantly enhanced the mechanical properties and thermostability,while the addition of collagen and chitosan effectively improved the biocompatibility and promoted the proliferation and spread of cells.Furthermore.The ratio of P(LLA-CL),/(COL/CS)=3:1 was comprehensively considered as the optimal one which could get a balance between the physical property and the biological function.Coaxial electrospinning method was used to fabricate core-shell nanofibers,in which P(LLA-CL)/(COL/CS)=3:1 was set as shell materials and 15%heparin solution was loaded in the core of fibers.The sustained released nanofirous scaffolds were fabricated successfully,and the sustained release of heparin would contribute to anticoagulation functionally.Moreover,the symmetrically str,uctural scaffolds were fabricated by bi-directionally gradient electrospinning method.P(LLA-CL)was set as component I,and collagen and chitosan with the ratio of 9:1 was set as component II.Through the sequential regulation of flow rates of both sides,the cotents of both components can be controlled.As a result,a symmetrically structural scaffold with P(LLA-CL)as the middle layer and COL/CS as inner or outer layer was obtained.By evaluating the fibers morphology,pore diameter,mechanical properties,thermostability,hydrophilcity,biocompatibility,and biodegradability,the overall performance was compared.The results showed that the symmetrically structural scaffolds remained the excellent properties of both components:the natural materials surfaces made it highly hydrophilic and biocompatible,which will enhance the biosecurity and functionality.Meanwhile,P(LLA-CL)layer ensured the scaffolds to have higher tensile strength and elasticity than blended scaffolds.Besides,its particular biodegradation mechanism could keep the fiber morphology and integral structure more longer,and the combination of synthetic and natural materials will reduce the acidity of degradation liquid and avoid inflammation.Also,the longitudinal gradient symmetrical structure enlargered its pore diameter,which will promote cells penetration.To conclusion,the symmetrically structural scaffolds fabricated by bi-directionally gradient electrospinning method will be a promising candidate for small-diameter vascular tissue engineering.