Construction And Performance Evaluation Of Vascular Grafts Based On Rapid Prototype By Rolling Membranes Around A Mandrel

Small-diameter vascular grafts are in urgent need in tissue engineering.Among various fabrication strategies for vascular grafts,rolling 2D films into 3D tubular grafts is one of the most promising methods.However,currently this technique cannot meet the requirements of tissue-engineered vascular grafts,mainly owing to the following reasons: the non-biodegradable substrate materials,time-and laborconsuming manipulations,incapability of forming cohesive graft wall in a short time,and disability of precise control of cell distribution in layers.A strategy that can overcome the issues above will greatly promote forward the practical application of the grafts fabricated by rolling 2D films into 3D tubes.Inspired by the structure of the foam tape and incorporating the advantages of previously published methods,we have developed two kinds of strategies for fabricating small-diameter vascular grafts by combining rolling thin films around a mandrel,fibrin biomedical glue and cell patterning.They are single-step rolling technique and layer-by-layer rolling technique.The in vitro(such as mechanical properties and cell behaviors,etc.)and short-term in vivo performances of the obtained small-diameter vascular grafts were evaluated.The details of the project are listed as following:Transformation of the structure of the foam tape to satisfy the requirements of blood vessel tissue engineering utilization and development of single-step rolling technique to fabricate vascular grafts.This technique integrates biodegradable electrospinning films,fibrin glue and cell patterning technique,which can produce artificial vascular grafts within 70 min simple and fast,featuring free substrate material option,precise control of scaffold diameter,flexible adjustment of scaffold layer number,and accurate regulation of cell type in each layer.Mechanical property and cell behavior evaluations of cell-free and cell-containing single-step rolling grafts.The results indicate that,with the increase of layer number,burst pressure and suture retention increase,liquid leakage and compliance decrease,and elastic modulus shows no significant differences;for cell-containing scaffolds,none of the wall thickness,burst pressure,suture retention,compliance,and elastic modulus have significant differences compared with those of cell-free ones,but only water leakage sharply decreases;cells survive and proliferate well in the scaffold and demonstrate little migration under our experiment condition.These investigations provide important references for future in vivo trials.Development of layer-by-layer rolling technique to fabricate vascular grafts with more functions by improving the single-step rolling technique.We can obtain vascular grafts with complex cell alignments within 90 min,including a longitudinally-aligned endothelial cell layer,two orthogonal smooth muscle cell layers(one is longitudinally-aligned and the other one is circumferentially-aligned),and a randomly-aligned fibroblast cell layer.This method lays the foundation of fabrication of multifunctional grafts with features of complex cell alignments,tunable material composition in each layer,and more flexible assembly.A pilot study in rabbit carotid artery replacement model of the rolling-based PCL scaffold.After implantation of 3 weeks,the grafts keep a patency rate of 33%,and show some positive healing properties,such as good cell infiltration and initial endothelial cell coverage and smooth muscle cell layer formation,but also some issues to be addressed,such as slow degradation of substrate materials,slow deposition of extracellular matrix,and unsatisfactory endothelialization rate.These results prove the potential of our single-step rolling grafts to be small-diameter tissue-engineered vascular grafts and also point out the direction of the improvement in the next stage.In summary,the proposed single-step rolling technique and layer-by-layer rolling technique developed in this thesis can address the issues resulted from previous reported approaches.They can achieve rapid and simple fabrication,tunable layer rolling number and mechanical strength,greatly diminished leakage,as well as controllable cell distribution in grafts.Between them,layer-by-layer rolling technique is a further improvement of the single-step rolling technique.It can realize not only the full functions of the single-step rolling one,but the control of cell alignments and material compositions in each layer of the graft,which exhibits a wider application potential.