Construction Of Vascular Tissue Engineering Scaffolds Using Gelatin/Chitosan Composite Hydrogel Via Dynamic Sacrifice Mechanism

In tissue engineering scaffold,vascular structures play a vital role,which can perform oxygen exchange,nutrient delivery and metabolic waste removal.Based on appropriate biomaterials and engineering technologies,the construction of vascular tissue engineering scaffold can meet the demand of various applications such as tissue transplantation,physiological/pathological research and drug development/screening,which has attracted widespread attentions.In this paper,two typical natural polymers,gelatin and chitosan,were chosen to prepare composite hydrogel.Based on the temperature sensitivity of gelatin(Gel)and the ionic cross-linking property of chitosan(Chit-H~+)-sodium citrate(Citr),a novel concept of"dynamic sacrifice"was first proposed and applied to construct various types of hydrogel-based vascular tissue engineering scaffolds.The temperature sensitivity of gelatin made Gel/Chit-H~+hydrogel form a single gelatin cross-linking network,which was thermally reversible and used as initial sacrificial material in this work.After the introduction of sodium citrate,Gel/Chit-H~+-Citr hydrogel further formed ionic cross-linking network of chitosan-citrate on the basis of gelatin network,which had thermal stability and was converted into non-sacrificial material.Using the differences in the thermal stability of Gel/Chit-H~+and Gel/Chit-H~+-Citr hydrogels,Gel/Chit-H~+sacrificial hydrogels can be selectively removed by hot water.Because the diffusion distance of citrate ions is related to the cross-linking time(the formation of Gel/Chit-H~+-Citr hydrogel),the spatial distribution of this transition from sacrificial material to non-sacrificial material was dynamically changed,which is called"dynamic sacrifice".Firstly,simple straight hydrogel tube was prepared based on"dynamic sacrifice",whose wall thickness was increased with ionic cross-linking time.The hydrogel tube with alkali treatment had the degradation performance that can maintain tubular structure for up to 21 days,the mechanical properties that can withstand radial burst pressure(411.034mm Hg)and axial cyclic stretching,the semi-permeability that can meet small molecule exchange and prevent red blood cells leakage,the blood compatibility that was in compliance with national hemolysis test standard.The above properties met the physicochemical requirements of artificial blood vessel.Secondly,with the help of 3D printing technology to form three-dimensional structure of the Gel/Chit-H~+hydrogel,the same tube formation method based on"dynamic sacrifice"can be used to construct complex multi-forked hydrogel tube with good mechanical property and high porosity.The tube size and three-dimensional structure varied with cross-linking time and cross-linking type.Based on this,it can also construct tubular network with interconnected or segregated networks,which had certain perfusion capacity.Finally,the same tube formation based on"dynamic sacrifice"can be used to achieve the coupling of tubular hydrogel and 3D printed porous scaffold.The heterogeneous porous vascularized tissue scaffold had various tube sizes and three-dimensional structures under different cross-linking times and internal/external structure combinations.This method was suitable for the vascularization of scaffold with various materials and had good biocompatibility to achieve co-cultivation and proliferation of different type of cells in heterogeneous regions.In summary,this paper used the"dynamic sacrifice"to provide a new strategy for the construction of vascular tissue engineering scaffold,which achieved the preparation of independent simple straight tube,complex multi-forked tube and heterogeneous porous vascularized tissue scaffold.The sacrificial hydrogel not only provided physical shape but also participated in the formation of the tube wall.Especially,the sacrificial material with same initial shape can satisfy the construction of different tubular sizes and three-dimensional structures.The constructed vascular scaffolds had flexible size/structure regulations and good physical/chemical properties,which laid the foundation for further research on vascular tissue engineering.