Study On 3D Bioprinting Of Liver Tissues Based On Coaxial Flow Technique

The material exchange function in the organism is provided by the vascular system.However,traditional biological manufacturing techniques have encountered difficulties in manufacturing and integrating vascular systems into engineering organizations.Without complete material exchange network,thick artificial tissues or organs cannot achieve adequate nutrient supply,gas exchange and waste removal,cells in three-dimensional tissue cannot maintain normal metabolic function.3D bioprinting provides a new technical possibility for the medical field,which can be widely used in the manufacture of artificial tissues and organs.In this study,a coaxial flow extrusion system was used to fabricate hollow filaments in encapsulated liver cells,combined with a 3D bioprinting system,so as to fabricate liver tissue with microchannel network by using a layer-by-layer approach.The microchannel can be used for transporting nutrient and removing waste,there is a great potential for the manufacture of vascularized artificial tissue in the future.(1)The background and research status of 3D bioprinting technology are introduced.The biological ink and printing methods are briefly reviewed.The method of printing gel channel was summarized,it lays the technical foundation for the manufacturing method based on coaxial flow.(2)In this paper,the 3D bioprinting system based on coaxial flow is constructed and the software and hardware components of biological 3D printers and injection pumps are introduced.The influence of material extrusion rate and material concentration was then studied on the size of hollow filaments and the velocity of wire.The results showed,the coaxial extrusion system can produce hollow filaments with uniform wall.When the parameters such as material concentration and material extrusion rate are changed,the outer diameter of the hollow wire is limited by the external needle.Therefore,the extrusion rate of the material directly influences the inner diameter of the hollow filament and the velocity of the wire.The optimal manufacturing parameters are obtained according to the size of the hollow filaments and the forming effect.(3)The coaxial extrusion system is combined with the 3D bioprinting system,the continuous printing path is also designed,realize the laminated manufacturing of hollow filaments.The perfusion test of the printing structure is carried out and use OCT to observe the three-dimensional structure.Experiments show that the hollow filaments fuse effectively and the three-dimensional channel inside the structure is complete.(4)The biomimetic liver tissue containing multi-layer networks was printed with the liver cell line C3 A as the material.Finally,the liver tissue containing microchannels was cultured separately.The cell survival rate of hepatocytes after 24 h,48h and 72 h of culture was detected by live-deadcell staining in perfusion group and non-perfusion group.The experiment showed that in organs using 3D printing technology based on coaxial flow technique,the damage of hepatocyte was smaller in the printing process,and the survival rate of hepatocytes was over 90% in hollow filaments.Furthermore,there was a significant difference in cell survival rate between the perfusion group and the non-perfusion group after culture for 72 h,suggesting that microchannel perfusion could promote the exchange of material within the tissue and increase the survival rate of liver cells around the microchannel.In conclusion,the manufacturing method based on coaxial nozzle has the following advantages:less damage to the cell,high flexibility,direct biological printing of complex media exchange networks.The microchannel can be used for irrigation,transport nutrient and discharge waste for cells,improve cell survival in the thick tissue.The printing technology and perfusion system presented in this paper provide a new study approach for the vascularization and culture of artificial tissues.