| Due to the lack of autologous transplantation and allograft rejection,skin burn damage has become a major problem for clinicians.Tissue engineering is an inter-discipline that integrates cytology,engineering,material science and bio-medicine.The 3D bio-printing technology is the application of Three Dimensional Printing technology to tissue engineering,which can complex physiological structure and biological function.3D bio-printing is a branch of 3D printing technology.3D bio-printing technology which is different traditional construction method of tissue engineering in the construction of skin scaffold.This study uses gelatin solution as a printing object.Gelatin is a biodegradable material from animal bones,which has excellent biocompatibility and degradation.Considering that the existing extrusion methods are prone to cause damage to biological materials.Pneumatic extrusion was adopted in this paper.Firstly,this study used gelatin solution as the experimental material,and the viscosity and density value of different temperature and concentration are obtained through the objectification experiment,which provided the material property parameters for CFD simulation.The viscosity coefficient and flow index were obtained through the Arrhenius equation.The results showed that the viscosity of gelatin solution increased with decreased temperature,and the viscosity coefficient also increased.However,the density of gelatin solution was not obvious with temperature and concentration.At the same time,the concentration of gelatin solution was greater;the viscosity was increased.The model of different nozzle diameters was constructed by Solidworks.and ANSYS FLUENT software was used to analyze the process of the flow field of the gelatin solution in the nozzle.The results showed that as the printing pressure increased from 0.20Mpa from 0.16Mpa,the flow rate at the tip of the nozzle was increased from 36.7mm/s to 121mm/s.But the pressure at the tip was decreased.As the diameter of the nozzle increased from 0.21mm to 0.41mm,the velocity of the tip outlet increased from 12.27mm/s to 965.9mm/s.However,the viscosity of the solution became smaller at the tip.The temperature field of the solution in the printing process has no significant on the position.The above conclusion was the main content of the third chapter of this study.Secondly,the influence of solution concentration,extrusion pressure,feed speed,printing temperature and nozzle diameter on the width of gelatine was studied.The study founded that as the concentration of solution decreased;The speed of the nozzle was reduced;The pressure of extrusion increased;The printing temperature increased and the diameter of the nozzle became larger,and the width of the gelatin filaments was increased.The above conclusion was the main conclusion of the fourth chapter of this study.Thirdly,based on the fluid non-Newtonian characteristic,the idea of calculus of cell body force was adopted to simplify the extrusion model of the nozzle.The Hershel-Bulkly power function model can be used to establish the relationship between the flow rate,the flow rate,the filament width and the printing parameters of the system.which can study the influence mechanism of different printing parameters on extrusion molding of the scaffold.It provided a theoretical basis for the experimental verification,which was the main content of chapter 4 of this study.Finally,chapter 4 and chapter 6 are used to verify chapter 3 and chapter 5.The experimental values and theoretical values of flow,velocity,the width of gelatin and porosity were verified by single factor experimental design.The results showed that:1)the experimental values was almost the same as the simulation values,and the printing pressure showed an exponential upward trend with the flow amount and flow rate.This verifies the accuracy of the model based on the pseudoplastic fluid.2)with the continuous increased of printing pressure,the width of gelatin was also increased.And both the experimental values and simulation values showed the same trend.3)by drainage method,the porosity of biological scaffolds was tested.There has same trend between the experimental value and simulation.The viability of the printed cells was analyzed by cell viability assay. |
