Study On Phase Equilibrium And Mass Transfer Dynamic Of 3D Porous Scaffold Of Tissue Engineering Based On Supercritical Fluid Technology

Defect and loss of function in tissues and organs are one of the major problems facing human health.The research of tissue engineering has become an international front topic in the field of life science.In recent years,based on the traditional phase separation and the special properties of SCF,the SCF induced phase separation cycle drying method has been widely concerned by researchers.And it is used in the preparation of three-dimensional porous scaffolds.With the progress of the research,the experimental results are related to the phase behaviors of ScCO₂/organic solvent/polymer ternary systems in different thickness layers within casting solution and bidirectional mass transfer between ScCO₂ and organic solvent within porous scaffolds.The path and the size and composition of the two region formed by the phase separation are the key factors that affect the formation and pore size of porous scaffolds.In this paper,the model and the parameters were determined.And the phase behaviour of ternary systems of ScCO₂ and polymer and the dynamics of bidirectional mass transfer between ScCO₂ and organic solvent are studied by using MATLAB software.Flory-Huggins theory is the basis theory on the study of polymer solution phase equilibrium.Based on this theory,the phase equilibrium thermodynamics behavior in the process of phase separation induced by ScCO₂ is studied,as the phase equilibrium models of different ternary systems are established.The phase diagram of ternary systems is obtained based on the data of binodal line,spinodal line and critical point in the calculation model under different working conditions.The thermodynamics behaviors of ScCO₂ / AC / PMMA and ScCO₂ / CH2Cl2 / PLA systems are analyzed according to the phase diagram of ternary systems drown above.The results show that the binodal line separates the axe of the Polymer/solvent and the amount of the ScCO₂ dissolves into the Polymer solution increases when the working pressure increases,as the opposite phenomenon when the temperature increases.The change of the homogeneous zone in the ternary system of ScCO₂/AC/PMMA is similar to that of the ternary system of ScCO₂/CH2Cl2/PLA.According to Reuvers model,the Mass diffusion dynamics model suitable for the process of phase separation induced by ScCO₂ is established.For the ScCO₂ / AC/PMMA ternary system,the model parameters under different working conditions are calculated,and the mass diffusion path under these working conditions are drown in the ternarysystems.The influence of different working conditions on the porous is analyzed combining with the experimental result.The diffusion coefficient in the ternary system is a key parameter in the process of mass diffusion.The diffusion coefficient decreases with the increase of pressure or the decrease of the temperature.The shorter the mass transfer path is,the less time is need for the ternary system to be separated,as the smaller the porous will be.In the process of manufacturing porous scaffolds,the phase equilibrium thermodynamics and kinetics of mass transfer influence the structure of the porous.