Studies On Some Key Issues On The Cryopreservation Of Biological Tissues

Cryopreservation is a widely accepted method for the long-term preservation of cells and tissues. It has many potential applications in various fields. For example, it is used for the long-term storage of cells in laboratory and, for various diseases treatment in clinical medicine, and for the fresh foods storage. During the process of cryopreservation, there exists a complex mass and heat transfer process in tissue and cell. Moreover it has been proven to be the dominating controlling step for a successful preservation. Therefore, the studying of some problems before, during and after freezing processes is much more significant to optimize the cryopreserve protocol and to deeply understand the principle of the cryopreservation of tissues and cells.This paper calculates the problem of moving boundary of pure water, then it uses commercial FLUENT code to simulate the heat transfer during water freezing, and obtains the temperature and pushing velocity distribution in the structure. It is helpful for the future work to cryopreserve the large-scale tissues.At the same time, this paper measures the osmolalities of DMSO by osmometer and absorption areas of the DMSO by chromatogram, and plot standard curve and make the linear aggression. The aim of the process is to measure the concentration of DMSO indirectly. By comparison, the experiment proves that the osmometer method is a more effective and more convenient one to measure the concentration of DMSO solution. And the methods can also be used to measure the concentrations of other cryoprotectants.Meanwhile, the existing moving boundary in the freezing tissues and cells makes the DMSO to diffuse in solution or within the tissue matrix. The work contributes to the future work on the cryopreservation of large tissues. This paper uses microcapsule as porous media and measured the porosity of the microcapsule by physical method and the diffusion of DMSO in microcapsule. Because there exists a moving boundary in the freezing tissues and cells, the boundary forces the DMSO in solution to diffuse. If the diffusing rate is larger than the pushing rate of the ice boundary, there willproduce a concentration gradient in unfrozen zone. And if the diffusing rate is smaller than the pushing rate of the ice boundary, the solute will be trapped in the frozen area and no concentration gradient, not resulting in a concentrated solution in the unfrozen zone.This paper designs and studies the cryopreservation system for the large-scale tissues and use the artificial intelligence adjuster to control the temperature and height to achieve the function of the program freezing equipment. The paper measures the temperature distribution in cryopreservation equipment and compares the size effect to the temperature distribution. The paper verifies that if the vessel is too large, the natural convection will dominate the process and affect the temperature distribution. The temperature distribution in freezing vessel fit linear better. Based on the experiment result, the paper improved the system and it can use fast freezing rate to cryopreserve large-scale tissues.