Visualization Of Freezing Characteristics Of Cryoprotectants

Cryogenic biomedicine itself is a marginal and interdisciplinary subject among thermal science,biology,medicine and engineering.With the rapid development of biomedical technology,the metabolic biochemical reaction rate of human organs,living cells and embryos in low temperature environment is inhibited,and the preservation time is prolonged.However,in the process of cooling and rewarming,the cells are damaged to different degrees,such as solution damage,osmotic pressure damage,mechanical damage,etc.This paper focuses on the crystallization and glass transition of the multi-component solution mixed by cryoprotectant(glycerol)and common sugar additives in the process of freezing and rewarming,and describes the thermodynamic and kinetic characteristics of the solution.The main research contents are as follows:(1)Visualization of ice crystal growth during the freezing and rewarming process of glycerol solution under different additive concentrations was performed by freeze-drying microscope.The overall appearance of ice crystal growth under different additive conditions was recorded under the conditions of rapid cooling and rapid warming.The number of crystal nuclei of ternary solution at different cooling rates under the two additive concentrations was calculated,and the morphological changes of single ice crystal growth in different additive glycerol solution during the freezing process were compared.The growth rate of ice crystal in the freezing process of glycerol aqueous solution under different cooling rate and different concentration of sugar additives was analyzed statistically.The results show that the nucleation of crystals is related to the degree of undercooling during the freezing process of solution.The greater the degree of undercooling,the greater the driving force required for crystallization,and the growth rate of crystals is affected by many factors,such as the shape of solution,the degree of wetting,thermal conductivity,specific heat capacity and the cooling condition of the outer surface of droplets.(2)The differential scanning calorimeter was used to record the heat flow curve of glycerol aqueous solution under different cooling rates and different concentrations of sugar additives,and to study the thermal physical parameters of the freezing process of the solution under different cooling rates and different concentrations of sugar additives,such as nucleation temperature,content of bonded water and specific heat capacity of the solution.It mainly adopts the theory of thermal science and the method of thermal technology to study some mechanism of solution freezing and reheating process,study the heat transfer and cooling law of solution in the process of freezing and reheating,and seek the best cooling rate.The results showed that the aqueous solution of glycerol with sucrose and trehalose had the strongest binding ability to water,and the best inhibition effect on the movement of water molecules and the probability of ice crystal formation.(3)The molecular dynamics software was used to predict whether the specific volume change of glycerol aqueous solution with different additives at different temperatures was abrupt,and the glass transition temperature of the solution was predicted.The addition of sugar additives greatly increased the glass transition temperature of glycerol aqueous solution;Through statistical analysis of the simulation results of glycerol aqueous solution system with different carbohydrate additives,the radial distribution function and coordination number between the oxygen atoms in glycerol and the oxygen atoms in water molecules in the solution at different temperatures were obtained,and the coordination number of glycerol aqueous solution with sucrose was the largest.The diffusion coefficient of glycerol aqueous solution was calculated after adding different carbohydrate additives,and the diffusion coefficient increased monotonically with the increase of temperature.The oxygen and hydrogen atoms in the amorphous structure solution system were calibrated,and scripts were written to calculate the changes in the number of hydrogen bonds and the average bond length at different temperatures in the stable conformation of the solution system,so as to better evaluate the intermolecular interaction forces in the solution.The results showed that the intermolecular hydrogen bond network changes during the cooling process,resulting in changes in the internal energy of the solution.Thus affecting the viscosity and diffusion of the solution.