Experimental Studies On Cryogenic Properties Of Artery And Vitrification Of Embryo

This research is supported by two projects, one is a key project from National Natural Science Foundation of China (NSFC), "some thermal problems in clinical medicine (No. 59836240)". And the other is a project for the youth from the same foundation, "A study on thermal stresses and fractures of biomaterials during freezing (No. 50206013)".Tissue and organ can be cryopreserved for a long time, but they are easily injured during cooling and warming processes. The characteristics of tissue and organ and the method of cryopreservation have direct or indirect influences on the result of cryopreservation. In this paper, the cryogenic thermo-mechanical properties of artery and the characteristics of embryo vitrificating using open pulled straw (OPS), and their influences on cryopreservation have been studied.Blood vessel transplantation is an effective way to treat cardiovascular disease. To avoid the fracture of artery during freezing, A series experiments have been done to measure the tensile strength, stress relaxation and heat capacity (Cp) change with the temperature of the frozen rabbit artery and the impact of cryoprotective agent (CPA) on them, using 15% (w/w) dimethylsulfoxide (MeSO₂) as CPA. And the influence of these experiment results on the thermal stress has been analysed.In the tension experiment, a tensile force is applied to a sample until the fracture happens using DMTA IV (static tensile mode) with the strain rate of 0.005/s under the temperature from 25 to -80℃, thus getting the tensile strength which is the stress relative to the biggest force. The conclusion is that the tensile strength of the frozen rabbit artery increases with the drop of temperature. The tensile strength of the artery without CPA increases from 0.41 MPa at 25℃ to 5.86 MPa at -80℃, while that with CPA increases from 1.11 MPa at 25 ℃ to 4.26 MPa at -80℃.In the stress relaxation experiment, with a constant initial strain of 2-8%, a testing force is applied to a artery using DMTA IV (static stress relaxing mode) under the temperature from 25 to -8 0℃, so that the changes of the stress on the sample over time can be determined. And the constitutive relationship of rabbit artery is deduced from the relaxation result. The conclusion is that the initial Young' s modulus of the frozen rabbit artery with or without CPA increases with the drop of temperature. The modulus of the artery without CPA increases from 0.072 MPa at 25℃ to 333.48 MPa at -80℃, while that with CPA increases from 0.139 MPa at 25℃ to 178.69 MPa at -80℃. From 25℃ to -80℃, the stress relaxation of rabbit artery with or without CPA becomes faster at first and then becomes slower with the decreasing of temperature. From 25℃ to -40℃, at the same temperature, the stress of the artery without CPA relaxes more quickly than...