ICE AGE - optimering av förhållanden vid kryopreservering av embryon

Examensarbete för kandidatexamen

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Bibliographical item details
Type: Examensarbete för kandidatexamen
Bachelor Thesis
Title: ICE AGE - optimering av förhållanden vid kryopreservering av embryon
Authors: Boström, Anna
Johansson, Sara
Karlberg, Martin
Lejonbäck, Isabel
Marton, Sofie
Wisitnan, Pakorn
Abstract: This report is a result of cooperation between Chalmers University and Vitrolife, a company based in Gothenburg. The purpose of the project has been to analyze and optimize the equipment Rapid-i and the process around it. Rapid-i is used for storing cells such as embryos at very low temperatures, so-called cryopreservation. More specifically, vitrification has been studied since it is a method that avoids the formation of ice crystals that may damage the cells. To make suggestions for improvements to the equipment or the procedures involving the cryopreservation, factors affecting the embryos survival were examined. To find these potential improvements a literature study, laboratory experiments and simulations and theoretical calculations of cryopreservation have been implemented. Since the vitrification particularly depends on high freezing and thawing rates, the study concludes that the equipment and the cryopreservation-process can be optimized by reducing the radius of Rapid-i and the surrounding device, hereinafter referred to as straw. Further improvements, in order to achieve more rapid freezing and thawing, can be achieved by selecting a material of the straw, and the Rapid-i with a higher thermal conductivity than previously. Because of the surrounding air layer between the straw and Rapid-i, a change in materials does not affect the freezing as much as the thawing. In order to prevent crystal formation during the cryopreservation, the embryo is protected by so-called cryoprotectants. Practical elaborations shows that the vitrification occurred at lower concentration of cryoprotectants if solely Rapid-i was put into liquid nitrogen, compared to if it was surrounded by the straw. The level of liquid air was also observed. Since the formation of liquid air affects the process in a negative way, the level must be minimized. Both laboratory experiments and calculations show a clear asymmetry in the temperature change during the freezing and thawing. Since the temperature gradient is greatest at the beginning of both processes, a difference in the speed when the cryoprotectants undergo vitrification, the glass transition, was observed. Hence the cryoprotectants will undergo glass transition more slowly during freezing than thawing. It is advantageous with a high freezing rate while the crystallization temperature seems to shift towards lower temperatures at higher freezing rate. Thus, since vitrification is desirable, higher freezing rates are beneficial because then the likelihood for vitrification is higher. The report shows consistently that it is important to streamline the transfer of heat to avoid the formation of damaging ice crystals during the cryopreservation. A more efficient heat transfer allows the use of lower concentrations cryoprotectants, which in turn means a reduced risk of toxic effects for the embryo.
Keywords: Biofysik;Biophysics
Issue Date: 2010
Publisher: Chalmers tekniska högskola / Institutionen för teknisk fysik
Chalmers University of Technology / Department of Applied Physics
Collection:Examensarbeten för kandidatexamen // Bachelor Theses

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