Vitrification as a technique of bovine embryo cryopreservation

Abstract

Over the last 40 years cells and embryos of mammals have been preserved, at room temperature, refrigeration temperature and by different cryoconservation methods. These techniques have evolved into more simple, practical and less expensive freezing procedures. One of these is vitrification, a process of solidification that uses a highly concentrated solution which does not crystallize during freezing; its viscosity increases with the descent of the temperature until the formation of an amorphous solid state similar to glass. For this reason, exposure and freezing rates should be quick enough to avoid toxicity and the formation of intracellular ice, which can cause embryonic damage. In order for the embryos to support the osmotic shock, they should be equilibriated with a less concentrated crioprotectant solution before being exposed to the vitrificant solution for their later freezing. Several vitrification procedures have been published about embryo preservation, using different crioprotectants, concentration, volume, addition method, temperatures, exposition time, freezing rate, thawing procedure and dilution, to maintain the function, normal structure and viability of the embryo. These techniques have also been experimented with in vitro and in vivo produced embryos, at different developmental stages. This paper aims to review the present bovine embryo cryopreservation methods, particulary vitrification, as well as to mention the latest procedures and progress so that new researchers may have an updated literature review to start their works.