Glycerol |
Cryoprotectants act by decreasing the freezing point of a substance, reducing the amount of salts and solutes present in the liquid phase of the sample and by decreasing ice formation within the spermatozoa. Importantly, the cryoprotectant should be non-toxic to the cells during the addition of the cryoprotectant and during freezing and thawing.
Glycerol is a permeating cryoprotectant which is most widely used for human sperm cryopreservation and meets all criteria indicated above. Glycerol acts on the membrane structure, permeability and stability of the lipid bilayer, the association of surface proteins and the cellular metabolism (Di Santo, et al. 2012).
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Macromolecules (4 g/L HSA and sucrose(20 mM)) |
Cryoprotective solutions have been supplemented with macromolecules such as sucrose and human serum albumin (HSA). Several studies have shown that such molecules help to reduce physical damage and help to maintain osmotic pressure of the extracellular fluid (Shaw, et al. 2000).
Besides its cryoprotective role, HSA facilitates gamete or embryo manipulation by preventing adsorption to the surface of petri dishes and pipettes through saturation of the potential binding sites.
Also, the increased viscosity of the media, caused by the addition of HSA, promotes the ease of embryo handling and manipulation (Trounson and Gardner 2000).
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