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Flash cooling holds promise for egg storage

24 March 2010
Appeared in BioNews 551
Droplet size, temperature and composition can affect the vitrification process, according to research published in PNAS (Proceedings of the National Academy of Sciences) last month. The findings could be used to improve the vitrification techniques used to store biological materials, including eggs for IVF treatment.

So-called 'egg freezing' involves cooling eggs removed from a woman's ovaries so they can be stored. At a later date, these eggs can be thawed, artificially inseminated and introduced back into the womb. Two main methods are used to cool eggs for IVF: slow cooling and vitrification. Both aim to minimise the formation of harmful ice crystals in eggs during cooling or warming, while also minimising any harmful effects of the cryoprotectants. In slow cooling, eggs are cooled slowly using lower concentrations of cryoprotectants. During vitrification, eggs are cooled quickly using higher concentrations of cryoprotectants.

Until now, no one had found a way to vitrify cells with low levels of cryoprotectants, according to Wired magazine. But this new research into droplet vitrification may provide some answers to this problem and has implications for fertility treatment.

During vitrification, tissues or cells are suspended in cryoprotectant liquid before being immersed in liquid nitrogen at temperatures of about -196 degrees Celsius. This results in the rapid removal of water. Vitrification keeps cells metabolically dormant and helps avoid the formation of damaging ice crystals. Dr Utkan Demirci from Harvard Medical School's Brigham & Women's Hospital led the study into droplet vitrification. The team studied the physical phenomena that occur when a droplet of cryoprotectant is injected into liquid nitrogen.

They found a droplet rises to the surface when injected into liquid nitrogen, buoyed by a vapour cloud which generates around it. After skimming around on the surface, the droplet sinks as its temperature reaches that of liquid nitrogen. This process is similar to the Leidenfrost effect, which is seen when water is sprinkled onto a hot pan.

According to Wired magazine, the team measured the droplets as they sank back into the nitrogen. They found that small droplets were completely vitrified, but larger droplets formed damaging ice crystals because their larger surface area prevented heat from escaping. This meant they froze more slowly.

After droplets froze and sank back into the nitrogen, they measured the droplets and used a microscope to determine how crystallized they were.

They found smaller droplets were almost completely vitrified, while larger droplets formed damaging ice crystals. That was because the larger droplets had more surface area to prevent heat from escaping, so they froze more slowly, Demirci said. Using smaller droplets of about the width of a human hair prevents the cells from crystallizing, which means they are more likely to survive the process.

This new research into droplet vitrification has implications for fertility treatments. According to Wired, Dr Demirci's team believe using droplets smaller than a human hair prevents cells from forming ice crystals so they are more likely to survive the vitrification process. They are currently applying the new droplet-based biopreservation technology to mouse eggs as an initial step towards clinical trials in the future. The findings could enable the development of high-throughput, automated methods of cryopreservation of biological samples such as blood and eggs.

Flash-Freezing Technique May Boost Egg Survival Rates
Wired |  26 February 2010
Vitrification and levitation of a liquid droplet on liquid nitrogen
PNAS |  22 February 2010
12 November 2012 - by Dr Gillian Lockwood 
After a decade of claiming that the technique was only applicable to young cancer patients whose treatment would render them prematurely infertile, the American Society for Reproductive Medicine (ASRM) has decided that vitrification and warming of unfertilised oocytes followed by fertilisation by ICSI results in acceptable subsequent pregnancy rates...
5 December 2011 - by Dr Rebecca Robey 
Progress Educational Trust (PET)'s annual conference, 2011, 'The Best Possible Start in Life: The Robust and Responsive Embryo', started with two fantastic sessions chaired by Dr Virginia Bolton, consultant embryologist at the assisted conception unit at Guy's Hospital, London, UK....
20 September 2010 - by Dr Charlotte Maden 
Scientists claim to have developed a new technique for sperm preservation, which allows more functioning sperm to be recovered. The Chilean and German team reportedly used vitrification, which is currently used for cryopreserving ('freezing') eggs and embryos, to successfully preserve sperm...
28 June 2010 - by Harriet Vickers 
A large number of female university students say they would undergo egg freezing to allow time to build a career, a relationship, or become financially stable. However, older women who go through the procedure say it is because they want time to find the right man...
24 May 2010 - by Victoria Kay 
A US study on mice has given hope to women with reduced fertility, including those receiving treatment for cancer. If transferable to humans, it seems activating dormant eggs could increase the chances of conception....
17 November 2008 - by Alison Cranage 
Three new independent studies have provided further evidence that embryos stored using slow-freezing techniques may be better than fresh for IVF. The studies were presented at the American Society for Reproductive Medicine conference in San Francisco, US, last week. The studies indicate that using frozen embryos rather...
2 October 2008 - by BioNews 
In BioNews 471 we published a story which used the term 'freezing' to describe a new embryo preservation technique known as 'vitrification'. It has been brought to our attention that 'freezing' is not an accurate description of the vitrification process, which in fact uses certain chemicals and processes to avoid...
10 July 2008 - by Alison Cranage 
A new study shows that it is better to use frozen, rather than fresh embryos in IVF treatment. The research was reported by Dr Anja Pinborg at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in Barcelona last week. The study has...
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