Not so long ago, researchers demonstrated that infusing tissues with nanoparticles could allow for safe and rapid thawing following low-temperature vitrification, avoiding damage that can occur due to ice crystal formation during a slower warming process. In the research noted here, a different scientific group is working on the nanoparticle approach as a way to cryopreserve fish embryos. They have achieved a proof of principle demonstration, but clearly have a way to go in terms of the quality of the result – it isn’t yet as good as the earlier work on tissue sections. Taken as a whole the nanoparticle approach has the potential to help expand the use of vitrification for tissue storage, something that could greatly improve the logistics of organ donation, tissue engineering, and many areas of research by allowing indefinite storage of large sections of tissue. Greater use and development of tissue vitrification should in turn also help to advance the state of the art in human cryopreservation, the most important backup plan for those who will not survive to benefit from the rejuvenation therapies of decades to come, and a field in need of far greater investment and attention.
Zebrafish embryos have for the first time been frozen, thawed, and brought back to life. Researchers have been working on cryopreservation of zebrafish embryos for decades. It’s never been done before. Over the past 60 years, scientists have had success preserving the sex cells and embryos of humans, cattle, mice, and many other animals. Trying to freeze and thaw fish embryos, however, has been more difficult because of their size and structure. The embryos are relatively large, bigger than a human egg. Fish embryos also have different compartments that freeze and thaw at different speeds. That can lead to the development of ice particles, which can damage the embryo.
Building on work by other scientists, researchers tweaked an existing cryopreservation method by injecting gold nanoparticles into zebrafish embryos, along with a cryoprotectant. The team froze the embryos in about one second using liquid nitrogen, then, after a few minutes, warmed them using a laser. The gold nanoparticles, which were distributed evenly throughout the embryos, absorbed the laser light and turned it into heat. The laser, which shown on the embryos for a millisecond, warmed developing fish so rapidly that they may have avoided being damaged by ice formation or other untoward effects of the quick-chill and thaw technique.
In the trials, only about 10 percent of the embryos survived to 24 hours. At this point, survivors started squirming and wiggling as their hearts, eyes, and nervous systems developed, proving their viability, yet none survived to day five, the final time point the team used. The advance is important for the field of genetics. Zebrafish have become an important model organism for studying the genetics of vertebrates and humans. Being able to preserve the different genetic lines of zebrafish generated in these studies means researchers wouldn’t need to maintain live populations or run the risk losing irreplaceable research lines. It is also the most cost-effective method for this kind of research. The team is continuing to work on the technique to improve the viability of the embryos. Tweaks to the laser, gold nanoparticles, and even the cryoprotectant could make the method more suitable for embryos with a diameter of a millimeter or smaller. That would mean there would be one way of cryopreservation for all organisms with embryos of that size.