Zebrafish embryo. (Photo: University of Guelph)
Zebrafish embryo cryopreservation achieved by using gold nanotechnology and laser
Tuesday, July 25, 2017, 00:40 (GMT + 9)
Researchers at the University of Minnesota and the Smithsonian Conservation Biology Institute (SCBI) have been able to provide the first-ever reproducible evidence for the successful cryopreservation of zebrafish embryos.
The scientists used new gold nanotechnology and lasers to warm the embryo—the stumbling block in previous studies performed for over 60 years. The results have profound implications for human health, wildlife conservation, and aquaculture.
“There’s no doubt that the use of this technology, in this way, marks a paradigm shift for cryopreservation and the conservation of many wildlife species,” said Mary Hagedorn, an SCBI research scientist and paper co-author.
“To get anything to work at such cold temperatures, you usually have to get creative. Here we take a unique approach by combining biology with an exciting engineering technology to do what has been impossible previously: to successfully freeze and thaw a fish embryo so that the embryo begins to develop, rather than falls apart,” Hagedorn added.
By freezing sperm, eggs and embryos, conservationists can safeguard at-risk species and their genetic diversity, making it possible to bolster the genetic pool and therefore health of wild populations years—or even centuries—later.
Successful cryopreservation of an embryo requires cooling the embryo to a cryogenically stable state, then warming it at a rate faster than it was cooled, and using an antifreeze (or cryoprotectant) to stop the growth of ice crystals, which are like pins in a balloon that pop the membrane and cause the embryo to fall apart.
Fish embryos, however, are very large, making it difficult to thaw them quickly and avoid ice crystal development. In addition, because aquatic animals need to survive harsh environments, their embryonic membranes are mostly impenetrable, blocking the cryoprotectants out.
Enter laser gold nanotechnology, a rapidly growing technological field being developed for cryopreservation applications by University of Minnesota Mechanical Engineering John Bischof was critical for the success of the study and has a wide variety of biomedical applications.
“In this case, by careful engineering and deployment of gold nanoparticles within a cryogenically stored and biological inactive embryo, we can use a laser pulse to quickly warm the embryo back to ambient temperatures and switch biological activity, and therefore life, back on,” stressed Bischof, senior author of the study.
The study’s authors injected both the cryoprotectant and nanogold particles into the embryos. The gold particles transferred heat uniformly throughout the embryo when hit with a laser, warming the embryo from -196 degrees C to 20 degrees C in just one thousandth of a second. The amazingly fast warming rate, in combination with the cryoprotectant, prevented the formation of lethal ice crystals.
Embryos that underwent this process went on to develop at least to the 24-hour stage where they developed a heart, gills, tail musculature and moved—proving their post-thaw viability.
The research is published in ACS Nano, a leading scientific journal published by the American Chemical Society.