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Scientists Have Found a Way To Rapidly Thaw Cryopreserved Tissue Without Damage (sciencealert.com)
schwit1 quotes a report from ScienceAlert: Researchers have developed a technique that allows them to rapidly thaw cryopreserved human and pig samples without damaging the tissue -- a development that could help get rid of organ transplant waiting lists. Cryopreservation is the ability to preserve tissues at liquid nitrogen temperatures for long periods of time and bring them back without damage, and it's something scientists have been dreaming about achieving with large tissue samples and organs for decades. Instead of using convection, the team used nanoparticles to heat tissues at the same rate all at once, which means ice crystals can't form, so they don't get damaged. To do this, the researchers mixed silica-coated iron oxide nanoparticles into a solution and generated uniform heat by applying an external magnetic field. They then warmed up several human and pig tissue samples ranging between 1 and 50 mL, using either their new nanowarming technique and traditional slow warming over ice. Each time, the tissues warmed up with nanoparticles displayed no signs of harm, unlike the control samples. Afterwards, they were able to successfully wash the nanoparticles away from the sample after thawing. The team also tested out the heating in an 80 mL system -- without tissue this time -- and showed that it achieved the same critical warming rates as in the smaller sample sizes, suggesting that the technique is scalable. You can view a video of tissue being thawed out in less than a minute here. The research has been published in Science Translational Medicine.
How does this work for organs that need to have their centre part thawed at the same rate?
There are a few ways of freezing samples without creating ice crystals. Part of the trick is to freeze it *fast*. But water is still a problem, becuase even with super rapid freezing, overtime the crystals will restructure into sharp ice. Bad. Nitrogen would seem the obvious, but it tends to boil at the contact point leaving pockets of gaseous nitrogen to slow down the penetration of cold leaving the centres of samples to slowly ice and form crystals. Isopentane doesnt have the low boiling point issue so it works a lot better Glycerine is often used in storing cell cultures. And so on.
I thought ice crystals form during freezing -- how do they form when thawing?