Scientists successfully thaw cryopreserved tissue without damage

A team of researchers announces that they have developed a technique allowing them to thaw cryopreserved human and pig samples without damaging the tissues. This is a major step forward that could lead to getting rid of organ transplant waiting lists.

Cryopreservation is a process where whole cells or tissues are preserved by cooling them to very low temperatures (typically 77 K or -196°C, the boiling point of liquid nitrogen). But « bringing these tissues back to life », whether human or animal, without damaging them is one of the great challenges of our time since the applications would not only enable humans to prolong their life, but the technology could more realistically allow hospitals to safely store organs over long periods of time.

The problem today is not the shortage of organs strictly speaking, but the conservation of these said organs, which can only be “frozen” for a few hours before being irreparably damaged. To give you an idea, it is now estimated that approximately 60% of the hearts and lungs available for transplant are “discarded” each year, as they cannot be stored for more than four hours. The problem is therefore logistical, since if even half of these discarded organs were transplanted, waiting lists would be wiped out in less than three years “, underlines John Bischof of the University of Minnesota, main author of this study published in the journal Science Translational Medicine.

All eyes then turned to cryopreservation. One of the main techniques, vitrification, involves supercooling biological samples to temperatures of -160°C. The technique makes it possible to store organs for several years and would make it possible, on paper, to constitute organ banks available for each need. But the problem is the thawing of these organs since ice crystals form and damage the tissues which can even crack during the thawing process.

There is already evidence that this thawing process can work on small tissue samples (up to approximately 1ml in volume), but as the tissue becomes larger and approaches the size of human organs, the technique current convection not working. That may be about to change as a team of researchers from the University of Minnesota announces the development of a new technique that allows the « rapid warming » of cryopreserved human and pig samples without damaging tissue.

Instead of using convection, the team here uses nanoparticles to heat the tissues quickly and evenly so that ice crystals cannot form and thereby protect the tissues. To do this, the researchers mixed silica-coated iron oxide nanoparticles in a solution and generated uniform heat by applying an external magnetic field. They then heated several human and pig samples between 1 and 50 ml using this new technique on the one hand and the convection technique on the other. Result: the fabrics heated with the nanoparticles did not show any signs of damage, unlike the control samples.

The team also tested the warming system in an 80 mL system (without tissue this time) and observed the same critical warming rates as with the small sample sizes, suggesting that the method is scalable. In the future, researchers hope to be able to apply it to larger tissues and organs up to volumes of 1 liter and possibly beyond. Note however that for the moment the team has not succeeded in demonstrating the effectiveness of this technique on real organs which are made up of complex arrangements of multiple types of tissue. It will therefore have to be refined, optimized, but the potential future applications could be extraordinary.


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