Cryogenics breakthrough could one day end transplant waiting lists

WHY THIS MATTERS IN BRIEF

  • Freezing objects is easy, defrosting them so they’re alive, or functional, is the hard part but now we’ve just made a giant leap forward


 

Recently we’ve seen breakthroughs in suspended animation, which one day might allow humanity to travel across galaxies and live to colonise new planets, and now researchers have developed a technique that allows them to rapidly thaw cryopreserved human and pig tissue samples without damaging them – a development that could help get rid of organ transplant waiting lists, and give a boon to both the cryopreservation and space industries.

 

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Cryopreservation is the ability to preserve tissues at liquid nitrogen temperatures for long periods of time and bring them back without damage. It’s something scientists, and the people who’ve opted to be cryogenically frozen over the years, such as a teenager in the UK who recently opted to be cryogenically frozen after she died of cancer, in order to try to cheat death, have been dreaming about for decades.

Cryogenics, for now atleast seems to have three main applications, two of which seem sci-fi by themselves – space travel and “hyper sleep,” of course, cheating death and perhaps more mainstream – the ability to help hospitals store organs used for transplants for long periods of time.

Right now, 22 people die in the US each day on average while waiting for an organ transplant. One of the biggest challenges isn’t organ shortages – it’s that organs can’t stay “on ice” longer than a few hours without being irrevocably damaged.

That means even when there are enough organs being donated, there’s still the huge logistical problem in finding a matching recipient and getting the organs to them fast enough.

Already it’s estimated that more than 60 percent of the heart and lungs donated for transplantation each year are thrown out, because they can’t be kept on ice more than four hours, and can’t make it to a patient who needs them in that time.

 

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“If only half of these discarded organs were transplanted, then it has been estimated that wait lists for these organs could be extinguished within two to three years,” says John Bischof from the University of Minnesota, who led the research which was published in the journal Science Translational Medicine.

A better solution could be cryopreservation – keeping tissue stored at temperatures around -80C to -190C (-112F to -310F).

One of the leading cryopreservation techniques is vitrification – which involves super-cooling biological samples to a glassy state at around -160 degrees Celsius (-256F). In fact, vitrification is already being used on human brains by cryonics companies such as Alcor.

Through vitrification, organs could be stored for years and potentially even longer, which would mean doctors could build up a bank of available organs and make it a lot easier for anyone who needs a heart or lung to find one straight away.

But while we’ve managed to get the cooling part down, the problem is that the thawing process can cause ice crystals to form and damage tissue, and potentially even crack it during the thawing process.

In the past, researchers have successfully shown that thawing can work in small tissue samples up to around 1mL in volume. But as tissue gets larger, and approaches the size of entire human organs, the current leading technique of convection – slow warming over ice – simply doesn’t work. That could be about to change.

“This is the first time that anyone has been able to scale up to a larger biological system and demonstrate successful, fast, and uniform warming of hundreds of degrees Celsius per minute of preserved tissue without damaging the tissue,” said Bischof.

 

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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 50mL, using either their new nanowarming technique and traditional slow warming over ice, and each time, the tissues warmed up with nanoparticles displayed no signs of harm – unlike the control samples.

You can see the comparisons below:

 

 

Afterwards, they were able to successfully wash the nanoparticles away from the sample after thawing.

The team also tested out the heating in an 80mL 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.

“In short, nanowarming matches fast convective warming viability and biomechanical testing at 1mL, is superior to convective warming at 50mL, and is physically scalable to 80mL systems,” the team writes.

“In the future, we believe that nanowarming can be applied to larger tissues and organs up to volumes of 1 litre and possibly beyond.”

 

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The team admits that larger tissue – and even whole organs – will need to have the nanoparticles injected into them, rather than just sitting around them, to achieve the same uniform heating, but it’s something they want to try next.

It’s important to note that the team hasn’t successfully shown that their technique actually works on whole organs yet, which are made up of complex arrangements of multiple tissue types. But hopefully that will come in time, and either way this is still the first time we’ve seen such large volumes of tissue successfully thawed from a cryopreserved state, and that alone could open up a whole host of new possibilities.

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