According to researchers at the University of Minnesota (UM), over 60 percent of the hearts and lungs donated for transplantation every year need to be disposed of because they can't be stored on ice for longer than four hours. While deep-freezing techniques exist to preserve organs for longer period of times (cryopreservation), they get damaged when being reheated. The UM researchers believe they've solved this problem thanks to tiny microscopic particles.

The process of vitrification involves cooling biological materials to temperatures of between -160 and -196 degrees Celsius. The rapid cooling of tissue to these temperatures along with a cryopreservative causes the tissue to enter a glass-like state without damaging ice forming. While this has proven a successful preservation method, when it's time to bring the tissue out of the deep-freeze, current convection-based warming techniques cause it to heat unevenly, which makes different parts of the tissue expand at different rates and can lead to tears and cracks. Speed and even heating are the keys to preventing this from happening.

According to the UM researchers, current methods can only warm small volumes of tissue measuring about 1 ml. Their new method can heat samples up to 80 ml and it can heat them at the rate of more than 130 degrees Celsius per minute.

The method involves placing silica-coated iron oxide nanoparticles in the cryopreservative before the the tissue is cooled. Then, when it's time to rewarm the tissue, the particles are beamed with electromagnetic waves which causes them to heat up, effectively meaning there are thousands of heaters surrounding the tissue warming up rapidly and at the same time.

The researchers demonstrated the effectiveness of the technique on fibroblasts (connective tissue found in animals), and on pig arteries and heart tissue. Compared to sample tissues that were rewarmed slowly over ice, the new technique showed no signs of harm to the test material.

"We've gone to the limits of what we can do at very high temperatures and very low temperatures in these different areas," said UM mechanical and biomedical engineering professor John Bischof, the senior author of the study. "Usually when you go to the limits, you end up finding out something new and interesting. These results are very exciting and could have a huge societal benefit if we could someday bank organs for transplant."

The researchers say the next step is to scale up the method and try it out on actual organs. They plan to start with the organs of smaller animals like rabbits and rats and then move on to pig organs. If that's successful, they are hopeful that they'll be able to try out the technique on human organs. They also indicate that their system might have applications outside of cryopreservation, and could, for example, be used to deliver deadly pulses of heat to cancer cells.

Their work has been published in the journal Science Translational Medicine.

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