Scientists use magnetic nanotechnology to safely rewarm frozen tissue for transplants

According to the Organ Procurement and Transplantation Network, as of August 2024, more than 114,000 people are on the U.S. national transplant waiting list, and about 6,000 will die annually before receiving an organ transplant. One reason is the loss of organs in cold storage during transport, when delays cause them to warm prematurely. Methods have been developed to rapidly freeze organs for long-term storage without risking damage from ice crystal formation, but ice crystals can also form during warming. To address this problem, Yadong Yin and colleagues developed a technique known as nanowarming, pioneered by their collaborator John Bischof, to employ magnetic nanoparticles and magnetic fields to thaw frozen tissue quickly, evenly, and safely.

Recently, Yin and a team developed magnetic nanoparticles (actually extremely small bar magnets) that, when exposed to alternating magnetic fields, generated heat. And that heat rapidly thawed animal tissues stored at -238 degrees Fahrenheit (-150 degrees Celsius) in a solution of the nanoparticles and a cryoprotectant. However, the researchers were concerned that the uneven distribution of the nanoparticles within the tissues could lead to overheating where the particles were concentrated, potentially leading to tissue damage and toxicity from the cryoprotectant at elevated temperatures.

To reduce these risks, the researchers have continued their research, working on a two-stage approach that more precisely controls nanoheating rates. They describe this process in the new Nano letters study:

• Cultured cells or animal tissues were immersed in a solution containing magnetic nanoparticles and a cryoprotectant and then frozen with liquid nitrogen.
• In the first stage of thawing, as before, an alternating magnetic field initiated a rapid reheating of the animal tissues.
• As the samples approached the melting temperature of the cryoprotectant, the researchers applied a horizontal static magnetic field.
• The second field realigned the nanoparticles, thus effectively slowing down heat production.

Warming slowed more quickly in areas with more nanoparticles, reducing concerns about trouble spots. Applying the method to cultured human skin fibroblasts and pig carotid arteries, the researchers found that cell viability remained high after rewarming for a few minutes, suggesting that thawing was rapid and safe. The ability to precisely control tissue rewarming brings us one step closer to long-term organ cryopreservation and the hope of more life-saving transplants, the researchers say.

The authors gratefully acknowledge funding from the U.S. National Science Foundation.