UC Berkeley researchers completed a study successfully reviving human heart tissue after preserving it in subfreezing conditions for one to three days.

The study was conducted by Boris Rubinsky, Professor of the Graduate School in the department of mechanical engineering, and Kevin Healy, professor of bioengineering, materials science and engineering. Other contributors include Matthew Powell-Palm, postdoctoral scholar in the department of mechanical engineering; Verena Charwat, postdoctoral researcher; Berenice Charrez, postdoctoral researcher; and researcher Brian Siemons.

To conduct the experiment, the researchers used a heart-on-a-chip system involving cardiac tissue grown from stem cells on a millimeter scale that replicate the functions of a regular heart, according to a campus press release.

The heart-on-a-chip was then preserved through isochoric freezing, allowing the tissue to be in subfreezing temperatures without forming ice crystals, Powell-Palm noted.

“By confining water into a container and denying access to the atmosphere, we find that its inclination to freeze decreases substantially,” Powell-Palm said. “There’s this energetic feedback loop that tells the ice, if you start to expand here, you’re gonna have to pay this energetic toll to pressurize the water.”

Preserving organ tissue via isobaric freezing, or traditional freezing, is not ideal because the ice crystals that form would destroy the tissue, according to the press release.

One implication of the study is that organ-on-a-chip platforms may be more easily transported and preserved beyond the few labs that currently manufacture them, according to Rubinsky.

There is also the possibility of preserving human organs for extended periods of time, since donor organs currently only last four to six hours before becoming unusable, Powell-Palm noted.

“The whole premise of cryopreserving these genetically human engineered tissue constructs, in the interest of using them as proxies for trying to figure out how to preserve whole organs, is extremely cutting-edge,” Powell-Palm said. “We’re the first ones to do it for working cardiac chips and then revive it and see that it starts beating again.”

The researchers plan to expand the experiment by preserving rat livers in the next two to three weeks, according to Powell-Palm.

If this is successful, this will be the first time a full-organ preservation is done in the world, he added.

In the future, they plan to repeat the experiment with multiple types of organs until they are able to preserve that of humans, Powell-Palm noted. However, because the rules of thermodynamics do not scale linearly according to volume, the process of preserving larger organs will take time to develop.

The researchers are also working to preserve other biological matter, including high-value foodstuffs and endangered coral species, Powell-Palm added.

“An interesting thing about this whole task of cryopreservation is it’s something that can be applied to any kind of sensitive biological matter. I think it really broadens your notion of the scope of the impact,” Powell-Palm said.