Pieces of heart tissue can be freeze-dried and later rehydrated for transplantation, according to research in sheep. The technique could allow donated human tissue to be stored cheaply for years, and enable doctors to choose the perfect transplants “off the shelf”, rather than having to use whatever is available at the time.
Cardiovascular diseases are the leading cause of death worldwide, and around 250,000 heart valve surgeries are performed each year. These involve repairing or replacing one or more of the four valves that help pump blood through the heart. The demand for these operations is growing, and is a year by 2050.
Currently, the replacement heart valves are either mechanical, donated from cadavers or sourced from pigs or cows. In most cases, the new valves can last for 10 to 15 years. But around 10 per cent of heart valve replacements are done in children. As the children grow, the valves fail to grow with them. This means that children who need new heart valves can end up having multiple risky operations.
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Like beef jerky
Another problem with the existing biological options is their short shelf life. “Once they’ve been processed they need to be stored in liquid, and that only leaves you four months to find a recipient,” says at Leibniz Research Labs for Biotechnology and Artificial Organs in Hannover, Germany. Some researchers are looking at freezing tissues and organs for donation, but the procedure seems to cause some damage.
Hilfiker’s solution is to freeze dry the tissues. In their experiment, Hilfiker and his colleagues first got hold of heart valves from sheep and cows at a slaughterhouse. They removed all the cells from the valves using a detergent, so that only the empty structure remained. The team then soaked the valves in a sugary solution to protect them, before freeze-drying them to remove all the moisture. “At the end you get something that looks like beef jerky,” says Hilfiker.
The team stored the valves in air-tight plastic containers at room temperature. When they wanted to use them, they simply rehydrated the valves by leaving them in a cup of sterile water for 24 hours. These were then transplanted into six young sheep, as these animals are thought to experience similar heart problems to humans. Three sheep were given freshly prepared valves instead.
Long-term storage
As Hilfiker’s team monitored the health, weight gain and heart function of the sheep over the next six months, all appeared to be doing well, except for one that had received a fresh heart valve. What’s more, the valves appeared to grow in size as the animals grew, possibly because the team avoided using the harsh chemicals used in other preparations.
In the study, the team stored their valves for a couple of weeks, but Hilfiker thinks that freeze-dried organs could be kept indefinitely. “I have one on my desk from last year and it looks the same,” he says.
Hilfiker hopes the technique could one day be used to store human tissues for transplantation, and potentially some simple organs. In priniciple, this would give doctors all the time in the world to find suitable recipients for donor tissues, he says.
“It’s hard to imagine that you could freeze-dry a complicated organ like the heart or kidney,” says of the Texas Heart Institute. “But I could see it working for the oesophagus and bladder, and maybe the liver,” she says.
Acta Biomaterialia
Read more: Welcome to the limb lab where organs are kept alive on shelves
