“With Cryobioprinting, you can print and store in the frozen state for basically as long as you want,” according to scientists.
The limited shelf-life of 3D tissues, which can range from a few hours to a few days, is a major impediment to widespread research and clinical usage. A bioprinted tissue, like an organ transplant, must be transferred quickly to the region where it is needed or it will not be viable.
Scientists from Brigham and Women’s Hospital in Boston and Harvard Medical School published a paper in the journal Matter describing their work combining 3D bioprinting with cryopreservation techniques to create tissues that can be preserved in a freezer at -196°C and thawed in minutes for immediate use.
“For conventional bioprinting, there is basically no shelf life. It’s really just print, and then use, in most cases,” said lead author Y. Shrike Zhang, a biomedical engineer at Brigham and Women’s Hospital.
“With cryobioprinting, you can print and store in the frozen state for basically as long as you want.”
It was twenty years ago when 3D bioprinting was first used to make artificial human tissue. Ink is extruded layer by layer through a nozzle into a pre-specified shape, just like in traditional 3D printing. Bioprinting ink is often composed of a gelatin-like structure embedded with living cells.
Cryobioprinting works similarly, except that the printing is done directly onto a cold plate stored at temperatures as low as -20°C. After printing, the tissues are immediately transferred to cryogenic storage for long-term storage.
Low-temperature printing provides the extra benefit of producing more detailed shapes than typical bioprinting processes.
“The bioink filament freezes within milliseconds of reaching the cold plate, so it has no time to lose its original shape,” added Zhang.
“Then you can build layers on top of each other, eventually creating a free-standing 3D structure that can withstand its own weight.”
The use of cryogenic temperatures also alleviates restrictions on the sorts of bioink that can be used. Traditional bioprinting processes require the bioink to be viscous in order to keep its shape, however, at lower temperatures, most fluids are naturally more viscous.
Cells must be accompanied by a cryopreservative agent to survive cryogenic temperatures, which minimizes osmotic shock and reduces the development of ice crystals that can damage their cell membranes. The majority of Zhang’s team’s efforts were focused on determining the best combination of cryopreservative chemicals for maximum cell viability.
They showed that the tissues could be preserved for at least three months before being resurrected.
“Reviving the tissues is pretty easy,” Zhang said. “It’s like reviving any type of cryo-stored cells. You return them into a warm medium and use a rapid thawing process.”
To demonstrate that the tissues can preserve their original functionality, Zhang and his colleagues performed a series of cell viability assays, which revealed that the cells could undergo differentiation in the same way that they had previously.
In the future, 3D-bioprinted tissues could be used as realistic models for testing novel medications or assisting people in need of replacement tissues following damage or disease. The ability to freeze bioprinted tissues for an extended period of time will allow for greater collaboration among researchers in the development of these applications, as well as extended storage for usage in preclinical and clinical settings.