The discovery happened, as so many discoveries do, by accident.
Adam Jakus, then a postdoctoral researcher in materials science at Northwestern University, was working with the biological “ink” his lab uses to 3D print ovaries. Earlier this year, the tissue ink was successfully used to build ovaries that actually functioned, leading to the births of healthy mice pups. Standing beneath the lab’s fume hood, Jakus knocked over the container, spilling it onto the lab bench. By the time he went to clean it up, it had formed a solid sheet.
“It felt great,” Jakus said. “If you make a new biomaterial and you can’t pick it up or it falls apart when you pick it up, it’s useless.
"I had this lightbulb go off – ‘we can do this with all the other tissues we’re working with in our lab.’”
So Jakus and his colleagues set about testing his hypothesis. They deliberately spilled ink or cast it in molds to create flat sheets. They tested various kinds of bio inks, made with different organs or tissues. For organs, they turned to local butchers in Chicago, buying pig hearts, pig livers and various muscle meats. To create the inks, they ‘decellularized’ the organs or tissues, meaning they removed the cells, leaving behind the structural proteins known as the extracellular matrix. This process was already well-established from the lab's work with 3D printing. The decellularized organs were then dried to a powder and combined with a polymer, then cast into paper.
The resulting papers contain traces of the chemicals and the protein architecture of the organs they were made from. Heart papers maintain some of their "heart memory," so to speak. This means the papers have the potential to stimulate nearby cells to behave in specific ways. This could lead to a variety of uses, which several labs at Northwestern have been investigating.
A reproductive science lab at the university has been testing ovarian tissue paper to grow ovarian follicles (cells that produce eggs and hormones). The paper-grown follicles have successfully produced the correct hormones. In theory, a strip of ovarian tissue paper could be implanted under the skin of a woman who has lost hormone function due to disease or chemotherapy, potentially restoring her hormone function and her fertility.
The papers could also potentially help 3D printed ovaries make the leap from mice to humans. Mice ovaries have a sac of fat around them, which makes it easy to implant a 3D printed ovary inside a mouse body. Humans don’t have this fat sac, so implanting an ovary would be much more difficult. But tissue papers could be used to make an artificial sac to then implant a 3D printed ovary, Jakus says.
Muscle tissue papers could also help with wound healing and reconstruction.
“Plastic surgeons said they would be perfect for repair and regeneration of facial muscle,” Jakus says. “It’s thin, so it’s perfect for the flat, intricate muscles of the face.”
This could help people whose facial muscles were damaged by trauma or botched plastic surgery, Jakus says, as well as for children who were born with congenital defects of the face.
The tissue papers feel similar to phyllo dough, says study coauthor Ramille Shah, the head of the lab where Jakus had his accidental spill. When dry, they can be stacked in a refrigerator or freezer. They can even be folded many times – Jakus has folded them into tiny origami birds. When wet, the papers do not fall apart like printer paper would, but can be rolled, folded, cut and stitched.
Regenerative medicine – making new organs and tissues through 3D printing and other techniques – has been the source of much excitement over the past few years. It’s also generated some controversy, with critics wondering if its promises are oversold, as true usefulness for humans may be many years down the road.
The next step for the new papers will be more animal testing, Jakus says. He estimates that some tissue papers, especially the muscle papers, could be used in operating rooms within five years. A human use for ovary papers might take a few more years, he says. In 20 years, Jakus says he’d like to see tissue papers being used in conjunction with 3D printing technology to create complex biological structures. For example, a 3D-printed bone could be surrounded by tissue paper muscles and nerves, recreating a leg badly damaged in an accident. There’s also potential to one day use 3D printing technology and tissue papers together to make full organs for transplantation.
“Making the tissue papers was relatively easy,” Jakus says. “The hard part is really going about testing them.”
The research was published earlier this month in the journal Advanced Functional Materials.