You can get by with only one kidney or one lung. You can live without a spleen, and you absolutely don’t need your appendix. Livers are so good at regeneration they can be cut in half and grow back. But your heart, that’s a much different story. You only have one, you can’t do without it, and it’s not great at regeneration. It’s not easy to get to either, sitting behind layers of protection inside the body. There is, of course, good reason for that protection, but these factors make it tough to study the heart. Given that heart disease remains the leading cause of death in the U.S. – though cancer could soon surpass it – better study of the heart is of vital importance. In the last few years, breakthroughs in making 3D-printed hearts have helped that study immensely.
True to Life
First up in a string of recent breakthroughs for 3D-printed hearts was a full-size model from Adam Feinberg and his team at Carnegie Mellon University in 2020. They used a technique they call Freeform Embedding of Suspended Hydrogels (FRESH), which uses a purpose-built 3D printer and a natural polymer called alginate that behaves like actual heart tissue. The FRESH technique involves injecting bioink into soft hydrogel, then melting the hydrogel once the ink is set.
“We can now build a model that not only allows for visual planning, but allows for physical practice,” Feinberg told Carnegie Mellon’s news division. “The surgeon can manipulate it and have it actually respond like real tissue, so that when they get into the operating site they’ve got an additional layer of realistic practice in that setting.”
Making a life-size model of the human heart was a real challenge, which was why Feinberg and his team ended up needing to build their own printer. The size and lifelike qualities of the 3D-printed hearts allow researchers to test operations they might one day perform on real hearts.
“While major hurdles still exist in bioprinting a full-sized functional human heart, we are proud to help establish its foundational groundwork using the FRESH platform while showing immediate applications for realistic surgical simulation,” said Eman Mirdamadi, lead author on the paper the team published in ACS Biomaterials Science and Engineering.
Eventually, Feinberg and his team hope to add cells from real heart muscle to make their models beat. They’ve already 3D-printed a coronary artery that pumped fake blood without spilling a drop. Feinberg told Wired that possibly by 2030 researchers will be able to make fully functional bioprinted organs.
Last spring, a project led by Boston University researchers successfully made a miniature replica of the human heart using heart cells derived from stem cells and small 3D-printed acrylic parts. The cardiac miniaturized Precision-enabled Unidirectional Microfluidic Pump, aka the miniPUMP, does beat on its own thanks to the live cardiomyocyte cells researchers inject into the models.
They purposely made the miniPUMP small (3 square centimeters) to ensure the acrylic scaffolds they used would be strong and flexible. Two-photo direct laser writing makes the scaffolds for the 3D-printed hearts, which the researchers hope will make it easier to study how the heart works and how particular diseases and medications affect it.
“We can study disease progression in a way that hasn’t been possible before,” Alice White, a Boston University College of Engineering professor, told 3D Printing Industry. “We chose to work on heart tissue because of its particularly complicated mechanics, but we showed that, when you take nanotechnology and marry it with tissue engineering, there’s potential for replicating this for multiple organs.”
The hope is the miniPUMP structure might lead to patches that surgeons can implant in hearts and other organs to correct defects. The larger CELL-MET project, of which the miniPUMP team is a part, has its sights set on regenerating heart tissue.
Printing Cardiac Tissue
Last June, a couple of months after the Boston University announcement, the Harvard Wyss Institute for Biologically Inspired Engineering revealed a team there had used a cardiomyocyte bioink derived from stem cells to print sheets of cardiac tissue that mimic the contracting elements of the heart. Jennifer Lewis’ team used their Sacrificial Writing in Functional Tissue (SWIFT) 3D bioprinting platform to produce the cardiac tissue. They hope to someday make it thick enough for use in regenerative heart treatments.
“Being able to effectively mimic the alignment of the heart’s contractile system across its entire hierarchy from individual cells to thicker cardiac tissue composed of multiple layers is central to generating functional heart tissue for replacement therapy,” Lewis said.
Like the Boston University team, the Wyss Institute scientists want to create patches that could replace scar tissue after heart attacks or patch holes in the hearts of newborns with congenital heart defects. The patches could even grow with the children as they age so they wouldn’t need replacements when they get bigger, the team hopes.
“One innovation at a time, we are moving closer and closer to engineering functional cardiac tissues for repair or replacement,” Sebastien Uzel, co-author of the study published in Advanced Materials, said.
And one innovation at a time, 3D-printed hearts and tissue are leading the fight against the most deadly disease known to humanity.