Back in 2007, a Missouri professor printed out several types of chicken heart cells onto large sheets using a support gel to keep them in place. When the cells eventually arranged themselves and began beating, it ignited a race to print the first fully functioning human organ.
Since then, researchers have printed all sorts of human tissue: living human kidneys and livers, albeit miniature in size; the first ever artificial cells of a beating human heart; and part of a kidney that survived in vitro for two weeks. Both the heart cells and the kidney tissue were remarkable for the complexity of the tissues recreated—the kidney tissue, for example, was made up of three different kinds of cells, a step towards creating even more complex tissues and eventually entire organs.
Using a 3D-printer, researchers “print” organs by using live cells as “ink” and layering them in a precise pattern, leaving them space to grow into fully formed organs. Set enough ear cells in approximately the right shape to make an ear and eventually, theoretically, you’ll get one. Think of it like a very complicated game of connect-the-dots.
But living tissue is complex. Until now, tissue that was 3D printed usually died pretty quickly. Existing 3D printers couldn’t create structures that were big enough or strong enough to support the tissue; it turns out it’s tricky to get the soft, water-based gel embedded with cells to stay in place. The idea of placing individual human cells in a precise pattern to replace a damaged jaw, missing ear or scarred heart muscle holds much promise. But the field has been limited by the huge challenge of keeping the cells alive - they become starved of oxygen and nutrients in tissues thicker than 0.2 millimetres.
The researchers at Wake Forest believe they have solved that problem. Their printing process includes a bio-degradable, plastic-like material that provides a strong, temporary outer structure to support the cells as they grow into formation. Researchers also optimized the “ink” that holds the cells with a latticework of tiny channels to allow nutrients and oxygen from the body to flow to the printed organ and keep it alive until it begins to form its own blood vessels.
According to Dr. Anthony Atala, the director of the Wake Forest Institute for Regenerative Medicine, the new printer could fabricate stable, human-scale tissue of any size or shape, using CT and MRI scans to create custom organs. “With further development,” Atala said in a statement, “this technology could potentially be used to print living tissue and organ structures for surgical implantation.”
According to the Wake Forest researchers’ paper in Nature Biotechnology, they successfully printed ear, bone and muscle structures and then implanted them under the skin of mice and rats. Two months later, the ears had kept their shape and formed cartilage tissue. For the muscle, the researchers found that just a few weeks after surgery, the muscle implant had prompted nerve formation in rats. The bone implants, which were printed using human stem cells triggered the formation of a blood vessel system that was observable after five months: a new jaw bone implanted in a rat formed bone tissue.
Connecting 3D-printed tissue to working blood vessels in the body may be the most significant step yet toward the creation of functional artificial organs for humans. It means that artificial organs that could survive long term in the body are technologically feasible. The researchers told the Gulf News that their next step is to print more complex organs.
This month, after a Russian company successfully transplanted a working thyroid gland onto a mouse, the company’s CEO remarked that fully-printed organs may be as few as 15 years away.
But 3D-printed organs aren’t quite ready for human transplant. For one, the parts need to be monitored longer, to make sure they do not eventually die or decay and to see how well they perform in the body over time.
The promise of 3D printing isn’t just creating a new liver for that person who has been waiting for one for years on the national transplant list. It’s creating tailor-made organs the right size and shape for a person’s body, grown from a person’s own cells so that the body doesn’t reject it.
Researchers at Wake Forest Institute for Regenerative Medicine report they kept a baby-sized ear alive on a mouse for two months. And the ear didn’t just survive—it formed new cartilage tissue and blood vessels, signs of a successful integration with the mouse’s body.
3D printing allows for the layer-by-layer construction of a particular organ structure to form a cell scaffold. This can be followed by the process of cell seeding, in which cells of interest are pipetted directly onto the scaffold structure. Additionally, the process of integrating cells into the printable material itself, instead of performing seeding afterwards, has been explored.
Surgeon Anthony Atala has demonstrated an early-stage experiment that could someday solve the organ-donor problem: a 3D printer that uses living cells to output a transplantable kidney. Using similar technology, Dr. Atala's young patient Luke Massella received an engineered bladder 10 years ago;
Experts describe the technology, developed in the US, as a "goose that really does lay golden eggs".