The Advent of 3D Bioprinting
Patients in desperate need of organ transplant certainly do not have the odds in their favor. Of the 123,000 patients currently awaiting a life-saving donation, less than one-fourth will receive one within the next year. And as that year ticks by, over 7,000 people on the rapidly-growing waitlist will pass away.
The reason behind this long wait time is more than just a lack of donors—even when organs are available for transplant, it is a tricky business to match donors to recipients. Before transplant can even be considered, doctors must perform a battery of tests to ensure that the organ is compatible with factors like the recipient’s blood type and MHC profile (a diverse class of proteins found on cell surfaces). Even when all these factors do line up, recipients still very often experience acute rejection as their immune system tries to attack the foreign object. About one in five kidney transplants will fail within 3 years, and almost half do so within 10 years. There is a new technology on the horizon, however, that shines light on the future of transplant patients: 3D bioprinting.
Most people have heard of 3D printing, a technique that has revolutionized production and design in recent years. A manufacturer loads a material, usually some type of plastic, into a machine. He selects a computer design, and the machine jumps to work, extruding melted plastic through a nozzle, layer upon layer, until a solid object is built. A 3D bioprinter works very much like this, but replace the plastic with live human cells. That’s right—the same technology that is used to print plastic toys and doorstops can be used to print functional human organs and tissues, and in a strikingly similar way.
Of course, bioprinting is considerably tougher. A toy can be constructed using a single plastic material, but a human organ is a complex interacting system with dozens of different cell types and interlinked supporting materials. But what may sound like something out of either a science-fiction universe or a young child’s imagination is already becoming a reality.
In 1999, scientists at Wake Forest 3D-printed the scaffold of a human bladder, then coated it with cells taken from patients to successfully grow working organs. In 2010, the bioprinting company Organovo printed the first fully-cellular blood vessel. In the May of 2013, doctors implanted a synthetic trachea into a six-week-old boy after he suffered from an airway collapse. And several groups already are working hard on creating the first bioprinted human heart.
But how do researchers print organs using a patient’s own cells? That is, where do they get the “bioink” for their printers? To print an organ, scientists need the right types of cells: cardiomyocytes for hearts and hepatocytes for livers, for instance. But organs are made up of more than just one type of cell—they also need an intricate network of arteries and veins to circulate blood, and structural cells to hold everything in shape. Scientists can’t just go to their patient and harvest a bit of every kind of cell they need. Rather, they make use of the patient’s stem cells—unspecialized cells that are able to differentiate into any other type of cell.
Scientists are able to harvest a bit of the patient’s skin cells, revert them back into stem cells, and chemically reprogram the stem cells into whatever type is needed. These cells can be cultured to build up a reservoir of bioink. Using computer-aided design (CAD) software, they can then build a model of an organ that would best fit the patient’s bodily architecture, and send off the design to the bioprinter. Because the resulting organ is made completely of the patient’s own cells, there is no risk of immune rejection.
There are certainly many challenges still facing this new technology. For example, scientists still have trouble printing the tiny capillaries that feed blood to organs, and as of yet have no way of printing the nerve cells required for normal tissue function. However, as research progresses and technology improves, 3D bioprinting promises to revolutionize the methodology of both medicine and research, and improve the lot of human patients everywhere.