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The Organ Trail

New advances in bioengineering will one day give us 3D-printed livers, kidneys and hearts— with impacts on pharmaceuticals, surgery and more

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The year is 2368, and Lt. Worf is paralyzed from a spinal column injury. The USS Enterprise officer would rather die than live paralyzed, so a prototype medical device called the "genitronic replicator" is brought on board in an attempt to save him. The device is programmed to create a new spinal column, which the starship's surgeons would implant. It has not yet been tested on a humanoid patient, but seems like the only way to save Worf.

This fictional scenario takes place in an episode of Star Trek: The Next Generation called "Ethics," which first aired March 2, 1992. The genitronic replicator is one of those fictional Star Trek tools that surely could never exist: a machine that scans a patient, then prints replacement body parts for implantation.

But if advances in the world of 3D bioprinting continue at their current pace, this technology will be far past the prototype stage by 2368—it will be commonplace.

The idea of "printing" a vital organ is lifesaving. Over 120,000 people are on the Organ Procurement and Transplantation Network waiting list in the United States (98,142 need kidneys and 15,839 need livers), and many more who need transplants don't qualify because of health risks, such as the risk of bodily rejection. By printing a kidney from one's own cells, the organ is more likely to be accepted by the body and thus function normally.

As recently as five years ago, experts mused on the possibility of printing internal structures like heart valves or complex systems like the pancreas, or even a complete heart, on demand and with a patient's own cells. The technology has the potential to revolutionize the way we view not only organ transplants, but drug research, cosmetic surgery and even space travel.

HOW IT WORKS

Though similar in theory, 3D bioprinting is vastly different from the 3D printing which has exploded in popularity in the past few years. Standard 3D printing uses a variety of inorganic materials (mostly plastics) to print everything from bobbleheads to handguns. One cannot simply print out a living tissue structure at home with a downloaded CAD drawing and a MakerBot home 3D printer. ("Hobby" versions of bioprinters do exist—a co-op lab called Biocurious in Sunnyvale offers one—but they're expensive and only print flat rows of cells.)

A modern 3D bioprinter looks somewhat similar to a conventional 3D printer except it's larger, has much more circuitry and uses multiple printing nozzles—one for modeling material, called "hydrogel," and others containing cells called "bioink." Early versions actually cannibalized inkjet cartridges, which were cleaned and sterilized, because human cells happen to be roughly the same size as older ink droplets (new ink cartridges are too fine for this).

Since living tissue is composed of many cell types, the different print heads expel the correct amount of a specific cell type along with the biodegradable hydrogel to hold it in place. The biogel structure creates a skeleton of sorts, called a scaffold, which degrades once the cells grow into the right shape. The trick is to find the right scaffold material that will support each different organ, promote cell growth and degrade after the right amount of time.

Because its cells regenerate on their own, the liver is a likely candidate to become the first bioprinted complex organ to be transplanted into a human. But as Wake Forest University's Institute for Regenerative Medicine director Anthony Atala tells the Bohemian, "It is really impossible to predict when this technology would be available to patients through clinical trials." He estimates it will take at least a decade, "and likely much longer."

One major hurdle scientists face is building the intricate blood vessel networks needed to keep an organ alive. "In efforts to engineer solid organs such as the kidney and liver," says Atala, "it is a challenge to incorporate the large number of cells required and to engineer a vascular system that can keep the structures alive until they integrate with the body after implantation."

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