Artificial organs promise to end the scarcity of human organs for transplants and also to make those transplants safer and easier to perform. In fact, the technology promises to turn them into routine procedures, rather than major operations with recovery periods lasting up to several years.
This simple and powerful promise belies the long and difficult journey of discovery that has led us to the present point. Since the BBC reported on artificial organs in 2012, there has actually been much less progress than we could have hoped for.
“A good way to think about it is that there are four levels of complexity,” says Anthony Atala from the Wake Forest Institute for Regenerative Medicine, one of the leaders of the field. “The first level includes flat organs like skin, which comprise just a few types of cells. Next up are tubes, like windpipes or blood vessels, with slightly more complex shapes and more varied collections of cells. The third level includes hollow sac-like organs, like the bladder or stomach. Unlike the tubes, which just act as pipes for fluid, these organs have to perform on demand – secreting, expanding or filtering as the situation arises.”
It is the fourth level that presents the greatest challenge: solid organs like the kidneys, heart, lungs and liver. They are thicker than most of the other organs, and each has a complicated architecture, featuring many different types of cells and an extensive network of blood vessels to provide them with oxygen and nutrients.
So far transplants of organs in the first three levels of the hierarchy have been performed successfully. On the first level: artificial skin was invented in the 1970s and has been perfected since then, according to IFL Science.
On the second level, a fully lab-grown stem cell bladder was grown and implanted in 2006, according to The Lancet.
And on the third, a trachea was implanted for the first time in 2012.
We have seen a slowdown since then because progress on the fourth level has proved tricky. Incorporating blood vessels into growing organs, especially at the microscopic scale required, is particularly difficult. For organs like the heart, which needs to have nerves as well as nutrients connecting the cells together, the problem becomes very complex.
This week an artificial sting ray was built to try to tackle the problems of building an artificial heart in a much less high-stakes environment.
“It turns out the musculature in the stingray has to do the same thing as the heart does: it has to move fluids,” said lead researcher, Prof Kevin Kit Parker of Harvard University, U.S.
The team built a robotic prototype, which contains a gold skeleton and a single layer of 200,000 cardiac cells wrapped in a gel-like material similar to the gel used for breast implants. The robot’s cells were genetically engineered to react to light. The researchers used pulses of light to control the contraction of the cells.
While the mechanics of the robot are fascinating in their own right, the robot’s heart is a fraction of the size of what one built using traditional methods would be, reports Popular Mechanics. The biggest breakthroughs come from the simplification of the control structures. Each light pulse creates a cascade of calcium waves in the cells causing them to contract. A muscle “circuit” was created by the silicone the heart cells grew in. This meant that the motion could be controlled precisely without the need for nerve cells anywhere in the sting ray. This idea was taken from simpler organisms like jelly fish which manage quite complex motions without a nervous system of any kind.
The team sees all this as a stepping stone to fully-functioning complex organs. Parker’s end goal is “to build replacement organs for sick kids,” he said. The team still has a few hurdles to surmount before that could happen. For example, Parker’s “living robot” needs to be kept in a salt-sugar solution warmed to the internal temperature of a rat, to sustain the muscle cells. “For me this was just a training exercise,” Parker told Science magazine. “I’m trying to get better and better at building muscular pumps. We’re already looking at building a robot based off another marine life-form to test our skill set a bit more.”
[Photo by Christopher Furlong/Getty Images]