If you were an inquisitive child, as many of us were, you may at some point have come across the humble lizard. If you’d tried to catch the little guy it would have come as a surprise when the lizard dropped his twitching tail and made a getaway.
This is an ability known as “autotomy” – when a creature casts off a body part on purpose. While that’s pretty amazing, the real magic happens when the lizard grows its tail back.
Look at this time lapse of a leopard gecko regrowing a dropped tail:
Pretty amazing right? Of course, lizards are far from the only animals that can regrow lost limbs. Spiders and insects also exhibit this ability, as well as some fish. So why do humans and other mammals lack this ability? This is a question that has garnered interest from biologists and medical researchers for a long time. Most mammals have limited and rather primitive regeneration in comparison. But imagine a world where you could regrow your limbs or missing organs; where losing a limb goes from a lifelong disability to a few weeks or months of discomfort. That’s the promise of regenerative medicine – you can be put back to either the way you were, or the way you were meant to be.
Why Can’t We Do It?
Before scientists can hope to figure out how to get humans to regenerate, they have to understand why we can’t. OK, it’s not strictly true that we can’t regenerate part of our body. Skin, for example, will grow back if you don’t lose too much of it. But the regenerated skin is incomplete. It lacks follicles, sweat glands, and other complex microstructures that your original skin had. That’s why we get those smooth patches of skin after burn wounds heal.
The spiny mouse, which, if you didn’t know, is a mammal, does a much better job of growing skin back. The new skin (which it sheds as a defense mechanism) grows back with all that fine detail intact. There’s barely any scarring at all. Scientists are clearly very interested in the genes that allow this mouse pull of the regeneration trick, in the hope that those genes can be used in humans as well.
Humans and other mammals also regenerate small structures pretty well. Veins, muscle, blood, and various other parts are renewed and come out just fine. Cut off a person’s arm however, and the best you can hope for is that the wound site closes up. Cut off a newt’s leg and 90 days later it has a fully-functional new one.
It seems that the larger and more complex an animal is, the less impressive its regeneration abilities are. Even in regenerating animals, the regenerated parts are often imperfect. That regrown lizard tail doesn’t have real vertebra in it. New insect legs may be misshapen and smaller than they should be. Colors don’t match up, and so on.
No one knows for sure why humans can’t regenerate. Some think it may be because of our fast, warm-blooded metabolism or that we are more prone to cancers. All we know is that the regeneration lottery in nature has not favored us.
One way that we could leverage the regenerative abilities of animals is by engineering our own genes with theirs. Obviously, this means that we need to understand and identify those genes in a lab. Salamanders are prime candidates because they can grow back whole limbs and yet they have bones, muscles, and a general body structure similar to ours. The thing is, their DNA has ten times the information human DNA does. The bad news is that it takes a salamander months to grow stuff back, which makes for long experimental cycles.
Regenerating Outside the Body
Another interesting idea is the regeneration of damaged organs outside the body. For example, there now exists a machine that can keep donor lungs alive for up to six hours.
During that time damage to the lungs can be repaired, and special conditioning for transplantation can be performed. This means that lungs which would otherwise have been thrown away can now be used. It’s not too far-fetched to theorize that at some point in the future we could keep a patient in a coma and, while he was on a blood oxygenation machine, take out his lungs so they can be repaired or treated. This would also be a patch towards cloning organs and keeping them alive for transplantation.
The Cloning Option
One way to overcome all this complicated stuff is to grow cloned organs and limbs completely separate from our bodies. Then we just have to transplant them as we do currently with donor organs. The difference, of course, would be that there’s no need for immune suppressing medication which, as you might imagine, comes with severe risks. There are even suggestions that one could clone a headless, or at least brainless, body to be kept for spare parts, although that’s pushing the term “regenerative”.
The Printer Option
3D printers have already revolutionized medicine in many ways, but they also have the potential to enable regenerative treatments. Solid organs are complex and we don’t yet know how to grow them, but what if you could use a 3D printer to actually build the structure of the kidney and then infuse it with kidney cells? That’s exactly what Dr. Anthony Atala’s research is aimed at doing. You can see the amazing prototype work here in this TED Talk.
The Nanobot Option
Nanobots are hypothetical robots that are built on a cellular scale or smaller. In theory, these little guys could be injected into your body, where they can execute programming aimed at regenerating lost organs or limbs. No one knows exactly how this will work, but presumably they could build up a new arm one cell at a time.
The Drug Option
The last option I’ll mention is that of drugs. One day it may be possible to take a pill or rub on a cream that triggers regeneration. This depends on whether latent regeneration abilities can be triggered – scientists have already been able to turn skin cells into other types of cells using chemicals, so it’s not off the table.
Like Wolverine, but Slower
The X-Men character Wolverine is a great fictional example of what we may one day have in our tool chests. When he gets cut or otherwise injured, he almost immediately recovers from the damage. With the gamut of regenerative methods we’ll have in the future, we won’t all be quite like Wolverine, but we’ll be close enough.