August 05, 2010
Lost Limb Regrowth And Rejuvenation

Only read this post if you do not get queasy easily.

I was reading a brief press release about research on limb regrowth (not much there really) and a thought hit me: future biotechnology for growing new limbs could have uses for people who haven't even lost a limb. I hear you asking "how?". Here's your last chance to move on to a different post and skip the next paragraph. Really, you might not want to go where I'm going.

The really weird and creepy idea: Cut off a limb in order to grow a new younger replacement limb.

Think about it. Researchers are going to keep pursuing limb regrowth technology. Some other organisms can regrow lost limbs. This ought to be possible for humans 10 or 20 or 30 years from now. Now picture yourself in your 80s with arthritic knees, shriveled muscles, clogged arteries, drooping skin, decayed peripheral nerves, and poor blood circulation to your feet. Well, could you bear to part with your existing legs if you could young and much better legs over the period of a couple of years?

I see the period of regrowth as a big problem. The body normally takes almost 20 years to reach full size. Will future biotechnologies that instruct cells to grow a new limb have to work at a slow pace in order to avoid development gone awry? Or will it be possible to grow new limbs much more rapidly?

Share |      Randall Parker, 2010 August 05 09:52 PM  Body Repair Limbs

PacRim Jim said at August 5, 2010 10:58 PM:

Regrowing lost limbsóbig deal!
When they can take a limb and regrow the person, then I'll be awed.

My right leg said at August 5, 2010 11:37 PM:

When I read posts of yours like this or even your more general rejuvenation-related posts, I always think of fixing my right leg, which ended up about 1.5 cm shorter than the other when I broke it as a teenager. I'm probably the only one who notices the difference, and I've had rare knee pain, but the leg works very well (I've run many, many miles on it). But I've always wanted my leg to be perfect again!

Maybe I'll cut it off one day and grow a new one! But anyway, it's hard to imagine how to make it perfect otherwise, since it healed this way and has been this way for so long. Maybe some nanotechnology some day could go in there and reconstruct it in place (might need anesthesia!). Or, if we ever develop some kind of real "rejuvenation" technology, then could it be used to restore the whole physical body (including the brain!) to some kind of optimal state by processing genomic information from the individual? Just some thoughts...

Also, it may not be helpful to have a demanding, young limb attached to weak, old body.

By the way, I've been enjoying your blogs for years!

Brett Bellmore said at August 6, 2010 3:51 AM:

The technology for lengthening a short leg was developed years ago. It involves breaking the bone deliberately, and then very gradually pulling the gap apart as the bone grows into it. 1.5cm is well within it's capacity, but you'd be in a cast for months.

Anonymous said at August 6, 2010 8:25 AM:

If you are old, there are a lot of things at the wrong level in your blood and immune system. This could stop your new leg from growing properly. I would rather replace the immune system, pancreas and liver first, so you have good homeostasis and then regrow the legs.

Only regrowing the legs wouldn't help a lot unless you need knee replacement or have some very bad circulatory problems. But in that later case it is likely you'll have problems elsewhere as well.

random said at August 6, 2010 8:52 AM:

Screw cutting a limb off. I want more arms!

PacRim Jim said at August 6, 2010 9:34 AM:

If you fail to treat the body systemically--say by boosting the heart or immune system--it could very well overwhelm the body by, say, rupturing a weakened artery. The trick will be to upgrade the gestalt. (Hurry up, researchers, my gestalt is almost gestorbt.)

Bruce said at August 6, 2010 11:22 AM:

I want a 2nd heart. Young, strong.

Micah said at August 6, 2010 12:10 PM:

I thought you were going to talk about adding a third arm.

Presumably any regenerative work that could re-grow an arm could also regenerate the damage to an existing arm.

Randall Parker said at August 6, 2010 8:29 PM:


Choose a unique pseudonym or I will delete your future comments.


I certainl hope it will be possible to grow a third arm and only lop off an old arm to move the new arm to its place once the new arm is fully developed.

But if you wanted to grow a third arm to have 3 arms I'd have no objectives.

PacRim Jum,

Certainly once should first do an upgrade of the immune system, bone marrow stem cells, and other system-wide cells that affect your ability to survive.

What I'd most like: an upgrade to my immune system that would make an immune system with exceptional abilities against cancer cells

My motto: First, don't die.

My right leg,

Thank you.

I agree with Brett Bellmore: the technology already exists for limb extension. Though it would be safer to first upgrade your stem cells, especially your immune system, before undergoing limb extension.

Brett Bellmore said at August 7, 2010 4:47 AM:

Randall, I assume that last remark has to do with the 'traditional' way of limb extension, where an external frame is fixed to the bone by wires penetrating the skin, with attendant risk of infection. Just last year they tried out doing it entirely internal, by pinning the bone together with 'nails' that could have their length adjusted by external magnetic field manipulation. Why it took this long is beyond me, it's an obvious approach to any engineer.

This approach is just experimental now, in Finland, but will probably be available in the next year.

Engineer-Poet said at August 7, 2010 8:28 AM:

Speaking from experience, what's obvious to an engineer is often shockingly radical to medical practitioners.  The modes and habits of thought are very, very different.

Randall Parker said at August 7, 2010 11:35 AM:

Brett Bellmore,

Yes, I should have been more clear: Existing limbs can already be lengthened. But the process does not rejuvenate the limb or fix gross abnormalities.

I was expecting someone to say that limb amputation is just too gross to consider, even if it meant eventually getting a much younger arm or leg.

Brett Bellmore said at August 7, 2010 6:40 PM:

I'm not going to say it's too radical, given that I think we'll probably resort to head decapitation, IOW, brain transplants. But it strikes me that, absent some means of radically accelerating the regrowth, an adult limb is going to take a good percentage of a normal lifespan to regrow to full size. I've regrown fingertips on multiple occasions, (My wife says I'm way too careless!) and it took more than a month each time, to regrow just a couple of millimeters. I hate to think how long an entire adult limb would take.

Probably before your limb was even finished getting up to size, they'd be running off entire limbs on tissue printers, and transplanting them in.

cancer_man said at August 8, 2010 9:30 AM:

A leading researcher in this field (I forget her name but she was one on the group that grafted a human ear onto a mouse in the 1990s) thought that full finger regeneration was possible by 2015 and limbs by 2025.

Mark your calender....

Kralizec said at August 8, 2010 3:08 PM:

As long as we're just brainstorming, I'll suggest an analogy to the difference between traditional laser resurfacing of the skin and Fraxel (TM). It may require less "downtime" and produce better results, if one fractionally ablates and replaces tissues in a series of treatments.

Randall Parker said at August 8, 2010 4:26 PM:


I am fond of incremental approaches. Maybe that'd work. For example, does one really need replace the bones in an arm? Or can one just hollow a bone out and put in new marrow cells? Then cut back the joints and grow new joints too.

If one could take out stretches of muscle and grow new stretches in their place I wonder how long it would take to do the muscle elongation and attachment.

There's also all the blood vessels. Grow replacements along side them? Then just cut over?

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