Biology and Self-Repair

By Sean Carroll | September 19, 2011 9:29 am

I’ve been traveling like crazy, then hosting visitors, and now am laid up with a nasty cold. So not much energy for blogging. On the other hand — plenty of time for non-expert reflections on the nature of microscopic complex systems!

The thing is, I’m pretty sure that my body will eventually overcome this cold virus. That’s one of the great things about living organisms — they can, in a wide variety of circumstances, repair themselves. From fighting off germs to healing broken bones, the body is pretty darn resilient.

Which brings up something that has always worried me about nanotechnology — the fact that the tiny machines that have been heroically constructed by the scientists working in this field just seem so darn fragile. It’s amazingly impressive what modern nano-engineers can do by way of manipulating matter at the atomic and molecular level, creating new materials and tiny machines and motors. But surely one has to worry about the little buggers breaking down. My macroscopic car is also an impressive feat of engineering, but it’s no good if a crucial component breaks.

So what you really want is microscopic machinery that is robust enough to repair itself. Fortunately, this problem has already been solved at least once: it’s called “life.” Even at relatively tiny scales, living organisms are sufficiently loose and redundant to be able to fix themselves when something small goes wrong, greatly extending their useful lifespan.

This is why my utterly underinformed opinion is that the biggest advances will come not from nanotechnology, but from synthetic biology. Once we get to the point that we can truly create new organisms from scratch, not simply modifying existing stock, many of the biggest dreams of nanotech will become much more real.

Some time ago John von Neumann proposed the idea of self-replicating machines. Not everyone believed that such a thing was possible — after all, the machine would have to include blueprints for another version of itself, including the self-replication mechanism, and how do you fit a copy of a machine into itself? (You might think that living organisms are an obvious counterexample to this argument, but some people used it as an argument against the idea that organisms are “just” machines.) But von Neumann figured it out, and immediately proposed the obvious plan: sending self-replicating spacecraft to seed the galaxy.

But if the machine breaks, it defeats the whole purpose. So you really want a self-repairing self-replicating machine. Which is awfully close to a working definition of “life.” It might not be human beings who eventually fill up the galaxy, but my suspicion is that it will be life in some form or another.

CATEGORIZED UNDER: Science, Technology, Top Posts
  • Matthew Putman

    I completely agree that synthetic biology is an exciting new field, but it is actually hard for me to completely separate it from nanotechnology. I combine the two actually in a course I teach at Columbia. The idea being that there is self-repair in certain polymer systems, as well as pure biological systems, both which can serve as excellent scaffolding for synthetic systems, like replacement organs. The thing is there are some engineered materials that can assist in the natural stem cell reproduction, by adding strength, aggregation, and optical markers. These, like quantum dots, nanosize silica and even graphene should be the partners in the synthetic bio compound, not a separate discipline.

  • Jim Harrison

    Recommending books in comment threads is about as popular as broken glass in a bathtub, but I’m mentioning Andreas Wagner’s Robustness and Evolvability in Living Systems because it is so specifically on topic. Wagner is especially good in explaining why and, crucially, how, living systems manage to be resistant to breakdowns compared to rationally engineered systems.

  • FmsRse12

    I doubt that self-replicating self-repairing machines will be realised in near future…..many theories at nano scale haven’t been experimentally verified yet and there are many more where both theories and experimental results are not conclusive enough, right now I am working on a topic which has atleast three dominant theories and there are experiments and computer simulations supporting all three to some extent, and only one of them can be correct or none of them …..I mean there are issues which haven’t been resolved even with different experimental approach and simulations

  • Mark Erickson

    Um, is it okay that I wish you were sick more often? Or some other wrench in your life that makes you post more non-expert reflections? All that is to say – Awesome!

  •,html Anthony A. Aiya-Oba

    Everything is self-replication of everything (Cosmos).-Aiya-Oba (Philosopher).

  • Kernal

    Much of the body’s apparent self-repair is simply self-replication. If something breaks, just replace the broken/dead cells with brand new ones and you’re (almost) as good as new. Because of this, it’s the parts that the body cannot simply be replaced (like nerves) that result in permanent injury when damaged.

    For (nano)robots, self-replication is more important than self-repair, and probably easier. So long as enough survive to continue replication, the ability to actually repair is irrelevant. The same may not be true for macro robots simply due to the resources required to build and distribute so many (ie, when your car breaks you fix it; you don’t buy another).

  • Low Math, Meekly Interacting

    The biological example is fraught with complexity. What you want are small, simple nanobots

  • Stu Savory

    tell us about WDM vs. CDM please.

  • spyder

    I suppose, once we figure out the gene sequencing for human consciousness, we have the capacity to put that into anything we want. Current SciFi edition!

  • Greg Davidson

    Given a modular design, a long model lifetime and an unrestricted replacement parts market you can “repair” a product and keep it in mint condition by simply replacing warn-out parts. Building repair capability into most products is much less efficient than making use of external production facilities. Self-diagnostic capability is very useful so you know when it’s time to replace something. Also important is to have each component designed for easy disassembly into recyclable elements. Most of our products wear out and cannot be economically repaired because manufacturers and allied powerful interests want them to. As personal object printers aka desktop fabbers become affordable I will gradually upgrade the manufactured items in my environment to systems with modular open-source designs. Eventually we will move to nanotech for just about everything and it will work much better than engineering biological systems which are stuck with architectures that are unrelated to our needs.

  • Dorothy Gale

    At some level, you could say that self-repair does not require life. For instance, we have all (I hope!) played with crystal growing kits. It’s like having a little crystal that fixes itself and then just grows. No intelligent design here, and yet self-healing and growth. Think about it!

  • Bob Flisser

    You have the same cold I do, at the same time. Anyway, I thought the idea of nanobots was that they’re supposed to be like bugs: quantity over quality. If thousands of them are deployed for a specific task, it doesn’t matter if a few break down. Or put another way: many of them are expected to break down, which is why they should be delivered in large quantities.

  • Pingback: Cells Repairing Themselves | Cosmic Variance | Discover Magazine()

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  • Brian Too

    @6. Kernal,

    Actually biology uses both repair and replication. My understanding is that repair is heavily used at sub-cellular scales. DNA is frequently repaired for instance. However if the damage is too great and the cell dies, or is killed by the immune system, then replacement becomes the go-to option.

    Having a structure or system consisting of large numbers of identical cell types is very useful from an organism maintenance perspective.

  • Pingback: Cells Repairing Themselves | Cosmic Variance | Theoretical Physics()

  • Kumar

    Brings back memories of a failed attempt getting into this sort of work! Learning from biology and making cool molecular constructs. Fascinating to think about… but not good to write as your statement of purpose in a grad school essay 😉

  • Low Math, Meekly Interacting

    @15 I think the cellular replication paradigm is the best. If I had to bet on an approach, I’d say invent a relatively simple “cell” that can assemble with copies of itself into a variety of useful machines, including one that can manufacture more “cells”. The ensemble of cells could fly around doing interesting things, stopping periodically to reassemble into a little cell factory to replace worn out or damaged cells.


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Cosmic Variance

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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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