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Supposing that we can create an entire synthetic being, what material would be best to make its bones of attending to:

  • Weight
  • Strength
  • Durability
  • Reparability

Let's set some scenarios:

Case 1:

The synthetic being is an animal that should be able to reproduce and grow, so it must be able to process food into "bone" material.

The food could be part of another synthetic animal or plant... (in that case the second one must be able to produce it from the current Earth ecosystem)

I'm especially interested in the weight/strength ratio in order to make the biggest flying animal posible.

Case 2:

Replacement for human body, this is done when the original body is not functional (consciousness is "moved" to the new body) any needed nutrient to repair tissues is provided in its refined form but the organism must be able to use it in a reasonable way (heat a metal to 800 degrees is not reasonable)

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    $\begingroup$ It is important to remember bone is not made of a single material, it is a composite made from several each with their own properties. That composites composition also varies from bone to bone to change the properties and achieve different purposes. Springy antlers vs super hard ear bones for instance. So the question is what materials plural can be used. $\endgroup$ – John Dec 21 '16 at 19:11
  • $\begingroup$ pound for pound bone has a better strength to weight ratio than mild steel. and is more elastic to boot. Read more on bone properties here. springer.com/cda/content/document/cda_downloaddocument/… $\endgroup$ – John Dec 21 '16 at 19:32
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    $\begingroup$ @ThomBlairIII anything plausible is fine, as in my second example things like melting a metal don't seem too life-friendly, but any other process that a organism can do without need an absurd quantity of energy, blow up itself etc.. is fine, and no, isn't need that it based on current technology. $\endgroup$ – Westside Tony Dec 22 '16 at 9:23
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    $\begingroup$ @WestsideTony, organisms can however dissolve and deposit metal quite well. Beaver even have iron reinforced teeth. $\endgroup$ – John Dec 22 '16 at 21:00
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    $\begingroup$ When the MythBusters rebuilt their crash test dummy "Buster," they would up making his bones from poplar. $\endgroup$ – cobaltduck Dec 22 '16 at 21:44
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There are a number of ultra-lightweight, ultra-strong materials that would be excellent for bones, if cells can be engineered to grow them:

  • Ultralight Ceramic Solid Metamaterial: New materials developed by a MIT/LLNL team are as light as aerogel, yet 10,000 times stronger. They aren't aerogels though, but are metamaterials. That is, artificial materials with properties that aren't found in nature. The idea is to structure it so that it has the lightness of aerogel, but is much stronger:

    "These lightweight materials can withstand a load of at least 160,000 times their own weight," said LLNL Engineer Xiaoyu "Rayne" Zheng. "The key to this ultrahigh stiffness is that all the micro-structural elements in this material are designed to be over constrained and do not bend under applied load."

    The team sees the materials as one day being used to develop parts and components for aircraft, motor cars, and space vehicles, and that in practical use, the material could end up being 100 times stronger than the experimental versions.

  • Magnesium Nano-Composite: Researchers from UCLA have created a new kind of metal composite made from magnesium infused with silicon carbide nanoparticles, and it’s both lightweight and super-strong. In a series of tests, the researchers have shown that, compared to materials with a similar density, it demonstrates ‘record levels’ of stiffness-to-weight ratio and strength-to-weight ratio. The team behind the new material reckons it could be used in aerospace applications, where high strength and light weight are qualities of choice. There’s no suggestion as to how expensive the nano-composite will prove, but the team does claim the manufacturing technique is ‘scaleable.’

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  • $\begingroup$ As far as I know aerogels are produced using supercritical CO2 to extract the liquids they're made in because their surface tension destroys them when trying to remove them in order to get their characteristic light weight. That might limit the posibility to produce it in a body. $\endgroup$ – Christoph Dec 22 '16 at 10:26
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    $\begingroup$ @Christoph I read that it should be possible with a slow solvent replacement as well (i.e., going from a solvent with high surface tension to one with slightly lower, then to one with yet lower, etc), but the aerographene in the example by Thom is not an actual aerogel. Thus, in theory, it could be made to either self assemble or one could find an ezymatic way to produce it in cells. $\endgroup$ – Mrkvička Dec 22 '16 at 20:55
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The problem with most suggestions for advanced materials is whether they could be grown and repaired by a biological system. Many are not at all biologically compatible: embedded in a body they corrode or cause inflammation or other adverse immune responses. We can make bone replacement implants from titanium and certain ceramics. Our biology tolerates these but cannot maintain them, and more surgery is needed when they wear out. Much medical research is directed at how to create a temporary framework that can be seeded with bone cells and implanted, to grow into natural bone with ultimate metabolism and elimination of the framework.

Bone, as already mentioned by others, is comparable to.mild steel for its strength to weight ratio. It is also a living tissue, continually repairing itself so that micro cracks do not propagate into fractures (c.f. metal fatigue!) It can grow, repair after severe damage, strengthen in response to repeated heavy stress. Hundreds of millions of years of evolution may have produced the optimal skeleton.

What about plants? Different requirement, different solution. Wood. Cellulose fibers bonded with lignin. Again, can be extremely strong. Now we have artificial glues to match lignin, we can re-form wood into "glulam" beams, which are pretty much the equal of structural steel. Interestingly heartwood is not living tissue. A tree protects it from external attack with a skin of living tissue, but in most mature trees it is rotting in the centre. Which does not matter to the tree, or which may even be of benefit. A cylinder is as strong as a solid trunk. As the core of the trunk rots, nutrients that were locked up in the heartwood are released back to the tree's roots. Droppings from creatures that take up residence in the trunk provide more nutrition. Eventually of course rot gets the upper hand and the tree dies if it cannot regrow from its roots. Death is part of nature's plan.

Insect exoskeletons and fungi use chitin, yet another remarkable biological material, though one better suited to small elastic structures than large ones.

In short, I think it likely that the materials evolved for skeletons cannot be bettered by purely biocompatible processes.

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I think the material matters less than the process by which it is assembled. The concept of a growing creature implies that this thing is able to absorb "fuel" of some sort, and slowly add it to various regions of itself, in a certain configuration and format.

I would argue that nothing short of nano-technology can accomplish this. And if we're dealing with nano-tech, then they might arguably be able to tear the "fuel" apart at the molecular level, and glue the needed material to its bones atom by atom.

At that point the bones could be made out of practically anything.

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    $\begingroup$ I believe by synthetic biology Westside Tony means he wants an organic creature, composed of cells with DNA, proteins, etc. but synthetic in origin, so man-made. $\endgroup$ – Mike Nichols Dec 21 '16 at 18:55
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    $\begingroup$ @mikenichols - but at that point the creature's bones could be made out of you know .. regular bone. $\endgroup$ – AndreiROM Dec 21 '16 at 18:57
  • $\begingroup$ Yes, but Tony wants a "better material" than bone. $\endgroup$ – Mike Nichols Dec 21 '16 at 18:58
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    $\begingroup$ @mikenichols - at which point you get into crazier materials, hence my interpretation that this "synthetic" creature be a blend of very advanced tech and biology :) $\endgroup$ – AndreiROM Dec 21 '16 at 19:00
  • $\begingroup$ I don't think you require nanotechnology to produce exotic bones. I suppose it depends on your definition of nanotechnology, but I believe you could create exotic bones with just synthetic biological processes. But yes, I agree with your conclusion that the bone could be made out of anything. However, I don’t think that invalidates the question. $\endgroup$ – Mike Nichols Dec 21 '16 at 19:13
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Carbon nano-tubes.

Satisfies Case 1 by nature of this being a carbon based planet. As a result, there would be some level of carbon available to be synthesized into replacement 'bone' material (given that the species bodies are adapted to undergo such synthesis).

Satisfies Case 2 somewhat because (if I'm understanding correctly) carbon nano-tube 'bones' could be replicated on a case by case basis, bespoke to the individual.

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