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Question: does a liquid or gelatinous substance exist that once outside a body could solidify and be hard enough to be used once as a tool?

The setting is low fantasy without magic, yet with creatures that went down a different path in evolution due to hard environmental pressure.

What I want to achieve

I want a creature to be able to make impromptu tools with materials from inside their body. The solidifying process should start once excreted and be done in seconds or minutes, hours would kill my intentions. They result does not need to be durable, a single use is enough. Basically a biological prototype 3d printer with limited use.

Is that possible without making up some fantasy substance/material? I looked into crystals and solidification but didn't find anything convincing. Sadly they take way too long to form.

If such a substance exists it would be nice if you could state whether there are conditions that need to be met like pressure, heat/cold/electricity or some kind of material that the creature must ingest. The creature can have some special attributes in order to meet these conditions but this is for me to handle.

Im kinda worried that such a solidifying process would generate heat or somewhat pain but im not knowledgeable in this field.

EDIT: Mixing two substances or adding another external factor to harden is a legit approach. Most important is the hardening speed as it needs to be solid in seconds. The result can be crude and only useable once. Fine Detail is not needed. This process would not replace the normal way of making objects, but help in special situations.

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    $\begingroup$ Could you define "tool" and "durable"? A hammer that you might use to crack open shellfish is a bit different from an axe you might use to fell a tree, for example. Are fine details needed, like the tips of jeweller's screwdrivers, or is coarse stuff sufficient? $\endgroup$
    – Starfish Prime
    Jan 7, 2020 at 12:16
  • $\begingroup$ Human blood can solidify in a matter of minutes to form clots and scabs. Maybe your creatures have a more advance form of that? $\endgroup$
    – alexgbelov
    Jan 7, 2020 at 22:12
  • $\begingroup$ Have you read Niven and Poole's "The Mote in Gods Eye"? Some of the aliens in it can do something similar, but we aren't really given any sort of biological explanation as to how they do it. $\endgroup$
    – Salda007
    Jan 8, 2020 at 5:49
  • $\begingroup$ @StarfishPrime Durable only as much as a 3d printed plastik. You could hit and hurt somebody with a plastik sword but it would break in the process. Thats enough for my purpose. $\endgroup$
    – TinyTinkerWorkshop
    Jan 8, 2020 at 7:55
  • $\begingroup$ @alexgbelov could blood in any process harden as much to form an object? Sounds kinda unplausible for me. Im open to the idea itself. $\endgroup$
    – TinyTinkerWorkshop
    Jan 8, 2020 at 7:57

13 Answers 13

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I expect a two-component epoxy resin will work best, like two-component glue that hardens quickly when mixed, or the material used to make light boats float when capsized.

When kept separate, both components are liquid, but once mixed, they quickly harden. Thiols react quickly with epoxides at room temperature and might be the answer you are looking for, though you should consider the toxicity of exopy.

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  • $\begingroup$ note epoxies are only gong to give you a rough shape, since you need to shape a biological container for it to form in. For instance you'll never make a sharp blade this way. $\endgroup$
    – John
    Jan 7, 2020 at 13:32
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    $\begingroup$ layer-paiting also helps the mixing of resin and hardner as and allows the use of much more 'aggressive' hardners to speed up the building of the tool. $\endgroup$
    – Borgh
    Jan 7, 2020 at 15:18
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    $\begingroup$ Or exude a single compound and harden via radiative exposure as is done with our UV-curing resins . $\endgroup$
    – Carl Witthoft
    Jan 7, 2020 at 16:26
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    $\begingroup$ I like this answer. I added another answer that tackles the “need a mold for the resin to set into” challenge. If you like the combo, feel free to incorporate my answer into yours. $\endgroup$
    – SRM
    Jan 8, 2020 at 6:24
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    $\begingroup$ @TinyTinkerWorkshop hardening time can vary from a few seconds to a few minutes depending on the exact epoxies used. You can also mix different amount of the hardening catalyst. Too much catalyst can make hardening near-instant but create cracking. Go to a hardware store and pick up a couple brands to play with. Look for “casting acrylic”. $\endgroup$
    – SRM
    Jan 8, 2020 at 15:24
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Spider silk might be useful. Although usually associated with thread structures there is no reason why it should not be wound or otherwise deposited into other shapes. Spider silk comes in a wide variety of types with various properties It can be sticky or not and some silk has exceptional strength.

But whatever organism produced it would have to have the capacity to store a large amount of it for such uses.

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    $\begingroup$ If capacity is the only worry, perhaps you could do some GMO shenanigans to transfer the spider silk genes into some larger creature (and while we're at, add friction pads for fingers, boost the base strength, cure myopia and maybe even some fancy skin coloration) $\endgroup$
    – John Dvorak
    Jan 8, 2020 at 5:55
  • $\begingroup$ If we are talking about a protection mechanism this would be totally viable but im kinda suspicious if you could somehow make spider silk into something like a hammer or dagger. $\endgroup$
    – TinyTinkerWorkshop
    Jan 8, 2020 at 8:03
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Spider Silk + Resins

Many different tree resins will polymerize upon drying and are used to make adhesives and varnishes. Combine something like that with a large number of spider-like spinnerets and you have the makings of a biological equivalent of carbon-fiber. Not necessarily the best if you want to make a hammer, but you could always incorporate a convenient rock or other found material to add some density to it.

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  • $\begingroup$ How long does the drying process take? The speed would directly influence the ability to shape the object. $\endgroup$
    – TinyTinkerWorkshop
    Jan 8, 2020 at 8:21
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    $\begingroup$ I think most resins or varnishes are typically on the "minutes to hours" level, but it depends on what point you want it to get to -- something might be usable well before it's fully cured. And if you're talking alien biology then you could certainly have something that cures faster. They might even be able to manipulate the concentrations of the resin they produce in order to adjust the curing time or other properties. $\endgroup$
    – Salda007
    Jan 8, 2020 at 9:09
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There isn't one, the problem is you are not just looking for a fast phase change, but a fast phase change in a controlled manner.

There are a lot of ways to make a material quickly there are far fewer ways to shape said material. No matter what you use you are still limited by how fast the material can be produced and moved, a biological system cannot produce significant quantities of material quickly. Even using epoxies you get one tool from stored material then have to wait days for the next.

On top of that the faster you want it to form the cruder and less precise you can make the tools, an epoxy cast in a shapeable sack in the body is just going to be a lump in the rough shape of a tool, if you use precision deposition to get a precise shape you are back to taking hours to days because you are limited by cell migration speed. You could use a lattice of specialized epoxy filled cells but it will flimsy and take forever to regenerate. Making a solid mass is easy making a controlled shape is hard.

worse the caloric cost of such an enterprise makes it so it can't evolve since it uses vastly more calories than you can harvest from a single tool in the short term. this is why using manufactured tools is so favorable, very small caloric investment.

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    $\begingroup$ OTOH if you posit an extruder organ, then you have a biological 3-D FDM printer. That might be at least plausible to the reader. $\endgroup$
    – Carl Witthoft
    Jan 7, 2020 at 16:24
  • $\begingroup$ @CarlWitthoft you are still talking about tens of minutes to hours to make something. $\endgroup$
    – John
    Jan 7, 2020 at 16:38
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    $\begingroup$ calories may not be an issue if you can eat it when you are done (like spider's eat their damaged webs) $\endgroup$
    – Nosajimiki
    Jan 7, 2020 at 19:30
  • $\begingroup$ @Nosajimiki-ReinstateMonica true but if it is weak enough you can chew it up and eat it it is going to function poorly for many tools. Spidersilk works because is has very high surface area and can be dissolved in the stomach acid. $\endgroup$
    – John
    Jan 7, 2020 at 20:17
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    $\begingroup$ @CarlF still involves a phase transition link.springer.com/article/10.1007%2FBF00729372 and sciencedirect.com/book/9780444519115/… $\endgroup$
    – John
    Jan 9, 2020 at 22:25
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This is like an answer and like a comment on all the other answers. I specifically want to address the shaping challenge.

The creature’s ability to naturally spit resin is probably an offensive talent, meant to spit in the face of opponents and prey. That likely means that the carapace has evolved to be non-stick to the same resin. Or the carapace can secrete an oil as needed to keep it from sticking. This makes it a great mold substance.

You need a form factor for the epoxy or resin to harden inside if you want to create tools. Why not have the creature use its own carapace? Suppose your creature has body armor. As they became civilized, there’s less need to maintain the armor to be combat ready. So they can carve shapes into it. You can make a reasonable hammer shape on a thigh. You could make a blade shape on a forearm. A fixed-length ruler, or even parts for a slide rule on the other arm. If you drill sideways into the carapace, you could create shafts that allow for spikes, nails (like for setting up a tent).

The carvings are like tattoos. The creature has to have picked their tools over lifetime.

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  • $\begingroup$ I really like where you are going. It may not suitable for one of my characters but a species with some deep lore in the world. Thank you. $\endgroup$
    – TinyTinkerWorkshop
    Jan 8, 2020 at 8:14
  • $\begingroup$ I especially like the idea that the carvings are like tattoos, they take on a significance beyond the practical, and become part of the being's personal history. $\endgroup$
    – barbecue
    Jan 8, 2020 at 14:13
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For a number of reasons described in the other answers, I think you'll have a hard time coming up with a solely biological process that accomplishes this. If you expand the requirements a bit, though, you'll have a lot more options.

Instead of placing the onus on the creature's biological systems, incorporate the environment as well. For instance, the creature could produce a fluid that when mixed with sand and kneaded together, causes it to set up and harden like a cement (some insects build nests this way). Or, if it produced a sufficiently acidic substance, it could use that to dissolve/etch certain minerals (like limestone) to shape them into tools. In these sorts of cases, most of the mass of the tools comes from the environment. Your creature only has to produce the reagent necessary to convert the raw materials into something sufficiently tool-like.

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  • $\begingroup$ That is actually a good idea, I like it. I want to keep the substance in body part but using something external to mix would be ok. Do you have some specific examples with information about hardness and how long the hardening takes? $\endgroup$
    – TinyTinkerWorkshop
    Jan 8, 2020 at 8:11
  • $\begingroup$ @TinyTinkerWorkshop "Hardness" is a very broad concept that can mean many different things. Something can be extremely "hard" and be brittle (diamonds), or can absorb lots of force in one direction but very little in another (paper). What type of tools are you talking about making? Knowing what sorts of forces they will endure will help determine what type of material you need. $\endgroup$
    – bta
    Jan 8, 2020 at 21:47
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Epoxy resins and glues often start to polymerize when exposed to outside moisture, while they stay liquid as long as they are in their tube protected from water molecules.

Yes, their reaction is exothermal, else it won't spontaneously happen.

If you ever left a glue tube open, you know that they turn pretty quickly into a solid.

The reaction rate can be tuned by adding proper addictive: when you glue two parts together you don't want to hold them pressed for hours, nor you want the glue to become so hot that it damages the parts.

If you ever spilled some rapid glue on your finger as a kid, you probably remember that it took seconds to set and that you could feel some warmth, but you got no burns.

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  • $\begingroup$ Could you give more details? Im not really knowledgeable in chemistry so here come some stupid questions: can you speed up the process with more moisture/water? What would the time span to harden be? Would mixing with water or another fluid to speed up the process be an option? How hot is the reaction? Im expecting some serious wounds. $\endgroup$
    – TinyTinkerWorkshop
    Jan 8, 2020 at 8:18
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The resin that dentists use for "white" fillings might be regarded as a proof of concept. For the dentist's convenience, this resin remains soft until setting is catalyzed by blue laser light. It is also anti-catalyzed by oxygen, so a thin surface film of a few molecules always remains un-set. This is so another layer of resin can be placed on top (thereby excluding oxygen) and the layers bonded together by the laser. It's hard and tough enough to be used as a tooth for decades.

So all that is needed is to replace the blue-light catalyst with a chemical catalyst added at the time the material is excreted. Or perhaps a greater degree of photo-sensitivity, and the creature can only use this excretion on a sunny day.

A hundred million years of evolution might well create a better resin than a few human chemical engineers have managed in a mere few years.

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Apart from epoxy resin, that is already mentioned there's another option.

Photo sensitive resin

This is a thing that is used in experimental 3D printing (google it, it's cool). If your creature can excrete tool-shaped blob, this blob can easily solidify in sunlight. Advantage is that you only need one component, but the solidification may take longer and it won't work at night.

But the fact it doesn't work at night can be useful from storytelling perspective.

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  • $\begingroup$ I was also going to suggest UV resins, like in SLA 3D printers. It would also not work indoors, unless there was a UV light involved. You can find a bunch of brands on sites like Amazon, although finding what chemicals they are made from isn't exactly easy. I've looked, so I can make my own, and have yet to find a definitive "recipe". $\endgroup$
    – computercarguy
    Jan 8, 2020 at 18:51
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Gallium is completely liquid above 85°F, and once it's below about 75°F, it's about as hard as "cold candle wax" (according to one guy who's played with it a while). While this wouldn't be hard enough for a spike or a bolt, it could be used to make some keys and locks, gears, or bowls/plates/cups (just avoid hot soup!).

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https://en.wikipedia.org/wiki/Non-Newtonian_fluid

What you may be looking for is a non-newtonian fluid.

Most famous examples are things that go from more fluid to less fluid when under pressure as they work well as armour. They do however go in the other direction - with the ability to become more fluid under pressure; and also can work with time.

This means that if the body were to keep an amount of this non-newtonian liquid under pressure; it would remain a liquid; but on release; would become more viscous to the point of seeming like a solid.

For most of these fluids, the process is not one way; meaning that if it gets put in the same conditions again; it will return to being as viscous as it was. So while this could be used as a tool; one might not be able to use it to apply much force on anything.

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As John's answer points out: There are many issues with resin epoxies as most other answers suggest. They are very hard to shape and biologically reabsorb, this makes for major recyclability and production issues. While shaping the thing could probably be overcome, it takes a lot of calories to create a resin tool compared to picking up a sharp rock or a stick: this makes it a very unlikely adaptation to evolve unless you can eat it when you are done with it.

A better solution might be something more like ABS plastic

ABS is an organic plastic that could just as theoretically be derived from organic compounds in a 2-part epoxy like process. It's not as hard as resin epoxy, but it is still hard enough to make many types of crude tools out of. The major reason for using this softer plastic is that it can be easily shaped and dissolved by another organic compound: acetone.

Acetone can be used to shape, smooth, and mend ABS plastics https://www.youtube.com/watch?v=Pm3Yn6XKufg, https://www.youtube.com/watch?v=2YIV0XVkkPE. So, instead of trying to spit out a fully finished tool with resin, your animal could spit out a clump of ABS in the rough shape it needs, then excrete acetone to mold the plastic in its hands like clay until it is the right shape. In this manor you meet the need for quick ad hoc tools without needing molds to cast them in.

When your animal is done, it just eats the plastic using acetone rich saliva. At 0:27 in this video: https://www.youtube.com/watch?v=AM3rl1JFsuY, you can see just how quickly acetone can dissolve large ABS things, meaning your animal can recover a lot of the lost calories pretty quickly and easily just like a spider that eats its own web.

ABS is strong enough on its own to make many simple tools: wrenches, cultary, water bottles, shives, etc. In cases where your animal needs something with more heft like a hammer or chopping ability like a an axe, it would still make a good handle making material so you could just pick up the rock you need and let your spit do the rest.

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A sharp edge could be formed by first producing a round-shaped blob of an epoxy-like substance and then, once it has solidified, shattering it into pieces. Some of the pieces can have blade-like edges, so they can be used like a knife or a dagger. An abrupt change in temperature could help to break a blob of solid substance that is otherwise hard to break. E.g. the creature has a high internal body temperature but lives in an arctic region. It produces a blob of epoxy-like material inside its body and then throws in the snow, where it breaks into shards.

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