Not really sure if this is the right place for this question... Wasn't too sure if I should start a thread on it either. Here goes nothing. It's a chemistry question (I think [edit: I guess not]). I work with different types of metal a lot at work, and every now and then, you cut yourself. My question is: Why do titanium cuts hurt so much? Of any metal I've ever been cut by, titanium hurts the most (stainless or aluminum cuts don't even compare). It stings (and burns) sorta like a paper cut (but more painful). Is it some kind of chemical reation with blood? If so, what is the nature of the reaction?

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OK, I'm no kind of chemist, so you might want to wait for a more knowledgeable answer. Still, I'm tempted to hazard a guess. I would doubt that there is any chemical reaction going on with the metal-- metals are tight lattices and so they should be able to cut you without leaving any titanium in your skin (I should think). So I wonder, could the pain be due to the lattice structure of titanium? For example, titanium is valued because it is strong even if you only have a little of it, so I'm imagining that titanium edges might be quite sharp-- the lattice could extend out to a single atom thickness and still be strong, perhaps? If so, the pain you feel is very much like a paper cut-- a very straight, very narrow cut from a very sharp edge. I may have heard that paper cuts take longer to heal because they are so straight, presumably because the skin doesn't "knit" at all as it heals. Could that be the reason it hurts?

That could be. A paper cut is the closest thing I could think of to the feeling. If you've never had a titanium cut, you don't want to. Mostly, it stings, A LOT. Even if you clean up the edge (nice square edge [of course, on a square edge, the 'corners' are still pretty sharp]), on a thin enough piece (.020" or so), it's still pretty easy to cut yourself.

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I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near the Tanhauser Gate. All those … moments will be lost … in time … like tears … in rain. Time … to die.

Titanium is special because it doesn't interact with the human body. This is a bit of an exaggeration, there are very slight interactions, but they are negligable unless the titanium is in the human body for a very, very long time. This is one of the reasons it is used so often in implants, it causes almost no biological response and can last an extremely long time without being degrading by the body's defense mechanisms (the other reasons are it's very low density and high strength). This is important because the body is one of the most inhospitable environments known to man, most materials simply can't survive any reasonable amount of time. There are plenty of metals that do cause adverse reactions from the body, in fact this is by far more common than not. It has been extremely hard to find metal, or actually materials in general, that do not cause adverse affects towards the human body and are not quickly degraded by the human body, and there are still not that many of them. In fact, there is no material that is completely immune to bioactivity, all materials interact and/or are degraded by the body to some extent, but titanium is about as close to completely biocompatible as materials come. This is not because titanium is not reactive, quite the opposite. Titanium is so incredibly reactive that upon exposure to air or water it almost instantly forms a very tightly bound oxide layer. This oxide layer forms a very strong barrier that prevents further corrosion. Most "corrosion-resistant" metals (like staintless steel and aluminum) operate this way, although none work anywhere near as well as titanium. So although I don't doubt it hurts more, it is extremely unlikely it is due to any chemical action of the Titanium. If there was such an adverse biological response to titanium it would be of no clinical use, the human body would not accept it.

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Have you tried cyanoacrylate (Super-, Crazy-) glue on the cuts? Yeah, yeah, medicinanl grade is expensive (Bandaid Liquid Bandage), and I'm not a doctor, so don't listen to me, ask your doctor, but I put Superglue on paper cuts, other light cuts (after disinfecting, of course) and they seem to stop hurting right away, I figure because whatever it is that triggers the pain nerves -- something in the air? friction with the other meat? -- is somehow prevented.

Also, I'm a big knife sharpening fanatic, with lots of sharpening tools and experience, and I much prefer a cut with a sharp, polished steel edge that a dull one. I have to wonder if paper cuts hurt because the edge of paper is rough, fibrous, and does a lot of tearing rather than sliicing. Maybe unpolished titanium edges are similarly rough.

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Ah, TheBlackCat's arguments are much more informed than mine, and I have to agree with 01101001 that blunt cuts have a worse reputation for pain than do sharp ones. Yet don't razor cuts bleed the worst? Still, the issue is pain, not bleeding, so I may have had it exactly backwards. It does sound like we are converging on a suspicion that it has something to do with the microscopic shape of the cutting surface, at least as a "straw man" hypothesis...

Pain, at least the type you are talking about, is triggered by the release of cellular components from punctured or torn cells into the extracellular matrix, where they are detected by pain receptor neurons called nociceptors (we covered this last week in neuroscience). It is possible the glue is preventing the damaged components from reaching the nociceptors, but don't quote me on that.

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My Website: The Black Cat's Web Page

Titanium itself might not react with the human body much, but in your shop environment, I must assume the titanium you cut yourself with is not sterilized or kept in clean room conditions. In other words, what might be on the metal? Coatings for whatever purpose, cleaners and lubricants and anti sieze compounds and who know what else that might be used in the processes you are involved in. The irritant might not be the metal itself.

True, but why would Titanium cause more pain than anything else? You would expect the materials in the work shop would all be subject to roughly the same coatings, lubricants, cleaners, debri, etc.

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My Website: The Black Cat's Web Page

It's easier to stop the pain of a paper cut with Oragel...topical treatment for teething...~ 10 % benzocaine. Splinters, athletic abrasions, blisters...etc. They also make a product at CVS with an antiseptic.....since you will see the reddening of an infection....but won't feel any pain with Benzocaine. Geat for daycare centers where little ones topple over frequently. (I am a chemist) I have no personal experience with titanium cuts....find it biologically interesting., though unfortunate for the recipients..Ciao. Pete

It must be something to do with the edge of the sheet. When you shear it, it is pretty jagged. If you've ever seen a crack in titanium, it is much more jagged than other metals. Even clean edges seem to hurt more though (as clean as a file and sandpaper can get it anyway). I don't think contamination from the shop environment is really an issue. Parts get cleaned pretty often while you're making them, most commonly with M.E.K. (Methyl-Ethyl Ketone). MEK is pretty unhealthy stuff to be around, but I don't think it leaves any residue.

Is there a metallurgist out there?

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I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near the Tanhauser Gate. All those … moments will be lost … in time … like tears … in rain. Time … to die.

I work in a restaurant, and I've cut myself many times on almost everything imaginable. One thing that I have noted is that serrated edges hurt far far more than straight edges, and they do far more damage (but don't normally cut as deep). My single worst cut (thus far) was on a plastic saran-wrap dispenser. The blade on the thing is similar to a hacksaw and man did that hurt.

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Got a microscope? Even one of those little (maybe not powerful enough) pen-sized microscopes? (Ooo, they've got pocket telescopes, too. Oh boy, a tool I don't yet have.) You've got the materials on-hand to observe. I think it would be interesting to see how different the titanium edges are from other metals -- if they are. I assume they are machined much the same. Maybe it's the inherent crystal structure that makes them different. Compare a sharp paper edge, too. Careful. Don't cut yourself!

(I miss my old job, where the electronics lab had two good high-power binocular scopes for working on components -- and satisfying curiosity about the world.)

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Good idea. I'll have to check that out.

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I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near the Tanhauser Gate. All those … moments will be lost … in time … like tears … in rain. Time … to die.

Good point Black Cat, perhaps the metal comes from a different process at the manufacturer than say aluminum and has different contaninants. it is just a hypothesis, no metal experience here.

Sorry, not a metallurgist, just a solid-state chemist who also used to be an EMT. I would agree with the hypothesis that it has nothing to do with the chemistry of the material but with the jaggedness of the cut. Paper cuts always hurt - paper is a terrible blade and makes a very jagged cut; I've cut my self with brand new Xacto knives and scalpels, while those cuts may be deep, they usually don't hurt.

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