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25 March 2017
Afternoon Sedition

Help! I’ve Glued My Fingers Together! Intentionally!

Packages of Commercial Cyanacrylate Glue

Common Cyanoacrylate Glues

I've been using cyanoacrylate glue (superglue) — commonly referred to as Krazy Glue, even though this is a trademark of Borden — for years to glue small cuts together, particularly paper cuts and the, fortunately rare, minor kitchen accidents. (I've read that mountain climbers use superglue to repair the rips and tears in their hands, and that windsurfers and sailors use it to repair ripped-off callouses and blisters; didn't they ever hear of gloves?)

Using it for unintended purposes like injury repair is easy: just hold the edges of the wound together, apply a dab with a toothpick and forget about it. (Disclaimer: do this at your own risk. If you manage to glue your hand to your genitalia, that's you with the problem, not me. If you slather it all over your fingers and stuff it in your nose, well, all I can say is: that'll teach you. So if you ruin your life, that's too bad. I ain't payin' you, or your lawyer, for it. As with anything in life, don't be stupid and talk to a doctor or someone with a brain before doing anything risky. Back to our story.) The result heals faster than doing nothing, and with fewer complications. Anyway, I was having a discussion about this with a friend who said that Krazy Glue wasn't the same as surgical glues like Dermabond. And so I set out to see if it was the same, as I steadfastly maintain.

The history of cyanoacrylate glues is interesting, even if you aren't a chemist or a jilted lover. (Gluing together body parts of the unfaithful is an urban legend.) During World War II, Harry Coover was trying to make a clear plastic for gunsights, since it had cost and weight advantages over glass. (Coover is an interesting fellow; he ended up with 460 patents.) His experiments turned up less than ideal results: "I was working with some acrylate monomers that showed promise. But everything they touched stuck to everything else. It was a severe pain."

Coover, Discoverer of Cyanacrylate Glue

Harry Coover
Discoverer of Cyanacrylate Glue

Coover didn't return to cyanoacrylates until nine years later, while attempting to create a heat-resistant polymer for the canopies on high-speed jets. One of the students working on the project accidentally glued together some very expensive — at the time $700, which was probably a month's pay for an Ph.D. engineer — optical prisms. Waving off the student's apologies, Coover excitedly started gluing together everything in sight, because he realized that, unlike other adhesives, this one rapidly bonded without pressure, heat, curing activators, or special preparation. Both properties turned out to be particularly useful in medicine, especially on the battlefield. (Ever watch a surgeon try to sew a piece of liver or lung tissue back together?).

Coover was also the first to recognize and patent cyanoacrylates as human tissue adhesives. These cyanolate adhesives are used in many sutureless surgeries such as the rejoining of veins, arteries, and intestines, ophthalmic surgeries, dental surgeries, uncontrollable bleeding and the repair of soft organs such as the liver and spleen. Coover's adhesive was first used in the Vietnam War to temporarily patch the internal organs of badly injured soldiers until conventional surgery could be performed. Since the 1970's, tissue adhesives have been used for a variety of surgical applications including middle ear surgery, bone and cartilage grafts, repair of cerebrospinal fluid leaks, and skin closure.

Hobard and William Smith colleges

Cyanoacrylate adhesives are formed from monomers (short building blocks) which are kept in a slightly acidic solution which prevents them from polymerizing, or linking together, into long, linear chains. All they need to cure is a weak base, like the microscopic amounts of moisture present on virtually every surface. Some items to be bonded, like wood, are naturally acidic which slows down curing, so special activators are used to start the process.

The cyanide (CN) groups on the molecule are highly polar, which means they enthusiastically grab onto things like skin. Polyethylene, which is what they make the bottles from, doesn't have any polar groups, for obvious reasons. (If you have a glue that sticks to everything, what do you keep it in?) Interestingly enough, the cyanoacrylate adhesives are made by making the cured (polymer) version and then cracking into pieces (monomer), while keeping it in an acidic solution so it can't recure (repolymerize). This is why acetone removes the cured adhesive — it breaks the bonds in the polymer. But, enough chemistry. (You still with us?) Back to the question: can cyanoacrylate glues be used instead of surgical glue? Ok, ok, we'll get to that right now!

The big difference between glue for objects (Krazy Glue) and glue for people (Dermabond) are:

  • Dermabond is monomeric 2-octyl cyanoacrylate, a weaker bonding agent than superglue which is typically ethyl 2-cyanoacrylate.
  • Dermabond comes in a sterile, single-use container.
  • Dermabond is colored with D&C Violet No. 2 to make it easier to see after it has been applied. (Normal superglue is clear.).
  • Superglue costs about $2 per tube; Dermabond is over $20. (Plus the hospital markup which can push it close to $70 per tube.)

Aside from the color, price, and single-use issues — bacteria don't live in cyanoacrylate — what does the formulation difference really mean? For starters, superglue is stiffer and liberates more heat when applied. This isn't an issue for "paper cuts", of course; I've never felt any heat at all. The formulation is basically safe but the surgical variant does have slightly different properties. So, the answer? Well, let's look at the history and the FDA's perspective. (I said I'd answer the question, ok?)

Although cyanoacrylate glues were useful on the battlefield, the FDA was reluctant to approve them for civilian use. In part, this was due to a tendency of the early compounds (made from "methyl-2-cyanoacrylate") to irritate the skin as the glue reacted with water and cured in the skin, releasing cyanoacetate and formaldehyde. A compound called "butyl-2-cyanoacrylate" was developed to reduce toxicity, but suffered from brittleness and cracking a few days after application. Finally an improved cyanoacrylate glue was developed for medical applications called "2-octyl-cyanoacrylate." This compound causes less skin irritation and has improved flexibility and strength — at least three times the strength of the butyl-based compound.

The Straight Dope

So, there you have it. The compounds are different, yet similar. The word on the street is that for small cuts the two are equivalent, but if you are repairing a lacerated liver or closing a large incision, the medical version is likely superior. (That's the one-line conclusion that you cared about, right?) The Straight Dope has a nice writeup of cyanoacrylates as surgical glues.

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