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Soldering irons get hot. Light bulb filaments also get hot. Cautery pen filaments get so hot that they can cut through flesh effortlessly. Physicians routinely use them for small surgical procedures. Unlike a scalpel, a cautery pen uses the heat from the filament to both cut and seal bloodflow, which can minimize the risk of infection and post-op complications. They are available at most online medical suppliers for around $12 each.

We ordered a handful after our surgeon friends in Ocotal, Nicaragua mentioned that these devices are a huge help, but their disposability makes them too expensive for them since they cannot be resterilized. That means that our friends can only use them when a donation of equipment comes into town. Opening one up and figuring out how it works led to some fun surprises.

The pens arrived like any other medical device, sealed in a bag with the proper warnings.

Do Not Reuse!

Sometimes that’s the most important warning in medical hardware. There are some medical devices, such as syringes, that you absolutely, never ever want to reuse. There are others that are designed for reuse after proper cleaning—laryngoscopes, stethoscopes, surgical forceps. The manufacturer of these cautery pens definitely wanted us to know that you cannot reuse this product. In practice, they run out power and then you are forced to throw them away.

There are other models of cautery pens that have detachable tips, but these are twice the price. Any possibility of using safety as an excuse for making these devices automatically disposable did not make any sense. So we decided to open up and understand the intricate mechanisms that make up a cauterizer.

I expected a transformer, some type of power converter, a super capacitor. Instead, $12 gets you the electronics complexity of a pocket flashlight. Maybe they weren’t so special after all?

Aah, the tips. Maybe the tips are in fact special, some sort of complex alloy that’s optimally designed to heat up using two AA batteries. That would justify the price, and why the manufacturers can rack up the cost of a reusable one to $24.

To investigate, we took the metal tips down the street to our friends at the MIT Materials Science Department, where they have a Scanning Electron Microscope. In the hands of material scientist Mike Tarkanian, we performed a chemical analysis on the tip using a technique called EDXA (energy dispersive X-Ray analysis). In a moment, the instrument told us what the material make-up of our tips were: Mostly aluminum, with a few other trace elements.

Additional research led us to something called Kanthal thermocouple wire, which costs around $25 for a spool of 1000 feet online. Given that our tips measure around 1.3 cm, that yields roughly 23,000 tips per spool. That’s a lot of surgeries for $25, and that’s the way it should be.

Jose Gomez-Marquez

I design medical devices for the developing world at MIT. Our lab creates DIY kits called MEDIKits for docs nurses in the field to come up with their own solutions.


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