Stent-testing smart robot makes the medical grade

The Raspberry Pi often makes the world a better place. This time, it’s helping to test 3D-printed stents using a smart stent-testing robot.

Stents are small tubes used to prop open a patient’s airway. They keep people alive, so it’s incredibly important they don’t fail.

In fact, the FDA (Food and Drug Administration) requires testing of each design by compressing it over 300,000 times. That’s a sturdy challenge for any human, which is why machines are normally used to mash up the stents.

The usual stent-destroying machines are dumb clamps, with no idea whether the stent is breaking or not.

Stent Testing Robot Camera

A smarter stent-testing robot

Enter the Stent-Testing Robot, an intelligent arm that mashes stents while a Raspberry Pi Camera Module keeps a sharp eye on how it performs.

It’s designed by Henry J. Feldman, Chief Information Architect at Harvard Medical Faculty Physicians.

“We start with a CT scan of the lungs, and via a 3D reconstruction get the size and shape of the bronchus that we wish to stent open,” explains Henry. “The trick is to make it the exact shape of the airway.”

The challenge with testing is if stents start to fail before the end of the test. The dumb devices currently used continue to pulverise the stent when this happens.

Stent Testing Robot Camera Squisher

Machine vision to control stent-testing

The Raspberry Pi, meanwhile, uses machine vision to stop the mashing at the moment of failure.

The instant-stop approach enables Henry’s team to check which part failed, and view a time-lapse leading up to the failure. The video helps them design more reliable stents in the future.

Henry explains:

Naturally, we turned to the Raspberry Pi, since, along with a servo control HAT, it gave us easy OpenCV integration along with the ability to control a Hitec HS-5665MH servo. We also added an Adafruit 16-channel Servo/PWM HAT. The servo controls a ServoCity Parallel Gripper A.

Python was used to write the servo controller application. The program fires off a separate OpenCV thread to process each image.

Henry and his medical team trained the machine learning system to spot failing stents, and outlined the likely points of failure with a black marker.

Each time the gripper released, the robot took a picture with the Pi Camera Module and performed recognition of the coloured circles via OpenCV. If the black marker had a split or was no longer visible, the robot halted its test.

The test was successful:

While the OpenCV could occasionally get fooled, it was remarkably accurate, and given this was done on an academic budget, the Raspberry Pi gave us high-performance multi-core capabilities for very little money.


Nick Murphy avatar

What a wonderful use of a Pi.

I first came across stents being used in the form of expanding mesh arterial stents.


Liz Upton avatar

Uses like this of the Pi get me quite fluttery. Have to admit: this sort of project was very, very far from what we were imagining we’d see when we launched back in 2012!

Pete Stevens avatar

My younger brother has had a kidney transplant. Whilst I understand sod all of the various medical words involved, stent has turned up remarkably frequently, they’re simple things that keep people alive.

Whilst mostly I think of Raspberry Pi as a toy, briefly I’m reminded that it’s an incredibly powerful computer that utterly blitzes the first really serious computer I used (a DEC alpha in 1995).

This is astonishing.

Tony avatar

Brilliant use of a Pi, makes you wonder how many other things this could apply to the testing of?

John Chinner avatar

Those aluminium parts are “actobotics”. Very useful collection of parts that fit together. Grown-up Meccano.

Lucy Hattersley avatar

Oh good spot! Thanks, I’m hoping to do a more detailed Project Focus on this build if I can get Henry to share a few more details. It is such a wonderful project.

I might buy some of those actobotics parts. They look great

Henry Feldman avatar

So the “build” was super simple. I was going to CAD design and print a whole cradle, and then looked into my box of Actobotics. A few looks back and forth, and I realized I could “build” the bulk in under 15 minutes with leftover parts (part of the challenge is I am a busy practicing doctor too!) so quickly screwed it together (I even had some servos and the claw from another project). The only custom part was the little spiky cone that holds the stent in place, which I printed on a form1 SLA printer, since the little spikes seemed beyond what at the time I could get my FDM printer to do. The Pi is attached using the ServoCity Pi-Actobotics holder (Have a box of those and arduino ones too). Everything except the cone (well and the electrical tape to prevent the servo hat from shorting on the ethernet jack) is off the shelf.

Tim avatar

For actobotics parts head to They have quite a big selection of parts.

Henry Feldman avatar

For the robot in this article I bought those at which has a huge actobotics assortment, but as of about 1 year ago, my local electronics store 5 minutes from my house has a whole robotics section and has a pretty big acrobatics assortment, which is great if you just need a plate, etc…

Craig Ede avatar

Stents are commonly put in the blood vessels to aid the flow of blood, not in airways.

Craig Ede avatar

I take my previous comment back. Stents are also used in dealing with airway obstructions, but here in the U.S. we normally see the word used in reference to occlusions of blood vessels. So with that I now have a question: Is this device testing only stents used for the airway obstructions or does it also test stents used in blood vessels?

Henry Feldman avatar

Um, I am a US based physician and I stent LOTS of hollow body parts. We routinely stent the esophagus, small and large bowel, bile ducts, airways, cardiac and non-cardiac arteries at our medical center.

These specific stents from the article were custom stents for people with tracheobronchomalacia and the reason they were custom, was we could use a CT 3D reconstruction to match the holes with your side branching bronchi so you had full lung capacity. These stents (unlike many) we only keep in for 2-3 weeks.

E Risi avatar

Henry, could a stent be used to keep the urinary tract open as it passes through the prostate?

Henry Feldman avatar

Sorry didn’t see this comment. Yes and we do, but urinary stents are a temporary solution, and for the prostate we need to replace the stent with a surgical option (you can’t keep it stented open or you would be incontinent) so typically a TURP is required (prostate surgery)

Jurrasic avatar

Stents are indeed used for many body parts. I had a damaged tube connecting a kidney to my bladder(ureter?) thanks to a particularly large kidney stone, and had to have a stent put in to handle the urine flow to the bladder while the tube healed.

It hurt like a bitch and I peed alot of blood while it was in, but nothing compared to an actual kidney stone attack.

I guess this is kind of pointless, but stents are used in many different ways and I am glad to see that they are so rigorously tested. Even gladder to see a Pi making that testing better!

Alexandra Crawford avatar

I’d love to name the company producing the stent testers as Pi4pi-pi

Really good to hear you are on the mend!

It might also be great to have an informative hydration monitor to avoid the concentrations of uric acid that promote stones? What would you think if this was a reality?

First question, how could hydration be monitored non-invasively? A normal water intake profile adjusted by a critically controlled sweat sensor could be a Pi-zero in a watch format? Anybody interested?

Henry Feldman avatar

Today’s story on is about 3D printed airway stents (we print the mold, not the stent, due to FDA rules)

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