Stent Manufacturing: From Palmaz's Garage to ABB Robots

A coronary stent is a small metal mesh tube that holds a narrowed artery open, and most stents used today also release a drug. More than 2 million people a year get one for coronary artery disease alone. Stent manufacturing started with a radiologist weaving wire around pins stuck in a pencil and now runs on lasers and microscopes in clean rooms. This post traces that path, looks at the quality questions raised around Indian-made stents this October, and asks where robots such as ABB's cleanroom arms and the single-arm YuMi could take over the handling between machines.

Two metal stents beside a centimetre scale, photographed in Baden-Baden in 2008. Photo: Frank C. Müller / Wikimedia Commons (CC BY-SA 2.5)

How stents went from pins in a pencil to laser cut tubes

The stent grew out of angioplasty. On 16 January 1964, at Oregon Health and Science University, radiologist Charles Dotter opened a tight narrowing in the leg artery of an 82-year-old woman with a guide wire and Teflon catheters, and blood flow returned to her leg. Andreas Gruentzig took the idea to the heart with a balloon catheter and performed the first coronary angioplasty in Zurich on 16 September 1977. The balloon pressed the plaque back, but the artery often narrowed again. Restenosis hit nearly half of patients, and doctors began looking for something that could stay behind and hold the vessel open.

The tip of a balloon dilatation catheter next to a centimetre ruler, the kind of device Gruentzig used for angioplasty. Photo: Magnus Maier / Wikimedia Commons (CC BY-SA 4.0)

Julio Palmaz, a vascular radiologist from La Plata in Argentina, got his idea after hearing Gruentzig lecture in New Orleans in 1978: a scaffold that would sit inside the vessel and stop it closing. He made the first prototypes by hand, sticking pins into a pencil and weaving wire around them, but the shape would not hold when squeezed. Soldering the wires where they crossed fixed that, at the cost of two different metals in one implant. The answer came from a piece of metal with staggered openings that a mason had left in his garage. Holes cut into a metal tube would fold down for delivery and stay rigid once expanded.

An enlarged stent model inside a model vein, shown in Basel in 2012 with a placard crediting Johnson & Johnson's Cordis division. Photo: Mattes / Wikimedia Commons (CC BY 2.0 de)

Palmaz, cardiologist Richard Schatz and restaurant founder Phil Romano patented the design in 1985, and Johnson & Johnson licensed it. The Palmaz stent was approved for peripheral arteries in 1991 and for coronary arteries in 1994, a year after the Gianturco and Roubin Flex-Stent became the first stent the FDA approved. Volume production meant cutting the pattern straight into tubing. A 1994 patent filing from Advanced Cardiovascular Systems describes a finely focused laser cutting a metal tube held in a CNC collet while a CNC table moves it. According to the patent, the cutting was automated except for loading and unloading the tube.

A metal stent seen at an angle, with the thin struts and open cells of its mesh. Photo: Frank C. Müller / Wikimedia Commons (CC BY-SA 4.0)

What a stent line checks today, and where robots fit

Stent quality made news in India this month. Medical Buyer reported on 16 October that Sri Lanka's device regulator had ordered three models of Indian-made drug-eluting stents withdrawn after an evaluation committee found improper positioning, dislodgement, acute stent thrombosis and failure to expand properly. On 5 October India's cabinet secretariat asked the health ministry to act on the concerns. The case covers three models, and no Indian regulator has found a defect. The proposals now on the table include batch and serial number tracking for every implanted stent. Stents have been under price control in India since 2017, and Medical Buyer argues that proof of quality now matters as much as price.

A Johnson & Johnson stent shown at actual size at a display in Basel, 2012. Photo: Mattes / Wikimedia Commons (CC BY 2.0 de)

A stent line still follows the steps in those old patents. A laser cuts the pattern into a thin tube, scrap is cleaned out in an ultrasonic bath, and the stent is electropolished as the anode of an electric circuit. Kern and Sohn, which makes balances and microscopes, describes the checks in between. Stents are weighed after laser cutting to catch leftover material and again after polishing to judge how much metal came off, and microscopes check strut width, polish, crimping and residues. Drug-eluting stents then get polymer and drug layers, for example on Sono-Tek's MediCoat ultrasonic sprayers, which move the stent under the nozzle. A crimper finally squeezes each stent onto its balloon catheter.

A pulmonary metal stent on its introducer, the delivery system that carries it into place, laid out on a drape. Photo: JBARRETO / Wikimedia Commons (CC BY 3.0)

Several of these steps already run on automatic machines. What is left is the moving between them: the loading and unloading the 1994 patent left to people, and carrying parts to scales, microscopes and crimpers. That is a possible job for ABB robots, though we found no public example of an ABB stent line. ABB says its cleanroom robots are certified to ISO 14644-1 for industries including medical devices. The IRB 1300, which ABB pitches for materials handling, machine tending, assembly and testing, comes in an ISO 4 cleanroom version with a particle filter and a fully sealed design. The single-arm YuMi IRB 14050, a 9.5 kg seven-axis cobot built for small parts assembly, has been used to spread glue beads on GE Healthcare's prototype line in Helsinki.

The single-arm YuMi IRB 14050 in its glue dispensing cell on GE Healthcare's prototype line in Helsinki. Photo: ABB

Printed stents, baby stents and the next stent factory

Tubes may not stay the only starting point. On 20 October, 3D Printing Industry reported that a team led by IMDEA Materials Institute and Universidad Politécnica de Madrid had printed braided nitinol stents in one step, with the work published in npj Metamaterials. The finished braids could be squeezed to half their diameter and still recover more than 90 percent of their shape, and they pressed on vessel walls up to five times more gently than printed lattices. They have not been tested in living tissue yet. The printed parts still needed chemical etching and electropolishing, which made each fibre 47.7 percent thinner, so a printed stent would still pass through finishing baths.

An 8 mm covered stent for iliac arteries, with a woven wire frame under its cover. Photo: Haudebourg / Wikimedia Commons (public domain)

Stents are also splitting into smaller product families. Cincinnati Children's wrote on 20 October about the Renata Minima and Lifeline stent systems, designed specifically for newborns and infants. Pediatric cardiologists have long had to adapt adult devices for these patients. The Minima can be enlarged in later catheter procedures as a child grows, and in its multicentre trial it was implanted successfully in 97.6 percent of 42 young patients. Patient-specific printed stents would push further in the same direction. More sizes and smaller batches suit cells that switch products through software, like the YuMi cell in Helsinki, where GE Healthcare staff say they can make major code changes in half an hour.

Two engineers in lab coats beside the single-arm YuMi cell at GE Healthcare in Helsinki. Photo: ABB

Regulation will set the pace for robots on stent lines. Vascular stents are class III devices in the United States, so they need premarket approval backed by clinical evidence and rigorous mechanical testing, and their submissions have to cover quality assurance such as ISO 13485 and the tests each finished unit passes before release. Price control in India keeps pressure on cost while buyers ask for better records, which suits machines that log every step. Someone also has to program and maintain the cells. Layouts like these are usually planned and tested first in RobotStudio, and our post on medical device assembly looks at ABB cobots on other medical lines.

Engineers watch the single-arm YuMi at work on GE Healthcare's Helsinki prototype line. Photo: ABB

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