George Osterhout, Senior Advisor and past President, Surface Solutions Group 01.31.24
What goes into developing coatings for medical devices? What drives the process? They don’t just magically appear, of course, though at times it may seem like it. Understanding the factors that motivate manufacturers to seek out new and better coatings and the processes that bring them to fruition can help medical device manufacturers and design engineers appreciate the big picture.
Many products relevant to the medical industry have been discovered practically by luck, fueled greatly by sheer determination, dedication, and (perhaps most importantly) curiosity.
Take the X-ray, for example. German physicist Wilhelm Conrad Röntgen won the very first Nobel Prize in Physics after noticing, quite by accident, that a cathode ray tube covered with barium platinocyanide caused a fluorescent effect. He wasn’t looking for this life-changing discovery; he was merely studying electric currents as they passed through a gas of very low pressure. But curiosity took him in a new scientific direction and medical technology was forever transformed.
There are many more examples, including one that directly relates to the topic of this article: polytetrafluorethylene (PTFE). PTFE was also discovered by accident in 1938—the by-product of another project. That was DuPont’s very first Teflon, which helped to revolutionize the manufacture of countless products we use every day. Medical devices—in particular the PTFE coatings used on guidewires and needles—represent many of these.
Subsequently, perfluoroalkyl and polyfluoroalkyl substances (PFAS) began to be used successfully as a chemical substitute until they also became a target for elimination (planned for 2026). Unfortunately, these “forever chemicals” were found to break down very slowly within the human body as well as in the environment, deeming them harmful. Newly motivated coatings manufacturers began developing more sustainable, functional coatings to meet the proposed new standards.
At the same time, a case was being made for avoiding a hasty, broad-brush-stroke type of elimination. PFAS comprise almost 15,000 chemicals1; however, the properties of fluoropolymers are distinctly different from fluorochemicals. A unique group of PFAS substances—fluoropolymers—are not water soluble and not shown to be harmful to the body or environment when used as intended. Industry advocates are working to dispel rumors based on supposition instead of facts, and the EPA is working toward categorizing the myriad PFAS into distinct groups for regulation.
To keep pace with ever-changing regulations and device design requirements, innovative coating companies continuously research, develop, and test new coatings. The following case studies explore some of the more notable challenges and solutions of late.
Problem: About 12 years ago, an OEM that manufactures medical devices with nitinol needed a way to overcome the temperature limitations of the alloy material to apply a coating to it. The problem with nitinol from a coating standpoint is it cannot be heated to a temperature over 500°F or the alloy’s memory will be destroyed, rendering it useless for medical procedures. At the time, existing coatings for guidewires and other medical devices had to be cured at higher temperatures.
Finding a solution proved quite challenging, because PFAS is used to manufacture PTFE—a widely used coating. PTFE provides the lubricity needed to reduce the dynamic efforts required for smoothly maneuvering a guidewire through the maze of tiny, delicate blood vessels and veins. Medical professionals rely on the lubricious properties of PTFE to see them through countless life-saving procedures. A suitable replacement was needed urgently.
Solution: The solution evolved out of a coating being used on another product made of stainless steel. Medical professionals commented the coated needles had a lower insertion pressure than those coated with other PTFE coatings. It offered great adhesion and was a water-based, biocompatible PTFE material. This triggered a lightbulb moment. If it worked on stainless steel, maybe it would also provide good adhesion on nitinol. Fortunately, it did.
It was discovered the coating, which had a cure temperature of 450°F as compared with the previously specified PTFE coating that had a cure temperature of 700°F, would not change the A(f) of the nitinol wire. It contained only 5% PTFE but performed with effective lubricity and easily competed against resin-based materials that had 40% PTFE.
Outcome: This low-PTFE coating was used on a nitinol guidewire for a neurosurgical procedure to remove a blockage in the brain of a stroke victim. It performed very well. Its properties provided permanent adhesion, durability, and low friction that, combined with the nitinol’s noted flexibility, has helped many patients.
Problem: When faced with the possibility of losing scientifically proven coatings the medical world has come to rely upon, the seriousness of the situation can become daunting and yet, it often motivates chemists and engineers to look at coatings science differently and push the boundaries of what is possible.
Knowing the low PTFE coating is water-based, biocompatible, and uses another polymer as the primary lubricant, it raises the question of what would happen if all the PTFE were to be taken out of it?
Solution: As in the previous case study, more experiments ensued. Existing medical coatings were tested for their frictional values—pure PTFE, resin-bonded PTFE, FEP, and many other medical coatings commonly used.
Work began to create the same coating with no PTFE, using established scientific data to reformulate existing proven coatings and create new versions that reduce the use of restricted chemicals. With much perseverance, it became clear to the coating chemists it was possible to remove the remaining PTFE and achieve the frictional values medical device manufacturers and their OEMs required.
Both this new PTFE-free coating and the low-PTFE formulation are free from any PFOS, PFOA, and hexavalent chromium (hex chrome) compounds, and are also REACH and RoHS compliant. They represent very promising alternatives.
Outcome: Stringent testing, including those for adhesion and wear, were performed and documented. Again, the new PTFE-free coating did not disappoint. It not only demonstrated excellent adhesion, but it was proven to provide permanently bonded, low friction properties that are a good, sustainable alternative to traditional PTFE coatings.
Presently, the coating without PTFE continues to be evaluated by major OEM device manufacturers and their tier one suppliers. The initial response to it as a viable alternative has been quite positive. In fact, feedback throughout the research and development process has been so positive that both the low- and no-PTFE coating formulations are currently available on the market.
The medical device industry has a way to go with testing and validation of newly developed coatings on legacy products, but there is time for this to be accomplished before present PTFE coatings are no longer available in the marketplace. With current advancements of medical science at risk, the EPA will do their due diligence before handing down new regulations.
The pursuit of sustainable coatings continues. Curiosity remains at the root of the continuous improvement process and is the motivation that drives coating innovators to embrace challenges as opportunities.
References
George Osterhout is senior advisor and past president at Surface Solutions Group, working alongside medical device and component OEMs and their contract manufacturers to transform their ideas into successful products. He has 48 years of coatings industry experience and holds two patents.
Many products relevant to the medical industry have been discovered practically by luck, fueled greatly by sheer determination, dedication, and (perhaps most importantly) curiosity.
Take the X-ray, for example. German physicist Wilhelm Conrad Röntgen won the very first Nobel Prize in Physics after noticing, quite by accident, that a cathode ray tube covered with barium platinocyanide caused a fluorescent effect. He wasn’t looking for this life-changing discovery; he was merely studying electric currents as they passed through a gas of very low pressure. But curiosity took him in a new scientific direction and medical technology was forever transformed.
There are many more examples, including one that directly relates to the topic of this article: polytetrafluorethylene (PTFE). PTFE was also discovered by accident in 1938—the by-product of another project. That was DuPont’s very first Teflon, which helped to revolutionize the manufacture of countless products we use every day. Medical devices—in particular the PTFE coatings used on guidewires and needles—represent many of these.
Regulatory Requirements Driving Change
In 2010, the U.S. Environmental Protection Agency (EPA) put forward restrictions on the use of perfluorooctanoic acid (PFOA)—the fluoropolymers used to manufacture PTFE. The EU followed up on this with the POPs Regulation, which went into effect at the end of 2020. The use of PFOA to make coatings ceased.Subsequently, perfluoroalkyl and polyfluoroalkyl substances (PFAS) began to be used successfully as a chemical substitute until they also became a target for elimination (planned for 2026). Unfortunately, these “forever chemicals” were found to break down very slowly within the human body as well as in the environment, deeming them harmful. Newly motivated coatings manufacturers began developing more sustainable, functional coatings to meet the proposed new standards.
At the same time, a case was being made for avoiding a hasty, broad-brush-stroke type of elimination. PFAS comprise almost 15,000 chemicals1; however, the properties of fluoropolymers are distinctly different from fluorochemicals. A unique group of PFAS substances—fluoropolymers—are not water soluble and not shown to be harmful to the body or environment when used as intended. Industry advocates are working to dispel rumors based on supposition instead of facts, and the EPA is working toward categorizing the myriad PFAS into distinct groups for regulation.
To keep pace with ever-changing regulations and device design requirements, innovative coating companies continuously research, develop, and test new coatings. The following case studies explore some of the more notable challenges and solutions of late.
A Case Study in Coating Nitinol
In the medical industry, there are stainless steel guidewires and there are nitinol guidewires. Nitinol—which is an alloy made from nearly equal amounts of nickel and titanium—has a shape memory that allows the user to bend it or even form a complete 360-degree loop with it, release it, and watch it return to its original contour. This “super elasticity,” combined with its ability to safely hold open vessels while inserting devices such as stents, makes nitinol an invaluable tool for medical professionals. This case study illustrates how beneficial a new, water-based, biocompatible PTFE coating solved one medical device maker’s challenge.Problem: About 12 years ago, an OEM that manufactures medical devices with nitinol needed a way to overcome the temperature limitations of the alloy material to apply a coating to it. The problem with nitinol from a coating standpoint is it cannot be heated to a temperature over 500°F or the alloy’s memory will be destroyed, rendering it useless for medical procedures. At the time, existing coatings for guidewires and other medical devices had to be cured at higher temperatures.
Finding a solution proved quite challenging, because PFAS is used to manufacture PTFE—a widely used coating. PTFE provides the lubricity needed to reduce the dynamic efforts required for smoothly maneuvering a guidewire through the maze of tiny, delicate blood vessels and veins. Medical professionals rely on the lubricious properties of PTFE to see them through countless life-saving procedures. A suitable replacement was needed urgently.
Solution: The solution evolved out of a coating being used on another product made of stainless steel. Medical professionals commented the coated needles had a lower insertion pressure than those coated with other PTFE coatings. It offered great adhesion and was a water-based, biocompatible PTFE material. This triggered a lightbulb moment. If it worked on stainless steel, maybe it would also provide good adhesion on nitinol. Fortunately, it did.
It was discovered the coating, which had a cure temperature of 450°F as compared with the previously specified PTFE coating that had a cure temperature of 700°F, would not change the A(f) of the nitinol wire. It contained only 5% PTFE but performed with effective lubricity and easily competed against resin-based materials that had 40% PTFE.
Outcome: This low-PTFE coating was used on a nitinol guidewire for a neurosurgical procedure to remove a blockage in the brain of a stroke victim. It performed very well. Its properties provided permanent adhesion, durability, and low friction that, combined with the nitinol’s noted flexibility, has helped many patients.
A Case Study in the Science of PTFE Coatings
Given the success of the low PTFE coating, the question inevitably arose of what would happen if all the proposed regulations against fluoropolymers and PTFE were imposed. It could significantly impact the businesses of all coating suppliers and their customers.Problem: When faced with the possibility of losing scientifically proven coatings the medical world has come to rely upon, the seriousness of the situation can become daunting and yet, it often motivates chemists and engineers to look at coatings science differently and push the boundaries of what is possible.
Knowing the low PTFE coating is water-based, biocompatible, and uses another polymer as the primary lubricant, it raises the question of what would happen if all the PTFE were to be taken out of it?
Solution: As in the previous case study, more experiments ensued. Existing medical coatings were tested for their frictional values—pure PTFE, resin-bonded PTFE, FEP, and many other medical coatings commonly used.
Work began to create the same coating with no PTFE, using established scientific data to reformulate existing proven coatings and create new versions that reduce the use of restricted chemicals. With much perseverance, it became clear to the coating chemists it was possible to remove the remaining PTFE and achieve the frictional values medical device manufacturers and their OEMs required.
Both this new PTFE-free coating and the low-PTFE formulation are free from any PFOS, PFOA, and hexavalent chromium (hex chrome) compounds, and are also REACH and RoHS compliant. They represent very promising alternatives.
Outcome: Stringent testing, including those for adhesion and wear, were performed and documented. Again, the new PTFE-free coating did not disappoint. It not only demonstrated excellent adhesion, but it was proven to provide permanently bonded, low friction properties that are a good, sustainable alternative to traditional PTFE coatings.
Presently, the coating without PTFE continues to be evaluated by major OEM device manufacturers and their tier one suppliers. The initial response to it as a viable alternative has been quite positive. In fact, feedback throughout the research and development process has been so positive that both the low- and no-PTFE coating formulations are currently available on the market.
Curiosity Continues to Forward Innovation
Developing something that has not been done before in the medical industry is exciting and drives innovation. New questions begin to emerge, and additional experimentation ensues to discover as much as possible.The medical device industry has a way to go with testing and validation of newly developed coatings on legacy products, but there is time for this to be accomplished before present PTFE coatings are no longer available in the marketplace. With current advancements of medical science at risk, the EPA will do their due diligence before handing down new regulations.
The pursuit of sustainable coatings continues. Curiosity remains at the root of the continuous improvement process and is the motivation that drives coating innovators to embrace challenges as opportunities.
References
George Osterhout is senior advisor and past president at Surface Solutions Group, working alongside medical device and component OEMs and their contract manufacturers to transform their ideas into successful products. He has 48 years of coatings industry experience and holds two patents.