Dave DiBiasio, Precision Coating’s (Precision Coating) Vice President of Sales and Marketing, and Dick Buxton, Precision Coating’s Director of Process and Application Engineering sat down to answer some of the most common questions customers ask related to high-performance coating for medical wires.
Being a global leader in the application of polymer coatings for guidewires used in interventional medicine, we work with all of the major medical device OEMs and CMOs, so have been asked—and have answered from our deep expertise and experience—many questions regarding the PFTE coating of guidewires. This video explores many of these questions, which we hope will help inform you in choosing the coating that’s best for your platform, and also expedite your platform to production.
Have a cup of coffee handy and watch the video for further insights about coating solutions for your guidewires. You can also follow along with the Q & A below.
Q: What is the most lubricious coating that I can apply?
A: It is our aqueous coating, which is PTFE based. The coefficient of friction in that application is probably down around a 0.9, maybe a 0.8. When you go to a solvent coating, it goes up a little bit—more of a 1 or 1.2—but still it is very lubricious; it reduces the coefficient of friction on the stainless or substrate by 80%.
Q: How would you check some of the specifications for lubricity?
A: We have a device in house to check the coefficient of friction on the guidewire.
Q: Is there a minimum coating thickness that’s effective for the guidewire?
A: As long as PTFE is on the substrate, it’s effective. What you will find is the color will vary as the material is thicker. It’s a more solid color.
Q: Is there a minimum coating thickness to achieve the best color?
A: Our coating tolerance is one to five-tenth as a standard. In letter colors, to maintain a solid color, you’d have to be about two-tenths or more. In essence, one to five-tenths and then two-tenths or more gives you the best application.
Q: Is there a coating that’s best for dielectric properties?
A: There is. PVDF is our standard for dielectric polyimides. There are other materials that would be dielectric. It depends on the application and the availability of thickness that we can put it on.
Q: Are all the coatings that are applied medical-grade coatings?
A: Yes, they are. The ones that we specify or actually purchase are medical grade. We perform biocompatibility testing on the coatings that we’ve purchased. Customers appreciate that the coating we apply will pass their bio testing as well.
Q: Is there a coating that you would specify for bondability?
A: There is a little difference between aqueous and solvent. We prefer to put solvent coatings on invasive wires; it does have a polyimide binder in it. It adheres to the substrate much better than the aqueous. Aqueous is more appropriate for a mandrel or an overmold type application versus the solvent. This means that the solvent has its own binder; with the aqueous, we perform a process to make it bind.
Q: As far as coating thickness is concerned, how many colors do we offer?
A: We offer a pretty standard color selection: blue, green, black, and yellow; clear is an option, as well.
Q: Are there any specific properties that are associated with the different colors, or can a customer use any color?
A: It does make a little bit of a difference as far as the colors chosen. Obviously, clear is pure PTFE. It has no pigment. Pigment, in a way, is almost a “contaminant” in the coating in the sense that it interferes a little bit with the coefficient of friction. The lighter colors require a little bit more load of pigment to bring out the brightness of the color. Think of it this way: if you have a test tube and you fill that test tube with the actual polymer, you would have to fill it with a pigment and then your binder or your other associated properties. And if you add more pigment, you have to take a little bit of polymer out, or vice versa.
Q: Are curing temperatures flexible throughout the different coatings?
A: We follow the recommended guidelines based on the manufacturer of the coating. Common cure temperatures are from 625 to 750 degrees, depending on the materials chosen.
Q: Is there a major difference between the aqueous and the solvent coatings?
A: The aqueous does require a higher cure temperature. It actually centers in the process and it’s done at a 725 to 750 F degree cure temperature. The solvent materials do bond at a lower cure temperature of 625 degrees.
Q: Would you recommend specific coatings for application other than guidewires? For instance, would you use an aqueous coating specifically for a mandrel?
A: Yes, definitely for a mandrel; a mandrel requires the ability for a low lubricious surface. Non-stick overmolding is preferred with aqueous.
Q: Would you recommend solvents for guidewires?
A: Yes, definitely, as they are invasive.
Q: Have we done bio testing on the coatings?
A: We do. In fact, our own internal blend, we have bio tested multiple times. We perform bio testing on store bought items, as well. But in the end, it’s the medical device that has to pass the bio test; it’s not just our coating. It’s nice for customers to know that you’re starting off with a coating that’s going to pass the tests. And we, we definitely make sure that what we’re applying will pass.
Q: Is there flexibility in the coating? In other words, if I’m putting it on a platform that’s going to have a lot of turns going through a torturous vessel, will it have any problem with the coating flexing along with the substrate?
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A: No, it will not.
Q: Is that because of the coating thickness that we apply, or is it a function of the coating itself?
A: It’s a combination of both. The coating itself is not applied in any real thickness or layers. It’s pretty much applied in a one-layer application. It adheres to the substrate and bonds—and will make it through your torturous path. It’s only generally a one and a half to 10-thousands of an inch, so it’s able to flex for the medical applications it is required for.
We hope we’ve answered question you may have in choosing the right coating for your medical guidewires.
Precision Coating for Your Medical Device Applications
Precision Coating provides high-tolerance coating and specialized metal-finishing services to the medtech industry for applications including vascular, endosurgical, and orthopedic instruments and devices.
The GlideLine™ family of medical device coating finishes is the broadest offering of applied fluoropolymer (PTFE) coatings in the industry, customized to optimize the design, quality, and performance characteristics of high-quality medical products.
InfiNiTiCoat™ is Precision Coating’s proprietary low-temp cure process, optimized for coating performance on nitinol devices; specifically optimized to preserve the desired characteristics of nitinol in wire, strip, and tube forms. Precision Coating has unique process control over challenging nitinol handling, coating, and curing.
The MICRALOX® portfolio of chemistries offers superior patented aluminum oxide coatings with a microcrystalline barrier that revolutionizes aluminum anodizing with exceptional barrier properties and corrosion resistance over industry leading product life cycles.
Interventional cardiology is one of the newest specialties within medicine, and I would venture to say it is the one that has undergone the most changes within the past decade. As fellows training for a career in this dynamic field, we can attest to the sacrifices we have made to achieve our goals of becoming interventional cardiologists. But now that we are well on our way, I think it is as important to look backward as it is to look forward.
You might know the name Andreas Gruentzig, but do you know where the word “stent” originated from? Here are my top 10 questions every interventionalist should be able to answer about the history of our field:
1. When was the first coronary angiogram performed?
Mason Sones performed the first coronary angiogram at the Cleveland Clinic (Cleveland, OH) in .
2. What were the events leading to this discovery?
Sones asked his associate Royston Lewis to withdraw the catheter tip from the left ventricle into the ascending aorta to perform aortography, and relied on the pressure tracing difference without imaging. He injected 40 cc of 90% diatrizoic acid (Hypaque) through the catheter into the dominant right coronary artery, and the patient developed asystole—not ventricular fibrillation as previously thought. Three to 4 explosive coughs were successful in restoring sinus rhythm.
3. Who proposed the concept of transluminal angioplasty?
Charles Theodore Dotter and Melvin Judkins proposed this concept in . They used large rigid dilators, which proved helpful in the peripheral arteries but were restricting.
4. Who refined this work for a coronary application?
Andreas Gruentzig continued exploring the concept of angioplasty in coronary practice using animals, cadavers, and patients undergoing bypass surgery starting in .
5. When was the first percutaneous transluminal coronary angioplasty performed in a conscious human?
On September 16, , by Gruentzig.
6. How was this innovation received by the international interventional community?
The worldwide community responded with great skepticism. In , a small group of cardiologists formed a registry of all coronary angioplasty cases sponsored by the National Heart, Lung, and Blood Institute. There were 3,000 cases registered by .
7. Was the first guidewire steerable?
No, the first guidewire was fixed onto a balloon catheter. The first steerable guidewire was not introduced until .
8. What is the famous quote from Dotter and Judkins?
“The guidewire is passed across the atheromatous block more by the application of judgment than of force.”
9. Where did the word “stent” originate from?
The English dentist Charles Stent built a career advancing the field of denture-making in the mid-nineteenth century. He refined the method of making dental impressions by improving the plasticity and stability of the material used in patients’ mouths, and built a company based on his technology. After his death in , variations of the material came to be used in nondental capacities for skin graft surgeries, urology, and gynecology. The term was first used in cardiology in —when researchers describing a prosthetic-stented aortic homograft used for mitral valve replacement assumed “stent” was a generic term for any kind of nonbiological support used for extending, stretching, or fixing in an expanded state.
10. How were coronary stents developed?
Ulrich Sigwart, Jacques Puel, and colleagues developed the first self-expanding stent in . Cesare Gianturco and Gary Roubin then invented the first balloon-expandable stent, which was FDA approved in . In , Julio Palmaz placed the first balloon-expandable stent with diamond shaped windows in Brazil. Then 2 randomized trials (STRESS and BENESTENT) compared balloon angioplasty alone with the Palmaz-Schatz stent and found the stent was associated with a 20-30% reduction in clinical and angiographic restenosis, markedly improved initial angiographic results, and a larger post-procedure minimal luminal diameter. This led the FDA to approve the device in . The first drug-eluting stent (Cypher; Cordis) was not approved for use by the FDA until .