Originally Published EMDM September 2002
PRODUCT UPDATE
Coatings Help Devices Live Up to Their PotentialSurface treatments make medical instruments better, more versatile, and easier to use.
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| PhotoLink technology developed by SurModics offers a diverse range of property enhancements on numerous substrates. |
When new medical technologies are on display, coatings are never the stars of the show. But think of them as indispensable supporting actors. Without them, the stars wouldn't shine as brightly.
Coatings enhance and enable many of today's medical devices. They add properties such as lubricity, blood compatibility, and antimicrobial action to device surfaces. Other coatings release drugs or heighten the visibility of implanted devices under ultrasound.
Without coatings, many medical devices would never reach their potential, according to Lise Duran, vice president of product development for SurModics Inc. (Eden Prairie, MN, USA). "You may have a very innovative device, but because of its surface you won't be able to get the full benefit from it," says Duran, whose company offers PhotoLink coating formulations for medical devices. "The device might even fail because of the surface. But add a coating to the surface and the device will function the way it should."
Many device coatings are polymer-based formulations. Hydrogel coatings manufactured by MCTec B.V. (Venlo, Netherlands) are based on a single specially developed polymer rather than blends of different polymers, explains Hans Hanssen, technical director of the company, which was recently acquired by STS Biopolymers Inc. (Henrietta, NY, USA). This approach adds stability to the coating formulation, Hanssen claims.
Besides making coatings, MCTec has developed a process for adding lubricity to device surfaces. The company coats cores that are made into balloon catheter hypotubes and various types of guidewires. Manufacturers will find that making devices out of the coated components is more cost-effective and easier than coating finished devices, Hanssen maintains. But perhaps most important, he says, coated components improve the quality of the final devices.
Spray coating catheters and guidewires with a thin layer of PTFE reduces their coefficient of friction by as much as 50%. But spraying doesn't produce coatings that are smooth and uniform enough for many manufacturers. MCTec replaces spraying with a proprietary process in which spooled wire or tubing is pulled through a PTFE coating bath. "Think of it as controlled dip and curing," says Michael Casalino, vice president of operations for Wytech Industries Inc. (Rahway, NJ, USA), which is working with MCTec to produce the coated components.
When the coating process is complete, the wire or tubing is respooled. This spool-to-spool process can coat tens of thousands of feet of wire or tubing at a time. "Rather than coating a piece of wire that's two feet long, we run very long lengths of wire continuously through the bath," Casalino explains, adding that the process is about 20% less expensive than spray coating.
The outcome is a spool of wire or tubing with a lubricious coating of very consistent thickness. Consistency is prized by designers whose task is complicated by core material with a varying diameter.
MCTec's process can coat components made of a variety of metals, including stainless steel, platinum, and even nitinol. Normally, nitinol can't be spray coated because heat from the process changes its properties. "But we can coat nitinol without affecting the properties," Casalino says.
Lubricious Coating for Silicone
Lubricious coatings normally have a hard time adhering to catheters and other devices made of silicone. To get a grip on adhesion-resistant surfaces, STS Biopolymers has developed Graft-Coat, a patent-pending formulation that creates a polymer coating right on the surface of a device.
To begin the Graft-Coat process, a device is placed in a water bath that contains a monomer. This monomer forms polymer chains by reacting with the surface of the device. Chemical bonds hook the chains to the surface.
The process creates a hydrophilic coating that gives silicone devices "both a dry and a wet lubricity," according to Richard Whitbourne, chief technology officer at STS. A soft polymer with a high coefficient of friction, silicone doesn't slide easily along surfaces. "If you try to pull [silicone] through your fingers while putting a moderate amount of pressure on it, it can feel like you're putting on the brakes," Whitbourne explains. "But if you put the Graft-Coat treatment on it, you'll be able to pull it through your fingers easily even if you're applying pressure."
This kind of lubricity could smooth out the rough spots in many procedures. Syringe needles, for example, will have a much easier time penetrating Graft-Coat–treated rubber and silicone septa on pharmaceutical bottles. And Graft-Coat–treated catheters will slide more easily through a patient's urinary system than uncoated catheters would.
Graft-Coat will make its market debut in the 2002–2004 time frame. Variations of the coating will be specially designed for different applications.
Another group of application-expanding materials are haemocompatible coatings. These products reduce platelet adhesion and thrombus formation on devices, thereby extending their effective lifetime in the body. SurModics is working on a variety of blood-compatible coatings, including a photo-heparin formulation. Because European regulators are concerned about possible heparin side effects, SurModics is also developing nonbiological alternatives to heparin. Most of these are polyvinyl-, pyrrolidone-, or polyacrylimide-based polymers that are part of the company's PhotoLink line.
Drug-Eluting Stents
Drug-delivery coatings can play a key role in a treatment that opens blocked arteries. At present, many companies are working on stent coatings that slow or prevent restenosis, the reclosing of an artery opened by a medical procedure.
One of the first companies out of the starting gate is SurModics, whose drug-eluting coating is being used on a stent manufactured by Johnson & Johnson's Cordis division. The stent received the CE mark in April, and US FDA approval is expected in early 2003. SurModics's PhotoLink technology, with some variances, is used to coat the stent.
The PhotoLink process involves dissolving reagents in water or a water and alcohol mixture. The solution is then applied to any hydrocarbon-containing substrate by means of dipping, spraying, ink-jetting, or roll coating. Exposure to UV light activates a chemical reaction and covalently bonds the coating to the surface of the device.
STS has also attracted considerable interest from stent manufacturers for its Medi-Coat product, according to Whitbourne. Medi-Coat is a patented hybrid polymer system that controls the flow of liquid into and out of the coating, ensuring that the restenosis-fighting drug is released at just the right rate. The coating's special polymer mixture also stabilizes the drug so it can withstand the sterilization process. And it provides the flexibility and adhesion required by stent-related applications.
More Products:
Specialty Coating Systems
STS Biopolymers Inc.
AST Products
Comelec
Avecia Protection & Hygiene
Carmeda AB
3DT LLC
SurModics Inc.
Plasma Electronic GmbH
MCTec B.V.
BioInteractions Ltd.
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