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Parylene Allows Prosthesis to Flex Its Muscle

Originally Published MPMN October 2002

PROFILE

Parylene Allows Prosthesis to Flex Its Muscle

Coating reduces wear caused by flexing stress

Zachary Turke

This erectile implant uses a parylene N coating from Specialty Coating Systems to allow three times as many elongation cycles as uncoated units.

Developing advanced urology devices since 1972, American Medical Systems Inc. (AMS; Minnetonka, MN; www.visitams.com) is no stranger to erectile dysfunction. The company's latest product to treat this malady consists of two implantable concentric silicone elastomer cylinders. Incorporating an intermediary layer of woven polyester fabric, this device is capable of expanding up to 50% radially and 25% in length. Because it is subject to repeated expansion, however, the unit requires a thin coating to increase wear resistance. After deeming ion implantation, gas plasma treatment, lubricious silane, and carbon coatings unsuitable, the company turned to Specialty Coating Systems (SCS; Indianapolis; www.scscookson.com) for a solution.

The challenges SCS faced in recommending an appropriate coating were significant. As with any material implanted into the body, the coating needed to be biocompatible. Additionally, it had to be compatible with the implant's silicone and polyester components. Perhaps most importantly, however, the coating had to be flexible, add strength and toughness to the cylinders, and tolerate multiple elongation cycles. SCS reviewed these design requirements and determined that its parylene N coating would be a perfect fit.

Using a pivot point stress test, AMS evaluated the material and found that it significantly strengthened the unit and met all other design criteria. Applied in a thickness of just 1.52 µm, the coating enabled the cylinders to withstand three times as many elongation cycles as uncoated units. Because it is applied in such a thin layer, the coating also did not contribute considerably to device size or weight.

Satisfied that SCS had suggested the appropriate coating, AMS still faced another challenge: how to apply it only to certain portions of the device. Here again, SCS was of service. "We worked with AMS to develop a masking technique that made it possible to achieve uniform coverage where desired, yet left the ends of the elastomer cylinders uncoated for attachment to the rest of the implant assembly," explains SCS medical product marketing manager Lonny Wolgemuth. He notes that this was accomplished without the use of latex sealants or other masking agents that are unsuitable for medical applications.

Gaining FDA approval and obtaining the CE mark in 2000, the AMS erectile implant is currently marketed in 50 countries and continues to use the SCS coating. And while Wolgemuth believes the success AMS has achieved is not unusual, he stresses that their application uses only some of parylene's many benefits. "The biocompatible material also offers dielectric properties, optical transparency, chemical inertness, and many other qualities," he says. "And the best part is that none of these traits cost extra to include; they're a natural property of the material."

SCS performs contract coating services and offers raw parylene materials and coating equipment. According to company officials, other medical devices that could benefit from parylene coating include electrosurgical instruments, stents, optics, catheters, mandrels, needles, endoscopes, microtrays, and pacemaker components.

Copyright ©2002 Medical Product Manufacturing News

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