Originally Published May 2000

Drawn to Perfection

Wire supplier meets catheter manufacturer's demanding guidewire specifications

Norbert Sparrow, Editor

Minute defects in the wire used in invasive devices can have tragic results. Even minor flaws or inconsistencies in the material are potentially life threatening for the patient; the OEM, who can face product recalls and paralyzing lawsuits when its product performs inadequately, may not survive either. To ensure the best possible outcome for its transluminal extraction catheter system, Interventional Technologies (San Diego) devoted significant resources to locating a supplier of fine wire able to meet its rigorous requirements. After an exhaustive nationwide search, the company settled on California Fine Wire (CFW), just up the Pacific coast at Grover Beach.

Wound into a coil with a radius that is very close to the diameter of the wire itself, the wire must be ductile yet strong enough not to pull apart or break easily.

Wire ductility and strength among primary concerns

"We found out the hard way that finding the right supplier is not an easy process," recalls Doug Rimer, vice president of operations. "Erratic wire properties increase the difficulty of the process and can be extremely costly. Variations in the raw material can cause all sorts of problems," Rimer explains. "You have to accommodate them by redesigning or by increasing sampling." One especially nettlesome issue, adds Rimer, was finding wire that met specifications in regards to yield strength and elongation at break.

Interventional Technologies designed a wire coil that is inserted over the tip of the guidewire core and joined to the device by means of a plasma arc welder. The guidewire coil is wound in an extremely tight radius, approximately 0.003 in., which is very close to the diameter of the wire itself. Consequently, a high level of elongation is required to wind the wire into a coil without engendering cracking or other defects. The wire needs to be ductile yet sufficiently strong not to pull apart or break.

In addition, wire quality is critical. If the tip coil is too rough, it can irritate the blood vessels; if it is too sharp or rigid, it can perforate the artery; and if the material has impurities, the tip bonding process can be compromised.

CFW made the grade simply because of its "ability to consistently manufacture wire that works for us and because of its remarkable turnaround time," says Rimer.

CFW has been producing fine wire since 1961 for more than 7000 customers worldwide. Currently about 20% of its customers are medical device OEMs. "Medical has always been a part of our business," says CFW president Mike Greenelsh, "and it's growing all the time." The firm has supplied wire products to a company that produces cochlear implants, he notes, and has had a great deal of success collaborating with manufacturers of specialized catheters that "may need an unusual material." Offering more than 1000 different metals and alloys in fine diameters and ribbons, CFW rarely finds that it can't fulfill even the most exacting customer demands, he adds.

To produce wire for Interventional Technologies, the company typically draws large-diameter wire through a series of progressively smaller-diameter dies and rewinds it onto spools. Particular attention is paid to the quality of the incoming materials and the condition of the die, because even a microscopic burr can produce an unacceptable scratch in the finished wire. The ultrafine gold alloy wire is then delivered to Interventional Technologies, which winds it into a coil and converts it into the guidewire tip.

CFW worked closely with Interventional Technologies to determine the purity required for the process while respecting exceptionally tight turnaround times, notes Rimer. "They also worked on the physical and mechanical performance specifications on drawn wire, which enabled them to become our sole supplier," he adds.

Companies primed for growth

That's especially good news for CFW, because Interventional Technologies has announced ambitious growth plans. Its newest product, the Cutting Balloon for angioplasty procedures, has captured 10% of the Japanese market and is in widespread use in Europe and other parts of the world. According to Rimer, the device should be approved for use in the United States in the very near future.

As Interventional Technologies continues to develop minimally invasive devices to combat heart disease, the company plans to expand its guidewire line. One current project involves the design and fabrication of guidewire tips with various taper configurations, such as a prebent "ready-to-go" model that is intended for use by cardiologists.

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