Engineering News : Page 4 of 7

producing such surgical implements. The high-temperature material it used to make these tools failed when it came to molding consistent colors in teal, maroon, and white. Also, the part exhibited a black speck marbling effect. Such defects can be catastrophic when you consider that the tool's size also indicates heart-valve size, and color indicates heart-chamber position.

The solution: switching to a precolored polysulfone compound supplied by RTP Co., Winona, MN, instead of a color concentrate. The result: improved dimensional stability, no material contamination, and the ability to undergo sterilization before and after performing a valve implant.


Urethane aids open-heart surgery

Buffalo, NY--In open-heart surgery, myocardial preservation--protecting the heart muscle--plays a critical role. An innovative tool, the Topical Cooling Device (TCD) made by the Ethox Corp., helps nurture this preservation. Lending an important assist in this effort: film made from urethane.

"Cooling protects the human heart during open-heart surgery," explains Mark Miller, product manager for COBE Cardiovascular, Inc., the Arvada, CO, company that markets the device. "When cooled, the heart's metabolic rate slows, the demand for oxygen is reduced, and the heart virtually stops. This process reduces stress on the heart muscle, and minimizes the potential of damaging the tissue."

During initial design stages, engineers considered making the TCD with polyvinyl chloride (PVC). Ultimately, they selected urethane because of its greater strength, flexibility, and efficiency in processing. "Flexibility was the driving force behind choosing urethane over PVC," says Bruce Tive, design engineer at COBE. "At low temperatures, urethane remains soft and flexible. Conversely, PVC can become so rigid that it could tear delicate muscle tissue."

For the TCD project, COBE selected urethane from JPS Elastomerics Corp., Northampton, MA. "JPS' urethane conforms well to the heart's shape and quickly goes from warm to cold and vice versa," Miller explains. "In addition, the material remains flexible at temperatures from 37C to 4C, which is deep hypothermia."

Purity proved another important factor in selecting urethane. "We required a virgin material that could be easily sterilized with ethylene oxide," Miller adds. "The JPS material has no plasticizers that can migrate out to weaken the original structure or contaminate the surgical setting."

How do customers feel about the TCD? "It has been widely accepted," says Miller. "In fact, we now have a large share of the market."


Spray process gives PEEK performance

Baltimore--Typically, coating components with polyetheretherketone (PEEK) requires two steps. First, the parts are sprayed with the PEEK powder, then they must be put through a heat cycle. Now, forget about step two.

Martin Marietta Laboratories has developed a way to apply PEEK to plastics, metals, and ceramics using a plasma spray-coating technique. "We can take the PEEK resin, put it in the hoppers, and in one step spray it and be finished," enthuses Greg Groff, a Martin Marietta engineer.

The process is not for neophytes, however. Groff cautions that the key to success lies in mastering the procedure. Groff spent more than five years varying process parameters in order to obtain the best results.

Did it pay dividends? Plasma spraying PEEK on various substrates provides "corrosion

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