Medical Device Daily National Editor

PALM DESERT, California — The meat and potatoes of the Materials and Processes for Medical Devices Conference here this week consisted of sessions short on “catchy” titles but long on information for the materials engineers and product designers who made up most of the attendee roster at the ASM International- (Materials Park, Ohio) sponsored meeting.

Those attendees were largely there for track presentations with no-nonsense titles such as “Advanced Materials,” “Corrosion Engineering,” “Fabrication Processes,” “Fatigue Life,” “Materials Information and Selection,” “Materials R&D,” “Regulatory Affairs Related to Materials” and “Surface Engineering.”

The fact that they’re serious about their work was reflected by the number of sessions, over two information-filled days, playing essentially to standing-room-only meeting rooms, despite the 11 – count ’em, 11 — pools and 36 golf holes that beckoned just outside those rooms.

The “Fatigue Life” I and II sessions provided a good example of the type of presentations that caught attendees’ attention, with such topics as “Statistical Methods for Life Prediction in Medical Devices,” “High-Cycle Fatigue Evaluation of Two Beta-Rich Titanium Casting Alloys” and “Durability Test for Patella Implants.”

In his “Statistical Methods” presentation, Hengchu Chao, PhD, an engineer in the heart valve therapy unit of Edwards Lifesciences (Irvine, California), emphasized the importance of materials fatigue in device performance.

He cited several important tests, including fatigue testing of a device under service load, testing to success to demonstrate reliability and testing to failure to establish a performance curve.

Chao said such testing provides clear interpretation of results, a platform for long-term testing and a basis for re-testing for different sizes, dimensions and processes.

Among the important design criteria in such testing, he said, is to evaluate a material’s reliability vs. safety factors.

Chao said that test-to-success on an actual device “provides clear evidence” of product performance, while, for instance, test-to-fracture “provides valuable information on failure reads.”

He added that the life-analysis testing approach “provides a statistical basis for fatigue life predictions,” while stress-analysis testing “mimics product service conditions.”

Proper testing design, including a fatigue/life parameter, “allows a good prediction of device performance,” a prediction that Chao said allows a clear “Go!” or “No!” message in evaluating whether a proposed design iteration should move forward.

He said a well-developed test-for-success on an actual device “is a useful confirmation to life-analysis testing.”

Jeremy Schaffer, of Fort Wayne Metals Research Products (Fort Wayne, Indiana), in a presentation on fatigue life in medical-grade wire, said that the fine 35Co-35Ni-20Cr-10Mo wire’s roots go back to 1965, when it was developed as an aerospace fastener alloy.

“It began being used in medical devices in the 1970s and 1980s,” he said, adding that the alloy was prized for “its resistance to corrosive attack and fatigue.”

In 2003, a “clean melt” version was introduced, so that the wire then could be developed for cardiac rhythm management (CRM) lead wires, coils and sensing elements.

Addressing the central question of the morning session, Schaffer asked, “Do they fail?” and answered his rhetorical query: “Eventually, yes.”

He used a quote from a medical-device executive to establish that a lead’s longevity cannot be predicted.

Schaffer cited the importance of the physical location of a lead as being important to the variability of its life. “These are very small products,” he said, “most being less than 1 mm in diameter.”

The small size of such specimens adds to the difficulties of failure analysis, he said. “They generate microscopically small crack effects.”

Testing brings evidence of “lots of characteristics, but fatigue failure is the one that stands out,” Schaffer said.

He cited a number of important considerations in such testing; among them:

• Development of a hierarchical model.

• Verification of the model results.

• Providing a statistical comparison.

• Making “dislocation pileup” assumptions.

• Assuring the validity of an upstream survey.

• Testing total fatigue life.

Turning to drug-eluting stents (DES), a hot topic in materials circles as well as in industry and clinical circles these days, Dr. James Conti, executive VP of Dynatek Dalta Scientific Instruments (Galena, Missouri), discussed methods for evaluating the shedding of particulates by DES.

“There’s a big problem with particulates” from DES devices, Conti said. With those and other particulates, as from orthopedic implants, “size matters,” adding that smaller particles, in particular, “are more toxic.”

The particulate problem is pretty pervasive, Conti said. “If you’re dealing with a medical product, you’ll be dealing with particulates.”

He said bifurcated products, a commonplace approach in the realm of stenting, “tend to break.” So, in the set-up stage, “you need to know that your product is physiologically compliant and that sanitation issues are addressed.”

For testing, “you have to set target values and have data-collection methods clearly identified.”

Conti said intermittent testing is better than one-time testing, which tends to get short shrift from the FDA.

“That allows you to be more stent-specific,” he said.

But most useful of all, in his view, is real-time data collection, which his firm does. “It’s the best method,” Conti said. “You can tell which stent the data is coming from, which better allows you to interpret the shower of particles.”