Moving on With Orthopedic Materials

In some medical device manufacturing circles, the tendency is to use the same materials over and over again, because OEMs and the FDA are familiar with them, so projects can proceed on a streamlined quality and regulatory path. But this is not always true with orthopedic manufacturing, where the market dictates that implants be made to last a long time and resist wear. Any new material or composite that can help with this goal is going to receive strong consideration for use.

That means firms that supply materials and processing services to orthopedic OEMs are experimenting with different materials all the time. Here are their insights into some of the materials that have come into greater use in recent years for orthopedic applications.

On the metals front, a nickel-free stainless steel alloy called Biodur 108 has been growing in popularity, according to Rich Hockman, director of sales for Veridiam Medical Inc., a  contract manufacturer based in San Diego. “A percentage of people who need implants are allergic to nickel,” he said. “Toxicity tests can determine who is affected before scheduled medical procedures, but there isn’t time to run them in trauma situations. Biodur 108 is a no-brainer, so you don’t have to worry about nickel allergy in any situation.”

Another benefit is that nickel-free stainless alloys are stronger than nickel-containing ones, and offer comparable corrosion resistance.

Also being used more in orthopedic instruments, said Hockman, is Carpenter 465, an age-hardening stainless alloy, which is much stronger and more resistant to stress corrosion cracking than its predecessors.

“It can be heat-treated to a much higher hardness than what was possible in the past,” he added. “Instruments that previously failed to last the entire procedure can now last throughout it, so the surgeon does not have to worry about tool life.”

Mike MacKay, president of MacKay Manufacturing, a precision manufacturing contractor in Spokane, WA, said his clients are using more 17-4 stainless steel.

“We use more 17-4 that in the past due to availability, ease of machining, and the ability to be heat-treated without an atmosphere oven,” he said. “The physical properties are equal to most other products, and in many cases the customer will agree to our suggestion.”

Instrument handles are also better made nowadays thanks to advances in materials, said Jeff Wilson, business development manager for engineering materials at Curbell Plastics, Inc., an Orchard Park, NY-based plastics supplier. These innovations mean that the handles are not as likely to crack during procedures as they once were.

“The largest shift I have seen is a move away from Canvas High Pressure Laminates and PEIs (polyetherimides) to more use of PPSUs (polyphenylsufones) in instrument handles,” he explained. “One of the main reasons I feel this has happened is because of the improved toughness (Notched Izod Impact Resistance) of the PPSU, which is 13.0 ft-lbs/in using ASTM D-256, as compared to 1.0 for PEI and 1.5 for Canvas High Pressure Laminates. We view toughness as the ability of the material to resist cracking as the result of an impact.”

For implants, alumina matrix composite materials have burst on the scene in recent years, thanks to the need for them to last longer, says Andrew Nield, director of sales and marketing for C5 Medicalwerks, an international medical ceramics firm based domestically in Grand Junction, CO.
“There is a major shift towards alumina matrix composite materials in the orthopedic field,” he said. “This is driven by a need to produce stronger and longer-lasting hip joints and knee joints.”
One ceramic product offered by c5, called Cerasurf, provides less friction and wear compared to metal and polymer-based surfaces.”

He added that there is much development work going on right now for orthopedic applications with ceramics, including resurfacing heads, mono block liners, large-diameter heads, pre-assembled liners, femoral knees, and dual mobility systems.

Those using thermoplastics for their implants are turning more to PEEK (polyetheretherkeytone),
said Mark Schaefer, corporate vice president of business development for Spectrum Plastics Group, a materials processor based in Minneapolis.

“In the last few years, the use of PEEK has gone up thanks to its compatibility with the body,” he said. “And it is being used more and more in orthopedic implants that require strength.”
Among PEEK’s advantages are that it is highly resistant to radiation, solvents, bases, and stress cracking.