The benefits from metal-to-plastic part conversion cuts across all parts of the health-care industry, from device makers, doctors, hospitals and patients, according to Jay Haverstraw of PMC LLC.
“It’s really predominately cost drivers, but there’s a bunch of side benefits to the other players in the food chain, so to speak,” said Haverstraw, technical sales manager at PMC, a Cincinnati-based injection molder, in a recent presentation at the Plastics in Medical Devices 2012 conference in Westlake.
Society of Plastics Engineers
Strong and Flexible Implants
In the late 1990s, polyetheretherketone (PEEK) was first used for implants. PEEK-based spinal spacers were used to hold vertebrae upright after disk removal. Unlike titanium, PEEK parts didn’t eventually subside into bone, and they allowed visualization of the bone surrounding the implant in X-ray or CT images.
These advantages and others have led to many more PEEK-based implants. Marcus Jarman-Smith is a technology leader at Invibio Ltd., which has been making PEEK-OptimaR polymer for over a decade. He says that in addition to spinal implants, the material holds clear benefits for knee-replacement and hip-replacement parts. PEEK parts don’t produce the health concerns associated with the metal against metal wearing of traditional hip replacements. The strength of Invibio’s bearing grade, MotisR, means it can be used alone to make hip-replacement cups instead of combining a metal cup with a polymer liner. The resulting thinner cup requires the removal of less bone. In addition, polymer parts flex and pass on stress to the bone rather than focusing the stress on the implant. This transfer of stress helps bone maintain strength and means that damage is less likely to occur.
“Because of the polymer’s high strength and bearing properties, it is starting to be looked at more for trauma applications,” says Jarman-Smith. He says that PEEK has a high strength-to-weight ratio and allows more flexing than metal plates and nails used to repair a broken arm or leg. If the patient is a child, or if the patient develops an infection, plates or nails may have to be need removed, which is difficult with metal because it tends to bind to the bone, whereas PEEK doesn’t. The QuantumTM Humeral Composite Nailing System from N.M.B. Medical Applications Ltd. was the first PEEK intramedullary nail to gain FDA approval (March 2010). The nail is made of Invibio’s EndolignR, a composite of continuous carbon fibers in a PEEK-Optima polymer matrix.
For future developments and applications, the company is considering options such as combining PEEK with additives that help it bind better with bone or encourage bone growth. “We also want to see if we can use it to make scaffolds or porous PEEK parts that can support tissue and allow tissue to grow inside and regenerate,” says Jarman-Smith.
Although PEEK has many advantages for medical implants, it can be difficult to mold in a clean-room environment because of its high melt temperature. PMC SmartSolutionsTM has been implementing new ways to handle this challenge. The company, founded in 1929, entered the medical molding market four years ago. It specifically focused on long-term surgical implants made of materials such as PEEK because of the potential growth in this market.
“Consistency is very important for implants,” says Lisa G. Jennings, president of PMC SmartSolutionsTM. Using heat-transfer oils for mold-temperature control can potentially cause product contamination. Electric cartridge heaters are subject to temperature problems that can affect product consistency because they cannot control the mold’s surface temperature in a tight window across a part and often have hot and cold spots along their length. Cartridge heaters are also unable to remove heat from the mold if it becomes too hot.
Thus, PMC examined using pressurized water for precise mold-temperature control. Pressurized water can be heated to temperatures as high as 400°F. The company partnered with Single Temperature Controls of Charlotte, North Carolina, USA, which sells temperature-equilibrium systems that pump water through the mold at a set temperature. Heat is transferred to the mold if the water is hotter than the mold and removed from the mold if the opposite is true.
In PMC’s experiments, it found a 44.2°F variance in mold temperature with electric heating and only 5.0°F variance with the water-heated system. The effects from this variance could be seen through a 0.003-inch increase in part shrinkage and average 18.5% reduction in relative crystallinity in the same parts produced using the electric-heated molds.
The pressurized water system has allowed the company to make complex parts of PEEK and other high-melt temperature plastics. For example, it has made insert-molded porous metal parts for orthopedic implants. “We were among the first to use high-pressure water to control mold temperature for making medical-device implants in a clean room,” Jennings says. Since PMC shared its data showing the benefits of using water to control mold temperatures, other companies have followed its lead in using this technology. The complete white paper is available on www.pmcsmartsolutions.com.
At the recent Plastics in Medical Devices conference in Westlake, several speakers touched on an emerging trend: implantable devices. Lisa Jennings, president of PMC LLC in Cincinnati, shares lessons learned in her 15 years’ experience with injection molding such products.
In this brief video clip, Jennings describes strategies for serving the implantable sector including partnering with supplier companies, as well as information about some of the most promising markets for implantable products.
Jennings is a fourth-generation owner of PMC, an 80-year-old injection molder and contract manufacturer serving the medical, commercial electronics and transportation markets.
Under her guidance, the Cincinnati firm has become a leader in supplying implantable and non-implantable medical devices and surgical instrumentation. In addition to its Ohio headquarters, PMC also operates a production facility in Shelbyville, Ind., as well as joint venture plants in Mexico and Germany.
WESTLAKE, OHIO (April 20, 1:40 p.m. ET) — The medical device market can be a rewarding one for plastics processors, but it’s not a market you can wander into and hope to succeed.
The volume of requests for medical projects is growing at Parker Hannifin Corp., a Cleveland-based manufacturing giant that uses engineering resins, fluoropolymers and urethanes in its seal products. But Dale Ashby — vice president of technology and innovation for the firm’s sealing and shielding group — said that those increased requests bring with them a lot of work in material selection, as well as part production.
“The main question that every customer has is : ‘How long can I expect this product to last in my application?’ “ Ashby said at the Plastics in Medical Devices conference, held April 12-14 in Westlake.
“We need well-defined expectations of performance from our customers to make predictions on seal life,” he added. “Modeling is very important. It’s step No. 1 in proving useful life. Tools and modeling continue to improve, and OEMs have more knowledge than ever before.”
Parker, a supplier to many major OEMs, rang up sales of more than $10 billion in 2009. The firm employs 62,000 at almost 300 plants worldwide.
Parker made a big move in the medical field in 2008, when it created a new medical systems division in its seals group. The new division was based on six businesses — five in California and one in Indiana — that Parker had acquired from HTR Holding Corp. Those businesses make plastic and elastomeric components for medical devices such as intravenous equipment, drug-infusion pumps, respirator hoses and catheters sold directly to OEMs. The group performs injection molding, rapid prototyping and similar services.
Ashby said that in material selection, it’s important for processors to consider physical properties such as elasticity and lubricity, and mechanical properties such as flex resistance and toughness. In thermal properties, processors need to be aware of melt flow index and thermal conductivity; while in electrical properties, surface resistivity and arc resistance can impact material choice. Chemical resistance to solvents and cleaning solutions also plays a role.
Injection molder PMC LLC of Cincinnati is among the ranks of firms that successfully have entered the medical field in recent years. But even for PMC, doing so took a pretty big leap of faith, according to President Lisa Jennings.
“We bought the equipment for medical molding, had a clean room ready and did sample molding before we even had a customer,” she said at the event. “But based on our evaluation of what PMC is capable of — making millions of parts at 0 PPM quality levels — we determined that medical was a good niche for us.
“We had best-in-practice standards that weren’t available to most of the medical device group.”
PMC also “had to develop a medical culture” that was different from automotive and other markets it had participated in over the course of its 81-year history.
“We needed to consider all areas of our business and manufacturing systems,” said Jennings, who is also a fourth-generation owner of the firm. “For clean-room classification, we had to create an environment to insure that implant molding is controlled and consistent.”
“We learned that having the right processing equipment is the foundation for repeatable processing of implantable polymers. We also learned that customer validations are custom and are up to interpretation.”
PMC — which operates plants in Indiana, Mexico and Germany — now produces medical items used in orthopedics, sports medicine, spinal care, cardiovascular care and drug delivery. PMC’s medical products are based on polyetheretherketone (PEEK), thermoplastic polyurethances and ultra-high-end bioabsorbable and bioresorbable resins, which are used in implants and other devices.
“Some of these materials can cost from $125 a pound to thousands of dollars per pound, so there can’t be any material wasted,” Jennings said. “That’s a huge consideration.”