Ensuring that Plastic Devices Can Withstand Rigorous Disinfecting Procedures

What can manufacturers do so their plastic medical devices don't crack or degrade under more-stringent cleaning?

To try to stem the increasing incidences of healthcare-associated infections (HAIs), hospitals are stepping up their disinfecting protocols on medical devices. But these more-stringent practices that may use either stronger chemicals, or the more frequent use of them, or maybe both, could have harmful effects on some plastic devices, causing them to break, crack, or degrade prematurely. Manufacturers need to understand, from the design stage forward, how their products will be cleaned and then plan to use plastic materials that will stand up to these various disinfecting formulations and procedures.

MD+DI spoke with several experts in the plastics materials industry, as well as an expert in reprocessing, to explore how manufacturers can ensure that their plastic materials remain durable despite frequent contact with these new chemicals.

For a little background, here are few facts about HAIs. On any given day, about one in 31 hospital patients has at least one healthcare-associated infection (HAI). And these infections can be deadly. Clostridium difficile (C. diff) alone caused almost a half a million illnesses and an estimated 15,000 deaths among patients in the United States in just one year. C. diff spores are easily spread to a variety of surfaces, and the spores can survive on these areas for up to five months.

So, it is critical that all surfaces that patients might possibly touch or be in contact with be thoroughly cleaned and disinfected before they can cause an HAI. Hospitals have gotten this message loud and clear.

“Hospitals are changing their disinfection protocols,” said Lauren Zetts, healthcare segment manager, Americas, Covestro. “They are looking to avoid getting a person sick while they’re helping them get well. They are looking for new disinfectants and other ways to ensure that their durable devices aren’t carrying different bugs from patient to patient.”

“It’s obviously the right thing for them to do for the patient,” agreed Ellen Turner, global market development manager, medical devices, Eastman Chemical. She added that there is also financial motivation to improve cleaning procedures, namely reimbursement from the Centers for Medicare & Medicaid Services (CMS).

The Affordable Care Act allows CMS to reduce payments by one percent to the worst-performing 25 percent of all subsection (d) hospitals with respect to their record of hospital-acquired conditions (HACs), of which HAIs are the largest percentage.

But, while good for patients, plastics used in medical devices don’t always fare as well. “Environmental stress cracking is a common and complex problem in medical devices,” said Ashir Thakore, global healthcare segment Leader, SABIC. To avoid this, manufacturers must have an in-depth knowledge of chemical disinfectants, polymer chemistries, and their compatibility, he said.

“The outcome of more rigorous disinfecting is that plastics that have been used for many years in the hospital are breaking down,” said Turner. “So now we see incumbent plastics not holding up over the 8 to 10 years of life that is expected of these longer-term reusable devices like an ultrasound, x-ray, or MRI coils.”

“The hospital makes a big investment in this equipment, and basically it’s cracking and breaking,” Turner continued. “And when you get cracks in the plastic, you have areas for infections to hang out, and you also have places for disinfectants to get inside to the electronics. It’s just a downward spiral.”

Can This Problem Be Solved on the Disinfectant Side?

If more-stringent disinfection is causing problems with durable medical devices, could the answer be to change the chemicals used?

“Disinfectant manufacturers are aware of the problem, and they do all they can on the formulation side to make disinfection chemicals as easy on the equipment and as fast-acting as possible, yet still have an effective kill rate,” Turner said. “However, they know that they can only go so far, depending on the different types of formulations at this point.”

Also, device manufacturers have little control over what actual chemicals or procedures are used in the healthcare setting. “If you’re launching a medical device that’s going to be sold all over the world and you can’t prescribe what is being used to disinfect, then you must make that device as failsafe as possible from a clean ability and durability perspective,” she added.

Pierre Moulinie, global technology lead for polycarbonates healthcare at Covestro, agreed. “When we’ve interacted with the disinfectant makers themselves about their new products, we’ve asked, ‘where is this going?’” he said, referring to future new disinfectants potentially causing plastic failure. “Today, there is no single disinfectant that seems to work on everything. They’re aware that their product may cause plastic equipment housings to break.”

Both Turner and Moulinie mentioned that disinfectant manufacturers are very responsive in trying to help with the problem of chemical attack from disinfectants. Moulinie said that his company has been approached to help with wording the instruction manuals of the disinfection procedures, so that operators can properly apply the chemicals to try to lessen harmful effects.

Disinfectant manufacturer Clorox has collaborated with Eastman to promote Eastman’s four-step test method for choosing materials that will withstand rigorous disinfecting procedures. “When they saw the test method, they wanted to promote it because if more people built devices with materials that had been screened with this test method, devices would be more compatible with disinfecting protocols from the start,” said Turner.

What Can OEMs Do?

To avoid problems with plastics failing, manufacturers should start at the very beginning, said Alpa Patel, senior scientist, healthcare reprocessing, Nelson Labs. “Cleaning is the first—and most important—step in processing devices. Manufacturers need to focus on the ability of their devices to be cleaned before moving on to the next processing steps.”

“Thinking of how a product should be reprocessed should be considered, when designing a reusable medical device,” she said. “At a minimum, manufacturers should be asking the following questions during the design phase. ‘What is the expected lifecycle of the device? Will the material hold up to repeated cleaning? Is the supplier of the raw materials validated to provide a consistent product to the manufacturer?’”

She stressed that human factors considerations are hugely important when it comes to reprocessing reusable medical devices. “They are the front-line people who are doing the processing,” she said, and urged companies to go to healthcare facilities and have their team look at how devices are being reprocessed and evaluate how it is done.

She added, “Instructions for use need to adhere to the guidelines outlined in AAMI TIR 55—where the directions are written as clear and simple as possible for the users who clean these devices.”

Training is also key, she said. “Manufacturers should have a team of people that go out and train regularly. Not just one-time training, it must happen regularly. That’s the only way we’re going to move forward in this industry, while ensuring patient safety.”

Materials Selection and Processing

“It can be challenging for medical device manufacturers to select materials that can meet requirements for both mechanical performance, such as stiffness and impact and creep resistance, as well as chemical resistance performance to withstand harsh disinfectants,” said Thakore of SABIC.

Sometimes, weaknesses in the plastics can be caused during processing. “In cases of injection molded parts, molded-in stresses can lead to early failures when subjected to external factors, such as cleaning protocols,” said Thakore. He said that achieving optimal performance in a component made from an engineering thermoplastic requires the use of a good design practices, such as minimizing concentrations of stress to prevent high localized areas of stress, and uniformly distributing stress.

“To achieve these design objectives, it is helpful to maintain a uniform and consistent wall thickness and to use gradual transitions when uniformity cannot be maintained,” said Thakore. “Also to reduce stress concentrations, all sharp corners should have as large a radius as is possible.”

However, when a manufacturer determines that an alternative material that can better withstand cleaning is the solution, Moulinie of Covestro said that one of the important parameters is the melt flow of the materials. “You may have a product on the data sheet that looks interesting, but you may not be able to fill the part with the existing tool design and gating, etc.,” he said.

“There are no easy answers for housing materials. Draft angles and rigidity can also be critical when choosing a material. At the end, you have to find the right balance of properties for the given application.”

Moulinie noted that if a manufacturer is going to be replacing PC/ABS, the shrinkage rate may be different. “This might not be a problem,” Moulinie said. “It comes to what does the part look like and what are the tolerances. Can you still join them?”

Turner said that Eastman has a lot of “watch outs” and specific tips that will allow the manufacturer to work closely with them to make the adjustments needed for existing tooling.

Her take on the shrinkage rate was a bit different. “Eastman’s Tritan-based materials have a similar shrink rate as PC/ABS,” she said. This means that manufacturers may be able to stay with existing tooling. However, she said that “If they move to a different blend of materials, there is a very good chance that the shrink rate is going to change quite a bit, and the existing tooling is no longer going to work at all.”

Eastman provides other help for manufacturers as well. “We do have a baseline of tips. For situations where you’ve always specified a material that is no longer holding up to the disinfectants, how do you move away from that material?” Turner said. “Plus we have a lot of very friendly molders who have been down that path, know Tritan very well, and are working closely with us. So, those are the types of things that we share to make sure that a design engineer or a tooling manager can efficiently make a material switch.”

“In cases of injection molded parts, molded-in stresses can lead to early failures when subjected to external factors, such as cleaning protocols,” said Thakore. He said that achieving optimal performance in a component made from an engineering thermoplastic requires the use of a good design practices.

For a lot more information, tips, and advice on how manufacturers can resolve these issues around plastics breaking down, some of these experts and other representatives from their companies will be presenting sessions and exhibiting their materials at MD&M West 2019 in Anaheim, CA, February 5-7.