Medical devices across the United States must not only keep pace with advances in technology but also with the increased use of harsh solvents and disinfectants. However, many materials commonly used in medical devices aren't able to withstand these new cleaning protocols. The nearly decade-long effort to combat healthcare-associated infections (HAIs) through increased disinfection has resulted in the degradation of their protective housings, causing cracking, crazing, discoloration, and premature failure of devices. Manufacturers must look to materials with higher levels of chemical resistance to strengthen device integrity and protect patient safety.

Eastman MXF221 copolyester is currently being deployed or considered for use in a variety of applications, including ultrasound probes.

Fortunately, a recently developed testing protocol is now available that helps medical device manufacturers combat these issues as they look to develop the next generation of devices or retrofit their current lines.

A Look Back

How did we get here? Back in 2008, the U.S. Department of Health and Human Services (HHS) established the prevention and reduction of HAIs as a top priority. An HAI Steering Committee, along with scientists and program officials, developed a road map for HAI prevention in acute care hospitals — including action steps such as reporting infection rates of specific HAIs and reducing Medicare/Medicaid reimbursements to hospitals with the highest infection rates beginning in 2015. To combat HAIs, new cleaning protocols were introduced that include the repeated application of isopropyl alcohol (IPA), IPA plus chlorhexidine, bleach, and other harsh chemical disinfectants.

As a result, fortunately, HAI rates in hospitals, ambulatory care centers, and clinics have tumbled, and patient well-being has dramatically improved. The downside is that problems with medical device housings have skyrocketed, since many of the plastic materials specified for these device housings begin to degrade after repeated exposure to harsh disinfectants. In many instances, this has led to equipment failures and reduced service life with the requisite repair and replacement costs.

The Four-Step Test

A simple four-step test can reveal a material's robustness in just 24 hours.

  1. Select the appropriate jig. Choose a strain level that most appropriately reflects environmental stress cracking.

  2. Load flex bars onto the jig. Remember to load control samples.

  3. Apply chemicals to flex bars using presoaked pieces of cotton. Enclose the entire sample jig in a plastic bag to prevent evaporation, and leave it at room temperature for 24 hours.

  4. Perform reverse side impact test. This is the differentiating step.

The medical device design industry has largely been unaware of the need to specify materials that can withstand the rigors of aggressive disinfectants. Furthermore, testing protocols to help guide decision making have been lacking — until now. Medical device manufacturers now have a new and welcome tool in their quest to design and develop more rigorous housings: a four-step testing protocol.

This four-step testing process, developed by material scientists at Eastman, is the first-ever protocol that allows device manufacturers to evaluate the heavy toll these harsh disinfectants take on different plastics. Based on sound science, the test enables designers to make better, more informed decisions regarding material choice.

While the first three steps will be familiar to any device manufacturer, it is the fourth step — the reverse side impact test — that determines a material's required robustness. It offers a more accurate assessment of how a given material will hold up in a hospital environment in light of today's HAI cleaning protocols (see the sidebar, “The Four-Step Test”).

Comparing Materials

Why do certain plastic housings perform better than others? It's due to a variety of factors, starting with the material itself and including how it is molded and assembled. Due to the large number of legacy plastics on the market, medical device designers have skillfully managed to “design out” some of the stress in particular device components.

Because designers have become familiar with common plastics such as polycarbonate, polycarbonate/PBT, polycarbonate/ABS, and PVC, they have grown accustomed to the relative strengths and weaknesses of each material. That legacy knowledge may have worked in the past, but in this new era of stringent cleaning demands, designers need more accurate and advanced testing to evaluate both standard and new materials.

The four-step test — in particular the critical fourth step — allows design engineers to accurately assess the impact of the molding process and the stress that results from device assembly. It also provides an accurate assessment of the impact from repeated rough handling and disinfection in hospital settings.

New Materials Meet the HAI Challenge

While standard plastics lack the strength to withstand the challenges of HAIs, a new generation of advanced plastics is now available that helps address what can't be worked around in today's hospital settings. These new plastics can lead to new and more durable medical device equipment with a cost difference that frequently pales in comparison to the repair and service costs of a failed device.

For example, Eastman has introduced Eastman MXF221 copolyester, a specialty plastic that has been proven to display greater impact resistance and durability than a host of legacy plastics before and after disinfection. The halogen-free polymer is currently being deployed or considered for use in a variety of applications, including MRI coils, ultrasound probes, buttons, handles, and portable patient monitor units.

The hard and soft costs to hospitals using device housings composed of existing plastics are real. Equipment originally designed to last 8–10 years is encountering early life-cycle failures. From a patient's perspective, devices that appear to be old and discolored can be quite unsettling, leading them to question their efficacy and safety. They are less likely to fault the manufacturer than to question whether the hospital is using the best and most up-to-date technology.

While successfully combating HAIs has greatly improved patient well-being and generated desirable bottom-line results for hospitals, it has changed the way medical devices need to be designed and manufactured. New testing protocols and new materials will drive the next wave of improved performance and durability. This is how innovation happens.

This article was written by Yubiao Liu, PhD, Medical Application Development Scientist, Eastman, Kingsport, TN. For more information, visit here .