As in any industry, new technologies and material choices present new opportunities and challenges for OEMs looking to build brand equity, bring products to market faster, and meet consumer demand. Medical device manufacturers are faced with multifaceted challenges to meet the highest degrees of performance, efficacy, regulatory compliance, and safety in the service of protecting the health and well-being of patients. From the integration of advanced technologies all the way through to the type of material used, every design decision has lasting real-world consequences.

Eastman’s four-step test can help manufacturers confidently choose the most suitable plastic material for medical housing.

Embracing and rising to these real-world challenges is the mainstay of medical device development experts. The increasing scrutiny of hospital-acquired infections (HAIs) — and the methods to combat them — places new importance on the smart selection and rigorous testing of medical device housings. This article explores the most recent cleaning protocols and their impact on medical device housings in terms of patient safety, device performance, and hospital operations. In addition, it explores new material options and testing that can guide manufacturers in choosing and testing materials that will meet these increased demands.

HAIs: Changing the Game

HAIs are a concern for all aspects of healthcare. In 2009, the Centers for Medicare and Medicaid Services (CMS) began refusing payment for some readmissions due to HAIs. Beginning in 2012, CMS lowered reimbursements across the board for hospitals with excess readmissions, including HAIs. Today, hospitals face an additional 1 percent reduction in reimbursement if they are in the top 25 percent of hospitals that don’t meet this year’s milestones.

To make sure they don’t lose these Medicare reimbursements, hospitals are preventing HAIs on two fronts: environmental cleaning and aseptic protocols. Both involve the frequent use of aggressive disinfectants that can damage device housings and other components.

New Cleaning Protocols: Great for HAI Prevention, Bad for Device Housings

Because of new cleaning protocols that require more frequent use of aggressive disinfectants, the number of HAIs has been significantly reduced. These new, stringent protocols include the repeated application of isopropyl alcohol (IPA), IPA + chlorhexidine, bleach, and other harsh chemical disinfectants. Additional recommended steps for some applications include sterilization with ethylene oxide (EtO) or gamma radiation.

Excellent progress has been reported in HAI prevention, according to the most recent CDC report. However, one unintended consequence has been that the repeated exposure to aggressive disinfectants has led to substantial deterioration of device housings and hardware. At the same time, greater portability and connectivity present new risks for accidental impact.

Cracking, crazing, discoloration, and premature failure are all leading clinicians to question the quality and safety of medical devices. In fact, many devices designed only a few years ago are already experiencing performance and functional issues that are negatively impacting the life cycle of housings made with commonly used materials. Keep in mind, most equipment is intended to last 8–10 years.

The reason for premature device failures could be that the materials used may be structurally unable to handle the increased frequency of cleaning required in today’s healthcare facilities.

The Real Cost of Device Failure

The design engineer may be the last one to hear about the effects of disinfectants on an innovative and promising product design — or may only get part of the story. And quality engineers can easily misdiagnose failures and blame them only on a drop or accidental impact — especially if they don’t have a good understanding of how plastics react to chemical attack.

By considering the impact that aggressive disinfectants have on plastics, it becomes more apparent that many failures could be prevented by simply changing to a different material. However, doing so is often viewed as risky and costly. But this is not always the case, as a manufacturer’s material cost differential for change may be insignificant compared with repair and service costs of a failed device. Even more critical is what unreliable devices can cost the hospital or clinic — in physical repairs, patient access, and satisfaction levels. And of course, there is the risk to patient health and safety.

It’s a simple fact that certain materials are better (and better suited) to certain medical device applications based on a variety of factors, such as molding, processability, end-use robustness, durability, cost, avoidance of repetitive failures, and varying degrees of chemical resistance. A material’s chemical resistance is now more important than ever given the current — and effective — HAI-prevention cleaning requirements.

Advanced Testing: Taking the Extra Step

Chemical resistance is a function of the material itself, the types of disinfectants and chemicals the material is subjected to, and its repeated handling. To better predict functionality in real-world hospital environments, stress should be factored into chemical resistance testing. This is because stress accelerates the effect of chemical attack and chemical exposure accelerates the reduction of impact strength.

Grounded in sound science, a new four-step testing protocol has been developed. This protocol, based on modified ASTM D543 and ASTM D4812 (step 4 only) standards, is designed to mimic failures from typical usage conditions to better understand why commonly used plastics fail and help medical device designers confidently choose the best material for their devices.

This new four-step test has been developed to ensure that it is replicable, reliable, and accurate. The first three steps will be familiar to any device manufacturer, but the fourth step is a key differentiator that is critical in determining the robustness required for today’s HAI protocols:

  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 fourth step — the reverse side impact test — offers a more accurate assessment of how a given material will hold up in a real-world setting. Results show that a material may or may not exhibit visually apparent changes after the first three steps. However, varying degrees of cracking and crazing become noticeable and significant after the reverse side impact test is performed.

To best interpret the results, it is recommended that testers document the impact strength of exposed and control samples to calculate the percentage of reverse side impact strength retention. Higher retention translates to better reliability after exposure.

All medical device manufacturers should consider applying this test as they develop or retrofit their current product lines.

Limits to Design

Many medical device designers have proved quite adept at trying to “design out” the stress in a particular device component. What this does not account for is the impact of the actual molding process and the stress that results from the assembly of a device. This includes the vibration impact from sonic welding and the repeated rough handling and disinfection in the hospital setting. This stress is precisely what step four attempts to replicate.

In repeated testing, a specialty copolyester material was compared to legacy polymers using this four-step protocol. Results indicated superior impact resistance and durability compared to polycarbonate, polycarbonate/PBT, polycarbonate/ABS, and PVC. The material was able to withstand rigorous use across a wide spectrum of disinfectants, including those made with bleach compounds, while offering increased durability and reduced product failures for a wide variety of applications.


The results of rigorous cleaning protocols have dramatically reduced HAI rates for patients in hospitals, ambulatory care centers, and other facilities where repeat-use medical devices are frequently employed. The impacts on hospitals and medical device manufacturers are now starting to be more widely understood and require affirmative steps.

These cleaning regimens are having a negative impact on device housings made with commonly used materials. Cracking, crazing, and discoloration are being observed, requiring costly repair, replacement, and shortened life cycles.

Beyond a strict cost-benefit analysis, this product degradation negatively affects the brand equity and brand promise of both the OEM and the hospital itself. Devices that appear old or damaged risk perceptions of equipment being out of date or, in the worst-case scenario, unsafe or ineffective.

Medical device manufacturers can take advantage of new materials — and new testing — that will ensure not only the reliability and safety of their products but the continued beneficial relationship with hospitals and medical care centers.

While issues with medical housings may well be an unintended and negative consequence of these new HAI-prevention cleaning protocols, they present new opportunities for the next generation of devices that will continue to enhance patient care, provide peace of mind and brand confidence for hospitals, and allow manufacturers to bring to market better performing products.

This article was written by Dr. Yubiao Liu, Medical Application Development Scientist for Eastman, Kingsport, TN. For more information, Click Here .