Hospital acquired infections (HAIs) represent one of the key challenges facing today’s healthcare industry. According to a recent study published by the Journal of the American Medical Association (JAMA) Network, total costs associated with HAIs reached an estimated $9.8 billion in 2013. More importantly, HAIs remain a significant threat to patient well-being. The JAMA study reports that the five most common HAIs afflict more than 440,000 patients every year and pose a significant financial burden to the US healthcare system.
While HAIs do not represent a new problem, they pose unique challenges to medical instrument, device, and equipment manufacturers who are working to steer a new course toward more robust product designs. Among the challenges faced by medical device makers, designers, and material suppliers are the increasingly aggressive disinfection and sterilization methods used on reusable medical devices.
Manufacturers and suppliers are also addressing growing demand for single-use instruments that, with their many benefits, introduce liability issues stemming from their potential reuse. And finally, there is intense debate over whether “design for sterilization” can keep pace with increasingly complicated medical devices, as illustrated by the recent outbreak of CRE (carbapenem-resistant Enterobacteriaceae)-related bacterial infections linked to the complexity of an endoscopic retrograde cholangiopancreatograph endoscope.
Sterilization and Sanitization Get Aggressive
Hospitals are looking for more effective cleaning/sanitizing agents, as well as new equipment designs that help ensure effective and complete sterilization. In Europe, the trend is toward more concentrated (i.e., higher pH) disinfecting agents, but overall chemical compositions are getting more stringent across the globe. Interestingly, many of the active cleaning agents themselves aren’t becoming more aggressive. Rather, the carriers are being modified to wet better and last longer on the surfaces to which they are applied.
The non-ionic surfactants or wetting agents used in these new cleaning/sanitizing agents target diverse healthcare applications, such as housings for handheld scanners, ultrasonic probes, and surgical instruments. Many of these applications have relied on engineering resin technologies, such as acrylonitrile-butadiene-styrene (ABS) or polycarbonate (PC). While these materials offer excellent toughness and impact resistance, they lack the necessary chemical resistance for emerging sanitizer formulations. Components such as sight glasses, display ports, and filter housing windows require the use of transparent plastics which are amorphous polymers and typically more susceptible to chemical attack. (See Figure 1)
Consequently, the more aggressive surfactants used in today’s sanitizing agents can cause stress cracking (embrittlement) and discoloration of conventional thermoplastic parts, and for transparent plastics, they may cause hazing over time.
Performance requirements for medical equipment, cases and trays, surgical instrumentation, and other non-implantable medical devices vary widely. But they share a common need for high-performance attributes that medical grade plastics provide. High-performance polymers, such as polysulfone (PSU), polyphenylsulfone (PPSU), and polyetheretherketone (PEEK) are suitable for limited exposure applications that are in contact with bodily fluids or tissue for less than 24 hours. They deliver a combination of strength, toughness, and intrinsic resistance to high temperatures as well as to chemicals. These qualities are all critical to withstanding conventional sterilization methods, such as steam, ethylene oxide, vaporized hydrogen peroxide, and gamma radiation. (See Figure 2)
PSU, PPSU, and PEEK also offer inherent flame retardance without the need for additives, which is a key advantage over other thermoplastics. Many additive technologies can compromise impact resistance and other desirable qualities as well as alter a material’s mold behavior and tooling requirements.
Multiple Challenges for Single-Use Instruments
A growing trend among healthcare original equipment manufacturers (OEMs) who previously only offered reus able surgical instruments is to now provide single-use sets. Single-use instruments can help reduce the frequency of HAIs, assuming the instruments are used as specified. The potential reuse of devices designed to be used only once raises potential liability issues of concern to both OEMs and end users.
Instruments intended for single use are typically de signed for sterilization with a gamma dosage between 40 and 100 kGy, although a single flash steam sterilization cycle or a wipe-down with a chemical cleaner in the operating theater is not uncommon. Steam sterilization is most frequently used for reuseable devices, with designs targeting service lives of hundreds of cycles.
OEMs are seeking ways to design single-use instruments that are robust enough to retain critical properties if they are properly sterilized with gamma radiation, but visibly change in appearance if incorrectly sterilized using steam processes. This allows hospitals to apply point-of-use secondary flash sterilization when required, while still providing visible evidence that the device has completed its single-use service life, preventing inadvertent repeat autoclaving.
High-performance polymers are increasingly used to replace metal in both single-use and reusable medical applications, such as specimen collection jars, syringes, and surgical instruments. Polymers, such as polyarylamide (PARA), may meet or exceed many design requirements for single-use instrument applications, in addition to being low-cost.
Select glass-fiber-reinforced grades of PARA products further enhance desired properties, and many are supported by a FDA master access file. PARA grades are compatible with gamma radiation sterilization, and combine high strength, metal-like stiffness and an exceptional surface finish, making them excellent candidate for metal replacement. Because these compounds contain 50 percent glass fiber reinforcement, their strength surpasses that of competitive thermoplastics, including carbon fiber-reinforced PEEK.
This enables instrument designs that offer comparable performance to their stainless steel counterparts. The material is injection molded, thus eliminating machining and reducing the fabrication cost over stainless steel. Seven healthcare colors are supported, enabling OEM flexibility for color identification and branding. (See Figure 3)
Design for Sterilization
Recent cases of failed sterilization due to instrument complexity have spurred OEMs and material suppliers to explore new strategies to minimize this risk. Replacing metal with plastics enables new options when designing for sterilization. Specifically, by virtue of their design flexibility and processability, high-performance plastics offer new opportunities to design more complex instruments that are nevertheless easy to sterilize. Some examples of complex applications include hybrid instrumentation, endoscopes, and minimally invasive surgical instruments.
Metal components require multiple fasteners, brackets, and other parts that can all be integrated into a single part if designed with plastic. Because thermoplastics can be injection molded, they allow consolidation and reduction of parts vs. metal-based designs. This not only reduces or even eliminates many assembly processes, it minimizes the number of surfaces that need to be sterilized.
As designers shift from metal to polymers, however, they will need higher performance materials that offer broader options for sterilization compatibility. Specifically, these instruments demand resistance to a broader range of chemicals and the ability to handle pre-treatment in aggressive disinfectants followed by steam-based techniques.
Candidate materials offering superior performance and sterilization compatibility include PSU, PPSU, and PEEK. In addition, polyaryletherketone (PAEK) is a versatile polymer able to provide new and unique combinations of performance and value. PAEK resins deliver excellent chemical resistance, good impact strength and can withstand more than 1,000 cycles of steam sterilization.
High-performance polymers will play a key role in the healthcare industry as OEMs steer toward more robust product designs aimed at reducing the occurrence of HAIs. Candidate materials will expand design freedom by delivering stronger mechanical and physical properties, along with improved chemical resistance. They will also offer innovative solutions to meet the challenges posed by the stronger sanitizing agents in use today.
Higher performing thermoplastics are also offering new options for limiting OEM liability for the single-use medical instruments that are finding growing use as a counter to HAIs. The excellent processability of high-performance plastics also supports emerging efforts to design parts for sterilization by enabling consolidation of parts to reduce assembly and help further limit the potential for HAIs.
This article was written by Jim Hicks, Technical Service Engineer at Solvay Specialty Polymers USA, LLC, Alpharetta, GA. For more information, Click Here . MD&M East, Booth 1661