Meeting the design challenges of tomorrow's healthcare industry with high-performance TPEs.

Medical designers challenged with addressing multiple, and sometimes conflicting, healthcare trends may dream of a super material that can do it all: Comply with expanding regulations; appeal to both consumers and clinicians; look great but withstand tough conditions; deliver higher quality at lower cost; and most important, expand design freedom. While no material can meet every requirement, thermoplastic elastomers (TPEs) can be a powerful addition to the medical designer's toolkit. These versatile materials, which combine the high-volume molding capability of thermoplastics with the elastomeric properties of thermoset rubber, lend themselves to a broad array of medical devices, equipment and packaging applications. TPEs offer designers new freedom to innovate, solve problems and successfully address key trends in health care.

Defining TPEs

Thermoplastic elastomers are low-modulus, flexible materials that can be stretched repeatedly to at least twice their original length at room temperature and return to their approximate original length when stress is released. The grandfather elastomers are thermoset rubbers, which are being replaced by TPEs in a variety of applications where time and cost savings result from molding in conventional, high-volume equipment instead of having to fabricate and assemble a thermoset part. Further, the softness and suppleness of TPEs appeal to consumers in particular, making them popular for a wide range of healthcare products used in a home setting. Other important properties of TPEs for healthcare include clarity; colorability; suitability for gamma, E-beam and autoclave sterilization: low leachables and extractables; and good sealing performance.

Helping to expand healthcare design flexibility

TPEs offer a fresh and highly effective solution to several current and potential medical design challenges. Their versatility and high performance are enabling designers to adapt to macro trends, the aging patient population, the move toward disposable devices, the emphasis on human factors and ergonomics, and the increasing stringency of regulations.

Improved safety for elderly patients

As people live longer, healthcare delivery is shifting to nursing home and home settings. For safety and ease of use, older patients, particularly those at home, need devices and equipment with a firm and secure yet comfortable grip. Cane and walker handles and even medication bottle caps overmolded with soft and supple TPEs can make it easier for frail elders to follow a treatment regimen. For example, patients with osteoarthritis or rheumatoid arthritis can benefit from cushioned grips that put less stress on joints. Further, the trend toward miniaturization of devices, such as glucose monitors, makes it even more important to design easy grasping and handling into the product.

In addition, TPEs are easily colored or given special effects that make them appealing to patients, potentially encouraging use of the product or device.

Increased consideration of "human factors"

Just as designers are working to improve ease of use for the elderly, they are putting greater focus on the science of "human factors" for devices used in the surgical suite. Human factors engineering evaluates how people interact with machines, technology and other aspects of their environment, with the goal of accommodating human limitations and preferences. Particularly in operating rooms, which have become tremendously complex thanks to advanced technology, TPEs can enhance human factors' effectiveness by making products simpler, more intuitive and easier to use.

For example, a microdebrider for surgeons operating on sinuses features an ergonomic handpiece with a grip molded from a TPE, which provides biomechanical control throughout all orientations of use. The TPE withstands repeated sterilization.

High-volume production for disposables

Another healthcare trend affecting device design is the move to disposables for improved cleanliness and avoidance of cross-contamination, as well as one-time home use. To make disposable devices cost-effective, manufacturers need to be able to produce large volumes using high-speed processing. TPEs help make this possible: In contrast to thermoset rubbers that require separate fabrication and assembly, parts made from TPEs can be molded on the same equipment and in the same clean room facility as other components. In addition, the precision of injection molding permits greater design latitude. Thanks to its high pressure and processing speed, injection molding enables complex geometries that are not achievable with low-pressure compression molding used for thermosets.

The benefits of TPEs in disposables can be seen in a closure system for pre-filled syringes. In place of traditional slip-on rubber tip caps, the tamper-resistant twist-off closures prevent reuse of the syringe and spilling of the contents (the inertness of TPE also prevents the needle from corroding over time, which causes pain to the patient during administration). Further, the TPE and the plastic used for the syringe can be injection-molded in the same process, saving time and avoiding secondary operations (and better quality product).

Compliance with regulatory requirements

A key focus area for the U.S. Food and Drug Administration (FDA) is reducing leachables and extractables from rubber and plastic packaging components that can affect patient health when introduced into drugs or other formulations. The FDA is concerned about PNAs, nitrosamines and 2-MBT, among other leachables and extractables. For example, health issues around 2-MBT, a vulcanization accelerator for rubber, have led to reformulation of rubber stoppers for parenteral drugs. Because TPEs do not undergo curing, they avoid creating by-products such as nitrosamines and other hazardous leachables.

Addressing environmental awareness

Another advantage of TPEs lies in replacing polyvinyl chloride (PVC) in tubing, bags and films. The industry is moving away from PVC due to environmental concerns about halogens, which are being restricted in Europe and several countries. Soft and clear, temperature-resistant TPEs can match or exceed the physical properties of PVC, while offering additional benefits of inertness and ability to undergo various types of sterilization. Further, TPEs can be overmolded without the use of harmful solvents, which are required to bond PVC to other plastics. To view different measures taken by different countries to avoid PVC, click here: (RW+} (http://www.nohann.org/europe/pvcDehp/governmentsanddehp)

A disposable resuscitator uses a soft and clear TPE instead of PVC or expensive silicone for the squeeze bag component used for ventilation. Further benefits are provided by the easy-grip surface of the bag and its flexibility, which makes usage less demanding.

Conclusion

Advancements in TPE compounding science have helped these versatile materials make significant inroads into a variety of healthcare sectors. The desirable combination of design freedom, system cost benefits, regulatory compliance and improved performance are fuelling strong growth of TPEs in a wide range of medical applications.

by Raj Varma, GLS (www.glscorporation.com)