In an industry where material failure can mean the difference between life and death, the materials available can either constrain development or open new possibilities. With engineered plastics, most specifically resins, the medical equipment industry has a powerful tool when developing new products or improving existing ones. The value of engineered resins is due to the versatility of its material properties and its ability to meet the most exacting tolerancing requirements.

Medical equipment manufacturers have many choices beyond standard resins. Resin manufacturers have been working closely with medical device companies to develop specialized resins that meet the highly specialized needs of these companies' products. The most popular of engineered resins being used today are polycarbonate, acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile copolymers (SAN), thermoplastic polyurethane (TPU) and polyamide. In addition, there are blends that combine elements of each to meet specific needs.

With its versatile combination of properties, polycarbonate has achieved a lasting popularity in the medical device market. This material blends rigidity, strength and toughness with ease of sterilization. It is also clear. As a result, polycarbonate has become the material of choice for many applications that traditionally called for glass or steel. One example of this would be the cartridge housing for the hemodialysis filter membrane used in kidney dialysis. The transparency of the material allows physicians to visually monitor blood flow while its rigidity helps in protecting the membrane.

Acrylonitrile-butadiene-styrene (ABS) is a strong, rigid, material that also provides creep resistance. Because of its tactile quality, ABS has been used in creating roller clamps, piercing pins, IV spikes and surgical instruments, just to mention a few applications. Because of its superior surface quality, its acceptance of pigmentation and good chemical resistance, ABS has also become prized for making the break-resistant housings for a variety of items including hearing aids, blood pressure measuring tools and X-ray film cassettes.

Styrene-acrylonitrile copolymers (SAN) combine a good surface gloss, high rigidity, hardness and chemical resistance with transparency. This combination, as well as the material's processability, makes it ideal for creating thin-section moldings with high strength and dimensional accuracy. Reaction chambers for automated diagnostic units are also well served by this material.

Thermoplastic polyurethanes (TPUs) are valued for their combination of design flexibility and excellent processability. Because of their pliability they have earned a reputation for promoting both patient comfort and ease of use. They are a popular choice for creating oxygen masks, medical tubing, catheters, and soft and pliable post-surgical appliances. TPUs don't have plasticizers and are less prone to cause allergic reactions. Furthermore, blood is not as likely to clot when it comes in contact with the material as it does with some others. TPUs also become more pliable at body temperature. Thus they are ideal for creating devices such as catheters that need to be strong enough for insertion but pliable enough to accommodate patient comfort.

Polyamide resins (nylons) combine high dynamic fatigue resistance, chemical resistance, high strength and rigidity and high abrasion resistance with an attractive surface finish. This combination makes polyamide resins a good candidate for many of the same applications as ABS, including clamps and piercing pins. Due to their high abrasion resistance, they are well suited for components that are likely to encounter undue mechanical and dynamic stress.

Finally, we have the blends. Resin blends have proved useful to the medical device industry due to their taking the best of both worlds, attribute-wise, of their respective constituents. As such, they are especially good choices for manufacturing housings of medical products. Polycarbate/ABS blends demonstrate toughness and impact resistance at low temperatures, dimensional and thermal stability, color stability and easy processing, as well as creep resistance. Likewise, polycarbonate/polyester blends retain their strength over a wide temperature spectrum and have an exceptional resistance to chemicals. They can be created in either general purpose or flame retardant grades. Last of the bunch, we have ABS/polyamide blends. These resin blends combine the process characteristics of ABS with the higher chemical and abrasion resistance of nylons. In addition, these blends also possess a greater resistance to heat than ABS.

Source: Engineering the Next Generation of Medical Plastics
George Paleos
Medical Design News, Nov. 13, 2001
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