Natural Rubber Substitutes

Medical Device & Diagnostic Industry Magazine
MDDI Article Index

Originally Published January 2000

HELP DESK

Len Czuba, director, medical sector, Herbst Lazar Bell Inc. (Chicago), suggests alternatives to using natural rubber in medical device components.

As the industry is moving away from latex products, could you please advise on a material—preferably injection- moldable plastic—to serve as a substitute for rubber in injection sites and ports. Where can I get this material?

In this question the phrases "latex products" and "rubber in injection sites and ports" refer to natural rubber (NR), the elastomer material widely used in the medical device industry. Latex is the liquid harvested from the rubber tree, which is coagulated to form natural rubber. Some manufacturers use a form of latex rubber—an aqueous suspension—to make healthcare products such as rubber gloves; however, injection sites and other molded medical device components use molding compounds derived from latex rubber feedstock, the NR elastomer made from the latex of the rubber tree. These thermoset materials are cross-linked or vulcanized by heat during molding.

In some cases, sensitized patients have suffered severe anaphylactic shock when exposed to NR. This is caused by an immune reaction to naturally occurring proteins on the surface and within the NR compound. Because of the severity and unpredictability of the reaction in some patients, there is a strong move to replace all NR components in medical devices.

The properties that make NR so useful in medical devices include its ability to be punctured by needles and its after-puncture resealability. It is a highly elastic, very-low-durometer material, making it a good choice for seals and septum-type closures. It also has high tear resistance and high elongation.

A direct replacement material that has all the good properties of NR is not currently available. But with a combination of good material selection and design modifications made to compensate for the limitations of the chosen material, replacement of NR is indeed possible. For example, designs might include preslitting, internal lubrication, molded-in reinforcements, or a combination of these.

Chemically, NR is a form of polyisoprene. My first recommendation to replace NR would be to look at synthetic polyisoprene. The compounded material would still need to be cross-linked during molding, just like NR compounds, but it does avoid the proteins inherent in NR. Goodyear Tire & Rubber Co., Chemical Div., supplies polyisoprene under the product name of Natsyn.

Silicone rubber elastomer can be made into puncture-resealable septum devices (injection sites and ports), but in order for this material to meet the pressure reseal requirement the molded silicone must generally be held under compression. The silicone does not reseal very well if not compressed. Higher-molecular-weight compounds should be selected for molded components.

This is also a thermoset material with processing requirements similar to NR, such as long cycle time in low-pressure, high-heat molding systems. The leading suppliers of medical-grade silicone elastomers in the United States are NuSil Silicone Technology, Applied Silicone Corp., Dow Corning Corp., and GE Silicones.

Thermoplastic elastomers (TPEs) are available with properties approaching those of NR elastomers used in medical devices. Although some of these are designed to be vulcanized or cross-linked, most are processable using thermoplastic molding systems. These materials are generally more compatible with radiation sterilization than is NR and can be selected to meet some of the stringent FDA requirements for biomaterials.

A few TPE suppliers claim that they have materials that are puncture resealable and can be used for medical injection sites or vial septa.

Other companies supply elastomers useful for NR replacement in other applications. These companies and their relevant products include the following: Advanced Elastomer Systems (Santoprene); DSM Thermoplastic Elastomers Inc. (Sarlink); J-Von, L.P. (Hercuprene); Ferro Corp. (Alcryn); Exxon Chemical Co. (Vistalon and Exxpro); Thermedics Inc. and DuPont-Dow Elastomers LLC (TPUs); Shell Chemical Co. and GLS Corp. (Kraton-based materials); and Consolidated Polymers Technologies Inc. and Dexco Polymers (styrenic block copolymers).

The replacement of NR continues to be a challenge, but the industry is exploding with activity in new materials development. If these suggestions cannot meet your requirements, I predict that, within a few years, newer and better materials will be developed that can.

"Help Desk" solicits questions about the design, manufacture, regulation, and sale of medical products and refers them to appropriate experts in the field. A list of topics previously covered can be found in our Help Desk Archives. Send questions to Help Desk, MD&DI, 11444 W. Olympic Blvd., Ste. 900, Los Angeles, CA 90064, fax 310/445-4299, e-mail [email protected]. You can also use our on-line query form.

Although every effort is made to ensure the accuracy of this column, neither the experts nor the editors can guarantee the accuracy of the solutions offered. They also cannot ensure that the proposed answers will work in every situation.

Readers are also encouraged to send comments on the published questions and answers.

Return to the MDDI January table of contents | Return to the MDDI home page

Copyright ©2000 Medical Device & Diagnostic Industry