Medical Injection Molding with FDA and USP Class VI Silicones

Medical injection molding produces quality components with reliable part-to-part consistency across high volumes. Although injection molded plastics are used in some healthcare applications, injected molded silicones are used in many medical products. Examples include medical tubes and valves, the external jacketing on medical cables, surgical tools, patient monitoring systems, and wearables. Not all silicones are the same, however, so product designers and medical manufacturers need to select materials with care. To ensure your molder is using the right materials, it’s also important to choose a trusted partner.

Silicones, a family of synthetic elastomers, are used in both medical and non-medical applications (such as infant care products) and offer an attractive balance of properties. For example, silicone rubber resists a wide range of temperatures, offers thermal stability, and provides electrical insulation. Silicones also resist water, ozone, ultraviolet light, and some chemicals. They can even be filled with metal or metal-coated particles to provide shielding against electromagnetic interference (EMI). Compounders supply silicones in various forms, including liquid silicone rubber (LSR) for medical injection molding.

Liquid injection molding (LIM) for medical manufacturing requires a mold made of tool-grade steel, hot or cold runner blocks, and related process automation equipment. The tooling and equipment are important, of course, but so is the choice of a medical grade silicone. To promote product safety and ensure regulatory compliance, medical manufacturers can select specialized silicones that meet stringent requirements from the U.S. Food and Drug Administration (FDA) and the U.S. Pharmacopeia, a non-profit organization that establishes requirements for medical materials and informs FDA decision making.

As a government agency, FDA publishes numbered rules in the Code of Federal Regulations (CFR). For medical materials, CFR 21 177.2600 lists the elastomers and additives that can be used. This list includes silicone, which can be cured to meet very low limits for extractables – materials that can migrate under conditions such as elevated temperature and pressure. Depending on the curing method, compounders can supply medical injection molders with elastomers that meet FDA regulations and USP Class VI requirements.

Among all USP classes, Class VI materials meet the most stringent testing requirements. USP Plastic Class VI, as this group is also known, includes silicones that have passed a systemic toxicity test, an intracutaneous test, and an implantation test. These tests are directly related to the intended end-use of the silicone article and account for patient contact time and temperature. For medical manufacturers, using a USP Class VI silicone might seem like a shortcut to safety. What’s important to understand, however, is that all USP Class VI silicones for medical injection molding aren’t the same.

Some compounders use USP Class VI compliant ingredients but can’t ensure the compliance of their end product. Others may change ingredient suppliers between different orders for the same materials. To mitigate these risks, medical manufacturers can ask injection molders about certificates. Otherwise, the molder may use materials that haven’t been properly validated, or that have lost their validation because of quality issues. A certificate of conformance (COC) from a third-party testing laboratory and a certificate of analysis (COA) from the compounder’s Quality and Compliance department provides such proof.

Extreme Molding of Watervliet, New York provides medical injection molding services and uses USP Class VI silicones that are fully validated for FDA and USP Class VI compliance. We also offer value-added services such as packaging and fulfillment. As a Made in the USA manufacturer, we’ve even helped companies with reshoring production. To learn more about us and how we can help you, contact us.