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.