What are the standards for the purity of medical silicone?

What are the standards for the purity of medical silicone?
There is no single independent purity numerical standard for medical silicone. Instead, it is comprehensively measured through a series of standards and tests to ensure its safety and applicability. The following are some common standards and related requirements:
USP (United States Pharmacopeia) Standard: The United States Pharmacopeia (USP) has established strict specifications for pharmaceutical and medical materials. For medical silicone, USP Class VI is a commonly used grade standard. To meet the USP Class VI standard, silicone needs to pass a series of biocompatibility tests, which indirectly reflects the requirements for silicone purity, because impurities may cause adverse biological reactions in the material. In this test, the silicone material needs to be implanted in animals (usually experimental animals such as rabbits) under specific conditions. After a certain period of observation, the material cannot cause obvious tissue inflammation, toxic reactions or other harmful biological changes. This means that the silicone must be of high purity and contain no impurities that can seep out and cause harm to the organism.
ISO 10993 Standard: This is a series of standards for biological evaluation of medical devices established by the International Organization for Standardization (ISO). It includes the biocompatibility evaluation requirements for medical devices (including medical devices using silicone), covering tests for cytotoxicity, sensitization, irritation, systemic toxicity, genotoxicity and other aspects. Through these test requirements, the purity of medical silicone is guaranteed to reach a certain level to ensure its safety in medical applications. For example, the cytotoxicity test requires that the silicone material cannot have a significant toxic effect on cultured cells, which limits the content of toxic impurities that may be present.
ASTM (American Society for Testing and Materials) Standards: ASTM has also developed some standard specifications for medical silicone, such as ASTM D6319. These standards specify the physical and chemical properties of medical silicone, including physical properties such as hardness, tensile strength, and tear strength, as well as requirements for chemical properties such as component analysis. Through strict control of the composition of silicone, the requirements for its purity are indirectly reflected, ensuring that the silicone material has stable performance and safety in the medical environment.
Related standards in China: In China, silicone used in medical devices needs to meet the standards approved by the State Food and Drug Administration (CFDA, now the National Medical Products Administration NMPA). For example, standards such as YY/T 0114-2008 "General Requirements for Medical Silicone Rubber Products" put forward specific requirements for the appearance, physical properties, chemical properties and biological properties of medical silicone rubber products. Among them, the chemical property requirements include restrictions on the content of heavy metals (such as lead, mercury, cadmium, etc.), as well as regulations on pH, soluble matter, etc. These are important indicators for measuring the purity of silicone, ensuring the safety of medical silicone in China and the controllable quality.