A silicone gasket in a food packaging machine and a silicone gasket in a bioprocessing system look identical on a shelf. Same color, same flexibility, same general shape. The difference is invisible and it is everything. The food-grade gasket meets FDA 21 CFR requirements for food contact. The bioprocessing gasket must meet USP Class VI biological reactivity testing, must be manufactured from platinum-cured (addition-cured) silicone to eliminate peroxide residuals, must come with extractables and leachables data demonstrating that the compound does not shed compounds into the process fluid, and must survive repeated sterilization cycles (autoclave at 121°C, gamma irradiation at 25 to 50 kGy, or ethylene oxide exposure) without degradation.
The sourcing challenge for bioprocessing gaskets is that most industrial gasket suppliers do not understand the regulatory distinction between “food-grade silicone” and “high-purity silicone for pharmaceutical and bioprocessing applications.” They are two different material specifications with two different compliance frameworks, and substituting one for the other is a regulatory violation even though both are technically “silicone.” This article covers the material specifications, compliance requirements, and selection criteria for high-purity silicone gaskets in pharmaceutical packaging, bioprocessing, and aseptic filling applications.
Quick Reference: Compliance Requirements by Application
| Application | Minimum Compliance | Additional Requirements |
|---|---|---|
| Food packaging (non-pharma) | FDA 21 CFR 177.2600 | None beyond FDA food contact. |
| Pharmaceutical packaging (solid dose, blister) | FDA 21 CFR + USP Class VI | Platinum-cured silicone. Extractables data may be required depending on drug contact. |
| Pharmaceutical liquid filling (vials, ampoules) | FDA 21 CFR + USP Class VI + ISO 10993 | Extractables and leachables (E&L) study. Platinum-cured. Autoclave-compatible. |
| Bioprocessing (upstream fermentation, downstream purification) | USP Class VI + ISO 10993 | E&L study per BPOG guidelines. Platinum-cured. Gamma and/or autoclave sterilization compatible. Animal-derived-component-free (ADCF) certification may be required. |
| Aseptic filling (sterile drug product) | USP Class VI + ISO 10993 + 21 CFR Part 211 (cGMP) | Full E&L. Validated sterilization compatibility. Traceability to lot level. Clean-manufactured (ISO Class 7 or better cleanroom). |
| Single-use bioprocessing assemblies | USP Class VI + ISO 10993 | E&L per BPOG. Gamma sterilization compatible at 25-50 kGy. ADCF certification. Lot traceability. |
That covers the regulatory framework. The sections below explain the material science behind the compliance requirements so you can evaluate whether a given silicone gasket actually meets the specification for your application.
Platinum-Cured vs Peroxide-Cured Silicone: The Material Distinction That Matters Most
All silicone elastomers are crosslinked (vulcanized) during manufacturing to convert them from a liquid or paste into a solid rubber. The crosslinking agent determines the purity of the final product, and there are two commercially used systems.
Peroxide-Cured Silicone
Peroxide curing uses an organic peroxide (typically dicumyl peroxide or benzoyl peroxide) to initiate the crosslinking reaction. The reaction is effective and inexpensive, which is why peroxide-cured silicone is the standard for general industrial and food-grade gaskets. The problem for pharmaceutical and bioprocessing applications is that the peroxide decomposition products remain in the cured rubber as residual byproducts. These byproducts are volatile organic compounds that can migrate out of the gasket and into the process fluid as extractable contaminants.
In a food packaging application, these residual levels are well within FDA limits and pose no safety concern. In a pharmaceutical or bioprocessing application, where the process fluid is a drug product, a cell culture medium, or a purified biologic, even trace extractables from the gasket can affect product purity, stability, or biological activity. This is why peroxide-cured silicone fails USP Class VI testing in many cases and is not acceptable for pharmaceutical fluid-contact applications.
Platinum-Cured (Addition-Cured) Silicone
Platinum curing uses a platinum catalyst (typically a Karstedt catalyst) to initiate a different crosslinking reaction (hydrosilylation) that produces no volatile byproducts. The only reaction product is additional silicone crosslinks. There are no organic peroxide residuals, no decomposition products, and no volatile compounds to migrate into the process fluid. Platinum-cured silicone passes USP Class VI biological reactivity testing because its extractables profile is orders of magnitude cleaner than peroxide-cured silicone.
USP Class VI: What the Test Actually Proves
USP Class VI is a biological reactivity test defined in the United States Pharmacopeia (USP) Chapter 88. It evaluates whether a material produces adverse biological responses when implanted in or contacted with living tissue. The test involves three procedures performed on animal models: an intracutaneous injection test, a systemic injection test, and an implantation test. A material passes USP Class VI when it produces no significant biological response in any of the three tests.
What USP Class VI does not prove is chemical purity. It proves biological compatibility. A gasket can pass USP Class VI and still contain extractable compounds that affect the chemistry of a sensitive drug product or cell culture. This is why bioprocessing applications require both USP Class VI compliance and extractables and leachables (E&L) data. The USP test confirms the gasket will not harm tissue. The E&L study confirms the gasket will not contaminate the process fluid.
Extractables and Leachables: The Data That Bioprocessing Buyers Actually Need
Extractables
Extractables are compounds that can be pulled out of the gasket material under aggressive laboratory conditions (high temperature, strong solvents, extended contact time). The extractables study uses conditions more aggressive than any real process condition to establish the worst-case chemical profile of the material. It answers the question: what is the maximum amount and type of contamination this gasket could theoretically contribute to the process fluid?
Leachables
Leachables are compounds that actually migrate out of the gasket material under the specific process conditions of the intended application (actual temperature, actual fluid, actual contact time). The leachables study is application-specific. A gasket that shows acceptable leachables in a room-temperature aqueous process may show unacceptable leachables in a hot solvent process because the higher temperature and more aggressive solvent extract more material from the gasket.
BPOG Extractables Protocol
The BioPhorum Operations Group (BPOG) published a standardized extractables testing protocol for single-use systems that has become the de facto industry standard for bioprocessing component qualification. The BPOG protocol specifies the solvents (50% ethanol, 0.1M NaOH, purified water), the temperature (40°C), the contact time (24 hours minimum), and the analytical methods (GC-MS, LC-MS, ICP-MS, TOC) that should be used to characterize extractables. Requesting BPOG-protocol E&L data from the gasket supplier ensures that the data is comparable across suppliers and meets the expectations of pharmaceutical quality auditors.
Sterilization Compatibility: What Happens to Silicone Under Repeated Sterilization
Bioprocessing and pharmaceutical gaskets must survive repeated sterilization cycles without degradation. The three common sterilization methods each affect silicone differently.
| Sterilization Method | Conditions | Effect on Platinum-Cured Silicone | Cycle Limit |
|---|---|---|---|
| Autoclave (steam) | 121°C, 15 psi, 15 to 30 minutes | Minimal. Platinum-cured silicone tolerates autoclave conditions without significant property change. Gradual compression set increase over many cycles. | 100+ cycles typical before measurable property change. Replace when compression set exceeds 50%. |
| Gamma irradiation | 25 to 50 kGy dose | Slight crosslink density increase (hardening). Slight yellowing. Mechanical properties remain within specification at standard doses. High doses (above 50 kGy) cause brittleness. | Single-use gaskets are typically gamma-sterilized once as part of the single-use assembly. Re-sterilization is not standard practice. |
| Ethylene oxide (EtO) | 450 to 1200 mg/L EtO, 30 to 60°C, 1 to 6 hours + aeration | EtO residuals can be absorbed by the silicone and released into the process fluid during subsequent use. Extended aeration (48+ hours) is required to reduce EtO residuals below ISO 10993-7 limits. | EtO is used for heat-sensitive assemblies where autoclave is not an option. Aeration time must be validated. |
For applications where the gasket is part of a reusable stainless steel system (bioreactor ports, column fittings, valve assemblies), autoclave sterilization is the standard and the gasket must survive 100+ cycles. For single-use assemblies (bag manifolds, tubing connectors, filter housings), gamma sterilization at 25 to 50 kGy is the standard and the gasket is used once and discarded with the assembly.
Gasket Applications in Bioprocessing and Pharmaceutical Equipment
Bioreactor Ports and Manways
Bioreactor systems use silicone gaskets at every port connection (sampling ports, probe ports, addition ports) and at the manway cover on larger vessels. These gaskets must maintain a sterile seal through the full fermentation cycle (typically 7 to 21 days for mammalian cell culture) and survive repeated autoclave sterilization between batches. The gasket is in direct contact with cell culture medium, which means extractables from the gasket material can affect cell viability, product yield, and product quality.
Chromatography Column Fittings
Downstream purification uses chromatography columns with gaskets at the top and bottom adaptor plates. The gaskets seal the column at pressures up to 5 bar while resisting the solvents and buffers used for column equilibration, elution, and cleaning (including 0.5M NaOH, 20% ethanol, and various chaotropic agents). Gaskets that swell, soften, or extract in these solvents compromise the column seal and contaminate the purified product.
Aseptic Filling Stations
Aseptic filling machines use silicone gaskets at the fill nozzle, the needle guide, the stopper bowl, and every fluid-path connection between the bulk product tank and the filled vial. The gaskets operate in a Grade A/ISO 5 cleanroom environment where particulate contamination is measured in particles per cubic meter. A gasket that sheds particles (from degradation, abrasion, or poor manufacturing) is a particulate contamination source that can trigger batch rejection based on visible particulate inspection per USP 790.
Single-Use Assemblies
Single-use (disposable) bioprocessing systems use pre-sterilized plastic assemblies that replace traditional stainless steel vessels, tubing, and connectors. Silicone gaskets in single-use assemblies are gamma-sterilized at the factory and must maintain their sealing properties and extractables profile through the gamma dose and subsequent shelf storage (typically 2 to 5 years). The BPOG extractables protocol was specifically developed for qualifying single-use system components including gaskets.
How to Specify a Bioprocessing Silicone Gasket
Specifying a high-purity silicone gasket requires seven parameters. Missing any one of them produces a gasket that may not be qualified for the application.
The Difference Between This Article and the General Silicone Gaskets Guide
Vanguard’s silicone seals and gaskets guide covers the elastomer comparison (silicone vs EPDM vs NBR vs FKM) for general packaging equipment applications, including FDA food-contact compliance, chemical resistance in washdown environments, and compression set behavior. That article is the right reference for maintenance teams sourcing gaskets for packaging machine enclosures, guard doors, heat tunnel seals, and general industrial sealing applications.
This article addresses a different audience with different requirements. Bioprocessing and pharmaceutical buyers need gaskets that meet regulatory frameworks beyond FDA food contact, with documentation beyond a material data sheet, manufactured from compounds that are controlled beyond standard industrial silicone specifications. The two articles serve different search intents, different buyer personas, and different compliance requirements.
Custom Fabrication for Bioprocessing and Pharmaceutical Gaskets
Bioprocessing equipment uses gaskets in non-standard dimensions that are specific to the vessel manufacturer, the column manufacturer, or the filling machine model. Standard gasket catalogs do not stock a 47.5mm ID, 5.33mm cross-section platinum-cured silicone O-ring with USP Class VI compliance and BPOG extractables data for a specific bioreactor sampling port. That gasket must be custom-manufactured to the exact dimensional, material, and documentation specification.
Vanguard’s custom fabrication process manufactures high-purity silicone gaskets to pharmaceutical and bioprocessing specifications. Provide the dimensional drawing (ID, OD, cross-section, tolerances), the material specification (platinum-cured, durometer, color), the regulatory requirements (USP Class VI, ISO 10993, BPOG E&L), and the sterilization method. Vanguard confirms fabrication feasibility within one business day and delivers with full documentation including Certificate of Compliance, lot traceability, and applicable test reports.
For general industrial silicone gaskets, browse the silicone rubber catalog. For PTFE pump gaskets for sanitary applications, see the pump parts catalog. For bioprocessing and pharmaceutical gaskets requiring USP Class VI compliance, platinum-cured manufacturing, or extractables data, submit your specification through the custom parts request. Vanguard confirms feasibility within one business day and ships across the US, Canada, and Mexico.
