USP Class VI certification is the highest biological reactivity classification in the United States Pharmacopeia’s plastics testing system, defined in USP General Chapter <88>. A material qualifies by clearing three in-vivo animal tests: systemic injection, intracutaneous reactivity, and implantation.
Here is the part most specifiers get wrong. USP publishes the method. It does not issue certificates, does not define grades for plastics, and does not police anyone who calls their resin Class VI. The compliance claim belongs to the manufacturer or converter, and it rests on a test report from a qualified third-party laboratory. The rest of this guide walks through what the tests actually measure, how the process runs, what you should demand from a resin supplier, and where the evidence stops.
Table of Contents
- What Is USP Class VI Certification?
- What Does USP Class VI Testing Evaluate?
- USP Class VI Certification Explained: The Testing Process
- Which Materials and Products Are Covered?
- USP Classes and Their Differences
- What Does a Manufacturer Need to Prepare?
- How Long Does USP Class VI Certification Take?
- How Much Does USP Class VI Certification Cost?
- How to Maintain Compliance After Certification
- Common Misunderstandings About USP Class VI
- Frequently Asked Questions
- Conclusion
What Is USP Class VI Certification?
A Class VI material is a plastic, elastomer, coating or adhesive whose extracted constituents produce no adverse biological response when tested in living animals. It is the most demanding of the six USP reactivity classes and the one that shows up most often in US medical device and biopharmaceutical submissions.
General Chapter <88> works by extracting the material into vehicles such as saline or vegetable oil under controlled conditions, then exposing animals to the extract or to the material itself. The chapter defines the classification. It does not hand out approvals.
That distinction matters commercially. A resin supplier brochure that says medical grade or Class VI without a report naming the exact grade, colour and formulation revision is a marketing claim, not evidence. The question to ask is simple: which document says this, and which formulation does it cover?
What does USP grade stand for?
It is a common source of confusion in procurement conversations. USP has no grade designation for plastics. There is no USP grade number, and no registry where a material is listed as approved. For polymers, USP provides classification methods, and Class VI is an outcome of testing a specific formulation, not a product designation attached to a resin family.
Two different resins from the same manufacturer can carry different outcomes, and a single formulation can change outcome after a colour or additive revision. Always attach the claim to a document and a formulation revision.
What Does USP Class VI Testing Evaluate?
Class VI evaluates biological response to extractables. Extractables are substances pulled out of the polymer by the extraction vehicle. Leachables are the subset that later migrates from a finished, processed, and sterilized part into a fluid or tissue. Class VI addresses the first, and only partially addresses the second.
Three tests make up the Class VI package. Each has its own animal model, observation window, and pass criterion, and all three must pass for a material to be classified as Class VI.
| Test | Animal model | Observation window | Pass criterion |
|---|---|---|---|
| Systemic injection | Mice, intravenous and intraperitoneal administration of the extract | Typically 48 to 72 hours | No mortality and no weight loss greater than 10 percent against controls |
| Intracutaneous reactivity | Rabbits, intradermal injection of the extract | Readings at 24 and 72 hours | No erythema or edema above the control site; irritation index of 1.0 or less |
| Implantation | Rabbits, material implanted subcutaneously | Five days, then histopathology | No adverse tissue reaction and capsule thickness differential of 1.0 or less against the control |
The implantation result is the one most often quoted in supplier literature, because a capsule thickness differential of 1.0 or less is a clean, checkable number. It is also the slowest of the three, and the fixed five-day observation period is a hard constraint when you are scheduling a launch.
What the package does not evaluate is just as important. Class VI does not cover cytotoxicity, sensitization, genotoxicity, carcinogenicity, hemocompatibility, or pyrogenicity. Those live in the ISO 10993 series, and a material that passes Class VI can still fail them.
USP Class VI Certification Explained: The Testing Process
The lifecycle is more predictable than most buyers expect, as long as the material is fixed before samples go out. Work through it in this order.
- Fix the formulation. Identify the exact resin grade, colour, masterbatch, additive package, and cure system. Testing starts here, and a change at this step restarts the process.
- Decide the test package. Confirm which of the three tests are required by the application and the destination market. A component in permanent contact usually justifies the full package.
- Engage a qualified laboratory. Ask which standards the lab runs, whether it is accredited for the relevant test methods, and what sample format it needs.
- Prepare samples and extraction conditions. The laboratory defines the extraction vehicle, temperature, duration, and surface-to-volume ratio. These parameters are part of the report, not details you choose.
- Run the animal studies. Systemic injection and intracutaneous reactivity are extract-based. Implantation places the material itself in the animal, so sample geometry and surface finish matter.
- Review the report carefully. Check that it names your exact grade, colour, and formulation revision, and that it states the vehicles, conditions, and observation windows.
- Obtain per-lot evidence. A one-time report covers the lot tested. Request a certificate of analysis per lot that references the report, so the evidence travels with the material.
- File it into your change control system. The report becomes a controlled document tied to the formulation, not a PDF in a shared drive.
Step six is where a lot of projects stall. A report that names a slightly different grade is not usable, and re-testing the correct formulation adds weeks to the schedule.
Which Materials and Products Are Covered?
Class VI applies to the polymer itself, so it transfers to any part moulded or extruded from that formulation. In practice it shows up in single-use bioprocess fluid paths, catheter and tubing components, syringe and vial hardware, seals, gaskets and O-rings, and implantable housings.
| Material | Form typically evaluated | Typical application | Note for specifiers |
|---|---|---|---|
| Polycarbonate | Moulded housings, connectors, clear fluid-path parts | Devices, diagnostic equipment | Available in medical grades; confirm the exact grade and colour |
| PMMA | Extruded tubing, moulded optical parts | Fluid paths, viewing components | Common in Class VI tubing; check grade revision |
| Silicone elastomer | Platinum-cured tubing, molded seals | Catheters, single-use bags, connectors | Platinum-cured is preferred; peroxide-cured carries reaction by-products |
| Polypropylene and polyethylene | Moulded components, film | Fluid paths, housings, caps | Widely available; verify additive package |
| PSU and PES | Moulded parts, membranes | Fluid handling, filtration | Fewer Class VI versions than commodity resins |
| ABS | Moulded housings, grips | Device shells | Usually indirect or skin-contact only |
| PEEK and other high-performance polymers | Machined or moulded implant parts | Implantables, drug delivery | Typically evaluated under ISO 10993 as well |
| TPE and TPU | Extruded seals, moulded grips | Seals, disposable components | Ask whether the TPE family report covers your specific grade |
Contact duration decides how much evidence you need. It is the framework that most often determines whether a Class VI report is sufficient or merely a starting point.
| Contact category | Duration | Typical components | Evidence normally expected |
|---|---|---|---|
| Limited | Under 24 hours | Single-use collection vessels, short-term fluid-path connectors | Class VI commonly sufficient with supporting chemical characterization |
| Prolonged | 24 hours to 30 days | Syringe components, catheter sets, bioprocess tubing and bags | Class VI plus chemical risk assessment under ISO 10993 |
| Permanent | Over 30 days, including implants | Implant housings, drug delivery components, long-term access ports | ISO 10993 endpoints expected, with Class VI as supporting data |
Food-contact compliance is a different system entirely. A resin meeting FDA food-contact requirements can carry no Class VI data at all, and a Class VI resin still needs its own food-contact status if the part ever touches food.
USP Classes and Their Differences
General Chapter <88> sorts plastics into six reactivity classes based on how the material responds to the same extract-and-test framework. Class VI sits at the top because it demands the most extensive evaluation.
| Class | Testing expectation | Typical use |
|---|---|---|
| I | Minimal evaluation, including limited in-vivo testing | Components with no direct or indirect body contact |
| II | Greater in-vivo coverage, including implantation for applicable uses | Components with limited indirect contact |
| III | Expanded in-vivo package | Brief limited-contact components |
| IV | Broad in-vivo package including implantation | Prolonged-contact components |
| V | Comprehensive in-vivo package | Permanent-contact components without implantation |
| VI | Full package: systemic injection, intracutaneous reactivity, and implantation | Permanent-contact components and implantable applications |
Now the comparison that engineers actually ask for. USP Class VI, ISO 10993, and FDA 21 CFR are often treated as interchangeable. They are not.
| Criterion | USP Class VI | ISO 10993 | FDA 21 CFR |
|---|---|---|---|
| Framework type | Classification method for plastics | Risk-management framework for biological evaluation | Regulation and material listing system |
| Scope | Three in-vivo tests on a formulation | Full endpoint set chosen by contact type and duration | Defines regulated materials and food-contact conditions |
| Cost driver | Fixed animal package per formulation | Number of endpoints and chemical characterization | Application and listing route |
| Typical timeline | Often quoted at four to six weeks | Broad, from weeks to many months depending on endpoints | Varies by pathway |
| Regulatory acceptance | Commonly cited in US submissions as supporting material evidence | Primary expectation for EU MDR and most international markets | Governs US market access and material listings |
| Key limitation | Does not cover cytotoxicity, sensitization, genotoxicity, or hemocompatibility | Requires a chemical risk assessment to close out | Not a biocompatibility test in itself |
The practical read: Class VI is strong baseline evidence for the US market and useful supporting data elsewhere. For an EU MDR submission it does not stand on its own, and a finished device still needs its own biological evaluation.
What Does a Manufacturer Need to Prepare?
Most delays trace back to incomplete preparation, not laboratory capacity. Assemble this before the first call with a lab.
- Exact resin identification. Resin family, grade, manufacturer, colour, and formulation or revision number.
- Composition and additive data. Full additive package, including colours, fillers, stabilizers, processing aids, and for elastomers the cure system and catalyst.
- Processing description. Injection moulding, extrusion, or both, plus drying conditions, regrind policy, and any secondary operations such as printing, coating, or bonding.
- Intended contact conditions. Body contact category, contact duration, fluid path versus tissue contact, and the destination market.
- Representative samples. Parts or plaques representative of production, including surface finish, thickness, and any assembly operations applied to the final part.
- Existing documentation. Any prior Class VI or ISO 10993 reports, chemical characterization, and material declarations from the resin supplier.
- Supplier information. Name and address of the resin manufacturer so the report can be traced back to the source formulation.
If a resin supplier already holds a Class VI report for the grade you intend to mould, ask for the full document rather than a summary. The report title page alone rarely shows enough.
How Long Does USP Class VI Certification Take?
A single formulation through the full three-test package is commonly quoted at four to six weeks from sample receipt. Treat that as a planning figure rather than a promise, because the variables below routinely move it.
- Formulation stability. A colorant or additive change sends you back to the start.
- Sample format. Implantation testing needs material in an implantable configuration, and poorly prepared samples generate retests.
- Test combination requested. The full Class VI package is longer than a single-test evaluation.
- Laboratory queue. Animal studies are scheduled around facility availability, which you do not control.
- Report review. A rushed first read is a common cause of a second cycle.
- Implementation. Adding the grade to the BOM, updating supplier approval, and retraining the receiving team add internal days.
There is no expiry date printed on a Class VI report. Validity runs as long as the formulation and the application stay the same, which is why change control matters more than any calendar reminder.
How Much Does USP Class VI Certification Cost?
Quotations vary widely, so it is more useful to know what moves the number than to chase a headline figure. Published ranges in this space typically land in the high four figures to low five figures for a standard three-test package, while ISO 10993 programs can run from several thousand dollars into five figures once chemical characterization and extended endpoints are added.
The drivers are consistent:
- Material complexity. A simple homopolymer extract is easier to evaluate than a multi-resin, heavily compounded grade.
- Number of components. Each distinct formulation is a separate testing line item.
- Sample preparation. Implantable sample fabrication and surface conditioning add handling and labor.
- Test combination. Running only intracutaneous reactivity costs materially less than the full package.
- Laboratory turnaround. Expedited scheduling is usually a premium.
- Retest exposure. A formulation that shifts mid-program is the most expensive line item of all.
- Certification scope. Whether you need one report per grade or a broader family evaluation changes the structure of the quote.
These are typical US ranges that depend on laboratory, scope, and current conditions, and they move over time. Request a written scope of work that itemizes which tests, which extraction vehicles, and which sample formats are included.
How to Maintain Compliance After Certification
A Class VI report is evidence about one formulation at one point in time. Keeping it valid is a change control exercise, and the rules are simple to write down.
What invalidates a Class VI report
- Changing the colour, colorant, or masterbatch
- Adding or removing fillers, stabilizers, pigments, or processing aids
- Changing the cure system or catalyst in a silicone or elastomer formulation
- Moving production between manufacturing sites
- Moving to a different resin supplier or a different grade within the same family
- Introducing new secondary operations such as printing, bonding, or coating with uncharacterized chemistry
Each of those changes the extractables profile, which is exactly what the test measured. Suppliers in the industry treat formulation change as voiding the classification, and that is the standard your quality system should adopt.
What to keep on file
Retain the full report, the scope of work, the extraction conditions, and the formulation revision it covers. Ask each supplier for a per-lot certificate of analysis that references the report number, so traceability runs from the finished part back to the tested formulation. Record the sterilization method used in your process, since ethylene oxide, gamma, and autoclave can all change a polymer surface.
Processing practice matters too, particularly for moulders. Excessive regrind, incomplete drying, and purge residue carried into production all change what a part can reasonably be claimed to contain. Keep regrind ratios and drying parameters inside controlled limits, and treat a purge schedule as part of the process rather than a line-side decision.
Common Misunderstandings About USP Class VI
That USP certifies materials. It does not. USP publishes methods and classifications. The compliance claim comes from the manufacturer or converter, supported by a third-party laboratory report, and no one at USP audits that claim.
That a Class VI resin makes the finished device compliant. It does not. A report covers the raw material. The moulded, assembled, sterilized part with its printed labels, adhesives, and packaging still needs its own evaluation for its actual contact conditions.
That Class VI replaces ISO 10993. It does not, and for EU MDR submissions it cannot. Class VI covers three endpoints. ISO 10993 covers cytotoxicity, sensitization, irritation, and a wider set depending on contact duration.
That Class VI is FDA approval. It is not. FDA 21 CFR governs materials and market access. A Class VI report is supporting evidence you may cite in a submission, not clearance.
That food-contact approval implies biocompatibility. The two systems answer different questions. One addresses substances migrating into food, the other addresses response of living tissue.
That the certificate expires. No expiry is printed on a Class VI report. What ends its usefulness is a change in formulation, application, or manufacturing site, which is why specification language matters more than a renewal date.
Is USP Class VI going away?
No, and the chapter is not being retired. What is changing is the framework around it. ISO 10993 has become the primary expectation for device biological evaluation, particularly under EU MDR, and more US companies are aligning early rather than maintaining two parallel programs. Class VI remains in current use and is still cited in US submissions, especially for single-use bioprocess components and material-level evidence. Treat it as a useful baseline, not as the whole evaluation.
Frequently Asked Questions
What are the USP Class VI requirements?
A material qualifies as USP Class VI by passing three in-vivo animal tests defined in USP General Chapter : systemic injection in mice, intracutaneous reactivity in rabbits, and implantation in rabbits with a five-day observation period. Pass criteria include no mortality, no weight loss greater than 10 percent, no erythema or edema above control, and a capsule thickness differential of 1.0 or less. All three tests must pass for the specific formulation tested.
Is USP Class VI the same as medical grade?
No. Medical grade is a marketing phrase with no test standard attached. USP Class VI is a defined outcome from a defined test package. A resin labelled medical grade may carry no Class VI report at all, and a Class VI resin still needs separate food-contact status if the part touches food. Always ask which document supports the claim and which exact grade and colour it covers.
Is USP Class VI being phased out?
No. USP General Chapter remains in current use and Class VI data is still cited in US submissions. What has changed is the surrounding framework: ISO 10993 is now the primary expectation for device biological evaluation, particularly under EU MDR, and many companies align early. Class VI remains useful baseline material evidence, but it no longer stands alone as a full biocompatibility evaluation.
Can I use my resin supplier’s USP Class VI report for my own molded part?
Usually yes, if the report names the exact grade, colour, and formulation revision you are moulding, and if your processing does not introduce uncharacterized chemistry. A report for a different grade does not transfer. You must also control regrind ratios, drying, and any secondary operations such as printing, bonding, or coating, since those change the extractables profile the test measured. Request the full report and a per-lot certificate of analysis.
How long does a USP Class VI certificate stay valid?
There is no printed expiry date on a Class VI report. It remains valid for as long as the formulation, application, and manufacturing site stay the same. A change of colour, colorant, filler, processing aid, cure system, resin supplier, or production site voids it, because each of those changes the extractables profile the test measured. Validity is therefore managed through change control rather than a renewal schedule.
Is a USP Class VI report enough for an FDA submission?
It is supporting evidence, not clearance. Class VI covers three in-vivo endpoints and does not address cytotoxicity, sensitization, genotoxicity, carcinogenicity, hemocompatibility, or pyrogenicity. Submissions commonly cite Class VI data for the material alongside a broader biological evaluation of the finished device in its sterilized, assembled, patient-contact form. Requirements vary by device class and pathway, so confirm the expectation with your regulatory specialist.
Conclusion
Start by listing every material that touches a patient, a fluid path, or a processing vessel in your system, then define the biological safety outcome each one needs to support. Once that list exists, take the highest-risk formulation to a qualified testing laboratory and ask for a written scope covering extraction vehicles, sample formats, and the full report, not a summary. That is USP Class VI certification explained in practice: the evidence is a report on your exact formulation, and the claim is yours to defend.