Industry Insights · Medical Polymers & Silicone
Restricted vs unrestricted: how implant-grade medical silicone is split and chosen
When choosing implant-grade medical silicone, the first cut is restricted vs unrestricted. It is not marketing language — it maps to different depths of biocompatibility testing and regulatory pathway.
The clean split: by contact duration
Restricted vs unrestricted is not about material quality but about qualification depth: the longer and deeper the contact, the more biocompatibility evidence required. 29 days is the common dividing line.
| Dimension | Restricted | Unrestricted |
|---|---|---|
| Contact duration | <=29 days, short-term / external | >29 days, long-term / permanent |
| Typical use | syringe O-rings, lubricants, external devices, hearing-aid domes | pacemaker leads, cochlear implants, IOLs, breast implants, heart valves |
| Biocompatibility testing | cytotoxicity, systemic/intracutaneous toxicity, 7-day implant | above + 12-week implant, hemolysis, genotoxicity, pyrogenicity, sensitization |
| Regulatory file | device master file + biocompatibility compendium | master file + extended testing |
| Barrier / cost | lower, for limited use | higher |
What is USP Class VI
Class VI is USP's stringent biocompatibility framework for plastics/elastomers, often including per-lot cytotoxicity, systemic/intracutaneous toxicity and a 7-day implant test. Important: passing Class VI / ISO 10993 does not equal device-level biocompatibility or approval — device-level testing and regulatory assessment are still required.
Mapping to MED grades
The table below shows representative classifications from training materials, for selection reference only; verify against current TDS and regulatory documentation:
| Code range | Class | Typical use |
|---|---|---|
| MED-41xx | HCR (restricted) | External devices |
| MED-45xx | HCR (restricted) | Short-term implant |
| MED-48xx | HCR (unrestricted) | Long-term implant |
| MED-59xx | LSR (restricted) | Class VI devices |
| MED-60xx | LCE / gels | Soft components / implant |
The BIO angle
FAQ
How are restricted and unrestricted defined?
Mainly by contact/implant duration, with ~29 days as the line: <=29 days short-term/external uses restricted; >29-day long-term implants use unrestricted.
Can restricted materials be used for long-term implants?
Not advised. Long-term implants should use unrestricted grades and complete the corresponding long-term implant biocompatibility testing.
Does passing USP Class VI mean it can be implanted?
No. Class VI / ISO 10993 are material-level supporting tests; whether a device can be implanted still needs device-level testing and regulatory approval.
How does this relate to ISO 10993?
ISO 10993 specifies the biological evaluation needed by contact nature and duration; restricted/unrestricted correspond to different evaluation depths.
Can you provide documentation for submissions?
We can provide TDS and citable supplier master-file information, with material selection support for your NMPA submission; subject to current documentation.
Related reading
- Silicone, Silicone Oil, Silicone Resin: How They Relate, in 3 Minutes | BIO Insights
- Medical Polymers: Which Biocompatibility Tests Do You Actually Need? | BIO Insights
- Biodegradable Medical Implants: Materials & Validation | BIO
Note: an original analysis compiled from public industry information; figures and conclusions per official/original sources. Not investment advice.
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