USP Class VI vs. ISO 10993 for Medical Silicone

When buyers source silicone parts for masks, catheters, respiratory valves or wearables, the first document they ask for is usually a USP Class VI certificate. It is a useful document. But many teams treat it as proof that the finished part is biocompatible, and that is where problems start.

USP Class VI and ISO 10993 answer different questions. One describes a material. The other evaluates a device in its intended use. Knowing the difference shapes how you choose a material, a molder and a test plan.

USP Class VI comes from the United States Pharmacopeia's biological reactivity tests for plastics and elastomers. Class VI is the most demanding of its classes. The tests typically cover:

Acute systemic toxicity, using extracts injected into test animals

Intracutaneous reactivity, a local irritation test

Short-term implantation of the material

The results apply to the material sample that was tested. They do not consider the device design, how long it contacts the body, or how the part was manufactured.

ISO 10993 is a series of standards for the biological evaluation of medical devices. ISO 10993-1 sets out a risk-based framework within a risk management process. Which tests are needed depends on two things: the type of body contact and the contact duration.

Contact types range from intact skin, through mucosal membranes, to external communicating and implant devices. A watch strap on skin and a long-term implanted part face very different evaluation endpoints, such as cytotoxicity, sensitization, irritation, systemic toxicity and more.

Biocompatibility is a property of the finished part, so manufacturing can change it. For LSR parts, these factors deserve attention:

Post-curing. Residual volatiles and low-molecular-weight siloxanes can affect extractables results. The post-cure profile should be defined and validated.

Colorants and additives. Pigment masterbatches need their own biocompatibility support. An approved base silicone plus an unapproved colorant is a new material.

Mold release agents. Many medical programs prohibit sprays. Mold surface and design should allow clean demolding without them.

Cleanliness. Particles, oil and handling contamination can cause test failures. Cleanroom molding or controlled packing may be required.

Sterilization. Steam, ethylene oxide or gamma sterilization can change silicone properties, so testing should use sterilized parts where relevant.

1.Which exact LSR grade will be used, and what biological data does the material supplier provide?

2.Is the colorant supported for the same contact type and duration?

3.What is the post-cure specification, and is it locked in the control plan?

4.Is molding done in a cleanroom, and to what ISO 14644 class?

5.How will changes to material, colorant or process be notified?

6.Can the molder provide samples made under production conditions for ISO 10993 testing?

USP Class VI helps you choose a suitable silicone. ISO 10993 tells you whether your device is safe in its intended use. A good molder protects both by keeping material, process and cleanliness under control.

TYM supplies LSR injection molding machines, molds and production cells for medical silicone parts, from respiratory components to wearable devices. To discuss a medical LSR project, contact our team through gdtym.com.