Selecting a Suitable Medical Silicone

Silicone materials can be compounded to create materials that are both, bio-inert and fully compatible with biological systems. Medical silicones are compounded in a similar manner as general purpose silicones to obtain certain characteristics, such as durometer, elongation and tear strength. However, medical silicones undergo additional processing to remove unwanted residuals. This allows for the purest silicones to be manufactured for use in medical devices.

Silicone manufacturers have created systems to determine which materials should be used for a variety of bio-contact applications. These suppliers have created in-house certifications that are based on the positive results of a series of USP (U.S. Pharmacopeial Convention) Tests. There are six separate USP tests, from Level I to Level VI. Materials that meet each of the six tests, are often referred to as “Grade 6” materials.

To better understand the requirements of each USP test, please see the table below.

table 1

Silicone manufacturers have created several groups in which to place these various medical silicones based on their anticipated use.

  1. Food Grade Silicones: Silicones of this group must meet USP tests, as well as FDA and USDA guidelines and criteria. Materials from this group would commonly be found in food processing equipment in the form of seals or even spatula blades.
  2. Medical Non-Implantable: Silicones of this type do not see use inside the body. Typical applications include tubing and one-time use disposables.
  3. Medical Short Term Implantable: These particular silicones can be implanted into the body for up to 29 days. A few applications include catheters and surgical tools.
  4. Medical Long Term Implantable: Silicones from this group can be implanted for a period greater than 29 days. Typically these materials are used in cardiovascular implants and remain in the body until end of life.
  5. Pharmaceutical: Silicone materials used in the pharmaceutical space, must pass all six USP tests and must be compatible with any drug coming into contact with the part. Drug delivery devices, such as punctal plugs, are typical applications in this group.

Determining which medical grade silicone material is required is based on the function and use of the medical device to be manufactured. Albright’s staff of engineers can assist you in material selection so that your medical application’s requirements are met. Please remember that although many silicone suppliers have conducted USP bio-compatibility tests on their respective materials, all finished medical devices will still need further USP testing. To learn more about medical silicone materials visit our Silicone Material page.