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Medical Grade Silicone

Silicone for Medical Applications

Background:  When considering any material for a medical application, the first question reasonably asked: “Is this material compatible with the human body and is the intended contact safe for each potential human user? The first answer to this concern is found through the application of a series of well-defined “USP” tests. The U.S. Pharmacopeial Convention (USP) is a scientific, nonprofit organization that sets standards for the identity, strength, quality, and purity of medicines, food ingredients, medical materials and dietary supplements manufactured, distributed and consumed worldwide. USP’s standards are enforceable in the United States by the Food and Drug Administration (FDA) and these standards are used in more than 140 countries. USP standards are developed and revised by more than 900 volunteer experts, including international participants, who work with USP under strict conflict-of-interest rules. Since its founding in 1820, USP has helped secure the quality of the American drug supply. Building on that legacy, USP today works with scientists, practitioners, and regulators of many nations to help protect public health worldwide.

USP tests and documented formulations are revised and published annually in “The Pharmacopeia of the United States of America and the National Formulary”. The 36th edition of the Pharmacopeia  (USP 36) and the 31st edition of the National Formulary (NF 31) were effective on May 1, 2013. These two documents are published and referenced together as USP 36 NF 31. Chapters 87, 88 and 1031 of the current USP edition are where details for biocompatibility testing of materials may be found.

USP Testing. Medical Silicone and Medical Silicone Components: USP tests are designed to determine the biological response of materials and/or formulations to direct or indirect human patient contact. Referring to Chapter 88 of the USP 36 NF 31, specific USP tests are used to evaluate the biological response to elastomerics, plastics and other polymeric material that may have direct or indirect patient contact. This chapter is where the in-vivo tests that screen to polymer and elastomer Grades I through VI are documented. Silicone manufacturers have aided their medical customers' material selection by noting to what Grade levels the specific silicone compound has been tested to and whether the material is suitable for short term (less than 29 days) or long term (greater than 29 days) implants. See Table 1 (below) for an overview of the tests and the Grades.

Important Note: The reader must expect to execute biocompatibility testing on each human contact material of the finished medical device and after product manufacturing steps that may affect material characteristics, including sterilization in product packaging. The use of a Grade VI material does not automatically certify a device as biocompatible for any application. Using a silicone manufacturer's Grade VI is the start of your biocompatibility process with a well-documented and process-controlled silicone material. Validation testing of each medical device to the appropriate human contact level is required by the FDA. 

Medical Parts

USP In-vivo tests:  There are three test regimes that may be run, depending on the specific application: the Systemic Injection Test, the Intracutaneous Test and the Implantation Test. Table 1 lists the specific tests that must be passed in order to apply a biocompatibility grade to the elastomeric, plastic and other polymeric material. 

Table 1. Classification of Plastics

Plastic Classes a

Tests To Be Conducted

I

II

III

IV

V

VI

Test Material

Animal

Dose

Procedureb

x

x

x

x

x

x

Extract of Sample in Sodium

Mouse

50 mL/kg

A (iv)

x

x

x

x

x

x

Chloride Injection

Rabbit

0.2 mL/animal at each of 10 sites

B

 

x

x

x

x

x

Extract of Sample in 1 in 20

Mouse

50 mL/kg

A (iv)

 

x

x

x

x

x

Solution of Alcohol in Sodium Chloride Injection

Rabbit

0.2 mL/animal at each of 10 sites

B

 

 

x

 

x

x

Extract of Sample in

Mouse

10 g/kg

A (ip)

 

 

 

 

x

x

Polyethylene Glycol 400

Rabbit

0.2 mL/animal at each of 10 sites

B

 

 

x

x

x

x

Extract of Sample in

Mouse

50 mL/kg

A (ip)

 

 

 

x

x

x

Vegetable Oil

Rabbit

0.2 mL/animal at each of 10 sites

B

 

 

 

x

 

x

Implant strips of Sample

Rabbit

4 strips/animal

C

a  Tests required for each class are indicated by “x” in appropriate columns.

b  Legend: A (ip)—Systemic Injection Test (intraperitoneal); A (iv)—Systemic Injection Test (intravenous); B—Intracutaneous Test (intracutaneous); C—Implantation Test (intramuscular implantation).

Plastics may be classified as USP Plastic Classes I–VI only on the basis of the response criteria prescribed in Table 1.

 

Still have questions?  For further information about medical silicones, see:

Albright's Glossary of Silicone Terms

CRI-Sil Silicone Technologies

Nusil Silicone Technology

Applied Silicone 

Download our free Silicone Molding Design Manual

Or contact Albright’s Inside Sales for assistance: 978-466-5870/info@albright1.com