Looking Beyond USP Class VI Testing. What is USP 87 Testing?

January 16, 2014
USP Class VI Sanitary Tri-clamp Gaskets

USP Class VI Sanitary Tri-clamp Gaskets

We wrote a post earlier on what is USP Class VI testing and it proved to be very popular.  As the use of single use high purity process components has grown in the biopharmaceutical industry, having products that meet USP Class VI testing standards has become an important issue.  But many firms require significant further testing of single use materials along with USP Class VI before they will approve the use of the product.  Today we will focus on biocompatibility and USP <87> testing.   In future posts we will look at other testing requirements not included in USP Class VI that many companies require before they will consider a single use product safe for use with direct product contact.

As our post on USP Class VI testing laid out, biocompatibility is the measure of a materials lack of interaction with living tissue or a living system by not being toxic or physiologically reactive. Essentially what this means is that the product does not evoke a response from the host’s immune system. To minimize negative effects to end users (in this case not OEMs, but real, live human beings), it is essential that biocompatibility assessments are conducted for all materials that are used in the manufacture of medical devices and the production of drugs. Depending on the application, no single test may be sufficient to define biocompatibility.
The two most common test regimens commonly used to measure biocompatibility are USP <87>, USP <88> Biological Reactivity Testing (USP Class VI) and ISO 10993 for the Biological Evaluation of Medical devices. This post will focus specifically on USP <87>, my next post will focus on USP <88>. Future posts will focus on the harmonization efforts taken by the International Standards Organization (ISO) to standardize the biological evaluation of medical devices.

To begin, USP <87> is an in vitro test designed to assess the biocompatibility of the test material in contact with a specific cell culture in a fast and sensitive way. There are three different ways this test can be carried out depending on the material tested; agar diffusion, direct contact, and elution.

The agar diffusion test is designed for elastomeric closures in a variety of shapes. The agar acts as a cushion to protect the cells from mechanical damage while allowing diffusion of the leachable from the polymeric specimens. The results are then rated on a scale from 0 (no reactivity) to Grade 4 (severe reactivity). The test item is considered non-cytotoxic if none of the cultures exposed to the test item show greater than mild reactivity (Grade 2). Grade 0 is no detectable zone around or under the specimen (in compared to controls), while 4 or severe reactivity is a large zone that extends 1.0 cm beyond the specimen. Reactivity grade 2, or mild reactivity is a zone limited to the area under the specimen.

The direct contact test is designed materials of many different shapes. It is comparable to the agar diffusion test and allows for the simultaneous extraction of leachable chemicals from the specimen with a serum-supplemented medium. This isn’t a good test for low or high density polymers that can cause mechanical damage to the medium. Results are evaluated in the same way as with agar diffusion testing.

The third test type is the Elution test. This test is designed specifically to test the extracts of polymers. The procedure allows for the extraction of the specimens at physiological or nonphysiological temperatures for varying time intervals. Bovine serum or NaCl are mixed with the test product and heated in an incubator to extract any potentially harmful product derivatives. This mixture is then added to mammalian cell suspension and incubated at 37 C for 48 hours. Results are also based on a scale of 0-4, but are evaluated based on the appearance of distinct cell lysis when viewed under a microscope. A passing grade of 2, or mild reactivity, indicates that no more than 50% of the cells are round and devoid of intracytoplasmic granules and that no extensive cell lysis exists.

Regardless of the test type, the basic idea is the same: the product (the plastic piece) is processed and prepared, exposed to L929 mouse fibroblast cell culture, fed by minimum essential medium, and viewed to determine if a response is elicited. Biocompatibility tests are important when selecting and specifying new products for an application. At Holland, we stay abreast of the changes in material qualifications of the products we sell and make this data available to our customers. We offer a wide range of products that comply with USP Class VI and ISO 10993. Stay tuned for future posts on additional biocompatibility tests.

With many of the single use products we provide, USP <88> testing has been completed, along with many other tests beyond USP Class VI.  We can provide these in comprehensive validation guides that potentially can save the end user some time and money to do this type of testing themselves.
Contact us if you have any questions on this or other single use issues.