Description of some commonly required tests

The purpose of cytotoxicity testing is to determine the biological reactivity of the mammalian cell lines following contact with the material or the extract of the material. During the test, cells are first grown on plates. Depending on the test being performed, the cells are either derived from the ovaries of Chinese hamsters or from fibroblasts of mice. Once the cells reach an appropriate confluence or density, the test article, or 

Cells are very sensitive and can be killed by minor changes in pH, salinity, or temperature. It is possible to have some incidence of this type of cell death without classifying the test article as cytotoxic. But if the vast majority of the cells are dead or dying, the test article will be classified as cytotoxic. Both in vitro and in vivo tests are required as part of a testing battery. 

Sensitization testing estabhshes the potential of the test article to elicit an allergenic response, hi particular, the testing is aimed at a delayed-type hypersensitivity (DTH) response. This is an immune response that takes a couple of days to develop. Poison ivy is a good example of a DTH response. 

The third commonly used sensitization test method is called the mouse local lymph node assay (LLNA). The LLNA is an acceptable test method, but device manufacturers have been using the guinea pig tests for decades and are satisfied with the results obtained using those methods. The LLNA, like any test, has its pros and cons. On the positive side, it is shorter in duration, uses animals of a lower phylum, and requires far less test material. However, it also generates radioactive waste and is not accurate in distinguishing a sensitization response from an irritation response, which increases the possibility of a false-positive outcome. 

Irritation testing determines whether the test article will cause irritation to the relevant tissue. Various models are available to test an article, the most common being the intracutaneous reactivity study (IC). In this test, extracts are typically used to inject five 0.2 mL boluses per extract into the skin of rabbits. The injections are usually the size of a mosquito bite. The skin sample area is observed every 24 h for 72 h following the injections and is scored for erythema and edema. The test sites are compared with control sites, and in order for the test article to pass, the difference of the average scores cannot exceed 1. The IC test can also be used with the test article directly if it is small enough to pass through a needle. 

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