 Dr. Jerry Nelson Nelson Laboratories Chief Science Officer Visit Website |
Jerry R. Nelson, Laboratory Director at Nelson Laboratories, has a PhD in microbiology and immunology from the University of Utah. He is a member of numerous standards-writing committees and associations, including the New York Academy of Sciences, American Society for Quality, Parenteral Drug Association, American Society of Testing and Materials, Association for Advancement of Medical Instrumentation, Society for Pharmaceutical Engineering, and the American Society for Microbiology. In addition to having published dozens of articles, he is also an adjunct professor of bioengineering at the University of Utah and an adjunct assistant professor of microbiology at Brigham Young University. Jerry was named by MPMN's sister publication, MD+DI, as one of the Top 100 Notable Individuals in the medical device industry.
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Sterilization and Biocompatibility Q&A
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What is the difference between the indirect contact method and the direct contact method in complement activation of C3a and SC5b testing? And which method is considered superior and a must-have as required by FDA in hemocompatibility test batteries for Class II medical devices with an external communicating device that will undergo less than 24 hours of contact with blood? In other words, which method is considered superior for testing a typical microcatheter device?Answered June 27th, 2011 by Expert:The indirect contact method is an extraction procedure in which the device or material is extracted in physiological saline for a given time and at a given temperature depending on the intended use of the product (for example, 37°C for 72 hours, 50°C for 72 hours, 70°C for 24 hours, or 121°C for 60 minutes). The extract fluid is then exposed to serum or plasma for a given period of time, and the complement levels are determined using ELISA assays specific for C3a and SC5b-9. This method determines the complement activation levels of leachables extracted from the device or material in saline. One of the problems with this method is that the saline must be diluted significantly (1:10) when exposed to the serum in order to perform the test, thereby potentially diluting the effects of the extracted leachables during complement activation.
The direct contact method directly exposes the device or material to serum or plasma, and the complement levels are determined using ELISA assays specific for C3a and SC5b-9. This method determines the direct material interactions with the serum or plasma and possible chemical leachables that may come off of the device or material during exposure. This method is typically more sensitive than the indirect method, and it shows the direct effect of the device or material in contact with the serum or plasma.
As a general rule, FDA accepts only the direct contact method because of its sensitivity and the direct material interaction with the serum or plasma. Moreover, because there is no industry standard acceptance criteria or pass/fail criteria for this test, Nelson Laboratories Inc. strongly recommends that when you perform this assay, you should include a predicate device or material (a comparative device or material already on the market similar in function and patient contact duration to the device you are testing). Typically the test device or material protein concentrations are compared statistically with negative control protein concentrations, and complement activation is determined based on the statistical similarities or differences. When a predicate device is included in the assay, the test device protein concentrations are statistically compared with the predicate device protein concentrations to determine statistical similarities or differences between the product you’re testing and a product already on the market.