In vitro cytotoxicity test of medical devices

How is cytotoxicity testing performed?

For the in vitro cytotoxicity test, connective tissue cells are used, so-called fibroblasts, because these cells have a high sensitivity to toxic substances. The cells are incubated either with the product itself or an extract from the product for 48 to 72 hours. At the end of the incubation, the cells are examined under the microscope for morphological changes as well as for altered growth behavior. Subsequently, the cells are stained to quantify the exact cell number.

The ratio of the number of cells that have come into contact with the product to control cells that have not come into contact with the product can be used to determine the influence of the product on the growth (proliferation) of the cells and to make statements about whether the product inhibits the growth of the cells.

A toxic effect can be caused by the product itself, i.e. by material and coating, by residues on the surface, e.g. from cleaning agents or disinfectants, or by contamination on the surface of the product. Therefore, a positive result of an in vitro cytotoxicity test may lead to a series of further tests to narrow down and determine the exact cause of the cytotoxicity of the medical device.

The Medical Devices Act obliges manufacturers of medical devices to subject them to comprehensive testing to protect patients before placing them on the market. Our accredited testing laboratory carries out tests on the cytotoxicity of medical devices in accordance with the specifications of DIN EN ISO 10993 - "Biological evaluation of medical devices".

This standard, which is primarily relevant for manufacturers of medical devices as well as for testing laboratories, pursues the goal of evaluating the biological compatibility of medical devices. The normative requirements apply not only to finished medical devices, but also to the individual starting materials from which they are manufactured.

DIN EN ISO 10993-5 defines limit values for assessing the cytotoxicity of materials and products. Two criteria are mentioned that can be used to determine whether a substance is to be classified as cytotoxic:

1. "A reduction of cell viability by more than 30% is considered a cytotoxic effect."
2. "Achieving a numerical degree classification of more than 2 according to Tables 1 and 2 is considered a cytotoxic effect."

(Source: DIN EN ISO 10993-5, Section 8.5)

However, a cytotoxicity test alone is not sufficient as proof of the biocompatibility or purity of a medical device. This is because a passed test is not in itself a guarantee that the medical device does not contain critical residues or that the material releases problematic substances. This is because even if many different substances show up well even in low concentrations: If the concentration is too low, the in vitro cytotoxicity test is nevertheless limited in its informative value and does not signal a cytotoxic effect, although the substances in question may in fact be toxicologically very relevant. For this reason, further analytical methods should always be selected in order to be able to completely exclude the risk of cytotoxicity of medical devices.