Cytotoxicity Testing

What is Cytotoxicity Testing in Medical Devices?

Cytotoxicity testing of medical devices is used by a manufacturer assesses the impact of materials in their product to ensure no toxic substances inhibit cell growth or cause cell death. When manufacturing a medical device, many materials can be toxic to cells resulting in risk to patient safety. Additionally, material composition changes can occur after radiation sterilization, which may impact the toxicity of those materials. Gas sterilization modalities may leave residues on a device resulting in leaching and harm to living cells.

How is Cytotoxicity Testing Performed?

Many biocompatibility tests are performed in animals (in vivo), however cytotoxicity testing is performed outside a living organism, such as within a test tube or culture plate (in vitro). Cytotoxicity testing is performed by exposing mammalian cells directly to the device or an extract of the device and assessing the impact to the cells.

What Methods are Used for Cytotoxicity Testing?

There are many established testing methods for assessment of cytotoxicity. Manufacturers should consider the method used to expose the cell line to toxic materials or leachables that may be present in the device.

Extraction methods (qualitative and quantitative):

• Solid devices extracted in solution: solid devices are extracted in solution and the liquid extract is then applied to the cells and the effects observed. An advantage of this method is that several dilutions of the sample extract may be tested. This can provide information about the concentration required to generate a cytotoxic result.

Direct contact methods (qualitative and quantitative):

• Liquid samples are directly added to the cells

• Solid samples are placed directly onto a layer of cells

Indirect contact methods (qualitative assessment only):

• Agar diffusion: the established cell line is suspended within an agar solution. Once solidified, samples are placed onto the agar. Leachables from the device diffuse through the agar and the cells are examined to determine if there is a cytotoxic effect. This method may not be appropriate for all devices as it can only detect cytotoxic effects for leachables that are able to diffuse through the agar layer.

• Filter diffusion: the cell line is established on top of a 0.45μm pore size filter. Filters are transferred to the surface of an agar layer and test samples applied to the filter. After exposure to the sample, the cells are examined for cytotoxic effects.

At STERIS we specialize in the neutral red uptake method (NRU). NRU is a quantitative extraction method that removes technician bias as found in qualitative methods such as MEM Elution.

What are the Benefits of Cytotoxicity Testing for Medical Devices?

Cytotoxicity testing is required for submission to regulatory bodies such as the Food and Drug Administration (FDA) and European Medical Device Regulation (EUMDR) for approval of most medical devices.

Cytotoxicity is one of the primary tests completed during a biocompatibility assessment and often the initial test performed during product evaluation.

Cytotoxicity testing can be used when evaluating material type or supplier changes for impact to biocompatibility. This test can be used in the absence of repeating other biocompatibility assays.

Historical data on materials is sufficient for many biocompatibility tests, however direct testing of the device itself is required for cytotoxicity assessment.

What is the ISO 10993 Testing Standard in Relation to Cytotoxicity?

ISO 10993 guides medical device manufacturers and testing laboratories through assessing the biocompatibility of medical devices. This series of standards describes the overall requirements for biological evaluation of medical devices through risk assessment in addition to providing instruction on performing each biocompatibility test. Cytotoxicity testing is conducted according to ISO 10993-5: Biological evaluation of medical devices — Tests for in vitro cytotoxicity.

STERIS Accreditation

The STERIS Brooklyn Park, Minnesota laboratory offers cytotoxicity testing that is accredited to ISO/IEC 17025 with the option to conduct testing as a nonclinical laboratory study per the requirements in FDA 21 CFR Part 58 for Good Laboratory Practice (GLP).