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Biocompatibility refers to the interaction between a medical device and the tissues and physiological systems of the patient treated with the device. The clinical success and safety of medical device largely depend on its safe interaction with body tissue. It is usually due to the release of toxins which causes the device to be “not compatible”. In order to monitor the biocompatibility on medical device, the device itself or its extract prepared in exaggerated conditions is often used to ensure the safety under normal physiological conditions.  The ISO 10993 set entails a series of standards from Part 1 to 20 for evaluating the biocompatibility of a medical device.

One of the methods to determine biocompatibility is to study the cytotoxic effect of the extracts on well-established cell line (in vitro study) according to ISO 10993 Part 5. The cost of ‘in vitro study’ is generally lower, and easier to be accepted in region against using animal for laboratory testing.
Cell culture assay is employed to determine the biocompatibility of a medical device. Generally, there are three methods used for studying medical devices’ cytotoxicity. The first method is Direct Contact which is recommended for low density materials, such as contact lens polymers. The test material is placed directly onto cells and incubated in a suitable condition. During incubation, any leachable chemicals from the test material can diffuse into the culture medium and contact directly with the cell layer. The chemicals released are concluded to be cytotoxic if malformation, degeneration and lysis of cells are observed around the test material.

The second method is Agar Diffusion assay which is applicable to high density materials, such as elastomeric closures. A nutrient-supplemented agar layer is placed over the cultured cells. Then, the test material is placed on top of the agar layer. The leachable chemicals can diffuse into the agar and contact the cell layer. Cytotoxicity is indicated by malformation, degeneration and lysis of cells under and around the test material.

The third method is MEM Elution assay which studies the cytotoxic effect of extracts of the test devices using different extracting media and conditions according to actual use or exaggerated conditions. Then, the extracts are transferred to the cell layer and incubated. The malformation, degeneration and lysis of cells are observed using microscope.

The three methods mentioned above determine cytotoxicity qualitatively. Cytotoxicity can also be determined quantitatively, including by measuring cell death, inhibition of cell growth, cell proliferation or colony formation.

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Alan Ng (Life Science)
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Systems and Services Certification
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