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Medical devices, like doctors, should do no harm. With that in mind, it’s important they don’t cause skin sensitization on contact with patients. Skin sensitization is the condition of responding to certain stimuli in a sensitive manner: it can manifest as erythema (skin reddening), pruritus (severe itching), oedema (swelling), raised bumps (papules), vesicles and bullae (small and larger blisters) or a combination of these. To reduce the likelihood of adverse reactions and ultimately to make medical devices safer, Biological evaluation of medical devices — Part 10: Tests for skin sensitization specifies procedures for assessing devices and their constituent materials for their potential to induce skin sensitization.

Biological evaluation

In fact, is the fourth edition of this standard, which is in itself the tenth in an extensive international series on the biological evaluation of medical devices. Other standards in the series cover e.g.: animal welfare requirements, sample preparation, and good clinical practice.

Part 10 assesses possible contact hazards from chemicals released from medical devices that may produce skin sensitization. Of course, some materials that are included in medical devices have been tested, and their skin sensitization potential is documented. This is especially the case for dental materials.

But there remain many other materials and their chemical components that are “unknowns”. They’ve not been tested and may induce adverse effects. It’s to weed these materials out that BS EN 10993-10 exists, since manufacturers are obliged to evaluate each device for potential adverse effects prior to marketing.

Test guidelines

At the same time, the standard is mindful that small animal testing – the traditional method prior to testing on humans to help predict human responses – is not without its drawbacks. In this light, since 2015, several in chemico and in vitro assays have been validated, and Organization for Economic Co-operation and Development (OECD) test guidelines released to assess the skin sensitization potential of chemicals.

However, these have only been validated for neat chemicals and not for medical devices. They are not sufficient alone to conclude on the presence or absence of the skin sensitization potential of chemicals, but can nevertheless be considered in the context of integrated approaches such as “integrated approaches to testing and assessment” (IATA), combining them with other complementary information.

A step-wise approach

Meanwhile to help minimize animal testing, takes a “step-wise approach” – whereby test materials are characterised and samples analysed, and a literature review undertaken first. Then in vitro testing is considered in preference to in vivo – the idea being that as and when in vitro tests become scientifically validated and practical, they should be used to detect the skin sensitization potential of chemicals instead. The standard goes on to emphasize that pre-test considerations may result in the conclusion that testing for sensitization is not necessary.

Finally, the 2023 revisions to the standard have meant that it now focuses solely on the description of skin sensitization testing only, while testing for irritation is now described in BS EN ISO 10993-23 (Tests for irritation). In addition, the content on non-animal methods for skin sensitization has been updated.

The result is a standard that can make skin sensitization testing more efficient by reducing the number of animals involved, as well as contributing to safer medical devices.