Irritation Testing of Medical Devices – Evaluation of Biocompatibility in Accordance with EN ISO 10993-23
Medical devices come into direct contact with the human body for diagnostic, therapeutic, or monitoring purposes. To ensure that this contact is safe, the product must be neither toxic nor irritating. The irritation test is a critical biocompatibility test used to assess whether a medical device or substances released by it cause local damage to the skin, eyes, or mucous membranes.
These tests are conducted in accordance with the internationally recognized standard EN ISO 10993-23 (Biological Evaluation of Medical Devices—Part 23: Irritation Tests). Published in 2021, this standard separates the sections on irritation and sensitization from the earlier ISO 10993-10 standard, thereby providing a more specific and up-to-date framework for irritation testing. For MDR (2017/745) and FDA 510(k) submissions, it is mandatory that these tests be conducted in accordance with GLP (Good Laboratory Practice) principles.
What is irritation, and why is it tested?
Irritation is a localized inflammatory reaction triggered by contact between a substance and the skin, eyes, or mucous membranes, and is not caused by the immune system. It is characterized by redness (erythema), swelling (edema), dryness, cracks, and sometimes necrosis. Irritation can result from a single exposure (acute) or from repeated exposure (cumulative).
The risk of irritation associated with medical devices is assessed, in particular, in the following cases:
- Products that come into contact with the skin: wound dressings, electrodes, bandages, sensors, wearable devices
- Products that come into contact with mucous membranes: nasal sprays, dental materials, urinary catheters
- Devices that come into contact with the eye: contact lenses, intraocular lenses (IOLs), surgical instruments
- Implantable devices: Orthopedic implants, stents, screws
- External communication devices: blood bags, infusion sets, catheters
These tests can be performed on the device itself (in solid form) or on extracts obtained from the device (in liquid form). Which approach is chosen depends on the intended use of the device and the duration of contact.
Irritation testing procedures in accordance with EN ISO 10993-23
EN ISO 10993-23 provides both in vivo (live animals) and in vitro (cell culture) methods for evaluating irritation. In accordance with the 3R principles (Replacement, Reduction, Refinement), in vitro methods are increasingly preferred.
1. In vitro irritation tests (preferred method)
The modern approach gives priority to in vitro models in order to minimize the use of animals. EN ISO 10993-23 accepts the following in vitro methods:
- Reconstructed Human Epidermis (RHE) Models: Three-dimensional tissue models derived from human skin cells are used. The test substance is applied to the tissue, and cell viability is measured (MTT assay). A loss of viability of more than 50% is considered an irritant effect.
- EpiDerm™, EpiSkin™, SkinEthic™: Commercially available, validated human skin equivalents.
- OECD TG 439: Internationally recognized test guideline for in vitro skin irritation.
- HET-CAM (Chicken Embryo Chorioallantoic Membrane Test): A method used specifically to test for eye irritation. The test substance is applied to the vascular network of a fertilized chicken egg, and the egg is examined for vascular damage.
2. In vivo irritation tests (if necessary)
In vivo tests are used when in vitro methods do not yield consistent results or when specific regulatory requirements apply:
- Skin Irritation Test (Rabbits): The test substance is applied to the shaved skin of healthy rabbits. Erythema and edema are assessed at 24, 48, and 72 hours.
- Eye Irritation Test (Rabbits): The test substance is applied to the rabbit's eye, and damage to the conjunctiva, iris, and cornea is assessed.
- Mucosal irritation test: Tests conducted on the vaginal, rectal, or oral mucosa.
3. Corrosion Test (OECD TG 431)
Corrosion potential is typically assessed in vitro. Under OECD TG 431, reconstructed human epidermis (RHE) models are used. The test substance is applied to the tissue for 3 minutes, 1 hour, and 4 hours, and cell viability is measured. A viability of less than 35% is classified as corrosion.
Comparison of Irritation Test Methods
The following table summarizes the test methods used in accordance with EN ISO 10993-23:
| Test Method | Model | Duration of Use | Evaluation criterion | Advantages |
|---|---|---|---|---|
| RHE (EpiDerm™) | Human Skin Equivalent | 18–24 hours | Cell Viability (MTT) | No animal testing, fast, reproducible |
| OECD TG 439 | Human Skin Equivalent | 18–24 hours | Cell Viability | Internationally recognized, validated |
| HET-CAM | chicken embryo | 5 minutes | Vascular Damage Score | Alternative to Eye Irritation |
| In vivo skin irritation | Rabbits | 4 hours of contact + 72 hours of observation | Erythema/Edema Score (0–4) | Clinical data, officially recognized |
| OECD TG 431 (Corrosiveness) | Human Skin Equivalent | 3 min., 1 hour, 4 hours | Zellviabilität (<35 % = Ätzwirkung) | Detection of corrosion; no animal testing |
How does the irritation test procedure work?
Conducting an irritation test on a medical device involves the following steps:
- 1. Extraction: The product is extracted using polar (water, saline solution) and nonpolar (vegetable oil, DMSO) solvents in accordance with ISO 10993-12.
- 2. Determining the dose: The extract concentration is calculated based on the product's surface-to-volume ratio.
- 3. Test Procedure: Depending on the method chosen (in vitro or in vivo), the test substance is administered.
- 4. Observation and Measurement: The reactions are evaluated at specified times.
- 5. Evaluation and Classification: The results are classified as “non-irritating/non-corrosive,” “mildly irritating,” “severely irritating,” or “corrosive.”
- 6. Report Preparation: A GLP-compliant report with test approval is prepared.
GLP-Compliant Irritation Testing Services with Nano-Test
The biocompatibility assessment of your medical device can be conducted by selecting the appropriate test method and presenting the results in a format acceptable to regulatory authorities. With its GLP-compliant irritation tests in accordance with EN ISO 10993-23, Nano-Test is your reliable partner in this process.
Nano-Test – Statement of Work
Nano-Test offers irritation tests for medical devices in accordance with EN ISO 10993-23. In our laboratories, which are accredited according to GLP (Good Laboratory Practice) and ISO/IEC 17025, we perform both in vitro methods (RHE, OECD TG 439, HET-CAM) and in vivo methods (skin and eye irritation in rabbits).
Our service process includes the ISO 10993-12-compliant extraction of your product, dosage optimization, the conduct of tests, as well as monitoring and evaluation. All work is performed with the approval of the Institutional Animal Care and Use Committee (IACUC) and under veterinary supervision. The results are provided as GLP-compliant reports with full traceability, which you can use for your MDR and FDA 510(k) submissions.
At Nano-Test, we place great emphasis on the 3R principles and recommend in vitro methods whenever possible. We support you in developing your biocompatibility strategy (Biological Evaluation Plan—BEP) and provide you with robust data for your communications with regulatory authorities.
Advantages of the Nano-Test irritation test:
- Expertise in both methods: Both in vitro and in vivo irritation tests from a single source.
- GLP-certified infrastructure: All studies are conducted in accordance with GLP principles and ALCOA+ requirements.
- Fast results: Report on in vitro tests within 3–5 business days.
- Specialized Staff: A team with experience in toxicology and histopathology.
- Regulatory Compliance: Full compliance with the requirements of EN ISO 10993-23, OECD TG 431/439, and the MDR.
Local irritation caused by medical devices poses a significant risk that directly affects patient comfort and safety. The irritation test—EN ISO 10993-23— is a crucial step in scientifically demonstrating whether your product poses this risk. Selecting the correct test method, properly performing the extraction, and reporting the results in accordance with GLP standards are prerequisites for a smooth regulatory approval process.
With its laboratory infrastructure, specialized staff, and GLP-compliant processes, Nano-Test fully meets the requirements of medical device manufacturers in the field of irritation testing. Partner with Nano-Test to enhance the safety of your product and accelerate market access.