Irritation Medical Devices

What is the definition of skin irritation for medical devices?

Assessment of skin irritation is an essential component of the safety evaluation of medical devices. Dermal irritation is generally defined as “the production of reversible inflammatory changes in the skin” (OECD 2002). This is induced by extracts of medical devices polymers, with a low concentration of irritant which penetrate the stratum corneum and lead to damages and cell loss of the underlying cell layers. The epiCS irritations test of medical devices measures the cell damage as reduction of cell viability using a human reconstructed epidermis. OECD Test Guideline 439 describes the use of reconstructed human epidermis (RhE) as an in vitro test system for classification of skin irritation by chemicals.

What is the current OECD Guideline for skin irritation testing and ISO for biological evaluation of medical devices?

The various toxicological endpoints for the safety evaluation of medical devices are described in the EN/ISO 10993 series of standards.

ISO 10993-1, Biological evaluation of medical devices — Part 1: Evaluation and testing within a risk management process

The endpoints considered depend up on the type, the contact and duration of the contact of device. Nevertheless, cytotoxicity, irritation and sensitization testing are recommended for almost all devices.

For determining skin irritation potential of medical devices are described:

Biological evaluation of medical devices - Part23: Tests for irritation (ISO/DIS 10993-23:2019);

The irritation potential of a medical device or its components can be predicted either by an in vivo animal irritation test or by an in vitro irritation test using a reconstructed human epidermis (RhE) as a model.

OECD TG 439 describes skin irritation testing using the RhE model.

OECD TG 439

How does the test work?

Samples and vehicles control are prepared according to ISO10993-12 by extraction using a polar and non-polar solvent

ISO(2012) ISO/TC 194 10993-12 - Biological evaluation of medical devices -- Part12: Sample preparation and reference materials.International Organization for Standardization, Geneva, Switzerland

The irritation is induced by extracts of medical devices polymers, with a low concentration of irritant which penetrate the stratum corneum and lead to damages and cell loss of the underlying cell layers. The epiCS irritations test of medical devices measures the cell damage as reduction of cell viability using a human reconstructed epidermis.

The test consists of a topical exposure of the extracts of medical devices polymers (medical devices extracts in saline and sesame oil), for 24 h, to a human reconstituted epidermis model followed by a cell viability test. Cell viability is measured by dehydrogenase conversion of MTT [(3-4,5-dimethyl thiazole 2-yl) 2,5-diphenyltetrazoliumbromide], present in cell mitochondria, into a blue formazan salt that is quantitatively measured after extraction from tissues. The reduction of viability of tissues exposed to chemicals in comparison to negative controls (treated with DPBS) is used to predict skin irritation potential.

Irritant chemicals in extracts of medical devices are identified by their ability to decrease cell viability below defined threshold levels (i.e. ≤ 50%, for UN GHS Category 2). Irritants Chemicals that produce cell viabilities above the defined threshold level, may be considered non-irritants (i.e. > 50%, No Category).

Irritation Medical Devices


Fig. 1 Illustration of the testing protocol

How can I translate viability data into substance classification?

Viability measured after 24 h exposure 
Prediction to be considered 
≤ 50% Irritant

Category 2 (Cat. 2) 
> 50% Non - irritant

Non - classified

How does this work in practice?

This case study illustrates skin irritation of medical devices testing results and the classification of test extracts for four medical devices polymers as an example.

Case study skin irritation of medical devices

Case A:

Medical devices A polymer. Extraction in a polar and non-polar solvent. Extracts of medical devices are applied topically to the Epidermis.

Exposure time 24 h
Viability Polar 100 %
Non-Polar 114%
Classification No Category (non irritant)

Case B:

Medical devices B polymer. Extraction in a polar and non-polar solvent. Extracts of medical devices are applied topically to the epidermis.

Exposure time 24 h
Viability Polar 1 %
Non-Polar 2 %
Classification Category 2 (irritant)

Case C:

Medical devices C polymer. Extraction in a polar and non-polar solvent. Extracts of medical devices are applied topically to the epidermis.

Exposure time 24 h
Viability Polar 0,5 %
Non-Polar 116%
Classification Category 2 (irritant)

Case D:

Medical devices D polymer. Extraction in a polar and non-polar solvent. Extracts of medical devices are applied topically to the epidermis.

Exposure time 24 h
Viability Polar 119 %
Non-Polar 1 %
Classification Category 2 (irritant)

Which methods are validated and accepted?

The Irritation Test for medical devices is based on a SOP of epiCS®Skin Irritations Test and Protocol n° 212: [epiCS® Skin Irritation Test (epiCS® SIT) published on EURL ECVAM DataBase service on Alternative Methods to animal experimentation (DB-ALM)] and the Round Robin Study (Round Robin study, 2017).The epiCS® method for skin irritation are integrated in the OECD/OCDE TG 439 in 2019.

Round Robin study

OECD TG 439, June 2019, English

OCDE LD 439, Juin 2019, French

SOP epiCS in vitro Skin Irritation, v5.2 , 2019

published on EURL ECVAM DataBase service on Alternative Methods to animal experimentation (DB-ALM) as Protocol n° 212: epiCS® Skin Irritation Test (epiCS® SIT)

This protocol for irritation testing for medical devices has been revised and adapted for the use for medical Devices with epiCS. A follow-up validation study with 7 polymer samples of medical devices was executed in 2019. The irritations test for medical devices extracts witch epiCS-models was evaluated form SkinInVitro GmbH, based on the study designs of Round Robin Study.

7 Polymer samples used and their predicteda Outcome.

Polymer SkinInvitro Classification Round Robin Classification
Saline extract Sesame oil extract Overall Saline extract Sesame oil extract Overall
100% Silicone NI NI NI NI NI NI
Polyurethane E80A NI NI NI NI NI NI
PVC + 4% Genapol I I I I I I
Silicone + 15% SDS I NI I I NI I
Silicone + 25% Heptanoic Acid NI NI NI NI I I
USP (was Y1) NI NI NI NI NI NI
Y-4 Lot 1,2,& 3 I I I I I I

The epiCS® method for skin irritation testing for medical devices reveals very good predictivity and reliability:

Contingency table individual samples for epiCS test method

What do I need for skin irritation testing?

We develop you a specific kit that you can use for in vitro skin irritation testing for medical devices. In addition, you need laboratory material which are standards in cell culture laboratories.

Example Kit content:

  • epiCS (tissues)
  • epiCS Culture Medium - to culture the tissues - for three medium changes (sufficient for skin irritation testing)
  • epiCS MTT-Assay Medium - for MTT-Assay
  • 6-well plates
  • Lot specific epiCS certificate of analysis

For further Information, please check the epiCS SOP and manual: 

SOP epiCS in vitro Skin Irritation Medical Devices, v1.1 , 2019

We provide competent swift technical and scientific support by telephone or e-mail.

References

  1. UN (2009), United Nations Globally Harmonized System of Classification and Labeling of Chemicals (GHS), Third revised edition, UN New York and Geneva.
  2. EC-ECVAM (2009), Statement on the “Performance under UN GHS of three in vitro assays for skin irritation testing and the adaptation of the Reference Chemicals and Defined Accuracy Values of the ECVAM skin irritation Performance Standards”, issued by the ECVAM Scientific Advisory Committee (ESAC30), 9 April 2009.
  3. EC-ECVAM (2009), ESAC Statement on the Performance Standards (PS) for in vitro skin irritation testing using Reconstructed human Epidermis, issued by the ECVAM Scientific Advisory Committee (ESAC31), 8 July 2009
  4. OECD (2015), OECD guidelines for the testing of chemicals; in vitro skin Irritation: reconstructed human Epidermis test method.
  5. OECD, 2019. OECD Guideline for Testing of Chemical, No. 439: In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method
  6. EURL ECVAM DataBase service on Alternative Methods to animal experimentation (DB-ALM) Protocol n° 212: epiCS® Skin Irritation Test (epiCS® SIT)
  7. SOP (epiCS® SKIN IRRITATION TEST; Standard Operating Procedure; (SOP epiCS SIT)) SkinInVitro, Troisdorf; Germany
  8. ISO 10993-1, Biological evaluation of medical devices — Part 1: Evaluation and testing within a risk management process
  9. Biological evaluation of medical devices - Part23: Tests for irritation (ISO/DIS 10993-23:2019)
  10. ISO(2012) ISO/TC 194 10993-12 - Biological evaluation of medical devices -- Part12: Sample preparation and reference materials.International Organization for Standardization, Geneva, Switzerland
  11. Round robin study to evaluate the reconstructed human epidermis (RhE) model as an in vitro skin irritation test for detection of irritant activity in medical device extracts Wim H. De Jonga,⁎, Sebastian Hoffmannb, Michelle Leec, Helena Kandárovád;Toxicology in Vitro; 2019.
  12. SOP epiCS in vitro Skin Irritation Medical Devices, v1.1 , 2019

(updated 14.01.2020)