Biological evaluation of medical devices - Part 12: Sample preparation and reference materials
1 Scope
This document specifies requirements and gives guidance on the procedures in the preparation of samples and the selection of reference materials for medical device testing primarily in biological test systems primarily in accordance with one or more parts of the ISO 10993 series.
Specifically, this document addresses the following:
——test sample selection;
——selection of representative portions from a medical device;
——test sample preparation;
——experimental controls;
——selection of, and requirements for, reference materials;
——preparation of extracts.
This document is not applicable to live cells but can be relevant to the material or medical device components of combination products containing live cells.
Extractions for chemical characterization are covered in ISO 10993‑18. Clause 7, 8, 9, 10 [with the exception of 10.3.5 and 10.3.11 b], and 11 can apply to extractions for chemical characterization. Information given in C.1 to C.4 can also be relevant.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
——ISO Online browsing platform: available at https://www.iso.org/obp
——IEC Electropedia: available at http://www.electropedia.org/
3.1
blank
extraction vehicle not containing the test material, which is exposed to identical vessels and conditions as the test sample during extraction
Note: The purpose of the blank is to evaluate possible confounding effects due to the extraction vessel, extraction vehicle and extraction process.
3.2
Certified reference material; CRM
reference material (RM) characterized by a metrologically valid procedure for one or more specified properties, accompanied by an RM certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability
Note 1: The concept of value includes a nominal property or a qualitative attribute such as identity or sequence. Uncertainties for such attributes may be expressed as probabilities or levels of confidence.
Note 2: Metrologically valid procedures for the production and certification of RMs are given in, among others, ISO 17034 and ISO Guide 35.
Note 3: ISO Guide 31 gives guidance on the contents of RM certificates.
Note 4: ISO/IEC Guide 99:2007 has an analogous definition (5.14).
[SOURCE: ISO Guide 30:2015, 2.1.2]
3.3
exaggerated extraction
extraction that is intended to result in a greater amount of a chemical constituent being released as compared to the amount generated under the simulated conditions of use
Note: It is important to ensure that the exaggerated extraction does not result in a chemical change of the material.
3.4
exhaustive extraction
extraction conducted until the amount of extractable material in a subsequent extraction is less than 10 % by gravimetric analysis (or that achieved by other means) of that detected in the initial extraction
Note: As it is not possible to demonstrate the exhaustive nature of residual recovery, the definition of exhaustive extraction adopted is as above. See also Annex C.
3.5
experimental control
substance with well-characterized responses, which is used in a specific test system to assist in evaluating if the test system has responded in a reproducible and appropriate manner
3.6
extract
liquid that results from extraction of the test sample or control
3.7
extractable substance
substance that can be released from a medical device or material using either extraction solvents or extraction conditions, or both, that are expected to be at least as aggressive as the conditions of clinical use
3.8
homogeneity
consistency of a material's chemical and physical compositions, and uniformity in response to a biological endpoint
Note: A reference material is said to be homogeneous if the biological response in a specific test is found to lie within the specified uncertainty limits of the test, irrespective of the batch or lot of material from which the test sample is extracted.
3.9
leachable substance
substance that can be released from a medical device or material during clinical use
3.10
negative control
well-characterized material and/or substance, which, when tested by a specific procedure, demonstrates the suitability of the procedure to yield a reproducible, appropriately negative, non‑reactive or minimal response in the test system
Note: In practice, negative controls are reference materials but can include blanks and extraction vehicles/solvents.
3.11
positive control
well-characterized material and/or substance, which, when evaluated by a specific test method, demonstrates the suitability of the test system to yield a reproducible, appropriately positive or reactive response in the test system
3.12
reference material; RM
material, sufficiently homogeneous and stable with respect to one or more specified properties, which has been established to be fit for its intended use in a measurement process
Note 1: RM is a generic term.
Note 2: Properties can be quantitative or qualitative, e.g. identity of substances or species.
Note 3: Uses may include the calibration of a measurement system, assessment of a measurement procedure, assigning values to other materials, and quality control.
Note 4: ISO/IEC Guide 99:2007 has an analogous definition (5.13), but restricts the term “measurement” to apply to quantitative values. However, Note 3 of ISO/IEC Guide 99:2007, 5.13 (VIM), specifically includes qualitative properties, called “nominal properties”.
Note 5: The laboratory is to demonstrate that the simulated‑use extraction is carried out under conditions that provide an appropriate representation of intended use. Product‑use simulation is carried out assuming the medical device is assigned to the most stringent category possible for the duration of exposure and takes into consideration both the tissue(s) exposed and the temperature of exposure.
[SOURCE: ISO Guide 30:2015, 2.1.1, modified]
3.13
stability
characteristic of a material, when stored under specified conditions, to maintain a specified property value within specified limits for a specified period of time
Note: See also the IUPAC Compendium of Analytical Nomenclature.
3.14
test sample
medical device, component or material (or a representative sample thereof, manufactured and processed by equivalent methods), or an extract or portion thereof that is subjected to biological evaluation testing
4 General requirements
When identifying hazards and estimating risk in relation to medical devices, hazards that arise from changes in the manufacturing process, or insufficient control of the manufacturing process, shall be considered in the design and preparation of test samples, as described in ISO 14971. Particular attention shall be given to material additives, unintentional base material impurities and manufacturing process residues, e.g. trace elements and cleaning and disinfection agents.
The ISO 10993 series describes many different biological assay systems. Therefore, the individual parts shall be consulted to ascertain whether these are appropriate for specific test systems.
Experimental controls shall be used in biological evaluations carried out in order to either validate a test procedure or compare the results between materials, or both. Depending on the specifications of a particular test, either negative controls, blanks or positive controls, or all three, shall be used.
Note: The same type of control can be applicable to different tests and can allow cross‑reference to other established materials and test methods. Additional guidance on the selection of experimental controls is given in Annex A. Use of positive controls for in vivo testing might be affected by animal welfare regulations.
5 RM
5.1 General
RM are established by individual laboratories. The extent of chemical, physical and biological characterization is determined by the individual laboratory. Commercially available articles may be used as RM.
Note: See also ISO Guide 35.
CRM are selected for their high purity, critical characteristics, suitability for the intended purpose and general availability. The critical chemical, physical and biological characteristics shall be determined by collaborative testing in three or more laboratories and made available to the investigator by the distributor.
It is desirable for users to obtain a commitment from suppliers of RM or CRM stating that these materials will be available to the user for at least five years. A second but less desirable option is for the source of the RM or CRM to publish an “open formulation” for the material, i.e. publication of the source materials and details of the processing needed to ensure uniform batches of the RM.
5.2 Certification of RM for biological safety testing
Qualification of an RM is a procedure that establishes the numerical or qualitative value of the biological response of the material under specified test conditions, ensuring reproducibility of the response either within laboratories or between laboratories, or both. The range of biological responses associated with the material shall be established through laboratory tests.
Biological evaluation of medical devices - Part 12: Sample preparation and reference materials
1 Scope
This document specifies requirements and gives guidance on the procedures in the preparation of samples and the selection of reference materials for medical device testing primarily in biological test systems primarily in accordance with one or more parts of the ISO 10993 series.
Specifically, this document addresses the following:
——test sample selection;
——selection of representative portions from a medical device;
——test sample preparation;
——experimental controls;
——selection of, and requirements for, reference materials;
——preparation of extracts.
This document is not applicable to live cells but can be relevant to the material or medical device components of combination products containing live cells.
Extractions for chemical characterization are covered in ISO 10993‑18. Clause 7, 8, 9, 10 [with the exception of 10.3.5 and 10.3.11 b], and 11 can apply to extractions for chemical characterization. Information given in C.1 to C.4 can also be relevant.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
——ISO Online browsing platform: available at https://www.iso.org/obp
——IEC Electropedia: available at http://www.electropedia.org/
3.1
blank
extraction vehicle not containing the test material, which is exposed to identical vessels and conditions as the test sample during extraction
Note: The purpose of the blank is to evaluate possible confounding effects due to the extraction vessel, extraction vehicle and extraction process.
3.2
Certified reference material; CRM
reference material (RM) characterized by a metrologically valid procedure for one or more specified properties, accompanied by an RM certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability
Note 1: The concept of value includes a nominal property or a qualitative attribute such as identity or sequence. Uncertainties for such attributes may be expressed as probabilities or levels of confidence.
Note 2: Metrologically valid procedures for the production and certification of RMs are given in, among others, ISO 17034 and ISO Guide 35.
Note 3: ISO Guide 31 gives guidance on the contents of RM certificates.
Note 4: ISO/IEC Guide 99:2007 has an analogous definition (5.14).
[SOURCE: ISO Guide 30:2015, 2.1.2]
3.3
exaggerated extraction
extraction that is intended to result in a greater amount of a chemical constituent being released as compared to the amount generated under the simulated conditions of use
Note: It is important to ensure that the exaggerated extraction does not result in a chemical change of the material.
3.4
exhaustive extraction
extraction conducted until the amount of extractable material in a subsequent extraction is less than 10 % by gravimetric analysis (or that achieved by other means) of that detected in the initial extraction
Note: As it is not possible to demonstrate the exhaustive nature of residual recovery, the definition of exhaustive extraction adopted is as above. See also Annex C.
3.5
experimental control
substance with well-characterized responses, which is used in a specific test system to assist in evaluating if the test system has responded in a reproducible and appropriate manner
3.6
extract
liquid that results from extraction of the test sample or control
3.7
extractable substance
substance that can be released from a medical device or material using either extraction solvents or extraction conditions, or both, that are expected to be at least as aggressive as the conditions of clinical use
3.8
homogeneity
consistency of a material's chemical and physical compositions, and uniformity in response to a biological endpoint
Note: A reference material is said to be homogeneous if the biological response in a specific test is found to lie within the specified uncertainty limits of the test, irrespective of the batch or lot of material from which the test sample is extracted.
3.9
leachable substance
substance that can be released from a medical device or material during clinical use
3.10
negative control
well-characterized material and/or substance, which, when tested by a specific procedure, demonstrates the suitability of the procedure to yield a reproducible, appropriately negative, non‑reactive or minimal response in the test system
Note: In practice, negative controls are reference materials but can include blanks and extraction vehicles/solvents.
3.11
positive control
well-characterized material and/or substance, which, when evaluated by a specific test method, demonstrates the suitability of the test system to yield a reproducible, appropriately positive or reactive response in the test system
3.12
reference material; RM
material, sufficiently homogeneous and stable with respect to one or more specified properties, which has been established to be fit for its intended use in a measurement process
Note 1: RM is a generic term.
Note 2: Properties can be quantitative or qualitative, e.g. identity of substances or species.
Note 3: Uses may include the calibration of a measurement system, assessment of a measurement procedure, assigning values to other materials, and quality control.
Note 4: ISO/IEC Guide 99:2007 has an analogous definition (5.13), but restricts the term “measurement” to apply to quantitative values. However, Note 3 of ISO/IEC Guide 99:2007, 5.13 (VIM), specifically includes qualitative properties, called “nominal properties”.
Note 5: The laboratory is to demonstrate that the simulated‑use extraction is carried out under conditions that provide an appropriate representation of intended use. Product‑use simulation is carried out assuming the medical device is assigned to the most stringent category possible for the duration of exposure and takes into consideration both the tissue(s) exposed and the temperature of exposure.
[SOURCE: ISO Guide 30:2015, 2.1.1, modified]
3.13
stability
characteristic of a material, when stored under specified conditions, to maintain a specified property value within specified limits for a specified period of time
Note: See also the IUPAC Compendium of Analytical Nomenclature.
3.14
test sample
medical device, component or material (or a representative sample thereof, manufactured and processed by equivalent methods), or an extract or portion thereof that is subjected to biological evaluation testing
4 General requirements
When identifying hazards and estimating risk in relation to medical devices, hazards that arise from changes in the manufacturing process, or insufficient control of the manufacturing process, shall be considered in the design and preparation of test samples, as described in ISO 14971. Particular attention shall be given to material additives, unintentional base material impurities and manufacturing process residues, e.g. trace elements and cleaning and disinfection agents.
The ISO 10993 series describes many different biological assay systems. Therefore, the individual parts shall be consulted to ascertain whether these are appropriate for specific test systems.
Experimental controls shall be used in biological evaluations carried out in order to either validate a test procedure or compare the results between materials, or both. Depending on the specifications of a particular test, either negative controls, blanks or positive controls, or all three, shall be used.
Note: The same type of control can be applicable to different tests and can allow cross‑reference to other established materials and test methods. Additional guidance on the selection of experimental controls is given in Annex A. Use of positive controls for in vivo testing might be affected by animal welfare regulations.
5 RM
5.1 General
RM are established by individual laboratories. The extent of chemical, physical and biological characterization is determined by the individual laboratory. Commercially available articles may be used as RM.
Note: See also ISO Guide 35.
CRM are selected for their high purity, critical characteristics, suitability for the intended purpose and general availability. The critical chemical, physical and biological characteristics shall be determined by collaborative testing in three or more laboratories and made available to the investigator by the distributor.
It is desirable for users to obtain a commitment from suppliers of RM or CRM stating that these materials will be available to the user for at least five years. A second but less desirable option is for the source of the RM or CRM to publish an “open formulation” for the material, i.e. publication of the source materials and details of the processing needed to ensure uniform batches of the RM.
5.2 Certification of RM for biological safety testing
Qualification of an RM is a procedure that establishes the numerical or qualitative value of the biological response of the material under specified test conditions, ensuring reproducibility of the response either within laboratories or between laboratories, or both. The range of biological responses associated with the material shall be established through laboratory tests.
