COMMITTEE DRAFT ISO/CD 10993-12
Date 1999-09-15
Reference number ISO/TC 194 /SC N 339
WARNING: This document is not an International Standard. It is distributed for review and comment. It is subject to change without notice and may not be referred to as an International Standard.
ISO/TC 194/SC
Title Biological evaluation of medical
devices
Secretariat DIN
Circulated to P- and O-members, and to technical committees and organizations in liaison for
comments by 1999-12-15 [date]
approval for registration as a DIS in accordance
with 2.5.6 of part 1 of the ISO/IEC Directives,
by 1999-12-15 [date]
(P-members vote only: ballot form attached)
P-members of the technical committee or subcommittee
concerned have an obligation to vote.
Title (English)
Biological evaluation of medical devices
- Part 12: Sample preparation and reference
materials (Revision of ISO 10993-12:1996)
Reference language version: English
Introductory note .
ISO/TC 1-94 decided at the Plenary meeting
held on 21 May 1999 in Helsingor by resolution
number 238 to distribute the enclosed document
as Committee Draft.
CONTENTS
This International Standard specifies methods of sample preparation and use of reference materials in biological evaluation. Because of the many different biological assay systems described in ISO 10993, the individual standards should be consulted to ascertain the appropriateness of these recommendations for a specific test system.
Sample preparation methods should consider both the biological evaluation methods and the materials being evaluated. Each biological test restricts selection of solid samples and extraction solvents or conditions by its own methodology.
This part of ISO 10993 is based on existing national and international specifications, regulations and standards wherever possible. It is open to regular review whenever new research work is presented to improve the state of scientific knowledge.
This part of ISO 10993 specifies requirements and gives guidance on procedures to be followed in the preparation of samples of medical devices for testing in biological systems in accordance with one or more parts of the ISO 10993 series. These include;
a) test material selection;
b) selection of representative portions from
a device;
c) test sample preparation;
d) the selection of reference materials to
demonstrate the suitability of the test system
and/or to enable relative comparison of the
biological activity of the test sample; and,
e) preparation of extracts.
The following standards contain provisions that, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this international Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of International Electrotechnical Commission (EC) and International Organization for Standards (ISO) maintain registers of currently valid International Standards.
lSO/IEC Directives, Part 2: 1992, Methodology for the development of International Standards, Annex B - Mention of reference materials
ISO Guide 30 Terms and definitions used
in connection with reference materials.
ISO Guide 31 Contents of certificates
of reference materials.
ISO Guide 33 Uses of certified reference
materials.
ISO Guide 35 Certification of reference
materials - General and statistical principles.
ISO 10993- 1: Guidance on selection of
tests
ISO 10993-3: Tests for genotoxicity, carcinogenicity
and reproductive toxicity.
ISO 10993-4: Selection of tests for interactions
with blood
ISO 10993-5: Tests for cytotoxicity, in
vitro method
ISO 10993-6: Tests for local effects after
implantation
ISO 10993-9: Tests for systemic toxicity
ISO 10993-10: Tests for irritation and
sensitization
3.1 blank: Extraction vehicle not containing the specimen used for comparison with the extract liquid.
3.2 certified reference material (CRM): Reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure which establishes its traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence (see ISO Guide 30).
NOTE: standard reference material (SRM): A trademark protected certification supplied by the National Institutes for Standards and Technology, Gaithersburg. MD, USA.
3.3 extract liquid: Liquid that is tested for biological response after it has been used for extraction of the device.
3.4 homogeneous: The condition of being of uniform structure or composition with respect to the biological endpoint under study. The RM is said to be homogeneous if the biological response to a specific test is found to lie within the specified uncertainty limits of the test, irrespective of the site in the batch or lot of material from where the test sample is taken.
3.5 negative control: A negative control is any well characterized material or substance, which when tested by the procedure described, demonstrates the suitability of the procedure to yield a reproducible, appropriate negative, non -reactive or background response in the test system.
3.6 positive control: A positive control is any well-characterized material or substance, which when tested by the procedure described, demonstrates the suitability of the procedure to yield a reproducible, appropriate positive or reactive response in the test system.
3 7 reference material (RM): A material or substance, one or more of whose property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to materials (see ISO Guide 30). For the purposes of the standard, a reference material is any well-characterized material or substance, which when tested by the procedure described, demonstrates the suitability of the procedure to yield a reproducible, predictable response. The response may be negative or positive.
3.8 reference method: A thoroughly investigated test method, clearly and exactly describing the necessary conditions and procedures, for the evaluation of a specific biological endpoint, that has been shown to have accuracy and precision commensurate with its intended use and that can, therefore, be used to characterize a RM (see ISO Guide 30).
3.9 stability of property values: The ability of a material, when stored under specified conditions, to maintain the stated biological response, within specified limits, for a specific period of time (see ISO Guide 30).
3.10 test material: Material, device, device portion, or component thereof subject to biological or chemical testing.
3.11 test sample: Test material or extract subject to biological or chemical testing.
3.12 exhaustive extraction: Extraction until the amount of residues in a subsequent extraction is less than 10 % of that detected in the first extraction, or until there is no significant increase in the cumulative residues detected. (see also 3.2 of ISO 10993-7)
3.13 simulated extraction: Extraction for evaluating hazard potential available to the patient or user from devices during the routine use of a device using an extraction method with an appropriate medium that simulates product use. (see also 3.1 of ISO 10993-7)
3.14 accelerated or exaggerated extraction: Extraction that provide a measure of the hazard potential of the device or material using the conditions that accelerate or exaggerate leaching of the substances to the medium, such as elevated temperature, agitation, changing medium, etc.
4.1 Experimental controls shall be used in biological evaluations to validate a test procedure and/or to evaluate the results from a new material. Depending on the biological test being used, negative and/or positive controls and blanks shall be used as appropriate. The same control may be applicable to different tests to allow cross-reference to established materials and test methods. Additional guidance on the selection of experimental controls is given in Annex B.
5.1 Reference or certified reference materials shall be used in biological tests as control materials to demonstrate the suitability of the procedure to yield a reproducible, predictable response, e.g. positive or negative. Use of a reference material in this way will ensure the comparability of the response between laboratories. The property values of any material used in this way shall be characterized with each biological test procedure for which the use of the material is desired. A material characterized and then certified for one reference test method or response, e.g. sensitization, shall not be used as a reference material for another, e.g. cytotoxicity, without additional characterization.
5.2 Reference materials used as experimental controls shall meet the established quality assurance procedures of the manufacturer and test laboratory. They shall be identified as to source, manufacturer, grade, and type. Reference materials used as experimental controls shall be fabricated, finished and their surfaces cleaned and sterilized in a manner appropriate to the projected application in human subjects. Where possible, the above processes should be identical to the processes employed in the manufacture of the finished device.
5.2.1 Reference materials used as experimental controls shall be in the same physical class as the test sample, i.e., polymer, ceramic, metal, colloid, etc. Pure chemicals may be used as Reference Materials for mechanistically based test procedures, e.g. mutagenicity. and immune sensitization.
5.3 A comparable, clinically accepted device will satisfy the requirement of 5.2. -
6.1 Material screening versus medical device biocompatability
The uses of the reference materials described in this document are limited to biological screening testing of the materials intended for use in the manufacture of medical devices. However, while not intended for the purpose, they are often used in the performance assessment of the finished device. The vertical standard for the device, when available, must address the biological testing of the product in the performance environment of the device. Biological testing described in the vertical standard takes precedent over testing performed to screen the materials for suitability.
6.2 Misuse of CRMs
The attention of the users of this standard is directed to the discussion of "proper use" and "misuse" of CRMs in the introduction to ISO Guide 33. This discussion points out areas of both potential under and over utilization of RMs and CRMs. Users of this standard should also note that the use of calibration materials to evaluate the biological response of materials under investigation within a single laboratory is acceptable.
6.3 One or more property values
RMs or CRMs used to determine the biological response in this way must be evaluated with each biological test procedure for which the use of the material is desired. It is not sufficient to qualify a material for one type of reference test method or response, e.g. sensitization, and declare it a reference material for another, e.g. cytotoxicity, without additional qualification testing.
6.4 Long term availability of the material
During the development of this standard, concern was expressed about the future availability of reference materials for determination of biological response. It is desirable for users to obtain a commitment of not less than 5 years from suppliers of the RMs or CRMs. A second, but less desirable, option is the publication by the source of the RM or CRM of an "open formulation" for the material, i.e. publication of the source materials and details of the processing needed to insure uniform batches of RM.
6.5 Certification of reference materials for biological safety testing
6.5.1 Individual laboratories certify reference materials. The individual laboratory determines the extent of chemical, physical and biological characterization. Commercially available articles may be used as reference materials (see Clause 5.3).
6.5.2 Certification of a reference material is a procedure that establishes the value of the biological response of the material under the test conditions specified, ensuring a traceability of . the response, which leads to the issuance of a certificate. The biological response of the material should be established through interlaboratory tests.
7.1 It is preferable to test medical devices in their final product form whenever practical. When that is not possible, the second choice is representative portions of the device (see Clause 9). When these are not possible or practical, representative molded or extruded test specimens of the formulated material that have been preconditioned by the same processing as the final product shall be tested.
7.2 The same test material selection procedure applies when an extract is required.
8.1 Test samples and reference materials shall be handled to prevent contamination. Any residues from the manufacturing, fabrication, cleaning, sterilization, etc., processes, if present, should be considered to be integral to the device, device portion or component. Additional guidance on the preparation is given in Annex C.
8.1.1 Test samples from sterilized devices and reference materials shall be handled aseptically if appropriate to the test procedure.
8.1.2 Test samples from devices which are normally supplied non-sterile but are sterilized before use shall be sterilized by the method recommended by the manufacturer and handled aseptically if appropriate to the test procedure.
8.1.3 If test samples are cleaned prior to sterilization, the influence of the cleaning process and cleaning agent shall be considered.
8.2 If sterile test samples are required for the test procedure, the effect of the sterilization or resterilization process on the test sample and reference materials shall be considered.
8.3 When test samples and reference materials need to be cut into pieces, the influence of previously unexposed surfaces, e.g. lumens or cut surfaces, shall be considered. Techniques used for cutting medical devices into representative portions for testing should be as clean as practical to prevent contamination.
9.1 If a device cannot be tested as a whole, each individual material in the final product shall be represented proportionally in the test sample.
9.1.1 The test sample of devices with surface coatings shall include both coating material and the substrate.
9.1.2 The test sample shall include a representative portion of the joint and/or seal if adhesives, radio frequency (RF) seals, or solvent seals are used
9.1.3 Composite materials shall be tested as finished materials.
9.1.4 Where extracts are used in the test methods for evaluation of materials that cure in situ, e.g. cements, adhesives and monomers, initiation of the extraction shall occur after the specified minimum cure that may occur during clinical use. For test methods that use these materials directly, e.g. direct contact or agar overlay cytotoxicity, implantation, some genotoxicity tests, and direct contact hemolysis, the material shall be used as in clinical use, with in-situ cure in the test system. Modification of the delivery system so that the designated size or weight of the material is delivered is appropriate.
9.2 When different materials are present in a single device, the potential for synergies and interactions shall be considered in the choice of test sample.
9.3 The test sample may be chosen to maximize the exposure of the test system to the components where components of a device are known to have a potential for a biological response.
If extracts of the device are required for a test protocol, the extraction media and conditions of extraction used shall be appropriate to the nature and use of the final product, and to the purpose of the test, e.g., hazard identification, risk estimation in exaggerated-use conditions, or risk assessment in actual use. Additional guidance on the extraction of samples is given in Annex D.
10.1 Containers for extraction
10.1.1 The extraction shall be performed in clean, chemically inert closed containers with minimum headspace.
10.1.2 To ensure that the extraction vessels do not adulterate the extract of the test materials the extraction vessels shall be:
a) Borosilicate glass tubes with caps having an inert liner [e.g., poly(tetrafluoroethylene)]
b) Other inert extraction vessels or as required
for specific materials and/or extraction
procedures.
10.1.3 Extractions shall be performed under conditions which prevent contamination of the sample.
10.2 Extraction conditions
Extraction conditions including extraction media shall differ for different test purposes: a) exhaustive extraction is applicable both for hazard identification and risk estimation in
exaggerated-use condition, b) accelerated or exaggerated extraction is applicable for risk estimation in exaggerated-use condition, and c) simulated-use extraction is applicable only for risk assessment in actual-use.
Extraction is a complex process influenced by time, temperature, surface-area-to-volume ratio, extraction medium and the phase equilibrium' of the material. The effects of higher temperatures or other conditions on extraction kinetics and the identity of the extractant(s) shall be considered carefully if exhaustive, accelerated or exaggerated extraction is used.
10.2.1 For estimation in exaggerated-use conditions or risk assessment in actual use
Based on current practices, standard conditions that have been used to provide a measure of the hazard potential (for risk-estimation in exaggerated-use conditions) of the device or material are described. Other conditions that simulate the extraction that occurs during clinical use (for risk assessment in actual use) or provide an adequate measure of the hazard potential may be used and shall be described and justified.
10.2.1. I Standard extraction temperatures and times (with permissible ranges) are as follows (see also Clause D3):
a) 37C +- 1C for 24 +- 2hours
b) 37C +- 1C for 72 +- 2hours
c) 50C +- 2C for 72 +- 2 hours
d) 70C +- 2C for 24 +- 2 hours
e) 121C +- 2C for 1 +- 0.2 hours
10.2.1.' Standard surface area, i.e., projected area, excluding indeterminate surface irregularity, and extractant volumes are:
--------------------
1 The phase equilibrium of a material at a temperature controls the relative amounts of amorphous and crystalline phases present. For the amorphous phase, the glass transition temperature, Tg, dictates the polymer chain mobility and the diffusion rate in the phase. Usually, the diffusion rate is considerably higher above the Tg compared with that below. The diffusion rate is lowest in the crystalline phase. The extraction conditions shall not alter the phase equilibrium of the material. Phase alteration may affect the amount and type of extractables.
----------------------
| Thickness (mm) |
Extraction ratio (surface area/volume) +- 10% |
Example of Materials |
| < 0.5 | 6 cm2/ml | film, sheet, tubing wall |
| 0.5 - 1.0 | 3 cm2/ml | tubing wall, slab, molded items . |
| > 1.0 | 1.25 cm2/ml | natural elastomer |
| Not applicable | 0.2 g sample/ml 6 crn2/ml |
powder, pellets foam, non-absorbent |
NOTE: While there are no standardized methods available at present for testing absorbents and hydrocolloids, the following is a suggested protocol: Determine the "absorption capacity" of the material, i.e. the amount of extractant absorbed per gram of the material. The test sample shall be 0.1 grams/ml beyond the absorptive capacity of the material.
10.2.1.2.1 Other surface area to volume extraction ratios, e.g. those related to evaluation of porous surfaces, may be used provided that they simulate the conditions during clinical use or result in a measure of the hazard potential.
10.2.1.2.2 Elastomers, coated materials, composites, laminates, etc., should be tested intact vhenever possible because of differences in extraction characteristics from the intact and cut surfaces.
10.2.1.2.3 Materials should be cut into small pieces before extraction to enhance submersion in the extract media, except when otherwise inappropriate. See, for example, Clause 10.2.2.2. For polymers, pieces approximately 10 mm x 50 mm or 5 mm x 25 mm are appropriate.
10.2.1.3 Examples of extraction media are
a) Polar medium: water, physiological saline;
culture media without serum
b) Non-polar medium: Freshly refined vegetable
oil (e.g., cottonseed or sesame oil) of quality
defined in various Pharmacopeia;
c) Additional media: alcohol/water, alcohol/saline,
polyethylene glycol 400 (diluted to a physiological
osmotic pressure), dimethylsulfoxide and
culture media with serum.
d) Other media appropriate to the nature
and use of the device may also be used if
their effects are known.
10.2.1.4 Extractions are commonly performed with agitation. When extraction under static conditions is considered to be appropriate, the method should be justified, specified and reported.
10.2.1.5 Liquid extracts shall, if possible, be used immediately after preparation to prevent sorption onto the extraction container or other changes in composition. If an extract is stored longer than 24 hours, then the stability of the extract under the conditions of storage should be verified.
10.2.1.6 The extract should not routinely be processed by filtration, centrifugation or other methods to remove suspended particulates. However, if such processing is necessary, the rationale must be presented.
10.2.1.7 For genotoxicity and delayed-type hypersensitivity, risks shall be estimated by considering long-term cumulative and/or repeated exposure, because the biological changes such as gene mutation and induction of hapten-specific T-lymphocyte are cumulated during repeated and/or long-term exposure. Therefore, exhaustive extraction shall also be considered not only for hazard identification but also for risk estimation of these hazards (see 10.2.2).
10.2.2 For hazard identification and risk estimation in exaggerated-use condition
10.2.2.1 Where the toxic potential is shown to be within the requirement for product tested by exhaustive extraction, there is no need further to challenge the device by simulated-use extraction.
10.2.2.2 An extraction procedure using a volatile solvent such as acetone, methanol, etc., followed by evaporation of the solvent and application of the evaporation residue to test system, shall be undertaken for polymeric materials for genotoxicity and delayed-type hypersensitivity testing.
NOTE: To estimate the effects of cumulated or repeated exposure shown in 10.2.1.7 by a single application to the test systems, it is necessary to increase the concentration of potential toxic chemicals in the extract.
10.2.2.3 Instead of extraction of metallic materials followed by application of the extract to the test systems, testing the solutions of various concentrations of appropriate salt of the specific metal(s) identified in the device shall be considered for identifying hazard of the specific metal ion(s) and to know its highest non-effect level(s).
NOTE: This principle is also applicable for organic materials when chemicals in the device are identified.
Documentation of sample preparation shall include, but not be limited to:
1. Source of material, device, device portion
or component;
2. Lot or batch number, where appropriate;
3. Description of processing, cleaning or
sterilization treatments, if appropriate;
4. Extraction techniques, as appropriate,
including documentation of the conditions
for extraction.
ASTM F 75 Specification for cast cobalt-chromium molybdenum alloy for surgical implants
ASTM F 90 Specification for wrought cobalt-chromium-tungsten-
nickel-alloy for surgical implant applications
ASTM F 136 Specification for wrought titanium
6Al-4V ELI alloy for surgical implant applications
ASTM F 138 Specification for stainless steel
bars and wire for surgical implants (special
quality)
ASTM F562 Specification for wrought cobalt-nickel-chromium-
molybdenum alloy for surgical implant applications
ASTM F 563 Specification for wrought cobalt-nickel-molybdenum-
tungsten-iron alloy for surgical implant
applications
ASTM F 648 Specification for ultra-high-molecular-weight
polyethylene powder and fabricated form for
surgical implants
Braybrook, J.H and G. A Mackay: Supercritical
fluid extraction of polymer additives for
use in biocompatibility testing: Polymer
International 27(1992), pp. 157-164.
NFS 90701 Medico-Surgical Equipment, Biocompatibility
of Materials and Medical Devices, Methods
for Extraction 1988.
Uphill, P F and D. H. Christopher: Developing
a Positive Control for Cytotoxicity Testing
of Medical Device Materials: Medical Device
Technology, Nov/Dec 1990, pp 24-27.
B.1 The materials listed in the following paragraphs may meet the criteria for an appropriate experimental control in selected tests. It is the responsibility of the investigator to make the appropriate choices. See Table B 1.
Table B I - Summary of reference materials and controls
| TEST | POSITIVE CONTROL* |
NEGATIVE CONTROL* |
REFERENCE MATERIAL* |
| IMPLANTATION | PVC-org. Sn | PE | |
| SPU-ZDEC | Silicone | ||
| Latex | Alumina | ||
| Stainless steel | |||
| CYTOTOXICITY | PVC-org. Sn | PE | |
| SPU-ZDEC | |||
| SPU-ZBEC | |||
| Latex | |||
| BLOOD COMPATIBILITY |
PVC 7506 PUR 2541 |
||
| SENSITIZATION |
* Abbreviations on this Table refer to specific materials available from sources designated in Clauses B.2 and B.3.
B.2 Examples of solid reference materials which have been used as negative controls are, for example, high density polyethylene 2,3,4,5, low density polyethylene 6,7, silica-free
-----------------------
2 Plastic, Negative Control: US Pharmacopeia; Cat. No. 54670-7 [Polyethylene, High Density], Rockville, MD, USA; Telephone 800-2278772, lnternet http: //www. usp. org/dsd/refstd/order. htm.
3 HDPE film: RM-C, Hatano Research Institute/Food
and Drug Safety Center, 1- 15-15 Toranomon,
Minato-ku, Tokyo, JAPAN; TEL: 81-463-82-4751,
FAX: 81 463-82-9627, E-mqil: tanac.noriho@nifty.ne.jp
;
4 HDPE sheet: RM-D, Hatano Research Institute/Food
and Drug Safety Center, 1-15-15 Toranomon,
Minato-ku, Tokyo, JAPAN; TEL 81-463-82-4751,
FAX 81463-82-9627, E-mqil:tanac.noriho@nifty
ne.jp
5 HDPE rod: RM-E, Hatano Research Institute/Food
and Drug Safety Center, 1-15-15 Toranomon,
Minato-ku, Tokyo, JAPAN; TEL: 81 463-824751,
FAX: 81 463-82-9627, E-mqil :tanac.noriho@nifty.ne.jp
------------------------
polydimethylsiloxane 8,9, polyvinylchloride 10, polyetherurethane 11, polypropylene 12, medical grade latex, aluminum oxide ceramic rods, stainless steel and titanium alloys. This information is given for the convenience of the user of this part of ISO 10993 and does not constitute an endorsement by ISO of the product.
B.3 Examples of materials which have been used as positive controls for solid samples are polyvinylchloride containing organo-tin additives 13, segmented polyurethane films containing zinc diethyl-dithiocarbarnate 14,15 or dibutyl-dithiocarbamate 16, certain latex formulations and- solutions of zinc salts. Substances which have been used as positive controls for extract samples are dilutions of phenol and water. This information is given for the convenience of the user of this part of ISO 10993 and does not constitute an endorsement by ISO of the product.
-----------------------
6 PE 140 tubing: Rehau AG, D-8673 Rehau, Germany.
PE film: Hoechst AG, D-6230 Frankfurt 80,
Germany.
7 Low density polyethylene: Biomaterials Program, Devices and Technology Branch, National Heart, Lung and Blood Institute, NIH,312 Federal Building, 7550 Wisconsin Ave. Bethesda, MD 20892, USA. .
8 Silica-free Silicone: Biomaterials Program, Devices and Technology Branch, National Heart, Lung and Blood Institute, NIH, 312 Federal Building, 7550 Wisconsin Ave., Bethesda, MD 20892, USA.
9 SIK 8363 tubing: Rehau AG, D-8673 Rehau, Germany.
10 PVC 7506 and PVC 7536 tubing: Rehau AG, D-8673
Rehau, Germany.
PVC-DEHP and PVC-TEHTM film: Hoechst AG,
D-6230 Frankfurt 80, Germany. " PUR
2541 tubing: Rehau AG, D-8673 Rehau, Germany.
11 PU film: Frontline Filmblasning, S-60003 Norrkoping, Sweden. ' PP 146 tubing: Rehau AG, D-8673 Rehau, Germany.
12 PP film: Hoechst AG, D-6230 Frankfurt 80, Germany.
13 At the time of this revision a positive control was not available from the US Pharmacopeia, Rockville, MD, 20852, USA. Telephone 800-227-8772; Internet http://www.usp.org/dsd/refstd/order.htm.
14 Polyurethane film-ZDEC: RM-A, Hatano Research Institute/Food and Drug Safety Center, 1-15-15 Toranomon, Minato-ku, Tokyo, JAPAN; TEL: 81-463-82-4751, FAX: 81-463-82-9627, E-mqil:tanac.noriho@nifty.ne.jp
15 Polyurethane rod-ZDEC: RM-F, Hatano Research Institute/Food and Drug Safety Center, 1-15-15 Toranomon, Minato-ku, Tokyo, JAPAN; TEL: 81-463-82-4751, FAX: 81 -463-82-9627, E-mqil:tanac.noriho@nifty.ne.jp
16 Polyurethane film-ZDBC: RM-B, Hatano Research Institute/Food and Drug Safety Center, I - 15- 15 Toranomon, Minato-ku, Tokyo, JAPAN; TEL: 81 -463-82-4751, FAX: 81 -463 -82-9627, E-mqil: tanac.noriho@nifty.ne.jp
This section provides general principles on and practices of material preparation and sample selection.
C.1 The material used in the biological assay should be representative of the composition, processes and surface characteristics of the final product. See Clause 7.
C.1.1 In the case of plastic and rubber materials, the composition should include resin, polymer and any additives. Alternate components of a formulation should be evaluated for substitution. The formulation description should specify the history of the material, e.g., thermal, virgin or regrind and the maximum allowable regrind.
C.1.2 Materials that may be re-sterilized by the same or alternative methods should be tested after treatment by the multiple sterilizations. For example, a material that is sterilized by radiation and re-sterilized by ethylene oxide should be tested after (a) irradiation and (b) irradiation plus ethylene oxide. If a "worst case" exposure can be identified with appropriate justification, testing may be performed after exposure to this treatment.
C.1.3 Ideally, all biological tests on a material should have the surface of the material exposed (as opposed to the bulk phase) to the cellular/biological environment. An alternative method to cutting the surface is fabrication of miniatures of the device using the same process (extrusion, dipping, etc.), temperatures, time, atmosphere, release agents, annealing, curing, cleaning, sterilization, etc., processes used in the manufacture of the device.
C.1.4 Metals used in biological tests should be from the same stock material used to fabricate the device and using the same machining, grinding, polishing, cleaning, passivation, surface treatment and sterilization used in the manufacture of the final product.
C.1.5 Ceramic materials used in biological tests should be manufactured from the same powder stock using the same casting, investing, molding, sintering, surface finishing and sterilization processes used to manufacture the device.
C.1.6 Bioprosthetic materials should be tested after they have been preserved under the manufacturer's maximum and minimum allowable fixation times to allow for varying penetration of the fixative.
C.2 Extraction conditions that may cause particle generation should be considered in the design of tests on the material.
C.3 The amount of material and surface area thereof shall be appropriate to the biological and physical constraints of the test system. In practice, the use of a standard sample size for a specific assay is recommended
The purpose of extraction of a medical device is to provide a suitable test sample for determining biological reactivity of any leachable substances in a biological system and to demonstrate the hazard potential (hazard identification and risk evaluation) for the use of the device in humans. If extracts of the device are prepared, the medium and conditions of extraction used should be appropriate to the nature and use of the final product as well as to the predictability (test purpose, rationale, sensitivity, etc) of the test method. Extraction conditions and application of the extract to test systems, therefore, should ideally reflect not only actual in-use conditions of the products but also purpose and predictability of the tests. Biological tests are carried out for identifying hazards and estimating risks of the hazards in exaggerated-use and/or in actual-use conditions. Extraction conditions including extraction media shall be differed with different test purposes: a) exhaustive extraction is applicable both for hazard identification and risk estimation in exaggerated-use condition, b) accelerated or exaggerated extraction is applicable for risk estimation in exaggerated-use condition, and c) simulated-use extraction is applicable only for risk assessment in actual-use.
D.1 This standard assumes that the amount of extractable substance(s) is/are related to the period of extraction, the temperature, the ratio of surface-area-of-material to volume-of-extractant and the nature of the solvent.
D.2 The period of extraction should be sufficient to maximize the amount of material extracted. In practice, standard time and temperature conditions are recommended in lieu of specific chemical analyses.
D3. An alternative practice is repeated extraction followed by concentration to obtain sufficient extractable substance(s). This practice is applicable for the purposes of hazard identification as well as risk estimation in exaggerated-use conditions.
D.4 The extraction temperature should maximize the amount of extractable substances as well as simulate any extremely high temperatures the device may incur during clinical use. This simulation should not initiate significant degradation of the material. The extraction temperature is dependent upon the physicochemical characteristics of the device material(s). For example, for polymers, the extraction temperature chosen should be below the glass transition temperature. If the glass transition temperature is below the use temperature, the extraction temperature shall be below the melting temperature. Recommended conditions are shown in Section 10.2.1.
The following examples are presented to illustrate the interpretation of this section:
a) Materials that have a melting or softening point less than 121 C will be extracted at a standard temperature less than the melting point (e.g. very low density polyethylene).
b) Materials that undergo hydrolysis will
be extracted at a temperature that minimizes
the amount of hydrolysis (e.g., polyamides
are extracted at 50 C).
c) Materials that are processed by steam
sterilization and contain a liquid during
storage will be extracted at 121 C (e.g.,
prefilled dialyzers):
d) Materials that are used only at body temperature
will be extracted at temperatures which provide
the maximum leachables without material degradation
(e.g., collagen may be extracted at 37C
whereas ceramic implants may be extracted
at 121 C).
D.5 The ratio of the surface area of the device to the volume of extractant or solvent should be sufficient to:
a) Attain the maximum amount of extractable
substance(s) in an appropriate dosage volume
for biological testing (i.e., dosage volume
within physiological limits) or chemical
analysis,
b)Demonstrate the hazard potential for the
use of the device in humans; and,
c) Cover the material in the solvent volume.
In practice, the use of a standard area and solvent volume is recommended as described in Section 10.2.1.2 in lieu of device specific parameters. Some test methods ( genotoxicity and delayed-type hypersensitivity) require concentration of extracts to increase the sensitivity of the test.
NOTE: Concentration of extracts may result in loss of volatile materials such as ethylene oxide.
D.6 The solvent(s) selected as extractants shall:
a) be suitable for use in the specific biological test systems
b) simulate the extraction which occurs
during clinical use of the device.
c) maximize the amount of extractives.
In practice, the use of standard polar and non-polar solvents are recommended in Section l 0.2.1 .3 in lieu of device specific solvents.
NOTE: Standardization of the parameters given in Clauses D5 and D6 permit the use of data obtained from biological tests of medical devices for other types of applications, e.g. for the estimation of risk and to develop standardized databases.
D.7 Other extraction and sample preparation concepts for hazard identification and risk estimation in exaggerated-use condition are described in Section 10.2.2.