Safety testing of a new medical device

Seeram Ramakrishna , ... Wee Eong Teo , in Medical Devices, 2015

6.3 Biocompatibility tests

Biocompatibility tests are necessary for medical devices that come into contact with the patient. ISO 10993 Biological evaluation of medical devices are recognized by most major national regulatory bodies including the FDA and CE mark as the standard for selecting the biological tests necessary for assessing the safety of a medical device. Manufacturers need to determine which tests need to be performed and this depends on how the medical device is intended to be used. To facilitate manufacturers in determining the tests to be performed, ISO 10993-1 has listed the tests to be performed based on the area of contact between the medical device and the patient and its duration of contact as shown in Tables 6.2 and 6.3.

Table 6.2. Initial evaluation test for consideration

Nature of body contact Biological effect
Category Contact Contact duration A—Limited <   24   h
B—Prolonged 24   h to 30 days
C—Permanent >   30 days		 Cytotoxicity Sensitization Irritation or intracutaneous reactivity Systematic/acute toxicity Subacute and subchronic toxicity Genotoxicity
Surface device Skin A X X X
B X X X
C X X X
Mucosal membrane A X X X
B X X X
C X X X X X
Breached or compromised surface A X X X
B X X X
C X X X X X
External communicating device Blood path, indirect A X X X X
B X X X X
C X X X X X
Tissue/bone/dentin A X X X
B X X X X X X
C X X X X X X
Circulating blood A X X X X
B X X X X X X
C X X X X X X
Implant device Tissue/bone A X X X
B X X X X X X
C X X X X X X
Blood A X X X X X
B X X X X X X
C X X X X X X

Reproduced from ISO 10993-1:2009 with permission from the International Organization for Standardization (ISO). All rights reserved by ISO.

Table 6.3. Supplementary evaluation test for consideration

Nature of body contact Biological effect
Category Contact Contact duration A—limited <   24   h
B—Prolonged 24   h to 30 days
C—Permanent >   30 days		 Implantation Hemocompatibility Chronic toxicity Carcinogenicity Reproductive/development Biodegradation
Surface device Skin A
B
C
Mucosal membrane A
B
C
Breached or compromised surface A
B
C
External communicating device Blood path, indirect A X
B X
C X X X
Tissue/bone/dentin A
B X
C X X X
Circulating blood A
B X X
C X X X X
Implant device Tissue/bone A
B X
C X X X
Blood A X X
B X X
C X X X X

Reproduced from ISO 10993-1:2009 with permission from the International Organization for Standardization (ISO). All rights reserved by ISO.

In many cases, after the biological effect to be tested has been determined using Tables 6.2 and 6.3, specific tests and procedures will still need to be selected. Medical devices come in many forms and the organ that comes into contact with it will differ and it is the manufacturer's responsibility to select appropriate tests. ISO 10993 and its subparts contain procedures for testing but manufacturers may need to look beyond those if they are not applicable. Most test procedures described are based on chemical testing which typically involves extracting any leachable substances from the medical device and using them for dosing followed by checking on its effect on the animal, cells, or other agents. Although this standard provides a recommendation on the type of tests to be performed, additional tests may still be warranted depending on the risk analysis, especially for higher risk medical devices.

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Alternate Antioxidants for Orthopedic Devices

PhD Venkat Narayan , in UHMWPE Biomaterials Handbook (Third Edition), 2016

19.7.1.2 Comprehensive Biocompatibility Evaluation

A comprehensive biocompatibility test plan developed to evaluate the antioxidant-stabilized UHMWPE material was in accordance with the ISO draft guidance on the Conduct of Biological Evaluation within a Risk Management Process (ISO/DTR 15499). The test plan included methods that address FDA guidance documents and specifically ISO 10993 parts 3–6, 10, and 11. In addition to the ISO 10993 tests, other USP tests to characterize leachable components were conducted. Biocompatibility tests were performed on bulk PBHP-stabilized GUR 1020 irradiated at 75 kGy, hereafter referred to as AOX. A summary of the various tests and the corresponding outcomes are summarized here.

Biocompatibility tests were performed using polar and nonpolar extracts of bulk AOX irradiated at 75 kGy to determine the potential for genotoxicity and red blood hemolysis.

1.

ISO 10993-3: Test for Genotoxicity, Carcinogenicity, and Reproductive Toxicity Using Bacterial Reverse Mutation Study

a.

Extracts were employed with negative controls of saline and DMSO, respectively and a positive control of Dexon. This study was conducted to satisfy, in part, the genotoxicity requirement of the standard.

b.

Outcome: Under the conditions of this assay, the extracts were considered to be nonmutagenic, while the negative and positive controls were performed as anticipated.

2.

ISO 10993-3: Test for Genotoxicity, Carcinogenicity and Reproductive Toxicity Using Mouse Lymphoma Study

a.

Extracts were employed with negative controls of RPMIo and DMSO, respectively and positive controls of 3-MCA and Dexon, respectively

b.

Outcome: Under the conditions of this assay, the extracts were considered to be nonmutagenic, while the negative and positive controls performed as anticipated.

3.

ISO 10993-3: Test for Genotoxicity, Carcinogenicity, and Reproductive Toxicity Using Mouse Peripheral Blood Micronucleus Study

a.

Extracts were employed with negative controls of saline and sesame oil, respectively and positive controls of methyl methane sulfonate.

b.

Outcome: Under the conditions of this assay, the extracts were not considered to be genotoxic to the mouse, while the negative and positive controls performed as expected.

4.

ISO 10993-4: Test for Interaction with Blood (ASTM Hemolysis)

a.

Diluted rabbit blood was added to bulk AOX irradiated at 75 kGy and to its extract in calcium and magnesium-free phosphate buffered saline (CMF-PBS) using HDPE as a negative control and sterile water for injection as the positive control. These combinations were evaluated to determine whether direct contact with the test article or an extract of the test article would cause in vitro red-blood hemolysis.

b.

Outcome: Under the conditions of this study, the mean hemolytic index for the test article in CMF-PBS was 0% and that for the extract in CMF-PBS was 0%. Therefore the direct contact of the test article as well as the test article extract was nonhemolytic. The negative and positive controls performed as expected.

c.

An in vitro biocompatibility test was performed on bulk AOX irradiated at 75 kGy to determine the potential for cytotoxicity.

5.

ISO 10993-5: Test for In Vitro Cytotoxicity Using MEM Extract

a.

A single extract of test article was prepared using single strength minimum essential medium supplemented with 5% serum and 2% antibiotic (IX MEM). The test extract was placed onto three separate monolayers of L-929 mouse fibroblast cells propagated in 5% CO2 with HDPE as a negative control and Tin-stabilized PVC as a positive control.

b.

Outcome: Under the conditions of this study, the IX MEM extract showed no evidence of causing cell lysis or toxicity. The negative and positive controls performed as expected.

Animal implantation tests were performed to evaluate local effects.

6.

ISO 10993-6: Test for Local Effects After Implantation Using a 2-week Muscle Implant Study

a.

The test article was implanted in muscle tissue of the rabbit using HDPE as a negative control. Rabbits were implanted and euthanized 2 weeks later. The muscle tissue was evaluated for evidence of irritation or toxicity.

b.

Outcome: Under the conditions of this study, the macroscopic reaction was not significant as compared to the negative control implant material. Microscopically, the test article was classified as a nonirritant as compared to the negative test article.

7.

ISO 10993-6: Test For Local Effects After Implantation Using a 12-week Muscle Implant Study

a.

The test article was implanted in muscle tissue of the rabbit using HDPE as a negative control. Rabbits were implanted and euthanized 12 weeks later. The muscle tissue was evaluated for evidence of irritation or toxicity.

b.

Outcome: Under these conditions, the macroscopic reaction was not significant as compared to negative control implant material. Microscopically, the test article was classified as a nonirritant as compared to the negative test article. Microphotographs of hematoxylin/eosin-stained muscle tissues surrounding the control implant (Figure 19.13A ) and the test implant after 12-week rabbit implantation (Figure 19.13B) showed comparable characteristics.

Figure 19.13. (A) Microphotograph of hematoxylin/eosin-stained muscle tissues surrounding the control implant (Polyethylene) following 12-week muscle implantation. (B) Microphotograph of hematoxylin/eosin-stained muscle tissues surrounding the test implant (PBHP-Stabilized UHMWPE) following 12-week muscle implantation.

Hypersensitivity tests were performed using AOX bulk material.

8.

ISO 10993-10: Test for Irritation and Delayed-Type Hypersensitivity Using Murine Lymph Node Assay

a.

Extracts were evaluated for delayed contact sensitization using the murine local lymph node (LLNA) assay. Saline and DMSO were employed as negative controls, respectively while DNCB and formaldehyde were used as the nonaqueous and aqueous positive controls, respectively.

b.

Outcome: Under these conditions, the saline and DMSO extracts of the test article were not considered to be sensitizing to the mouse. The stimulation indices were calculated to be less than 3.0. The negative and positive controls performed as anticipated.

9.

ISO 10993-10: Test for Irritation and Delayed-Type Hypersensitivity Using ISO Intracutaneous Study

a.

Extracts were evaluated for intracutaneous reactivity using saline and sesame oil as negative controls, respectively. The test article extracts were injected by the intracutaneous route into five separate sites on the right side of the back of the rabbits. Observations for erythrema and edema were conducted at 24, 48, and 72 h after injection.

b.

Outcome: Under the conditions of this study, there was no erythrema or edema from the saline extract injected intracutaneously into rabbits. There was very slight erythrema and very slight edema from the sesame oil extract injected intracutaneously into rabbits. The test article extracts met the requirements of the test since the difference between the test extracts and corresponding control mean score was one or less.

Systemic toxicity tests were performed using AOX bulk material.

10.

ISO 10993-11: Test for Systemic Toxicity for 72 Hours on Polar (Saline) and Non-Polar (DMSO) Extracts

a.

Test articles were extracted with saline and sesame oil. The extraction vehicles without test article were similarly prepared to serve as controls. The purpose of the study was to determine whether leachables extracted from the material would cause acute systemic toxicity following injection into mice. A single dose of each extract was injected into mice by either the intravenous (IV) or intraperitoneal route. The animals were observed immediately and at 4, 24, 48, and 72 h after systemic injection.

b.

Outcome: Under the conditions of this study, there was no mortality or evidence of systemic toxicity from the extracts.

11.

ISO 10993-11: Test for Systemic Toxicity Using 4-week Subcutaneous Method

a.

Test articles were surgically implanted into the subcutaneous tissue of rats to evaluate the potential subchronic toxicity of the test article using HDPE as a negative control. Animals were weighed prior to implantation and at weekly intervals throughout the study. At 4 weeks, the animals were euthanized and blood specimens were collected for hematology and clinical chemistry analysis. A necropsy was conducted and select organs were excised, weighed and processed histologically. The subcutaneous tissue around each implant site was also excised and examined macroscopically. A microscopic evaluation of the implant sites as well as the selected organs was conducted.

b.

Outcome: Under the conditions of this study, there was no evidence of systemic toxicity from the test article following subcutaneous implantation in the rat. The local macroscopic tissue reaction was not significant as compared to the negative control implant material. Microscopically, the test article was classified as a nonirritant as compared to the negative control article.

12.

ISO 10993-11: Test for Systemic Toxicity Using 26-week Subcutaneous Method

a.

Test articles were surgically implanted into the subcutaneous tissue of rats to evaluate the potential chronic toxicity of the test article using HDPE as a negative control. Animals were weighed prior to implantation and at weekly intervals throughout the study. At 26 weeks, the animals were euthanized and blood specimens were collected for hematology and clinical chemistry analysis. A necropsy was conducted and select organs were excised, weighed and processed histologically. The subcutaneous tissue around each implant site was also excised and examined macroscopically. A microscopic evaluation of the implant sites as well as the selected organs was conducted.

b.

Outcome: Under the conditions of this study, there was no evidence of systemic toxicity from the test article following subcutaneous implantation in the rat. The local macroscopic tissue reaction was not significant as compared to the negative control implant material. Microphotographs of hematoxylin/eosin-stained subcutaneous tissues surrounding the control implant (Figure 19.14A ) and the test implant (Figure 19.14B) showed no signs of adverse effects after 26-week rat implantation.

Figure 19.14. (A) Microphotographs of hematoxylin/eosin-stained subcutaneous tissues surrounding the control implant (Polyethylene) following 26-week subcutaneous implantation. (B) Microphotograph of hematoxylin/eosin-stained muscle tissues surrounding the test implant (PBHP-Stabilized UHMWPE) following 26-week subcutaneous implantation.
c.

Therefore, the comprehensive biocompatibility evaluation of PBHP-stabilized GUR 1020 UHMWPE confirms the biosafety of the formulation. Similar evaluations are warranted if the antioxidant, composition or irradiation dose is altered in other stabilized systems.

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UHMWPE–Hyaluronan Microcomposite Biomaterials

PhD Susan P. James , ... PhD Herb Schwartz , in UHMWPE Biomaterials Handbook (Third Edition), 2016

23.16 Biocompatibility of UHMWPE–HA Biomaterials

In vitro biocompatibility tests performed on UHMWPE–HA materials at NAMSA (Northwood, Ohio) included leachable and cytotoxicity testing. Leachables were measured using isopropyl alcohol as a solvent and cytotoxicity was measured using the ISO Elution Method (ISO 10993 – Biological Evaluation of Medical Devices, Part 5: Test for Cytotoxicity: In Vitro Methods). HDPE and tin stabilized poly(vinyl chloride) were used as negative and positive controls, respectively, in the cytotoxicity tests. Negligible leachables were detected and there was no evidence of cell lysis or toxicity with the UHMWPE–HA samples. No differences between the UHMWPE–HA material and HDPE were detected (unpublished data) indicating, among other things, that the variety of chemicals used during UHMWPE–HA material processing are removed from the material during processing.

UHMWPE–HA implants for partial knee resurfacing are currently being tested in a long-term large animal model. A short-term (6 week) pilot study of UHMWPE–HA implants in a large animal knee indicated excellent in vivo biocompatibility with no adverse reactions to the UHMWPE–HA material (unpublished data).

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A practical approach to analytical chemistry of medical devices

D.E. Albert , in Biocompatibility and Performance of Medical Devices (Second Edition), 2020

4.10.1 Background information on risk assessments

Risk assessment is not new, but has only recently (approximately 10 years) been publicized by international standards organizations and endorsed as an integral part of chemical characterization and biocompatibility studies for medical devices. The suitability of a medical device for a particular use involves balancing any identified risks with the clinical benefit to the patient associated with its use. ISO 10993-17 states that "among the risks to be considered are those arising from exposure to leachable substances arising from medical devices." This standard provides a method for calculating maximum tolerable levels that may be used by "other standards-developing organizations, government agencies, and regulatory bodies. Manufacturers and processors may use the allowable limits derived to optimize processes and aid in the choice of materials in order to protect patient health." Risk assessment, as explained in ISO 10993-17, is really a decision-making tool that has evolved over time. Manufacturers and processors may use derived allowable limits to aid in choosing the most appropriate material for a particular medical device application. Toxicological risk assessments have a long history with strong ties to Europe (the BS 5736 series of standards), and the US FDA, Environmental Protection Agency and Occupational Safety and Health Administration. Now ISO 10993 standards for medical devices prescribe the use of toxicological risk assessments for biological studies including material characterization and degradation studies.

The risk assessment must be well organized, documented and evidence- based for effective use in support of decision-making with respect to product or material safety. The aim of the assessment should be to identify any biological hazards inherent in the materials used in the medical device and to estimate the risks resulting from these in light of the intended use. The goal is to develop a process that ultimately protects public health and establishes the safety of medical devices. This objective is supported by ISO 10993-17 in subclause 4.3 of the general principles for establishing allowable limits which states that "the safety of medical devices requires an absence of unacceptable health risk." The manufacturer of a medical device is responsible for assuring its biological safety, for documenting the assessment of toxicological risks, and establishing the effectiveness of the analysis. Evidence must be provided that an appropriate toxicological risk assessment has been carried out so that it can ensure that public health is not endangered. ISO 10993-17 also adds that "where risk associated with exposure to particular leachable substances are unacceptable, this part of ISO 10993 can be used to qualify alternative materials or processes." This is another example of the way risk assessment can be used as a mechanism for critical decision-making processes.

Additional information from biocompatibility tests or on the prior use of the materials may be used to provide a basis for further assessment of risks. Acceptable results from appropriate biological tests (e.g., those listed in the ISO 10993 series of standards) may give a degree of assurance that the risk of adverse reactions occurring during clinical use is low. These tests differ from classical toxicity tests in that they typically attempt to mimic the conditions of clinical exposure to medical devices. Standardized toxicological tests are amenable to the generation and comparison of data from a wide range of test materials within or across chemical platforms. As standardized protocols must be broadly applicable for the study of a variety of different materials, they cannot realistically be expected at the same time to address highly focused mechanistic toxicological issues associated with only one or a few chemical compounds ( ISO 14971, 2007). This point of view was also expressed in UK Medicines and Healthcare products Regulatory Agency's updated Guidance Note 5 EC Medical Devices Directives: Guidance on the Biological Safety Assessment (Guidance Note 5 EC Medical Devices Directives, 2006). The Guidance Note states that:

These tests, commonly termed biocompatibility tests, differ from basic toxicity tests in that they typically attempt to mimic the conditions of clinical exposure to medical devices and thus provide an indication of the probability of adverse effects arising during use. They tend, as a result, to be less sensitive than basic toxicity tests and are thus a less discriminating indicator of risk. Biocompatibility test data should therefore be used to complement an assessment based on materials characterization, rather than as a replacement for it.

Toxicological hazard is a property of the chemical constituents of the materials from which a medical device is made and chemical composition should be considered in relation to hazard identification. Where significant risks arising from hazardous residues are identified by chemical characterization, their acceptance should be assessed in line with established toxicological principles. Biocompatibility tests identified in the ISO 10993 series of standards may be used to provide further assessment of risk.

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Alumina- and Zirconia-based Ceramics for Load-bearing Applications

Corrado Piconi , ... Tomaž Kosmač , in Advanced Ceramics for Dentistry, 2014

11.3.5 Biocompatibility

Extensive reviews on biocompatibility tests performed in vitro and in vivo on zirconia have already been published elsewhere. 38 Briefly, zirconia has been tested in vitro under different physical forms (e.g. powders and dense ceramics). The results of these tests are usually influenced by the physical form, reactivity of the surface, chemical composition, impurity content, etc. as well as by cell conditions during the tests. Nevertheless, the absence of acute toxic effects has been reported by most of the authors; the materials were tested on different cell lines (e.g. macrophages, lymphocytes, fibroblasts, and osteoblasts) using direct and indirect contact tests. There is a general agreement on the absence of local or systemic toxic effects after the implantation of zirconia, regardless of its physical form. In the early post-operative phase, connective tissue was frequently observed at the bone–ceramic interface, a reaction typical of non-bioreactive ceramics. It was noted that the results of the tests were dependent upon the preparation of the implant site as well as on the surface properties of the implants (e.g. an increase in bone–implant contact has been reported after treatments that increased the surface roughness). 84

In vitro mutagenic tests showed that in the absence of any such reactions on cells, 85,86 no tumors were observed after long-term implantation in rabbits. 38 The direct apposition of bone to zirconia implants as evidenced in earlier works 42,43 has been confirmed by several other authors (e.g. Cerroni 84 and Hisbergues). 87

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Boron nitride nanotubes as drug carriers

Xia Li , Dmitri Golberg , in Boron Nitride Nanotubes in Nanomedicine, 2016

5.6 Biocompatibility, distribution, and excretion of BNNTs as drug carriers

Pilot in vivo biocompatibility tests of the glycol chitosan-functionalized BNNTs were done by intravenous injection of a 1 mg/kg BNNTs solution into the marginal ear vein of male New Zealand rabbits, 8–9 months of age, and weighing 2.0 ± 0.1 kg [13]. Blood samples from the contralateral marginal ear vein were collected for analyzing and evaluating any acute alteration of hematological parameters at intervals of 0, 2, 24, and 72 h, which reflected the functional impairment in blood, liver, and kidneys. The hematological analyses suggested no significant difference between the BNNT-treated group and the control group for typical blood values, such as white cell count, red cell count, platelet count, etc. Although the platelet count increased at 72 h for the BNNT-treated group, the value was still in the healthy range for rabbits. In addition, no significant difference was observed for blood biochemical parameters which quantify the renal (eg, urea, creatinine) and hepatic (eg, alkaline phosphatase, γ-glutamyl transferase, aspartate transferase, and alanine amino transferase) functions.

Further biocompatibility investigation of BNNTs was made by injecting at a dose up to 10 mg/kg of BNNTs into rabbits by Ciofani et al. [39]. There were no significant adverse effects after the administration of BNNTs up to 7 days. Moreover, no obvious impairments in blood, liver, and kidney functionality were observed. The half-life circulation of BNNTs was about 90 min.

Another in vivo biocompatibility investigation was carried out by the injection of gum Arabic-functionalized BNNTs into the gut of planarians at a dose of 100 or 200 µg/g of BNNTs [40]. The gum Arabic-functionalized BNNTs exhibited good biocompatibility without the induction of oxidative DNA damage and apoptosis. Moreover, no adverse effects on planarian stem cell biology and on de novo tissue regeneration were observed.

To investigate in vivo distribution and excretion of the BNNTs, glycol chitosan-functionalized BNNTs radiolabeled with 99mTc (40 mg/kg) were intravenously put into the tail of Swiss mice [12]. After 30 min of injection, the BNNTs reached systemic circulation and accumulated in the liver, spleen, intestinal tissues, and bladder. The presence of high concentration of BNNTs in the bladder was also observed after 1 and 4 h of injection, which reflected the elimination of the BNNTs from the body by renal excretion. After 24 h, a low percentage of the injected dose could be detected in all the studied organs, but a reduction of radiation was observed. The ex vivo results indicate that BNNTs could circulate in the blood vessels for a certain time interval, and were easily taken up by phagocyte system cells, which are abundant in the liver and spleen tissue. In addition, the scintigraphic imaging biodistribution results were consistent with the ex vivo studies. Initially, BNNTs rapidly accumulated in the liver, spleen, and gut tissue, and in the large amounts, even in the kidneys and bladder; later, a slight clearance from all organs, except an accumulation in the bladder due to the excretion process, was observed.

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Cable-driven flexible endoscope utilizing diamond-shaped perforations: FlexDiamond

Bok Seng Yeow , ... Hongliang Ren , in Flexible Robotics in Medicine, 2020

3.4.5 Biocompatibility test

In addition to mechanical and functionality tests, biocompatibility tests need to be conducted to ensure the safety of the prototype for subject use. This ensures that the prototype does not induce an unwanted immune response that results in inflammation, infection, and irritation when the prototype is in contact with the mucosal tissue. However, at this stage of the design process, biocompatibility tests are yet to be performed since the prototype is not ready to be used for clinical trials. Nonetheless, we need to keep in mind the importance of the biocompatibility of the prototype. Generally, the evaluation of the biocompatibility of the prototype can be made based on the ISO-10993. This standard provides guidelines on the biocompatibility test selection related to the prototype and includes the protocol needed to perform tests such as cytotoxicity, pyrogenicity, carcinogenicity, and sensitization tests. Test report components are also included for consideration.

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Biological evaluation and regulation of medical devices in Japan

K. Kojima , K. Sakaguchi , in Biocompatibility and Performance of Medical Devices (Second Edition), 2020

17.3.10 Confirmation of the extraction rate and production of an extraction substance (extract)

So-called exhaustive extraction is a requirement of the Japanese biocompatibility test method guideline not found in other countries. It is thought that this method was adopted to make it possible to detect the toxicity of a chemical substance which is dangerous to the human body even if it is a trace amount. For example, some finished products for medical devices that include a polymer material, or a polymer material as a component material, add various kinds of chemical substances of low molecular weight to that polymer material in order to improve processability and formability and to stabilize and maintain performance. There are also some in which a leachable chemical substance of low molecular weight is additionally contained in finished products of complex medical devices that consist of various kinds of composite materials. It is usually predicted that the extraction rate will go up along with an increase in the amount of such low molecular weight substances and an increase in ingredients with a low degree of polymerization in the polymer material. It can be considered that these low molecular weight substances present a high possibility of bringing a greater biological disadvantage than substances of high molecular weight. Thus, as mentioned above, Attachment of Current MHLW Guidance notes that a problem is especially posed by how much of the extraction substance can be obtained from the medical device, etc., that requires evaluation when conducting the sensitization and genotoxicity tests. This is because the test method must be selected according to the difference in the extraction rate.

As a solvent for the exhaustive extraction, Attachment of Current MHLW Guidance mentions methanol and acetone as first choice. As mentioned above, the second option for solvent in the sensitization test is different from that of the genotoxicity test, either n-hexane or a 1:1 mixture of cyclohexane to 2-propanol is specified in the sensitization test. In contrast, it is not specified in the genotoxicity test. A criterion to which the exhaustive extraction is applied to the medical device is the extraction rate 0.5% or higher (when the weight of the medical device is 0.5 g or more) and the extraction rate 1% (when the weight of the medical device is <   0.5 g). In addition, when the medical device is deformed or dissolved, to such a degree that its original form is lost in a solvent, other suitable solvent should be used. Since physicochemical stability from raw materials that are used in the medical device to be evaluated is often unknown, it is desirable that the produced extract or extraction substance be promptly utilized in the test (within 24 h, in principle). The preparation method of the test solution used for the biological test of ISO 10993 series is described on behalf of ISO 10993-12. In the 2012 edition of this standard describes a standard extraction method using polar/nonpolar extraction vehicle (ex. physiological saline solution/vegetable oil) and in annex D of this standard there is description of exhaustive extraction method adopted in the Current MHLW Guidance for sensitization and genotoxicity tests (Fig. 17.1).

Fig. 17.1

Fig. 17.1. Comparison between the exhaustive extraction and the standard extraction.

The organic solvent extraction method described so far is an evaluation method for a medical device made of an organic polymer material. For example, a medical device that consists solely of metal and ceramics, there is no need to apply exhaustive extraction. Rather than conducting leachables analysis, clarifying the eluting elements and compounds may give important information for safety assessment. ISO 10993-14 (2001) and ISO 10993-15 (2000) are noteworthy as reference in that case.

As the detailed above exhaustive extraction method is a special method, Attachment of Current MHLW Guidance could lead to cause confusion when the extraction and preparation in test facility familiar with non-Japanese guideline. In order to understand sample preparation in the Attachment of Current MHLW Guidance, the outline of sample preparation is shown in Table 17.11. As you can see, fundamentally, except for the cytotoxicity, sensitization, and genotoxicity tests, preparation of the extract is carried out under the same conditions as non-Japanese guidelines.

Table 17.11. Example of test sample preparations for each examination used in biological safety testing.

Test item Test sample (Test substance) Extraction medium (test solution) or extract
Cytotoxicity test 1. Substance that dissolves or is suspended in water 1. Dissolves or is suspended in water or a culture medium
2. Substance that does not dissolve in water 2. Culture-medium extract or direct contact
Sensitization test 1. Metal or ceramic 1. Use existing findings
2. Substance that dissolves in water or alcohol 2. Dissolves in distilled water or alcohol
3. Low molecular organic compound 3. Dissolves or is suspended in an appropriate organic solvent
4. Composite material or product containing polymer resin 4. Extraction substance (first method a ) or extract (second method b ) from an organic solvent
Genotoxicity test 1. Substance that dissolves or is suspended in water 1. Dissolves or is suspended in water or a culture medium
2. Substance that does not dissolve in water, and from which an extraction substance cannot be obtained using an organic solvent 2. DMSO extract or culture-medium extract
3. Substance that does not dissolve in water, but from which an extraction substance can be obtained using an organic solvent 3. Extract from an organic solvent a
Implantation test Cylinder length: 10 to 12 mm, width: 1.0–1.5 mm
Irritation test At the ratio specified in Table 17.6, extraction under the highest temperature conditions that satisfy the conditions from the temperature and duration conditions shown in Table 17.5. Extract of a physiological saline solution or vegetable oil
Systemic toxicity test Same as irritation test Extraction medium for the acute toxicity test: physiological saline solution and/or vegetable oil
Extraction medium for the subacute (subchronic) toxicity test: physiological saline solution
Pyrogen test Same as irritation test Extract of a physiological saline solution
Blood compatibility test Depend on test item (Extract of a phosphate buffered physiological saline solution)
a
Method of obtaining residue from an extract by evaporation a solvent with a rotary evaporator under as low a temperature as possible.
b
Method of condensing or inspissating an extract using a rotary evaporator, etc., and, whether condensing and preparing 1 mL per 1 g of test sample, in an appropriate evaporated solvent after solvent evaporation and preparing 1 mL, conducting the test with that as the test solution.

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Material Requirements for Plastics Used in Medical Devices

Vinny R. Sastri , in Plastics in Medical Devices (Second Edition), 2014

4.7 ISO 10993

ISO 10993 is a series of standards that detail all characterization and biocompatibility tests needed for medical grade materials and medical devices before clinical studies ( Table 4.10). Before the ISO 10993 standard came into being, the United States used the Tripartite standard for the evaluation of biocompatibility. The Tripartite guidance was replaced in July 1995, when FDA issued a modified version of ISO 10993-1, "Guidance on Selection of Tests," as a blue book memorandum [22]. The ISO 10993 standards are used throughout Europe, and the FDA version of ISO 10993-1 is used in the United States. The blue book memorandum adopted the same ISO nomenclature for device categories but developed a modified flowchart assigning the type of testing needed for each device category and added more requirements in some of the device categories.

Table 4.10. ISO 10993 Standards

Standard Description
ISO 10993–1:2003 Biological evaluation of medical devices. Part 1: Evaluation and testing.
ISO 10993–2:2006 Biological evaluation of medical devices. Part 2: Animal welfare requirements.
ISO 10993–3:2003 Biological evaluation of medical devices. Part 3: Tests for genotoxicity, carcinogenicity, and reproductive toxicity.
ISO 10993–4:2002 Amd 1:2006 Biological evaluation of medical devices. Part 4: Selection of tests for interactions with blood.
ISO 10993–5:1999 Biological evaluation of medical devices. Part 5: Tests for in vitro cytotoxicity.
ISO 10993–6:2007 Biological evaluation of medical devices. Part 6: Tests for local effects after implantation.
ISO 10993–7:1995 Biological evaluation of medical devices. Part 7: EtO sterilization residuals.
ISO 10993–8:2000 Biological evaluation of medical devices. Part 8: Selection and qualification of reference materials for biological tests.
ISO 10993–9:1999 Biological evaluation of medical devices. Part 9: Framework for identification and quantification of potential degradation products.
ISO 10993–10:2002 Amd 1:2006 Biological evaluation of medical devices. Part 10: Tests for irritation and delayed-type hypersensitivity.
ISO 10993–11:2006 Biological evaluation of medical devices. Part 11: Tests for systemic toxicity.
ISO 10993–12:2007 Biological evaluation of medical devices. Part 12: Sample preparation and reference materials (available in English only).
ISO 10993–13:1998 Biological evaluation of medical devices. Part 13: Identification and quantification of degradation products from polymeric medical devices.
ISO 10993–14:2001 Biological evaluation of medical devices. Part 14: Identification and quantification of degradation products from ceramics.
ISO 10993–15:2000 Biological evaluation of medical devices. Part 15: Identification and quantification of degradation products from metals and alloys.
ISO 10993–16:1997 Biological evaluation of medical devices. Part 16: Toxicokinetic study design for degradation products and leachables.
ISO 10993–17:2002 Biological evaluation of medical devices. Part 17: Establishment of allowable limits for leachable substances.
ISO 10993–18:2005 Biological evaluation of medical devices. Part 18: Chemical characterization of materials.
ISO/TS 10993–19:2006 Biological evaluation of medical devices. Part 19: Physico-chemical, morphological, and topographical characterization of materials.
ISO/TS 10993–20: 2006 Biological evaluation of medical devices. Part 20: Principles and methods for immunotoxicology testing of medical devices.

ISO 10993-1 is an important standard as it details all the relevant biological tests needed for the material evaluation protocols for medical devices. Subsequent ISO 10993 standards are more specific to the type of biocompatibility or toxicity tests. ISO 10993-18 is another important standard. It details the various material characterization tests needed for plastics used in medical devices.

Table 4.11 is used to identify the appropriate biocompatibility tests required for a material or device depending upon its end use. There are similarities between this and the USP classification given in Table 4.9.

Table 4.11. ISO Biocompatibility Matrix

Figure 4.6 details the decision tree that can be used to assess whether or not biocompatibility tests are required. Biocompatibility tests are required for most devices that come into contact with the human body. The type and degree of testing will differ depending upon the extent and location of contact (Table 4.11). Existing data might be sufficient for submission if they are scientifically valid.

Figure 4.6. ISO 10993 Biocompatibility evaluation decision tree.

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Volume 2

Michel Assad , Nicolette Jackson , in Encyclopedia of Biomedical Engineering, 2019

Biomaterials Preparation and Extraction

Prior to completing the in vivo animal performance testing, a majority of the biocompatibility tests use solutions containing primary extractables and any degradable products. The extractables and degradable products are released using semiphysiological extraction conditions that are expected to mimic the conditions of clinical use ( FDA, 2016). This preliminary phase is performed on the biomaterials from a final finished form of the device, which includes all manufacturing processes (e.g., packaging and sterilization) that will be used when the device will be marketed (FDA, 2016). Using the final finished device, the extraction occurs in vitro utilizing small tubes or containers filled with a liquid and the device. The liquid consists of a semiphysiological medium, either polar (e.g., saline solution), nonpolar (e.g., cottonseed or sesame seed oil), or a cell culture medium. The tubes are then sealed and placed in an incubator for 24–72   h at 37°C; alternatively, a higher temperature can be used with a reduced amount of time. Following incubation, the tubes containing extracts are vigorously shaken and the resulting extract solutions are decanted into sterile glass containers. Typically, the undiluted extracts are utilized for testing in most cases, except in genotoxicity tests, for example, where they can additionally be subject to subsequent dilutions of the initial solution. The resulting extract solutions are then used for the following biocompatibility tests.

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