50.1 Historical Development of European Norm International Organization for Standardization 10993 Series of Standards

Since 1989, European Committee for Standardization/Technical Committee 206—in liaison with ISO/Technical Committee 194—developed standards to guide the biological safety assessment of medical devices and to propose appropriate test and evaluation procedures. Meanwhile, 18 working groups have become active 13 and developed 25 published ISO standards (number includes updates), with active contribution of 22 countries and 25 additional countries observing the process. 14

With regard to the EN ISO 10993 series of standards, the standards in Table 50.2 have been prepared by the various Working Groups of European Committee for Standardization/Technical Committee 206 and ISO/Technical Committee 194.

The standardization work is not completed after publishing a final version or after formal harmonization by referencing the standard in the Official Journal of the European Union. Based upon the regulations of the ISO, all standards are being reviewed regularly and, if necessary, revised. Therefore, Table 50.2 only represents the current status of standardization (November 2012). Furthermore, additional standards will be prepared if needed. Therefore, ISO/TC 194 WG 17 is currently working on biocompatibility issues of nanomaterials.

50.2 Biological Categorization of Medical Devices

Following the categorization rules of EN ISO 10993–1 Chapter 5, the following categorization by nature of body contact must be considered for the purpose of defining an appropriate biological evaluation program:

1. 
   

   Surface-contacting devices with contact to

   
   
   
   
   • 
     

     Intact skin surfaces

     
     
   • 
     

     Intact mucosal membranes

     
     
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     Breached or compromised body surfaces

   
   
2. 
   

   External communicating devices with contact to

   
   
   
   
   • 
     

     Blood path, indirect contact to the blood path for entry into the vascular system

     
     
   • 
     

     Tissue, bone, or dentin

     
     
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     Circulating blood

   
   
3. 
   

   Implant devices with contact to

   
   
   
   
   • 
     

     Tissue or bone

     
     
   • 
     

     Blood

Further to this, the following categorization regarding duration of body contact is proposed:

1. 
   

   Limited exposure: Devices whose cumulative single, multiple, or repeated use or contact is up to 24 hours

   
   
2. 
   

   Prolonged exposure: Devices whose cumulative single, multiple, or repeated use or contact is likely to exceed 24 hours but not 30 days

   
   
3. 
   

   Permanent contact: Devices whose cumulative single, multiple, or repeated use or contact exceeds 30 days.

If a medical device has neither direct nor indirect contact to the human body or a patient, no biocompatibility assessment needs to be performed. However, based upon the provisions of EN ISO 14971 (risk management), biocompatibility testing may additionally be necessary to not expose other persons to biological hazards (e.g., doctors, nurses, or nonpatient operators).

50.3 General Principles to be Applied

Clause 4 (“General principles applying to biological evaluation of medical devices”) and Clause 6 (“Biological evaluation process”) of EN ISO 10993–1 describe both general and specific provisions that must be followed in order to attain a reliable biological assessment for a medical device. In addition to that, ANSI/AAMI/ISO TIR15499:2012, 15 which is a “technical information report” prepared by a group of authors responsible for the preparation of the EN ISO 10993 series of standards, gives further guidance and interpretation support regarding EN ISO 10993-1. In an attempt to summarize, the following principles were found to be of particular importance:

1. 
   

   The process of biological evaluation must be based upon a well-structured biological evaluation program, which is in accordance with a risk management system following EN ISO 14971.3 This program “shall be planned, carried out and documented by knowledgeable and experienced professionals” (Clause 4.1), who will assess any relevant “advantages and disadvantages” of a material or final product under consideration, and who draw “informed decisions” (Clause 4.1) relative to the intended use of a given medical device.

   
   
2. 
   

   The biological evaluation process should follow the flowchart provided in EN ISO 10993–1, Chapter 4, Figure 1. This chart gives a compulsory route to follow and assists to select appropriate chemical and biological test procedures as well as to appropriately include existing chemical, toxicological, and human exposure data from literature before a final biological assessment report can be issued.

   
   
3. 
   

   The biological evaluation must consider potential risks relating to final products as well as to raw materials, breakdown products, leachables, extractables, and metabolites. Therefore, degradable devices must be evaluated extensively following the requirements of EN ISO 10993–9, 16 -13, 17 -14, 18 and -15. 19 Further to this, the biological evaluation must also evaluate the influence of intended additives (e.g., colors or plasticizers), process contaminants (e.g., oil or lubricants), and residues (e.g., detergents after cleaning the final product).

   
   
4. 
   

   The biological evaluation must also investigate the potential influence of other products or components or treatments that may interact with the device under consideration. This could be, for example, the packaging materials, permitted accessories to be used in combination with the product, pharmaceutical products being in contact or medical treatments (e.g., X-ray) to potentially interact with the device, or its primary packaging.

   
   
5. 
   

   Because biocompatibility of a final product is not only based upon its particular chemistry, physical and morphological properties of the device or material under consideration must also be evaluated and tested. This may require testing of certain mechanical properties as well as surface properties such as porosity, surface morphology, or surface charging. For this purpose, the provisions of EN ISO 10993–18 (“Chemical characterization of materials” 20) and ISO/TS 10993–19 (“Physico-chemical, morphological and topographical characterization of materials” 21) apply.

   
   
6. 
   

   In order to avoid unnecessary animal testing, EN ISO 10993–1 requests to start the biological evaluation process always with a physical and chemical material characterization (Clause 4.3) and also to use in vitro test procedures before in vivo tests are initiated (Clause 4.6). Further to this, EN ISO 10993–1 Clause 6.2.1 describes particular conditions where animal experimental studies are not justifiable in terms of EN ISO 10993–2. 22 Such conditions occur if previous study results and/or conclusive toxicological data are available for chemically identical products or materials, or if preclinical and clinical data (including a human history of safe use) exists for a chemically identical material or final product.

   
   
7. 
   

   Another important general requirement of EN ISO 10993–1 is found in Clause 4.6. According to this, “all tests shall be conducted according to recognized current/valid best laboratory/quality practices, for example Good Laboratory Practice (GLP) or ISO/IEC 17025.” Therefore, any subject matter expert preparing a written biological assessment report must check the available documents whether the reported study results were obtained under such a quality management system. The guidelines for Good Laboratory Practice 23 are available free of charge from public sources, whereas the ISO/IEC 17025 standard, 24 like any other official standard, must be purchased from one of the national standardization organizations.

   
   
8. 
   

   Following the general principles of risk management, the biocompatibility files must be kept updated by the responsible manufacturer during the entire life cycle of a medical device or material under consideration. Therefore, EN ISO 10993–1 specifies five conditions in Clause 4.7 where a biological re-evaluation must be performed:

   
   
   
   
   1. 
      

      If a material′s specifications or its supplier changes

      
      
   2. 
      

      If the manufacturing formulation, processing, primary packaging, or sterilization changes

      
      
   3. 
      

      If shelf life and/or transportation routines are changed

      
      
   4. 
      

      If the intended use of a product (i.e., its nature and/or duration of body contact) is changed

      
      
   5. 
      

      e) If any evidence becomes available that a product may cause unexpected adverse effects in humans

Considering these points, a medical device manufacturer must also re-evaluate biological hazards if changes occur to parts of the manufacturing equipment, to manufacturing aids (e.g., lubricants, grease, cooling agents), or to manufacturing processes (e.g., temperature profiles during manufacturing or introduction of product surface modifications).

In the case of “minor” changes (e.g., new supplier, changes to manufacturing equipment or manufacturing conditions), the medical device manufacturer may initiate some limited comparative physicochemical and biological tests to investigate whether the aforementioned changes are likely to have a relevant impact on the biocompatibility of the modified material.

50.4 Requirements for Sample Preparation

An appropriate sample preparation and selection of reference materials, comparative devices, as well as positive and negative controls are crucial for obtaining meaningful experimental results. Therefore, EN ISO 10993–12 29 addresses the following topics:

• 
  

  Test sample selection

  
  
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  Selection of representative portions from a device

  
  
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  Test sample preparation

  
  
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  Experimental controls

  
  
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  Selection of and requirements for reference materials

  
  
• 
  

  Preparation of extracts

An appropriate test sample may be the final product, a representative sample from the final product, or a particularly manufactured test item that has been processed in the same manner as intended for the final product. If applicable, this must also include cleaning and sterilization processes, aging or reprocessing processes, or intended or unintended degradation processes (e.g., through aging during shelf life).

If the final product or material cannot be tested directly, exaggerated extraction is performed with both polar and nonpolar extraction media in order to identify potential chemical hazards relating to leachable or extractable substances and manufacturing residues.

Extractions must be performed in clean, chemically inert, and closed containers that are gently agitated during extraction. Extraction vehicles as well as extraction temperatures may vary for different materials, test procedures, and medical purposes, and must be justified appropriately. Extraction vehicles must be appropriate to the nature and use of the final product, and must be compatible with the intended test procedure (e.g., not dissolve or etch the product or material).

Because extraction is a complex process, standardized procedures are requested with defined temperature conditions and defined extraction periods using appropriate polar and nonpolar extraction vehicles at defined surface-area-to-volume ratios. Based upon the provisions of Clause 10.3.1, the following extraction temperatures and periods shall be applied, as appropriate:

• 
  

  37 ± 1°C for 72 ± 2 hours

  
  
• 
  

  50 ± 2°C for 72 ± 2 hours

  
  
• 
  

  70 ± 2°C for 24 ± 2 hours

  
  
• 
  

  121 ± 2°C for 1 ± 0.1 hours

Clause 10.3.5 proposes the following extraction vehicles:

• 
  

  Polar extraction vehicles: water, physiological saline solution, cell culture medium without serum

  
  
• 
  

  Nonpolar extraction vehicles: freshly refined vegetable oil (e.g., cottonseed or sesame oil)

  
  
• 
  

  Additional extraction vehicles: ethanol/water mixtures, ethanol/saline mixtures, physiologically diluted polyethylene glycol 400, dimethyl-sulfoxide, and culture media with serum

The latter is preferred for devices or material extractions that are to be tested for cytotoxicity or in vitro genotoxicity. A cell culture medium containing serum is considered to represent both polar and nonpolar extraction conditions.

Regularly formed test samples where a surface area can clearly be determined must be extracted based upon the surface-area-to-volume ratios as provided in Clause 10.3.3 Table 1 of the standard. For thin materials (< 0.5 mm thickness), 6 cm²/mL extraction vehicle must be used. For materials > 0.5 mm thickness, 3 cm²/mL extraction vehicle is required. For irregularly shaped materials, a gravimetric approach is to be used. Depending on the nature of the investigational material, 0.1 mg/mL (membranes, textiles) or 0.2 mg/mL extraction vehicle (powders, pellets, foam, nonabsorbent molded items) is required. For the extraction of absorbent materials and hydrocolloids, a saturation step with extraction vehicle is proposed before an additional volume representing 0.1 g or 1.0 cm² test material per mL extraction vehicle is achieved.

50.5 Biological Evaluation Tests

In addition to the aforementioned general principles, EN ISO 10993–1 refers to a series of specific biological test models that must be considered when planning the biological part of a biocompatibility assessment program. The biological evaluation tests applicable for a given medical device or material are listed in relation to the intended nature and duration of body contact (Clause 5, see previous discussion) in Annex A. This table “Evaluation tests for consideration” is not intended to serve as a “checklist,” but it provides a “framework for the development of an assessment program,” allowing for product-specific adjustments based on a risk management output. Such adjustments may be due to the particular short-term or long-term hazards relating to a device under normal conditions of use. Therefore, EN ISO 10993–1 principally allows for a strategy of reduced experimental testing provided that this strategy is appropriately justified in the final biological assessment report. It shall be noted that this approach is well supported by ANSI/AAMI/ISO TR15499.15

Even though EN ISO 10993–1 is a harmonized international standard, the FDA issued a guideline that amends the Table A.1 of EN ISO 10993–1 for some medical device categories. According to this “Blue Book Memorandum G95–1,”8 for example, the hazard of acute toxicity must be evaluated for all categories except skin contact and limited mucosal membrane contact.

Furthermore, both EN ISO 10993–1 and Blue Book Memorandum #G95–1 declare that serious biological hazards such as chronic toxicity, carcinogenicity, reproductive and developmental toxicity, biodegradation, and immunotoxicity must be addressed for any medical device or material if applicable from a risk management point of view.

It shall be noted that the FDA just recently published a new draft guideline document that is intended to later replace the aforementioned Blue Book Memorandum #G95–1. This document, which was published on April 23, 2013, “for comment purposes only,” gives extensive guidance on the issue of biocompatibility assessment of medical devices and provides helpful additional information and recommendations from an FDA perspective.

Table 50.3 and Table 50.4 summarize the “evaluation tests for consideration” as of EN ISO 10993–1 Annex A and Blue Book Memorandum G95–1 and the new draft FDA guidance as of April 23, 2013.