Chemical Characterization vs Biological Testing: When Each is Required for Medical Devices

Medical device biocompatibility evaluation involves two distinct but complementary approaches: chemical characterization and biological testing. Understanding when each is required—and how they work together—is essential for efficient regulatory submissions and comprehensive safety evaluation.

Many manufacturers struggle with determining the appropriate balance between these approaches. Over-reliance on biological testing can miss critical chemical safety concerns, while focusing solely on chemical characterization may not address all biological endpoints. The key is understanding when each approach is necessary and how they integrate into a complete biocompatibility strategy.

Understanding Chemical Characterization

Chemical characterization involves identifying and quantifying extractable and leachable compounds that may migrate from a medical device during clinical use. This process provides detailed information about the chemical composition of device materials and potential patient exposure to specific compounds.

What Chemical Characterization Evaluates

Extractables Analysis:

Compounds that can be extracted from device materials under controlled laboratory conditions using appropriate solvents and extraction parameters. This represents the universe of potentially leachable compounds.

Leachables Analysis:

Compounds that actually migrate from the device under simulated or actual clinical use conditions. This represents real-world patient exposure.

Chemical Identification:

Structural characterization of detected compounds using analytical techniques such as gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS).

Quantification:

Determining the concentration of identified compounds to support toxicological risk assessment.

When Chemical Characterization is Required

According to ISO 10993-18, chemical characterization is necessary when…

Material Information is Insufficient:

When existing material safety data doesn't adequately characterize potential patient exposure to chemical constituents.

Novel Materials are Used:

Devices incorporating new materials without established biocompatibility history require comprehensive chemical characterization.

Complex Material Systems:

Devices with multiple materials, coatings, or additives benefit from detailed chemical analysis to understand potential interactions and extractables.

Long-Term Contact Applications:

Permanent implants and prolonged contact devices require understanding of chemical exposure over extended timeframes.

Regulatory Requirements:

Many regulatory agencies now expect chemical characterization data as part of comprehensive biocompatibility evaluation, particularly for higher-risk devices.

Understanding Biological Testing

Biological testing evaluates how device materials and extractables interact with biological systems. These tests use standardized methods to assess various biological endpoints that could indicate safety concerns.

What Biological Testing Evaluates

Cytotoxicity:

Cell viability and metabolic function when exposed to device extracts or materials.

Sensitization:

Potential for delayed hypersensitivity reactions or allergic responses.

Irritation:

Local inflammatory responses at contact sites.

Systemic Toxicity:

Whole-body effects from absorbed compounds or materials.

Genotoxicity:

Potential for genetic material damage that could lead to mutations.

Implantation:

Local tissue response to physically implanted materials over time.

When Biological Testing is Required

ISO 10993-1:2025 introduces a fundamentally different approach to determining when biological testing is required. Rather than relying on a prescriptive matrix of biological endpoints, the new standard emphasizes a risk-based biological evaluation process.

Risk-Based Biological Evaluation Framework:

The 2025 revision requires manufacturers to conduct a comprehensive biological risk assessment that considers:

Device Characteristics Related to Biological Safety:

- Design and materials of construction (all materials with direct or indirect contact)

- Physical characteristics including porosity, particle size, shape, and surface morphology

- Manufacturing process impacts on materials (e.g., passivation, laser marking, sterilization)

- Introduction of additional constituents during manufacturing and reprocessing

- Primary packaging materials that may transfer constituents to the device

- Interactions with other medical devices or medicines

- Constituents available on the device surface or released from the finished device

- Potential degradation products (where applicable)

Contact Categorization:

Devices are categorized by type, frequency, and duration of contact:

Contact Types:

- Skin, mucosal membrane, breached or compromised surface

- Blood path indirect, circulating blood

- Tissue without circulating blood contact

Contact Duration:

- Limited exposure: ≤24 hours cumulative contact

- Prolonged exposure: >24 hours to 30 days cumulative contact  

- Permanent contact: >30 days cumulative contact

Biological Risk Analysis Process:

Rather than automatically requiring specific tests based on contact category, ISO 10993-1:2025 requires a systematic biological risk analysis that:

1. Identifies biological hazards associated with the device

2. Estimates biological risks based on available information

3. Evaluates whether those risks are acceptable

4. Determines what additional information (if any) is needed

When Biological Testing May Be Required:

Biological testing is conducted only when:

- Existing information is insufficient to estimate biological risks

- Chemical characterization data alone cannot adequately address relevant biological endpoints

- There is no history of safe use for the materials in the specific application

- Biological equivalence to a predicate device cannot be established

- Post-market data indicates previously unidentified biological hazards

Information Hierarchy:

The standard emphasizes gathering existing information before conducting new testing:

1. Material information (composition, manufacturing processes, history of use)

2. Literature data (published studies on materials and similar devices)

3. Chemical characterization data (extractables, leachables, degradation products)

4. Existing biological test data (from similar materials or devices)

5. Post-market surveillance data (clinical experience with the device or similar devices)

Only after evaluating all available information should additional biological testing be considered.

Animal Welfare Considerations:

ISO 10993-1:2025 strengthens requirements to minimize animal testing by requiring manufacturers to:

- Refine biological risk estimation using additional information analysis

- Replace animal testing with alternative techniques (in vitro or in silico) where appropriate

- Reduce the number of animals used to the minimum necessary

- Refine experimental procedures to minimize animal pain and distress

In vivo testing shall not be conducted where valid information related to released constituents and degradation products have been addressed by other means and the constituents have a known and acceptable toxicity profile.

Regulatory Expectations:

While the risk-based approach provides flexibility, regulatory agencies still expect:

- Thorough documentation of the biological risk assessment process

- Scientific justification for decisions to conduct, not conduct, or limit biological testing

- Appropriate biological testing when risk assessment identifies data gaps

- Consideration of device-specific standards that may have additional requirements

Chemical Characterization vs Biological Testing: Key Differences

Information Provided

Chemical Characterization:

• Identifies specific compounds present

• Quantifies exposure levels

• Enables compound-specific toxicological assessment

• Provides data for risk-benefit analysis

Biological Testing:

• Evaluates overall biological response

• Assesses integrated effects of all extractables

• Identifies potential hazards through biological endpoints

• Provides functional safety data

Regulatory Perspective

Chemical Characterization:

Increasingly emphasized by regulatory agencies as essential for understanding device safety. Provides transparent, compound-specific data that supports detailed risk assessment.

Biological Testing:

Remains a fundamental requirement for demonstrating biocompatibility. Provides direct evidence of biological safety through standardized test methods.

Limitations of Each Approach

Chemical Characterization Alone:

• Cannot predict biological responses to complex mixtures

• May not detect all biologically relevant compounds

• Requires toxicological expertise for interpretation

• Doesn't address physical or mechanical biological interactions

Biological Testing Alone:

• Doesn't identify which compounds cause observed responses

• Limited ability to predict long-term effects

• May not detect low-level chronic toxicity

• Provides less information for risk mitigation strategies

Integrated Approach: When Both Are Needed

Modern biocompatibility evaluation typically requires both chemical characterization and biological testing working together.

Understanding Systemic vs. Local Biological Endpoints

A critical distinction in biocompatibility evaluation is the difference between systemic and local biological endpoints, which determines how effectively chemical characterization can address biological risks.

Systemic Biological Endpoints:

These endpoints evaluate risks from compounds that are absorbed and distributed throughout the body:

• Systemic toxicity (acute and chronic)

• Genotoxicity

• Carcinogenicity  

• Reproductive and developmental toxicity

Chemical characterization is highly effective for addressing systemic endpoints because:

• Toxicological risk assessment can estimate systemic risks based on identified compounds and their concentrations

• Extensive toxicological databases exist for many chemical compounds

• Dose-response relationships for systemic effects are well-established for many substances

• Threshold of toxicological concern (TTC) approaches can be applied

Local Biological Endpoints:

These endpoints evaluate tissue responses at the site of device contact:

• Cytotoxicity

• Irritation

• Sensitization (skin and systemic)

• Local tissue responses

Chemical characterization alone is rarely sufficient for addressing local endpoints because:

• Toxicological databases for local tissue effects are limited

• Local tissue responses depend on complex interactions between multiple compounds

• Physical characteristics (surface texture, particle size, configuration) significantly impact local responses

• Synergistic or antagonistic effects between compounds cannot be predicted from chemical data alone

• Insufficient data exists to establish reliable dose-response relationships for local tissue effects

Practical Implication:

Even when comprehensive chemical characterization is performed and successfully addresses systemic biological risks through toxicological risk assessment, biological testing of local endpoints is almost always still required.

This means devices requiring evaluation of both systemic and local biological endpoints will need:

1. Chemical characterization to address systemic risks (systemic toxicity, genotoxicity, carcinogenicity, reproductive toxicity)

2. Biological testing to address local tissue responses (cytotoxicity, sensitization, irritation, implantation)

This integrated approach is not optional—it's necessary because the two methods address fundamentally different types of biological risks that cannot be adequately evaluated by either approach alone.

Complementary Information

Chemical characterization informs biological testing:

Understanding extractables profiles helps interpret biological test results and identify compounds of concern.

Biological testing validates chemical assessment:

Biological responses confirm whether detected extractables pose actual biological risks at observed concentrations.

Risk Assessment Integration

Comprehensive Safety Evaluation:

Chemical data provides compound-specific toxicological assessment while biological testing confirms overall safety through functional endpoints.

Regulatory Defensibility:

Combined approaches create robust safety narratives that address both chemical and biological aspects of device safety.

Decision Framework: Determining Your Testing Strategy

Start with Device Classification

Low-Risk Devices:

Surface contact devices with limited exposure may rely more heavily on biological testing with targeted chemical characterization.

High-Risk Devices:

Implants and long-term contact devices typically require comprehensive chemical characterization plus full biological testing.

Consider Material History

Established Materials:

Materials with extensive biocompatibility history may require less comprehensive chemical characterization if biological testing demonstrates safety.

Novel Materials:

New materials or formulations require thorough chemical characterization to understand potential risks before or alongside biological testing.

Evaluate Regulatory Requirements

FDA Expectations:

Increasing emphasis on chemical characterization, particularly for devices with significant patient contact or novel materials.

EU MDR Requirements:

Chemical characterization often necessary to support clinical evaluation and risk-benefit analysis.

Other Jurisdictions:

Regional differences may affect the balance between chemical and biological approaches.

Practical Testing Strategies

Sequential Approach

Phase 1: Initial Assessment

Conduct biological screening tests (cytotoxicity, sensitization) to identify obvious safety concerns.

Phase 2: Chemical Characterization

Perform extractables studies to identify and quantify chemical constituents.

Phase 3: Toxicological Risk Assessment

Evaluate detected compounds for toxicological significance.

Phase 4: Additional Biological Testing

Complete remaining biological endpoints based on device classification and chemical findings.

Parallel Approach

Simultaneous Testing:

Conduct chemical characterization and biological testing concurrently to reduce overall timeline.

Integrated Analysis:

Correlate chemical and biological findings to create comprehensive safety assessment.

Risk-Based Approach

Prioritize Based on Concern:

Focus resources on areas of highest potential risk based on device characteristics and intended use.

Iterative Evaluation:

Use initial findings to guide additional testing needs rather than conducting all possible tests upfront.

Common Mistakes in Balancing Chemical and Biological Testing

Over-Reliance on Biological Testing

The Mistake:

Assuming passing biological tests means chemical characterization is unnecessary.

The Risk:

Missing compound-specific concerns that biological tests may not detect, leading to regulatory deficiencies.

Inadequate Chemical Characterization

The Mistake:

Performing minimal extractables analysis without comprehensive identification and quantification.

The Risk:

Incomplete toxicological assessment that cannot support regulatory submissions.

Poor Integration

The Mistake:

Treating chemical and biological data as separate evaluations rather than integrated safety assessment.

The Risk:

Missing connections between chemical findings and biological responses that could strengthen or weaken safety arguments.

Ignoring Material Changes

The Mistake:

Failing to reassess chemical characterization when materials, suppliers, or processing changes occur.

The Risk:

Existing biological test data may not represent current device extractables profile.

Regulatory Submission Considerations

Documentation Requirements

Chemical Characterization Reports:

• Detailed analytical methods and validation

• Complete compound identification and quantification

• Extraction condition justification

• Analytical limitations and sensitivity

Biological Test Reports:

• Standardized test methods per ISO 10993 parts

• Complete test article description

• Statistical analysis of results

• Biological significance interpretation

Integrated Biocompatibility Evaluation:

• Combined assessment of chemical and biological data

• Toxicological risk assessment of identified compounds

• Overall safety conclusion with supporting rationale

• Risk-benefit analysis where appropriate

Reviewer Expectations

Chemical Data:

Reviewers expect comprehensive identification of extractables with toxicological assessment of all detected compounds above relevant thresholds.

Biological Data:

Reviewers expect appropriate biological endpoints tested per ISO 10993-1 matrix with clear pass/fail criteria.

Integration:

Reviewers look for coherent safety narratives that address both chemical composition and biological response.

Cost and Timeline Considerations

Chemical Characterization

Typical Costs:

Extractables studies with comprehensive analytical characterization typically range from $15,000 to $50,000+ depending on complexity.

Timeline:

3-6 months for complete extractables analysis, compound identification, and toxicological assessment.

Biological Testing

Typical Costs:

Individual biological tests range from $2,000 to $15,000 each. Complete biological evaluation can total $20,000 to $100,000+ depending on required endpoints.

Timeline:

2-6 months depending on number of endpoints and test complexity.

Strategic Planning

Budget Allocation:

Balance investment between chemical and biological approaches based on device risk profile and regulatory requirements.

Timeline Optimization:

Parallel testing strategies can reduce overall timeline but require careful coordination.

Future Trends in Biocompatibility Evaluation

Increasing Emphasis on Chemical Characterization

Regulatory agencies worldwide are placing greater emphasis on understanding chemical composition and patient exposure to specific compounds.

Computational Toxicology

In silico methods and structure-activity relationship (SAR) analysis may supplement traditional biological testing for certain endpoints.

Integrated Testing Strategies

Movement toward comprehensive approaches that combine chemical, biological, and computational methods for more efficient evaluation.

Expert Guidance for Integrated Biocompatibility Strategy

Chemical characterization and biological testing are not competing approaches—they're complementary tools that together provide comprehensive biocompatibility evaluation. The question isn't which to choose, but how to strategically integrate both approaches to create robust safety assessments that meet regulatory requirements efficiently.

Understanding when each approach is required, how they inform each other, and how to integrate findings into coherent safety narratives is essential for successful medical device development and regulatory approval.

Determining the right balance between chemical characterization and biological testing requires deep understanding of both toxicological principles and regulatory expectations. At JL Tox Consulting, we help medical device manufacturers develop strategic biocompatibility evaluation plans that integrate chemical and biological approaches efficiently.

Our comprehensive biocompatibility services include:

• Strategic planning for chemical characterization and biological testing integration

• ISO 10993-18 extractables and leachables study design

• Toxicological risk assessment of chemical characterization data

• Biological testing strategy development per ISO 10993-1

• Integrated biocompatibility evaluation report preparation

• Regulatory submission support for global markets

With over a decade of specialized experience in medical device biocompatibility, Dr. James Lyons and the JL Tox team provide the toxicological expertise needed to navigate the complex interplay between chemical characterization and biological testing.

Contact JL Tox Consulting today to develop an integrated biocompatibility strategy tailored to your device and regulatory requirements.

Email: info@JLTox.com