Biocompatibility Requirements for Wearable Medical Devices: Unique Considerations

Wearable medical devices are transforming healthcare with continuous monitoring, real-time diagnostics, and improved patient engagement. However, their design introduces distinct challenges from a biocompatibility perspective. These devices often involve prolonged skin contact (sometimes can be even long term), contain adhesives and flexible polymers, and are worn in dynamic, moisture-prone environments. Regulatory expectations for biocompatibility evaluation of wearables require special consideration.

1. Unique Biological Risks of Wearables

Wearables differ from traditional medical devices in key ways:

• Prolonged contact duration: Many devices are worn 24 hours or more, often daily. This prolonged exposure increases the risk for irritation and sensitization due to sustained interaction between skin and material components. Watches or other products can be also considered as long (contact exceeding 30 days)
• Mechanical friction and motion: Wearables experience continuous movement and pressure on the skin, which can lead to micro-abrasions, localized stress, or enhanced penetration of leachable substances.
• Moisture exposure: Sweat and humidity during use can enhance leachability of chemicals and compromise barrier function of the skin, increasing systemic absorption.
• Temperature and environment: Warm or outdoor environments may accelerate degradation of materials, influence bacterial growth on device surfaces, or change material biostability.

2. Regulatory Classification and Testing Requirements

The FDA and other global regulators assess wearable biocompatibility under ISO 10993-1. Typically, wearables are classified as:

• Surface-contacting medical devices (intact skin)
• With prolonged (24h–30d) or long-term (>30d) contact durations

These classifications determine the required test endpoints, including:

• Cytotoxicity (ISO 10993-5): To evaluate whether materials or extractables damage cells at the tissue interface.
• Skin irritation (ISO 10993-10): To assess acute inflammatory reactions that may result from exposure.
• Sensitization (ISO 10993-10): To determine the potential for allergic skin reactions following repeated use.

For extended-wear devices, cumulative exposure studies or repeated application protocols may be necessary. Comprehensive chemical characterization (ISO 10993-18) and toxicological risk assessments are increasingly expected to address possible leachables from adhesives or multilayer structures.

It’s also worth noting that FDA’s guidance includes Attachment G, which lists certain materials with a history of safe use. For these well-characterized materials in contact with intact skin, biocompatibility testing may not be required. However, a scientific justification and appropriate documentation are still expected.

3. Special Focus: Adhesives and Skin-Contact Materials

Adhesives, films, foams, and flexible polymers used in wearables often contain sensitizers, residual monomers, or plasticizers that can lead to irritation or allergic reactions. Consider the following:

• Comprehensive chemical characterization: Include all skin-contacting components in extractables testing, including adhesive layers, cover films, and printed inks.
• Supplier data: Use safety data sheets and toxicological profiles when available, but confirm unknown components with laboratory analysis.
• Worst-case scenario testing: Evaluate fully assembled, sterilized devices under simulated or exaggerated use conditions — including repeated application and exposure to sweat or heat.

4. Best Practices and Common Pitfalls

Do:

• Integrate biocompatibility early in design: Start evaluating contact type, duration, and material safety before finalizing components. Early planning avoids last-minute delays and redesigns.
• Gather complete supplier data: Request full compositional data, including additives, leachables, and processing aids. This enables targeted testing and justification strategies.
• Document realistic exposure assumptions: Clearly explain how the device is used, how often it contacts the skin, and whether repeated applications are expected. This information is critical for accurate risk assessment.
• Consult with labs experienced in wearable testing: Look for expertise in skin-contact materials, flexible substrates, and adhesive risk assessments.

Avoid:

• Avoid assuming short contact duration automatically means low risk. Real-life factors like sweat, friction, or repeated use may lead to cumulative exposure and increase potential safety concerns.
• Overreliance on generic supplier data: Unverified data or partial declarations can lead to gaps in toxicological evaluation, potentially triggering retesting or regulatory pushback.
• Delaying testing until final submission: Biocompatibility evaluation is often iterative — deferring it risks delays and non-compliance at the final stage.

5. Key Tests for Wearable Devices — and Why They Matter

In addition to standard tests like cytotoxicity, irritation, and sensitization, certain evaluations are especially important for wearables:

• Repeated insult patch test (RIPT): Particularly useful for consumer-facing or cosmetic-wearable hybrids, this test assesses cumulative skin reactivity over time.
• Sweat- or moisture-enhanced extract testing: Simulates exposure under real use conditions to evaluate the effect of perspiration on chemical release.
• Long-term extractables analysis: Identifies low-level leachables that may only appear after days or weeks of contact.
• Microbial assessment: For wearables in humid environments, biocompatibility can be influenced by microbial colonization — assessments may be warranted for extended use devices.

Final Thoughts

Wearable medical devices offer tremendous value, but their unique use environment introduces real biocompatibility challenges. Success requires more than standard test packages — it demands a thoughtful, risk-based approach tailored to the specific materials and usage patterns. Early planning, realistic exposure assessments, and experienced lab partners are key to safe, compliant, and market-ready wearables.

About the Author: Prof. Łukasz Szymański

Prof. Łukasz Szymański is an expert in medical device biocompatibility testing, serving as the Chief Scientific Officer (CSO) of the ISO 17025-accredited and GLP-certified European Biomedical Institute (EBI) and North American Biomedical Institute (NABI). As a dedicated researcher and a key contributor to advancing safety standards in the biomedical field, Prof. Szymański plays an integral role in shaping scientific innovations and regulatory compliance within the industry.