When a medical device makes direct contact with human skin for hours or days at a time, the materials it is made from become as clinically significant as the signals it captures. Biocompatibility is not a box to tick at the end of development — it is a foundational design consideration that shapes material selection, manufacturing decisions, and the entire regulatory pathway. For engineers developing wearable medical devices such as ECG patches, biosensors, or flexible electrodes, understanding what biocompatibility requires in practice is essential to building products that are safe, effective, and approvable.
This guide covers the regulatory frameworks that govern biocompatibility testing, how to select skin-contact materials, the manufacturing factors that can introduce biological risk, and how to integrate biocompatibility thinking into the development process from the earliest stages.
Regulatory frameworks governing biocompatibility testing
The primary international standard governing the biological evaluation of medical devices is ISO 10993, a multi-part framework that defines how to assess the potential biological risks of materials that contact the body. For wearable medical devices, the most relevant parts cover biological evaluation planning (ISO 10993-1), cytotoxicity (ISO 10993-5), sensitization (ISO 10993-10), skin irritation (ISO 10993-23), and chemical characterization (ISO 10993-18). Each part addresses a specific risk category, and the combination of tests required depends on the nature of the contact: surface contact, duration, and whether the device contacts intact skin, breached skin, or mucosal tissue.
Regulatory bodies including the FDA and the European Medicines Agency align closely with the ISO 10993 framework, though they apply it differently. In the US, FDA guidance documents reference ISO 10993-1 as the starting point for biocompatibility assessment under 21 CFR Part 820. In Europe, the Medical Device Regulation (MDR 2017/745) requires biological safety evaluation as part of the technical documentation for CE marking. Developers should treat ISO 10993 as a risk-based process — the standard requires a biological evaluation plan that justifies which tests are needed and why, based on the specific device and its intended use.
For short-term skin-contact wearables (contact duration under 24 hours), the minimum testing scope is typically narrower than for extended-wear devices worn continuously for several days. Getting this classification right early in development avoids costly retesting later.
Material selection criteria for skin-contact wearables
Choosing materials for a wearable device is a multidimensional problem. Biocompatibility is one axis, but it intersects with signal performance, mechanical flexibility, adhesion, moisture management, and sustainability — and trade-offs between these properties are common.
Substrates and structural layers
Flexible substrates such as polyurethane (PU), polyethylene terephthalate (PET), and nonwoven fabrics are widely used in wearable electrodes. Each has a different moisture vapor transmission rate, mechanical behavior, and surface chemistry that affects both skin tolerance and manufacturing compatibility. PU films tend to offer better conformability and breathability, which supports extended-wear comfort. PET offers dimensional stability and is easier to process in reel-to-reel printing, but its lower breathability can contribute to skin occlusion over time.
Conductive inks and electrode materials
Silver and silver/silver chloride (Ag/AgCl) pastes are the most established conductive materials for biopotential electrodes. However, silver ions can cause localized skin reactions in sensitive individuals, and the chloride chemistry of Ag/AgCl can interact with sweat electrolytes in ways that affect both signal quality and skin tolerance. Carbon-based inks offer an alternative with a different biocompatibility profile, though they typically have higher impedance. Material selection at this layer directly influences both the ISO 10993 testing scope and the clinical performance of the device.
Adhesive and hydrogel systems
The adhesive or hydrogel layer is often the most clinically sensitive component in a skin-contact wearable. Acrylic adhesives, hydrocolloids, and hydrogels each have distinct skin interaction profiles. Hydrogels used in wet electrodes must be evaluated for both their electrical properties and their potential to cause maceration or sensitization under occlusion. Adhesive intolerance is one of the most common causes of skin adverse events in wearable device use, and it is a failure mode that frequently only becomes visible through extended clinical testing rather than standard bench tests.
How manufacturing processes affect biocompatibility outcomes
Biocompatibility is not determined solely by the raw materials specified in a bill of materials. The manufacturing process itself can introduce or modify biological risk in ways that are easy to overlook during early development.
Screen printing, flexographic printing, and lamination processes all involve solvents, curing agents, and process chemicals that may leave residues on the finished device. If these residues are not fully removed or neutralized during processing, they can affect the cytotoxicity or irritation potential of the final product. This is why chemical characterization under ISO 10993-18 is increasingly important — it requires identifying and quantifying extractables and leachables from the finished device, not just the individual materials in isolation.
Sterilization is another critical process variable. Many wearable sensors and electrodes are supplied sterile or require sterile packaging. Ethylene oxide (EtO) sterilization, for example, can leave residues that must be assessed under ISO 10993-7. Gamma irradiation can alter the mechanical and chemical properties of some polymers and adhesives, potentially changing their biocompatibility profile. Developers working with a CDMO partner should confirm that manufacturing process validation includes biocompatibility considerations, not just functional performance.
Process consistency also matters. A material stack that passes biocompatibility testing at the prototype stage must behave identically at production scale. Variability in ink cure levels, lamination pressures, or drying temperatures can introduce batch-to-batch differences that affect extractable profiles and, ultimately, biological safety.
Common biocompatibility failures in wearable device development
Understanding where biocompatibility problems typically arise helps development teams prioritize testing and design decisions more effectively. Several failure modes appear repeatedly across wearable device programs.
Adhesive sensitization is among the most frequent clinical issues. Acrylate-based adhesives, while effective for skin fixation, contain monomers that can act as contact allergens in a subset of users. This risk is difficult to predict from standard cytotoxicity tests alone and often requires sensitization testing under ISO 10993-10 as well as real-world wear trials. Switching adhesive systems late in development is expensive and can require repeating parts of the regulatory submission.
Silver ion release from Ag/AgCl electrodes is another known failure mode, particularly in extended-wear applications where sweat accumulation accelerates ion migration. Developers who select silver-based electrode materials without accounting for wear duration and occlusion conditions may encounter skin reactions that were not predicted by short-duration bench testing.
Substrate occlusion leading to skin maceration is a common issue with impermeable film substrates. When moisture cannot escape through the device, prolonged wear causes softening and breakdown of the stratum corneum, increasing irritation risk and reducing adhesion performance. This is a design and material selection problem as much as a biocompatibility one — selecting a more breathable substrate or incorporating moisture management features can prevent it.
Inadequate chemical characterization is a systemic failure mode at the process level. Teams that rely on supplier data sheets rather than conducting their own extractables and leachables analysis on the finished device assembly can miss interactions between materials that only occur in the combined, processed state.
Integrating biocompatibility into the design and development process
The most effective approach to biocompatibility is to treat it as a continuous risk management activity rather than a late-stage testing milestone. This means making material decisions with regulatory consequences in mind from the earliest feasibility work.
A biological evaluation plan, as required by ISO 10993-1, should be drafted before prototyping begins. This document defines the device’s contact classification, identifies the applicable biological endpoints, and maps out which tests will be needed and in what sequence. Having this plan in place early allows the development team to select materials that minimize testing burden and avoid late-stage surprises. For example, choosing materials with an established history of safe use in equivalent applications can reduce the need for extensive new testing.
Material changes made after biocompatibility testing has been completed are one of the most common sources of regulatory delay. Even seemingly minor substitutions — a different adhesive supplier, a reformulated ink, a change in substrate thickness — can trigger the need for additional testing under ISO 10993. Building a change control process that flags biocompatibility implications from the outset protects development timelines.
Screentec’s work developing disposable wearable electrodes across ECG, EEG, EMG, and other modalities has generated practical knowledge of how material choices affect skin tolerance, signal quality, and regulatory documentation. That experience — spanning wet, dry, and hydrogel electrode formats — informs how biocompatibility considerations are embedded in manufacturing decisions, not treated as an afterthought.
For development teams moving from prototype to scalable production, the relationship between material specification, manufacturing process validation, and biocompatibility documentation needs to be explicit and traceable. Regulatory reviewers will expect to see that the tested device is representative of what will be manufactured at scale, and that any process changes have been evaluated for biological safety implications.
Biocompatibility is ultimately a discipline that rewards early investment. The teams that build it into their design and manufacturing decisions from the start spend less time in remediation and reach regulatory submission with a stronger, more defensible technical file. If your team is navigating material selection or ISO 10993 planning for a wearable device program, get in touch with Screentec to discuss how manufacturing expertise can support your biocompatibility strategy.
Frequently Asked Questions
How do I know which ISO 10993 tests are required for my specific wearable device?
The required tests depend on three key factors: the nature of the body contact (surface skin, breached skin, or mucosal tissue), the duration of contact (short-term under 24 hours, prolonged up to 30 days, or permanent), and the materials used in the device. Start by drafting a Biological Evaluation Plan (BEP) as outlined in ISO 10993-1, which maps your device’s contact classification to the relevant biological endpoints. Working with a regulatory consultant or an experienced CDMO early in development can help you scope the testing matrix correctly and avoid over- or under-testing.
Can I rely on my material supplier's biocompatibility data instead of running my own tests?
Supplier data sheets and certificates can support your biological evaluation, but they cannot replace testing on your finished device assembly. ISO 10993-18 specifically requires extractables and leachables analysis on the device as manufactured, because interactions between materials — and the effects of your specific manufacturing processes such as curing, lamination, and sterilization — can introduce risks not captured by individual material data alone. Treat supplier documentation as a starting point for your chemical characterization, not a substitute for it.
What should I do if a skin adverse event is reported during a clinical wear trial?
First, systematically document the event: the wear duration, the skin site, the nature of the reaction (erythema, maceration, papules, etc.), and any user-specific factors such as known allergies or skin conditions. Then trace the event back to the most likely material candidates — adhesive systems and occlusive substrates are the most common culprits. Depending on the severity and frequency of events, you may need to initiate additional sensitization or irritation testing under ISO 10993-10 or ISO 10993-23, and potentially revisit your material selection before proceeding to larger studies.
How does switching to a new adhesive supplier mid-development affect our regulatory submission?
Even if the new adhesive appears chemically equivalent, a supplier change is considered a material change under ISO 10993 and typically triggers a biocompatibility impact assessment. In many cases, this will require repeating cytotoxicity and sensitization testing at a minimum, and potentially a full re-evaluation depending on how different the extractable profiles are. This is why establishing a robust change control process early — one that explicitly flags biocompatibility implications for any material or process substitution — is critical to protecting your development timeline and submission readiness.
Are there material combinations that are generally considered lower risk for extended-wear skin-contact devices?
Yes. Materials with a well-established history of safe use in equivalent applications — such as medical-grade polyurethane films, certain hydrocolloid adhesives, and Ag/AgCl electrode formulations validated for extended wear — can reduce your testing burden because ISO 10993-1 allows existing safety data to be leveraged. However, ‘lower risk’ is always relative to wear duration and patient population: a material suitable for a 24-hour patch may not be appropriate for a 7-day continuous wear device, particularly if the user population includes individuals with compromised or sensitive skin.
How does sterilization method selection affect biocompatibility, and how early should this decision be made?
Sterilization method selection should be made as early as possible in development — ideally before biocompatibility testing begins — because the sterilization process itself is part of the finished device’s biological risk profile. Ethylene oxide (EtO) can leave residues assessed under ISO 10993-7, while gamma irradiation can degrade certain polymers and adhesives, potentially altering their extractable profiles. If you test an unsterilized prototype and later introduce EtO sterilization, you may need to repeat portions of your biocompatibility evaluation. Aligning sterilization method, packaging, and material selection early prevents this costly sequencing problem.
What is the most common mistake development teams make when approaching biocompatibility for the first time?
The most common mistake is treating biocompatibility as a late-stage testing event rather than an ongoing design constraint. Teams that finalize material selections, manufacturing processes, and even clinical protocols before drafting a Biological Evaluation Plan often discover mid-development that their chosen materials require extensive testing, or that a process change has invalidated earlier test results. Starting with a BEP, selecting materials with regulatory history in mind, and building biocompatibility checkpoints into design reviews from feasibility onward significantly reduces the risk of costly late-stage redesign or regulatory delays.