Immunotoxicity, Neurotoxicity, Reproductive Toxicity, and Pyrogenicity: When ISO 10993-1 Requires Evaluation Beyond the Standard Endpoints

Most biological evaluations focus on the endpoints that appear prominently in Tables 1 through 4 of ISO 10993-1:2025: cytotoxicity, sensitization, irritation, systemic toxicity, genotoxicity, and hemocompatibility. These are the endpoints that apply broadly across device categories and contact types, and they are the ones that most regulatory teams evaluate as a matter of course.

But the standard also identifies biological effects that are not universally required but must be evaluated when specific conditions are met. These include immunotoxicity, neurotoxicity, reproductive and developmental toxicity, and material-mediated pyrogenicity. Each has defined triggers in the standard, and each generates deficiency findings when the triggers are met but the biological evaluation does not address them.

The challenge for regulatory teams is that these effects are easy to overlook. They do not appear in the main table entries for most device categories. They require the evaluator to assess whether the device's specific materials, contact conditions, or patient population trigger the requirement. This is an area where the evaluator's scientific judgment is essential, because the standard defines the conditions but the determination of whether those conditions apply to a specific device is a device-specific decision that requires qualified expertise.

Immunotoxicity

ISO 10993-1:2025 states that immunotoxicity shall be considered when the physical or chemical properties of the device or its materials are suggestive of immunotoxicological effects, or when the immunogenicity potential of any of the device's constituents is unknown.

This means immunotoxicity is not a blanket requirement for all devices. It is triggered by specific material properties. For example, a device containing novel polymers whose immunogenic potential has not been characterized in the literature would trigger the requirement, because the immunogenicity of the constituents is unknown. Similarly, a device that releases metal ions known to modulate immune function (such as nickel or cobalt from a cobalt-chromium alloy) could trigger the requirement based on the physical and chemical properties being suggestive of immunotoxicological effects.

Conversely, a device made entirely from well-characterized materials with extensive published data on their immunological properties (such as medical-grade silicone or titanium) would typically not trigger this requirement, provided the BER documents why the immunogenicity potential is considered known and acceptable based on the existing data.

ISO 10993-20 provides additional guidance on principles and methods for immunotoxicology testing of medical devices. When the requirement is triggered, the biological evaluation should reference this standard for the testing approach.¹

Where SME judgment is needed

Determining whether a material's properties are "suggestive of immunotoxicological effects" requires scientific expertise in immunology and material science. The standard does not provide a checklist of properties that qualify. A qualified toxicologist or biocompatibility expert must assess whether the specific materials, their degradation products, and their release characteristics present immunotoxicological concerns for the specific clinical use scenario. This is not a determination that can be made from the standard alone.

Neurotoxicity

The requirement for neurotoxicity evaluation in ISO 10993-1:2025 is more specific than the other effects discussed here. Devices that have direct or indirect contact with tissues of the central or peripheral nervous system, or with cerebrospinal fluid, shall be evaluated for neurotoxicity.

This is a contact-based trigger, not a material-based trigger. It applies regardless of what the device is made from. If the device contacts neural tissue or cerebrospinal fluid, neurotoxicity evaluation is required.

For example, a spinal implant that contacts the dura mater or cerebrospinal fluid requires neurotoxicity evaluation. An intracranial pressure monitoring catheter requires it. A peripheral nerve stimulator with electrodes in direct contact with nerve tissue requires it. A cochlear implant with components in contact with neural tissue of the inner ear requires it.

A device that contacts tissue adjacent to but not in direct or indirect contact with nervous system tissue does not trigger this requirement based on proximity alone. For example, an orthopedic bone plate that is implanted near a nerve but does not contact the nerve or its surrounding sheath would not typically trigger neurotoxicity evaluation, unless the device releases substances that could migrate to neural tissue. That migration assessment is where scientific judgment comes in.

Where SME judgment is needed

The direct contact cases are straightforward. The harder determination is indirect contact: can substances released from the device reach neural tissue through diffusion, systemic circulation, or local migration? This requires understanding the device's extractable profile, the local anatomy at the implant site, and the pharmacokinetics of any released substances. A toxicologist or biocompatibility expert should make this determination, especially for devices implanted in anatomical regions where neural tissue is nearby but not directly contacted.

Reproductive and developmental toxicity

ISO 10993-1:2025 requires evaluation of reproductive and developmental toxicity when any of the following conditions are met: the device contains materials with known reproductive or developmental toxicity or novel materials whose reproductive toxicity profile is unknown; the device is indicated for use in relevant sensitive populations, including foetuses, pregnant women, or lactating women; or there is potential for local presence of medical device materials or constituents in the reproductive organs.

This requirement has three independent triggers, any one of which is sufficient to require evaluation.

The first trigger is material-based. If chemical characterization identifies a constituent with known reproductive toxicity (such as certain phthalate plasticizers classified as CMR substances under EU regulations), the biological evaluation must address reproductive and developmental toxicity regardless of the patient population or device location. Similarly, if the device contains novel materials whose reproductive toxicity profile has not been established, evaluation is required because the absence of data does not constitute evidence of safety.

The second trigger is population-based. A device intended for use during pregnancy, on foetuses, or by lactating women requires reproductive and developmental toxicity evaluation even if the device is made from well-characterized materials with no known reproductive toxicity. For example, a fetal monitoring electrode made from standard medical-grade stainless steel would still trigger this requirement because of the patient population, not the material.

The third trigger is anatomy-based. A device that contacts or releases substances into the reproductive organs requires evaluation regardless of the intended patient population. For example, an intrauterine device or a urological catheter that contacts reproductive tract tissue would trigger this requirement based on the anatomical location.

Where SME judgment is needed

The population and anatomy triggers are usually determinable from the device's intended use and contact description. The material trigger is harder. Determining whether a constituent has "known reproductive or developmental toxicity" requires reviewing toxicological databases and published literature for each identified extractable. Determining whether a material is "novel" in the context of reproductive toxicity requires understanding what published safety data exists for that material in reproductive applications. These are toxicological determinations that require qualified expertise.

Additionally, under the EU MDR, substances classified as CMR (carcinogenic, mutagenic, or toxic to reproduction) above 0.1% w/w concentration in the device trigger specific requirements under Annex I, Section 10.4.1 that go beyond what ISO 10993-1 alone requires. Manufacturers seeking CE marking should ensure their reproductive toxicity assessment addresses both the ISO 10993-1 requirements and the EU MDR CMR requirements.²

Material-mediated pyrogenicity

Material-mediated pyrogenicity is the induction of a febrile (fever) response caused by chemical constituents of the device rather than by biological contamination (such as bacterial endotoxins) or pharmaceutical pyrogens. The 2025 standard notes that chemically induced pyrogenicity is rare and has been demonstrated for only a small number of substances.

ISO 10993-1:2025 removed material-mediated pyrogenicity from the main evaluation tables (Tables 1 through 4). However, this does not mean the effect has been eliminated from the standard. It is addressed separately, and devices containing materials that have previously elicited a pyrogenic response or whose pyrogenic potential is unknown should be evaluated.

In many cases, the standard indicates that it can be sufficient to justify that the composition of the finished medical device does not contain risk for material-mediated pyrogenicity and that adequate controls are in place. This means that for most devices made from well-characterized materials with no history of pyrogenic response, a documented justification in the BER can satisfy this requirement without specific pyrogenicity testing.

For example, a device made from medical-grade titanium, PEEK, and silicone with established biocompatibility data and no published reports of material-mediated pyrogenic responses can address this requirement with a documented statement that the device's material composition does not present a risk for material-mediated pyrogenicity, supported by reference to the specific materials and available data.

Where this becomes more complex is with devices made from materials that have limited characterization history, devices that introduce novel material combinations, or devices where the manufacturing process could introduce pyrogenic contaminants. In these cases, the justification needs to address why the specific material composition and manufacturing controls are adequate to prevent material-mediated pyrogenicity.

Additionally, reusable devices that undergo reprocessing (cleaning, disinfection, sterilization) between uses present a consideration worth addressing. Reprocessing can introduce residual chemicals from cleaning agents or sterilants, and repeated reprocessing cycles could potentially alter the device's material surface in ways that affect its pyrogenic profile. While the standard does not explicitly require pyrogenicity evaluation for all reprocessed devices, the BER for a reusable device should document whether the reprocessing protocol introduces any materials or surface changes that could present a pyrogenicity concern.

Where SME judgment is needed

Determining whether a material has "previously elicited a pyrogenic response" requires knowledge of the published literature on that specific material's biological response history. Determining whether adequate controls are in place requires understanding the manufacturing process, sterilization method, and any post-manufacturing treatments that could introduce pyrogenic substances. A qualified biocompatibility expert should make these determinations, particularly for devices with complex material compositions or novel manufacturing processes.

Why these effects generate deficiency findings

The most common deficiency pattern for these biological effects is not that the evaluation was conducted incorrectly. It is that the BER did not address them at all. A reviewer opens the biological evaluation and finds thorough coverage of cytotoxicity, sensitization, irritation, systemic toxicity, and genotoxicity, but no mention of immunotoxicity, neurotoxicity, reproductive toxicity, or pyrogenicity. The reviewer then has to determine whether the triggers apply to this device, and if they cannot make that determination from the documentation provided, they issue a deficiency asking the manufacturer to address it.

The fix is straightforward: address every one of these effects in your BER, even if the conclusion is that evaluation is not required. For each effect, document whether the trigger conditions are present, what data or reasoning supports that determination, and whether evaluation was conducted or why it was not necessary. A short paragraph per effect that explicitly states the trigger assessment is far better than silence, which forces the reviewer to guess whether you considered it and decided it was not applicable, or simply overlooked it.

This is especially important for the 2025 standard transition. BERs written against the 2018 edition may not have explicitly addressed these effects because the triggers were less prominently stated. Updating your BER for the 2025 standard should include a review of whether these trigger conditions apply to your device, even if the conclusion is unchanged.

If your biological evaluation documentation is approaching submission and you want to verify that these additional biological effects are properly addressed, request a gap analysis or get in touch to discuss your package.