Toxicological Assessment of Extractables and Leachables (E&L) for Medical Devices

Toxicological assessment of medical device leachables is a risk-based scientific process that identifies, quantifies, and evaluates chemical substances migrating from device materials to patients, ensuring that exposure remains within demonstrably safe limits. Anchored in ISO 10993-17, ISO 10993-18, and the broader ISO 10993 (GB/T 16886) framework, this assessment is a cornerstone of modern biological safety evaluation and regulatory submissions worldwide. This article explains the technical rationale, sample types, testing items, analytical and toxicological methods, and frequently asked questions related to extractables and leachables toxicological assessment for medical devices.

Technical Overview

Leachables are chemical substances that migrate from a medical device, its components, or its materials into a patient, or into fluids that are subsequently delivered to a patient, under actual clinical use conditions. Because direct measurement of patient exposure is rarely feasible, laboratory extraction studies are conducted to generate extractables profiles—substances released under exaggerated or exhaustive solvent conditions that define the universe of potential leachables. The toxicological assessment then evaluates whether the identity, quantity, and duration of exposure to each reported compound pose an unacceptable risk to patient safety.

This evaluation is embedded in the risk management process defined by ISO 10993-1 and ISO 14971. ISO 10993-18 governs the chemical characterization of device materials and extracts, while ISO 10993-17 provides the methodology for toxicological risk assessment and the establishment of allowable limits such as tolerable intake (TI) and tolerable exposure (TE). The corresponding Chinese national adoption is the GB/T 16886 series. Supplementary references include ISO 10993-7 for ethylene oxide sterilization residuals, USP <1663> and USP <1664> for extractables and leachables assessment concepts, and ICH M7 principles for potentially mutagenic impurities.

A typical assessment workflow proceeds through the following stages:

• Material, formulation, and manufacturing process review to anticipate expected extractables;
• Extraction study design (simulated-use, exaggerated, or exhaustive extraction) per ISO 10993-12 and ISO 10993-18;
• Analytical screening, identification, and quantification using orthogonal chromatographic and spectrometric techniques;
• Compound reporting against the analytical evaluation threshold (AET);
• Hazard and exposure assessment, calculation of margin of safety (MOS), and risk characterization per ISO 10993-17;
• Documentation of conclusions within the biological evaluation plan and report.

Toxicological endpoints considered include systemic toxicity, local irritation and sensitization, genotoxicity, carcinogenicity, reproductive and developmental toxicity, endocrine activity, and immunotoxicity. Quantitative benchmarks include tolerable intake values derived from NOAEL or LOAEL data, the threshold of toxicological concern (TTC) approach with a commonly applied safety concern threshold (SCT) of 1.5 µg/day for organic leachables lacking compound-specific toxicological data, and Cramer classification-based TTC values.

Testing Samples

Sample selection follows ISO 10993-12 and should represent the final device in its clinically supplied condition, including its final sterilization state. Both complete devices and individual components of concern may be evaluated.

Polymer-Based Device Components

PVC infusion sets and blood bags, polyurethane and silicone catheters and tubing, polyolefin syringes, oxygenator and dialyzer membranes, wound dressings, hydrogels, and polymer housings are commonly submitted. Typical leachables of interest include plasticizers, hindered phenolic and phosphite antioxidants, oligomers, slip agents, residual monomers, and colorants.

Metallic and Ceramic Components

Stainless steel, titanium, cobalt–chromium, and nitinol implants, instruments, and structural components, as well as ceramic parts, are assessed for elemental release. The focus is on metal ion toxicity from elements such as nickel, cobalt, chromium, vanadium, aluminum, and molybdenum, consistent with the degradation assessment concepts of ISO 10993-15.

Elastomeric Components and Closures

Rubber stoppers, septa, seals, gaskets, and O-rings are evaluated for vulcanization accelerators such as mercaptobenzothiazoles, nitrosamines and nitrosatable amines, polycyclic aromatic hydrocarbons (PAHs) associated with carbon-black fillers, and peroxide crosslinking decomposition products.

Coatings, Adhesives, Inks, and Primary Packaging

Hydrophilic and antimicrobial coatings, pressure-sensitive and drug-layer adhesives, printed labels and inks that may transfer through films, adhesive systems, thermoformed trays, blister films, and sterile barrier pouches are assessed for migration potential under relevant contact conditions.

Fluid-Path Devices and Combination Products

Infusion and transfusion assemblies, hemodialysis and ECMO circuits, inhalation and nebulization pathways, prefilled syringes, and drug-eluting or drug-device combination products are evaluated where contact between device materials and medicinal products or circulating fluids may generate leachables.

Testing Items

Testing items combine broad untargeted screening for unknown compounds with targeted quantification of chemical classes of established concern, followed by evaluation of toxicological endpoints.

• Non-volatile organic compounds (NVOCs): antioxidants, stabilizers, oligomers, lubricants, dyes, and polymer degradation products;
• Semi-volatile organic compounds (SVOCs): phthalate and adipate plasticizers, curing agents, and slip agents;
• Volatile organic compounds (VOCs): residual solvents and residual monomers such as acrylates and epoxides;
• Elemental impurities and heavy metals: lead, cadmium, mercury, arsenic, chromium, nickel, cobalt, vanadium, aluminum, copper, zinc, and related elements;
• Specific target analytes: bisphenol A (BPA), di-2-ethylhexyl phthalate (DEHP), nitrosamines, PAHs, 2-mercaptobenzothiazole, and per- and polyfluoroalkyl substances (PFAS) where formulation or regulatory expectations indicate relevance;
• Sterilization residues: ethylene oxide (EtO), ethylene chlorohydrin (ECH), and ethylene glycol (EG) per ISO 10993-7, as well as radiation sterilization byproducts;
• Anionic and cationic species by ion chromatography where applicable.

Toxicological Endpoints Evaluated

• Acute, subacute, subchronic, and chronic systemic toxicity;
• Irritation and sensitization associated with local tissue contact;
• Genotoxicity and mutagenicity, including structural alert screening and ICH M7 categorization;
• Carcinogenicity;
• Reproductive and developmental toxicity;
• Endocrine activity and immunotoxicity where compound structure or class indicates concern.

Quantitative decision criteria include tolerable intake values derived from NOAEL or LOAEL data with appropriate uncertainty factors, the default 1.5 µg/day safety concern threshold for organic compounds, Cramer class-based TTC values, and an acceptable margin of safety, generally MOS ≥ 1.

Testing Methods

Extraction Study Design

Per ISO 10993-12 and ISO 10993-18, extraction conditions are selected according to the intended use, contact duration, and physicochemical properties of the device materials. Simulated clinical-use extraction mimics actual patient contact; exaggerated extraction applies accelerated temperatures and extended durations; and exhaustive extraction repeats the process until successive extracts fall below a defined fraction of the initial yield. Both polar media (water, saline) and non-polar media (such as ethanol or hexane) are typically employed, with extraction temperature, duration, and solvent-to-surface-area ratios scientifically justified and documented.

Analytical Characterization Techniques

• Gas chromatography–mass spectrometry (GC-MS) for semi-volatile organic compounds;
• Headspace GC-MS for volatile organic compounds and residual solvents;
• Pyrolysis GC-MS for polymer identification and deformulation support;
• Liquid chromatography–tandem mass spectrometry (LC-MS/MS) and high-resolution LC-MS for non-volatile and thermolabile compounds;
• Inductively coupled plasma mass spectrometry or optical emission spectrometry (ICP-MS, ICP-OES) for elemental impurities;
• Ion chromatography (IC) for anionic species;
• FTIR spectroscopy and complementary techniques for structural confirmation.

Screening data are evaluated against the analytical evaluation threshold (AET), which is derived from the safety concern threshold, the clinically realistic worst-case patient exposure scenario (number of devices, contact duration, and daily fluid volumes), and an analytical uncertainty factor, commonly 50%. Compounds detected above the AET are identified, typically with a documented identification confidence grade, and semi-quantified; compounds below the AET are excluded from further risk assessment.

Toxicological Risk Assessment

For each reported leachable, the assessment proceeds through hazard identification using authoritative peer-reviewed toxicological databases; dose–response assessment to establish NOAEL or LOAEL values with route-to-route extrapolation and uncertainty factors; exposure assessment based on realistic worst-case clinical use; and risk characterization comparing predicted patient exposure with the tolerable intake and calculating the margin of safety. Where compound-specific data are unavailable, the TTC approach using Cramer structural classification, in silico (QSAR) predictions, and read-across from structural analogues is applied. Conclusions are documented in accordance with ISO 10993-17 and integrated into the biological evaluation file under ISO 10993-1 and the risk management documentation under ISO 14971.

Applications

Toxicological assessment of extractables and leachables supports decision-making across the entire medical device lifecycle, from design input to post-market surveillance. Typical applications include:

• Regulatory submissions, including premarket notifications and approvals with FDA, CE technical documentation under the EU MDR (Regulation 2017/745), NMPA registration in China under the GB/T 16886 series, and PMDA submissions in Japan;
• Biological evaluation files that demonstrate chemical safety and provide scientific justification for reducing or omitting certain biological endpoint tests;
• Change control evaluations following changes in material suppliers, formulations, manufacturing processes, or sterilization methods;
• Vendor and incoming material qualification programs;
• Long-term contacting devices and permanent implants, fluid-path devices such as infusion, transfusion, dialysis, and ECMO systems, and combination products;
• Responses to regulatory deficiency questions and post-market safety investigations.

FAQ

What is the difference between extractables and leachables?

Extractables are compounds released from device materials under exaggerated laboratory extraction conditions (elevated temperature, aggressive solvents), representing the potential chemical universe. Leachables are the subset that actually migrates under real clinical use conditions and to which the patient is genuinely exposed. Extractables studies are used to predict and screen for leachables that are difficult to measure directly.

Which standards govern this assessment?

The core standards are ISO 10993-1 (risk management framework), ISO 10993-12 (sample preparation), ISO 10993-17 (toxicological risk assessment and allowable limits), and ISO 10993-18 (chemical characterization), together with ISO 10993-7 for ethylene oxide residues. In China, the GB/T 16886 series corresponds to ISO 10993. USP <1663>, USP <1664>, ICH M7, and the emerging ICH Q3E guideline provide supplementary methodological and threshold guidance.

What is the analytical evaluation threshold (AET)?

The AET is the concentration below which an analyte does not need to be identified or reported because the corresponding patient exposure would be below the safety concern threshold. It is calculated from the SCT (commonly 1.5 µg/day for organic compounds), the clinical exposure scenario (daily volumes and device quantities), dilution and concentration factors, and an analytical uncertainty factor.

When is a leachables toxicological assessment required?

It is expected whenever chemical characterization data are insufficient to conclude biological safety under ISO 10993-1, and particularly for devices with prolonged or permanent patient contact, fluid-path devices that deliver substances intravenously, devices with new or changed materials, combination products, or when requested by regulatory authorities.

Can E&L toxicological assessment replace biological testing?

It cannot replace all biological testing, but a well-substantiated chemical characterization and toxicological risk assessment can provide scientific justification for reducing or omitting certain biological endpoint tests, such as subchronic toxicity or genotoxicity, in accordance with the risk-based approach of ISO 10993-1.

What are typical study timelines and deliverables?

Depending on device complexity, extraction and analytical characterization typically require six to twelve weeks, with the toxicological risk assessment report following an additional two to four weeks. Deliverables from accredited third-party laboratories generally include the extraction study protocol and report, the analytical data package with AET-based compound identification and quantification, and the toxicological risk assessment report with margin-of-safety conclusions suitable for regulatory submission.

Overall, a rigorous extractables and leachables toxicological assessment transforms raw analytical data into defensible patient-safety conclusions. Manufacturers are advised to engage accredited third-party laboratories with integrated analytical chemistry and toxicology capability to ensure that studies are designed, executed, and interpreted in full compliance with the ISO 10993 and GB/T 16886 frameworks.