ISO 10993-18 Chemical Characterization — Scoping the Analytical Programme

Chemical characterization under ISO 10993-18 builds the material and extractables evidence that frames a device's biological evaluation. Scoping the analytical programme to the device's contact type and duration avoids both gaps and uninterpretable over-testing.

Start from the biological evaluation plan

The contact category and duration determine how much chemistry is needed. Surface devices, externally communicating devices and implants pose different questions, and existing material data or clinical history may reduce the analytical burden. Agree what the characterization must demonstrate within the overall ISO 10993-1 evaluation rather than ordering a maximal chemistry package by default.

Document materials before extraction

Characterization begins with composition: base polymers, additives, colorants, processing aids, adhesives, coatings and residual sterilants. Supplier disclosures and manufacturing knowledge sharpen the target list and reduce unexplained peaks. Ask the laboratory how it reconciles declared composition with analytical findings and how discrepancies are reported.

Confirm the current framework

ISO 10993-18 and related parts have been revised in recent years; confirm with the laboratory and assessor which editions the programme cites and how a toxicological risk assessment will use the output. A report that names compounds without identification confidence, thresholds or method descriptions is difficult to defend in a submission.

Extractables, leachables and product context

Extractables describe constituents released under defined laboratory extraction conditions; leachables concern release under actual or justified simulated use. Start with composition, polymers, additives, adhesives, coatings, processing aids and manufacturing/sterilization residues. Device patient exposure differs from drug-container interactions and pharmaceutical stability programmes. Combination products need coordinated device and drug evidence—not an unqualified device protocol applied to every container.

Distinguish final guidance from draft recommendations

FDA's September 2024 chemical-analysis guidance is draft — not for implementation; it is not final guidance or mandatory law. FDA's September 2023 risk-based biological-evaluation guidance remains final. Agree the applicable evidence strategy rather than treating draft chemistry recommendations as a universal test requirement.

What to include in your buyer brief

Start with the decision the work must support. Unknown details can be clarified after the initial inquiry.

Product, materials/formulation, patient or drug contact, contact duration, intended use and target market; identify changed materials, suppliers or processes.
Finished configuration, sample count and lots, sterilization modality/cycles, aging and storage history; justify worst-case variants and destructive allocations.
Existing evaluation plan, drawings, specifications, methods/editions, previous reports and acceptance criteria; send confidential files only through the private intake.
Required report, quality/accreditation scope, budget range, location, shipping constraints and decision deadline; ask the provider to explain exclusions and subcontracted work.

Reference versus candidate medical plastics and colorants

Compare the reference and candidate finished components, documented resin identity when available, pigment/dye or additive changes, manufacturing and cleaning/sterilization histories, and actual exposure. Unknown composition, sample allocation and test panels remain questions to resolve—not inferred facts. Material identification and color comparison do not establish biological safety.

Propose methods around the evidence gap

Ask the provider whether FTIR, DSC or other material identification, targeted chemistry, extraction studies and toxicological interpretation can answer the comparison question. These are possible proposals, not prescribed tests. Biological compatibility, chemical/material resistance and product interactions are different scopes. A qualified evaluator should justify existing evidence, chemical characterization and any targeted biological testing after a material or colorant change.

Plan, evaluate and test: separate the deliverables

A biological evaluation plan (BEP) identifies contact, duration, existing evidence and gaps; a biological evaluation report (BER) integrates the evidence and rationale. An endpoint laboratory report answers a scoped test question, not the entire biological evaluation. A qualified evaluator should justify endpoint selection and use of prior evidence; not every material change requires every test.

Chemistry versus toxicological interpretation

ISO 10993-18 chemical characterization addresses what substances may be present or released and the analytical coverage/limitations. ISO 10993-17 toxicological risk assessment interprets constituent exposure, toxicological evidence and uncertainty in the device-use context. A chemical list alone is not a safety conclusion, and a TRA cannot cure poorly justified extraction or uncharacterized analytical gaps.

Extractables, leachables and residuals

Forced extractables explore potential release under justified exaggerated conditions; actual or simulated-use leachables address release under relevant contact conditions. Neither automatically substitutes for the other. Distinguish manufacturing residuals such as monomers, solvents and processing aids from sterilization residuals such as ethylene oxide and relevant reaction products. Define analytical targets, exposure assumptions, recovery, reporting thresholds and uncertainties with the provider; no universal panel.

Sample considerations

Provide full material disclosure where available, plus processing and sterilization history.
State device contact type, duration and the role of the study within the biological evaluation plan.
Agree extraction conditions, analytical platforms, thresholds and reporting format with the assessor.

Questions to ask a laboratory

Which ISO 10993-18 edition and related parts will the programme follow?
How does the laboratory resolve discrepancies between declared and found composition?
What identification confidence and reporting thresholds will the data carry?

Laboratories with relevant capabilities

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Frequently asked questions

How does this differ from extractables and leachables work on packaging?: The analytical techniques overlap heavily. The difference is the framework: device chemical characterisation feeds a biological evaluation and toxicological risk assessment for the device as used.
Do I need a toxicologist as well as a laboratory?: Usually yes. The laboratory produces identification and quantitation; interpreting it against exposure is a toxicological assessment, and some laboratories offer both.