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Test the finished, processed print with a method and cell model that match its intended use. A material is not simply “biocompatible” in every situation: cell type, exposure route, cleaning, curing, coatings and sterilization can all affect the result. A cytotoxicity assay is a useful biological screen, but it does not establish broad safety, identify every leachable chemical or prove that an item is sterile.
What does “safe for cell culture” mean?
It means that the specific printed article, after the processing it will actually receive, has been evaluated for the way it will contact the intended cells. That conclusion is bounded by the cell type, exposure method, test conditions and endpoints used. It is not a general property that can automatically be transferred to every print made from the same material.
For example, a result with one cell model may not predict another model’s response. A print tested before cleaning or curing may not represent the final article, and a test for cell damage does not answer whether the material releases particular chemicals or whether sterilization was successful.
ISO 10993-5, ISO 10993-12 and ISO 10993-18 are standards for biological evaluation of medical devices and their materials. They can provide a structured reference for a cell-culture evaluation, but the intended application and applicable requirements determine what evaluation is appropriate. A single assay is not proof of regulatory clearance.
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- Biocompatibility Data: ISO 10993-10 (Sensitization), -5 (Cytotoxicity), & -23 (Irritation) test data available to support evaluation for skin-contact applications (User validation required).
What should I define before testing?
Start by specifying the intended use and the exact test article. The objective is to evaluate a representative finished print, not an abstract material name or an untreated feedstock sample.
Describe the complete print and processing route
Record enough detail to make the tested article identifiable and reproducible. Include the material formulation, printer and print parameters, support materials, cleaning, curing, coatings, sterilization or disinfection, and storage. If these steps differ between test specimens and the intended cell-culture item, the results may not apply to that item.
ISO 10993-12:2021 addresses sample selection and preparation, controls, reference materials and extract preparation. Its official listing shows Amendment 1 published in 2025. Use the applicable standard and protocol to determine specimen preparation and extraction details; do not assume that one extraction recipe suits every material.
Specify the culture context
Name the cell type and how the print will be used: for example, whether cells will sit directly on a surface, encounter a liquid extract, or be exposed indirectly through a barrier or diffusion path. Also define the processing state being evaluated. Those choices determine which exposure method and assay can answer the practical question.
Decide what conclusion the test should support
Before running an assay, state the biological endpoint you intend to assess, such as cell morphology, cell damage, growth or cellular metabolism. The endpoint should fit the culture use and the assay’s capabilities. ISO 10993-5 does not prescribe one universal endpoint for every test.
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- Versatile Industrial & Engineering Applications: Designed for manufacturing aids, jigs, fixtures, protective covers, seals, vibration dampeners, and other components demanding a tough, wear-resistant, semi-rigid elastic material.
- Optimized for Reliable Printing: Formulated for smoother extrusion, reduced stringing, and clog resistance compared to many flexible filaments. Flex tpu 64d white filament is compatible with most standard FDM/FFF printers (ensure proper flexible material setup).
- Biocompatibility Data: ISO 10993-10 (Sensitization), -5 (Cytotoxicity), & -23 (Irritation) test data available to support evaluation for skin-contact applications (User validation required).
Which exposure method should I use?
ISO 10993-5:2009 describes three broad approaches: direct contact, indirect contact or diffusion, and testing with a liquid extract. The choice depends on the material, expected exposure and intended use; these methods are not interchangeable versions of the same question.
| Approach | What it evaluates | When it may be relevant | Key limitation |
|---|---|---|---|
| Direct contact | Cells in contact with the material or printed surface. | When the intended culture use places cells against the print. | It answers a contact-specific question; it does not by itself characterize every substance that could be released under other exposure conditions. |
| Indirect contact or diffusion | Effects on cells when exposure occurs indirectly, such as through diffusion rather than direct placement on the material. | When the intended use separates cells from the print but allows indirect exposure. | The result applies to the tested arrangement and conditions, not to every direct-contact or extract scenario. |
| Liquid extract | Cell response to liquid that has been exposed to the material under defined extraction conditions. | When released constituents are a concern or the intended exposure is mediated by liquid. | The result depends on the specimen preparation and extraction conditions; it does not inventory all chemicals in the print. |
Use the method that represents the actual exposure, or a justified combination if one method cannot address the relevant use cases. Document why that method was chosen. Do not treat a favorable result from an extract test as automatic evidence that cells will behave the same way on a printed surface.
How do I run a useful cytotoxicity evaluation?
Build the test around a representative finished article, a suitable cell model, a stated endpoint and controls that help interpret the result. The detailed laboratory protocol, including specimen preparation and assay conditions, must be selected for the material and intended use rather than assumed from a generic checklist.
- Prepare representative specimens. Make them using the same material and print route as the intended article, including relevant support removal, cleaning, curing, coatings and sterilization or disinfection. Record any difference from the final-use workflow.
- Select the exposure route. Choose direct contact, indirect contact or a liquid extract based on how the cells are expected to encounter the printed item. For an extract, document the preparation and extraction conditions used.
- Choose a relevant cell model. Use the cell type that matters to the intended culture application where practicable. If results from a different model are used as supporting evidence, label that difference rather than implying equivalence.
- Include controls. Include an extraction blank and suitable negative and positive controls. The blank helps distinguish effects associated with the specimen from effects associated with the extraction setup; positive and negative controls help establish whether the assay can show an effect and a comparatively non-harmful response under the selected conditions.
- Measure the defined endpoint. State whether the readout concerns morphology, cell damage, growth, metabolism or another specified endpoint. A quantitative readout can be paired with visual inspection when that helps interpret cell appearance.
- Report the conditions with the result. Identify the cell type, exposure route, extraction conditions where applicable, exposure duration, processing state, controls, assay and observed effect. Without those details, readers cannot judge how closely the result matches their own use.
ISO 10993-5:2009 covers in vitro cytotoxicity methods using direct contact, indirect contact or extracts. The ISO listing says the edition, published in June 2009, was reviewed and confirmed in 2022 and remains current. The standard provides options rather than one universal assay or endpoint.
When should I investigate leachables or chemical composition?
A cell-based cytotoxicity result is a biological screen, not a chemical inventory. If the intended use or observed response raises concern about released constituents, chemical characterization can help identify and, where needed, quantify them as part of hazard identification and risk estimation.
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ISO 10993-18:2020 provides a stepwise framework for chemical characterization within a risk-management process. The ISO listing says it was confirmed in 2025, with Amendment 1 published in 2022. Chemical characterization complements biological testing: one does not substitute for the other, and detecting a constituent is not by itself a complete risk conclusion.
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Published findings show why the distinction matters. Huang and colleagues’ 2023 study assessed leachable cytotoxicity in three stereolithography polymers and reported toxicity from leachables in the tested materials. Flexibility and treatment method affected the observed response. Soxhlet solvent extraction was the most effective treatment among those tested in that study; it is not a universal detoxification recipe for other formulations or workflows.
Why must I test after cleaning, curing and sterilization?
Processing can change what cells encounter, so a raw coupon may not represent the finished item. Evaluate the print after the cleaning, curing, coating and sterilization or disinfection steps intended for actual use. If those steps change, the earlier result may no longer describe the new test article.
Cell compatibility and sterilization are separate questions. A cell assay does not demonstrate sterility, and a sterilization method should not be presumed compatible with a material just because another process or another material performed acceptably.
In a 2022 study, Winkler and colleagues found no different cell effects between autoclaving and ethanol disinfection for the specific heat-resistant polyacrylate and cell systems they tested. That finding is limited to those materials, cells and conditions; it does not establish that the two processes are interchangeable for other prints.
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Licata and colleagues’ 2024 bioreactor study reported that photoresins affected human induced pluripotent stem cells while not affecting primary human dermal fibroblasts. Among the thermoplastics tested, only Nylon 12 withstood autoclaving. These are study-specific findings, not guarantees about every resin, thermoplastic, printer or sterilization cycle.
What do published cell-culture studies show?
The studies below illustrate why a material name or a result from one cell line is not enough to predict performance in another culture system. Each finding applies to the study’s particular material, processing and test conditions.
| Study | What was evaluated | Reported finding | What not to infer |
|---|---|---|---|
| Huang et al., 2023 | Leachable cytotoxicity in three stereolithography polymers and treatment methods. | Leachables were toxic in the tested materials; flexibility and treatment method affected response. Soxhlet extraction performed best among the treatments tested. | That Soxhlet extraction is a standard solution for other materials, or that the same result applies to other print workflows. |
| Winkler et al., 2022 | Extraction media from a heat-resistant polyacrylate, evaluated with L929 mouse fibroblasts, HEK 293E cells and yeast. | No negative effect was reported for L929 cells and yeast under the study conditions, while HEK 293E viability or growth was reduced. | That a favorable result for one model predicts a favorable result for all cell types. |
| Licata et al., 2024 | Printed plastics considered for bioreactors, including tests with human induced pluripotent stem cells and primary human dermal fibroblasts. | Photoresins affected the stem cells but not the fibroblasts in the reported evaluation. Of the tested thermoplastics, only Nylon 12 withstood autoclaving. | That all photoresins affect all cell types, or that every Nylon 12 print withstands every autoclave process. |
| “Evaluating the Cytotoxicity of Commercial Materials for Additive Manufacturing of Soft Tissues,” 2026 | Formlabs Biomed Elastic 50A, Biomed Flexible 80A and Biomed Durable resin, tested with human dermal fibroblasts and human mesenchymal stromal cells. | The study reported minimal cytotoxicity after its tested printing and post-processing conditions. | That other resins, material lots, cell types or processing workflows will have the same result. |
When comparing candidate materials, prioritize evidence for the target cell type and exposure route, then consider chemical characterization and compatibility with the cleaning and sterilization steps the application requires. A result is more useful when the tested specimen and workflow closely match the proposed use.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How should I interpret and report the result?
Make the conclusion no broader than the evidence. Say what was tested, under which conditions, and what effect was observed; avoid an unqualified statement that a material is “safe” or “biocompatible.”
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- Identify the article: formulation or material, printer and print parameters, support materials, specimen selection and relevant batch or lot information if tracked.
- Describe processing: cleaning, curing, coatings, sterilization or disinfection, and storage before testing.
- Describe exposure: direct contact, indirect contact or extract; include extraction conditions and exposure duration when applicable.
- Describe biology: cell type, assay, endpoint, controls and observed effects, including relevant visual observations.
- State the limits: name the tested workflow and cell model, and avoid extending the claim to untested cell types, materials or processing conditions.
If a result is unfavorable or inconsistent, first check whether the controls behaved as expected and whether the tested article accurately represented the intended workflow. A discrepancy between cell models is not necessarily a contradiction: the Winkler study, for example, reported different outcomes among L929 cells, HEK 293E cells and yeast under its conditions.
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Which standards are relevant?
These ISO documents provide complementary reference points, not a shortcut to a universal pass/fail judgment for every printed culture item.
| Standard | Relevant scope | Version context |
|---|---|---|
| ISO 10993-5 | In vitro cytotoxicity test methods, including direct contact, indirect contact and extract approaches. | 2009 edition; ISO says it was confirmed in 2022 and remains current. |
| ISO 10993-12 | Sample preparation, reference materials, controls and extracts. | 2021 edition; Amendment 1 published in 2025. |
| ISO 10993-18 | Chemical characterization within a risk-management process. | 2020 edition; confirmed in 2025, with Amendment 1 published in 2022. |
For a formal protocol or evaluation plan, consult the applicable standard’s official listing and the standard text. The ISO 10993-5 listing identifies purchasable formats; obtaining the document does not establish that a particular print is safe. The intended application determines which evaluation and requirements apply.
Frequently Asked Questions
Can a negative cytotoxicity test guarantee that my printed culture device is safe?
No. It supports a conclusion only for the tested specimen, cell model, exposure route, processing state and endpoint. It does not establish sterility or rule out every chemical or biological concern relevant to a different use.
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Cell models can respond differently to the same material or extract. Winkler et al. reported different outcomes among L929 fibroblasts, HEK 293E cells and yeast, while Licata et al. reported different responses for stem cells and dermal fibroblasts.
Does ISO 10993-5 tell me exactly which assay to use?
It describes in vitro cytotoxicity approaches, including contact and extract methods, but does not mandate one universal endpoint. The choice depends on the material, expected exposure and intended application.
Can I rely on a published test of the same resin brand?
Only as evidence for the conditions actually studied. A published result may not transfer to a different material lot, printer, post-processing route, sterilization process or cell type.
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