EpiDerm vs SkinEthic RHE vs EPiTRI: reconstructed human epidermis compared

The short answer: EpiDerm and SkinEthic RHE are the two RhE models you will realistically buy, both are validated under OECD TG 439 and TG 431, and the choice between them is operational rather than scientific. EPiTRI is a fully validated third model that meets the TG 439 performance standards and detects at least one chemical the reference methods miss, but you should confirm supply before specifying it.

The genuinely useful difference is not accuracy. All seven models in TG 439 cleared the same minimum predictive capacity — 80 percent sensitivity, 70 percent specificity, 75 percent accuracy — before inclusion. The differences are in barrier tightness, protocol parameters, formats and how the tissue arrives.

Validation status: what is in the guideline

TG 439 currently lists seven validated test methods. Six are commercially available; EpiSkin was withdrawn from commercial availability in December 2024, though data generated with it remains covered by Mutual Acceptance of Data.

Barrier function: the ET-50 and IC50 acceptance windows

Barrier function is the property that separates these models most sharply, and OECD publishes the batch release criteria directly. Models are qualified either by ET-50 — the exposure time to 1% Triton X-100 that reduces viability by half — or by IC50 against SDS.

How to read this table without over-reading it. These are release windows, not measured performance. A model with a wider window is not worse; it is a model whose developer has set a wider acceptable range. The one substantive comparison is that epiCS qualifies from an ET-50 of 2.0 hours, a genuinely lower floor than EpiDerm’s and SkinEthic’s 4.0 hours, which indicates a comparatively less resistant barrier at the permissive end of its range.

What matters practically: ask the supplier for the actual measured ET-50 of the lot you are being shipped, not just confirmation that it passed. OECD requires the developer to provide these data to users so they can be included in the test report, so you are entitled to them. Two lots at the opposite ends of a 4.0-to-8.7-hour window are not equivalent tissues for a borderline chemical.

TG 439 also recommends that users verify the barrier properties of the tissues after receipt, as specified by the model producer — particularly if tissues are shipped over long distances or long transit times. That recommendation exists because transit degrades barrier function, and it is the single most commonly skipped step in this workflow.

Protocol parameters: the models are not interchangeable in practice

All seven use a 42-hour post-treatment incubation at 37°C. Everything else varies, and the variation is exactly what stops you swapping models mid-programme.

Two observations worth acting on.

Application time varies fourfold across the guideline, from 15 minutes for LabCyte to 60 minutes for EpiDerm. That is not sloppiness — the exposure periods are optimised per method to compensate for each model’s intrinsic barrier properties. But it means a laboratory running EpiDerm cannot simply substitute SkinEthic tissues into the same SOP. Model change means protocol revalidation.

EpiDerm and epiCS both require the positive control to drop below 20 percent viability, against 40 percent for the others. That is a tighter run acceptance criterion and it means an EpiDerm run is marginally more likely to be invalidated by a weak positive control. Tighter is generally better for data quality and worse for throughput.

Proficiency substance performance

OECD publishes indicative cell viability ranges for the ten proficiency substances across all seven methods. These are not part of the guideline and are provided for information, but they are useful because they show where models diverge on the same chemical.

The interesting entries are the variances, not the means. epiCS on 1-methyl-3-phenyl-1-piperazine returns 38.8 ± 37.9 percent — a standard deviation as large as the mean, straddling the 50 percent classification threshold. SkinEthic on potassium hydroxide gives 16.7 ± 17. EpiDerm on cyclamen aldehyde gives 18.5 ± 16.2. OECD itself notes that 1-methyl-3-phenyl-1-piperazine and 1-bromohexane can give variable results depending on the supplier of the substance.

If your test chemical resembles a class where a model shows high variance, that is a reason to choose a different model or to plan additional runs. TG 439 already anticipates this: for borderline results, including non-concordant replicates or mean viability at 50 ± 5 percent, a second run should be considered and a third if the first two disagree.

EPiTRI: the case for the third model

EPiTRI was developed at the Industrial Technology Research Institute in Taiwan and validated against the TG 439 performance standards in GD 220. The published results:

• Twenty reference chemicals from GD 220: 100 percent sensitivity, 70 percent specificity, 85 percent accuracy.
• International validation across four laboratories: phase I/II within-laboratory reproducibility 100 percent and 95 percent, between-laboratory reproducibility 95 percent.
• Overall performance: 96 percent sensitivity, 70 percent specificity, 83 percent accuracy — meeting the OECD criteria.
• A specific advantage: EPiTRI correctly identified di-n-propyl disulphide as an irritant (UN GHS Category 2), whereas most validated reference methods classified it as a non-irritant.

That last point is the substantive reason to know about EPiTRI. A model that catches a false negative the reference methods miss has genuine value in a weight-of-evidence assessment, particularly for chemical classes where the reference methods are known to under-call.

The countervailing consideration is procurement rather than science. We could not establish routine commercial supply arrangements for EPiTRI outside its region of origin. Before you specify it in a study plan, confirm you can actually buy it on your timeline and confirm its current listing status in the guideline version your regulator accepts.

Formats, shipping and what arrives

Two operational notes that catch first-time buyers.

The shipping cadence is a scheduling constraint. A Monday dispatch with a four-day shelf life including transit means your assay window is determined by the supplier’s calendar before you book anyone’s time. Ordering on a Tuesday does not save you a week.

The two suppliers handle temperature oppositely on arrival. One ships cold on agarose gels; the other explicitly instructs leaving tissues at room temperature and warns against refrigerating or freezing. Read the arrival instructions for the model you actually ordered, not the one you used last time. Both warn that tissues dry out rapidly when not in contact with medium.

Price

Neither major supplier publishes a price. Distributor listings for these products commonly show “Inquiry” rather than a number, and the vendor sites route to contact.

We are not going to invent a figure. What we can say about the structure of the cost:

• The unit that gets quoted is the kit, not the tissue. The standard EpiDerm kit is 24 tissues.
• Format materially changes price per tissue. A 4 cm² insert and a 96-well HTS tissue at 0.11 cm² are not the same product priced per unit area.
• Media variants are a real line item. Phenol-red-free, antibiotic-free, anti-fungal-free and hydrocortisone-free tissues are produced as separate runs with the agent removed at least three days before shipment, which is a production decision and not a picking decision.
• Shipping is not trivial. Priority courier on a fixed day with a four-day shelf life is expensive and non-negotiable, and international delivery adds both cost and risk.

If you need a real number, ask for a quote against a specific format, kit size, media variant and delivery date. Anything less specific will not produce a comparable answer from two suppliers.

Choosing

What we would verify before ordering

• Which guideline version and which model your regulator or client accepts.
• The measured ET-50 or IC50 of the specific lot being shipped, not just a pass statement.
• Barrier verification on receipt, per the producer’s instructions, especially for long transit.
• Delivery day, transit route and remaining shelf life on arrival.
• Whether the media variant you need is a stocked variant or a scheduled production run.
• Kit size, format and price per tissue in that format, from two suppliers, for the same delivery date.
• Whether your protocol will need revalidation if you change model.

Related

The tissue availability map puts RhE in context against everything else you can and cannot buy as living tissue. If you want us to run the quote across suppliers against one specification and delivery date, send it over. We do not manufacture tissue and we are not a distributor for any model named here.