Is the particle count NTA-verified on the final product?

Nanoparticle Tracking Analysis (NTA) counts individual particles in the finished vial. Ask whether the count on the label comes from NTA on the lot you receive, or from an estimate, a protein assay, or a pre-processing figure. Ask for the NTA report itself, including size distribution.

Is there a lot-specific Certificate of Analysis?

The CoA should match the lot number on your vial. A product-line spec sheet or a "representative lot" CoA is not the same document.

Is the CoA confirmed by an independent laboratory?

In-house testing alone means the manufacturer is grading its own work. Dual-lab testing — in-house plus an independent third-party lab — gives you a second, unaffiliated result for the same lot.

Does the CoA cover sterility, endotoxin, and mycoplasma?

These are baseline safety tests. Ask for the method and the result for each, not just the word "passed."

How is the source material cultured — 2D flask or 3D bioreactor?

Culture method is a manufacturing variable that affects yield and lot-to-lot consistency. Published comparisons report higher extracellular vesicle yield per cell from 3D bioreactor systems than from 2D flat culture. Ask which method the supplier uses and whether it's documented.

Is the process xeno-free and serum-free?

Fetal bovine serum (FBS) in culture media can carry animal-derived vesicles into the final product. Ask whether the process is xeno-free and FBS-free, and whether that's stated on the documentation.

Liquid cryopreserved or lyophilized — and what does the format do to the product?

Freeze-drying (lyophilization) adds membrane stress and reconstitution steps. Liquid cryopreserved products avoid that but need frozen storage. Ask which format you're buying and whether the NTA count reflects the product after reconstitution.

Is the cold chain documented from facility to your door?

Frozen products should ship on dry ice with temperature monitoring and clear storage instructions. Confirm you have appropriate storage (typically −80°C) before your first order, or plan just-in-time ordering.

Is the manufacturing facility FDA-registered and cGTP-compliant (21 CFR Part 1271)?

These are facility credentials, not product approvals. A supplier describing a tissue-derived product as "cGMP" is citing the drug-manufacturing framework instead of the tissue framework — ask why.

Does the supplier's marketing stay within topical cosmetic positioning?

A supplier's website can create exposure for the practices that buy from it. Disease names, mechanism claims, "injectable-grade" language, or any suggestion of FDA approval are compliance red flags — for them and for you.