What a real specification sheet shows
The measurements that constitute proper characterisation of a vesicle preparation, and how to tell a specification from a description.
Proper characterisation of a vesicle preparation uses several measurements that are independent of one another: particle concentration and size distribution, total protein, the ratio between them as a purity indicator, a marker profile including markers that should be absent, and imaging showing particles with the expected morphology.
A specification states what the product will contain within defined limits on every batch. A description states what one batch contained when someone measured it. Most documents in this market are descriptions written in the register of specifications, and telling them apart takes about a minute once you know what to look for.
The measurements that constitute characterisation
Particle concentration and size distribution
How many particles per unit volume, and how their sizes are distributed. Useful, limited, and discussed at length in why a nanoparticle count is not a dose. A distribution curve is far more informative than a mean, because it reveals whether the preparation is one population or several.
Total protein
Straightforward to measure and essential as a denominator. On its own it says little.
Particle to protein ratio
The simplest widely used purity indicator. A preparation with many particles per unit of protein carries relatively little non-vesicular protein. A preparation with few particles per unit of protein is protein-heavy, which in a preparation sold on the vesicle name means much of the material is not the thing named. This single number tells you more than the particle count it derives from.
Marker profile, including negative markers
Detecting proteins expected to be present on or in vesicles supports the identification. Equally important, and much rarer, is testing for markers that should be absent if the preparation is what it claims. Markers of cellular compartments not expected to be exported, for example, indicate cellular debris. A profile that reports only positive markers has tested only for confirmation.
Imaging
Electron microscopy shows whether particles have the expected morphology. It is qualitative and low throughput, and it detects gross problems that scattering-based counts cannot, such as aggregation or a preparation dominated by non-vesicular material.
Sterility, endotoxin and residuals
Covered separately in sterility, endotoxin and cold chain. A characterisation package without them is incomplete for any product applied to breached skin.
A published particle count and mean size constitute characterisation of a vesicle preparation.
- Proposed mechanism
- Measuring particle number and size identifies the product sufficiently for use.
- What has been shown
- Consensus reporting frameworks in the extracellular vesicle field require multiple independent categories of measurement, including protein-based quantification, at least two categories of marker analysis and single-particle imaging, precisely because size and count alone cannot distinguish vesicles from other particles.
- Highest level reached
- In vitro only
- Main confounders
- None material. This is a documentation standard rather than an empirical question.
GradeNOT SUPPORTED
What would change thisNothing would change this. A count and a mean size are two measurements of one property and cannot establish identity. The relevant reporting frameworks are public and a supplier can be asked directly which of their requirements the product meets.
Specification versus description
This distinction is the practical core of the article. A specification says: this product contains between X and Y particles per millilitre, with a particle to protein ratio not less than Z, meeting the following marker criteria, on every batch, verified by the following tests. A description says: analysis of a representative batch found the following.
The difference is release criteria. A specification implies that batches failing the criteria are not released. A description implies that a batch was measured. Only the first tells you anything about the vial in front of you.
| If the document says | It is telling you | Ask |
|---|---|---|
| Contains over N particles per millilitre | A count, from an unstated platform | Per what volume, on what instrument, at what threshold, and is it a release limit or one measurement? |
| Analysis of a representative batch | One batch was measured | What are the release criteria, and what happens to a batch that fails them? |
| Proprietary isolation technology | A trade name | Which separation methods, in what order? |
| Characterised to international standards | A claim about a claim | Which framework, and which of its requirements are met? |
| Contains the following growth factors | Detection in a sample | Inside vesicles or free in solution, and was that distinguished? |
What a good document looks like
In our reading of this sector, a document worth taking seriously has four properties. It names methods rather than trade descriptions. It reports at least one measure of purity, not only of quantity. It includes at least one negative result, meaning something tested for and not found. And it distinguishes release criteria from observations.
The third of those is the most telling. Documents that contain only positive findings have been written to persuade. Documents that report a negative control, a marker absent, an assay below the limit of detection, have been written to inform. That is a difference in intent visible on the page.
Why suppliers resist
Some resistance is commercial confidentiality, and some of that is legitimate: nobody expects a manufacturer to publish a process. But release criteria are not a process. Publishing that a product meets a purity threshold discloses no method. The reluctance to publish criteria usually indicates that criteria do not exist, which is a different and more informative fact.
It is worth saying that developing release criteria is genuinely demanding, especially for a product whose active principle is not identified. A supplier who says frankly that they publish batch analyses because they cannot yet define potency criteria is being more useful than one who implies criteria exist. We would rather publish that statement than a confident number.
What we do with this on the site
Our listings record, for each listed supplier, which of these disclosures they make and which they decline. The listing is alphabetical, labelled paid where paid, and it is not a ranking. A supplier cannot buy a better characterisation record, because the record is a statement of what they disclosed, and declining to disclose is itself published. We set that out in the rate card.
Questions readers ask
What should be on a specification sheet for a vesicle product?
Particle concentration and size distribution, total protein, a particle to protein ratio, a marker profile including markers expected to be absent, imaging showing expected morphology, and sterility and endotoxin data. Release criteria should be distinguished from single-batch observations.
What is the difference between a specification and a certificate of analysis?
A specification states the limits every batch must meet. A certificate of analysis reports what one batch measured. A certificate without a specification tells you what was found, not what the product is guaranteed to contain.
Why are negative markers important?
Because testing only for markers expected to be present tests only for confirmation. Testing for markers that should be absent, such as those indicating cellular debris, is what demonstrates the preparation is not contaminated with material it should not contain.
Is a particle count enough?
No. Consensus reporting frameworks in the field require several independent categories of measurement precisely because count and size cannot distinguish vesicles from protein aggregates or lipoprotein particles.
How can I check a document quickly?
Look for numbers with ranges or limits attached rather than single figures, and look for at least one reported negative result. Documents containing only single positive figures are describing one measurement, not specifying a product.