Few areas of medicine generate as much confusing vocabulary as this one — or as much marketing built on top of that confusion. Terms get used loosely, interchangeably, and sometimes in ways that imply more than they should.
This is a plain-language guide to the words you will encounter, written for clinicians and for anyone trying to make sense of what they are reading. We have tried to define each term as it is actually used in regulation and practice, not as it appears in advertising.
Where tissue comes from
Autologous
From your own body. Blood drawn from a patient and processed for use in that same patient is autologous. Nothing is transferred between people, so there is no risk of disease transmission from a donor and no immune rejection.
Allogeneic
From another human being. An allograft is tissue transplanted from one person to another — bone, skin, tendon, cornea, amniotic membrane. This is where donor screening, testing, and traceability requirements come in.
Xenograft
From another species — porcine, bovine, or piscine sources are all used in various products.
Common product categories
Platelet-Rich Plasma (PRP)
A concentrate prepared by drawing a patient's blood and spinning it in a centrifuge to separate components, producing a plasma fraction with a higher platelet concentration than whole blood. Because platelets carry growth factors, PRP is studied in a range of settings. Preparation methods, final platelet concentrations, and the presence or absence of white blood cells vary widely between systems — which is a major reason study results are difficult to compare.
Amniotic and placental tissue
Tissue derived from the placenta, amniotic membrane, or umbilical cord, donated with consent following live birth. Amniotic membrane has a long documented history of use as a biological wound covering, particularly in ophthalmology.
Extracellular matrix (ECM)
The structural scaffolding that surrounds cells in every tissue — collagens, proteoglycans, and associated proteins. Some products are processed to leave this matrix behind as a scaffold.
Mesenchymal stromal cells
A population of cells found in marrow, fat, and other tissues, widely studied in laboratory and clinical research. Note the terminology drift: these are often called "stem cells" in marketing, though many researchers now prefer "stromal" precisely because the broader term overstates what has been demonstrated.
Regulatory vocabulary
HCT/P
Human Cells, Tissues, and Cellular and Tissue-Based Products — the FDA's umbrella category, regulated under 21 CFR Part 1271, covering requirements for donor screening, testing, processing, labeling, and tracking.
Minimal manipulation
Processing that does not alter the tissue's original relevant characteristics. Cleaning, cutting, and cryopreserving generally qualify. Culture-expanding cells generally does not. This is one of the criteria that determines which regulatory pathway a product falls under.
Homologous use
Using tissue for the same basic function it performed in the donor. Skin used as a covering is homologous use. The same tissue promoted for an unrelated systemic effect is not.
Section 361 vs. Section 351
Two pathways under the Public Health Service Act. A 361 HCT/P meets criteria including minimal manipulation and homologous use, and does not undergo premarket review. A 351 product is regulated as a biologic drug and requires an approved Biologics License Application — a demonstration of safety, purity, and potency.
The distinction most worth understanding
"FDA registered" does not mean "FDA approved"
- Registered means an establishment filed paperwork with the FDA identifying itself and listing its products. It is an administrative step. No review of safety or effectiveness occurs.
- Cleared (for devices) means the FDA agreed a product is substantially equivalent to something already on the market.
- Approved or licensed means the FDA reviewed evidence and concluded the product is safe and effective for a specific use.
These are not synonyms, and the gap between them is wide. If a product is described as "FDA registered," that tells you a form was filed — nothing more. It is one of the most commonly blurred distinctions in this field, and one of the most useful to hold onto.
When a claim sounds bigger than the evidence behind it, the vocabulary is usually where the stretching happens.
A note on reading claims
Regenerative medicine is an active research field with genuine scientific interest behind it. It is also a field where marketing has, at times, run ahead of evidence. A few habits help:
- Ask what regulatory pathway a product falls under, and ask for it in writing.
- Notice when a mechanism is described as though it were a demonstrated outcome. "Contains growth factors" and "produces healing" are very different statements.
- Treat testimonials as what they are — individual accounts, not controlled evidence.
- Be skeptical of any single product presented as appropriate for a long list of unrelated conditions.
None of that is cynicism about the science. It is the ordinary discipline that lets good science be distinguished from good salesmanship — and in a field this young, that distinction is worth protecting.