3D Organ

Bioprinting glossary

Every term you will meet in a bioprinting paper or press release, defined in one or two sentences.

Bioprinting borrows vocabulary from manufacturing, materials science and cell biology at once, which is why press coverage of it so often goes wrong. These are the terms you will meet, defined plainly.

A – C

Acellular
Containing no living cells. An acellular scaffold provides structure and is expected to be populated by the body's own cells after implantation. Many "printed organ" headlines describe acellular constructs.
Additive manufacturing
The formal name for 3D printing: building an object by adding material layer by layer, as opposed to cutting it away from a block.
Alginate
A polysaccharide from brown seaweed, the most widely used bioink base. Gels within seconds in calcium solution. Cheap and gentle, but biologically inert — cells cannot attach to it unmodified.
Angiogenesis
The growth of new blood vessels from existing ones. Encouraging it into an implanted construct is one of the main strategies for keeping thick tissue alive.
Anastomosis
Surgically joining two vessels or tubes. A printed organ would ultimately have to be anastomosed to the patient's own circulation.
Autologous
Derived from the same individual who will receive it. Autologous tissue is not rejected by the immune system, which is the central promise of bioprinting.
Allogeneic
Derived from a different individual of the same species. Can be manufactured in advance but carries rejection risk.
Bioink
A printable material containing living cells at the time of printing. Distinguished from a biomaterial ink, which is printed first and seeded with cells afterwards. Full guide →
Bioreactor
A vessel that keeps a printed construct alive and maturing — controlling temperature and gas, perfusing nutrients, and applying mechanical stimulation such as flow, stretch or compression.
Biofabrication
The broad term for automated manufacture of biological products, of which bioprinting is one branch.
Cardiomyocyte
A heart muscle cell. Those derived from stem cells tend to resemble foetal cells and require prolonged conditioning to mature.
Cross-linking
Forming bonds between polymer chains so a printed liquid becomes a solid gel. Triggered by light, ions, temperature or enzymes.
Cytotoxicity
The extent to which something kills or damages cells. Every component of a bioink, including photoinitiators and cross-linking agents, must be assessed for it.

D – H

dECM (decellularised extracellular matrix)
Real tissue stripped of its cells, leaving the native matrix, which is then made into an ink. Carries the biochemical signature of the source organ, at the cost of batch variability.
Decellularisation
Removing all cells from a tissue or whole organ with detergents while preserving the matrix and, in whole organs, the entire vascular tree. An alternative route to organ engineering that avoids printing vessels.
Differentiation
The process by which an unspecialised stem cell becomes a specific cell type.
DLP (digital light processing)
Light-based printing in which a projector cures an entire layer of photosensitive resin at once, rather than tracing it point by point.
Endothelial cell
The cell type lining the inside of blood vessels. Printed channels must be lined with them to behave like real vessels.
Extracellular matrix (ECM)
The network of proteins and sugars that cells build around themselves. It provides structure and continuously signals to the cells embedded in it.
Extrusion bioprinting
Squeezing bioink through a nozzle as a continuous filament. The most common method: versatile and inexpensive, but it subjects cells to shear stress.
Fibrin
The clotting protein, formed from fibrinogen by thrombin. Strongly encourages blood-vessel growth, which makes it useful despite being mechanically weak.
FRESH
Freeform Reversible Embedding of Suspended Hydrogels. Printing inside a supporting gelatin bath that holds soft material in place until it sets, then melts away. What made collagen printable at scale.
GelMA (gelatin methacryloyl)
Gelatin chemically modified so it can be permanently cross-linked with light. Retains gelatin's cell-attachment sites while gaining tunable, stable stiffness. Close to a default bioink for soft tissue.
Hepatocyte
The main functional cell of the liver. Loses its liver-specific behaviour within days in flat culture, which is why three-dimensional arrangement matters so much for liver models.
Hydrogel
A polymer network swollen with water. The physical basis of almost every bioink, because cells need a wet, soft environment.

I – P

In situ bioprinting
Printing directly onto or into the patient, rather than making a construct in the laboratory and implanting it. Furthest advanced for skin.
Inkjet bioprinting
Firing individual droplets of cell suspension on demand. Fast, gentle and precise, but restricted to low-viscosity inks.
iPSC (induced pluripotent stem cell)
An adult cell reprogrammed back to an embryonic-like state, from which it can be differentiated into almost any cell type. The basis of patient-specific tissue without embryonic stem cells.
LAB / LIFT (laser-assisted bioprinting)
Laser-induced forward transfer: a laser pulse propels tiny volumes of bioink from a ribbon onto a substrate. No nozzle, so no clogging and minimal shear stress, but slow and expensive.
Microfluidics
Controlling fluids in channels of micrometre scale. Used inside some print heads to blend or sheath bioink as it is deposited.
Nephron
The functional filtration unit of the kidney. Each kidney contains around a million.
Organoid
A small, self-organising three-dimensional structure grown from stem cells that reproduces some architecture and function of a real organ. Millimetre-scale, and not a miniature organ.
Organ-on-a-chip
A microfluidic device containing living tissue arranged to reproduce an organ's key functions for testing purposes. Often combined with printed tissue.
PCL (polycaprolactone)
A slowly resorbable synthetic polymer, printed hot as a structural frame alongside soft bioinks to give a construct mechanical strength.
Perfusion
Flowing fluid through a tissue rather than around it. Required to keep anything thicker than a few millimetres alive.
Photoinitiator
A molecule that starts a cross-linking reaction when it absorbs light. Older ultraviolet-activated initiators can damage cells; visible-light alternatives such as LAP are now preferred.

Q – Z

Recellularisation
Repopulating a decellularised scaffold with new cells, ideally the recipient's own.
RGD
A short peptide sequence (arginine–glycine–aspartic acid) that cells recognise and bind to. Grafted onto otherwise inert materials such as alginate to give cells something to hold.
Sacrificial ink
A material printed where a channel is wanted, then dissolved and flushed away to leave a hollow, perfusable tube. Pluronic F-127 is the common choice.
Scaffold
A structure that supports cells and guides tissue formation. May be printed with cells inside it or seeded afterwards.
Shear stress
The mechanical force on cells as they are pushed through a nozzle. The main cause of cell death in extrusion bioprinting.
Shear thinning
The property of becoming less viscous under stress and recovering afterwards. A shear-thinning ink flows easily through a nozzle and stiffens the instant it leaves — ideal behaviour for printing.
Spheroid
A small ball of cells that have clustered together. Used as a building block in scaffold-free bioprinting, where adjacent spheroids fuse into continuous tissue.
SLA (stereolithography)
The original 3D printing method: curing photosensitive resin with light. Adapted for bioprinting using cell-compatible resins.
Tissue engineering
The broader discipline of combining cells, scaffolds and signals to restore or replace tissue. Bioprinting is one of its manufacturing techniques.
Vascularisation
Providing a tissue with a blood supply. The single greatest obstacle to printing solid organs. Why it is so hard →
Viability
The percentage of cells still alive after printing. Commonly 80–95 per cent depending on method, though it is usually measured within a day or two rather than after weeks of culture.
Volumetric bioprinting
Projecting light into a rotating vial of resin from many angles so that an entire object forms at once, in tens of seconds instead of hours.
Xenotransplantation
Transplanting organs between species, in practice from gene-edited pigs to humans. Not bioprinting, but currently the fastest-moving competing solution to organ scarcity.

Related

Last reviewed . Educational information only — not medical advice.