Bioprinting Glossary: Key Terms and Concepts

Bioprinting combines terminology from additive manufacturing, cell biology, biomaterials science, rheology, optics, tissue engineering, and pharmaceutical development. Understanding the relationships among these terms is essential because apparently similar concepts, such as viability and function, or pixel size and effective resolution, describe different aspects of a bioprinting experiment. This glossary defines the field through the complete workflow: Design, Material, Process, and Biology. It follows consensus biofabrication terminology, relevant scientific literature, and the current ASTM guide for bioinks.

3D bioprinting brings together concepts from engineering, biology, chemistry, materials science, medicine, and computer-aided manufacturing. As a result, the literature contains terms that appear interchangeable but describe meaningfully different processes or measurements.

For example:

• A hydrogel is not automatically a bioink.

• High post-print viability does not demonstrate tissue function.

• A printer’s pixel size does not establish its effective biological resolution.

• Perfusable channels do not necessarily constitute mature vasculature.

• A three-dimensional cell aggregate is not automatically an organoid.

• Regulatory interest in New Approach Methodologies does not automatically qualify a tissue model for regulatory use.

This glossary is organized alphabetically, but the terms belong to an interconnected system through four domains: Design, Material, Process, and Biology. Decisions in any one domain affect the others, and the construct continues to change during post-print culture and maturation.

Terms that are commonly confused

Term 1	Term 2	Main difference
Biofabrication	Bioprinting	Biofabrication is the broader field; bioprinting is one of its automated fabrication strategies.
Bioink	Biomaterial ink	A bioink contains living cells during fabrication; a biomaterial ink does not.
Hydrogel	Bioresin	A hydrogel is a hydrated polymer network; a bioresin is a light-processable precursor formulation.
Printability	Shape fidelity	Printability is the broader suitability for fabrication; shape fidelity describes how closely the result matches the intended geometry.
Resolution	Accuracy	Resolution concerns distinguishable feature size; accuracy concerns closeness to the intended position or dimension.
Accuracy	Precision	Accuracy is closeness to the correct value; precision is consistency among repeated results.
Cell viability	Tissue function	Viability indicates that cells remain alive; function indicates that they perform the required biological activity.
Spheroid	Organoid	A spheroid is a three-dimensional cell aggregate; an organoid additionally exhibits self-organization and aspects of organ-specific structure or function.
Vascularization	Perfusion	Vascularization concerns vessel formation; perfusion concerns fluid flow through a channel or vascular network.
Biocompatibility	Cytocompatibility	Biocompatibility concerns the response of a biological system; cytocompatibility focuses specifically on cellular responses.
DLP	MSLA	Both expose entire patterned layers, but DLP uses projected micromirrors whereas MSLA uses an LCD photomask.
Pixel size	Effective feature size	Pixel size is a hardware property; effective feature size also depends on optics, material chemistry, exposure, and processing.

Consensus terminology is particularly important for distinguishing biofabrication, bioprinting, bioassembly, bioinks, and biomaterial inks.

A

Acellular construct

A structure fabricated without living cells. Cells may be introduced later through surface seeding, perfusion, injection, or migration from surrounding tissue.

Additive manufacturing

A family of manufacturing processes that build objects from digital models by adding material, commonly in successive layers. Most bioprinting approaches are additive, although volumetric bioprinting polymerizes a complete three-dimensional region rather than tracing conventional layers.

Allogeneic

Cells or tissues obtained from another individual of the same species. Allogeneic cells can offer scalable, standardized sources but may introduce immune-compatibility considerations.

Anastomosis

The connection between two vessels or tubular structures. In tissue engineering, vascular anastomosis commonly refers to the connection of engineered vessels with host circulation or with another perfusion circuit.

Anisotropy

The property of behaving differently depending on direction. Skeletal muscle, myocardium, tendon, nerve, and many other tissues are anisotropic because their cells and extracellular matrices are directionally organized.

Accuracy

How closely a measured or fabricated feature matches its intended position, dimension, or value. Accuracy should not be confused with precision, which describes repeatability.

Autologous

Cells or tissues obtained from the same individual who will receive or be represented by the construct. Autologous approaches may reduce immune incompatibility but are often limited by patient-specific manufacturing time, cell availability, and variability.

B

Bioassembly

The automated organization of preformed biological building blocks—such as spheroids, organoids, cell sheets, or tissue strands—into a larger construct.

Unlike conventional extrusion, bioassembly does not necessarily deposit a cell–hydrogel formulation. It may instead position multicellular units that subsequently fuse and remodel.

Biofabrication

The automated production of biologically functional products with structural organization from cells, biomaterials, bioactive molecules, cellular aggregates, or hybrid constructs.

Biofabrication is the broadest relevant term and includes bioprinting and bioassembly as complementary strategies.

Biofabrication window

The range of material properties and processing conditions in which acceptable fabrication performance overlaps with acceptable cellular compatibility and biological function.

For extrusion, this may involve balancing viscosity, yield stress, recovery, flow, nozzle diameter, and cell stress. For light-based printing, it may involve polymer concentration, optical penetration, photoinitiator concentration, wavelength, exposure dose, and cell density.

The biofabrication window is not a universal specification for a material. It depends on the entire material–printer–cell–geometry combination.  

Bioink

A formulation containing living cells that is processed during biofabrication.

The cells are an intrinsic part of the formulation at the time of printing or assembly. A cell-free hydrogel should therefore not be called a bioink merely because cells will be seeded onto it later.

Biomaterial ink

A material formulation processed without cells. It may form a scaffold, mechanical frame, sacrificial structure, microfluidic device, support material, or cell-seeding substrate.

A formulation can function as a biomaterial ink in one experiment and become a bioink when living cells are added before fabrication.

Biocompatibility

The ability of a material or construct to perform in a particular biological application with an appropriate host response.

Biocompatibility is context-dependent. A material suitable for short-term in vitro culture may not be suitable for implantation, blood contact, or long-term degradation in vivo.

Bioprinting

The computer-controlled spatial organization of cells, biomaterials, and biological components to fabricate three-dimensional constructs.

Most bioprinting methods use additive or layer-wise deposition. Modern usage also includes technologies such as volumetric bioprinting that spatially polymerize an entire volume rather than building it through conventional layers.

Bioreactor

A controlled culture system used to support tissue growth, differentiation, remodeling, or maturation.

Depending on the tissue, a bioreactor may provide perfusion, oxygen control, electrical pacing, mechanical loading, cyclic strain, pressure, or automated medium exchange.

Bioresin

A liquid or flowable formulation designed for light-based fabrication.

A bioresin normally contains a photo-reactive polymer or macromer and a compatible photoinitiator. It may be cell-laden, in which case it can meet the definition of a bioink, or cell-free, in which case it is more precisely a biomaterial ink.

C

CAD

Computer-aided design: software-based creation or modification of three-dimensional geometries.

CAD models may describe simple lattices, perfusion channels, tissue interfaces, anatomical shapes, or microfluidic devices.

Cell density

The number of cells per unit volume of bioink, tissue, or culture medium.

Cell density affects biological signaling, viscosity, optical scattering, sedimentation, nutrient consumption, crosslinking, and the probability of nozzle obstruction.

Cell-laden

Containing living cells within a material or structure.

A cell-laden hydrogel may be a bioink before printing or a cell-containing construct after gelation.

Cell sedimentation

The movement of cells toward the bottom of a syringe, cartridge, or vat under gravity.

Sedimentation can create spatial differences in cell density during long prints, particularly in low-viscosity formulations.

Cell viability

The proportion or number of cells that remain alive under defined conditions.

Viability does not demonstrate that cells retain the correct phenotype, proliferate, differentiate, communicate, or perform tissue-specific functions.

Coaxial bioprinting

Extrusion through two concentric flow channels to produce a core–shell filament.

Coaxial printing can be used to fabricate hollow tubes, encapsulated cell populations, layered filaments, or structures in which the core contains a crosslinker or sacrificial material.

Construct

A general term for the physical structure produced during tissue engineering or biofabrication.

A construct may be cell-free or cell-laden, temporary or mature, scaffold-based or scaffold-free. Calling something a construct does not imply that it has achieved tissue-level function.

Crosslink density

The degree of connectivity among polymer chains within a network.

Higher crosslink density commonly increases stiffness and reduces swelling, molecular diffusion, and chain mobility. Its biological effect depends on the polymer, degradation mechanism, ligand availability, and cell type.

Crosslinking

The formation of connections between polymer chains that converts a liquid or weak precursor into a more stable network.

Crosslinking may be physical or covalent and may occur before printing, during deposition, after printing, or sequentially through more than one mechanism.

Cure depth

The depth to which a photosensitive formulation polymerizes under a specified wavelength, irradiance, exposure time, and composition.

Cure depth must be coordinated with layer height in MSLA and DLP printing. It is influenced by photoinitiator concentration, absorbers, cells, particles, polymer concentration, and optical scattering.

Cytocompatibility

The compatibility of a material or process with living cells.

Cytocompatibility can include viability, proliferation, morphology, phenotype, metabolism, and function. It should always be evaluated using the intended cells and exposure conditions.

D

Decellularization

The removal of cellular material from a tissue while attempting to retain useful extracellular-matrix components and architecture.

The result depends on the tissue, detergents, enzymes, physical processing, sterilization, and quality-control criteria.

Decellularized extracellular matrix

dECM: extracellular material derived from a decellularized tissue.

Solubilized dECM can form hydrogels or be chemically modified for printing. Its principal rationale is source-tissue biochemical context, although the resulting material is not identical to living native ECM and may vary with processing and biological source.

MatriXpec™ is TissueLabs’ family of tissue-derived dECM hydrogels, available in thermal, photo, and ionic formats for 15 source tissues.

Degradation

The breakdown or loss of a material network over time.

Degradation may occur through hydrolysis, enzymes, ion exchange, dissolution, reversible bond exchange, or cellular remodeling. The appropriate rate depends on whether the matrix is intended as temporary support, a long-term scaffold, or an in vitro assay environment.

DICOM

Digital Imaging and Communications in Medicine: the standard format and communication system used for many clinical imaging datasets.

DICOM files can contain image data, patient metadata, voxel dimensions, slice geometry, and spatial orientation information. Patient data must be handled according to applicable privacy and research requirements.

Digital light processing

DLP: a light-based vat-polymerization method that uses a digital micromirror device to project a patterned image onto a photosensitive material.

An entire layer can be exposed simultaneously. Effective performance depends on projection optics, irradiance, calibration, resin chemistry, and optical penetration.

Droplet-based bioprinting

A family of techniques that deposits discrete droplets rather than continuous filaments.

Examples include thermal inkjet, piezoelectric inkjet, valve-based deposition, acoustic droplet ejection, and some laser-assisted methods.

E

Effective resolution

The smallest feature that can be reproduced consistently in the intended material and geometry.

Effective resolution is generally more meaningful than motor step size, nozzle diameter, or pixel pitch alone because it includes material spreading, light diffusion, crosslinking, shrinkage, swelling, and post-processing.

Embedded bioprinting

Printing within a temporary support medium rather than depositing material into air.

The support medium prevents weak or slow-gelling filaments from collapsing and can enable the fabrication of soft collagen, fibrin, dECM, and other biologically relevant hydrogels.

Endothelialization

The formation of an endothelial-cell lining on the internal surface of a channel, tube, or scaffold.

Endothelialization is important for vascular models because a hollow channel alone does not reproduce vascular barrier function, antithrombotic behavior, or endothelial signaling.

Extracellular matrix

ECM: the noncellular network of proteins, glycoproteins, proteoglycans, glycosaminoglycans, and associated molecules surrounding cells.

The ECM provides structural support but also regulates adhesion, signaling, migration, differentiation, diffusion, and tissue remodeling. Tissue-specific differences in ECM composition and mechanics are a central rationale for tissue-derived bioinks.

Exposure dose

The optical energy delivered per unit area during photocrosslinking.

As a first approximation, exposure dose is irradiance multiplied by exposure time. Biological and polymerization effects also depend on wavelength, spectrum, photoinitiator absorption, oxygen, formulation, and repeated exposure.

Extrusion bioprinting

The deposition of a continuous material filament through a nozzle using pneumatic, piston-driven, screw-driven, or related actuation.

Extrusion is particularly useful for multimaterial constructs, high cell concentrations, organoids, support-bath printing, large structures, and coaxial fabrication.

F

Filament

The continuous strand deposited during extrusion printing.

Filament diameter can differ from nozzle diameter because of material swelling, spreading, flow rate, print speed, nozzle height, rheology, and crosslinking.

FRESH

Freeform Reversible Embedding of Suspended Hydrogels: an embedded-printing method in which a soft material is deposited within a removable support bath.

FRESH enables complex fabrication using materials that would otherwise collapse before gelation, including collagen and other soft hydrogels.

Functional validation

Testing whether a construct performs the biological activity relevant to its intended tissue or application.

Examples include contraction in cardiac tissue, albumin production in liver tissue, insulin secretion in pancreatic constructs, barrier resistance in epithelial models, or electrophysiological activity in neural tissues.

G

G-code

A machine-control language used by many extrusion and additive-manufacturing systems.

G-code can specify motion coordinates, speed, extrusion, tool changes, temperature, crosslinking, and pauses. Light-based printers commonly represent layer geometry through image-mask stacks rather than conventional extrusion toolpaths.

Gel point

The transition at which a polymer system develops a connected network and begins to behave predominantly as a gel.

In oscillatory rheology, it is sometimes approximated by the point at which storage and loss moduli intersect, although the appropriate interpretation depends on the material and test method.

GelMA

Gelatin methacryloyl: gelatin chemically modified with methacryloyl groups so it can undergo light-initiated polymerization.

GelMA retains some gelatin-derived cell-interaction and degradation motifs while enabling tunable photocrosslinking. Its performance depends on source gelatin, bloom strength, degree of functionalization, concentration, temperature, initiator, and light dose.

Grayscale printing

A light-based fabrication method in which pixel intensity is varied to change local exposure dose.

In a calibrated material, grayscale exposure can generate spatial differences in crosslink density, stiffness, swelling, or degradation. Grayscale values do not correspond to universal material properties.

H

Hydrogel

A water-rich polymer network.

Hydrogels are widely used because their hydrated environment can support cell encapsulation and molecular transport. A hydrogel is not automatically printable, cell-compatible, tissue-specific, or a bioink.

Hydrogel precursor

The polymer-containing formulation before complete gelation or crosslinking.

A precursor may be a liquid, shear-thinning paste, partially gelled formulation, or light-sensitive bioresin.

I

Infill

The internal pattern and material density generated within an extrusion-printed object.

Common infill patterns include rectilinear, honeycomb, and gyroid-like designs. Infill affects pore size, permeability, mechanical properties, print time, and available space for cells.

Inkjet bioprinting

Droplet generation using thermal, piezoelectric, or related actuation.

Inkjet methods can provide rapid, localized deposition but generally require low-viscosity formulations and careful control of droplet formation, cell concentration, and nozzle obstruction.

In situ bioprinting

Fabrication directly at a tissue defect or surgical site.

The method may use extrusion, spraying, light-based curing, or robotic deposition. Important challenges include sterility, anatomical registration, tissue motion, crosslinking, and integration.

Intravital bioprinting

Fabrication within living tissue, potentially without fully exposing the target site.

Experimental approaches have used multiphoton or trans-tissue light-based polymerization. Intravital bioprinting remains primarily a research concept rather than a routine clinical process.

Induced pluripotent stem cell

iPSC: a somatic cell reprogrammed into a pluripotent state.

iPSCs can generate many specialized cell types and support patient-specific modeling. Their limitations include differentiation complexity, batch variability, genetic quality control, incomplete maturation, and potential residual pluripotent cells.

Ionic crosslinking

Network formation through electrostatic interactions between polymers and multivalent ions.

Calcium-mediated alginate gelation is the most familiar example. Ionic crosslinking is rapid and light-free, but the resulting bonds may weaken through ion exchange during culture.

L

Layer height

The vertical distance between successive layers or build-platform positions.

In extrusion, layer height must be coordinated with nozzle diameter and filament dimensions. In vat photopolymerization, it must be compatible with measured cure depth.

Laser-induced forward transfer

LIFT: a nozzle-free printing method in which a laser pulse transfers material from a donor layer to a receiving substrate.

LIFT can achieve localized deposition without nozzle clogging but requires specialized donor preparation and optical equipment.

Light-based vat-polymerization bioprinting

A family of methods that uses patterned light to polymerize photosensitive biological or biomaterial formulations in a vat.

This family includes stereolithographic, DLP, MSLA, and volumetric approaches. Hardware, software, bioresin design, optical penetration, and biological assessment must be evaluated together.

Loss modulus

G″: the viscous, energy-dissipating component measured during oscillatory rheology.

A larger G″ contribution indicates more liquid-like behavior under the selected testing conditions.

M

Mask image

A two-dimensional exposure pattern used to define a layer in MSLA or DLP fabrication.

A print file contains an ordered series of masks plus parameters such as exposure, layer height, platform motion, and light intensity.

Maturation

The post-print development of more tissue-like structure and function.

Maturation may involve prolonged culture, perfusion, mechanical loading, electrical stimulation, differentiation, matrix remodeling, and cell–cell organization. It often requires much longer than fabrication itself.

Matrix remodeling

Cell-mediated alteration of the surrounding matrix.

Cells may degrade, reorganize, contract, or replace the original bioink through secretion of enzymes and new ECM. Remodeling means that the final tissue can differ substantially from the day-zero print.

Mechanotransduction

The conversion of mechanical information—such as stiffness, stretch, pressure, or shear—into cellular biochemical signals.

Mechanotransduction explains why the mechanical properties of a bioink are biological variables rather than purely structural specifications.

Mesh

A digital surface representation composed of vertices, edges, and faces.

Meshes must generally be watertight, manifold, consistently oriented, and free of problematic self-intersections before reliable slicing.

Microphysiological system

MPS: an in vitro system designed to reproduce selected aspects of human tissue or organ physiology.

MPS platforms may incorporate several cell types, flow, mechanical cues, sensors, and tissue interfaces. Organ-on-chip devices are a prominent subset of MPS. The FDA and NCATS describe MPS as potentially useful New Approach Methodologies.

Multimaterial bioprinting

Fabrication using more than one material, bioink, cell population, or crosslinking system.

Multimaterial printing may use several printheads, sequential deposition, coaxial nozzles, vat changes, or inline mixing.

MSLA

Masked stereolithography: a vat-photopolymerization method in which an LCD panel acts as a programmable mask between an LED source and the bioresin.

MSLA exposes an entire patterned layer at once. Its effective performance depends on pixel size, irradiance, uniformity, wavelength, formulation, and calibration.

TissueRay™ is TissueLabs’ MSLA system and uses 405, 450, and 530 nm illumination with grayscale exposure.

N

New Approach Methodology

NAM: a broad term covering methods that may improve or replace traditional approaches to safety, efficacy, or biological assessment.

FDA usage includes in vitro, in chemico, and in silico methods and may encompass organ-on-chip systems, computational models, advanced cell assays, and human tissue models. A model’s classification as a NAM does not by itself establish regulatory qualification.

Nozzle gauge

A standardized size designation commonly used for dispensing needles.

Gauge number and inner diameter are inversely related: a higher gauge generally corresponds to a smaller opening. Because dimensions vary among manufacturers and nozzle types, inner diameter should be reported directly whenever possible.

Nominal resolution

A resolution value derived from a hardware property, such as motor step, nozzle diameter, pixel pitch, or optical voxel.

Nominal resolution should not be interpreted as the smallest biological feature that can be fabricated reproducibly.

O

Organoid

A self-organizing three-dimensional cellular system that reproduces selected structural, developmental, or functional characteristics of an organ.

Organoids may originate from pluripotent stem cells, adult stem cells, progenitors, or tissue fragments. They do not reproduce every component or function of the corresponding organ.

Organ-on-chip

A microengineered system that recreates selected tissue interfaces and physiological conditions in a controlled device.

Organ-on-chip platforms may incorporate perfusion, mechanical forces, epithelial barriers, vascular compartments, or interactions among tissues. They are generally a subset of microphysiological systems.

Optical penetration depth

The distance through a photosensitive material over which light remains sufficient to drive meaningful polymerization.

It depends on wavelength, absorbers, scattering, cells, particles, initiator, and polymer composition.

P

Parenchymal cell

A cell responsible for a tissue’s principal specialized function.

Examples include hepatocytes in liver, cardiomyocytes in myocardium, neurons in neural tissue, and β-cells in pancreatic islets.

Perfusion

The controlled movement of fluid through a tissue, channel network, or culture chamber.

Perfusion improves convective transport and can provide physiologically relevant shear. A perfused channel is not necessarily a mature blood vessel.

Photoinitiator

A molecule or molecular system that absorbs light and generates reactive species capable of initiating polymerization.

The initiator must be matched to the illumination spectrum. Its concentration, by-products, radical generation, and exposure conditions can affect both curing and cellular performance.

Photocrosslinking

The formation of a polymer network triggered by light.

Photocrosslinking offers spatial and temporal control but depends on polymer functionalization, initiator, wavelength, irradiance, exposure, oxygen, and optical attenuation. Visible light can be advantageous in some systems, but wavelength alone does not establish cytocompatibility.

Piston-driven extrusion

Mechanical extrusion in which a motor or actuator advances the syringe plunger.

Piston actuation provides direct control over nominal displacement and usually faster start–stop response than compressed-gas actuation. Material rheology, syringe compliance, friction, and nozzle resistance still influence the deposited filament.

TissueStart™ and TissuePro™ use piston-based volumetric microextruders.

Pneumatic extrusion

Extrusion in which compressed gas applies pressure to a syringe or cartridge.

Pneumatic systems have simple printhead architecture and extensive historical use. Flow is controlled indirectly and depends on pressure, material rheology, temperature, nozzle resistance, and gas compressibility.

Precision

The consistency of repeated measurements or fabricated features.

A system can be precise but inaccurate if it produces the same dimensional error repeatedly.

Printability

The suitability of a material for a specified fabrication process.

For extrusion, printability may include extrusion continuity, recovery, filament formation, pore fidelity, stacking, and collapse resistance. It does not automatically include cell function or long-term tissue performance. The absence of universally applied tests is a recognized standardization challenge.

R

Recovery

The ability of a material to restore structure after deformation or shear.

Rapid recovery can help an extruded filament retain its shape after leaving the nozzle.

Regenerative medicine

A field focused on restoring, replacing, or regenerating damaged cells, tissues, or organs.

Regenerative medicine includes but is not limited to bioprinting, stem-cell therapy, gene therapy, tissue engineering, biomaterials, and endogenous repair strategies.

Resolution

The ability to distinguish or fabricate separate features.

Resolution can refer to XY detail, Z layer definition, spatial cell placement, or imaging. The measurement method and material must be stated.

Rheology

The study of material deformation and flow.

In bioprinting, rheology is used to characterize viscosity, shear thinning, yield stress, viscoelasticity, recovery, gelation, and time-dependent behavior. The relevant rheological requirements differ between extrusion bioinks and vat bioresins.

S

Sacrificial ink

A temporary material printed to occupy space and subsequently removed.

Sacrificial inks are commonly used to create hollow channels, perfusion networks, or temporary supports.

Scaffold

A material structure intended to support cell attachment, organization, transport, or tissue formation.

Scaffolds can be acellular, cell-seeded, degradable, permanent, porous, fibrous, or hydrogel-based.

Scaffold-free bioprinting

Fabrication primarily from cells, spheroids, organoids, or tissue strands without relying on a persistent exogenous structural matrix.

Temporary supports or handling materials may still be used during assembly.

Segmentation

The process of identifying and labeling a target structure within imaging data.

Segmentation converts CT, MRI, microscopy, or other volumetric datasets into defined regions that can be transformed into three-dimensional models.

Shear stress

Tangential force per unit area generated by material flow.

During extrusion, shear stress varies across the nozzle and depends on geometry, flow, rheology, and wall interactions. Its biological effects depend on magnitude, duration, cell type, and protective characteristics of the material.

Shear thinning

A flow behavior in which apparent viscosity decreases as shear rate increases.

Shear thinning can facilitate extrusion because the material flows more easily inside the nozzle while becoming more viscous after deposition. It should not be confused with thixotropy, which specifically includes time-dependent structural change.

Shape fidelity

How closely the fabricated construct matches the intended geometry.

Shape fidelity can be assessed through filament width, pore shape, channel diameter, layer alignment, dimensional error, collapse, or volumetric comparison.

Slicing

The conversion of a three-dimensional digital model into fabrication instructions.

Extrusion slicing generates toolpaths and parameters such as layer height, speed, infill, and material assignment. Light-based slicing generates exposure masks and layer-specific optical settings.

Spheroid

A three-dimensional multicellular aggregate, commonly produced through cell–cell adhesion and self-assembly.

Spheroids may be homogeneous or contain several cell types. Unlike organoids, they do not necessarily reproduce organ-specific developmental architecture or functions.

Storage modulus

G′: the elastic, energy-storing component measured during oscillatory rheology.

G′ is useful for comparing gel-like behavior but is not equivalent to Young’s modulus, compressive modulus, or native tissue stiffness.

Stress relaxation

The time-dependent decrease in stress when a viscoelastic material is held at constant deformation.

Stress relaxation influences how cells spread, grow, migrate, and remodel a matrix even when two materials have similar initial stiffness.

Support bath

A temporary medium that mechanically supports a material during embedded printing.

An effective support bath yields around the moving nozzle, rapidly recovers afterward, stabilizes the deposited filament, and can be removed without damaging the construct.

SWIFT

Sacrificial Writing Into Functional Tissue: a method in which sacrificial channels are written within a dense cellular or organoid-based matrix.

Removal of the sacrificial material creates perfusable channels through an already cell-dense tissue.

T

Thermal gelation

Temperature-driven formation or strengthening of a polymer network.

Examples include collagen fibrillogenesis near physiological temperature, gelatin gelation during cooling, and thermogelling dECM. Thermal gelation is sometimes called thermal crosslinking, although many such networks are stabilized by reversible physical interactions rather than permanent covalent bonds.

Thixotropy

Time-dependent structural breakdown under sustained shear followed by recovery when shear is removed.

A material can be shear-thinning without being strongly thixotropic; the concepts describe related but distinct behavior.

Tissue engineering

The use of cells, materials, biological signals, and engineering principles to restore, maintain, replace, or model tissue function.

Bioprinting is one tool within tissue engineering, not a synonym for the entire field.

Tissue model

An experimental biological system designed to reproduce selected characteristics of a tissue.

A model does not need to recreate an entire organ to be useful, but it must reproduce the mechanism or functional endpoint relevant to its intended question.

Triaxial bioprinting

Extrusion through three concentric channels.

Triaxial configurations can produce multilayer tubes, more complex encapsulation systems, or constructs resembling layered vessel walls.

V

Validation

The documented demonstration that a method, model, or assay is fit for its intended purpose.

Validation may examine accuracy, precision, robustness, reproducibility, sensitivity, specificity, and comparison with reference data. Regulatory validation is substantially more demanding than showing feasibility in a research publication.

Vascularization

The formation or incorporation of vessel-like networks within a tissue.

Vascularization can include printed macrochannels, endothelialized lumens, self-assembled capillaries, angiogenic sprouting, and connection with host circulation.

Viscoelasticity

Material behavior combining viscous flow and elastic recovery.

Hydrogels and tissues are commonly viscoelastic rather than perfectly elastic or perfectly fluid.

Viscosity

A measure of resistance to flow.

For non-Newtonian bioinks, viscosity must be reported together with shear rate, temperature, and measurement method. A single viscosity value may not describe how the material behaves during printing.

Voxel

A three-dimensional volume element.

In optical fabrication, a voxel may refer to the smallest addressable or polymerized three-dimensional region. It should not be confused with a two-dimensional pixel.

Y

Yield stress

The minimum stress required for a material to begin flowing appreciably.

An extrusion bioink with sufficient yield stress can resist spreading after deposition. Excessive yield stress may require greater extrusion force and increase process difficulty.

Young’s modulus

A measure of elastic stiffness based on the ratio of stress to strain under defined loading conditions.

Young’s modulus should not be treated as interchangeable with storage modulus. The values are obtained through different tests and represent different aspects of material behavior.

TissueLabs platform terminology

These terms describe specific implementations of the scientific concepts defined above.

MatriXpec™

A portfolio of tissue-derived dECM hydrogels for 15 source tissues.

• MatriXpec Thermo: thermogelling format for 3D culture, casting, and support-bath workflows.

• MatriXpec Photo: photocrosslinkable format for extrusion or compatible light-based fabrication.

• MatriXpec Ionic: alginate-containing format stabilized through calcium-mediated ionic crosslinking.

Mixtrusor™

An inline mixing system that combines material streams before extrusion. It can support homogeneous mixtures, changing compositions, or material gradients.

TissueCloud™

TissueLabs’ software environment for preparing and controlling compatible bioprinting workflows.

TissuePro™

A five-head piston-extrusion platform designed for multimaterial, coaxial, triaxial, temperature-controlled, and multiwavelength workflows.

TissueRay™

A masked-stereolithography platform for photocurable bioresins, fine hydrogel architectures, grayscale exposure, microfluidics, and organ-on-chip applications.

TissueStart™

A compact two-head piston-extrusion platform intended for open-material, multimaterial, coaxial, and integrated photocuring workflows.

How to use bioprinting terminology correctly

Terminology should be connected to the actual measurement or experiment.

Instead of writing:

“The bioink had high viscosity and excellent printability.”

Report:

“The formulation showed shear-thinning behavior between the tested shear rates, recovered 82% of its pre-shear storage modulus within 60 seconds, and produced continuous filaments with a spreading ratio of 1.15.”

Instead of:

“The printer has 35 µm resolution.”

Report:

“The system has a nominal XY pixel pitch of 35 µm; the minimum reproducible channel width in the specified bioresin was measured separately.”

Instead of:

“The cells were biocompatible.”

Report:

“Post-print viability, metabolic activity, phenotype, and tissue-specific function were assessed at the stated time points.”

Instead of:

“The model is a validated NAM.”

Report:

“The model was evaluated for the defined context of use using reference compounds, acceptance criteria, intra-run precision, inter-run reproducibility, and comparison with relevant human data.”

Precise terminology improves reproducibility because it forces researchers to distinguish hardware specifications from material performance, material performance from cellular responses, and cellular survival from functional tissue behavior.

Conclusion

The language of bioprinting reflects the field’s interdisciplinary nature. Digital-design terms describe how the construct is represented; rheological and chemical terms describe how the material flows and stabilizes; biological terms describe how cells respond and mature; and translational terms describe how the resulting model or therapeutic product must be validated.

The most important conceptual distinctions are:

• Biofabrication is broader than bioprinting.

• Bioinks contain cells; biomaterial inks do not.

• Printability is not the same as tissue function.

• Nominal resolution is not effective resolution.

• Perfusion is not equivalent to vascularization.

• Viability is only the first level of biological assessment.

• The printed construct is the beginning of tissue development, not its end.

Using these terms consistently helps laboratories design better experiments, report them more clearly, and compare results across materials, printers, and institutions.

Frequently asked questions

What is the difference between biofabrication and bioprinting?

Biofabrication is the broader field encompassing automated production from cells, biomaterials, bioactive components, and cellular aggregates. Bioprinting is one fabrication strategy within biofabrication. Bioassembly is another.

Can a material without cells be called a bioink?

Under the consensus definition, no. A printable formulation without cells is a biomaterial ink. It becomes a bioink when living cells are incorporated as an intrinsic component of the formulation during fabrication.

What is the difference between a hydrogel and a bioink?

A hydrogel is a hydrated polymer network. A bioink is a cell-containing formulation used during biofabrication. A hydrogel may be used as a bioink, biomaterial ink, culture matrix, coating, or support bath.

What is the biofabrication window?

The biofabrication window is the application-specific range in which a formulation can be fabricated with adequate quality while preserving acceptable cellular compatibility and function.

Is printability the same as shape fidelity?

No. Shape fidelity is one component of printability. Printability may also include reliable flow, filament continuity, stacking, recovery, curing, process stability, and compatibility with the intended printer.

What is the difference between a spheroid and an organoid?

A spheroid is a three-dimensional cell aggregate. An organoid additionally shows self-organization and selected organ-specific developmental, structural, or functional characteristics.

What is the difference between MSLA and DLP?

Both expose patterned layers of photosensitive material. DLP projects the image using a digital micromirror device, while MSLA transmits patterned light through an LCD photomask.

Does high cell viability mean a bioprinted tissue is successful?

Not by itself. Viability establishes that cells remain alive. A successful tissue model must also demonstrate appropriate organization, phenotype, maturity, reproducibility, and function.