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International Journal of Bioprinting 3D-printed nanocomposites: Synthesis & applications

stress is usually one order of magnitude lower than ink • Structural support: Shear-thinning materials can
yield stress to prevent filament breaking and enable fine support printing. The bioink’s viscosity can be
filament deposition. Ink and supporting bath should adjusted to maintain structural integrity during
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have equal viscosity, osmolality, and density to increase layer-by-layer printing by changing the shear rate.
print resolution. Supporting bath material and ink with Printing delicate scaffolds or complex anatomical
a weak interfacial tension prevents printed structures structures requires structural support.
from deforming. Microparticle size also affects extruded • Cell viability and biofunctionality: Shear-thinning
filament surface shape in granular supporting bath. materials can be biocompatible and promote cell
Microparticle “spurs” link filaments. In comparison to survival, proliferation, and differentiation. The
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larger granular gels, smaller and more uniform microgel controlled decrease in viscosity during printing
supporting media exhibit higher-resolution structures due reduces shear stress and mechanical damage to
to their lower stiffness, viscosity, and yielding stress.
encapsulated cells, preserving their viability and
3. Rheological aspects of 3D-printed functionality; therefore, living cells can be added
to bioink to create functional tissues and organs.
composites
• Complex tissue architecture: Shear-thinning
Previous studies suggest that bioinks must meet certain materials can create complex tissue architectures
chemical and physicochemical requirements to print with precise microstructure control. The
high-resolution constructs and provide a cell-friendly bioink’s ability to flow and conform to intricate
environment. Rheological property, which describes geometries allows it to create vascular networks,
material’s flow and deformation under stress, is the main heterogeneous tissue structures, and biochemical
factor affecting its printability and fidelity. Microextrusion- cue gradients. Biomimetic tissues that mimic
based bioprinting is widely studied due to its broad viscosity native tissue organization can be created.
range processability, ease of use, multimaterial printing
possibility, and high cell loading density; therefore., this Bioinks should have shear-thinning behavior and a
review will discuss the required rheological properties for viscosity suitable for extrusion to optimize flow during
microextrusion-based bioprinting. printing and stability after deposition. To achieve the
desired viscosity profile, rheological characterization
In microextrusion-based printing, bioink undergoes helps determine the bioink composition, including
high shear strains during extrusion and rests after biomaterials, crosslinkers, and additives. The printed
deposition. Viscosity, dynamic modulus, yield stress, structure is also required to solidify via a crosslinking
and elastic recovery are used to characterize the process; mechanism, such as physical crosslinking (temperature
extrudability, printability, and shape fidelity affect tissue or pH changes), chemical crosslinking (reactive groups),
construct feasibility; printability describes bioink’s ability or light-mediated crosslinking (photoinitiators).
to be extruded, form filaments, and stack up to create Additionally, the bioinks should be compatible with
constructs, while printing fidelity refers to the filaments’ encapsulated cells for high cell viability and functionality.
shape retention and is usually assessed by filament Cell adhesion, proliferation, and differentiation should be
diameter, uniformity, and gravity resistance. supported by the bioink composition while minimizing
3.1. Shear thinning and its impact in bioprinting cytotoxicity and inflammatory responses. These
Viscosity decreases with increasing shear rate in shear- interactions depend on biomaterials, growth factors, and
thinning materials. Due to their unique properties and cell-encapsulation methods.
potential to fabricate complex biological structures, 3.2. Viscoelasticity
these materials have garnered interest in 3D bioprinting. Viscoelasticity is a fundamental characteristic of materials
Effects of shear-thinning materials on 3D bioprinting, in demonstrating both elastic and viscous behaviors,
bioink formulation, and printed constructs are described significantly impacting the printed constructs’ structural
as follows:
integrity, cell viability, and functionality. The present
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• Printability and precise deposition: Shear-thinning section delves into the influence of viscoelasticity on
behavior allows bioinks to flow easily through the the process of bioprinting and deliberates on its effects
printing nozzle, allowing precise layer deposition. on the formulation of bioink, printing parameters,
Under shear stress, viscosity decreases, ensuring and the potential applications of tissue engineering.
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smooth flow and accurate cell and biomaterial The general method for determining a fluid’s viscosity
placement for high-resolution printed structures. involves placing the sample in the annulus of a series

Volume 10 Issue 2 (2024) 84 doi: 10.36922/ijb.1637