Page 12 - IJB-9-2

International Journal of Bioprinting Extrusion-based biomaterial inks

of 3D microstructure or scaffolds and cause collapse or embedded bioprinting and co-axial bioprinitng. For
deformation. The mechanical behavior like structure– gel-bath embedded bioprinting, the properties of ink
property relationships should also be given attention as printability mentioned above are more applicable to
they could affect the degradability and degradation process supporting matrix. The supporting matrix should possess
of biomaterials ink. rheological properties, including yield stress, shear-
thinning, and self-healing . To easily allow nozzle
[21]
2.3. Mechanical strength movement, the yield stress should be lower than the shear
Biomaterial inks possess suitable mechanical strength to stress, which is generated by the moving of nozzle inside
maintain the structural stability of 3D-printed construct the supporting matrix. This property allows the nozzle to
and balance the specific forces within the structure. It insert, translate, and deposit bioinks inside the supporting
is very important to maintain the function of printed matrix. In addition, the storage modulus G’ should be
construct, which can be done by selecting biomaterial larger than that of supporting matrix, or else, the printed
inks with corresponding mechanical and structural filaments would become discontinuous.
properties according to different tissue or organ types and
the requirements of their elastic modulus. In this regard, However, the printability performances of liquid-bath
bioprinting a scaffold-based or embedded hollow vessel embedded bioprinted and co-axial bioprinted bioinks focus
with biomaterial inks will also affect the mechanical strength on fast curing, instead of rheological properties. Alginate
of the final printed structure. Therefore, it is necessary to is commonly used in co-axial bioprinting and liquid-
reasonably optimize the design of 3D structure according bath bioprinting. Colosi et al. investigated the printability
to material properties and experimental requirements, of core ink with different alginate concentrations and
especially to meet the mechanical properties of the native shell crosslinking solution with different calcium
tissue. chloride concentrations in microfluidic-based co-axial
bioprinting . The printability of the bioinks was achieved
[22]
2.4. Printability by increasing the concentration of alginate and decreasing
Extrusion-based bioprinting renders biomaterial inks with the concentration of the calcium chloride solution. The
a continuous linear shape, rather than a droplet shape, at bioinks exhibited a Newtonian behavior in the range of
the nozzle by extrusion, and directly stacks the inks into shear rate and low viscosity, which are different from the
3D structure. The printability of biomaterial inks relies on general extrusion-based bioprinting inks.
neither liquid nor solid state, but non-Newtonian fluids
with certain viscosity. Generally, biomaterial inks with 2.5. Solidification formability
viscosity greater than 30 mPa·s are suitable for extrusion- Solidification formability refers to the performance of
based bioprinting . The extrusion of biomaterial inks is biomaterial inks related to hydrogel forming or material
[10]
a process of applying shear force, and the rheology and curing, which is a prerequisite to construct 3D structure.
viscoelasticity of biomaterials affect its printability. The The gel crosslinking method will affect the deposition of
rheological properties of biomaterial inks are the decisive 3D structure and further affect its printability. According
factor of printability in extrusion-based bioprinting . to the external action mode, extrusion-based bioprinting
[20]
The fluid viscoelasticity has two important parameters hydrogel can be divided into five types of crosslinking
named viscosity modulus and elastic modulus. The methods: temperature-dependent crosslinking, reagent
viscosity modulus is also called storage modulus G’, which AB crosslinking, photopolymerization crosslinking, self-
represents the solid property of fluid. The elastic modulus is assembly polymerization, and combinatory type, as shown
also known as loss modulus G’’, which represents the liquid in Figure 3.
property of fluid. Extrusion-based printability reflects that In temperature-dependent crosslinking, the
the solid properties of biomaterial inks are not weaker printing temperature will affect printability, and the
than the liquid properties under printing conditions, crosslinking of hydrogels or biomaterial inks can be
that is, the viscosity modulus should be equal to or even achieved by controlling the temperature during or after
higher than the elastic modulus to ensure the formation printing process. 3D constructs based on decellularized
of 3D structures. Shear thinning performance is the basic extracellular matrix (dECM) were precisely stacked
performance of extrusion-based printability to form a using a cell printing system equipped with heating
continuous fluid; the apparent viscosity of biomaterial inks modules . Different heating conditions altered the
[23]
decreases with the increase of shear stress, and increases saturated temperature, resulting in a change in the
the fluidity during extrusion process. elastic modulus of the dECM bioink, affecting the gel
The principles of extrusion-based printability are formation, and ultimately causing an increase or decrease
different for specific bioprinting strategies, such as in printing fidelity. The crosslinked photopolymers, such

Volume 9 Issue 2 (2023) 4 https://doi.org/10.18063/ijb.v9i2.649