Page 432 - IJB-9-2

International Journal of Bioprinting Shear-thinning and bioprinting parameters

manage to imitate the desired scenario. In the present 2.2. Rheological characterization
study, we used the COMSOL multiphysics software The rheological properties of the hydrogels were determined
package. This allows the model to be defined in terms with a rotational rheometer (Discovery DHR-2, TA
of its geometry and constraints and the fluid’s physical Instruments), using a 40 mm parallel plate with a gap of
conditions. It applies adaptive meshing to allow the 550 μm. Before testing, the samples were left to stand for
problem to be solved through use of finite element 5 min to allow them to reach mechanical and temperature
method calculations. equilibrium.

In short, the purpose of this study was to form and Shear viscosity experiments were carried out with shear
characterize different alginate-based hydrogels, determine rates between 0.01 and 1000 s , at a temperature of 37°C,
-1
and catalogue their rheological behavior parameters, to obtain the mathematical relationship between shear
and finally simulate bioprinting processes under certain stress and shear rate and hence the dynamic viscosity of
conditions. The intention was to analyze the possible the hydrogels.
existence of relationships between the rheological
parameters or behavior of the hydrogel and the parameters 2.3. Modeling
of the bioprinting processes used. COMSOL multiphysics were used to construct a 2D

2. Materials and methods axisymmetric model together with a two-phase flow level
set interface. We started from the real model (Figure 1)
2.1. Reconstitution of hydrogels which consists of the union of the syringe containing
Alginate-based hydrogels were selected and used, because the biomaterial, where the bioprinter exerts pressure, the
®
they are the most widely used hydrogels by the scientific nozzle (model 22G, Cellink ), and the extrusion zone of
community for bioprinting . The proportions of 3.5%, air at ambient conditions. The geometry was modeled
[12]
4.0%, and 5.0%, combined with 3.5% CaCl , were chosen using trapezoids, rectangles, and ellipses, taking into
2
to study the influence of these variations since these account different subdivisions of the extrusion zone to give
proportions are commonly used. an adaptive mesh.
The main materials to reconstitute the biomaterial Table 1. Composition and pH of the hydrogels used
were lyophilized alginate, a type-M reconstitution agent
(buffer solution was prepared so that the final solution has Hydrogel nomenclature % alginate % calcium chloride pH
physiological pH, making the resulting bioink suitable for Alginate 3.5% (3.5% CaCl ) 3.5 3.5 7.23
2
cell culture), and the ionic crosslinking agent CaCl , all of Alginate 4.0% (3.5% CaCl ) 4.0 3.5 7.21
2
them of the Cellink brand. 2
®
Alginate 5.0% (3.5% CaCl ) 5.0 3.5 7.19
2
The protocol followed to conform the alginate-based
hydrogel with CaCl ionic crosslinking agent begins by A B
2
preparing 2 mL of the reconstitution agent M. This solution
was mixed with 70 mg of CaCl to achieve a proportion
2
of 3.5% w/v. Once mixed, the solution was filtered into
a sterile 15-mL Falcon tube using a syringe and a sterile
0.22-μm syringe filter. Then, 2 mL of the resulting filtered
solution was mixed with 100 mg of lyophilized alginate,
previously tempered at room temperature, to obtain the
alginate-based hydrogel at 5% w/v. This mixture was
stirred with a magnetic stirrer at room temperature
for 1 h or until the lyophilized material has completely
dissolved. To obtain hydrogels in other proportions, the
corresponding proportions were modified and mixed
accordingly.
Once the hydrogel was formed, the pH was measured
and adjusted to within the physiological range of
between 7.0 and 7.4. The pH is also an important factor
for obtaining appropriate viscosity of the material. The Figure 1. (A) Real model. (B) The COMSOL multiphysics representation
resulting materials are listed in Table 1. of the model.

Volume 9 Issue 2 (2023) 424 https://doi.org/10.18063/ijb.687