Page 435 - IJB-9-2

International Journal of Bioprinting Shear-thinning and bioprinting parameters

speed, the thinner the printing line that is deposited. For 3.3. Relationship between the rheology parameters
this reason, the extrusion time at which the 3 mm height and the bioprinting
mark is reached (ordinate scale in Figure 6) was determined Once the rheological parameters of the hydrogels had
for samples defined with the pressures set so that they been characterized and obtained (Table 2) and the values
would result in similar geometries. It would then be found related to bioprinting were found for similar extrusion of
how much faster or slower the extrusion is performed, and the different biomaterials (Table 3), the possible existence
this could be related to the head’s speed of movement.
of a relationship between these was sought.
The times required to pass the mark were set at 0.395
First, a relationship was sought between the pressure
s for the 3.5% alginate sample, 0.780 s for the 4% alginate applied by the bioprinter at the inlet and the flow behavior
sample, and 1.610 s for the 5% alginate sample. In other index, n, presented by various samples. Figure 7 shows a
words, to achieve the same line thickness in the 4% alginate straight-line fit for this relationship.
sample, it is necessary to apply 1.97 times the speed defined
for the 3.5% sample, and 4.07 times for the 5% alginate As shown in Figure 7, the linear fit is insufficiently
sample. acceptable to affirm that there is a clear relationship
between the two parameters. Similarly, a relationship was
The resulting pressure and time parameters related to
bioprinting for the different hydrogels are listed in Table 3. sought between this pressure and the second rheological
parameter obtained, that is, the consistency index, k
(see Figure 8).
According to Figure 8, which shows a good linear fit
for such parameters, it can be said that the consistency
index rheological parameter, k, is directly related to the
pressure that the bioprinter must apply to the biomaterial
for extrusion. In this way, with just one rheological test that
uses 0.620 mL of material, it is possible to determine the
input pressure that will allow good bioprinting with any
bioink. A present, a trial-and-error technique is usually
applied to find the said inlet pressure, leading to a large
amount of wasted biomaterial. By applying the relationship
presented above, the amount of material and the time used
can be reduced.
The second parameter that we intended to relate is
the dispensing head displacement speed that allows the
Figure 5. Volumetric fraction and extrusion geometry of the hydrogels line of extruded material to have the desired thickness.
studied at the droplet detachment limit achieved at different pressures. This variable is linked to the extrusion time reflected in

A B C

Figure 6. Time for extrusion to reach the 3 mm mark in samples of hydrogel with 3.5% alginate with CaCl at an inlet pressure of 950 kPa (A), of hydrogel
2
with 4% alginate with CaCl at an inlet pressure of 930 kPa (B), and of hydrogel with 5% alginate with CaCl at an inlet pressure of 750 kPa (C).
2
2
Volume 9 Issue 2 (2023) 427 https://doi.org/10.18063/ijb.687