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Materials Science in Additive Manufacturing Bioactive hydrogels for 3D bioprinting

3.3. Evaluation of printing outcomes

We evaluated the 3D printing outcomes by first testing the
extrudability of each hydrogel-BBG sample to determine
the ideal printing temperature for each biomaterial ink.
Once ideal gelation was achieved at a certain temperature,
filaments were printed to study filament uniformity,
measured by filament line width variation as defined
in Equations I and II. Filament uniformity was used to
establish the desired extrusion pressure for each set of
biomaterial ink composition and nozzle temperature.
Afterward, scaffolds were printed using H-BBG0,
H-BBG10, H-BBG15, and H-BBG20, each at the desired
nozzle temperature and extrusion pressure. Subsequently,
the shape fidelity of printed scaffolds was measured to
identify the effect of BBG content on printability.
Figure 4. Dynamic viscosity of hydrogel-BBG (H-BBG) inks at various
temperatures was taken as the average of the shear rate data for Figure 6 shows the extrusion tests performed at the
1<shear rate<10 s . temperature of 20, 25, 30, 35, and 40°C for H-BBG0 and
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observed drop in gelatin-alginate viscosity is influenced H-BBG20 inks at the extrusion pressure of 35 and 75 kPa,
by the concentration of BBG, as shown in Figure 4. respectively, to study the extrudability of these samples
Unlike H-BBG10, we observed a significant impact of due to temperature-dependent gelation behavior. Among
thermal energy, i.e., the elevated temperature on the drop the various temperatures tested, H-BBG0 ink exhibited
of viscosity in H-BBG15 and H-BBG20. These findings the best extrudability at 25°C, with continuous flow and
suggest that the concentration of BBG is a key factor in no droplet formation. Therefore, the desired extrusion
determining its effectiveness in modulating the hydrogel temperature for H-BBG0 was determined to be 25°C. At
viscosity. higher temperatures, the viscosity of H-BBG0 decreased
The applied extrusion pressure affects the flow rate substantially, resulting in the formation of ink droplets,
of hydrogel-BBG inks through a nozzle in the printing which should be avoided. The addition of BBG to
process. Therefore, the ink’s shear rate is a function gelatin-alginate hydrogel in H-BBG20 led to a significant
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of pressure and viscosity (which is influenced by increase in viscosity and, thus a different result from
temperature). Figure 5 shows the shear thinning behavior the extrusion test. At the lower temperatures of 20 and
of biomaterial inks with various BBG amounts (H-BBG0, 25°C, the high viscosity resulted in over-gelation, causing
H-BBG10, H-BBG15, and H-BBG20) across the shear irregular filament formation that could be detrimental
rate range from 0.1 to 1000 s and different temperatures to the printing process. The gelation state was improved
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including 25, 30, 35, and 40°C. All samples exhibited shear at 30°C, and H-BBG20 reached an ideal gelation state at
thinning behavior, featuring the rheological behavior of 35°C, resulting in a viscosity suitable for extrusion and
non-Newtonian fluids whose viscosity decreases with high extrudability, indicating that the biomaterial ink
increasing shear rate. Our data here consistently showed at this temperature achieves a desired balance between
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a decrease in viscosity as a result of an increase in shear fluidity and rigidity for printing. At 40°C, the viscosity
rate across all temperatures in all samples with various of H-BBG20 substantially decreased, leading to the
BBG contents. At 25°C, they exhibited the highest level formation of droplets, an indication of under-gelation.
of viscosity, which decreased rapidly as the shear rate Therefore, the desired extrusion temperature for H-BBG20
increased. However, this decrease in viscosity was less was determined to be 35°C. From the extrusion test results,
sharp when the temperature was raised to 30, 35, and 40°C which are not included in Figure 6, we also found a near-
across all samples. H-BBG20 ink, which has the highest optimal extrusion temperature of 25°C for H-BBG10 and
amount of BBG, exhibited the highest viscosity among 30°C for H-BBG15.
all samples. This sample also showed the largest drop in Visual assessment of the filament quality for H-BBG0,
viscosity as temperature increased from 25 to 40°C. It H-BBg10, H-BBG15, and H-BBG20 is depicted in
indicates that BBG modifies the rheological behavior of Figure 7, for different extrusion pressures at the identified
the gelatin-alginate hydrogel, which is caused by alteration temperature for each ink through the extrudability
to the chain alignment and the strength of intermolecular study described above. Uniform, high-quality prints are
bonds in the hydrogel chain crosslinks. marked with blue dash-line borders in Figure 7. As can

Volume 3 Issue 1 (2024) 8 https://doi.org/10.36922/msam.2845