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3D Printing of Food Foams
Figure 2D shows the peak hold study of the inks. support structures, the foam bubbles grew in size in the
Under low a shear rate from 0.1 to 1 s , all the inks cartridge and became unstable in the subsequent second
−1
gradually reduced their viscosities, which is in line and third print. Even though the viscosity of Ink 1 was
with the flow ramp study that depicts the inks as shear the highest amongst all the inks, but its stability was not
thinning. When the inks experienced a spike in shear high enough. This was also observed in Ink 5. While the
rate, the viscosity dropped drastically. This suggests that first print was good, it was less able to self-support and
the viscosities of the foam inks reduced during printing, spread more in the later prints. The best prints were from
and inks flowed effortlessly out of the nozzle, allowing Inks 2 and 4 with scores of approximately 9, where they
smooth printing. Once the shear stress was removed, consistently presented good self-supporting structures in
simulating the shear rate after printing, the viscosities three consecutive prints.
of the inks recovered quickly. This implies that the inks The effect of XG on the printability of the inks
were able to return to their original rheological properties within the EW and HPMC groups was compared. The
after printing and held their structures. first three prints of the inks were rated visually from 1
(poorest) to 5 (best) on two categories, self-supporting
3.4. Printability of the inks structure and shape fidelity. The printability of inks with

The printability is dependent on the rheology and the XG shows significant improvement regardless of the base
stability of the inks. Out of all the inks, Ink 3 was not ingredients. XG is an important factor to achieve a good
printable at all as shown in Figure 3 where the printed printable structure for the foam inks.
ink was a pool of liquid and it has an average printability 3.5. Microstructure of the baked inks
score of 2. The foam stability, as described earlier, was
very low for Ink 3 as it collapsed too quickly. While in the The scanning electron micrographs in Figure 4 show
foam stability test, the half-life of Ink 3 was 15 min under the microstructure of the EW foams and the HPMC
atmospheric pressure, the stability within the syringe and foams. Only the printable inks (i.e. Inks 1, 2, 4, and 5)
during printing was lower due to significantly higher were assessed. The pure EW or Foam Magic only foam
pressure. Therefore, Ink 3 was extruded as a liquid instead samples were included for comparison.
of foams. This was also seen in Ink 1 (Figure S1). While Comparing the foam formed by EW and by Foam
it was printable in the first print and was able to form self- Magic only (Figure 4A & D), the EW foam had a

A

B

Figure 3. (A) Six-pointed star (first) prints with Inks 1 – 5 with the average score in each frame. (B) The printability scores for each ink.
*P ≤ 0.1, **P ≤ 0.01, ***P ≤ 0.001, ****P ≤ 0.0001 for the t-test results (n = 3).

162 International Journal of Bioprinting (2021)–Volume 7, Issue 4