4.4.1 Printability of carrageenan/sodium alginate hydrogel
The printability of the hydrogel was simulated to present the printing
conditions with various printing parameters and to predict the optimal
printing parameters based on the measured rheological properties. The
printability was calculated as shown in Figure 5(b), with the printing
speed of 0–18 mm/s and pressure of 10–40 kPa, by using the equations
described above. The cross marks on the printability map represent the
actual printing conditions shown in Figure 5(a), and they were labelled
with the printing numbers from 1 to 16. Moreover, Figure 5(a) shows the
microscopic images of the printed struts at various nozzle velocities
(1, 2, 4, and 8 mm/s) and pressures (10, 20, 30, and 40 kPa). The
obtained microscopic images were quantitatively analysed to measure the
printing resolution and the quality shown in Figure 5(c).
As shown in Figure 5(a), the diameter of the printed gel filament was
inversely proportional to the printing rate, while the diameter of
printed gel filament decreased with increasing printing rate at low
printing pressure (10 kPa). In other words, the samples in the higher
printing rate (4 mm/s, 8 mm/s) No. 3 and No. 4 did not acquire an
integrated cylindrical structure. At the same printing pressure, the
samples No. 1 and No. 2 gel filament were printed with a lower printing
speed, resulting in a relatively full cylindrical structure. Thus,
unmatched printing speed and printing pressure resulted in insufficient
flow filling.
The incomplete shape of gel filament caused by increased printing
pressure to 20 kPa existed. The sample No. 8 with 8 mm/s was
particularly obvious; however, the uniformity of its diameter and shape
integrity was significantly better than that of sample No. 4 (i.e. the
same printing speed and lower printing pressure), which demonstrated
that the coordination effect of printing pressure and printing speed had
an obvious influence on the shape and diameter of the extrusion gel
filament and that a higher printing rate cannot be applied with lower
printing pressure.
Furthermore, the printability values of samples No. 5, 9, 10, 13, 14,
15, and 16 were greater than 0.5. In Figure 5(b), the printability of
samples No. 1, 2, 6, 7, 11, and 12 were assigned according to their
print parameters, which matched with the values measured and calculated
from the actual printing samples. The results demonstrated that the
simulation of printability of kc-sa-1.0 hydrogels were basically
accurate. As shown in Figure 5(d), the diameter of the printed gel
filament was mainly distributed between 1.0 and 1.8 mm.