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International Journal of Bioprinting 3D-bioprinted respiratory disease model

Figure 1. Temperature dependence of viscosity of the 5% alginate/5% gelatin/0.05% collagen solution undergoing constant shear stress sweeps as the
temperature was increased from 20 to 40°C at a rate of 1°C/min.

3.2. Printability has larger pores on the outer edges. These statistically
Based on the rheological results, an initial printing insignificant differences, i.e., p = 0.737 for strand diameter
temperature of 37°C was selected to balance the trade-off and p = 0.991 for pore size (determined via ANOVA
of printability, process-induced mechanical forces, and cell and pair-wise analysis), demonstrate the consistency in
viability. Printability was tested and characterized with printability between inks with and without nanoparticles,
and without the presence of nanoparticles to confirm that as reported in previous studies. The influence of printing
33
the addition of 4 µg/mL nanoparticles would not have a temperature was examined at the optimized printing
significant impact. It should be noted that in bioprinting, pressure and speed to determine if the altered temperature
nanoparticles with diameters less than 1000 nm are would significantly influence printability. Lowering the
generally preferred to allow for smooth extrusion through printing temperature was found to have inconsistent results
printing needles (often around 200 µm in diameter), as on strand diameter, and it was determined that printing at
the use of smaller particles helps to avoid clogging even if physiological conditions (37°C) was most favorable. Some
some particle aggregates form. bubbles trapped during the mixing and printing process

The optimal printing parameters that allowed for can be seen in Figure 2A and B.
repetitive printing of structures with consistent strand
diameters and pore sizing were determined to be 25 3.3. Scaffold degradation and mass loss
kPa and 10 mm/s (Figure 2). As observed in Tables 2 Degradation studies, carried out in both static and
and 3, a decrease in pressure resulted in smaller average dynamic conditions, were used to test if the inclusion of
strand diameters, lesser strand adhesion, and higher 20 mM CaCl crosslinker in the 3D media was sufficient to
2
strand discontinuities (Figure 3). Increased pressures maintain the constructs’ stability over an extended culture
and speeds resulted in larger pore sizes with increased period. As observed in Figure 4, up to 20% mass loss was
amounts of strand swelling. Average strand dimensions still seen over 28 days, but there was never a significant
using these parameters were found to be 555 ± 78 µm difference in mass loss between static and dynamic culture
for solutions without nanoparticles and 544 ± 56 µm for conditions. More rapid mass loss appears to occur in the
solutions containing 4 µg/mL nanoparticles. Similarly, seven-day period between days 7 and 14 in comparison to
the average pore sizes for these parameters were 577 the 14-day period between days 14 and 28. This suggests
µm ± 218 µm without nanoparticles and 578 µm ± 214 that the decrease in mass is primarily driven by the loss
µm with nanoparticles. The large standard deviation for of gelatin and collagen from the matrix that was not fully
pore spacing was due to the design of the scaffold, which contained by the crosslinked alginate polymeric network.

Volume 10 Issue 6 (2024) 415 doi: 10.36922/ijb.3895