Page 49 - IJB-9-5

International Journal of Bioprinting Precise fabrication of engineered vascular networks

and 175 μL/min. The results indicate that the sacrificial which shows great potential for the precise fabrication of
templates for the vasculature with the designed dimension engineered vasculature.
could be printed by varying the feed rates of the sacrificial
PF-127. 3.2. Effect of PNIPAM/GelMA (P/G) concentration on
Then, the P/G hydrogel scaffolds with vasculature swelling compensation
x
were prepared to observe the compensation phenomenon, The concentration of P/G hydrogel determines its volume
where x represents the mass fraction of the GelMA in shrinkage degree. Thus, the effect of P/G hydrogel
the P/G hydrogel. In this experiment, 1.5 mL freshly concentration on the swelling compensation was studied in
prepared P/G hydrogel was crosslinked in a 35-mm this section. Different concentrations of GelMA were mixed
3
Petri dish. Subsequently, the crosslinked hydrogel film with PNIPAM to form P/G , P/G , and P/G hydrogels.
1
3
5
was transferred to the 3D printing platform to print the NIPAM, MBA, and LAP concentrations were fixed at 10,
sacrificial PF-127, as shown in Figure 2G. The 20-G needle 0.15, and 0.075 wt%, respectively. A 20-G needle was used
was used in this printing process. The printed zigzag in this section. Images of the P/G hydrogel scaffolds before
sacrificial template is shown in Figure 2H. Another 1.5 mL and after shrinking at 37°C were captured (Figure 3A). The
P/G hydrogel was utilized to cover the printed sacrificial diameter of the prepared vasculature during this process
3
template (Figure 2I). The ends of the sacrificial templates and the shrinkage ratio of the P/G hydrogel scaffolds were
were cut to facilitate the outflow of sacrificial PF-127, as analyzed, as shown in Figure 3B and C, respectively. The
shown in Figure 2J. After placing at 4°C for 20 min, ice- results demonstrated that all scaffolds showed significant
cold ultrapure water was gently injected into the channel shrinkage within the first 2 h at 37°C. Subsequently, the
to further clear the fabricated vasculature. The air was shrinking process of the P/G hydrogel scaffolds slowed
injected into the channel to verify the connectivity of the down, which was consistent with the results in section 3.1.
fabricated vasculature. The air bubbles flowed smoothly The diameter of the fabricated vasculature increased with the
from one end of the vasculature to the other, verifying the increase of GelMA concentration, and only the diameter of
successful preparation of the designed zigzag vasculature, vasculature in P/G hydrogel scaffolds was maintained around
3
as shown in Figure 2S. The FTIR spectra of PF-127 the designed size, as shown in Figure 3B. This is mainly
shows characteristic C-O-C stretching band at 1098 cm , attributed to the dense crosslinked network in GelMA with
-1
and C-H stretching band at 2880 cm -1[36] . As shown in high concentration. The dense crosslinked network impedes
Figure S1 (Supplementary File), the P/G hydrogel after the water release in the P/G hydrogel at 37°C, which further
the sacrificial template is removed does not contain the hinders the volume shrinkage of the P/G hydrogel. This is
characteristic peak of PF-127, so the sacrificial template also demonstrated by the shrinkage ratio of P/G hydrogel
was completely removed. Finally, the hydrogel scaffold constructs. Specifically, the volume shrinkage degree of the
with the 35-mm Petri dish was floated in a 37°C water bath P/G hydrogel scaffold gradually decreased with the increase
to observe the shrinking process. Images of the hydrogel of GelMA concentration, as shown in Figure 3C.
scaffold with vasculature were captured at 0.5, 1, 2, 3, 4, 5, The contact angle of P/G , P/G , and P/G hydrogel
3
and 24 h and are shown in Figure 2K–Q, respectively. The scaffolds at 25°C and 37°C was measured to explore
5
1
vasculature was still noticeable after the volume shrinkage the surface characteristics. As shown in Figure S2
(Figure 2R). (Supplementary File), the contact angles of all the P/G
The diameters of the prepared vasculature before and hydrogel scaffolds were maintained at around 20°. The
after shrinking were recorded in Figure 2T. After printing, contact angle of P/G , P/G , and P/G hydrogel constructs
3
1
5
the diameter of the fiber in the sacrificial template was increased to 67.4 ± 8.0°, 42.2 ± 1.3°, and 29.5 ± 3.8° after
609.8 ± 0.7 μm, which is close to the inner diameter of increasing the temperature to 37°C. The increase of GelMA
the 20-G needle (I. D. 610 μm). However, after dissolving, concentration denotes the decrease in the concentration
the diameter of the prepared vasculature increased to ratio of PNIPAM and GelMA. The volume shrinkage
711.4 ± 13.8 μm. After shrinking at 37°C for 2 h, the of P/G hydrogel is caused by the hydrophilicity and
diameter of the vasculature was maintained at around hydrophobicity switch of PNIPAM below and above the
610 μm. The results indicate that although the vasculature LCST, respectively, at around 32°C. Below the LCST, the
with a designed diameter can be fabricated by switching PNIPAM hydrogel is hydrophilic. When above the LCST,
the feed rate of the sacrificial PF-127, the swelling of the PNIPAM becomes hydrophobic [37,38] . Thus, the decrease
sacrificial template during the dissolution process still in the P/G concentration ratio reduces the shrinkage
leads to the deformation of the vasculature size. However, ability of the hydrogel. This further shows that the high
the volume shrinkage of the thermosensitive P/G hydrogel concentration of GelMA can negatively affect the volume
can compensate for the swelling of the sacrificial template, shrinkage ratio.

Volume 9 Issue 5 (2023) 41 https://doi.org/10.18063/ijb.749