Page 43 - IJB-9-4

International Journal of Bioprinting 3D-Bioprinted human lipoaspirate-derived cell-laden skin constructs

adECM was 99.71% lower than that of native tissue (2.34 ± extruded through the 3D printer nozzle without blockage,
0.87 vs. 804.02 ± 72.74 ng/mg dry weight, respectively; making them suitable for 3D-bioprinting.
Figure 2E) and substantially below the minimal criterion We also observed the modulus change after
for decellularization (<50 ng/mg dry weight) . The sGAG photocrosslinking. After 10 s of UV irradiation, the
[37]
content was 2.58 ± 0.26 and 3.03 ± 0.41 μg/mg dry weight in moduli of both bioinks increased rapidly, and the value
adECM and native tissue, respectively, indicating that most of G′ changed from being lower than that of G″ before
sGAG components were retained in adECM, although the crosslinking to being much higher than that of G″. The
difference between them was not significant (p > 0.05) G′ value of adECM–GelMA–HAMA increased by >79-
(Figure 2F). The collagen content levels in adECM and fold, whereas the value of G″ increased by approximately
native tissues were 100.38 ± 4.21 and 90.8 ± 4.84 μg/mg 11-fold, and the respective increases for G′ and G″ values
dry weight, respectively (Figure 2G). The collagen content for GelMA–HAMA were approximately 72- and 4-fold,
was remarkably increased in the adECM compared with respectively (Figure 3E and F).
that in native adipose tissue, and this may be due to the
low proportion of collagen in adipose tissue, which would These results indicate that the bioink may have acceptable
naturally increase with the removal of adipocytes. This is printability and shape retention ability. In particular,
consistent with the results of Pati et al., who reported that this shape retention ability could enable the printed
the GAG content decreased, while the collagen content scaffold to more effectively fill and contact the wound
increased after decellularization of adipose tissue . microenvironment for a sufficient time throughout wound
[38]
This elevated collagen content could be an advantage for healing, thus establishing a dynamic microenvironment
adECM as a component of bioink for a 3D-printed skin where cells in the scaffold interact with the wound and
substitute. those surrounding the wound interact with the scaffold.
3.2. Printability of bioinks
The rheological properties of hydrogels are an important 3.3. Physical characterization of bioinks
basis for evaluating their printability . First, the The water uptake capacity is an important criterion
[39]
gelation kinetics of bioinks were evaluated by performing to consider because the encapsulated cells absorb
temperature sweep experiments. Both bioinks exhibited nutrients from the wound to maintain their growth and
[41]
thermally sensitive properties, with the storage (G′) and proliferation . For analysis of bioink scaffold swelling, the
loss modulus (G″) values changing abruptly when the weight of hydrogel samples was measured at different time
temperature neared the gel point, indicating that the bioinks points within a 24 h incubation at 37°C. GelMA–HAMA
were changing from a liquid to a gel, which is a prerequisite and adECM–GelMA–HAMA samples exhibited rapid
for ensuring that hydrogels form after printing. The gel water absorption after 1 h of incubation, with SRs of 3.94 ±
point is the temperature corresponding to the intersection 0.32 and 4.89 ± 0.34, respectively. After 12 h of incubation,
point of G′ and G″. The gelation temperature ranges the swelling plateaued, and by 24 h, the swelling ratios
of adECM–GelMA–HAMA and GelMA–HAMA were were 8.95% ± 0.72% and 11.18% ± 0.45%, respectively. The
16.5°C and 17.4°C, respectively (Figure 3A). The viscosity swelling ratio of GelMA–HAMA was remarkably lower
of both bioinks decreased with increasing temperature than that of adECM–GelMA–HAMA at different time
from 0°C to 30°C (Figure 3B). The loss tangent (tanδ = points (Figure 4A).
G″/G′) tended to increase as the temperature increased, To analyze bioink degradation, we used collagenase
showing a transition from solid-like behavior (tanδ < 1) to treatment at several time points >72 h to calculate the rate
liquid-like behavior (tanδ > 1; Figure 3C). of weight loss. The RM of adECM–GelMA–HAMA was
remarkably higher than that of GelMA–HAMA after the
Bioinks required a viscosity that was appropriate
for controllable printing with excellent shape fidelity . experimental time course, and approximately 53.06% ±
[40]
5.16% of the adECM–GelMA–HAMA mass remained
Bioink viscosity was recorded over the shear rate range at 72 h compared with only 37.53% ± 4.52% of GelMA–
of 0.1–100 Hz at 17°C. Rheological analysis showed that HAMA (Figure 4B).
the viscosity of adECM–GelMA–HAMA at 0.1 Hz was
82.67 ± 6.71 Pa•s, which decreased to 1.62 ± 0.13 Pa•s at SEM was performed to observe the pore structure of the
the highest shear rate of 100 Hz. The viscosity of GelMA– two bioinks, as this property can affect cell behaviors, such
HAMA was 110.33 ± 5.02 Pa•s at 0.1 Hz and decreased as cell spreading, as well as the nutrient and oxygen supply
to 1.98 ± 0.09 Pa•s at the highest shear rate of 100 Hz. and metabolite removal. The 3D structures of the two bioink
Both bioinks exhibited shear-thinning properties, with hydrogels showed a reticular porous morphology (Figure 4C
the viscosity decreasing under increased shear strain and D). The porous structure with a network distribution
(Figure 3D). Therefore, both bioinks could be smoothly is an important basis for promoting the attachment and

Volume 9 Issue 4 (2023) 35 https://doi.org/10.18063/ijb.718