Page 289 - IJB-10-5

International Journal of Bioprinting 3D printing of collagen II-scaffolds

Figure 3. Measurements of the viscoelasticity of the hydrogel inks. (A)
Oscillation frequency sweep test of the hydrogel inks: G’ and G’’ versus
frequency. (B) Oscillation temperature sweep test of the hydrogel inks:
Figure 2. Steady-shear flow test of the hydrogel inks: (A) viscosity versus Tan-delta versus temperature. Abbreviation: CNF, cellulose nanofiber; G’,
shear rate; (B) shear stress versus shear rate. Abbreviation: CNF, cellulose storage modulus; G’’, loss modulus.
nanofiber.

Similarly, the storage modulus of the collagen II-based movement of collagen II macromolecules and reduced
hydrogel was significantly increased after the addition their flow and elasticity.
of CNF, corresponding to an increase in ink rigidity 3.3. Morphology of 3D-printed collagen
(Figure 3A). The effects of temperature were observed as II-containing scaffolds
the gelatin-based ink exhibited apparent gelation during Based on our results in Figure 4, the collagen II/alginate
the cooling process, while the change in the collagen ink had a larger creep strain over time, reflecting limited
II-based hydrogel was less apparent. Interestingly, shape fidelity. Consistently, CNF addition greatly reduced
the addition of CNF resulted in higher viscoelasticity the rod diameter of the printed structure (Figure 5A and
(Figure 3B), possibly due to disruption in the entanglement B), resulting in resolution enhancement.
of collagen macromolecules by CNF. A creep test was The planar and cross-sectional views of the 3D-printed
conducted to evaluate ink shape fidelity (Figure 4). The scaffolds are displayed in Figures 6 and 7, respectively. The
gelatin-based hydrogel exhibited a quick strain recovery at printed rods had a self-supporting overhang structure and
1 s, presumably due to the formation of rigid and elastic a relatively round shape instead of a flattened shape. This
triple helix microstructures during gelation. In contrast, all suggests good shape fidelity during the printing process,
collagen II-based hydrogels did undergo gelation during successful post-treatment, and SEM sample preparation
cooling, resulting in loose intermolecular bonding and in maintaining the sample geometry and dimensions. The
little resistance to shear deformation. Within the collagen combined use of the CNF and cryogenic printing techniques
II-based hydrogels, CNF addition significantly reduced led to high printing resolution (Table 2). Furthermore, to
creep strain over time, thereby enhancing ink shape fidelity. evaluate the dimensional change after swelling, the pore size
The rigid nanoscale network structure of CNF limited the and rod diameter of the printed scaffolds were measured

Volume 10 Issue 5 (2024) 281 doi: 10.36922/ijb.3371