Page 295 - v11i4

International Journal of Bioprinting Dual tuning of 3D-printed SilMA hydrogel

cell proliferation, chondrogenesis, and angiogenesis. As The regenerative capacity of the scaffold also
shown in Figure S3, the spacing between the two strands fundamentally depends on its mechanical properties. These
of the PEO/SilMA group scaffold (612.6 ± 32.8 μm) properties must be robust enough to withstand articulation
closely matched the strand spacing and layer height set and handling during implantation. Additionally, they
for 3D printing (600 μm). However, with the addition of should not be overly strong to the extent that they cause
44
NFs, the distance between the strands decreased. When stress shielding of mechanosensitive cells. In this study,
2% NF was added, the spacing between the strands was to investigate the differences in the mechanical properties
reduced to approximately 400 μm (378.9 ± 89.2 μm). This between grid-like hydrogels with macroporous structures
phenomenon may be due to: (i) the relatively large length fabricated via 3D printing and those without macropores,
of the NFs, causing the fibers located at the edges of the we also prepared cylindrical samples using molds and
strands to be fixed at the mesh edges after the hydrogel was subjected them to compression testing. Figure 4B and
photocured, or (ii) the introduction of NFs led to a decrease C shows the compression test results of the cylindrical
samples, while Figure 4D and E displays the mechanical
in the fluidity of the printing bio-ink, reducing the printing properties of the 3D-printed grid-like samples. In general,
accuracy. Although this large pore size did not reach the the compressive strength of cylindrical samples was
size recommended in the literature (about 200 µm), a slightly higher than that of the corresponding 3D-printed
41
previous study has reported that scaffolds with a pore size samples. The compressive strength of the cylindrical
of 400 μm could promote proteoglycan production and SilMA hydrogels reached 1235.8 ± 172.1 kPa, while the
chondrogenic marker gene expression more effectively strength of the grid-like samples was only 930.2 ± 85.6
than those with smaller pore sizes of 200 and 100 μm. kPa. Although the latter is slightly lower, this value was also
42
While smaller macropores could be achieved by setting a close to the compressive strength of 3D-printed 30% SilMA
smaller strand spacing or layer height to 400 μm before 3D hydrogel reported in previous studies. Regarding the
20
printing, the possible unevenness or aggregation of NFs compressive modulus, the grid-like samples in each group
during preparation could reduce printing reproducibility. exhibited better performance compared to the cylindrical
Therefore, a strand spacing of 600 μm was chosen for 3D samples. It is speculated that the cylindrical samples
printing in this study. could transfer and disperse stress better, reducing local
stress concentration and resulting in higher compressive
3.3.2. Swelling and mechanical properties strength. In the grid structure, stress tends to concentrate
The swelling behavior of hydrogels was systematically at the nodes, leading to earlier material failure. The reason
evaluated to assess their hydrophilicity and structural for the larger compressive modulus of the grid structure
stability—two critical determinants for nutrient diffusion could be attributed to the better force dispersion by the
and long-term functionality in cartilage regeneration. truss structure, causing less deformation of the scaffold.
Macroscopic observation (Figure S4) revealed significant Notably, using PEO in the preparation of SilMA hydrogel
volumetric expansion in PEO-modified groups, with significantly reduced its compressive strength and modulus.
pore architectures maintained throughout the 24-h PBS However, the addition of NFs could reverse this negative
immersion, contrasting with the non-porous controls. influence. The PEO/2%NF/SilMA group possessed similar
Quantitative swelling kinetics (Figure 4A) demonstrated mechanical properties to the SilMA group for both cylinder
a biphasic absorption pattern: rapid initial swelling (0–12 shape and grid-like structure. Specifically, the compressive
h, >80% equilibrium absorption) followed by gradual modulus of the 3D-printed PEO/2%NF/SilMA (815.0
stabilization. Notably, PEO/SilMA and PEO/1%NF/SilMA ± 73.1 kPa) had reached that of native cartilage (around
45
groups exhibited prolonged swelling phases, achieving 0.81 ± 0.56 MPa), indicating the promising potential for
cartilage repair applications. In addition, the strength of
equilibrium swelling ratios of 170.1 ± 7.50% and 162.7 the hydrogel is not invariably augmented with an increase
± 2.76% at 24 h, respectively. This delayed equilibration in the concentration of NFs. The 2%NF/SilMA exhibited
might be attributed to the hierarchical pore structure obvious mechanical deterioration compared to SilMA
(relative macroporosity from PEO leaching combined with and 1%NF/SilMA. This aligns with previous reports
inherent SilMA microporosity), which creates capillary- suggesting that excessive nanomaterial concentrations
driven fluid transport pathways distinct from conventional may compromise mechanical reinforcement. 32,33 This could
homogeneous networks. Compared to a previous study also be explained by the percolation theory predictions—
that reported the swelling rate of only 6% for nanosilicate- excessive NF loading induces aggregation, creating stress
reinforced SF hydrogel, measured using the same concentration points rather than continuous reinforcing
method, the NF/SilMA/PEO hydrogels in this study had networks. However, the 3D-printed PEO/2%NF/SilMA
43
outstanding swelling behavior. groups showed better mechanical properties than the

Volume 11 Issue 4 (2025) 287 doi: 10.36922/IJB025140118