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International Journal of Bioprinting Swelling–shrinking behavior of hydrogel

To provide a quantitative basis for evaluating the of 20 mm (length) × 10 mm (width) × 10 mm (height)
printing quality of the hydrogel constructs under different is successfully generated. This outcome confirms that 3D
RH conditions, the overall height of each printed structure printing with optimal RH conditions can alleviate moisture
was measured as a representative indicator of structural loss and enhance the structural fidelity of 3D architectures.
integrity. Given the complexity of the ear-shaped geometry, F-127 was selected as the model hydrogel in this study
conventional image analysis techniques, such as edge due to its pronounced and stable geometric deformation
detection, contour extraction, or pixel-wise segmentation, under varying RH conditions, along with its excellent
were not feasible for consistent quantitative assessment. printability and reproducibility. These characteristics made
Therefore, vertical height was selected as a measurable it suitable for controlled investigation of humidity-driven
and reproducible metric that reflects the degree of swelling–shrinking mechanisms and for quantitative
structural collapse or swelling caused by humidity-driven FEM modeling. However, it is important to note that the
deformation. The height of each sample was obtained proposed finite element framework—including two-phase
from side-view images and is presented in Table 3. The flow modeling, water vapor transport simulation, and
results demonstrate that samples printed under optimal RH–geometry coupling—is not limited to the specific
RH conditions exhibited significantly greater structural material properties of F-127. The model is designed
retention compared to those printed under inappropriate to be generalizable and can be applied to other widely
RH conditions. used hydrogel-based inks, such as GelMA with tunable
Currently, numerous studies have explored 3D printing crosslinking density, ionically crosslinked alginate, and
using F-127 materials. However, a majority of these photopolymerizable PEG-DA, provided that key physical
printed structures exhibit shrinkage and collapse during parameters (e.g., swelling ratio, viscosity, and diffusion
the extrusion process due to inappropriate ambient RH. coefficient) are available. These hydrogels are extensively
Moisture loss significantly limits the fabrication of large- used in tissue engineering and bioprinting, indicating the
scale 3D architectures with complex structures. Table 4 strong applicability and scalability of our model in practical
compares the 3D-printed F-127 architectures of various biomanufacturing settings.
sizes in existing studies. It demonstrates that the effective
lengths and widths of recently proposed structures usually 4. Conclusion
fall within the range of 5–10 mm, with effective heights In this study, the humidity-driven swelling–shrinking
generally not higher than 8 mm. Meanwhile, the shapes behavior of hydrogel filaments during 3D printing
of these architectures are not complex enough to meet was investigated through numerical simulations and
the requirements of medical applications. In contrast, in experimental validation. A novel FEM coupling field
this study, a 3D-printed ear model with an effective size simulation model was developed to identify optimal

Table 3. Overall heights of printed structures with various humidity levels
Figure Filament diameter (mm) Ambient humidity (%) Overall height (mm)

A 90 5.4
0.2
D 80 4.5
B 80 8.5
0.3
E 70 7.6
C 60 10.0
0.4
F 50 8.8

Table 4. Results of printed F-127 structures in recent studies
Reference Structure Filament diameter (mm) Effective size (length × width × height, mm )
3
41 0.5 8×8×1
Reticulate structure
42 0.2 10×10×5
Cube structure 5×5×5
43 0.4
Pyramid structure 10×10×8

Volume 11 Issue 4 (2025) 422 doi: 10.36922/IJB025220222