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International Journal of Bioprinting Swelling–shrinking behavior of hydrogel

Figure 4. Humidity distribution in the ambient air with a filament diameter of 0.2 mm, illustrating the geometric variation of the printed filament under
various relative humidity (RH) conditions.

moisture gradient in the radial direction. When the RH is demonstrate the geometric variations of the 0.3 and 0.4
defined to a low value, such as 50%, the rate of moisture mm filaments, respectively.
loss is significantly increased, leading to the most severe With increasing filament diameter, the geometric
geometric shrinkage of the printed filament. shrinkage of the hydrogel filaments is alleviated. Among

The process from deposition to the complete collapse the three types of hydrogel filaments with various
of the entire hydrogel structure lasts for approximately diameters, the 0.4 mm filament exhibits the largest initial
180 s. Given that 3D printing of large-scale architectures volume and contains the greatest amount of water. This
is typically time-consuming, such a rapid geometric implies a higher moisture retention capacity during the
decrease is unacceptable during the fabrication process. evaporation process. Therefore, compared with the 0.2
As the ambient RH increases, the concentration of water and 0.3 mm filaments, the 0.4 mm filament demonstrates
in the ambient air approaches that within the hydrogel superior shape stability when exposed to moist air at the
filament. This leads to insufficient moisture transfer and same RH.
vapor diffusion, moderating the geometric shrinkage As the RH increases, both the 0.3 and 0.4 mm filaments
of the just-printed hydrogel filaments. Figure 5 and 6 ultimately demonstrate swelling behavior. When the

Volume 11 Issue 4 (2025) 416 doi: 10.36922/IJB025220222