Investigation of humidity-driven swelling–shrinking behavior of filaments in material extrusion of medical-grade biodegradable hydrogel

Material extrusion using medical-grade biodegradable hydrogel demonstrates significant potential for manufacturing biocompatible scaffolds in regenerative medicine. However, unpredictable geometric variations in the fabricated models, such as swelling or shrinking, impede the development of complex three-dimensional (3D) hydrogel architectures for in vitro-functionalized tissues and organs. A primary cause of structural deformation, such as wrinkling or even collapse, is improper humidity control during the 3D printing process. Therefore, there is a need to investigate the swelling–shrinking behavior of hydrogels under varying ambient humidity and to determine optimal humidity levels for the printing process. This study established a thermal–humidity–multiphase flow coupling field simulation model to numerically investigate the humidity-driven swelling–shrinking behavior of hydrogel filaments. The optimal 3D printing humidity levels were determined for hydrogel filaments with diameters of 0.2, 0.3, and 0.4 mm, which were found to be 90, 80, and 60%, respectively. Using these humidity settings, several structures were fabricated, demonstrating moderated moisture loss of 3D architecture. Notably, a human ear model was successfully printed, achieving an effective size of 20 mm (length) × 10 mm (width) × 10 mm (height). Our research can benefit the future development in tissue engineering and regenerative medicine.