3D Printing of Gelatin-Based Hydrogels for Mimicking the Mechanical Properties of Ultrasoft Tissues

In ultrasoft tissue regeneration, the mechanical properties of implanted scaffolds do not correspond with those of ultrasoft tissues and are prone to inflammation, fibrosis, and other comorbidities. Light-cured 3D-printed gelatin methacrylate (GelMA) scaffolds are widely used in soft tissue regeneration due to their excellent biocompatibility. However, during the printing of ultrasoft GelMA, defects such as delamination, damage, and fracture are prone to occur due to process factors such as interlayer peeling forces, which lead to molding difficulties. In this study, a GelMA/Collagenase II composite bioink was developed, in which GelMA with favorable mechanical properties was used to ensure the formation of the scaffolds; Collagenase II was used to shear the peptide bonds of the GelMA molecular chain to regulate the degree of sparseness of the molecular network, thereby softening the mechanical properties of the scaffolds. Combining finite element analysis and experimental verification, the compression modulus of GelMA was reduced from 18 to 1 kPa by regulating the softening time. Porous structures with tunable mechanical properties (1.4 kPa–0.1 kPa) were printed, and ultrasoft material modulus (1 kPa) molding of multiple structures (conduit, vascular, solid) was achieved while demonstrating excellent cell proliferation. This work provides a bioink for the 3D printing of ultrasoft bioscaffolds, which has great potential in the field of ultrasoft tissue repair.