Influence of pre-printing aging time on the printability and performance of chitosan-polyacrylic acid double-network hydrogels for skin graft application.

Three-dimensional (3D) bioprinting of hydrogels offers great promise in tissue engineering, as it enables precise fabrication of cell-laden scaffolds with complex architectures. The formulation and rheological tuning of bioinks are critical for successful printing and scaffold performance. While considerable efforts have focused on optimizing composition and crosslinking chemistry, the influence of time on material behavior, such as pre-printing aging, remains insufficiently studied. In this study, we developed dual-crosslinked chitosan-polyacrylic acid (CSAA) hydrogels with varied aging times (5.0, 7.5, 10.0, and 12.5 min) prior to printing, and investigated their printability and chemical, physical, and biological properties. Rheological analyses revealed that all inks were suitable for extrusion-based 3D printing (G' > G″), with CSAA 7.5 demonstrating optimal print fidelity and uniformity. Aging time significantly influenced pore structure, mechanical strength, and swelling behavior-key factors in biomedical use. CSAA 12.5 showed the highest swelling ratio and dye uptake/release due to enlarged, interconnected pores, while CSAA 5.0 exhibited unexpectedly high adsorption from its large surface area. All CSAA hydrogels demonstrated excellent biocompatibility (cell viability >81.05 ± 3.72%) and antibacterial efficacy (up to 99.99% reduction). In addition, fibroblast assays confirmed that CSAA hydrogels promoted cell migration and collagen production, supporting tissue regeneration. These findings highlight the importance of aging time in bioink design and demonstrate that the developed materials hold strong promise for skin grafting applications.