3D bioprinting of mechanically graded GelMA hydrogels with tri-layered vascularized architecture for full-thickness skin regeneration

Skin is the largest organ of the human body and serves as the primary barrier against external environmental insults. However, in cases of severe skin damage or pathologic conditions, the body's natural physiological repair mechanisms are often insufficient to meet the requirements for skin tissue repair and regeneration. Bioprinting, a form of 3D printing technology, utilizes a variety of materials and cells to construct complex three-dimensional structures, offering the potential to overcome the limitations of tissue-engineered skin and create functional skin substitutes. In this study, we developed a 3D bioprinter with excellent printing performance to fabricate vascularized skin substitute. Through methacrylic anhydride-mediated modification of gelatin, we synthesized GelMA with varying degrees of substitution, and the results demonstrated that GelMA exhibits excellent mechanical properties, swelling ratio, porosity and rheological properties. The hydrogel-multicellular composite ink was fabricated by adjusting the concentration of the GelMA solution with co-culturing HaCaT cells, HFF cells and HUVECs to achieve optimal biological function. Importantly, through adjustments to the printing process parameters, the 3D extrusion-printed lines fused into a membrane and the interlayer bonding of bioink with mechanical differences was enhanced, thereby constructing a vascularized skin substitute containing reticular and papillary layers. In addition, the 3D-printed vascularized skin was implanted into the skin defect models of BALB/c-nu and New Zealand rabbits to further investigate the repair effect of vascularized skin on the defective tissues. The findings of this study hold significant implications for utilizing 3D-printed vascularized skin to enhance skin injury repair and will provide an effective pathway for the advancement of skin tissue engineering technologies.