Construction of gelatin methacryloyl-based artificial skin substitutes with “small-micro” vascular networks via hybrid double-crosslinked coaxial and extrusion bioprinting

The repair of deep skin defects involving subcutaneous tissue urgently requires vascularized skin substitutes capable of providing immediate blood perfusion. However, existing engineering strategies struggle to construct multi-level vascular networks in vitro. This study aimed to develop a multi-layered skin substitute with both biomimetic structure and physiological function, incorporating a perfusable "small-micro" hierarchical vascular system. We employed a composite coaxial-extrusion bioprinting strategy. First, a composite bioink of 2% sodium alginate/5% gelatin methacryloyl (GelMA) was formulated and evaluated for its printability and biocompatibility. Subsequently, using an ionic-photo dual-crosslinking coaxial printing technique, we fabricated subcutaneous small vessels with controllable dimensions and adequate mechanical properties. Finally, these small vessels were integrated with an extrusion-bioprinted dermal microvascular network and an epidermal layer to form a complete "small-micro" vascular pathway. This multi-layered construct was designed to mimic the stratified characteristics of natural skin. In vitro functional experiments confirmed that the epidermis possesses excellent barrier function, and the subcutaneous small vessels demonstrated effective drug molecule delivery capability. The dual-crosslinking coaxial printing and composite manufacturing strategy proposed in this proof-of-concept study successfully achieved the construction of vascularized skin with a hierarchical tubular structure, offering a new solution with clinical translation potential for treating full-thickness skin defects.