Core–shell fibrous threads loaded with VEGF plasmid polyplexes for sustained, threshold-guided gene delivery

Precise regulation of vascular endothelial growth factor (VEGF) delivery is essential for angiogenesis-oriented tissue engineering, because excessive or poorly controlled VEGF exposure may lead to abnormal and immature vascular structures. In this study, aligned core-shell fibrous threads loaded with deoxycholic acid-modified branched polyethylenimine/plasmid encoding VEGF (bPEI1.8-DA/pVEGF) polyplexes were developed as a scaffold-mediated platform for sustained VEGF gene delivery. The polymer/plasmid DNA weight ratio was first optimized in human umbilical vein endothelial cells (HUVECs), and a ratio of 2 was selected based on reporter-gene expression and cytocompatibility. The pVEGF polyplexes were then incorporated into the aqueous core of gelatin/poly(ε-caprolactone) (70:30) fibers using modified coaxial electrospinning equipped with a rotating disk collector. Electron and fluorescence microscopy confirmed the formation of bead-free aligned fibers with a core-shell architecture and successful polyplexes incorporation. The aligned fibers were twisted into cohesive fibrous threads with an average diameter of approximately 148 μm. Genipin crosslinking preserved the fibrous morphology, improved scaffold stability, and increased Young's modulus from 37.13 to 49.81 cN/Tex while reducing extensibility. In vitro release studies showed that the core-shell structure, crosslinking, and compact thread architecture reduced the initial burst release and prolonged polyplex delivery over 33 days. The initial polyplex release from crosslinked threads was 16.59%, approximately 35% lower than that from crosslinked webs, and the released polyplex amount remained below the 100 ng threshold level for up to 16 days. Released polyplexes retained reporter-gene expression capability, and enzyme-linked immunosorbent assay confirmed prolonged VEGF secretion by HUVECs. The scaffolds also supported cell adhesion and metabolic activity. These findings indicate that aligned core-shell fibrous threads can provide sustained plasmid polyplex availability, prolong downstream VEGF secretion, and serve as a promising platform for localized angiogenic gene delivery, particularly in applications requiring directional fibrous architecture and localized vector delivery.