Spatially distributed bFGF and VEGFA gene delivery to tendon and peritendinous tissues enhances early tendon healing

Tendon healing is limited by inadequate vascularity and low cellularity within the tendon, whereas surrounding peritendinous tissues include vascular, stromal, and extrinsic reparative cells. Building on prior work involving tendon-only co-delivery of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor A (VEGFA), this study investigated whether spatially expanding gene delivery to both the tendon and adjacent peritendinous subcutaneous tissue would enhance early repair. PLGA/PEI nanoparticle complexes carrying bFGF and VEGFA plasmids were characterized for morphology, particle size, plasmid complexation, surface charge, and in vitro release, with local reporter expression assessed in vivo. Therapeutic effects were evaluated in chicken digital flexor tendon and rat Achilles tendon injury models through non-injection, tendon-only, peritendinous subcutaneous-only, and combined injection groups. The complexes demonstrated effective plasmid complexation, sustained release, and detectable local EGFP reporter expression within both tissue compartments. Combined injection significantly increased the ultimate strength of chicken tendons at 2, 4, and 6 weeks, and rat Achilles tendons at 2 weeks, compared to non-injection controls; tendon-only injection did not yield similar improvements in early strength. Higher total local bFGF and VEGFA protein levels, more visually prominent Ki-67-positive staining and CD31-positive vascular structures, together with qualitatively more organized collagen morphology. These results indicate that expanding gene expression from the tendon proper to the tendon-peritendinous microenvironment can mitigate an early limitation of tendon-only delivery, supporting the concept of enhanced dual-compartment delivery, though dose-matched studies are needed to establish synergy.