Norepinephrine-loaded thermoresponsive hydrogel-like system for enhanced angiogenesis in tissue engineering

Inadequate vascularization in thick biofabricated tissues and organs leads to hypoxia and graft failure, highlighting the critical role of angiogenesis in the clinical translation of tissue engineering. Norepinephrine (NE), a neurotransmitter and hormone, regulates vascular tone and modulates angiogenesis through proangiogenic factors, offering an option for improving vascularization and tissue integration. This study aimed to characterize an injectable and in situ forming hydrogel-like system made of poly(N-vinylcaprolactam) (PNVCL) loaded with NE, and evaluate its effects on endothelial cell models. PNVCL was successfully synthesized via free-radical polymerization, as indicated by ¹H NMR and FTIR spectroscopy. The polymer exhibited a glass transition temperature (Tg) of 194 °C and thermoresponsive behavior with a lower critical solution temperature of 34 °C. NMR spectroscopy indicated through-space dipolar couplings between NE and PNVCL hydrogens, which suggest interaction groups within the NE-PNVCL system. This system protects NE from degradation, as indicated by absorption spectroscopy. The PNVCL system exhibited a burst release of NE followed by a controlled release profile, with approximately 80 % and 87 % of the NE released within 24 h and 72 h, respectively. In human umbilical vein endothelial cells (HUVEC) culture, NE reduced migration and enhanced tubulogenesis, indicating a dual role in angiogenesis. In addition, NE promoted sprout formation in endothelial cell spheroids. These findings highlight the potential of NE-loaded PNVCL systems to enhance angiogenesis and vascularization in tissue engineering.