Perivascular injection of a pH-responsive and protease-degradable hydrogel with rapamycin-loaded liposomes inhibits neointimal hyperplasia after carotid wire injury in mice

Neointimal hyperplasia is a major cause of restenosis and graft failure after vascular interventions. Perivascular drug delivery offers a potential solution, but achieving sustained and condition-dependent release at injured sites remains challenging. Here, we developed an injectable hydrogel with pH-sensitive and protease-susceptible characteristics (OHA-CS/GelMA) encapsulating rapamycin-loaded liposomes (Rapa-Lipo@Gel). The Schiff-base network enabled pH-triggered degradation, while GelMA provided mechanical stability and intrinsic susceptibility to protease-mediated degradation. The hydrogel degraded faster and released more rapamycin at pH 6.5 than at pH 7.4 in vitro, with further enhancement by protease. Liposomes suppressed burst release. In PDGF-BB-stimulated VSMCs, Rapa-Lipo@Gel inhibited proliferation, migration, and phenotypic switching (α-SMA↑, OPN↓). In a mouse carotid wire injury model, perivascular application of Rapa-Lipo@Gel at day 14 significantly reduced neointimal area and intima-to-media ratio compared to controls. Mechanistically, treatment reduced Ki67⁺ proliferating cells, decreased CD68⁺ macrophage infiltration, reduced overall α-SMA burden, increased MYH11 expression in the neointima, and did not reduce CD31⁺ endothelial coverage. Collectively, this pH-responsive and protease-susceptible hydrogel with liposomal rapamycin provides a promising platform with preliminary safety evidence for local treatment of neointimal hyperplasia, with potential for preventing restenosis.