Representative images of hypoxia-inducible factor-1α immunohistochemical staining in each group at 1, 2 and 3 months. GO@RAPA-SEMS: graphene oxide-loaded rapamycin-coated self-expandable metallic airway stent; PLGA@RAPA-SEMS: poly(lactic-co-glycolic) acid-loaded rapamycin-coated self-expandable metallic airway stent; SEMS: self-expandable metallic stent.