EGF and Oral ulcer: Although some commercial oral ulcer patches (chitosan, flavonoids, etc.), powders (vitamins, etc.)and ointments (recombinant human epidermal growth factor gel, etc.)have been developed to accelerate oral ulcer healing, they suffer from low treatment efficiency due to their short retention time on the surface of mucosa in the highly humid and dynamic environment of the oral cavity (<2 h)10,11.