Barnacle-Inspired robust and aesthetic Janus patch with instinctive wet adhesive for oral ulcer treatment

Oral ulcers (OUs) are the most common lesions of the oral mucosa and severely reduce patients' quality of life. Several types of patches for the self-treatment of OU have been developed, which have partially alleviated the problems caused by OUs. However, their wide application is limited by a few factors, including the suboptimal adhesion to the wound in the complex oral environment and the discoloration of the degraded products. Herein, an ideal Janus patch for the accelerated treatment and cure of OUs, comprising bifunctional sides, was designed. Inspired by the composition and hybrid adhesive mechanism of barnacles, glycine was modified and combined with hydroxyapatite nanoparticles (HAp) to create an adhesive layer that would form abundant covalent bonds with tissues; the HAp act as a bridge to bond polymer chains mimicking the organic–inorganic hybrid mechanism of barnacles, achieving analogous instant wet adhesion. Additionally, double bond-modified gellan gum served as a slippery layer to avoid undifferentiated adhesion and secondary damage. When applied to rat OUs, the Janus patch exhibited instant wet adhesion, with the longest residue time, overcoming the limitations of commercial products, and withstood chewing and biting and other mouth movements, thus achieving an excellent therapeutic efficacy.