The bonding of adhesives to enamel is reliable and strong because enamel is highly mineralized. However, the bonding of adhesives to dentine is less satisfactory because dentine contains, by weight, 20% organic material (mainly collagens) and 10% water. Mussels can attach to various surfaces in aqueous conditions, ranging from natural inorganic materials and organic materials to synthetic materials . Such adhesive properties rely on exhaustively repeated 3,4-dihydroxy-L-phenylalanine (DOPA) and amine . Dopamine was identified as a small-molecule compound that contains both DOPA and amine (Figure 7). It has strong and good biodegradability and low cytotoxicity . The oxidative polymerization of dopamine in aqueous solutions spontaneously forms polydopamine . It mimics repeated DOPA and amine and therefore exhibits a strong adhesive property in relation to various substrates under wet conditions . Polydopamine is used for biomaterial surface modification because it is easy to obtain abundant active groups. These active groups are mostly phenolic hydroxyl/o-quinone and amino/imino for bimolecular immobilization on the material surface with minimal change in the chemical structure of biomaterials . The plausible mechanism of polydopamine-induced-PEG coating is shown in Figure 7. Polydopamine connects PEG with an active group of o-quinone. It can also attach to hydroxyapatite with phenolic hydroxyl (Figure 7c). This mechanism could be the reason for the promising anti-biofouling effect of polydopamine-induced-PEG coating on dentine.