Mussel foot inspired bionic adhesive material enhanced by a reconstructed in vitro system for interfacial adhesion

The strong adhesion abilities of mussel adhesive protein in wet environment rely on complicated solidified processes. Among these processes, several are found to be key factors affecting underwater interfacial adhesion, including post-translational modification for tyrosine catalyzed by tyrosinase in gland cells, protein storage and DOPA antioxidation in vesicles after the modification reaction, delayed oxidation at the interface and pH change after protein secretion in seawater. In view of this, an in vitro system simulating the natural underwater adhesion process is reconstructed in this study to prepare the mussel inspired bionic material. First, a mussel foot protein (Mfp) -3/5 mimetic precursor (PGA-Tyr-Arg) is prepared as substrate in the reaction. Second, different reductants are compared to prevent DOPA-catechol groups oxidation. Tannic acid proves to have minimal inhibition of tyrosinase activity while functioning properly as the suitable antioxidant during tyrosinase catalyzed modification reaction. And Mfp6 biomimetic protein (PGA-Cys) is used as antioxidation for storage and adhesion phases after modification reaction, because it has more negative effects on tyrosinase activity and better oxidation resistance. Third, the new immobilized tyrosinase, IEAMNP-Cu2+ -Tyrosinase overcomes the deficiencies of free tyrosinase and other immobilized tyrosinases in catalyzing large molecule substrates and achieves enhanced activity recovery (similar to 150% to 300%), rapid separation from the catalyzed system, and high conversion of tyrosine to DOPA (93%). The bionic adhesive material prepared by this reconstructed in vitro system can achieve up to 9.5 MPa of lap shear strength, showing it can improve the interfacial adhesion of mussel inspired bionic materials.