3,4-Dihydroxyphenylalanine (DOPA)-Containing Silk Fibroin: Its Enzymatic Synthesis and Adhesion Properties.

Silk fibroin (SF) is a fascinating natural biomaterial that exhibits remarkable mechanical properties and biocompatibility. Meanwhile, biological adhesive materials have gathered much attention as biomedical and ecofriendly materials as a result of their characteristic properties. Herein, we report the excellent adhesive function of enzymatically modified SF. The tyrosine residues of SF were successfully converted to the dihydroxy-l-phenylalanine (DOPA) unit using tyrosinase as a biocatalyst. The content of DOPA was evaluated by amino acid composition analysis. Adhesive functions of DOPA-modified SF (DOPA-SF) among several material surfaces including mica, paper, polypropylene, wood, and silk film were elucidated by lap shear tests. Fourier transform infrared measurements demonstrated that the adhesion strength of DOPA-SF was not directly related to the β-sheet formation of silk molecules. This ecofriendly and facile method offers a new perspective for fabricating natural adhesive materials for various application areas.