Injectable Hydrogels of Stimuli-Responsive and Surface-Adhesive Multi-Block Copolypeptides

Surface adhesive proteins biomimicked from mussel foot proteins (MFPs) have been of interest for tissue engineering and regenerative medicine. Especially, 3, 4-dihydroxyphenylalanine (DOPA) residues of MFPs play a major role in controlled adhesion on the various surfaces under wet conditions. In addition, stimuli-responsive multi-block copolypeptides composed of elastin- or resilin-based blocks are applied as injectable hydrogels for facile administration of various biomedical applications. In this study, ABA type tri-block copolypeptides composed of MFP and elastin-based polypeptide (EBP) with thermal responsiveness were genetically engineered, over-expressed in <i>E. coli</i> and non-chromatographically purified. Hydroxylation of Tyr residues of MFP middle block was executed by either mushroom tyrosinase or bacterial co-expression to finely control the degree of modification. Hydroxylated EBP-MFP-EBP (hEME) triblock copolypeptides showed different lower critical solution temperature (LCST) behaviors depending on concentration and hydroxylation as compared to those of unmodified ones. Especially, the hEME triblock copolypeptides under concentrated conditions showed thermally triggered hydrogelation within several minutes because of physical cross-linking of the aggregated EBP blocks above LCST and oxidation of DOPAs into dopaquinones with sodium periodate. Furthermore, the hEME triblock copolypeptide hydrogels exhibited controlled surface adhesion properties on the metal surface as well as porcine skin under wet conditions due to DOPA-mediated intermolecular cross-linking via oxidation. Moreover, to finely tune the surface adhesiveness on the various surface, concentration of sodium periodate, incubation time, and temperature were optimized so that the hEME triblock hydrogels showed maximum adhesive strength of approximately 0.7 MPa. In conclusion, the injectable hydrogels of stimuli-responsive block copolypeptides with surface adhesive properties would be potential as tissue adhesives or hemostasis biomaterials for tissue engineering and regenerative medicine.