(692e) Enhancing Water-Responsive Actuation Energy of Silk through Tyrosine Residue Engineering

Bombyx mori regenerated silk fibroin, which significantly expands and contracts in response to changes in environmental relative humidity, has the potential to be used in developing high-performance water-responsive actuators. Here, we found that the water-responsive actuation energy density of regenerated silk fibroin can be more than doubled through tyrosine residue modification, increasing from 1.6 MJ m^-3 to 3.5 MJ m^-3. To achieve this, diazonium coupling chemistry was employed to attach a hydrophilic-charged sulphonate group to silk fibroin’s tyrosine residues. A greater degree of modification increased the material’s bulk hydrophilicity, resulting in a lower water contact angle, and an increase in the maximum water adsorption. Fourier transform infrared spectroscopy studies demonstrated that, while this modification did not alter the secondary structure of regenerated silk fibroin, it influenced the structure of the adsorbed water and resulted in a higher proportion of mobile water. These findings suggest that water-responsive performance of regenerated silk is highly sensitive to the properties of confined water, and that tyrosine residue modification could serve as a scalable method for developing silk-based WR actuators.