Silk fibroin protein is a biomaterial with excellent biocompatibility and low immunogenicity. These properties have catapulted the material as a leader for extensive use in stents, catheters, and wound dressings. Modulation of hydrophobicity of silk fibroin protein to further expand the scope and utility however has been elusive. We report that installing perfluorocarbon chains on the surface of silk fibroin transforms this water‐soluble protein into a remarkably hydrophobic polymer that can be solvent‐cast. A clear relationship emerged between fluorine content of the modified silk and film hydrophobicity. Water contact angles of the most decorated silk fibroin protein exceeded that of Teflon®. We further show that water uptake in prefabricated silk bars is dramatically reduced, extending their lifetimes, and maintaining mechanical integrity. These results highlight the power of chemistry under moderate conditions to install unnatural groups onto the silk fibroin surface and will enable further exploration into applications of this versatile biomaterial.

Weaving a tunable hydrophobic web! Silk fibroin, a protein extracted from the silkworm cocoon can be tailored to possess different properties by means of chemical functionalization. In this study, we sought to induce hydrophobicity using fluorination. Fluorocarbon‐appending iodonium salts accomplish the fluorination in one step. A trend of increasing hydrophobicity with the number of fluorine atoms was observed, with the most hydrophobic material exhibiting a water contact angle greater than that of Teflon! This work shows the first development of directly modified silk fibroin to create hydrophobic films. More information can be found in the Research Article by L. M. Davis, D. L. Kaplan, K. Kumar et al.