Tailorable Hydrogel Fibers from High-Yield Recombinant Hagfish Intermediate Filament Proteins: A New Frontier in Biomimetic Materials

Protein-based hydrogel fibers represent a promising class of biomaterials for biomedical applications. Previous work has demonstrated high expression yields for recombinant hagfish intermediate filament (rHIF) proteins and the ability to form rHIF-based fibers with tunable mechanical properties. Given that the natural environment of native HIF threads is aqueous, this study investigated the formation and characterization of rHIF-based hydrogel fibers in aqueous environments. Individual rHIF-α (α) and rHIF-γ(C387S) (γ) proteins, as well as the 1:1 α/γ, were solubilized in formic acid (97%) at concentrations ranging from 10 to 25% w/v and spun into either deionized or saltwater coagulation baths. The resulting hydrogel fibers exhibited highly tunable mechanical properties, with elastic moduli ranging from ∼102 to ∼103 kPa, depending on protein concentration and coagulation conditions. Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) analysis suggests β-sheet content of 45.9–59.2% across deionized or saltwater spinning conditions, while scanning electron microscopy (SEM) revealed nanoporous structures along the hydrogel fiber axis. The combination of tunable mechanical properties, nanoporous architecture, and high recombinant protein yields, achieved using recombinant proteins alone with a green solvent and water-based coagulation, positions rHIF hydrogel fibers as a scalable, sustainably processed platform for various applications.