Hydrogel formation by liquid-solid phase transition of hagfish intermediate filament protein condensates

Hagfish intermediate filament (IF) proteins, which are released from their cells in response to external stimuli, exhibit excellent mechanical properties and biodegradability, with broad material development applications. This study aims to construct hagfish IF-based hydrogels by modulating intermolecular interactions through the coexistence of electrolytes and polymers that are capable of inducing phase separation and subsequent phase transition. Analyses of monomerized and purified IF proteins revealed condensate formation in the presence of appropriate polymer and electrolyte concentrations. Furthermore, the condensate formed by liquid-liquid phase separation and/or liquid-liquid crystalline phase separation underwent a liquid-solid phase transition to form a macroscopic hydrogel. During hydrogelation, the proteins exhibited a structural shift toward β-sheet-rich conformations, indicating that intermolecular β-sheet interactions serve as the primary driving force for structuring. These findings suggest that condensates and hydrogels can be generated via phase separation and phase transitions of hagfish IF proteins, offering a promising route toward sustainable biomaterial development.