Protein Biomaterials with Muscle-like Water-Driven Actuation.

Unlike muscles, man-made shape-morphing biomaterials take much longer times to perform their actuation. Here we report a novel class of protein-based actuators that mimic muscle contraction through ethanol-induced fibril formation in bovine serum albumin (BSA) hydrogels, enabling reversible shape changes and fast, water-driven motion. These structural changes result in mechanical stiffening, enabling programmable and reversible shape changes, which take place over minutes to hours. At intermediate ethanol concentrations (40-80%), fibril formation dominates and contributes to shape retention, while at high ethanol concentrations (80-99%), aggregation outpaces fibrillation, allowing full recovery of the original shape upon rehydration. Furthermore, upon reinsertion into water, ethanol retention triggers stochastic pulsating motion in cylindrical samples and spins on the a protein-based propeller motor (rotational speeds up to 471 deg·s-1), a process driven by a surface tension gradient. These findings address the challenge of achieving rapid, reversible motion in biomaterials, resembling that of muscles, with promising applications in smart biomaterials, microactuators, and bioresponsive systems.