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.