Engineered β-Crystal Domains Enable Strong Humidity-Responsive Actuation in Recombinant Spider Silk

Area of Science:

• Biomaterials Engineering
• Protein Engineering
• Soft Robotics

Background:

• Conventional polymer actuators lack mechanical strength and humidity tolerance.
• Replicating spider silk's water-responsive actuation is difficult due to hydration-induced structural changes.
• Need for robust protein fibers for soft actuators under physiological conditions.

Purpose of the Study:

• To engineer humidity-responsive protein fibers with enhanced recovery stress and structural integrity.
• To overcome limitations of conventional actuators using a recombinant spidroin system.
• To develop a generalizable molecular design for moisture-resilient protein actuators.

Main Methods:

• Engineered recombinant spidroin fibers with terminal cysteine crosslinking.
• Utilized shear-assisted wet spinning for site-specific disulfide bond formation.
• Employed molecular dynamics simulations and spectroscopic analyses to confirm structural integrity.

Main Results:

• Optimized C4S fibers exhibited preserved beta-sheet alignment even at 90% relative humidity.
• Achieved reversible and controllable humidity-driven actuation with rapid contraction.
• Delivered a recovery stress of 45 MPa and work density of 122 kJ m⁻³.

Conclusions:

• Sequence-encoded crystalline locking provides a robust strategy for moisture-resilient protein actuators.
• The engineered fibers significantly outperform synthetic actuators and human skeletal muscle.
• Potential applications include soft robotics, adaptive textiles, and biomedical devices.