Light- and Solvent-Responsive Bilayer Hydrogel Actuators with Reversible Bending Behaviors.

Area of Science:

• Materials Science
• Polymer Chemistry
• Robotics

Background:

• Light-responsive hydrogels exhibit controlled swelling in response to light.
• Combining responsive and non-responsive polymers enables self-folding capabilities for soft robotics.
• Achieving rapid response times in these systems remains a significant challenge.

Purpose of the Study:

• To develop a simple and versatile bilayer polymeric design for light-induced self-folding.
• To investigate the swelling behavior of light-responsive hydrogels under varying conditions.
• To demonstrate the potential of these hydrogels in soft robotic actuator applications.

Main Methods:

• Fabrication of bilayer hydrogels using light-responsive spiropyran-polyacrylamide (SP-PAAm) and non-responsive polyacrylamide (PAAm).
• Evaluation of hydrogel swelling degrees using LED light irradiation (varying wavelengths) and different solvent media.
• Assessment of self-folding capabilities in one-armed and four-armed bilayer hydrogel platforms.

Main Results:

• SP-PAAm hydrogels achieved a swelling ratio of approximately 370% under blue LED illumination in DMF.
• One-armed bilayer hydrogels demonstrated self-folding ability with a 40° angle in 30 minutes.
• Four-armed bilayer platforms exhibited enhanced and rapid folding, reaching a 75° angle in approximately 15 minutes.

Conclusions:

• The developed bilayer hydrogel design offers a simple and efficient method for creating light-responsive self-folding systems.
• The rapid folding behavior of the four-armed platforms highlights their potential for advanced soft robotic actuators.
• This work opens new avenues for designing polymeric actuators and soft robotic systems with tunable light responsiveness.