Michell's-Instability-Mediated Fast Reconfiguration of Hydrogel-Based Ring Actuators

Area of Science:

• Soft robotics
• Mechanical engineering
• Materials science

Background:

• Michell's instability is a classic mechanical phenomenon in elastic rings, rarely applied to soft actuators.
• Instability occurs when pre-torsion exceeds a critical value, causing shape transition to a figure-of-eight.
• Soft actuators typically lack rapid shape-morphing capabilities.

Purpose of the Study:

• To develop novel hydrogel-based ring actuators utilizing stimulus-triggered Michell's instability.
• To achieve fast shape morphing in soft actuators through controlled mechanical instability.
• To explore the potential of Michell's instability in designing advanced soft machines.

Main Methods:

• Fabrication of hydrogel ring actuators with anisotropic structures.
• Triggering shape transitions using external stimuli like heating and light irradiation.
• Conducting experiments and simulations to analyze instability mechanisms and influencing factors.

Main Results:

• Hydrogel rings rapidly transformed from saddle-shape to figure-of-eight configuration upon heating or light exposure.
• Stimuli-induced changes in bending and torsional stiffnesses were identified as the mechanism reducing critical twist for instability.
• Actuators demonstrated fast actions in aqueous conditions, performing tasks like screwing and object manipulation.

Conclusions:

• Stimulus-triggered Michell's instability provides an effective mechanism for fast-acting soft actuators.
• The design principle can be applied to develop other soft machines with rapid, large-amplitude shape changes.
• This work highlights the potential of exploiting mechanical instabilities in soft robotics design.