Hard- and Soft-Coded Strain Stiffening in Metamaterials via Out-of-Plane Buckling Using Highly Entangled Active...

Area of Science:

• Materials Science
• Mechanical Engineering
• Polymer Science

Background:

• Metamaterials exhibit complex mechanical properties like strain stiffening, typically fixed during design.
• Post-manufacturing adaptation of these properties has been a significant challenge.

Purpose of the Study:

• To create hydrogel metamaterials with highly programmable strain-stiffening responses.
• To enable post-fabrication tuning of stiffness onset in metamaterials.

Main Methods:

• Integration of pH-switchable hydrogel actuators into metamaterial structures.
• Exploitation of out-of-plane buckling of active hydrogel beams to control stiffness.
• Tuning of acrylic acid concentration and pH to program stiffening behavior.

Main Results:

• Demonstrated hydrogel metamaterials with tunable strain-stiffening behavior.
• Achieved a step-function increase in stiffness upon reaching a specific extension due to beam straightening.
• Showcased post-fabrication programmability of stiffening onset via pH control.

Conclusions:

• Out-of-plane buckling of active elements offers a novel mechanism for tunable strain stiffening in metamaterials.
• This approach allows for pre- and post-fabrication programmability, enhancing the versatility of hydrogel actuators in mechanical metamaterials.