Light reshapes hydrogels into reversible twists, helices and rotating robots

A uniform light-sensitive gel can form and erase handed shapes, then use those shapes to rotate for movement.

Editorial illustration — not from the study.

The study describes uniform hydrogels that change shape in response to spatially controlled light. They can form structures with a defined left- or right-handed character, including helices, twists and tendril-like shapes, despite having no built-in handedness.

The transformation is driven by photoexpansion: the gel's volume grew by more than 80,000% within 40 seconds. By coordinating regions with opposing handedness, the researchers used the resulting structures to produce self-propelled rotation for robotic locomotion.

What the gel can do

The researchers demonstrated homogeneous photoactive hydrogels that rapidly and programmably form handed shapes under controlled illumination. These included twists, helices and complex tendril-like geometries, with opposing handedness synchronized within a single material. The shape changes could be erased in darkness and reprogrammed reversibly with light. The hydrogel underwent more than 80,000% volumetric expansion within 40 seconds, driven by spiropyran photoisomerization and interactions within the polymer network. The researchers also used the programmed handedness to generate self-propelled rotation for robotic locomotion.

Why changing handedness matters

Controlling handedness—the distinction between mirror-image forms—in synthetic materials is difficult, particularly in materials that are structurally uniform and do not have inherent chirality. This work shows a way to encode and repeatedly change that property with light in a soft material. The ability to create different shapes and use them for rotation links light-controlled shape change with a form of movement relevant to soft robotics.

Evidence and open questions

This is an experimental research article reporting demonstrations in photoactive hydrogels. The abstract describes the material's shape changes, expansion and rotational motion, but it does not give sample sizes, operating conditions beyond the reported illumination-driven expansion, performance comparisons, or information about long-term durability and energy efficiency. It also does not establish how broadly the method applies beyond the demonstrated hydrogel designs and robotic movement.

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