A soft robotic system uses liquid crystal elastomers to merge shape shifting, gripping, and color change, demonstrating fully integrated motion and optical feedback within a single flexible material.
(Nanowerk Spotlight) Soft and rigid architectures now coexist across robotics, from industrial arms to wearable devices. What remains uncommon is a single body that can change shape, grip objects, and communicate its state through visible color under one control signal. The barrier is not only how to move but how to coordinate movement with optical output without adding extra sensors or fragile interfaces. Materials that perform well in motion often lose color stability or durability, while those that maintain bright structural color usually cannot stretch or bend repeatedly.
Advances in responsive polymers are beginning to close this gap. Researchers can now program molecular alignment so that heat or electrical input produces controlled changes in both shape and reflected light. Liquid crystal elastomers, networks of flexible polymer chains containing organized molecules, are central to this progress. Their structure gives them both elasticity and order, allowing heat to trigger contraction or expansion and a corresponding color shift. The same physical process that drives movement can also generate an optical signal that reflects the material’s state.
A study published in Advanced Functional Materials (“OCTOID: A Soft Robotic System Featuring Programmable Shape Morphing and Dynamic Structural Coloration”) extends this concept into a complete device. It introduces an octopus-inspired system that unites programmable shape change, color adaptation, and gripping within one material platform powered by localized heating. The work demonstrates how careful control of polymer chemistry and molecular alignment can replace separate sensors, actuators, and skins with a single integrated structure.
a) Chemical structures used in the fabrication of cholesteric liquid crystal elastomers and its property change according to the concentration of the component. b) Transmittance spectra and c) stress–strain curves of active layer (AL) and passive layer (PL). (Image: Reprinted from DOI:10.1002/adfm.202520014″, CC BY) (click on image to enlarge)
Earlier robots modeled on soft-bodied animals often focused on motion alone. Some crawled or swam effectively, while others used color-changing coatings for camouflage. Achieving both functions in one device required incompatible materials or complex external control. The OCTOID system addresses this problem by using one chemical family, cholesteric liquid crystal elastomers (CLCEs), to form both soft and stiff layers.
A CLCE is a polymer in which rod-like molecules arrange into a helical pattern that reflects specific wavelengths of light. The resulting color does not come from pigments but from interference between light waves scattered by the periodic structure. When the spacing between the turns of the helix changes, so does the reflected color. The researchers use this direct link between structure and optics to create a robot whose movements are visible through color shifts.
The material design relies on two layers with different mechanical properties. The active layer is soft and brightly colored. The passive layer is stiffer and nearly transparent. Both start from the same liquid crystal monomers and follow the same reaction sequence, but two formulation variables produce their contrast in behavior.
The first is the amount of a chiral reactive mesogen, a molecule that twists the alignment of neighboring molecules into a helix. The tighter the twist, the shorter the wavelength of reflected light. Low chiral content reflects red, high content reflects blue, and very high content shifts the reflection into the ultraviolet, which appears transparent. The second variable is the amount of crosslinker that binds polymer chains together. A higher concentration yields a stiffer network; a lower one remains flexible. By adjusting these parameters, the team fabricates a red-reflecting, soft active layer and a transparent, stiff passive layer using the same basic chemistry.
Mechanical tests confirm the difference. The active layer stretches nearly three times its length before breaking and has a stiffness, or modulus, of about 2 megapascals. The passive layer stretches less than half its length and is roughly 11 times stiffer at 22 megapascals. This mechanical mismatch drives bending when the two layers are bonded.
The layers are joined using a two-step curing process. The first stage, known as Michael addition, partially links the monomers into short chains. The second stage uses ultraviolet light to complete crosslinking while the layers are stretched to align the molecules. Unreacted chemical groups left from the first stage form covalent bonds between layers in the second, producing a seamless interface. Microscopy shows no separation, and shear tests reveal that failure occurs within the soft layer rather than at the bond. The composite material endures at least 100 heating cycles without degradation.
Heating powers the motion. Thin nichrome wires arranged in wavy lines act as resistive heaters embedded in the material. When current passes through them, the wires warm the surrounding elastomer. Heat disrupts the molecular order of the liquid crystal, causing the active layer to contract along its alignment and expand across it. The helix spacing widens, shifting the reflected color toward longer wavelengths. A single input thus produces simultaneous shape change and color change.
The researchers construct three functional legs to demonstrate different behaviors. One leg changes color for camouflage, one bends to move the body, and one wraps around objects for gripping. Each module operates through the same thermal response.
a) OCTOID design integrating camouflaging, moving, and grabbing legs. b) Macroscopic images of OCTOID to demonstrate its independent color modulation and circular polarization properties. c) Simulated prey-hunting process of the OCTOID. (Image: Reprinted from DOI:10.1002/adfm.202520014″, CC BY) (click on image to enlarge)
The camouflaging leg contains two active layers with a heater between them. During fabrication, the layers are stretched and fixed so their molecules align in a single direction. In its resting state the leg reflects blue light. As it heats, the alignment decreases, the leg shortens, and the reflected color moves from blue to green and finally to red. At a power of 2 watts the leg turns green within 40 seconds. At 4 watts it turns red and contracts by about 30 percent in less than one minute.
Infrared imaging shows the surface temperature reaching about 70 degrees Celsius at maximum power. Above 80 degrees, the ordered structure collapses and the surface becomes transparent. When power is removed, the leg cools, returns to its initial length, and regains its blue color. The motion and color remain stable after 100 heating cycles.
The moving leg combines one active and one passive layer. The stiff layer restricts one side so that contraction in the active layer bends the whole strip. The degree of bending depends on layer thickness. With an active layer 400 micrometers thick, a passive layer about 50 micrometers thick gives the best curvature. Thinner passive layers produce only contraction, while thicker ones resist motion. At 4 watts, the leg bends to a radius of about 9 millimeters within 6 seconds. Alternating current between left and right legs drives crawling at roughly 0.5 millimeters per second. The motion remains consistent after 100 cycles.
The grabbing leg introduces patterned geometry. Two active layers with an internal heater form the base, while passive regions are placed only where bending is desired. Heating then causes certain zones to curl and others to contract, closing the grip around an object. A single leg weighing 0.2 grams lifts up to 6 grams within one minute at 4 watts and retains 90 percent of its strength after 100 cycles.
The leg can handle objects of varied shape and texture. Adjusting the taper angle along its length changes performance. Sharper angles grip thin objects more securely but reduce lifting capacity, providing a trade-off that can be tuned for specific tasks.
A complete OCTOID robot combines 5 color-changing legs, 2 moving legs, and 1 grabbing leg. Each leg is powered independently. In demonstrations, the robot adjusts leg colors to match surrounding materials. When placed among green vegetation and red algae, some legs appear green at moderate power, others red at higher power, and the rest remain blue with no input.
The reflected light also shows circular polarization, a property where the electric field of the light rotates as it travels. When viewed through a right-handed circular polarizer, the colors appear vivid; through a left-handed one, they fade. Many marine organisms detect such polarized light, so this feature could support signaling or concealment in future designs.
In a staged test, the robot crawls by alternating its moving legs, shifts leg colors to blend with its environment, and uses the grabbing leg to secure a small object. The demonstration shows that motion, camouflage, and grasping can all operate together through a single, unified material system.
The paper also defines current limitations. Thermal actuation is slower than electrical or pneumatic systems because heating and cooling take several seconds. Metal heaters add mass and may cause fatigue during extended use. The authors suggest that conductive polymer or carbon-based heaters, as well as improved heat transfer within the elastomer, could increase speed and efficiency. Long-term tests will be needed to measure durability beyond the reported 100 cycles.
The value of this work lies in integration. By deriving both layers from the same CLCE chemistry, the system avoids mechanical incompatibility and achieves strong bonding between components. The same process that causes movement also produces a color signal, removing the need for external sensors or coatings. The modular legs can be rearranged for different tasks, showing that a single materials platform can support multiple robotic functions.
The study in Advanced Functional Materials demonstrates that material design alone can coordinate optical and mechanical behavior. The result is a soft body that can move, display, and grip through one controllable mechanism. This approach could influence the development of adaptive surfaces, artificial skins, and responsive sensors that use visible changes to represent internal state. OCTOID illustrates how a single material framework can bring mechanical motion and visual communication together within a coherent, self-contained system.
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Dae-Yoon Kim (Korea Institute of Science and Technology)
, 0000-0002-1790-6170 corresponding author
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