Pusan National University Team Develops 3D-Printed Switchable Soft Actuators

A new 3D-printable material can be programmed to either stretch or shrink when heated, giving researchers a powerful new way to build soft robots, artificial muscles, adaptive surfaces, and other shape-changing devices. The material, a smectic liquid crystal elastomer, can switch its internal molecular alignment during printing, allowing a single ink to produce opposite responses to heat.

The study, led by Professor Suk-kyun Ahn of Pusan National University in South Korea in collaboration with researchers at Oak Ridge National Laboratory in the United States, addresses a longstanding limitation in the 3D printing of responsive soft materials. Their findings, published in Nature Communications, show that adjusting the printing speed or temperature can determine whether a printed filament elongates or contracts when heated.

Liquid crystal elastomers are rubber-like polymer networks containing rigid, rod-shaped molecules known as mesogens. These molecules can change their orientation in response to temperature, causing the surrounding elastomer to deform. When the molecules are aligned along one direction, heating can produce contraction along that axis. If the alignment is oriented differently, the same thermal stimulus can instead cause the material to extend in the direction of interest.

In conventional extrusion-based printing, the flow of material through the nozzle generally aligns the liquid crystal molecules with the direction in which the filament is deposited. As a result, each filament typically has one fixed mode of actuation. Once the material has been printed, its molecular orientation cannot easily be changed, making it difficult to create structures that combine contraction and elongation without using multiple materials or complicated fabrication steps.

The new approach takes advantage of the distinctive flow behavior of smectic liquid crystal inks. Smectic liquid crystals are organized into layered molecular structures, and the layers can respond to changes in temperature and mechanical stress. During direct ink writing, the researchers discovered that altering the printing conditions could switch the molecular orientation between two perpendicular directions. A filament printed under one set of conditions could therefore contract upon heating, while the same formulation printed under another could elongate.

To understand why the alignment changed, the team combined several techniques. Rheological measurements were used to examine how the ink flowed and deformed during extrusion. Wide-angle X-ray scattering revealed the orientation of the liquid crystal molecules and their layered organization. Molecular dynamics simulations provided an atom-level view of how the molecules responded to changes in flow and temperature. Together, these results showed how processing conditions influenced the balance between molecular ordering, shear forces, and relaxation within the ink.

The researchers used this control to print both two-dimensional and three-dimensional structures with programmable shape changes. Their demonstrations included lattice-like architectures, curved forms, and surfaces capable of switching between different topographies. By placing regions with different molecular alignments next to one another, the printed structures could be designed to bend, expand, contract, or transform into more complex configurations when heated.

The material also retained its performance over repeated heating and cooling cycles, an important requirement for practical soft machines. Reversible actuation means that a device can be used repeatedly rather than functioning as a one-time shape-changing component. Such durability could be valuable in soft robotic grippers, wearable systems, adaptive textiles, haptic interfaces, and minimally invasive medical tools that must respond reliably to changes in temperature.

The ability to program both elongation and contraction using one printable ink could also simplify the design of 4D-printed devices—structures that change shape or function over time in response to an external stimulus. Potential applications include artificial muscles, reconfigurable surfaces for touch-sensitive displays, and adaptive textures that alter aerodynamic drag. The same principle could eventually allow engineers to print objects that do more than maintain a predetermined shape: they could move, grip, fold, or alter their surface properties on demand. The researchers emphasize that the current work was performed under laboratory conditions with a single smectic liquid crystal elastomer formulation. Additional studies will be needed to test other materials, improve actuation speed and strength, and determine whether the process can be scaled for industrial manufacturing. Even so, the ability to switch molecular alignment during printing represents a major step toward making shape-changing materials more versatile, programmable, and accessible for next-generation soft technologies.

News Publication Date: 10-Jul-2026

Web References: Nature Communications article; DOI link

References: Nature Communications. “Alignment switching in 3D-printed smectic liquid crystal elastomers.” DOI: 10.1038/s41467-026-75368-z

Keywords

3D printing, liquid crystal elastomers, smectic materials, soft robotics, artificial muscles, 4D printing, programmable materials, shape-changing materials, responsive polymers, materials science