Carbon fibers bend and straighten under electric control

by Robert Schreiber
Berlin, Germany (SPX) Feb 27, 2026
Controlled manipulation of fibers that are as thin as or thinner than a human hair remains a major challenge in micromechanics and soft robotics. Researchers at the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw have now shown that bare carbon fibers can be bent and straightened reversibly using electricity, without any additional coatings or structural modifications to the fibers themselves. Their proof-of-concept experiments demonstrate how asymmetric electrochemical processes within the material can turn pristine carbon fibers into miniature actuators.

The work targets a long-standing gap in the manipulation of microfibers and nanofibers. Advances in materials engineering have delivered many so-called smart materials that change color, shape, or other properties in response to stimuli such as electric fields, light, temperature, or pH, enabling applications in sensors, textiles, and medicine. In many of these systems, however, fibers must be specially engineered or coated to respond in a controlled way, which complicates fabrication and limits scalability. The new approach instead exploits the intrinsic structure and electrochemical behavior of commercially available carbon fibers.

The team led by Dr. Wojciech Nogala at the Institute of Physical Chemistry (IChF) placed a single carbon fiber with a microscale diameter in a closed bipolar electrochemical cell. Bipolar cells, used for decades in biosensing, electrochemical reactors, and batteries, allow redox reactions to occur at both ends of an electrically floating conductor when an external voltage is applied across the electrolyte. In this setup, the carbon fiber serves as a freestanding bipolar electrode immersed in an electrolyte that contains lithium and perchlorate ions, along with benzoquinone and hydroquinone as a redox couple.

Two types of carbon fibers were investigated: one with a smooth surface and another with an asymmetrically rough surface. Ions from the supporting electrolyte insert into the fiber surface when sufficient voltage is applied, and they are expelled when the potential is reversed. In the asymmetrically rough fiber, the distribution of pores is uneven along the surface, which leads to a nonuniform ion insertion profile and, in turn, an asymmetric mechanical response. As a result, the rough fiber bends under applied voltage and returns to its original straight configuration when the potential is removed or reversed, while the smooth fiber exhibits a different and more symmetric response.

The actuation mechanism is rooted in the way the electrical double layer and redox reactions develop along the asymmetric fiber. According to Dr. Nogala, "We successfully used the closed bipolar cell to wirelessly actuate a freestanding carbon fiber electrochemically. An uneven electrical double layer is enabled by the naturally asymmetric groove configuration in the fiber, which is one of the fundamental factors in producing the necessary initial asymmetry. This leads to asymmetric tension and contraction in the fiber. Simultaneous oxidation and reduction reactions in the two compartments of the bipolar cell allow for wireless actuation." In practical terms, ions move into the carbon structure on one side of the fiber while leaving it on the other, creating differential strain that bends the fiber.

Because the process is reversible, cycling the voltage causes the fiber to repeatedly bend and straighten, effectively functioning as a microscopic tweezer. The amplitude of the motion depends on both the applied voltage and the fiber length, allowing the actuation to be tuned for specific tasks. The researchers also show that voltage pulses can drive periodic motion, with the frequency and magnitude controlled by the pulse shape and duration. This wireless control avoids the need for direct electrical connections to the fiber, which can be difficult to implement at very small scales.

The demonstrated system points toward new designs for microactuators and synthetic muscles based on prefabricated asymmetric carbon fibers. Arrays of such fibers could be integrated into miniaturized devices for microrobotics, targeted manipulation of materials, or other applications that require precise movement on small length scales. In soft robotics, where compliant and lightweight actuators are crucial, the combination of low density, high mechanical strength, and favorable electrical properties makes carbon fibers particularly attractive.

Beyond robotics, the authors note that the concept could be extended to other electrochemically active carbon-based structures and to different electrolytes or redox systems. Adjusting the pore structure, surface chemistry, or electrolyte composition could tailor the actuation characteristics, such as bending direction, response speed, or operating voltage range. The work thus opens a route toward engineering families of carbon-fiber actuators optimized for specific environments or functions without fundamentally changing the underlying actuation principle.

Research Report: Bipolar electrochemical tweezers using pristine carbon fibers with intrinsically asymmetric features