Toward 3D Printable Non-Planar Electroadhesive Structures for Active Anchoring

Imagine a world where robots could climb walls or grip slippery objects not with mechanical claws that pinch and clamp, but simply by turning on a switch. This is the promise of electroadhesion, a technology that uses electricity to create a sticky force between two surfaces. In its simplest form, it works like a powerful, invisible magnet that only appears when you apply a voltage. Unlike traditional grippers that need moving parts or constant energy to hold on, these electric pads can grab and let go instantly, making them ideal for delicate tasks or for moving through complex environments. For years, however, this technology has been stuck in a flat world. The pads are manufactured as thin, flat sheets, much like a sticker, which engineers then have to bend or wrap around curved objects like pipes or robot arms. This process is clumsy; it forces the technology to fit the object rather than letting the object's shape guide the design.

A team of researchers at the University of Twente in the Netherlands has taken a significant step toward solving this problem by printing the sticky pads directly onto curved shapes. Instead of bending a flat sheet, they used a specialized 3D printer to build the entire device, including the internal electrical components, in one go. They created two versions to test their idea: a standard flat pad to serve as a baseline, and a cylindrical pad that mimics a curved surface. The key innovation was printing the conductive electrodes—the parts that carry the electricity—directly inside the plastic body of the pad, rather than attaching them later. By using a multi-material printer, they could lay down insulating plastic and conductive plastic in the same motion, creating a single, solid object where the electricity flows exactly where it is needed, even on a curve.

The researchers tested these printed pads by pressing them against a surface and applying a high voltage to see how much extra holding force they could generate. They found that both the flat and the curved pads worked as intended. When the voltage was turned on, the pads pulled harder against the surface, creating a measurable increase in grip. The flat pad, which served as the control, generated a holding force of about 0.11 to 0.13 newtons when the voltage reached 3,000 volts. The cylindrical pad, which represented the more difficult non-flat shape, performed even better under specific conditions, reaching a holding force of approximately 0.16 newtons at the same voltage, provided it was pressed against the surface with a moderate amount of initial pressure. This result confirms that the electrical pattern can be successfully printed onto a curved body and still function effectively.

However, the experiment also revealed that shape matters. While the flat pad's performance was stable regardless of how hard it was pressed, the curved pad was more sensitive to the amount of pressure applied. The holding force increased as the pressure went up to a certain point, but then began to drop if the pressure became too high. The researchers suggest this happens because the curved surface does not touch the wall perfectly evenly. When pressed too hard, the curve might deform slightly or create tiny gaps in the contact, weakening the electrical connection. This sensitivity is a natural consequence of trying to make a curved object stick to a flat one, and it highlights that future designs will need to account for how the surface conforms to the object it is gripping.

The study also observed how quickly the pads could turn on and off. When the voltage was applied, the grip strength rose quickly, but when the power was cut, the pads took longer to release their hold. This delay is likely due to the way electrical charges linger in the plastic material and at the surface of the pad, a phenomenon common in these types of materials. This means the technology is currently better suited for holding objects in place for a while, rather than for rapid, high-speed grabbing and releasing. Despite this, the ability to print the electrodes directly into a curved structure is a major advancement. It moves the field away from the idea of a sticky pad as a separate component that must be glued or wrapped onto a robot, and toward the idea of a robot part that is inherently sticky by design. The researchers plan to continue refining the process, aiming to print the insulating layers directly into the structure as well, which would eventually allow for a completely seamless, one-piece device capable of active gripping on any shape.