A micro-scale gripper uses a liquid-permeable surface to handle fragile components like chips and thin films without applying mechanical force or contact.
(Nanowerk Spotlight) Micromanipulation may sound like a solved problem—after all, robotic arms and automated pick-and-place machines are standard tools in modern manufacturing. But at sub-millimeter scales, the rules change. Objects become too light for gravity to help. Mechanical grippers that work at larger sizes risk tearing or crushing thin, flexible components. Even minimal contact can damage the fragile structures used in next-generation micro-LEDs, bioelectronic sensors, and flexible circuits.
This scale-dependent mismatch between force and fragility creates a persistent obstacle for engineers building small devices with high performance and dense integration. Handling a 600-micron LED chip or a 25-micron-thick inductor might seem trivial in theory, but the physical realities are unforgiving. Existing tools often rely on van der Waals forces, suction, or mechanical pressure—all of which either fail to grip consistently or apply too much stress during release. Worse, ultrathin structures tend to stick to the substrate after pickup, making detachment unreliable and potentially damaging.
Researchers have explored a range of non-mechanical adhesion strategies to address these issues. Electrostatic, magnetic, and viscoelastic methods have shown promise but introduce their own complexities or require specialized surfaces. Capillary adhesion—using a thin layer of liquid to generate attractive force between surfaces—offers a different path. It doesn’t need applied pressure, works on many materials, and is naturally scalable. However, its practical use has been limited by a lack of control: gripping is easy, but release is slow and difficult to fine-tune. Switching between strong adhesion and near-zero contact without mechanical intervention remains a major technical gap.
This gap is precisely where a new approach developed by researchers at KAIST and MIT offers a solution. By engineering a nanoscale surface that interacts precisely with small volumes of liquid, they have created a capillary-based gripper that can switch between adhesion and release with minimal force and no physical contact (Advanced Science, “Nanoporous Capillary Gripper for Ultragentle Micro‐Object Manipulation”).
The key lies in a carefully structured surface made from vertically aligned nanowires that are both liquid-permeable and mechanically stable. This allows the gripper to handle fragile micro-objects—such as sub-millimeter chips and thin polymer films—with precision, repeatability, and no solid contact during release.
Nanoporous capillary gripper for small object pick and place. A) Sequential depiction of the process flow and working principle. Upon liquid introduction, capillary adhesion enables object pickup, and as the liquid evaporates, the reduced adhesion allows for non-contact placement, B) Representative surface morphology before and after liquid wetting. (Image: Reprinted from DOI:10.1002/advs.202508338, CC BY) (click on image to enlarge)
The system operates by regulating capillary adhesion through a nanoporous interface. This surface is composed of a dense forest of vertically aligned carbon nanotubes, each about 79 nanometers in diameter, grown on a rigid or flexible backing. A thin ceramic coating of zinc oxide is applied to reinforce the structure and maintain its form through repeated wetting and drying.
When liquid is introduced into the porous surface, it infiltrates the array, creating a meniscus between the gripper and the object. This liquid bridge generates attractive pressure through two mechanisms: the curvature-induced Laplace pressure and the surface tension along the contact perimeter. Together, they provide sufficient grip to pick up small objects with no applied preload.
To release the object, the liquid is simply allowed to evaporate. Once dry, the gripper’s surface loses its adhesive strength, since only a few nanoscopic contact points remain. The number of contact asperities—the tiny regions where actual surface-to-surface contact occurs—is minimized by the surface’s rough, porous architecture. This transition between strong grip and minimal adhesion occurs without moving parts or external pressure. In practical terms, it enables contact-free placement of delicate micro-objects, with the grip-and-release process controlled entirely through liquid addition and removal.
To study the system’s performance, the researchers fabricated two variants of the gripper: one with a silicon backing and another using a polyimide film perforated with micrometer-scale holes. The latter allowed for continuous liquid delivery from the back side, improving efficiency for repeated pick-and-place operations. In both designs, the nanotube arrays were grown using chemical vapor deposition, then refined using plasma etching to remove surface entanglement and improve porosity. Atomic layer deposition of zinc oxide added structural stiffness, preventing collapse or deformation during use.
Microscopic adhesion tests confirmed the gripper’s performance across both dry and wet states. Using atomic force microscopy, the pull-off force for a dry surface was measured at just 2.6 nanonewtons. In contrast, when the surface was wetted with tetradecane—a low-volatility liquid with moderate surface tension—the pull-off force increased to 195 nanonewtons. This 75-fold difference in adhesion demonstrates the system’s ability to switch states with high contrast. Importantly, this adhesion modulation is independent of preload. Unlike traditional contact-based methods, the gripper does not need to press against the object to activate adhesion.
The team also explored how the choice and volume of liquid affected grip strength. Higher surface tension fluids produced stronger capillary adhesion, and smaller liquid volumes enhanced the effect by increasing Laplace pressure within the meniscus. This finding matches theoretical predictions: as the volume of the liquid bridge decreases, the pressure difference it generates increases, strengthening the grip. The gripper’s nanoporous design makes this possible because it supports uniform liquid distribution at very small volumes. This contrasts with traditional droplet-based systems, which require larger fluid quantities and offer less control.
Millimeter-scale tests demonstrated that even objects with negligible weight could be released without solid contact. In one test, a 0.22-milligram LED chip measuring 600 micrometers on each side was picked up and placed using ethanol. As the ethanol evaporated, the chip detached cleanly without physical contact between the gripper and the target surface. A similar result was achieved with a thin polyimide film weighing 0.33 milligrams and covering an area of 1.8 square millimeters. The nominal adhesive pressure was under 2 pascals—lower than the gravitational force acting on the film.
While the liquid-driven adhesion is effective, its release time depends on evaporation, which can be slow under ambient conditions. To accelerate this process, the researchers integrated a Joule heater into the gripper. A thin-film heater on the gripper’s back side supplied controlled thermal energy, reducing the time needed to transition from wet to dry state. With a heating power of approximately 5 watts, the release time improved by a factor of five. A more efficient version using a 40-nanometer platinum layer deposited directly on the gripper backing achieved object release in under 10 seconds.
Modeling showed that the release time is inversely proportional to heating power, assuming most of the thermal energy is used to convert liquid into vapor. This relationship matched experimental results and confirmed that evaporation-driven release could be controlled reliably through modest heating. This feature is essential for practical use, where rapid pick-and-place cycles are needed.
The dry-state adhesion remained low even under varying mechanical conditions. This was attributed to the nanowire geometry, which limits the number of actual contact points. Pull-off force increased only slightly with preload, confirming that the surface does not deform significantly under applied force. Modeling using established contact mechanics principles showed that the number of active contact points—and hence total adhesion—rises gradually as the indenter compresses the nanowire forest. But even at higher preload levels, adhesion remains low because the structure resists deformation and maintains sparse contact.
In applied demonstrations, the gripper successfully manipulated a range of fragile objects. A micro-architected structure measuring 3 by 3 millimeters was picked up and placed with less than 5 pascals of applied pressure. A 25-micrometer-thick copper inductor on a polyimide film was transferred and measured before and after placement. Inductance and resistance values showed no significant changes after seven full pick-and-place cycles, confirming that the device was not mechanically or electrically damaged.
The gripper also handled multiple components simultaneously. A patterned array of nanoporous contact zones allowed the placement of three small capacitor chips (0.5 by 1 millimeter each) in a single operation with sub-millimeter placement accuracy. Repeatability tests showed that the gripper could perform 45 consecutive pick-and-place cycles without loss of function or change in adhesion. The system remained effective even when handling lightweight materials such as aluminum foil after multiple uses.
Taken together, the results suggest that the nanoporous capillary gripper provides a reliable and adaptable method for manipulating small, delicate materials. Its combination of tunable adhesion, contact-free release, and mechanical robustness addresses key limitations in current microassembly tools. By eliminating the need for mechanical preload or solid contact, it reduces the risk of damage to fragile structures. The ability to handle ultrathin electronics, architected materials, and sub-millimeter components with precision makes it a strong candidate for integration into flexible device manufacturing and advanced semiconductor packaging.
Future extensions may involve integrating electrostatic or magnetic forces to further enhance performance. Since both capillary and electrostatic forces scale favorably at small sizes, a combined system could achieve stronger adhesion without compromising release precision. Active control over wetting—using techniques such as electrowetting—could also enable more complex gripping behaviors. For now, the demonstrated approach shows that careful control over liquid interaction and surface geometry can enable new capabilities in ultragentle micro-object handling.
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