Researchers from Hanyang University have developed a novel DLP 3D printing method that harnesses overcuring to produce gecko-inspired soft actuators. Published in Microsystems & Nanoengineering (April 2025), the technique offers improved wafer handling and points to broader applications in soft robotics and biomedicine.
The team, led by Sooheon Kim and Hongyun So, exploited the overcuring phenomenon, usually seen as a defect, to create anisotropic microstructures that mimic the natural adhesion capabilities of gecko feet. These structures, produced without complex lithography, demonstrate controlled directionality in adhesion and detachment, ideal for delicate surfaces like silicon wafers.
Turning a flaw into a feature
In traditional DLP 3D printing, each layer of an object is formed by exposing a liquid photopolymer resin to patterned UV light, triggering a chemical reaction that solidifies the resin where light is concentrated. However, due to the optical properties of the resin and the scattering or transmission of light beyond the target layer, unintended curing, known as overcuring, can occur in adjacent areas, often leading to feature distortion or loss of resolution. Rather than treating this as a flaw to be mitigated, the researchers strategically embraced the phenomenon. By precisely tuning exposure time, light intensity, and layer geometry, they manipulated the depth and direction of UV penetration, causing parts of the structure to cure asymmetrically.
This controlled overcuring leads to the spontaneous formation of tilted, anisotropic microstructures from otherwise symmetrical CAD models, transforming a passive side-effect into an active design tool. The result is a simplified and scalable method to produce functional microstructures with high repeatability, eliminating the need for complex CAD modifications or secondary fabrication processes.
Testing and Performance
The anisotropic pillars fabricated via controlled overcuring were employed to produce PDMS-based soft grippers through a double-casting process. These grippers exhibited strong, reversible adhesion on smooth surfaces, reliably lifting a range of test objects, including 4-inch and 8-inch wafer analogs and heavy glass dishes, up to 165 g in weight, using only minimal mechanical input.
Finite element simulations comparing standard 3D printed structures to the overcured designs revealed a reduction of up to 18.7% in maximum von Mises stress under loading conditions. This indicates that the smoother surfaces and continuous geometry of the overcured pillars reduce stress concentrations typically found at layer junctions in additive manufacturing. As a result, the grippers showed improved structural durability, withstanding repeated deformation during gripping and release without significant degradation.
Durability tests further validated the robustness of the adhesive surfaces. After deliberate dust contamination, the adhesive strength initially dropped to near-zero but was restored to 96.78% of its original value following simple cleaning with isopropyl alcohol, demonstrating reusability in practical environments. Additionally, under a preload of 9 N, the grippers maintained consistent performance across ten consecutive adhesion-detachment cycles, highlighting the reliability of the overcuring-based anisotropic design in repeated-use scenarios.
Beyond Robotics: A Platform for Functional Microstructures
While the immediate application is focused on wafer handling, the implications of this controlled overcuring technique extend well beyond soft robotics. By intentionally manipulating light exposure during DLP printing, the process enables the fabrication of geometrically complex and directionally biased microstructures in a single print step, without the need for lithography or post-processing. This opens the door to novel applications in microfluidics, where precisely tilted or constricted pathways could regulate fluid flow passively, enabling the design of smart channels for lab-on-a-chip diagnostics or autonomous chemical processing.
In filtration systems, the ability to create structures with gradient porosity could be harnessed to develop membranes capable of selective particle capture or variable flow resistance, potentially useful in biomedical implants or environmental monitoring. Similarly, pressure-sensitive valves or self-regulating flow components could be created by locally adjusting overcuring depth and orientation, allowing structures to mechanically respond to internal pressure or temperature changes without requiring electronic control systems. These possibilities suggest a future where the overcuring phenomenon, once considered a printing flaw, could become a cornerstone for functional microstructure engineering in biomedicine, wearable devices, and microelectronic packaging.
Biomimetics and Additive Manufacturing
Biomimetic design is increasingly being considered in design for additive manufacturing, enabling researchers to replicate complex natural functions through engineered materials. Back in 2021, scientists from Zhejiang University used 3D printing to recreate the layered microarchitecture of cuttlefish cuttlebones, resulting in lightweight yet highly impact-resistant structures that could inform next-generation protective gear or aerospace components. In another example, researchers developed a method to produce safer, structurally colored 3D printed parts by mimicking butterfly wing nanostructures, avoiding the use of toxic pigments. More recently, Harvard scientists 3D printed biomimetic blood vessels with helical flow patterns inspired by real arteries, showing promise for vascular grafts and regenerative medicine. The use of overcuring in DLP to create anisotropic adhesive surfaces modeled after gecko setae fits squarely within this growing field, pushing biomimicry beyond visual resemblance into functional emulation.
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Featured image shows gecko-inspired anisotropic soft gripper surface fabricated using DLP 3D printing. Image via Kim et al., Microsystems & Nanoengineering, 2025.
