| Jul 14, 2025 |
These novel materials can change, fix, and retain their shape reversibly by using magnetic fields and ultraviolet light.
(Nanowerk News) Magnetic micropillar arrays consist of tiny, vertical pin-shaped structures, arranged in a grid-like pattern. These micropillars can change their shape to a pre-programmed geometry when exposed to a magnetic field. They are made from magnetically responsive composites, comprising rubbery polymers like polydimethylsiloxane (PDMS) embedded with magnetic particles. These composites can change their shape and recover repeatedly without any deterioration.
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Unfortunately, conventional magnetic micropillar arrays can only hold their changed shape temporarily while the magnetic field is being applied. Previous studies have explored various approaches to address this issue, including water-soluble polymeric binders and coating the base of deformed micropillars with thermosetting resins that harden and fix their shape when heated. While effective for shape fixation, they introduce their limitations, i.e., water-soluble binders prevent use in aqueous environments, while thermoset resins do not allow reversible shape change.
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In a breakthrough study, a research team led by Associate Professor Chae Bin Kim from the Department of Polymer Science and Engineering at Pusan National University, South Korea, developed new materials, called disulfide-based covalent adaptable networks (DS-CAN). These materials enable shape fixation either through heating or ultraviolet (UV) light exposure.
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“We have introduced a solvent- and resin-free shape fixation strategy that addresses the drawbacks of previous methods,” explains Prof. Kim. “These new materials support UV-based activation at room temperature, allowing non-contact, precise, and spatiotemporally controlled processing that is also energy efficient.”
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team also included Associate Professor Jeong Jae Wie from Hanyang University, South Korea, and Assistant Professor Sohdam Jeong from Dong-Eui University, South Korea. Their study was published in the journal Advanced Materials (“Light‐Fueled In‐Operando Shape Reconfiguration, Fixation, and Recovery of Magnetically Actuated Microtextured Covalent Adaptable Networks”).
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| Proposed DS-CAN-based magnetic micropillar arrays. (Image: Pusan National University) (click on image to enlarge)
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Covalent adaptable networks (CANs) are a novel class of polymer, featuring dynamic covalent bonds that can break and reform under external stimuli. This allows CANs to be reprocessed, reshaped, and reconfigured. Most CANs have dynamic bonds that are temperature-dependent, allowing bond exchanges only above a certain temperature called the freezing transition temperature. In this study, the researchers incorporated disulfide bonds into CANs, enabling dynamic bond exchanges not only with heat but also under UV light, even at room temperature.
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This ability allows DS-CANs to repair damage or weld two samples together using UV light or heat. They also allow the reprocessing of pulverized samples into consolidated solid samples. Most importantly, DS-CANs enable UV- or heat-assisted shape fixation after deformation, which is also reversible, unlike traditional thermosetting polymers.
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To better understand how heat- and UV-light trigger dynamic disulfide bond exchanges, the researchers used non-equilibrium molecular dynamics (NEMD) simulations combined with Monte Carlo (MC) modeling. These methods offered key insights into their mechanisms and helped build a prediction model for future designs.
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To demonstrate potential for reversible, on-demand, contact-free shape fixation, the team embedded magnetic neodymium-iron-boron (NdFeB) particles into DS-CANs, creating new DS-CAN/NdFeB magnetic micropillar arrays. These micropillars can change their shape in response to a magnetic field, and the new shape can be fixed using UV light. Even when the magnetic field is removed, the shape is retained. This shape change is also reversible by applying an opposite magnetic field, followed by UV light-assisted fixation.
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Additionally, these micropillar arrays allow spatial control over shape change, changing the shape of micropillars only in a certain area on the grid through masked UV exposure. The researchers also fabricated DS-CAN/NdFeB microdenticles—ribbed micropillars that mimic shark skin—demonstrating the material’s ability to form complex 3D microstructures.
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“Our technology will prove valuable for a variety of technologies, including tunable robotic grippers that can conform to delicate shapes, programmable smart surfaces, switchable adhesives, and precisely controllable drug delivery systems,” says Prof. Kim, highlighting the potential of this study.
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Overall, this study marks a major advancement in shape-changeable materials, leading to the development of new microdevices with unique capabilities.
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