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In a Nature publication, scientists from the Max Planck Institute for Intelligent Systems and the National University of Singapore introduce an innovative optofluidic 3D micro- and nanofabrication technique that overcomes the material limitations of traditional two-photon polymerization. Inside a liquid, the team utilizes a femtosecond laser to generate localized thermal gradients and fluid flows that drive a wide range of micro- and nanoparticles into pre-printed microtemplates. This light-driven assembly enables the printing of structures made from a wide range of materials, sometimes even combined, overcoming the previous limitation to polymers. This technology can now be used to construct tiny micro-robots that can be controlled magnetically or by using light.
Stuttgart – Building things so small that they are smaller than the width of a human hair was previously achieved by using a method called two-photon polymerization, also known as 2PP – today’s state-of-the-art in 3D micro- and nanofabrication. Tiny sculptures such as a miniature replica of the Eiffel Tower or the Taj Mahal made the headlines. While such creations are impressive to look at, their impact reaches much further. 3D micro-/nanofabrication techniques are important for many scientific fields, such as medicine, engineering and of course robotics.
However, there has been one major limitation up to now: miniature 3D objects can usually only be made from a few materials, primarily polymer. It's a bit like being able to print strikingly detailed models, but only with a single type of modeling clay.
In a paper published in Nature on January 28, 2026, a team of scientists from the Max Planck Institute for Intelligent Systems (MPI-IS) and from the National University of Singapore (NUS) demonstrates a new 3D fabrication method at the micro- and nanoscale which is no longer exclusively restricted to polymers. In their work, the researchers show how they make use of all sorts of materials as building blocks: from metals to metal oxides, carbon materials or semiconductors.
Caption: Concept of the optofluidic 3D micro- and nanofabrication. a, Schematic illustration of the optofluidic 3D micro- and nanofabrication process, in which a localized temperature gradient induced by a femtosecond laser heating generates a strong convective flow, guiding the 3D assembly of micro- and nanoparticles within a confined hollow 3D microtemplate, printed by 2PP. b,c, Scanning electron images (SEM) of a SiO2 colloidal-particle-assembled microcube. d,e, SEM images of a dangling croissant-shaped microstructure with a 3D curved surface assembled from SiO2 particles. Credit: MPI-IS
The key idea of this study is to manipulate optofluidic interactions (light-driven flow) precisely, guiding 3D assembly of various micro- or nanoparticles within a confined 3D space,” says the co-corresponding author, Mingchao Zhang, who is an Assistant Professor at National University of Singapore.
The deciding factor is the heat-induced localized fluid flow, which arises from a femtosecond laser heating a tiny point inside the liquid where particles are dispersed randomly. At this hot spot, the particles are deliberately “guided” together by this optofluidic flow. If the laser is placed right next to a prefabricated polymer micromold – very much resembling a cake pan – which features one small opening on the side, the particles assemble at and pass through this gap, accumulating inside the shaped mold.
“The femtosecond laser induces a localized thermal gradient which generates a strong flow that propels particles towards and into the template exactly where we want them to be. Meanwhile, the mold can be any shape: from a cube structure to spheres, a croissant shape, or other,” says the first author of the publication, Xianglong Lyu, who was with MPI-IS and is now a postdoc at the Karlsruhe Institute of Technology (KIT). “Once we have assembled all particles, the polymer template is removed in a post-processing step, leaving a free-standing structure composed entirely of the target material with the shape and size we want. So now we have not just one type of modeling clay, but a whole toolbox full of materials with different properties.”
To show what is possible with their optofluidic assembly method, the team built various tiny devices, such as microvalves that are able to sort particles by size in hair-thin channels. Or they built micro-robots that are made of more than just one material and can be moved in different ways, depending on whether they are actuated by light or an external magnetic field. All structures show structural stability: The assembled particles are held together by strong van der Waals forces, making the structures self-supporting and mechanically stable even without chemical bonding.
“Optofluidic assembly overcomes the material limitations of traditional two-photon polymerization. Our new technology allows us to form tiny 3D objects from almost any material. This opens up new frontiers for multifunctional micro-robots, micro-scale technology, and many other applications that still sound like science-fiction today,” concludes Metin Sitti, who led the Physical Intelligence Department at MPI-IS and who is now President of Koç University in Istanbul.
Reference: Xianglong Lyu, Wenhai Lei, Gaurav Gardi, Muhammad Turab Ali Khan, Shervin Bagheri, Mingchao Zhang, and Metin Sitti “Optofluidic three-dimensional microfabrication and nanofabrication” https://doi.org/10.1038/s41586-025-10033-x
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