Understanding and controlling the dynamic interactions between fluid flows and solid materials and structures-a field known as fluid-structure interaction-is central not only to established disciplines such as aerospace and naval engineering, but also to emerging technologies such as energy harvesting, soft robotics, and biomedical devices. In recent years, the advent of metamaterials has provided exciting opportunities to rethink and redesign fluid-structure interactions. The idea of engineering the internal structure of materials that interface with fluid flows opens a new horizon for the precise and effective manipulation and control of coupled fluidic, acoustic, and elastodynamic responses. This review focuses on this relatively unexplored interdisciplinary theme with broad technological significance. Salient potential applications, such as reduction of fuel consumption in transport systems, efficiency of renewable energy extraction, noise mitigation, and resilience against structural fatigue, depend on controlling interactions among flow, acoustic, and vibration mechanisms. Flow control, for example, which spans a wealth of regimes such as laminar, transitional, turbulent, and unsteady separated flows, is strongly influenced by fluid-structure interaction. This review surveys and discusses conceptual frameworks that describe the interplay between fluids and elastic solids, with a focus on contemporary and emerging concepts. The paper is organised into three main sections: fluid-structure and flow-phonon interactions, flow-induced acoustic interactions with metamaterials, and exotic metamaterial concepts with potential impact on fluid-structure interaction. It concludes with perspectives on current challenges and future directions in this rapidly expanding area of research.

Advances in 3D laser-nanoprinting enable us to fabricate 3D nanophotonic devices with a wide range of functionalities on demand. By exploiting all three spatial dimensions, an enormous design space becomes available for these nanophotonic devices. However, such an immense design space is impossible to explore efficiently by intuition alone, especially when designing free-form nanophotonic devices. Density- based topology optimization offers a natural tool for 3D nanophotonic design by allowing the efficient design of devices with millions of degrees of freedom. Traditional density-based topology optimization relies on heuristic measures to account for limitations imposed by the fabrication method. Indeed, the fabrication method is rarely considered as part of the forward model in the design pipeline. In this work, we introduce an inverse design method that explicitly models the direct-laser-writing process used in 3D nanoprinting. Incorporating a differentiable formulation of the direct-laser-writing model allows us to design 3D nanophotonic devices within the experimentally available design space and to precompensate for fabrication-specific effects. Optimizing inside the experimentally available design space ensures that the constraints we put on the optimization are given by our parametrization of the fabrication method and not by heuristic methods, which might over- or underconstrain the optimization problem. Furthermore, modeling the 3D laser-nanoprinting process explicitly allows us to not only take fabrication-specific effects, such as the proximity effect, into account but also enables the optimization to actively make use of these fabrication-specific effects to increase the functionality of the device.

Using two-step absorption instead of two-photon absorption in 3D laser nanoprinting reduces demands on necessary laser systems but still poses a challenge for chemistry. Photoresists consisting of a photoinitiator and a viscous monomer are hardened through photopolymerization with one or two different laser sources. Until now, the influence of the photoinitiator type on printing behavior has remained unclear, limiting the rational design of new materials. In this study, we demonstrate a direct connection between molecular design and printing performance, providing new insights that guide the targeted development of novel photoinitiators. One essential parameter in designing new photoinitiators is the laser power required to initiate photopolymerization, which varies with molecular size, regioisomeric substitution, and substituent type. Screenings in this and a previous study about two-step absorption show that, thus far, the only applicable molecules for this specific 3D printing technique are 1,2-diketones, primarily benzil derivatives. These compounds are mainly synthesized using a Sonogashira cross-coupling reaction followed by an oxidation of the resulting triple bond. The photoinitiators introduced in this work can be referred to as two-step, one-color systems, allowing 3D structures to be printed using only a single 405 nm laser source.

Fast localization and monitoring of airborne pathogens, such as fungal spores, are crucial for efficient crop disease management. Wheat rust fungi represent a major threat, as their urediniospores disperse rapidly via wind or raindrops, causing severe crop damage and yield losses. Given that wheat is the most extensively cultivated crop worldwide, outbreaks of rust diseases pose a significant risk to global food security. In this work, we present a compact optical imaging platform integrated with a machine-learning-based classification algorithm, forming an autonomous sentinel unit for in-field detection and identification of airborne urediniospores of wheat rusts. This automated device collects multichannel images of airborne particles under different illumination conditions, including a luminescence channel, and processes them using a Bayesian algorithm for fast image segmentation and spore identification within minutes and achieves an F1 score of 97.7% for spore detection and 91.6% for identifying wheat rust spores. Using this system, wheat rust diseases can be localized in their early development stages, and preventative control strategies deployed even before the first symptoms become visible.

Abstract In optical microscopy, high spatial resolution comes at the cost of a short depth of field. This trade-off prevents the formation of sharp images of three-dimensional objects or objects moving in and out of focus. Moreover, it is often difficult to know the extent to which the object is out of focus, which makes it challenging to determine the point spread function that describes the blurring. This hinders the ability to restore the blurred image using digital postprocessing. To resolve these issues, we design a phase mask that, when inserted into the microscope, extends the depth of field, making the point spread function insensitive to the location of the object. We leverage end-to-end machine learning tools to design this phase mask together with a Richardson-Lucy-type deconvolution algorithm to remove image blurring. The phase mask is then manufactured with a commercial 3D nanoprinter and used in a microscope to demonstrate defocus-insensitive imaging of microfabricated objects. The experiments successfully verify the operation of both the phase mask and the image restoration algorithm.

Light-based 3D printing processes 1 are unmatched in micro/nano-manufacturing owing to their high resolution and potential for scalability. Increases in the printing speeds of these technologies have mostly relied on parallelization approaches such as multiple laser foci 2,3 or image projection 4–6 . Yet these directions are ultimately limited due to the need to mechanically scan the light for printing 7 . A new approach to 3D nanoprinting is therefore required to realize further substantial increases in print speed. Here, we introduce a fully parallel holographic approach that leads to peak print rates 100,000,000,000× faster than existing techniques. To achieve this breakthrough, we encode the information of a target 3D object in a single, femtosecond laser pulse via a computer-generated hologram. As the pulse then propagates through a photo-sensitive medium, it exposes the entire complex-shaped 3D microstructure in a single shot, thereby printing at the speed of light. Our single-pulse approach enables 3D nanoprinting to transition from rapid prototyping to mass fabrication, critical for technology fields including metamaterials 8 , microrobotics 9 , inertial fusion energy 10,11 , or drug delivery 12 , in which many millions or billions of printed objects are needed.

Photothermal laser printing using liquid inks has emerged as a facile alternative to multi-photon laser nanoprinting of semiconductor and metal structures. Applications lie, for example, in printed microelectronics. In previous experiments on ZnO, steady-state local temperatures in the laser spot, temperature dynamics, temperature profiles, and the dynamics of material growth have essentially been unknown. Herein, to determine these unknowns, we present in situ experiments using two co-focused lasers. A first continuous-wave laser at 405 nm wavelength heats a thin silicon film that serves as an absorber and thereby induces material deposition from a liquid ink. A second continuous-wave laser at 730 nm wavelength probes the local temperature via the calibrated temperature-dependent silicon-film optical transmission. The second laser also allows for monitoring the time-dependent laser-induced ZnO deposition via scattering of light. We find temperature increases of about 113 degrees Celsius at 1 mW laser power at 405 nm wavelength, with a fast component of the temperature change that rises and decays in the range of 1 & micro;s. Furthermore, we find smooth material deposition beyond some ms timescales at low laser powers, whereas the transmission signal exhibits pronounced rapid temporal fluctuations at elevated laser powers.

Abstract Optical oxygen detection and sensing are essential for fields such as pharmaceutical and food packaging, anaerobic bioprocessing, or battery assembly. To date, sensors are often based on costly, toxic, and/or photolabile precious-metal complexes. Herein, we present a low-cost, biocompatible, and photostable alternative. A 2D/3D-printable composite ink composed of zirconyl flavin mononucleotide ([ZrO]2+[FMN]2–) inorganic–organic hybrid nanoparticles (IOH-NPs), an acrylate cross-linker, and a photoinitiator. The saline IOH-NPs consist of flavin mononucleotide anions ([FMN]2–) and zirconyl cations ([ZrO]2+). Oxygen detection relies on the redox state of FMN. In its oxidized form, FMN is yellow and shows intense fluorescence, whereas it becomes colorless and non-fluorescent after reduction. This redox-mediated transition of FMN introduces a concept for reliable and reversible oxygen sensing. The oxygen sensitivity can be tuned via the IOH-NP concentration and the composite material's thickness. Critically, we explore the time dependence of the oxygen detection. Low-cost biocompatible materials, optical readability, and light-based printing make the composite material and material concept ideal for simple, equipment-free oxygen detection and sensing (e.g., in food and pharmaceutical packaging, battery assembly, and semiconductor manufacturing).

Abstract Contact-free and object-agnostic three-dimensional (3D) rotation remains a challenge at both the micro and nanoscale, with broad relevance to advanced imaging, biology, microrobotics, and materials science. Specifically, precise 3D rotation is desirable in diffusion-suppressing environments, where conventional micromanipulation methods fail. Here we introduce an opto-thermoviscous strategy that scans a focused laser spot within a two-dimensional plane to robustly generate 3D helical thermoviscous flows (TVFs) within highly viscous media. We further report on the discovery of opto-hydrodynamic focusing that converges a spiral motion to a defined particle height. By exploiting symmetry relations, we use rational design to decouple out-of-plane rotation from lateral displacements, leading to stable spinning with positional fluctuations below 200 nm, and demonstrate compatibility with a broad range of microstructures, from nano-printed tiles to stained biological cells, and even perfectly round homogenous spheres. Finally, leveraging the kinematic nature of thermoviscous manipulations, we demonstrate how stepwise rotation, alternated with 3D volumetric microscopy, can be combined with established multi-view image fusion strategies to increase resolution in biological imaging. Conceptually, this elevates TVFs from planar transport to symmetry-engineered volumetric actuation, delivering robust, material-agnostic, out-of-plane rotational control and sheathless opto-hydrodynamic focusing for all-optical micromanipulations and augmented microscopy.

When performing optical high-speed single-molecule spectroscopy and identification, low signal intensities pose a challenge. Fortunately, for many applications, the number of possible molecules in the specimen is small or limited. For such cases, a protocol is presented that uses only a small number of very sensitive hence expensive detectors. The protocol starts with optimizing spectral regions, one per detector, so that different molecules become best distinguishable. Experimentally, the spectral regions are extracted from the continuous spectrum using a custom-made micro-optical element. In the ray-optics picture, it guides all rays in a spectral region onto the entrance of an optical fiber connected to one detector. The shape of the micro-optical element is derived by applying Snell's law to the given geometrical boundary conditions. A proof-of-concept measurement using a dedicated demonstrator refractive optical element in combination with a continuous white-light source is performed. Indeed, the element selects the correct spectral regions and couples the light into the correct fibers. For the example of the identification of single amino acids in a protein, the protocol leads to a higher correct identification rate. Therefore, this protocol is useful for such protein identification experiments as performed in the EU project ProID.

Manufacturing three‐dimensional (3D) microstructures with multi‐material properties via two‐photon 3D laser printing (2PLP) remains a significant challenge due to restrictions inherent to conventional chain‐growth photoresins. Herein, an additive‐ and initiator‐free resin formulation is introduced that allows for the printing of 3D microstructures with disparate mechanical properties via the step‐growth photopolymerization‐based self‐dimerization of visible‐light‐active ortho ‐methylbenzaldehydes ( o MBA) within a single fabrication step in 2PLP by altering the printing parameters (i.e., laser power, scan speed). It is established that the laser exposure dose ( D exp ) directly influences the material properties by varying the degree of crosslinking. While stiff materials with a Young's modulus above 1300 MPa at the higher edge of the D exp can be produced, soft materials with a Young's modulus of < 10 MPa at the lower edge of the D exp can also be fabricated. Thus, the herein pioneered resin offers a very broad material property window – spanning more than two orders of magnitude in Young's modulus – for multi‐material printing via 2PLP, which is not achievable with conventional resins. The capabilities of the advanced resin are demonstrated by printing structures with hard and soft segments in a single fabrication step, visualizing their unique mechanical response to compression via in situ measurements.

Ohm's law of electric conduction is local in the sense that the current density at one position only depends on the electric field at that same position. For a nonlocal medium, the current density at one position depends on the electric field at other positions within the medium as well. As a result of Ohm's law, doubling the length of a wire doubles its resistance. Here, electrically conducting nonlocal architectures are discussed theoretically and experimentally for which changing the length of the metawire rather leads to a complex oscillatory behavior versus wire length. This oscillatory behavior is connected to local currents inside of the metawire flowing in the opposite direction than the externally applied field. The theoretical and experimental results for electric conduction can directly be transferred to thermal conduction or particle diffusion and may enable remote sensing applications.

We introduce an ink system for light-driven 3D printing that consists of electrostatically stabilized inorganic-organic hybrid nanoparticles (IOH-NPs), a crosslinking monomer and a photoinitiator, enabling the printing of color- and fluorescence-switchable 3D objects. Nanoparticles (NPs) are often prone to aggregation in photoresins, causing significant light scattering that hinders the printing process. Furthermore, the particles may degrade upon exposure, resulting in the loss of their properties. These issues result in poor printing quality or a loss of functionality. By carefully selecting NPs and resin composition, we successfully incorporate IOH-NPs into a soft-matter 3D network, enabling a fast pH-dependent color and fluorescence change over a wide pH range. In-depth characterization of the printed structures via imaging, spectroscopic and spectrometric techniques reveals that the IOH-NPs remain intact after printing, exhibiting repeatable color and fluorescence switching. We further demonstrate that multi-material objects can be fabricated entailing both color-switchable and non-switchable structural elements. The hybrid materials for 3D printing introduced here enable tunable optical properties and hold promise for applications in sensors or optical devices.

Multiphoton 3D laser printing of polymers has become a widespread technology for manufacturing 3D architectures on the micro‐ and nanometer scale, with booming applications in micro‐optics, micro‐robotics, and micro‐scaffolds for biological cell culture. However, many applications demand material properties that are not accessible by conventional polymer inks. These include large stiffness, for which recent breakthroughs based on inorganic materials have been reported. Conversely, some applications require very low stiffness and high mechanical compliance. Existing solutions achieve softness by low crosslinking densities, at the inherent expense of deteriorated spatial resolution and structure quality. Herein, this apparent contradiction is resolved by introducing multiphoton inks based on deep eutectic systems, comprising Lewis or Brønsted acids/bases. The 3D printed materials support extremely large strains and bulk Young's moduli as low as 260 kPa under aqueous conditions, well suited for biological applications – at comparable ease of use and spatial resolution as well‐established commercially available polymer inks.