Author(s): Victor Buratto Tinti, Jin Kyu Han, Valdemar Frederiksen, Huaiyu Chen, Jesper Wallentin, Innokenty Kantor, Anton Lyksborg-Andersen, Thomas Willum Hansen, Garam Bae, Wooseok Song, Eugen Stamate, Daniel Zanetti de Florio, Henrik Bruus, and Vincenzo Esposito

DOI: 10.1126/sciadv.adq344

Abstract: Electromechanical metal oxides, such as piezoceramics, are often incompatible with soft polymers due to their crystallinity requirements, leading to high processing temperatures. This study explores the potential of ceria-based thin films as electromechanical actuators for flexible electronics. Oxygen-deficient fluorites, like cerium oxide, are centrosymmetric nonpiezoelectric crystalline metal oxides that demonstrate giant electrostriction. These films, deposited at low temperatures, integrate seamlessly with various soft substrates like polyimide and PET. Ceria thin films exhibit remarkable electrostriction (M33 > 10−16 m2 V−2) and inverse pseudo-piezo coefficients (e33 > 500 pmV−1), enabling large displacements in soft electromechanical systems. Our study explores resonant and off-resonant configurations in the low-frequency regime (<1 kHz), demonstrating versatility for three-dimensional and transparent electronics. This work advances the understanding of oxygen-defective metal oxide electromechanical properties and paves the way for developing versatile and efficient electromechanical systems for applications in biomedical devices, optical devices, and beyond.

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Author(s):Simone Santucci, Milica Vasiljevic, Haiwu Zhang, Victor Buratto Tinti, Achilles Bergne, Armando A. Morin-Martinez, Sandeep Kumar Chaluvadi, Pasquale Orgiani, Simone Sanna, Anton Lyksborg-Andersen, Thomas Willum Hansen, Ivano E. Castelli, Nini Pryds & Vincenzo Esposito

DOI: https://doi.org/10.1038/s41467-024-55393-6

Abstract:Electrostriction is the upsurge of strain under an electric field in any dielectric material. Oxygen-defective metal oxides, such as acceptor-doped ceria, exhibit high electrostriction 10-17 m2V-2 values, which can be further enhanced via interface engineering at the nanoscale. This effect in ceria is “non-classical” as it arises from an intricate relation between defect-induced polarisation and local elastic distortion in the lattice. Here, we investigate the impact of mismatch strain when epitaxial Gd-doped CeO2 thin films are grown on various single-crystal substrates. We demonstrate that varying the compressive and tensile strain can fine-tune the electromechanical response. The electrostriction coefficients achieve a large M11 ≈ 3.6·10-15 m2V-2 in lattices of in-plane compressed films, i.e., a positive tetragonality (c/a-1 > 0), with stress above 3 GPa at the film/substrate interface. Chemical and structural analysis suggests that the high electrostriction stems from anisotropic distortions in the local lattice strain, which lead to constructively oriented elastic dipoles and Ce3+ electronic defects.

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Author(s): Michael Gerlt, Thomas Laurell

DOI: https://doi.org/10.1021/acs.analchem.4c06105

Abstract:We present a novel acoustofluidic chromatography platform for high-throughput nanoparticle trapping and enrichment, focusing on extracellular vesicles (EVs) from blood plasma. The system consists of a packed bed of polystyrene beads within a rectangular glass capillary, acoustically excited by a piezoelectric element. Using fluorescent polystyrene particles (1.9 µm and 0.27 µm) as model nanoparticles, we characterized the device by evaluating its trapping efficiency across a frequency range of 0.45–4 MHz. Our results demonstrate efficient trapping of micro- and nanoscale particles, with increased efficiency at higher acoustic powers and lower flow rates. EV isolation from 4 µL of diluted blood plasma showed that abruptly increasing the flow rate during the release step significantly enhanced particle recovery, likely due to hydrodynamic effects. Nanoparticle tracking analysis confirmed the release of EVs at concentrations of ~2×10⁹ particles/mL, with low protein background suitable for downstream mass spectrometry. This platform offers a promising approach for nanoparticle trapping and EV enrichment with minimal sample volumes, presenting potential applications in diagnostics and therapeutic development. Future work will focus on optimizing bead materials and sizes for EV subpopulation separation and scaling the system for clinical use.

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Author(s):Victor Buratto Tinti, Milica Vasiljevic, Mathias Grønborg, Huaiyu Chen, Valdemar Frederiksen, Innokenty Kantor, Jesper Wallentin, Henrik Bruus and Vincenzo Esposito

DOI: https://doi.org/10.1088/2515-7655/adc628

Abstract: Oxygen-defective metal oxides like cerium oxides exhibit giant electrostriction and field-induced piezoelectricity due to a dynamic electrosteric interplay between oxygen defects, V··O, and the fluorite lattice. While such mechanisms are generally attributed to oxygen vacancies, recent results
also highlight that trapped cationic defects, Ce′Ce, i.e. small polarons, can contribute to the electromechanical properties of ceria. Here, we study nanocrystalline 5% Ca- and 10% Gd-doped ceria thin films with a high density of point defects and a constant oxygen vacancy concentration at
5% molar. We deposit thin films at low temperatures to promote microstructure disorder, i.e. nano-crystallinity, where the oxygen vacancies have low mobility due to high grain boundary interface densities. Still, the Ca2+ and Gd3+ dopants’ sizes and valence differences modulate trapping effects toward the defects in the lattice, giving an insight into the electromechanical nature of the defects in the material dominating the electrostriction. We find that electrosteric dopant-oxygen vacancy interactions only slightly affect the electromechanical properties, which mainly depend on the frequency and intensity of the applied electric field. On the other hand, n-type polaron, Ce′Ce, transport can emerge below the breakdown limit. These effects lead to an electromechanical coupling with a longitudinal electrostriction coefficient, M33, above 10−16 V2 m−2. Our results suggest that polaronic mechanisms substantially contribute to the electromechanical coupling in ceria. Also, the large ionic radius difference between Ce3+ and Ce4+ induces a large electro-strain upon polaron hopping, coupling electric stimuli to the observed electrostriction. This analysis provides new insights into the electromechanical effect of small polaronic semiconductive materials, opening new designing criteria for efficient electromechanical energy conversion.

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Author(s):Michael S. Gerlt, Melinda Rezeli, and Thomas Laurell

DOI: https://doi.org/10.26434/chemrxiv.10001635/v1

Abstract:Extracellular vesicles (EVs) hold promise as biomarkers for early disease detection, yet their nanoscale size and the protein-rich plasma background make enrichment essential. Conventional approaches such as ultracentrifugation and size-exclusion chromatography require ≥150 µL input, hours of processing, and are poorly compatible with clinical workflows.We present a low-cost polymer-based acoustochromatography device that enables EV enrichment from 1 µL of blood plasma within 2–10 minutes – significantly faster than current gold-standard methods. A novel ultrasound-driven release mode increased recovery by up to two orders of magnitude compared to the previously reported acoustofluidic chromatography method. Comprehensive proteomic analysis confirmed highly pure EV fractions after acoustofluidic enrichment. Apolipoproteins were depleted by >99.6%, below levels reported for other methods, lifting 712 mostly EV associated proteins above background as compared to neat plasma. This low-cost, scalable platform unlocks proteomic profiling of ultra-low-volume samples, paving the way for rapid and clinically compatible EV biomarker diagnostics.

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Author(s): Sazid Z. Hoque and Henrik Bruus

DOI: https://doi.org/10.1103/m1rf-tkpw

Abstract:In fluid-filled microchannels embedded in solid devices and driven by megahertz ultrasound transducers, the thickness of the viscous boundary layer in the fluid near the confining walls is typically three to four orders of magnitude smaller than the acoustic wavelength and five orders of magnitude smaller than the longest dimension of the device. This large span in length scale renders direct numerical simulations of such devices prohibitively expensive in terms of computer memory requirements, and consequently the so-called boundary-layer models are introduced. In such models, approximate analytical expressions of the boundary-layer fields are found and inserted in the governing equations and boundary conditions for the remaining bulk fields. Since the bulk fields do not vary across the boundary layers, they can be computed numerically using the resulting boundary-layer model without resolving the boundary layers. However, current boundary-layer models are only accurate for hard solids (e.g., glass and silicon) with relatively small oscillation amplitudes of the confining wall, and they fail for soft solids (e.g., polymers) with larger wall oscillations. In this work, we extend the boundary-layer model of Bach and Bruus, J. Acoust. Soc. Am. 144, 766 (2018) to enable accurate simulation of soft-walled devices. The extended model is validated by comparison (1) with direct numerical simulations in three and two dimensions of tiny submillimeter- and larger millimeter-sized polymer devices, respectively, and (2) with previously published experimental data.

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