BUSCADOR RECOLECTA

Dense systems of magnetic nanoparticles may exhibit dipolar collective
behavior. However, two fundamental questions remain unsolved: i) whether
the transition temperature may be affected by the particle anisotropy or it
is essentially determined by the intensity of the interparticle dipolar interactions, and ii) what is the minimum ratio of dipole–dipole interaction (Edd)
to nanoparticle anisotropy (KefV, anisotropy⋅volume) energies necessary to
crossover from individual to collective behavior. A series of particle assemblies with similarly intense dipolar interactions but widely varying anisotropy
is studied. The Kef is tuned through different degrees of cobalt-doping
in maghemite nanoparticles, resulting in a variation of nearly an order of
magnitude. All the bare particle compacts display collective behavior,
except the one made with the highest anisotropy particles, which presents
“marginal” features. Thus, a threshold of KefV/Edd ≈ 130 to suppress collective
behavior is derived, in good agreement with Monte Carlo simulations. This
translates into a crossover value of ≈1.7 for the easily accessible parameter
TMAX(interacting)/TMAX(non-interacting) (ratio of the peak temperatures of
the zero-field-cooled magnetization curves of interacting and dilute particle
systems), which is successfully tested against the literature to predict the
individual-like/collective behavior of any given interacting particle assembly
comprising relatively uniform particles., and by “ERDF
A way of making Europe”, grant No. PID2019-106229RB-I00 funded
by MCIN/AEI/10.13039/501100011033 and the Spanish MEC (through
the contract No. BEAGAL18/00095). The authors also acknowledge
funding from UCLM’s Plan Propio, the Swedish Research Council (VR),
the Universidad Pública de Navarra (grant No. PJUPNA2020) and the
Generalitat de Catalunya (grant No. 2017-SGR-292). ICN2 is funded by
the CERCA program/Generalitat de Catalunya and supported by SEV2017-0706 grant funded by MCIN/AEI/10.13039/501100011033. K.T., D.P.,
and M.V. acknowledge support from the European Union’s Horizon
2020 Programme: under gran agreement No. 731976 (MAGENTA) and
partially the Horizon Europe EIC Pathfinder Programme: under grant
agreement No. 101046909 (REMAP).The authors acknowledge financial support from grant No. MAT2015-
65295-R funded by MCIN/AEI/10.13039/501100011033

Heterogeneous bi-magnetic nanostructured systems have had a sustained interest during the last decades owing to their unique magnetic properties and the wide range of derived potential applications. However, elucidating the details of their magnetic properties can be rather complex. Here, a comprehensive study of Fe3O4/Mn3O4 core/shell nanoparticles using polarized neutron powder diffraction, which allows disentangling the magnetic contributions of each of the components, is presented. The results show that while at low fields the Fe3O4 and Mn3O4 magnetic moments averaged over the unit cell are antiferromagnetically coupled, at high fields, they orient parallel to each other. This magnetic reorientation of the Mn3O4 shell moments is associated with a gradual evolution with the applied field of the local magnetic susceptibility from anisotropic to isotropic. Additionally, the magnetic coherence length of the Fe3O4 cores shows some unusual field dependence due to the competition between the antiferromagnetic interface interaction and the Zeeman energies. The results demonstrate the great potential of the quantitative analysis of polarized neutron powder diffraction for the study of complex multiphase magnetic materials., I.V.G. acknowledges financial support from the Russian Foundation for Basic Research under Grant No 20-02-00109. A.G.R. and J.N. acknowledge financial support from the grants PID2019-106229RB-I0 funded by MCIN/AEI/10.13039/50110001103 and 2021-SGR-00651 from Generalitat de Catalunya. I.K. and A.G. acknowledge the European Union's H2020 reserach and innovation program, Grant agreement No 871072. A.G.R. acknowledges financial support from RYC2019-027449-I funded by MCIN/AEI/10.13039/501100011033. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the CEX2021–001214–S grant funded by MCIN/AEI/10.13039/501100011033. M.E. acknowledges the grants RYC2018-024396-I and PID2019-106165GB-C22 funded by MCIN/AEI/ 10.13039/501100011033 and by “ESF Investing in your future.” A.L.O. acknowledges financial support from the grants PID2021-122613OB-I00 funded by MCIN/AEI/ 10.13039/501100011033 and PJUPNA2020 from Universidad Pública de Navarra.

Interfaces play a crucial role in composite magnetic materials and particularly in bimagnetic core/shell nanoparticles. However, resolving the microscopic magnetic structure of these nanoparticles is rather complex. Here, we investigate the local magnetization of antiferromagnetic/ferrimagnetic FeO/Fe3O4 core/shell nanocubes by electron magnetic circular dichroism (EMCD). The electron energy-loss spectroscopy (EELS) compositional analysis of the samples shows the presence of an oxidation gradient at the interface between the FeO core and the Fe3O4 shell. The EMCD measurements show that the nanoparticles are composed of four different zones with distinct magnetic moment in a concentric, onion-type, structure. These magnetic areas correlate spatially with the oxidation and composition gradient with the magnetic moment being largest at the surface and decreasing toward the core. The results show that the combination of EELS compositional mapping and EMCD can provide very valuable information on the inner magnetic structure and its correlation to the microstructure of magnetic nanoparticles., The authors acknowledge the financial support from the Spanish Minister of Science and Innovation (MICINN) through the projects PID2019-106165GB-C21, PID2019-106165GB-C22, and PID2019-106229RB-I00. They also acknowledge funding from Generalitat de Catalunya through the 2017-SGR-292 and 2017-SGR-776 projects. In addition, research at UCM was supported by MINECO/FEDER MAT2015-66888-C3-3-R and RTI2018-097895-B-C43 grants. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, Grant SEV-2017-0706). M.E. thanks the Spanish MICINN and AEI/FSE for Ramón y Cajal contract (RYC2018-024396-I). A.L.O. acknowledges support from the Universidad Pública de Navarra (Grant PJUPNA2020). STEM-EELS observations carried out at the Centro Nacional de Microscopía Electrónica at Universidad Complutense de Madrid, Spain (ICTS ELECMI).

New multi-stimuli responsive materials are required in smart systems applications to overcome current limitations in remote actuation and to achieve versatile operation in inaccessible environments. The incorporation of detection mechanisms to quantify in real time the response to external stimuli is crucial for the development of automated systems. Here, we present the first wireless opto-magnetic actuator with mechanochromic response. The device, based on a nanostructured-iron (Fe) layer transferred onto suspended elastomer structures with a periodically corrugated backside, can be actuated both optically (in a broadband spectral range) and magnetically. The combined opto-magnetic stimulus can accurately modulate the mechanical response (strength and direction) of the device. The structural coloration generated at the corrugated back surface enables to easily map and quantify, in 2D, the mechanical deflections by analyzing in real time the hue changes of images taken using a conventional RGB smartphone camera, with a precision of 0.05°. We demonstrate the independent and synergetic optical and magnetic actuation and detection with a detection limit of 1.8 mW·cm-2 and 0.34 mT, respectively. The simple operation, versatility, and cost-effectiveness of the wireless multiactuated device with highly sensitive mechanochromic mapping paves the way to a new generation of wirelessly controlled smart systems., We acknowledge funding from the Generalitat de Catalunya through the 2017-SGR-292 project. The funding from the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN) through the PID2019-106229RB-I00, MAT2016-77391-R, PCIN2016-093 (M-ERA-NET), DPI2015-68197-R, and RTI2018-096786-B-I00 projects and the Ramon y Cajal Fellowship (RyC2013-14479) is acknowledged. The PhD fellowship CIBAE-023-2014 (from SENESCYT) is also acknowledged. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706).

The emerging stretchable photonics field faces challenges, like the robust integration of optical elements into elastic matrices or the generation of large optomechanical effects. Here, the first stretchable plasmonic-enhanced and wrinkled Fabry–Pérot (FP) cavities are demonstrated, which are composed of self-embedded arrays of Au nanostructures at controlled depths into elastomer films. The novel self-embedding process is triggered by the Au nanostructures’ catalytic activity, which locally increases the polymer curing rate, thereby inducing a mechanical stress that simultaneously pulls the Au nanostructures into the polymer and forms a wrinkled skin layer. This geometry yields unprecedented optomechanical effects produced by the coupling of the broad plasmonic modes of the Au nanostructures and the FP modes, which are modulated by the wrinkled optical cavity. As a result, film stretching induces drastic changes in both the spectral position and intensity of the plasmonic-enhanced FP resonances due to the simultaneous cavity thickness reduction and cavity wrinkle flattening, thus increasing the cavity finesse. These optomechanical effects are exploited to demonstrate new strain-sensing approaches, achieving a strain detection limit of 0.006%, i.e., 16-fold lower than current optical strain-detection schemes., The authors acknowledge the financial support from grant nos. MAT2016-77391-R, PID2019-106229RB-I00, PCIN2016-093 (M-ERA-NET), DPI2015-68197-R, and DPI2015-72948-EXP and the Ramon y Cajal Fellowship (RyC2013-14479) funded by MCIN/AEI/10.13039/501100011033. The funding from Generalitat de Catalunya through the 2017-SGR-292 project is also acknowledged. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the SEV-2017-0706 grant funded by MCIN/AEI/10.13039/501100011033. The Swedish Foundation for Strategic Research (SFF) grant no. FFL15-0026 and framework grant RMX18-0039 (HEALiX), the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU no. 2009-00971) are also acknowledged.

Dense systems of magnetic nanoparticles may exhibit dipolar collective behavior. However, two fundamental questions remain unsolved: i) whether the transition temperature may be affected by the particle anisotropy or it is essentially determined by the intensity of the interparticle dipolar interactions, and ii) what is the minimum ratio of dipole–dipole interaction (Edd) to nanoparticle anisotropy (KefV, anisotropy⋅volume) energies necessary to crossover from individual to collective behavior. A series of particle assemblies with similarly intense dipolar interactions but widely varying anisotropy is studied. The Kef is tuned through different degrees of cobalt-doping in maghemite nanoparticles, resulting in a variation of nearly an order of magnitude. All the bare particle compacts display collective behavior, except the one made with the highest anisotropy particles, which presents “marginal” features. Thus, a threshold of KefV/Edd ≈ 130 to suppress collective behavior is derived, in good agreement with Monte Carlo simulations. This translates into a crossover value of ≈1.7 for the easily accessible parameter TMAX(interacting)/TMAX(non-interacting) (ratio of the peak temperatures of the zero-field-cooled magnetization curves of interacting and dilute particle systems), which is successfully tested against the literature to predict the individual-like/collective behavior of any given interacting particle assembly comprising relatively uniform particles., The authors acknowledge financial support from grant No. MAT2015-65295-R funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”, grant No. PID2019-106229RB-I00 funded by MCIN/AEI/10.13039/501100011033 and the Spanish MEC (through the contract No. BEAGAL18/00095). The authors also acknowledge funding from UCLM's Plan Propio, the Swedish Research Council (VR), the Universidad Pública de Navarra (grant No. PJUPNA2020) and the Generalitat de Catalunya (grant No. 2017-SGR-292). ICN2 is funded by the CERCA program/Generalitat de Catalunya and supported by SEV-2017-0706 grant funded by MCIN/AEI/10.13039/501100011033. K.T., D.P., and M.V. acknowledge support from the European Union's Horizon 2020 Programme: under gran agreement No. 731976 (MAGENTA) and partially the Horizon Europe EIC Pathfinder Programme: under grant agreement No. 101046909 (REMAP)., Peer reviewed

With the aim to locally enhance the efficacy of cancer nanotherapies, here we present metal iron based magnetoplasmonic drug-loaded nanocapsules (MAPSULES), merging powerful external magnetic concentration in the tumor and efficient photothermal actuation to locally boost the drug therapeutic action at ultralow drug concentrations. The MAPSULES are composed of paclitaxel-loaded polylactic-co-glycolic acid (PLGA) nanoparticles partially coated by a nanodome shape iron/silica semishell. The iron semishell has been designed to present a ferromagnetic vortex for incorporating a large quantity of ferromagnetic material while maintaining high colloidal stability. The large iron semishell provides very strong magnetic manipulation via magnetophoretic forces, enabling over 10-fold higher trapping efficiency in microfluidic channels than typical superparamagnetic iron oxide nanoparticles. Moreover, the iron semishell exhibits highly damped plasmonic behavior, yielding intense broadband absorbance in the near-infrared biological windows and photothermal efficiency similar to the best plasmonic nanoheaters. The in vivo therapeutic assays in a mouse xenograft tumor model show a high amplification of the therapeutic effects by combining magnetic concentration and photothermal actuation in the tumor, leading to a complete eradication of the tumors at ultralow nanoparticle and drug concentration (equivalent to only 1 mg/kg PLGA nanoparticles containing 8 μg/kg of paclitaxel, i.e., 100-500-fold lower than the therapeutic window of the free and PLGA encapsulated drug and 13-3000-fold lower than current nanotherapies combining paclitaxel and light actuation). These results highlight the strength of this externally controlled and amplified therapeutic approach, which could be applied to locally boost a wide variety of drugs for different diseases., This work was financially supported by the European Research Council (ERC-StG) under the European union’s horizon 2020 research and innovation program, ERC proof of concept grant (ERC-2022-PoC1). We acknowledge financial support from grants No MAT2016-77391-R, PID2019-106229RB-I00,PID2020-116844RB-C21,PGC2018-095032-B-100, PCIN2016-093 (M-ERA-NET), RTI2018-095495-J-I00, and RYC2019-027449-I funded by MCIN/AEI/10.13039/501100011033. We thank the Ramon Areces foundation through grant CIVP19A5922. The funding from Generalitat de Catalunya through the 2017-SGR-292 project is also acknowledged. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the SEV-2017-0706 grant funded by MCIN/AEI/10.13039/501100011033., Peer reviewed

Soft optomechanical systems have the ability to reversibly respond to optical and mechanical external stimuli by changing their own properties (e.g., shape, size, viscosity, stiffness, color or transmittance). These systems typically combine the optical properties of plasmonic, dielectric or carbon-based nanomaterials with the high elasticity and deformability of soft polymers, thus opening the path for the development of new mechanically tunable optical systems, sensors, and actuators for a wide range of applications. This review focuses on the recent progresses in soft optomechanical systems, which are here classified according to their applications and mechanisms of optomechanical response. The first part summarizes the soft optomechanical systems for mechanical sensing and optical modulation based on the variation of their optical response under external mechanical stimuli, thereby inducing mechanochromic or intensity modulation effects. The second part describes the soft optomechanical systems for the development of light induced mechanical actuators based on different actuation mechanisms, such as photothermal effects and phase transitions, among others. The final section provides a critical analysis of the main limitations of current soft optomechanical systems and the progress that is required for future devices., The authors acknowledge the financial support from grant nos. MAT2016-77391-R, PID2019-106229RB-I00, and PCIN2016-093 (M-ERA-NET) funded by MCIN/AEI/10.13039/501100011033, and grant nos. RTI2018-096786-B-I00 funded by MCIN/AEI/ 10.13039/501100011033 and by “ERDF A way of making Europe”. The funding from Generalitat de Catalunya through the 2017-SGR-292 project is also acknowledged. ICN2 was funded by the CERCA programme/Generalitat de Catalunya. The ICN2 was supported by the SEV-2017-0706 grant funded by MCIN/AEI/10.13039/501100011033. F.P.-V. acknowledge funding from the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement no. 801342 (Tecniopring INDUSTRY) and the Government of Catalonia's Agency for Business Competitiveness (ACCIÓ) (TECSPR19-1-0021)., Peer reviewed

Electrochemiluminescence (ECL) is widely employed for medical diagnosis and imaging. Despite its remarkable analytical performances, the technique remains intrinsically limited by the essential need for an external power supply and electrical wires for electrode connections. Here, we report an electrically autonomous solution leading to a paradigm change by designing a fully integrated all-optical wireless monolithic photoelectrochemical device based on a nanostructured Si photovoltaic junction modified with catalytic coatings. Under illumination with light ranging from visible to near-infrared, photogenerated holes induce the oxidation of the ECL reagents and thus the emission of visible ECL photons. The blue ECL emission is easily viewed with naked eyes and recorded with a smartphone. A new light emission scheme is thus introduced where the ECL emission energy (2.82 eV) is higher than the excitation energy (1.18 eV) via an intermediate electrochemical process. In addition, the mapping of the photoelectrochemical activity by optical microscopy reveals the minority carrier interfacial transfer mechanism at the nanoscale. This breakthrough provides an all-optical strategy for generalizing ECL without the need for electrochemical setups, electrodes, wiring constraints, and specific electrochemical knowledge. This simplest ECL configuration reported so far opens new opportunities to develop imaging and wireless bioanalytical systems such as portable point-of-care sensing devices., The research was funded by ANR (LiCORN - ANR-20-CE29-0006), Nouvelle Aquitaine-Euskadi-Navarre Euroregion (project ECLiCare), and the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN) through the PID2019-106229RB-I00 and PCI2019-111896-2 (Euronanomed 2019) projects funded by MCIN/AEI/10.13039/501100011033. NHB acknowledges the financial support of the UMBM Scholarship from Lebanon., Peer reviewed

Heterogeneous bi-magnetic nanostructured systems have had a sustained interest during the last decades owing to their unique magnetic properties and the wide range of derived potential applications. However, elucidating the details of their magnetic properties can be rather complex. Here, a comprehensive study of Fe3 O4 /Mn3 O4 core/shell nanoparticles using polarized neutron powder diffraction, which allows disentangling the magnetic contributions of each of the components, is presented. The results show that while at low fields the Fe3 O4 and Mn3 O4 magnetic moments averaged over the unit cell are antiferromagnetically coupled, at high fields, they orient parallel to each other. This magnetic reorientation of the Mn3 O4 shell moments is associated with a gradual evolution with the applied field of the local magnetic susceptibility from anisotropic to isotropic. Additionally, the magnetic coherence length of the Fe3 O4 cores shows some unusual field dependence due to the competition between the antiferromagnetic interface interaction and the Zeeman energies. The results demonstrate the great potential of the quantitative analysis of polarized neutron powder diffraction for the study of complex multiphase magnetic materials., I.V.G. acknowledges financial support from the Russian Foundation for Basic Research under Grant No 20-02-00109. A.G.R. and J.N. acknowledge financial support from the grants PID2019-106229RB-I0 funded by MCIN/AEI/10.13039/50110001103 and 2021-SGR-00651 from Generalitat de Catalunya. I.K. and A.G. acknowledge the European Union's H2020 reserach and innovation program, Grant agreement No 871072. A.G.R. acknowledges financial support from RYC2019-027449-I funded by MCIN/AEI/10.13039/501100011033. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the CEX2021–001214–S grant funded by MCIN/AEI/10.13039/501100011033. M.E. acknowledges the grants RYC2018-024396-I and PID2019-106165GB-C22 funded by MCIN/AEI/ 10.13039/501100011033 and by “ESF Investing in your future.” A.L.O. acknowledges financial support from the grants PID2021-122613OB-I00 funded by MCIN/AEI/ 10.13039/501100011033 and PJUPNA2020 from Universidad Pública de Navarra., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001214-S)., Peer reviewed

Nanotherapies are gaining increased interest for the treatment diverse diseases, particularly cancer, since they target the affected area directly, presenting higher efficacy and reduced side effects than traditional therapies. A promising nanotherapy approach is hyperthermia, where the nanoparticle can induce a local temperature increase by an external stimulus in the sick tissue to selectively kill the malignant cells. Among the diverse hyperthermia methods, photothermia is based on the absorption of light by the nanoparticles and further conversion into heat. Within the very wide range of nanostructured photothermal agents, iron oxides offer remarkable features since they are already approved by the FDA/EMA for various biomedical applications, they are biodegradable, easily manipulated using magnetic fields and can be imaged by diverse techniques. Here, we summarize the advantages of using the second biological window, both from the perspective of the skin and the optical properties of iron oxides. Further, we review the photothermal performance of iron oxide nanoparticles in the first, second and third biological windows. Overall, the results show that, for different types of iron oxide nanoparticles (Fe3O4, γ-Fe2O3, wüstite-FeO), both the heating capacity (i.e., induced temperature increase) and the photothermal conversion efficiency, n, vary in a complex way with the light wavelength, depending critically on the measurement conditions and physiochemical properties of the materials. Despite the spread in the reported photothermal properties of iron oxides, Fe3O4 particles tend to perform better than their γ-Fe2O3 counterparts, particularly in the second biological window. Interestingly, FeO, which has not been exploited so far from a photothermal perspective, shows very appealing absorption properties. Our preliminary studies using FeO/Fe3O4 core/shell nanoparticles evidence that they have excellent photothermal properties, outperforming Fe3O4 in both first and second biological windows. Finally, some applications beyond cancer treatment of iron oxide nanoparticles, exploiting the enhanced properties in the second spectral window, are discussed., This work was financially supported form grants No MAT2016-77391-R, PID2019-106229RB-I00, PDC2021-121303-I00, PDC2022-133036-I00, RTI2018-095495-J-I00 and RYC2019-027449-I funded by MCIN/AEI/10.13039/501100011033. We thank the Ramon Areces foundation through grant CIVP19A5922. Funding from Generalitat de Catalunya through the 2021-SGR-00651 project is also acknowledged. FÖ acknowledges the support of TUBITAK (The Scientific and Technological Research Council of Turkey) through the Project No. 1059B192000021. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, Grant CEX2021-001214-S, funded by MCIN/AEI/10.13039.501100011033. The authors thank Iris Nogués for preparing Fig. 1., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001214-S)., Peer reviewed

Multifunctional drug-loaded polymer-metal nanocapsules have attracted increasing attention in drug delivery due to their multifunctional potential endowed by drug activity and response to physicochemical stimuli. Current chemical synthesis methods of polymer/metal capsules require specific optimization of the different components to produce particles with precise properties, being particularly complex for Janus structures combining polymers and ferromagnetic and highly reactive metals. With the aim to generate tunable synergistic nanotherapeutic actuation with enhanced drug effects, here we demonstrate a versatile hybrid chemical/physical fabrication strategy to incorporate different functional metals with tailored magnetic, optical, or chemical properties on solid drug-loaded polymer nanoparticles. As archetypical examples, we present poly(lactic-co-glycolic acid) (PLGA) nanoparticles (diameters 100-150 nm) loaded with paclitaxel, indocyanine green, or erythromycin that are half-capped by either Fe, Au, or Cu layers, respectively, with application in three biomedical models. The Fe coating on paclitaxel-loaded nanocapsules permitted efficient magnetic enhancement of the cancer spheroid assembly, with 40% reduction of the cross-section area after 24 h, as well as a higher paclitaxel effect. In addition, the Fe-PLGA nanocapsules enabled external contactless manipulation of multicellular cancer spheroids with a speed of 150 μm/s. The Au-coated and indocyanine green-loaded nanocapsules demonstrated theranostic potential and enhanced anticancer activity in vitro and in vivo due to noninvasive fluorescence imaging with long penetration near-infrared (NIR) light and simultaneous photothermal-photodynamic actuation, showing a 3.5-fold reduction in the tumor volume growth with only 5 min of NIR illumination. Finally, the Cu-coated erythromycin-loaded nanocapsules exhibited enhanced antibacterial activity with a 2.5-fold reduction in the MIC50 concentration with respect to the free or encapsulated drug. Altogether, this technology can extend a nearly unlimited combination of metals, polymers, and drugs, thus enabling the integration of magnetic, optical, and electrochemical properties in drug-loaded nanoparticles to externally control and improve a wide range of biomedical applications., This work was financially supported by the European Research Council (ERC-StG) under the European Union’s Horizon 2020 Research and Innovation Program (Grant Agreement No. 0305260), the ERC proof of concept grant (ERC-2022-PoC1) (Grant Agreement No. 756762), and the M-ERA.NET transnational grant. We acknowledge funding from Generalitat de Catalunya through the 2017-SGR-292 and 2021-SGR-0065 projects. We acknowledge the financial support from the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN) through the MAT2016-77391-R, PDC2022-133036-I00, PID2019- 106229RB-I00, PCIN2016-093 (M-ERA-NET), RTI2018-095495-J-I00, and RYC2019-027449-I funded by MCIN/AEI/10.13039/501100011033. We thank the Ramon Areces foundation through grant CIVP19A5922. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 has been supported by the Severo Ochoa Centres of Excellence programme [SEV-2017-0706] and is currently supported by the Severo Ochoa Centres of Excellence programme, Grant CEX2021-001214-S, both funded by MCIN/AEI/10.13039.501100011033)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001214-S)., Peer reviewed

Due to their high potential energy storage, magnetite (Fe3O4) nanoparticles have become appealing as anode materials in lithium-ion batteries. However, the details of the lithiation process are still not completely understood. Here, we investigate chemical lithiation in 70 nm cubic-shaped magnetite nanoparticles with varying degrees of lithiation, x = 0, 0.5, 1, and 1.5. The induced changes in the structural and magnetic properties were investigated using X-ray techniques along with electron microscopy and magnetic measurements. The results indicate that a structural transformation from spinel to rock salt phase occurs above a critical limit for the lithium concentration (xc), which is determined to be between 0.5< xc ≤ 1 for Fe3−δO4. Diffraction and magnetization measurements clearly show the formation of the antiferromagnetic LiFeO2 phase. Upon lithiation, magnetization measurements reveal an exchange bias in the hysteresis loops with an asymmetry, which can be attributed to the formation of mosaic-like LiFeO2 subdomains. The combined characterization techniques enabled us to unambiguously identify the phases and their distributions involved in the lithiation process. Correlating magnetic and structural properties opens the path to increasing the understanding of the processes involved in a variety of nonmagnetic applications of magnetic materials., The authors thank the Swedish Research Council, VR, for the financial support (VR Grant no. 2016-06959). We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at Petra III, and we would like to thank Ida Nielsen Gjerlevsen for assistance in using P21.1. Beamtime was allocated for proposal(s) I-20211661 EC and RAt-20010278. A.G.R. and J.N. acknowledge financial support from the grants PID2019-106229RB-I0, PID2022-138588OB-C32, and RTI2018-095495-J-I00 funded by MCIN/AEI/10.13039/50110001103 and 2021-SGR-00651 from Generalitat de Catalunya. A.G.R. acknowledges financial support from RYC2019-027449-I, funded by MCIN/AEI/10.13039/501100011033. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the CEX2021-001214-S grant funded by MCIN/AEI/10.13039/501100011033. We acknowledge Myfab Uppsala for providing facilities and experimental support. Myfab is funded by VR (grant no. 2019-00207) as a national research infrastructure., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001214-S)., Peer reviewed

Magneto-mechanical actuation (MMA) using the low-frequency alternating magnetic fields (AMFs) of magnetic nanoparticles internalized into cancer cells can be used to irreparably damage these cells. However, nanoparticles in cells usually agglomerate, thus greatly augmenting the delivered force compared to single nanoparticles. Here, we demonstrate that MMA also decreases the cell viability, with the MMA mediated by individual, non-interacting nanoparticles. The effect was demonstrated with ferrimagnetic (i.e., permanently magnetic) barium-hexaferrite nanoplatelets (NPLs, ∼50 nm wide and 3 nm thick) with a unique, perpendicular orientation of the magnetization. Two cancer-cell lines (MDA-MB-231 and HeLa) are exposed to the NPLs in-vitro under different cell-culture conditions and actuated with a uniaxial AMF. TEM analyses show that only a small number of NPLs internalize in the cells, always situated in membrane-enclosed compartments of the endosomal-lysosomal system. Most compartments contain 1-2 NPLs and only seldom are the NPLs found in small groups, but never in close contact or mutually oriented. Even at low concentrations, the single NPLs reduce the cell viability when actuated with AMFs, which is further increased when the cells are in starvation conditions. These results pave the way for more efficient in-vivo MMA at very low particle concentrations., The support of the Slovenian Research and Innovation Agency (ARIS) within the Project L2-3040, P2-0089, P1-0207 and P3-0108 is acknowledged. BS and JN acknowledge the support of the PID2019-106229RB-I00 grant by MCIN/AEI/10.13039/ and the 2021-SGR-00651 project by the Generalitat de Catalunya. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the CEX2021-001214-S grant funded by MCIN/AEI/10.13039/501100011033., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001214-S)., Peer reviewed

With the progressive aging of the population, bone fractures are an increasing major health concern. Diverse strategies are being studied to reduce the recovery times using nonaggressive treatments. Electrical stimulation (either endogenous or externally applied electric pulses) has been found to be effective in accelerating bone cell proliferation and differentiation. However, the direct insertion of electrodes into tissues can cause undesirable inflammation or infection reactions. As an alternative, magnetoelectric heterostructures (wherein magnetic fields are applied to induce electric polarization) could be used to achieve electric stimulation without the need for implanted electrodes. Here, we develop a magnetoelectric platform based on flexible kapton/FeGa/P(VDF-TrFE) (flexible substrate/magnetostrictive layer/ferroelectric layer) heterostructures for remote magnetic-field-induced electric field stimulation of human osteoblast cells. We show that the use of flexible supports overcomes the clamping effects that typically occur when analogous magnetoelectric structures are grown onto rigid substrates (which preclude strain transfer from the magnetostrictive to the ferroelectric layers). The study of the diverse proliferation and differentiation markers evidence that in all the stages of bone formation (cell proliferation, extracellular matrix maturation, and mineralization), the electrical stimulation of the cells results in a remarkably better performance. The results pave the way for novel strategies for remote cell stimulation based on flexible platforms not only in bone regeneration but also in many other applications where electrical cell stimulation may be beneficial (e.g., neurological diseases or skin regeneration)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’
accreditation (CEX2021-001214-S), This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreements no. 861046 and no. 861145 (Bioremia and BeMAGIC European Training Networks), grants PID2020-116844RB-C21, PID2020 116844RB-C22, and PID2019-106229RB-I00 funded by MCIN/AEI/10.13039/501100011033 and the Generalitat de Catalunya (2021-SGR-00651, 2021-SGR-00122). We also acknowledge the European Research Council (2021-ERC-Advanced REMINDS grant no. 101054687). A.N. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 892661-MAGNUS. A.B. has received funding from a postdoctoral fellowship within the Beatriu de Pinós programme, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 programme of research and innovation of the European Union under Marie Sklodowska-Curie grant agreement no. 801370. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, Grant CEX2021-001214-S, funded by MCIN/AEI/10.13039.501100011033. The authors would like to thank the staff from the Servei de Microscòpia of Universitat Autònoma de Barcelona. The authors also want to thank Iris Nogués for preparing Scheme 1 and Nicolau López-Pintó for his help in growing some of the samples., Peer reviewed

New multi-stimuli responsive materials are required in smart systems applications to overcome current limitations in remote actuation and to achieve versatile operation in inaccessible environments. The incorporation of detection mechanisms to quantify in real time the response to external stimuli is crucial for the development of automated systems. Here, we present the first wireless opto-magnetic actuator with mechanochromic response. The device, based on a nanostructured-iron (Fe) layer transferred onto suspended elastomer structures with a periodically corrugated backside, can be actuated both optically (in a broadband spectral range) and magnetically. The combined opto-magnetic stimulus can accurately modulate the mechanical response (strength and direction) of the device. The structural coloration generated at the corrugated back surface enables to easily map and quantify, in 2D, the mechanical deflections by analyzing in real time the hue changes of images taken using a conventional RGB smartphone camera, with a precision of 0.05°. We demonstrate the independent and synergetic optical and magnetic actuation and detection with a detection limit of 1.8 mW·cm -2 and 0.34 mT, respectively. The simple operation, versatility, and cost-effectiveness of the wireless multiactuated device with highly sensitive mechanochromic mapping paves the way to a new generation of wirelessly controlled smart systems.

Interfaces play a crucial role in composite magnetic materials and particularly in bimagnetic core/shell nanoparticles. However, resolving the microscopic magnetic structure of these nanoparticles is rather complex. Here, we investigate the local magnetization of antiferromagnetic/ferrimagnetic FeO/Fe3O4 core/shell nanocubes by electron magnetic circular dichroism (EMCD). The electron energy-loss spectroscopy (EELS) compositional analysis of the samples shows the presence of an oxidation gradient at the interface between the FeO core and the Fe3O4 shell. The EMCD measurements show that the nanoparticles are composed of four different zones with distinct magnetic moment in a concentric, onion-type, structure. These magnetic areas correlate spatially with the oxidation and composition gradient with the magnetic moment being largest at the surface and decreasing toward the core. The results show that the combination of EELS compositional mapping and EMCD can provide very valuable information on the inner magnetic structure and its correlation to the microstructure of magnetic nanoparticles.

Ultrabroadband light absorbers are attracting increasing interest for applications in energy harvesting, photodetection, self-regulated devices or soft robotics. However, current absorbers show detrimental insufficient absorption spectral range, or light angle and polarization dependence. Here we show that the unexplored optical properties of highly-damped plasmonic materials combined with the infrared absorption of thin polymer films enable developing ultrabroadband light-absorbing soft metamaterials. The developed metamaterial, composed of a nanostructured Fe layer mechanically coupled to a thin polydimethylsiloxane (PDMS) film, shows unprecedented ultrabroadband and angle-independent optical absorption (averaging 84% within 300-18000 nm). The excellent photothermal efficiency and large thermal-expansion mismatch of the metamaterial is efficiently transformed into large mechanical deflections, which we exploit to show an artificial iris that self-regulates the transmitted light power from the ultraviolet to the long-wave infrared, an untethered light-controlled mechanical gripper and a light-triggered electrical switch.

With the aim to locally enhance the efficacy of cancer nanotherapies, here we present metal iron based magnetoplasmonic drug-loaded nanocapsules (MAPSULES), merging powerful external magnetic concentration in the tumor and efficient photothermal actuation to locally boost the drug therapeutic action at ultralow drug concentrations. The MAPSULES are composed of paclitaxel-loaded polylactic-co-glycolic acid (PLGA) nanoparticles partially coated by a nanodome shape iron/silica semishell. The iron semishell has been designed to present a ferromagnetic vortex for incorporating a large quantity of ferromagnetic material while maintaining high colloidal stability. The large iron semishell provides very strong magnetic manipulation via magnetophoretic forces, enabling over 10-fold higher trapping efficiency in microfluidic channels than typical superparamagnetic iron oxide nanoparticles. Moreover, the iron semishell exhibits highly damped plasmonic behavior, yielding intense broadband absorbance in the near-infrared biological windows and photothermal efficiency similar to the best plasmonic nanoheaters. The in vivo therapeutic assays in a mouse xenograft tumor model show a high amplification of the therapeutic effects by combining magnetic concentration and photothermal actuation in the tumor, leading to a complete eradication of the tumors at ultralow nanoparticle and drug concentration (equivalent to only 1 mg/kg PLGA nanoparticles containing 8 μg/kg of paclitaxel, i.e., 100-500-fold lower than the therapeutic window of the free and PLGA encapsulated drug and 13-3000-fold lower than current nanotherapies combining paclitaxel and light actuation). These results highlight the strength of this externally controlled and amplified therapeutic approach, which could be applied to locally boost a wide variety of drugs for different diseases.

Dense systems of magnetic nanoparticles may exhibit dipolar collective behavior. However, two fundamental questions remain unsolved: i) whether the transition temperature may be affected by the particle anisotropy or it is essentially determined by the intensity of the interparticle dipolar interactions, and ii) what is the minimum ratio of dipole-dipole interaction (E) to nanoparticle anisotropy (KV, anisotropy⋅volume) energies necessary to crossover from individual to collective behavior. A series of particle assemblies with similarly intense dipolar interactions but widely varying anisotropy is studied. The K is tuned through different degrees of cobalt-doping in maghemite nanoparticles, resulting in a variation of nearly an order of magnitude. All the bare particle compacts display collective behavior, except the one made with the highest anisotropy particles, which presents "marginal" features. Thus, a threshold of KV/E ≈ 130 to suppress collective behavior is derived, in good agreement with Monte Carlo simulations. This translates into a crossover value of ≈1.7 for the easily accessible parameter T(interacting)/T(non-interacting) (ratio of the peak temperatures of the zero-field-cooled magnetization curves of interacting and dilute particle systems), which is successfully tested against the literature to predict the individual-like/collective behavior of any given interacting particle assembly comprising relatively uniform particles.

Soft optomechanical systems have the ability to reversibly respond to optical and mechanical external stimuli by changing their own properties (e.g., shape, size, viscosity, stiffness, color or transmittance). These systems typically combine the optical properties of plasmonic, dielectric or carbon-based nanomaterials with the high elasticity and deformability of soft polymers, thus opening the path for the development of new mechanically tunable optical systems, sensors, and actuators for a wide range of applications. This review focuses on the recent progresses in soft optomechanical systems, which are here classified according to their applications and mechanisms of optomechanical response. The first part summarizes the soft optomechanical systems for mechanical sensing and optical modulation based on the variation of their optical response under external mechanical stimuli, thereby inducing mechanochromic or intensity modulation effects. The second part describes the soft optomechanical systems for the development of light induced mechanical actuators based on different actuation mechanisms, such as photothermal effects and phase transitions, among others. The final section provides a critical analysis of the main limitations of current soft optomechanical systems and the progress that is required for future devices.

Nanotherapies are gaining increased interest for the treatment diverse diseases, particularly cancer, since they target the affected area directly, presenting higher efficacy and reduced side effects than traditional therapies. A promising nanotherapy approach is hyperthermia, where the nanoparticle can induce a local temperature increase by an external stimulus in the sick tissue to selectively kill the malignant cells. Among the diverse hyperthermia methods, photothermia is based on the absorption of light by the nanoparticles and further conversion into heat. Within the very wide range of nanostructured photothermal agents, iron oxides offer remarkable features since they are already approved by the FDA/EMA for various biomedical applications, they are biodegradable, easily manipulated using magnetic fields and can be imaged by diverse techniques. Here, we summarize the advantages of using the second biological window, both from the perspective of the skin and the optical properties of iron oxides. Further, we review the photothermal performance of iron oxide nanoparticles in the first, second and third biological windows. Overall, the results show that, for different types of iron oxide nanoparticles (FeO, γ-FeO, wüstite-FeO), both the heating capacity (i.e., induced temperature increase) and the photothermal conversion efficiency, η, vary in a complex way with the light wavelength, depending critically on the measurement conditions and physiochemical properties of the materials. Despite the spread in the reported photothermal properties of iron oxides, FeO particles tend to perform better than their γ-FeO counterparts, particularly in the second biological window. Interestingly, FeO, which has not been exploited so far from a photothermal perspective, shows very appealing absorption properties. Our preliminary studies using FeO/FeO core/shell nanoparticles evidence that they have excellent photothermal properties, outperforming FeO in both first and second biological windows. Finally, some applications beyond cancer treatment of iron oxide nanoparticles, exploiting the enhanced properties in the second spectral window, are discussed.

Multifunctional drug-loaded polymer-metal nanocapsules have attracted increasing attention in drug delivery due to their multifunctional potential endowed by drug activity and response to physicochemical stimuli. Current chemical synthesis methods of polymer/metal capsules require specific optimization of the different components to produce particles with precise properties, being particularly complex for Janus structures combining polymers and ferromagnetic and highly reactive metals. With the aim to generate tunable synergistic nanotherapeutic actuation with enhanced drug effects, here we demonstrate a versatile hybrid chemical/physical fabrication strategy to incorporate different functional metals with tailored magnetic, optical, or chemical properties on solid drug-loaded polymer nanoparticles. As archetypical examples, we present poly(lactic- co -glycolic acid) (PLGA) nanoparticles (diameters 100-150 nm) loaded with paclitaxel, indocyanine green, or erythromycin that are half-capped by either Fe, Au, or Cu layers, respectively, with application in three biomedical models. The Fe coating on paclitaxel-loaded nanocapsules permitted efficient magnetic enhancement of the cancer spheroid assembly, with 40% reduction of the cross-section area after 24 h, as well as a higher paclitaxel effect. In addition, the Fe-PLGA nanocapsules enabled external contactless manipulation of multicellular cancer spheroids with a speed of 150 μm/s. The Au-coated and indocyanine green-loaded nanocapsules demonstrated theranostic potential and enhanced anticancer activity in vitro and in vivo due to noninvasive fluorescence imaging with long penetration near-infrared (NIR) light and simultaneous photothermal-photodynamic actuation, showing a 3.5-fold reduction in the tumor volume growth with only 5 min of NIR illumination. Finally, the Cu-coated erythromycin-loaded nanocapsules exhibited enhanced antibacterial activity with a 2.5-fold reduction in the MIC50 concentration with respect to the free or encapsulated drug. Altogether, this technology can extend a nearly unlimited combination of metals, polymers, and drugs, thus enabling the integration of magnetic, optical, and electrochemical properties in drug-loaded nanoparticles to externally control and improve a wide range of biomedical applications.

With the progressive aging of the population, bone fractures are an increasing major health concern. Diverse strategies are being studied to reduce the recovery times using nonaggressive treatments. Electrical stimulation (either endogenous or externally applied electric pulses) has been found to be effective in accelerating bone cell proliferation and differentiation. However, the direct insertion of electrodes into tissues can cause undesirable inflammation or infection reactions. As an alternative, magnetoelectric heterostructures (wherein magnetic fields are applied to induce electric polarization) could be used to achieve electric stimulation without the need for implanted electrodes. Here, we develop a magnetoelectric platform based on flexible kapton/FeGa/P(VDF-TrFE) (flexible substrate/magnetostrictive layer/ferroelectric layer) heterostructures for remote magnetic-field-induced electric field stimulation of human osteoblast cells. We show that the use of flexible supports overcomes the clamping effects that typically occur when analogous magnetoelectric structures are grown onto rigid substrates (which preclude strain transfer from the magnetostrictive to the ferroelectric layers). The study of the diverse proliferation and differentiation markers evidence that in all the stages of bone formation (cell proliferation, extracellular matrix maturation, and mineralization), the electrical stimulation of the cells results in a remarkably better performance. The results pave the way for novel strategies for remote cell stimulation based on flexible platforms not only in bone regeneration but also in many other applications where electrical cell stimulation may be beneficial (e.g., neurological diseases or skin regeneration).

Magneto-mechanical actuation (MMA) using the low-frequency alternating magnetic fields (AMFs) of magnetic nanoparticles internalized into cancer cells can be used to irreparably damage these cells. However, nanoparticles in cells usually agglomerate, thus greatly augmenting the delivered force compared to single nanoparticles. Here, we demonstrate that MMA also decreases the cell viability, with the MMA mediated by individual, non-interacting nanoparticles. The effect was demonstrated with ferrimagnetic (i.e., permanently magnetic) barium-hexaferrite nanoplatelets (NPLs, ∼50 nm wide and 3 nm thick) with a unique, perpendicular orientation of the magnetization. Two cancer-cell lines (MDA-MB-231 and HeLa) are exposed to the NPLs in-vitro under different cell-culture conditions and actuated with a uniaxial AMF. TEM analyses show that only a small number of NPLs internalize in the cells, always situated in membrane-enclosed compartments of the endosomal-lysosomal system. Most compartments contain 1-2 NPLs and only seldom are the NPLs found in small groups, but never in close contact or mutually oriented. Even at low concentrations, the single NPLs reduce the cell viability when actuated with AMFs, which is further increased when the cells are in starvation conditions. These results pave the way for more efficient in-vivo MMA at very low particle concentrations.