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Recently, metasurfaces have been proven to be effective and compact devices for the design of arbitrary wavefronts. Metasurfaces are planar metamaterials with a subwavelength thickness that allows wavefront shaping by introducing in-plane variations, namely, gradients, in the spatial wave response of these flat structures. Here we report a new class of acoustic gradient-index (GRIN) metasurfaces engineered from soft graded-porous silicone rubber with a high acoustic index for broadband ultrasonic three-dimensional wavefront shaping in water. The functionalities of these soft flat lenses are illustrated through various experiments, which demonstrate beam steering and beam focusing, as well as vortex beam generation in free space. These new GRIN metasurfaces may have important applications in various domains using designed ultrasonic fields (biomedical imaging, industrial non-destructive testing, contactless particle manipulation), since their fabrication is very straightforward with common polymer science engineering. Here, the authors report an approach for creating various acoustic wavefronts in free space by using soft gradient-index porous metasurfaces. These flat lenses generate steered planar, focused spherical and helical ultrasonic beams in water by manipulating the spatial distribution of the material porosity.

Bianisotropy is common in electromagnetism whenever a cross-coupling between electric and magnetic responses exists. However, the analogous concept for elastic waves in solids, termed as Willis coupling, is more challenging to observe. It requires coupling between stress and velocity or momentum and strain fields, which is difficult to induce in non-negligible levels, even when using metamaterial structures. Here, we report the experimental realization of a Willis metamaterial for flexural waves. Based on a cantilever bending resonance, we demonstrate asymmetric reflection amplitudes and phases due to Willis coupling. We also show that, by introducing loss in the metamaterial, the asymmetric amplitudes can be controlled and can be used to approach an exceptional point of the non-Hermitian system, at which unidirectional zero reflection occurs. The present work extends conventional propagation theory in plates and beams to include Willis coupling and provides new avenues to tailor flexural waves using artificial structures.

Negative refraction of acoustic waves is demonstrated through underwater experiments conducted at ultrasonic frequencies on a 3D locally resonant acoustic metafluid made of soft porous silicone-rubber micro-beads suspended in a yield-stress fluid. By measuring the refracted angle of the acoustic beam transmitted through this metafluid shaped as a prism, we determine the acoustic index to water according to Snell’s law. These experimental data are then compared with an excellent agreement to calculations performed in the framework of Multiple Scattering Theory showing that the emergence of negative refraction depends on the volume fraction Φ of the resonant micro-beads. For diluted metafluid ( Φ = 3 % ), only positive refraction occurs whereas negative refraction is demonstrated over a broad frequency band with concentrated metafluid ( Φ = 17 % ).

IntroductionAcute pneumonia (AP) remains a leading cause of death in the older population. Excess risk of death after AP is partly due to cardiovascular (CV) events. We aim to evaluate whether aspirin at a preventive dose (100 mg daily) introduced at the acute phase of AP reduces 90-day mortality.Methods and analysisThe ASPirin for Acute Pneumonia in the elderlY study is a phase III multicentre randomised double-blind, placebo-controlled, superiority clinical trial, which will investigate the efficacy and safety of aspirin in older patients with AP hospitalised in a French university and non-university hospitals. Patients will be randomised in a 1:1 ratio between two groups receiving daily either 100 mg of aspirin or a placebo, within 84 hours following radiologically proven AP diagnosis for 90 days. This study aimed at assessing the efficacy of aspirin on all-cause mortality after AP at 90 days (D90) (primary objective), D30 and D120 after randomisation, CV mortality, major adverse CV events (MACE) (ie, myocardial infarction, stroke, heart failure, new atrial fibrillation and pulmonary embolism, CV death and sudden death) incidence, length of intensive care unit and hospital stay, unscheduled rehospitalisation, dependence, overall and MACE-free survival, as well as safety outcomes (bleeding incidence). The sample size, calculated considering a 90-day mortality of 25% and a reduction of 10% in the aspirin group, a two-sided alpha risk at 5% and power of 80%, is 500 patients to prove the superiority of aspirin over placebo. To account for screening failures and consent withdrawals, 600 patients (300 per arm) will be included.Ethics and disseminationThis study has full approval from an independent Ethics Committee. Participants will sign a written informed consent ahead of participation. Findings will be published in peer-reviewed journals and conference presentations.Trial registration numberEU CTIS: 2024-510811-32-00.

Background Older patients with cancer require specific and individualized management. The 3-group Multidimensional Prognostic Index (MPI) based on the Comprehensive Geriatric Assessment (CGA) has shown a predictive interest in terms of mortality. The objective of our study was to assess the prognostic value of MPI for 1-year mortality in an external prospective French cohort of elderly patients with cancer. Methods From March 2015 to March 2017 a prospective single-center cohort study enrolled all patients with cancer, aged 75 years and older referred to the geriatric oncology clinic. We used a proportional hazard model for 1-year mortality adjusted for age, sex, tumor sites and metastatic status. C-statistics were used to assess the incremental predictive value of MPI index to these risk factors. Results overall, 433 patients underwent CGA with MPI (women 42%; mean age 82.8 ± 4.8 years). The most common tumor sites were prostate (23%), skin (17%), colorectum (15%) and breast (12%); 29% of patients had a metastatic disease; 231 patients (53%) belonged to the “MPI-1” group, 172 (40%) to the “MPI-2” group and 30 patients were classified in the “MPI-3” group. One-year mortality rate was 32% (23% in MPI-1, 41% in MPI-2 and 53% in MPI-3, p  = 0.024). All domains of MPI except cognition and living status were significantly associated with mortality at one-year, as well as tumor sites and metastatic status. Higher MPI was associated with a higher mortality risk (adjusted HR 1.56 [95%CI 1.70–2.09] and 1.72 [1.33–2.22] for MPI groups 2 and 3 compared to 1; p  < 0.0001). Conclusions In addition to established risk factors, MPI improves risk prediction of 1-year mortality. This practical prognostic tool may help to optimize management of these vulnerable patients.

Bile acids (BA) are key for liver regeneration and injury. This study aims at analyzing the changes in the BA pool induced by ischemia-reperfusion (IRI) and investigates the impact of hypothermic oxygenated perfusion (HOPE) on the BA pool compared to static cold storage (SCS). In a porcine model of IRI, liver grafts underwent 30 min of asystolic warm ischemia followed by 6 h of SCS (n = 6) ± 2 h of HOPE (n = 6) and 2 h of ex-situ warm reperfusion. The BA pool in bile samples was analyzed with liquid chromatography coupled with tandem mass spectrometry. We identified 16 BA and observed significant changes in response to ischemia-reperfusion, which were associated with both protective and injury mechanisms. Second, HOPE-treated liver grafts exhibited a more protective BA phenotype, characterized by a more hydrophilic BA pool compared to SCS. Key BA, such as GlycoCholic Acid, were identified and were associated with a decreased transaminase release and improved lactate clearance during reperfusion. Partial Least Square-Discriminant Analysis revealed a distinct injury profile for the HOPE group. In conclusion, the BA pool changes with liver graft IRI, and preservation with HOPE results in a protective BA phenotype compared to SCS.

Soft materials that embed small resonators in a host material can dampen or focus sound. Resonance phenomena occur with all types of vibrations or waves and may play a part in spectacular events, such as the collapse of structures—for example, the fall of the Broughton suspension bridge near Manchester in 1831 ( 1 ). Indeed, the oscillations of a structure submitted to harmonic excitation reaches its maximum amplitude at the resonance frequency ω 0 of the system. At low driving frequencies (ω < ω 0 ), its response is in phase with the forcing but becomes out of phase just beyond (ω 0 < ω). Such an out-of-phase response has been exploited with “locally resonant materials” ( 2 ). The proposed strategy is to embed a large enough collection of identical mechanical resonators in a passive structure to control wave propagation. These features are used to reach unusual macroscopic behaviors such as ultradamping of noise or negative refraction for imaging ( 3 ).

Soft acoustic metamaterials that consist of a concentrated suspension of macroporous microbeads and that show a broadband negative acoustic refractive index are now demonstrated. Many efforts have been devoted to the design and achievement of negative-refractive-index metamaterials since the 2000s 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . One of the challenges at present is to extend that field beyond electromagnetism by realizing three-dimensional (3D) media with negative acoustic indices 9 . We report a new class of locally resonant ultrasonic metafluids consisting of a concentrated suspension of macroporous microbeads engineered using soft-matter techniques. The propagation of Gaussian pulses within these random distributions of ‘ultra-slow’ Mie resonators is investigated through in situ ultrasonic experiments. The real part of the acoustic index is shown to be negative (up to almost − 1) over broad frequency bandwidths, depending on the volume fraction of the microbeads as predicted by multiple-scattering calculations. These soft 3D acoustic metamaterials open the way for key applications such as sub-wavelength imaging and transformation acoustics, which require the production of acoustic devices with negative or zero-valued indices.

Acoustical tweezers are recently developed experimental tools that enable the contactless manipulation of a wide range of particles in fluid media. Their good penetrability, high trapping strength and biocompatibility have poised these acoustic methods as interesting alternatives to other well established optical and magnetic manipulation techniques. This work describes preliminary steps in the development of an active approach to measure the local elasticity of soft hydrogels using single-beam acoustical tweezers. The displacement of a microbubble embedded in a hydrogel is induced by the acoustic radiation force of a focused vortex beam. Microbubbles approximately 100 µm in size can be displaced by a few microns in soft hydrogels with a typical shear modulus ranging from 10 to 100 Pa, consistent with a radiation force in the micronewton range. The applied force can be modelled using resolved measurements of the spatial properties of the incident pressure field. Using a simple elastic model for the bubble motion in the medium, the net displacement enables the experimental estimation of the applied force. We find a relatively good quantitative agreement between the radiation force model and our experimental discussion. Possible reasons for the discrepancies are discussed. Overall, the proposed approach presents real benefits compared to other conventional methods to assess the mechanical properties of soft and fragile materials, as it can be considered minimally intrusive, local, and well-adapted to probe thick and opaque-to-light materials in bulk.

One way to obtain materials with a negative index is to achieve media with doubly negative constitutive parameters. We show that the double negativity required for perfect (non-dissipative) media is not necessary for real passive (lossy) metamaterials, for which single negativity of one of the two constitutive parameters may be sufficient. The analysis is presented through original diagrammatic representations involving both the real and imaginary parts of the dynamic constitutive parameters for isotropic media. A valid demonstration for acoustic and electromagnetic metamaterials is supported by considering an actual soft 3D locally-resonant ultrasonic metafluid having a negative acoustic index while being a single-negative medium. The crucial role of the imaginary parts of the constitutive parameters is then discussed through its impact on the figure of merit. Finally, the analysis is extended to an example of an electromagnetic negative-index metamaterial exhibiting both single and double negativity.