Ref HAL: hal-04851455_v1
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The aim of this work is to provide a rheological description of biomimetic tissues in microfluidic confinement, as a simplified model for the flow of cellular tissues observed in complex physiological problems such as in embryogenesis or tumour metastasis. We designed a microfluidic chip that allowed us to tune the assembly of GUVs and to synthesize prototissues with controlled shape and size. GUV-GUV adhesion was mediated by the inclusion of complementary DNA strands enabling the control of prototissue cohesivity and the quantification of GUV-GUV adhesion by fluorescence microscopy. Rheological properties of prototissues were probed in a “pipette-aspiration” inspired microfluidic device, under controlled pressure conditions (creep test). We reported a viscoelastic response, which was well captured by a generalized Kelvin-Voigt fluid model. The prototissue rheology was complemented with a velocimetry analysis which allowed us to identify spatial reorganizations taking place within the prototissue, and with the quantification of the deformation field at the scale of individual vesicles.

Ref HAL: hal-04851435_v1
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The aim of this work is to provide a multiscale rheological description of biomimetic synthetic tissues in microfluidic confinement, as a simplified model for the flow of cellular tissues observed in complex physiological problems such as in embryogenesis or tumour metastasis. Providing a complete description across length scales which relates the properties of individual cells to the rheological behavior of complex 3D-tissues remains an open challenge. The development of biomimetic model tissues with simplified biochemical complexity, but capable of reproducing essential mechanical features of living tissues, can help in achieving this major goal. We designed a simple microfluidic device that allowed us to achieve simultaneously the conception of biomimetic prototissues and their in-situ multiscale rheological characterization. By the controlled assembly of Giant Unilamellar Vesicles (GUVs) inside a microfluidic trap we were capable of synthesizing model prototissues with tailored mechanical properties (size, shape and GUV-GUV adhesion). Rheological properties of prototissues were probed in a “pipette-aspiration” inspired microfluidic device (an example is shown in the figure), under controlled pressure conditions. We reported a viscoelastic response, which was well captured by a generalized Kelvin-Voigt fluid model. The prototissue rheology was complemented with an analysis at the scale of individual vesicles based on segmentation methods, which allowed us to quantify the deformation of vesicles under flow and the reorganizations taking place between vesicles within the prototissue.

Ref HAL: hal-04850843_v1
Ref Arxiv: 2412.11887
Ref. & Cit.: NASA ADS
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The Ni-Au-Ga interdiffusion mechanisms taking place during rapid thermal annealing (RTA) under oxygen atmosphere of a Ni-Au/p-GaN contact are investigated by high-resolution transmission electron microscopy (HR-TEM) coupled to energy dispersive X-ray spectroscopy (EDX). It is shown that oxygen-assisted, Ni diffusion to the top surface of the metallic contact through the formation of a nickel oxide (NiOx) is accompanied by Au diffusion down to the GaN surface, and by Ga out-diffusion through the GaN/metal interface. Electrical characterizations of the contact by Transmission Line Method (TLM) show that an ohmic contact is obtained as soon as a thin, Au-Ga interfacial layer is formed, even after complete diffusion of Ni or NiOx to the top surface of the contact. Our results clarify that the presence of Ni or NiOx at the interface is not the main origin of the ohmic-like behavior in such contacts. Auto-cleaning of the interface during the interdiffusion process may play a role, but TEM-EDX analysis evidences that the creation of Ga vacancies associated to the formation of a Ga-Au interfacial layer is crucial for reducing the Schottky barrier height, and maximizing the amount of current flowing through the contact.

Ref HAL: hal-04849158_v1
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Ref HAL: hal-04847829_v1
Ref Arxiv: 2412.10101
Ref INSPIRE: 2859433
Ref. & Cit.: NASA ADS
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Massive sterile neutrinos, also known as heavy neutral leptons, can have a mixing with active neutrinos, $\theta$, as well as a dipole coupling to the photon, $d$. We study the interplay between these two portals, considering the production from meson decays of sterile neutrinos with mass $0.1$ GeV $\lesssim M_N \lesssim 10$ GeV, at beam-dump facilities such as NA62 and SHiP, and at the FASER2 experiment. These sterile neutrinos can be long-lived and decay into a photon in a distant detector, via the dipole operator. We find that all these experiments will be sensitive to values of $d$ which are presently unconstrained. The experimental reach varies strongly with the mass $M_N$ and the mixing $\theta$, and one observes specific correlations with the flavour of active neutrinos. The SHiP experiment will mark a jump in sensitivity, as it will probe dipole couplings as small as $d\sim 10^{-8}$ GeV$^{-1}$, thus testing new physics well above the electroweak scale.

Ref HAL: hal-04843701_v1
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Hollow Periodic Mesoporous Organosilica Nanoparticles (HPMO-NPs) with a controlled core cavity and a Periodic Mesoporous Organosilica (PMO) shell have been synthesized using a dual templating approach. A dense silica hard template is firstly prepared following classical Stöber sol-gel protocol. The hybrid silica shell is then deposited through a one-pot strategy by the co-condensation of the organosilane precursor with surfactant. HPMO-NPs are then obtained after the final etching steps of the hard and soft templates. In this work, we demonstrate that this strategy can be applied to synthesize:a/ HPMO-NPs with controlled diameter sizes ranging from 600 nm to 40 nm, b/ HPMO-NPs with various shell composition by adjusting the nature of the organosilane precursor, c/ Yolk shell structures with a functional central nanoparticle. We will detail the structural properties of the HPMO-NPs using a multi-scale experimental study at the various stages of synthesis, highlighting the role of mesoporosity and the structural organization of the PMO shell on its properties.Finally, in view of medical applications, we will also present endocytosis and biocompatibility preliminary results.

Ref HAL: hal-04843459_v1
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