Digital Inline Holography (DIH) is a fast-developing 3D coherent imaging technique. With a single, compact and low-cost optical set-up, it has the potential to provide, with an unsurpassed large depth of field and multi-scale capabilities, detailed information on complex shape and low contrast micro- to milli- meter objects encountered in many scientific, industrial and health areas. ATICS (Advanced Three-dimensional Imaging of Complex particulate Systems) is a four-year research and collaborative project carried out by four university, CNRS, engineer schools and CEA laboratories. Its main objective is to develop a set of advanced and robust light scattering and reconstruction tools and methods, than can increase tenfold the practical capabilities of DIH. All for the purpose of in-situ characterization of the 3D dynamics, shape, size and composition of particulate and biological media encountered in, today’s research of primary societal importance, and most notably for recycling, materials processing, biological imaging and ultrasound therapies. Based on the partners complementary expertise, all scientific aspects of the problem are fully addressed in this project. First, it is necessary to improve the modelling of the hologram formation, propagation, and recording (electromagnetic simulations and asymptotic light scattering models). A next step is to better account for issues raised by hologram magnification (with camera lenses, microscopes objectives, as well as converging and diverging illumination beams) and optical aberrations introduced by optics and interfaces. Another issue is to account for more realistic object shapes and properties (distorted droplets, particle aggregates, details of bacterial morphology…). The development of advanced reconstruction methods, based on back propagation and inverse problems approaches, is certainly a major contribution of the ATICS project. These new methods are to be implemented into fast parallel computing and machine learning algorithms to solve the time-consuming issue and provide efficient tools for applications. The applicability of these tools is demonstrated via four experiments in different up to date research areas: (i) cold sprays, with surface deposition issues on thermosensitive support; (ii) bubbly flow interacting with an acoustic field, for innovative ultrasound therapies; (iii) reactive droplets in milli- and micro-fluidic flows and in levitation, with liquid-liquid transfer and recycling issues; (iv) living micro-organisms, with detection issues in various biological fluid samples. These four applications are also designed to bring physical insight and validation data for the modelling aspects as well as to increase the impact and benefits of the project for the scientific and industrial communities involved. Dissemination of knowledge and transfer is also an important part of the ATICS project, with notably the training of 9 Master of Sciences and 2 PhD students, and 1 postdoctoral researcher. Special attention is also paid to the publication and communication of scientific results in high-level journals, national and international conferences, as well as the organization of a thematic day, a conference, the sharing of digital tools on a GitHub repository and, as part of the open science movement, publications in media with a large audience (Wikipedia articles).

This project aims at understanding the physics of the thinning and breakup of a liquid stream highly loaded with solid particles. Using model concentrated suspensions, it will built on experiments that will (1) go from quasi-statics to slow viscous dynamics, (2) monitor both stresses and deformations, (3) measure interphase stresses in relation with capillary confinement, (4) vary the particle aspect ratio and (5) address the case of ‘small’ repulsive particles. It is expected that these innovative these innovative concerns and observations will provide a ground for a solid physical picture of the breakup of dense, viscous, particulate suspension jets.

Robotics is today experiencing a paradigmatic revolution. The “stiffer is better” of our rigid robots is challenged by a new generation of robots with controlled deformations of finite amplitudes. This is the case of trunk-robots in soft robotics, continuum robots in medical robotics or hyper-redundant eel/snake-robots in bio-inspired robotics. In contrast to the rigid elder sibling, this novel robotics lacks a solid and unified corpus of modelling tools for control. Building on a novel parametrization of the Cosserat theory of rods, COSSEROOTS aims at producing for the first time a comprehensive and unified corpus of methods and models devoted to the control of slender robots with actuated large deformations. Beyond modelling, COSSEROOTS will use these novel modelling tools to address challenging control problems in the fields of soft, medical, and bio-inspired robotics.

Natural biological structures, e.g. plants and insects, are a fantastic source of inspiration featuring strategies where control of form and motion often relies on interacting elementary units that exhibit a simple actuation mechanism. This ERC Starting grant proposal builds on these bioinspired strategies to devise and formalize a new class of soft structures that expand, change shape or respond to external stimulus by harnessing the collective effects of ordered and disordered network of actuators. Physical coupling between actuators leads to the emergence of complex nonlinear dynamics. The project is concerned with the directed control of these collective effects, which must first be understood predictively and then exploited for their functions. Specifically, I will focus on three actuation mechanisms, from simple hydraulic actuators in organized networks to coupled unstable actuators in disordered networks: (i) hydraulic expansion of the Drosophila wing, (ii) elastic instability in the rapid deployment of the trigger plant and (iii) dynamic heterogeneities in the dense assembly of disordered fibers in Marchantia. In all three cases, I will first characterize structural shape changes at the organ and tissue level and build a fundamental understanding of biomechanical actuation. Hand in hand with direct observation of biological systems, I will develop model experiments using digital fabrication and rapid prototyping techniques to reduce the complexity of the system to its essential physical ingredients, rationalize the actuation processes, and understand the physical mechanisms supported by theory and computation. I will address the inverse problem, optimizing the spatial arrangement of individual actuators to program the targeted shape, mechanical and dynamic response of the structure. Finally, I will transfer these robust mechanisms to engineering applications at all scales, from deployable space structures to soft robots and medical devices.

Shear thickening occurs in dense particulate suspensions whose viscosity increase dramatically, sometimes by several orders of magnitude, when the imposed shear rate exceeds a critical value. Considered as an ubiquitous phenomenon in suspended materials, this behavior can be highly problematic for instance damaging pumps and mixers, or clogging pipes in industrial processes. It can also be very useful to technological applications such as liquid armors, smart dampers or modern concretes. For long considered as a puzzle, shear thickening has received a coherent framework within the frictional transition model which is supported both by discrete numerical simulations and experiments. These results indicate that shear thickening is driven by the activation of friction between particles above an onset stress needed to overcome repulsive forces between them. At low shear stress, particles immersed in the suspending fluid, behave as if frictionless since a short range repulsive force prevents them from making contact: the suspension flows easily. Conversely, above a critical stress, the suspension suddenly turns into a solid because particles are pressed into frictional contacts which are highly dissipative. With this new paradigm, it is, for the first time, possible to consider establishing constitutive laws and build an hydrodynamics for shear thickening suspensions. These are the guidelines of the present ScienceFriction project. A major need to achieve this goal is to access to the friction coefficient of these suspensions, composed of micro-metric particles, where both contacts and colloidal interactions are simultaneously at play. This information is key to characterize them, however, it is inaccessible to conventional rheology. The ground of our project is the development of news experimental and numerical rheological tools enabling frictional measurements close to jamming thanks to pressure-imposed rheology (WP1). We will then use these tools to establish the constitutive laws of shear thickening suspensions in both steady and transients states (WP2). We will finally apply these constitutive laws beyond rheometry to tackle the flow of shear thickening suspensions in hydrodynamic configurations (flow down incline, pipe flow). These topics are largely unexplored, yet critical for industrial applications (WP3). A distinctive feature of our project is that the above points will be addressed on model suspensions but also on industrial suspensions thanks to a collaboration with the French company CHRYSO (P3), a world leader for the development of polymers (superplastisizer) entering the composition of concrete. Altering the particle surface physical-chemistry has long been used by industrials to modify the flowing properties of suspensions but the approach remained mainly empirical. The recent understanding that the macroscopic behavior of shear-thickening suspensions is controled by the combined effect of friction and short range repulsive forces opens new perspectives. The advanced rheometers developed in this project will give the means to make the connection between friction coefficients and polymer technologies and dosages. It may therefore help design more efficient molecules, leading to better modern concrete formulations. To achieve this program, 4 partners are involved: 2 French academic laboratories, IUSTI Marseille (expert in granular and suspension flow experiments) and LiPhy grenoble (expert in numerical simulations), 1 foreign laboratory EPFL Lausanne (expert in modeling suspension flows) and the company CHRYSO (expert in the formulation of superplastisizer for modern concretes). Our project also relies on 2 other external collaborations with academic laboratories : the LGC Toulouse (surface physico-chemistry), the InPhyNi Nice (characterizing friction at the particle scale).