Development of an injectable composite for bone regeneration

With the development of minimally invasive surgical techniques, there is a growing interest in the research and development of injectable biomaterials especially for orthopedic applications. In a view to enhance the overall surgery benefits for the patient, the BIOSINJECT project aims at preparing a new generation of mineral-organic composites for bone regeneration exhibiting bioactivity, therapeutic activity and easiness of use to broaden the application domains of the actual bone mineral cements and propose an alternative strategy with regard to their poor resorbability, injectability difficulties and risk of infection. First, a physical-chemical study demonstrated the feasibility of self-setting injectable composites associating calcium carbonate-calcium phosphate cement and polysaccharides (tailor-made or commercial polymer) in the presence or not of an antibacterial agent within the composite formulation. Then, bone cell response and antimicrobial activity of the composite have been evaluated in vitro. Finally, in order to evaluate resorption rate and bone tissue response an animal study has been performed and the histological analysis is still in progress. These multidisciplinary and complementary studies led to promising results in a view of the industrial development of such composite for dental and orthopaedic applications

Genetic signatures of variation in population size in a native fungal pathogen after the recent intensive plantation of its host tree

Historical fluctuations in forests’ distribution driven by past climate changes and anthropogenic activities can have large impacts on the demographic history of pathogens that have a long co-evolution history with these host trees. Using a population genetic approach, we investigated that hypothesis by reconstructing the demographic history of Armillaria ostoyae, one of the major pathogens of the maritime pine (Pinus pinaster), in the largest monospecific pine planted forest in Europe (south-western France). Genetic structure analyses and approximate Bayesian computation approaches revealed that a single pathogen population underwent a severe reduction in effective size (12 times lower) 1080–2080 generations ago, followed by an expansion (4 times higher) during the last 4 generations. These results are consistent with the history of the maritime pine forest in the region characterized by a strong recession during the last glaciation (~19 000 years ago) and massive plantations during the second half of the nineteenth century. Results suggest that recent and intensive plantations of a host tree population have offered the opportunity for a rapid spread and adaptation of their pathogens

Multidimensional Electron Imaging of Catalyst Layer Materials

The proton exchange membrane fuel cell (PEMFC) is an important technology for clean power generation in a decarbonized hydrogen system and is notably envisioned for applications in heavy-duty transportation. However, for cost and performance competitiveness, improvements are still required in efficiency and durability. Optimization of the complex structure of multicomponent cathode catalyst layers (CL), where the oxygen reduction reaction (ORR) takes place, is a promising strategy to conciliate low mass transport resistances, high kinetics, and good performance retention. Yet, much of the morphology of this layer remains poorly known. This includes the interactions of the ionomer network, the nature of the micropores, the influence of the porosity on performance losses and calls for advances in characterization of the CLs at the nanoscale. In this thesis, I used advanced transmission electron microscopy (TEM) methods to study these questions in CLs fabricated with Pt nanocatalysts dispersed on (porous) carbon supports and perfluorinated sulfonate acid ionomers. Electron tomography (ET) at cryogenic temperature was first used to gain three-dimensional (3D) insights into the preserved morphology of intact CLs. By operating at a low electron dose and using advanced image processing methods for denoising and segmentation, accurate volumetric reconstruction with limited electron beam-induced degradation was achieved. The results reveal the intricacy of the ionomer morphology at the nanoscale and show that this is a highly continuous network with remarkable thickness heterogeneities which, furthermore, connects all Pt catalysts at the surface of the supports. Next, to gain further insights into the interior microporosity of the carbon supports, a sample preparation method enabling full-range, high-resolution ET was established. The reconstructions uncover typically large interior mesopores with few-layers carbon walls, separated from the external CL pores by compact carbon shells in which rare and mostly sub-nm pores are seen. Finally, to ultimately understand how this porosity influences degradation pathways in the CL, progress is detailed towards the study of Pt/C catalysts in real time with electrochemical liquid phase (ec-LP)TEM. As a whole, the knowledge gathered herein offers a more accurate 3D picture of the CL in PEMFC and pathways towards their operando characterization at the nanoscale. A such, this thesis shows how multidimensional TEM can aid the development of improved PEMFCs.IN

Interior Morphology and Pore Structure in High Surface Area Carbon Catalyst Supports

In proton exchange membrane fuel cells, the interior porosity of the standard high surface area carbon (HSC) supports anchors and shields catalysts, offering benefits in performance and durability. Yet, these carbons also add mass transport resistance. This delicate tradeoff relies on their interior diffusion pathways, which are difficult to fully characterize and remain poorly understood. Here, the multiscale morphology of HSCs is reported using full-range electron tomography, resolving features down to single carbon planes. It is found that the supports typically feature a core-shell morphology with large central pores and compact shell in which pores are slit-shaped and sub-nm in size, while entry points are 7-8 & Aring; in diameter and are rarely in close proximity to Pt catalysts. This remarkably resolved structural landscape reveals that O-2 diffusion pathways in HSCs are narrower and longer than previously assumed, indicating the critical value of the carbon support redesign for optimizing cell performance.IN

Electrochemical Behavior of Carbon Electrodes for <i>In Situ</i> Redox Studies in a Transmission Electron Microscope

AbstractElectrochemical liquid cell transmission electron microscopy (TEM) is a unique technique for probing nanocatalyst behavior during operation for a range of different electrocatalytic processes, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), or electrochemical CO2 reduction (eCO2R). A major challenge to the technique's applicability to these systems has to do with the choice of substrate, which requires a wide inert potential range for quantitative electrochemistry, and is also responsible for minimizing background gas generation in the confined microscale environment. Here, we report on the feasibility of electrochemical experiments using the standard redox couple Fe(CN)63−/4− and microchips featuring carbon-coated electrodes. We electrochemically assess the in situ performance with respect to flow rate, liquid volume, and scan rate. Equally important with the choice of working substrate is the choice of the reference electrode. We demonstrate that the use of a modified electrode setup allows for potential measurements relatable to bulk studies. Furthermore, we use this setup to demonstrate the inert potential range for carbon-coated electrodes in aqueous electrolytes for HER, OER, ORR, and eCO2R. This work provides a basis for understanding electrochemical measurements in similar microscale systems and for studying gas-generating reactions with liquid electrochemical TEM.</jats:p

Electrochemical Behavior of Carbon Electrodes for In Situ Redox Studies in a Transmission Electron Microscope

Electrochemical liquid cell transmission electron microscopy (TEM) is a unique technique for probing nanocatalyst behavior during operation for a range of different electrocatalytic processes, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), or electrochemical CO2 reduction (eCO(2)R). A major challenge to the technique's applicability to these systems has to do with the choice of substrate, which requires a wide inert potential range for quantitative electrochemistry, and is also responsible for minimizing background gas generation in the confined microscale environment. Here, we report on the feasibility of electrochemical experiments using the standard redox couple Fe(CN)(6)(3-/4)(-) and microchips featuring carbon-coated electrodes. We electrochemically assess the in situ performance with respect to flow rate, liquid volume, and scan rate. Equally important with the choice of working substrate is the choice of the reference electrode. We demonstrate that the use of a modified electrode setup allows for potential measurements relatable to bulk studies. Furthermore, we use this setup to demonstrate the inert potential range for carbon-coated electrodes in aqueous electrolytes for HER, OER, ORR, and eCO(2)R. This work provides a basis for understanding electrochemical measurements in similar microscale systems and for studying gas-generating reactions with liquid electrochemical TEM

Insights into Electrocatalyst Transformations Studied in Real Time with Electrochemical Liquid-Phase Transmission Electron Microscopy

The value of operando and in situ characterization methodologies for understanding electrochemical systems under operation can be inferred from the upsurge of studies that have reported mechanistic insights into electrocatalytic processes based on such measurements. Despite the widespread availability of performing dynamic experiments nowadays, these techniques are in their infancy because the complexity of the experimental design and the collection and analysis of data remain challenging, effectively necessitating future developments. It is also due to their extensive use that a dedicated modus operandi for acquiring dynamic electrocatalytic information is imperative. In this Account, we focus on the work of our laboratory on electrochemical liquid-phase transmission electron microscopy (ec-LPTEM) to understand the transformation/activation of state-of-the-art nanocatalysts for the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and CO2 electroreduction (CO2ER). We begin by describing the development of electrochemical microcells for TEM studies, highlighting the importance of tailoring the system to each electrochemical process to obtain reliable results. Starting with the anodic OER for alkaline electrolyzers, we demonstrate the capability of real-time monitoring of the electrowetting behavior of Co-based oxide catalysts and detail the fascinating insights gained into solid-liquid interfaces for the reversible surface reconstruction of the catalystic surfaces and their degradation processes. Importantly, in the case of the OER, we report the exceptional capacity of ec-LPTEM to probe gaseous products and therefore resolve solid-liquid-gas phenomena. Moving toward the cathodic ORR for fuel cells, we summarize studies that pertain to the evaluation of the degradation mechanisms of Pt nanoparticles and discuss the issues with performing real-time measurements on realistic catalyst layers that are composed of the carbon support, ionomer network, and Pt nanocatalysts. For the most cathodic CO2ER, we first discuss the challenges of spatiotemporal data collection in microcells under these negative potentials. We then show that control over the electrochemical stimuli is critical for determining the mechanism of restructuring/dissolution of Cu nanospheres, either for focusing on the first stages of the reaction or for start/stop operation studies. Finally, we close this Account with the possible evolution in the way we visualize electrochemical processes with ec-LPTEM and emphasize the need for studies that bridge the scales with the ultimate goal of fully evaluating the impact of the insights obtained from the in situ-monitored processes on the operability of electrocatalytic devices.IN

Un projet de microélectronique numérique original : Contrôle autonome d'un micro-drone par caméras externes

International audienceCe papier présente un travail réalisé par des étudiants en deuxième année d'école d'ingénieurs dans le cadre d'un projet de 56h sur la conception numérique. L'objectif de ce travail est de programmer une séquence de vol d'un drone en utilisant une carte FPGA, des caméras et un module de communication radio