Focus on some peculiar behaviors of polymers in the context of additive manufacturing processes

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Geochemical Study of Natural CO2 Emissions in the French Massif Central: How to Predict Origin, Processes and Evolution of CO2 Leakage

International audienceThis study presents an overview of some results obtained within the French ANR (National Agency of Research) supported Géocarbone-Monitoring research program. The measurements were performed in Sainte-Marguerite, located in the French Massif Central. This site represents a natural laboratory for CO2/fluid/rock interactions studies, as well as CO2 migration mechanisms towards the surface. The CO2 leaking character of the studied area also allows to test and validate measurements methods and verifications for the future CO2 geological storage sites. During these surveys, we analyzed soil CO2 fluxes and concentrations. We sampled and analyzed soil gases, and gas from carbo-gaseous bubbling springs. A one-month continuous monitoring was also tested, to record the concentration of CO2 both in atmosphere and in the soil at a single point. We also developed a new methodology to collect soil gas samples for noble gas abundances and isotopic analyses, as well as carbon isotopic ratios. Our geochemical results, combined with structural geology, show that the leaking CO2 has a very deep origin, partially mantle derived. The gas rises rapidly along normal and strike-slip active faults. CO2 soil concentrations (also showing a mantle derived component) and CO2 fluxes are spatially variable, and reach high values. The recorded atmospheric CO2 is not very high, despite the important CO2 degassing throughout the whole area

Transcriptomic and Epigenetic Regulation of Disuse Atrophy and the Return to Activity in Skeletal Muscle

Physical inactivity and disuse are major contributors to age-related muscle loss. Denervation of skeletal muscle has been previously used as a model with which to investigate muscle atrophy following disuse. Although gene regulatory networks that control skeletal muscle atrophy after denervation have been established, the transcriptome in response to the recovery of muscle after disuse and the associated epigenetic mechanisms that may function to modulate gene expression during skeletal muscle atrophy or recovery have yet to be investigated. We report that silencing the tibialis anterior muscle in rats with tetrodotoxin (TTX)—administered to the common peroneal nerve—resulted in reductions in muscle mass of 7, 29, and 51% with corresponding reductions in muscle fiber cross-sectional area of 18, 42, and 69% after 3, 7, and 14 d of TTX, respectively. Of importance, 7 d of recovery, during which rodents resumed habitual physical activity, restored muscle mass from a reduction of 51% after 14 d TTX to a reduction of only 24% compared with sham control. Returning muscle mass to levels observed at 7 d TTX administration (29% reduction). Transcriptome-wide analysis demonstrated that 3714 genes were differentially expressed across all conditions at a significance of P ≤ 0.001 after disuse-induced atrophy. Of interest, after 7 d of recovery, the expression of genes that were most changed during TTX had returned to that of the sham control. The 20 most differentially expressed genes after microarray analysis were identified across all conditions and were cross-referenced with the most frequently occurring differentially expressed genes between conditions. This gene subset included myogenin (MyoG), Hdac4, Ampd3, Trim63 (MuRF1), and acetylcholine receptor subunit α1 (Chrna1). Transcript expression of these genes and Fboxo32 (MAFbx), because of its previously identified role in disuse atrophy together with Trim63 (MuRF1), were confirmed by real-time quantitative RT-PCR, and DNA methylation of their promoter regions was analyzed by PCR and pyrosequencing. MyoG, Trim63 (MuRF1), Fbxo32 (MAFbx), and Chrna1 demonstrated significantly decreased DNA methylation at key time points after disuse-induced atrophy that corresponded with significantly increased gene expression. Of importance, after TTX cessation and 7 d of recovery, there was a marked increase in the DNA methylation profiles of Trim63 (MuRF1) and Chrna1 back to control levels. This also corresponded with the return of gene expression in the recovery group back to baseline expression observed in sham-operated controls. To our knowledge, this is the first study to demonstrate that skeletal muscle atrophy in response to disuse is accompanied by dynamic epigenetic modifications that are associated with alterations in gene expression, and that these epigenetic modifications and gene expression profiles are reversible after skeletal muscle returns to normal activity

Additive manufacturing of polymer parts : industrial expectations and scientific reality

International audienc

Flow properties of polymeric powders for SLS

In order to properly take into account real process conditions relevant to Selective Laser Sintering (SLS), the effect of temperature on the flow properties of polymeric powders was assessed. Shear tests were carried out at temperatures from ambient values to values close to the melting temperature of the polymeric powders. Experiments were performed on two powders with similar chemical compositions but with different melting temperature, very distinct particle shapes and different particle size distributions resulting from different production processes. Experiments indicate that flowability significantly worsens when temperature rises and approaches a value of about 20-30°C lower than the melting point of the polymers. These results are in good agreement with the working temperatures preconized by the SLS machine users. The average intensity of the interparticle forces is calculated from the powder flow properties and the Bond number is considered to verify the suitability of the powder in the SLS process

Fundamental study of the processing of polyamide 12 by selective laser sintering : analysis of the relations between polymer features, process conditions and final properties of parts

International audienc

Fundamental study of the processing of polyamide 12 by selective laser sintering : analysis of the relations between polymer features, process conditions and final properties of parts

International audienc

Processing and Characterization of Composites Based on Hybrid Thermosets Systems

International audienceAdditive manufacturing techniques based on liquid resins, such as digital light processing (DLP), demonstrate higher resolution and accuracy than other printing techniques, but their applications have been hindered by the limited materials selection. Overall, there have been numerous successes in printing acrylic-epoxy resins but the final parts generally suffer from relatively poor mechanical properties. In this study, hybrid printable formulations that are based on acrylic-epoxy resins and ceramic filler are introduced and their printability on DLP machines is demonstrated. Here, we present an ultraviolet (UV) printed acrylic-epoxy with high Young modulus via a two-stage curing approach. Herein, different experiments are used to investigate the evolution of the materials properties during the post-process. Indeed, we conduct experiments to characterize the physico-chemical features and the evolution of mechanical properties before and after post-process. Finally we report the preparation of polymeric rapid tooling inserts with tailored mechanical and physical properties, which were used as injection molding cavities for prototyping and low volume production