International audience

We have shown earlier that low molecular weight gels based on N-heptyl-d-galactonamide hydrogels can be 3D printed by solvent exchange, but they tend to dissolve in the printing bath. We wanted to explore the printing of less soluble N-alkyl-d-galactonamides with longer alkyl chains. Less soluble hydrogels could be good candidates as cell culture scaffolds. N-hexyl, N-octyl and N-nonyl-d-galactonamide solutions in dimethylsulfoxide are injected in a bath of water following patterns driven by a 2D drawing robot coupled to a z-platform. Solubilization of the gels with time has been determined and solubility of the gelators has been measured by NMR. Imbricated structures have been built with N-nonyl-d-galactonamide as a persistent ink and N-hexyl or N-heptyl-d-galactonamide as sacrificial inks. Human mesenchymal stem cells have been cultured on N-nonyl-d-galactonamide hydrogels prepared by cooling or by 3D printing. The conditions for printing well-resolved 3D patterns have been determined for the three gelators. In imbricated structures, the solubilization of N-hexyl or N-heptyl-d-galactonamide occurred after a few hours or days and gave channels. Human mesenchymal stem cells grown on N-nonyl-d-galactonamide hydrogels prepared by heating–cooling, which are stable and have a fibrillar microstructure, developed properly. 3D printed hydrogels, which microstructure is made of micrometric flakes, appeared too fragile to withstand cell growth.

International audience | Although silicates are the most common anions in aquatic systems, little is known on the roles they play on the transport of emerging contaminants, such as antibiotics. Using dynamic column experiments, we revealed the controls of Si loadings on goethite (α-FeOOH) coated sands on the transport of a widely used quinolone antibiotic, here focusing on Nalidixic Acid (NA). We find that dynamic flow-through conditions (2.98 cm/h and 14.92 cm/h) sustain monomeric Si species with loadings of up to ∼0.8 Si/nm2 but that oligomeric species can form at the goethite surfaces under static (batch, no-flow conditions). While these monomeric species occupy no more than ∼22 % of the reactive OH groups on goethite, they can effectively suppress NA binding, and therefore enhance NA mobility in dynamic conditions. NA can also bind on goethite when it is simultaneously injected with high concentrations of Si (2000 µM), yet it becomes progressively replaced by Si over time. Combining kinetics and surface complexation modeling, we present a new transport model to account for the stepwise polymerization of Si on goethite and NA transport. Our findings show that dissolved Si common to natural surface waters can play a determining role on the surface speciation and transport of antibiotics in the environment.

Although silicates are the most common anions in aquatic systems, little is known on the roles they play on the transport of emerging contaminants, such as antibiotics. Using dynamic column experiments, we revealed the controls of Si loadings on goethite (α-FeOOH) coated sands on the transport of a widely used quinolone antibiotic, here focusing on Nalidixic Acid (NA). We find that dynamic flow-through conditions (Darcy velocities of 2.98 cm/h and 14.92 cm/h) sustain monomeric Si species with loadings of up to ~ 0.8 Si/nm² but that oligomeric species can form at the goethite surfaces under static (batch, no-flow conditions). While these monomeric species occupy no more than ~ 22% of the reactive OH groups on goethite, they can effectively suppress NA binding, and therefore enhance NA mobility in dynamic conditions. NA can also bind on goethite when it is simultaneously injected with high concentrations of Si (2000 µM), yet it becomes progressively replaced by Si over time. Combining kinetics and surface complexation modeling, we present a new transport model to account for the stepwise polymerization of Si on goethite and NA transport. Our findings show that dissolved Si, common to natural surface waters, can play a determining role on the surface speciation and transport of antibiotics in the environment.

International audience | Hypothesis: The value of the maximal weight of a pendant drop formed at the end of a syringe needle is lower than the intensity of the corresponding capillary force. The balance of the external forces applied to the maximal pendant drop must be completed by the overpressure generated by the piston of the syringe. Inside the drop, the Laplace pressure corresponds to this overpressure.Experiments: Pendant drops are made with three liquids and five different needle diameters. The influence of Laplace pressure on the maximal weight is experimentally highlighted by modulating the drop curvatures thanks to glass beads placed at the apex of the pendant drop. Their maximal weight and curvatures are measured by image analysis.Findings: Experiments confirm that the balance of external forces must be completed by the force acting on the syringe piston. The overpressure on the piston has an impact on the drops via the Laplace pressure. A master curve between the mean curvature and the maximal volume of the pendant drops is observed. This result allows to validate an expression of the maximal weight which integrates the Laplace pressure. This work contributes to a better understanding of the maximal pendant drop properties and beyond, of the capillary phenomenon.

Hypothesis: The value of the maximal weight of a pendant drop formed at the end of a syringe needle is lower than the intensity of the corresponding capillary force. The balance of the external forces applied to the maximal pendant drop must be completed by the overpressure generated by the piston of the syringe. Inside the drop, the Laplace pressure corresponds to this overpressure. Experiments: Pendant drops are made with three liquids and five different needle diameters. The influence of Laplace pressure on the maximal weight is experimentally highlighted by modulating the drop curvatures thanks to glass beads placed at the apex of the pendant drop. Their maximal weight and curvatures are measured by image analysis. Findings: Experiments confirm that the balance of external forces must be completed by the force acting on the syringe piston. The overpressure on the piston has an impact on the drops via the Laplace pressure. A master curve between the mean curvature and the maximal volume of the pendant drops is observed. This result allows to validate an expression of the maximal weight which integrates the Laplace pressure. This work contributes to a better understanding of the maximal pendant drop properties and beyond, of the capillary phenomenon.