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Grafting antibiotics on cellulose for a new generation of strictly contact-active antimicrobial materials

The researchers form the Laboratory for Pulp and Paper Sciences and their colleagues have achieved the first chemical grafting of penicillin directly on the surface of micro-fibrillated cellulose films, giving them unprecedented nonleaching and contact active antimicrobial properties.

Published September 2016

Julien BRAS

Pictorial representation of a surface grafted micro-fibrillated cellulose film

Micro-fibrillated cellulose is a bio-based material prepared from wood by a mechanical disintegration of the fibres. To exploit their amazing properties in the industry, one of the main challenges lies in the development of chemical modification processes aiming to increase the compatibility of micro-fibrillated cellulose with other materials or molecules, and produce a number of advanced materials with new functionalities.

Working in this way, the researchers from the Laboratory for Pulp and Paper Sciences have designed a new esterification reaction under aqueous conditions, to covalently bind the antibiotic penicillin directly to the surface of micro-fibrillated cellulose films. This process was proved efficient in grafting the antibiotic in a way that confers the film an antimicrobial effect occurring exclusively by contact, preventing any leaching or diffusion in the medium as demonstrated by their colleagues from the Paper Division of INNOVHUB (Milano, Italy). Such strictly contact-active antibiotic materials could find many applications, particularly in medical, food packaging or for the design of wound dressings.


Ref: Saini S, Belgacem N, Mendes J, Elegir G and Bras J, 2015 : Contact Antimicrobial Surface Obtained by Chemical Grafting of Microfibrillated Cellulose in Aqueous Solution Limiting Antibiotic Release. Applied Materials & Interfaces, 7, 18076-18085.



The amazing coils of the entangled wire

The researchers from Laboratoire 3SR and their colleagues from ILM (Lyon) have designed a new material consisting in a single long coiled elastic or super elastic wire which showed unprecedented mechanical behaviour.

Published February 2016

Laurent ORGEAS

X-Ray tomographic image of a NiTi entangled wire (sample height = 35 mm) showing the internal homogeneity of the material (Credit: 2015 Macmillan Publishers Limited)

When squeezing a saturated wet sponge at low strain rates, its volume usually decreases causing the water to spill out. In the opposite direction, stretching the sponge will increase its volume inducing the sucking up of water. Most porous or dense materials actually behave this way, and a few rare types show the opposite behaviour, i.e. increase their volume when squeezed and decrease their volume when stretched.

However, for all these materials, the volume change is always symmetric, occurring in opposite directions under compression and tensile loadings. For the first time, researchers from the 3SR Lab and their colleagues from ILM Lyon have designed a mesoscale organisation of the matter able to break this “ancestral” symmetry, opening new material design possibilities for biomedical, mechanical or civil engineering applications.

Their porous material, made from a single entangled coiled wire (see image), actually expands whether being compressed or stretched. Moreover, the use of an elastic or a superelastic coiled wire confers the material the ability to bear repeated cycles of compression and tension without losing its amazing properties.

Thanks to discrete element simulations and mechanical experiments with 3D in situ observations using X-ray microtomography, they captured the complex mesomechanics of this material, which turn out to be a combination of the coiled wire's initial curvature, aspect ratio and level of entanglement as well as strain-induced coils deformation, all of which lead to an overall increase of the material porosity both in tension and compression.

Quite a weird sponge indeed, that could find many applications!


Ref: David Rodney, Benjamin Gadot, Oriol Riu Martinez, Sabine Rolland du Roscoat and Laurent Orgéas. Reversible dilatancy in entangled single wire materials. Nature Materials 15, 72–77 (2016).



Low intensity ultrasound treatment for high efficiency milk filtration

The researchers from the Rheology Lab and their collaborators have demonstrated the efficiency of ultrasound to avoid membrane fouling during tangential ultrafiltration of skimmed milk.

Published December 2015

Frédéric PIGNON

In-situ characterization by SAXS of the accumulated casein micelles near the membrane surface during ultrafiltration of skim milk and control of aggregation and filtration performance thanks to an original coupled ultrasonic cross-flow filtration module

Thanks to an original experimental design based on small angle X ray scattering (SAXS), the researchers form the Laboratory for Rheology and Processes and their collaborators have monitored the real-time evolution of casein micelle suspensions during cross-flow membrane filtration of skimmed milk.

At the nano-scale, they observed that over the process of filtration, a dense colloidal layer maintained by strong interactions between micelles was formed near the membrane. The formation of this viscous layer and its microstructure was studied and correlated to an important reduction of the transmembrane flow.

Interestingly, when applying low intensity ultrasound during the process, a clear disruption of the dense layer was obtained together with a significant increase in the permeation flux through the membrane.

Such unique results could find interesting applications in dairy industry, where cross-flow membrane filtration is widely used and encounters the major obstacle of irreversible membrane fouling.


Ref: Y. Jin, N.Hengl, F. Pignon, N. Gondrexon, M. Sztucki, G. Gésan-Guiziou, A. Magnin, M. Abyan, M. Karrouch, D. Blésès. Effect of ultrasound on cross-flow ultrafiltration of skim milk: characterization from macro-scale to nano-scale, J. Memb. Sci 470 (2014) 205-2018.



Grain of snow, or no grain of snow?

By coupling experimental observations and mechanical modelling, the researchers from IRSTEA Grenoble have developed a new computational method to simplify the identification of individual snow grains in the complex network of ice crystals that makes up the snow.

Published June 2015

Guillaume CHAMBON

3D image of a snow sample (1 cm3). The bonds between snow grains were defined using either the method of mechanical stress computation (black rings)

or the new algorithm based on geometrical clues (pink zones).

Snow is made of an assembly of sintered ice crystals forming a complex skeleton. At the microscale, the ice matrix has zones of mechanical weakness that delimit entities which can be viewed as snow grains. Rapid deformations of snow are mostly controlled by the dynamics of these mechanically-defined snow grains, their spatial rearrangements and contact interactions. When it comes to understanding the mechanical behaviour of snow in avalanche release processes for instance, the thorough identification of snow grains is of prime importance.

 

By comparing the distribution of mechanical stresses in snow samples and their 3D architecture, the researchers from IRSTEA have developed a new algorithm which uses local geometrical clues to infer zones of mechanical weakness in the ice matrix, and therefore simplifies the segmentation of the snow microstructure into grains.

 

When compared to the segmentation method based on the full computation of mechanical stress in the matrix, their algorithm enables a drastic reduction of the computational costs by a factor of 20. These results pave the way to a better consideration of the granular nature of snow in numerical simulations, in particular during rapid deformation phenomena where the large rearrangements of the microstructure render direct simulations extremely time consuming.


Ref: P. Hagenmuller, G. Chambon, F. Flin, S. Morin and M. Naaim: Snow as a granular material: assessment of a new grain segmentation algorithm. Granular Matter 16: 421-432.



Liquid micro-motors: the power of non-muscular cells

By coupling experimental and numerical approaches, researchers from the Laboratory for Interdisciplinary Physics and their colleagues from Paris have recently elucidated the mechanisms by which a cell adapts its shape and regulates its traction forces to a substrate's stiffness.

Published Fevrier 2015

Jocelyn ETIENNE

Transmission microscopy image of a single cell adhering between two parallel microplates and submitted to a vertical traction force.

The upper microplate is used as a nanonewton force sensor to measure the cell’s response (Credit: MSC Paris Diderot)

Living cells, just like muscles, exert forces on their surroundings. This mobility is at the heart of many biological processes such as cell division, embryogenesis, healing, infection, and immunity.

Although the molecules involved are of the same nature in muscles and non-muscle cells, their organisation is quite different: muscle cells have crystalline solid-like sarcomeres, whereas non-muscle cells have a disordered liquid-like actomyosin network.

A group of researchers from Grenoble and Paris have recently shown that in spite of these major differences, the key motor properties of muscles and cells result from similar mechanical phenomena. By comparing experiments and the predictions of a rheological model, they have been able to dissect and quantify the energy usage of a cell when pulling on its substrate, and to explain its amazing versatility and resilience regarding abrupt changes of its near environment.


RefJ. Etienne, J. Fouchard, D. Mitrossilis, N. Bufi, P. Durand-Smet and A. Asnacios: Cells as liquid motors. Mechanosensitivity emerges from collective dynamics of actimyosin cortex. PNAS 112(9):2740–2745.



Undulations, waves, drops: from the virtual to the real

Researchers from the laboratory LEGI and their colleagues from the Virtual Assisted Atomisation Consortium have taken a big step towards the simulation of the complex flow instabilities occuring in gas assisted injection systems.

Published: March 2014

Alain CARTELLIER

Air assisted atomisation of liquid films: experiments and simulations within the VAA project from the partner laboratories LEGI, IJLRDA, CORIA and IMFT

When a high speed gas flow impacts upon a liquid, we witness the formation of undulations, waves and droplet. Atomisation phenomena, commonly observed at the crests of waves, are a key principle of a number of propulsion systems. The efficiency and the reliability of such engines directly depend on the characteristics and the behaviour of the droplets produced.

By combining the results of controlled experiments with direct numerical simulations, researchers from the “Virtual Assisted Atomisation” consortium have developed a model to better understand where the droplets are formed and in what amount, as well as to calculate their size and velocity.

This leading-edge numerical code gives unprecedented access to the computation of severe flow conditions, equivalent to those encountered in gas assisted injection systems used in aeronautic propulsion. The VAA consortium is now actively working on the optimisation of the code with the aim of reducing the computational time.


More videos from our partners:Link 1Link 2

Ref: Fuster D, Matas JP, Marty S, Popinet S, Hoepffner J, Cartellier A and Zaleski S, Instability regimes in the primary breakup region of planar coflowing sheets, J. Fluid Mech., 736 150-176 (2013)



Light control of swimming algae: new perspectives for bioprocesses

By studying the behaviour of swimming microalgae, the researchers from the laboratory LIPhy have highlighted an interesting photo focusing phenomenon that could serve some applications.

Published: July 2013

Salima RAFAI

Chlamydomonas reinhardtii is a swimming microalgae sensitive to light intensity. The researchers from the Interdisciplinary Laboratory of Physics in Grenoble studied the mechanical behaviour of a suspension of these algae in a pipe stream. They showed that the microorganisms will spontaneously migrate and concentrate around the center of the flow when stimulated by a light source placed upstream.

This focusing phenomenon was demonstrated to be due to the interactions between the algae movements towards the light source and the vorticity of the flow.

Considering the important potential of these microorganisms in bio-conversion, this result represents the first step towards new algae separation techniques, a major obstacle in bio-production processes. In an environmental perspective, the presence of certain pollutants was observed to significantly alter the phototaxis of these microswimmers, reducing their self-focusing ability. They could therefore be used in bio-sensors for the accurate detection of water contaminants.


Ref: Garcia X, Rafaï S, Peyla P (2013) Light Control of the Flow of Phototactic Microswimmer Suspensions. Phys. Rev. Lett.



Four dimensional characterisation of sand deformation

For the first time, the researchers from the 3SR lab were able to observe the motion of fifty thousand sand particles in 3D using x-ray micro-tomography. 

Published: April 2013

Edward ANDO

3D image from x-ray microtomography of a granular assembly (grey-scale) overlayed with measured 3D grain rotation angles (colour-scale) during axial loading

Each particle in the sample is identified by its 3D geometry, and its kinematics (translation and rotation) are measured at every 1% shortening of the sample (around 0.22 mm) while it is deformed. This technique opens the way towards the understanding of strain localization and global deformation in granular materials through the dynamics occurring at the particle scale.

 


Ref: Andò E, Hall S A, Viggiani G, Desrues J, Bésuelle P (2012) Grain-scale experimental investigation of localised deformation in sand: a discrete particle tracking approach. Acta Geotechnica.



3D X-ray imaging of biofilm deposition

Researchers from the 3SR lab have obtained the first 3D images of a biofilm, formed on a fixed bed of biolite beads.

Published: January 2013

Sabine ROLLAND

DU ROSCOAT

Bio filtration: three dimensional image of a biofilm (purple) on biolite beads (yellow) obtained at the ESRF facility 

This development opens up possibilities to better understand processes which rely on bio filtration or any other area which is affected by biofilm deposition.