Chung-Hae Park, Mines Douai, Composite materials

Flax and hemp among tomorrow’s high-performance composite materials

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Composite materials are increasingly being used in industry, especially in the transport sectors (automotive and aeronautics). These lightweight and multifunctional materials have great potential for limiting environmental footprint, and will play a major role in the materials of future. At Mines Douai, Chung-Hae Park is contributing to the development of high-performance and economically viable composites. A distinguishing feature of these materials is that they are made using plant-based resources: they are composed of at least 45% natural fibers (by volume), combined with polymer matrices which are also bio-based, and exhibit high mechanical performance while they can be rapidly manufactured.

 

In a restrictive environmental context (the European Union aims to lower greenhouse gas emissions by 80 to 95 % between now and 2050), it is absolutely necessary to reduce energy consumption, and that of fuel in particular. However, the improvements of automobile and aircraft engines seem to be reaching their limits. The other solution is to make vehicles and their components lighter by using composite materials. “This idea has been implemented for several decades and fiberglass and carbon fibers are increasingly being incorporated into polymer matrices“, explains Chung-Hae Park. “In civil and military aviation, composites already represent 50% of the total mass of certain models (Airbus 350 and Boeing 787 Dreamliner).”

However, there are still some problems: to begin with, the cost of these materials is much higher than that of metals (steel or aluminum), and it is no easy matter to recycle these heterogeneous materials since their components are extremely difficult to separate once assembled. This is where plant fibers come into play.

 

Getting flax and hemp to the same level as the conventional synthetic fibers

The Composites and Hybrid Structures group of the TPCIM (Polymers and Composites Technology & Mechanical Engineering) department at Mines Douai, led by Chung-Hae Park, is currently the only academic partner involved in two important but complementary national projects: FIABILIN and SINFONI, both of which were selected as part of the Future Investments Program.

These projects were launched in 2012 for five years, and are helping to structure the French industry producing plant fibers for use in engineering materials (insulation, reinforced plastics, agro-based composites), with final applications in a wide range of industries (automotive, aeronautics, railways, building, etc.) Besides being lightweight and agro-based (annually renewable resources), plant fibers offer the advantage of being degradable and therefore recyclable. “Unfortunately many of them aren’t yet strong enough compared with fiberglass and carbon fiber. In France, flax and hemp are the most promising,” comments Chung-Hae. “Our goal, through the FIABILIN and SINFONI projects, is to establish their position among the most widely-used fibers for composites, just behind fiberglass and carbon fibers.”

Researchers at the TPCIM department are contributing to these projects by studying the natural variability of plant fibers and the consequences of this variability on the properties for composite applications (molding characteristics, mechanical performance). This involves overcoming a great technological barrier for this type of material, and developing the necessary numerical simulation tools for virtual engineering which can be used for industrial product development while taking their specific features into account (fiber variability, as well as porosity or process –induced defects, for example) and including this information in models for simulating manufacturing process technology and performance prediction.

Additionally, the experts in polymer and composites processing at Mines Douai are developing novel molding processes by direct impregnation of reinforcements for manufacturing 100% agro-based and high performance parts, i.e. parts that have a volume ratio of at least 45% plant fibers. One of the biggest challenges is lowering the production cost of these parts by reducing the time required to manufacture one component in a chain (i.e. by increasing production speed) to a maximum of two minutes, as required by the automobile industry for example. “In this group we are interested in every step of a product’s life, from material characterization, part production, and its integration in a multi-material assembly with metals or elastomers, to its structural health monitoring during the service life and recycling at the end of life,” emphasizes Chung-Hae.

 

Smart processes and materials

Matériaux composites, Chung-Hae Park, Mines DouaiA complete understanding of the long-term behavior of these materials and their assemblies is crucial for the development of industrial applications, but these aspects are difficult to predict for these new materials with such a short history (unlike metals). In order to monitor how these industrial parts evolve over several decades (the operational life of a civil aircraft for example), nondestructive testing must be carried out over the service life, today. The Composites and Hybrid Structures group is working on the possibility of removing this expensive and tedious nondestructive testing by integrating in-situ sensors in the structure of the material itself, making it a smart composite which can be remotely monitored online.

There are plans to take this idea a step further, integrating the same type of sensor into tools for manufacturing composite parts in order to test or even improve the product quality in real time. The goal is to head toward a digital chain integrating design/production/testing of composites and their assemblies in response to high industrial demand. “We are doing things differently with this research“, states Chung-Hae, “and even though there are many teams in France and Europe working on agro-based composites, we stand out for the range of performances we strive for, with a minimum of 45% of fibers in the form of textile reinforcements by a cost-effective manufacturing technology, i.e. direct impregnation technique, guaranteeing high mechanical properties, as well as for our level of expertise in numerical simulation of manufacturing processes for the industrial parts involved.”

Composite materials will undoubtedly remain one of the major areas of interest for research in the future. This subject is also included in the seven themes defined by the Industry of the Future Alliance, in which Institut Mines-Télécom participates and which strives to implement the governmental plan with the same name, launched in 2015.

 

Chung-Hae Park, Mines Douai, matériaux compositesAfter earning his bachelor’s and master’s degrees from Seoul National University (South Korea), in 2000 Chung-Hae Park began working on a Ph.D. thesis on composite materials through a joint-supervision arrangement. For three years, he spent six months a year at Seoul National University and six months a year at Mines Saint-Étienne. This great challenge was exceptional in South Korea, where this type of thesis is extremely rare.

Chung-Hae received his PhD in 2003 then started working in Korea for the petrochemical branch of LG, in collaboration with many international companies, in the automotive industry in particular. He left LG to pursue his passion for teaching and passing on knowledge, obtaining an assistant professor/associate professor position at the Université du Havre in 2005. In 2011, Chung-Hae earned a Diplome of Habilitation (HDR), still in the field of composite materials. Drawn to Mines Douai’s breakthrough research in this field, he joined the team as a full professor two years later.

He has been the head of the Composites and Hybrid Structures group of the TPCIM (Polymers and Composites Technology & Mechanical Engineering) department since 2014. This group gathers together some 30 people (full professors/assistant & associate professors, technicians, research engineers, post-doctoral researchers; Ph.D. students).

Formula 1, composite material

What is a composite material?

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Composite materials continue to entice researchers and are increasingly being used in transport structures and buildings. Their qualities are stunning, and they are considered to be indispensable in addressing the environmental challenges at hand: reducing greenhouse gas emissions, creating stronger and more durable building structures, etc. How are these materials designed? What makes them so promising? Sylvain Drapier, a researcher in this field at Mines Saint-Étienne, answers our questions in this new addition to the “What is…?” series, dedicated to composite materials.

 

Does the principle behind a composite mean that it consists of two different materials?

Sylvain Drapier: Let’s say at least two materials. For a better understanding, it’s easier to think in terms of volume fractions, in other words, the proportion of volume that each component takes up in the composite. In general, a composite contains between 40 to 60% of reinforcements, often in the form of fibers. The rest is made up of a binder, called the matrix, which allows for the incorporation of these fibers. Increasingly, the binder percentage is being reduced by a few percentage points in order to add what we call fillers, such as minerals, which will optimize the composite material’s final properties.

 

composite material, Sylvain Drapier, Mines Saint-Étienne

50 % of the structure of the Airbus A350 is made of composite materials. The transportation industry is particularly interested in these materials.

Are these fibers exactly like those in our clothing?

SD: Agro-sourced composites, using natural fibers like flax and hemp, are starting to be developed. In this regard, it’s a little like the fibers in our clothing. But these materials are still rare. For composites that are produced for widespread distribution, the fibers are short — at times extremely short — glass fibers. To give an idea of their size, they have a diameter of 10 micrometers and are 1 to 2 millimeters long. They can be larger in products that must absorb limited strain, such as sailboards and electrical boxes, in which they are a few centimeters long. However, high-performance materials require continuous fibers that measure up to several hundred meters, which are wound on reels. This is the case for aramid fibers, with the best known being Kevlar, and is the case for glass fibers used to make wind turbine blades, as well as for carbon fibers used in structures that must withstand heavy use, such as bicycles, high-end cars and airplanes …

 

Can these fibers be bound together by soaking them in glue to form a composite?

SD: It all starts with fiber networks, in 2D or 3D, produced by specialized companies. This involves textiles that are actually woven, or knitted, in the case of revolving parts. After this, there are several production methods. Some processes involve having the plastic resin, in liquid form, soak into this network as a binder. When heated, the resin hardens: we refer to this as a thermosetting polymer. Other polymer resins are used in a solid state, and melt when heated. They fill the spaces between the fibers, and become solid when they return to room temperature. These matrices are called thermoplastic, made from the same polymer family as the plastic recyclable products we use every day. Metal and ceramic matrices exist too, but they are rarer.

 

How is the choice of fiber determined?

SD: It all depends on its use. Ceramic matrices are used for composites inserted into hot structures; thermoplastic resins melt above 200-350°C, and the thermosetting matrices are weakened above 200°C. Some uses require very unusual matrix choices. This is the case for Formula 1 brakes, and the Ariane rocket nozzles, designed with 3D carbon: not only are the fibers carbon, but the binder is carbon too. Compared with a part made completely of carbon, this composite resists much better to crumbling, and can used at temperatures well in excess of 1,000°C.

 

Vinci motor, European Space Agency

The Vinci motor is made for European space agency rockets. Its nozzle (the black cone in the picture), which enables the propulsion, is made of a carbon-carbon composite. Credits: DLR German Aerospace Center.

What are the benefits of composites?

SD: These materials are very light, while offering physical properties that are at least equivalent to those of metallic materials. This benefit is what has won over the transportation industry, since a lighter vehicle consumes less energy. Another benefit of composites is they do not rust. Another feature: we can integrate functions into these materials. For example, we can make a composite more flexible in certain areas by orienting the fibers differently, which can allow sub-assemblies of parts to be replaced by just one part. However, composite resins are often water-sensitive. This is why the aeronautics industry simulates ageing cycles in specific humidity and temperature conditions.

 

What approach is envisaged for recycling composites?

SD: Thermoplastic matrices can be melted. The polymers are then separated from the fibers and each component is processed separately. However, thermosetting matrices lack this advantage, and the composites they form must be recycled in other ways. It is for this reason that researchers, seeking materials with a reduced carbon footprint, are looking to agro-based composites, by using more and more plant fibers. There are even composites that are 100% agro-based, associating bio-sourced polymers with these organic reinforcements. Composite recycling concerns do not yet attract the attention they deserve, but research teams are currently investing in this means of development.

 

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Agro-based composite materials – a Mines area of expertise

Mines Alès, Mines Douai, Agro-based composite materials

Agro-based composite materials – a Mines area of expertise

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The materials of the future need to be more than just high-performance. They must also be environmentally friendly: more recyclable and based on renewable resources. This is why scientists and industrialists are taking a closer look at composite materials developed from plant fibers. They represent a major research focus for Institut Mines-Télécom (IMT) schools — especially at Mines Alès and Mines Douai — which participated in the symposium on March 30th on “Materials: realities and new frontiers”.

 

 

Patricia Krawczak is convinced: for certain structures, composite materials developed from plant fibers can now compete with those developed with fiberglass. This researcher from Mines Douai, who led the session on “The opportunities and limits of eco-materials” at the IMT Materials symposium at the end of March, has been working on this topic for around ten years. She has witnessed the emergence and development of these agro-based composites: “In the beginning, it was just plastics reinforced with short lengths of natural fibers (flax, hemp, or cellulose and wood). This produced materials with poor mechanical performance,” she explains. It is only over the past few years that the industrial field has been restructured to develop solutions capable of manufacturing high-performance parts with a rigidity, strength and durability comparable to fiberglass, which currently predominates. “Agro-based composites are no longer used only as cladding components; they can also be used to develop semi-structural parts,” explains Patricia Krawczak. This is the case in transport sectors (automobile, aeronautics, rail, ship building, etc.) and in the building sector.

Among the plants tested for these new uses, flax and hemp stand out from the others, especially in France. They have the advantage of being abundant resources in our country. As Patricia Krawczak reminds us, “the emergence of agro-based materials is rooted in a sustainable development approach.” The use of plant fibers can potentially result in composites that are more easily recycled. The use of local crops therefore enables supply and transport with a low carbon footprint, consistent with this principle of limiting the impact on the environment. In addition to being abundant, these plants also offer benefits of a scientific and technical nature. A great deal of work is being carried out to improve the understanding and mastery of the resulting composite materials.

 

Mines Douai, Mines Alès, Agro-based composite materials

France is the world’s leading producer of textile flax. Credits: BERTFR.

 

Mastering the performance of agro-based composites

At Mines Alès, Anne Bergeret’s team is therefore seeking to identify the parameters that influence the wear properties of plant fiber-based composites, such as mechanical properties, thermal stability, and durability. The manner in which the plant fibers are dispersed within the polymer matrix has proven to be a key parameter. This depends on the fiber’s intrinsic characteristics, such as its chemical composition, surface chemistry, structure, and the application conditions. Another decisive parameter is the quality of the interface between the plant fiber and the polymer matrix. Research carried out at Mines Alès has shown that certain plant fiber treatments, though commonly used, such as caustic soda processing, have an impact on the fiber’s structure, and therefore on its properties and state of dispersion within the matrix. In light of this paradox, Anne Bergeret reminds us of “the need for a full understanding of the fiber’s processing conditions and the application of agro-based composites”.

“If a part needs to conform to a particular functional specification or a specific request, lightening the material at the expense of its strength and rigidity is not a solution”

This a view shared by Patricia Krawczak, whose research work at Mines Douai has also been subject to a compromise between lightening and performance. “If a part needs to conform to a particular functional specification or a specific request, lightening the material at the expense of its strength and rigidity is not a solution. Therefore, we always think in terms of specific properties, in other words, performance/density ratios,” she explains. This partially explains why plant fibers can compete with fiberglass for certain uses, but will probably not rival carbon fiber, which has an indisputably superior mechanical property/density ratio.

 

Integrating the specific characteristics of natural fibers into digital simulation tools

Despite the performance characteristics of plant fibers, such as flax, they are in no position to replace more conventional fibers in all product specifications. To think otherwise would be to ignore the intrinsic characteristics of these fibers. Plants, by their nature, have variable characteristics, due to their growing conditions (seasonality, climate, place of production, etc.). They are also porous, which makes their fibers sensitive to humidity. They also have a low level of tolerance for high temperatures; it would therefore be difficult to associate them with polymer matrices with forming processes that require heating to very high temperatures. But agro-based composites are already highly suitable for use in more favorable conditions, in which their sensitivity to humidity does not present a problem, or by associating them with polymer matrices that can be transformed at lower temperatures. Furthermore, research is underway to remedy these problematic aspects. The goal is to make natural fiber reinforcements water-repellent, or to adapt plastic manufacturing processes to allow for the production of composite parts under gentler conditions.

“We will not be able to compensate for the porous nature of the fibers, and it will be difficult to overcome their variable characteristics due to their natural origin,” Patricia Krawczak points out. “However, we can make sure these specific features are taken into account in the models and simulations, and in this way ensure that designers, processers and users of industrial parts fully understand the behavior of agro-based composites.” The development of the virtual engineering chain for these materials is booming. The same is true for the market growth of these agro-based composites. “Industrialists from different fields of application are open to using them, but will only do so if the simulation tools they use in their design offices are compatible,” explains the researcher. Her team is working on these aspects as well.

 

Turning the weaknesses of the plant fibers into strengths

While in Mines Douai scientists are focusing on modeling in order to better understand the limits of plant fibers, Anne Bergeret and her team at Mines Alès are seeking to turn these limitations into advantages. The plants have low thermal stability (decomposition beginning at 250°C), making them relatively inflammable. However, they have the particular feature of forming a stable carbonaceous residue after decomposition. The combustion of flax-based composites therefore produces this residue on the surface, which has the property of protecting the underlying material and slowing down its deterioration. Anne Bergeret’s team has therefore sought to promote this appearance of charred residue by grafting phosphorous flame-retardants onto the surface of fibers. The results have shown an improvement in the reaction to fire, and should therefore improve the resilience of the composite, whose structure will be less severely damaged.

Whether the aim is to understand the limitations of agro-based composites or to take advantage of them, either way, researchers are dedicated to using biomass and turning it into new useful materials for the industrial sectors seeking innovations — in aeronautics, as well as in electronics and medical equipment. With them, the sectors are being reorganized, through projects like Fiabilin (PIA-PSPC) and Sinfoni (PIA-PSPC), in which Mines Douai has participated, and Enafilia (ADEME) and Hermes (H2020), with the involvement of Mines Alès, involving flax and hemp growers alongside multidisciplinary scientists, plastics manufacturers, and end users. The emergence of these materials is not merely a hope, it is a necessity because, as Anne Bergeret puts it: “In all our studies, we see the need for an integrated, interdisciplinary approach, combining the skills of materials specialists like us with those of farmers, biologists and chemists, for a comprehensive understanding and the optimal use of biomass.”

Read more on the blog What is a composite material?

Find out more about the research in agro-based composites at Mines Douai
Find out more about the use of biomass for materials

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Reminder: What is a composite material?

Just like wattle and daub, made of straw and mud, a composite material is created from a fiber reinforcement and a binder called the matrix. Glass and carbon fibers are currently the most commonly used fibers, but they are facing competition from plant fibers, which facilitate recycling and decrease the material’s environmental impact.

The composite’s matrix is generally a thermoplastic or thermosetting polymer. When it is thermoplastic, the polymer is heated to be liquefied and combined with fibers, then cooled to form the final solid material. A thermosetting polymer is originally liquid and easily incorporates the fibrous reinforcements, but it must then be heated in order to harden and form the final composite material. Polymer matrices are also called organic matrices, but they are not the only matrices that exist. There are also ceramic and metal matrices.

Through the careful combination of fibers and the matrix, composite materials offer unusual mechanical properties, which few other materials can offer. The specifications, which dictate the final target properties based on the future use of the part, are what generally define the choice of fibers (type, content, orientation, cut/continuous/woven/braided, etc.) and of the matrix.[/box]

Croquis cerveau

The brain: the mechanics of convolutions

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Why do our brains have so many folds? The answer to this question is far from simple. In fact, the answer only came at the beginning of 2016, from a team of researchers including members from Harvard University and Télécom Bretagne. Unlike some of the theories previously proposed, this answer has nothing to do with genetics. The convolutions in our brains are caused by mechanical constraints. This work was published in the Nature Physics journal, and co-authored by François Rousseau, a researcher at Télécom Bretagne.

 

With its multiple convolutions, the strange structure of our brains fascinates some people and frightens others, but leaves few people indifferent. The fact that this convoluted shape is not common to all species only increases this fascination. While humans and several primates have a sinuous brain, this is not the case for rodents, which have a smooth cortex. The scientific community has been debating the origins of these convolutions for years. Some researchers believe it is the result of complex biochemical complexes. In 1975, researchers from Harvard University proposed another theory: the brain’s development into convolutions is the result of mechanical constraints that emerge during its growth. Forty years later, an international collaboration has just confirmed this second hypothesis. This work, involving researchers from the universities of Harvard, Jyväskylä (Finland), Aix-Marseille and Télécom Bretagne, was published in the Nature Physics journal in February 2016.

 

Work with an international scope

To prove the role of physical constraints in the development of folds, the scientists first developed mechanical models by growing shapes similar to that of the brain. The team from Harvard first published the observations from these experiments in 2014. “But the physical models developed up until now were simulations carried out on a type of sphere, and the physicists merely observed whether or not folds appeared,” explains François Rousseau, researcher at Télécom Bretagne, and co-author of the publication. It was precisely for this purpose of refining the model, and making it closer to reality, that French scientists joined the team. Between 2008 and 2013, François Rousseau participated in the European Research Council project (ERC) on fetal brain MRI. His skills in signal processing were then used to extract data from the images. “It is difficult to obtain a good image of the fetal brain, since the fetus may move during the examination for example,” the researcher mentions. After developing and applying algorithms to correct the movement on the MRI images, the fetal brain can be identified and isolated from the surrounding liquid. After this point, the data can be used as the basis for 3D modeling.

 

François Rousseau, IMT Atlantique, brain, convolutions

Based on cross-sectional images of a fetal brain, François Rousseau sought to create 3D models.

 

It was during this process that François Rousseau met Nadine Girard and Julien Lefèvre, the recent winner of the young researcher grant from the French National Research Agency (ANR) on the study of the brain during its development. When they discovered the 2014 publication on the work by Tuomas Tallinen, Jun Young Chung and Lakshminarayanan Mahadevan, they decided to join them, with the conviction that their work could benefit the project by improving the physical model used by the researchers from Harvard and Jyväskylä. The work on the extraction of shapes carried out on fetal MRIs at different stages of prenatal development enabled the scientists to better understand brain development during the gestation period. This is how the twenty-second week of pregnancy came to be identified as a pivotal period, since it is the moment at which the brain enters a rapid growth phase. From this moment and until adulthood, its volume increases twentyfold. However, this increase does not take place in a consistent manner. Over the same period, the cerebral cortex – the brain’s outer layer – therefore increases to thirty times the volume it occupied during the twenty-second week of pregnancy.

 

Heterogeneous cerebral growth

And, it was precisely this asynchronicity that was identified as the potential source of mechanical stresses leading to the formation of convolutions. But the researchers still needed to prove it. Using MRI imaging of the fetal brain at twenty-two weeks, the team 3D-printed a replica, which was then used to form a silicon mold. Using this, the physicists then created imitation brains out of a gel material, which were then covered with another gel that could swell by absorbing a solvent such as hexane. After being exposed to the solvent for sixteen minutes, the brain model developed convolutions and folds that greatly resembled those of real brains. In addition, the stages in the development of these shapes were similar to those observed via MRI imaging. According to the researchers, the gyrification — the process of forming the folds — “is initiated by the formation of linear grooves, which grow longer and branch out, establishing most of the patterns before birth.”

 

François Rousseau, IMT Atlantique, brain, convolutions

The researchers observed a development in the mechanical model (in pink above) similar to real brain development (in white, shown using synthetic imaging).

 

Although the results already supported the hypothesis presented in 1975, the researchers still wanted to improve on their simulations. This process has certain limitations. First of all, the observations reveal a notable asymmetry between the two hemispheres of the imitation brain. While perfect symmetry does not exist in a real human cortex either, the scientists noted that the two halves of the model “differ more than in real life”. Why is this? François Rousseau believes that this could be caused by “slight errors in the digital segmentation during the image processing stage, which may be amplified during the transition to the mechanical model and distort the simulation”. Secondly, due to the need to ensure the feasibility of the experiment, the researchers considered the growth of the cortex to be uniform, although they knew this was not the case. The model also omits the skull’s role in the development of the brain’s surface. Finally, the mechanical model is not yet able to attain a thirtyfold increase in its volume by absorbing the solvent, as the human brain does during its growth.

The researchers will seek to correct all of these details in the next stages of their work. And their exploration of this subject does not stop there. Beyond improvements to the model, the scientists want to take the simulations a step further, seeking to make the folding process take place in reverse order. This project could improve the detection and understanding of lissencephaly disorders – diseases caused by a genetic abnormality that results in a smooth cortex. “Using MRI imaging taken at a specific point-in-time, we would like to return to that point through simulation, to better understand how the changes occur in the folds’ structure,” explains François Rousseau.

Additive manufacturing, a process for the industry of the future

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As a major component of the Industry of the Future project, additive manufacturing — or 3D printing — is leading to ever-increasing research on materials. Researchers at Mines Douai seized on the opportunity to explore this line of research a little over two years ago. Today, the many requests the school has received for research partnerships show the importance of issues surrounding additive manufacturing.

 

“Additive manufacturing probably constitutes the most promising market in the materials sector,” assures Jérémie Soulestin, a researcher at Mines Douai. According to this polymers specialist, it is a “mature” field, but is “still rarely addressed by plastics manufacturers.” The Polymer and Composite Technology & Mechanical Engineering Department (TPCIM), where Jérémie Soulestin works, has seized the opportunity offered by this field. For two years, additive manufacturing has been the focus of the research carried out by the department’s teams. Of course, 3D printing processes for materials are no longer new. “Other colleagues have been addressing the issue by using laser sintering for some years now,” admits Jérémie Soulestin. But the innovation lies in the new combinations of materials and processes.

Laser sintering uses dry powders that are melted by a laser in specific places. The drops that form remain malleable for a few moments before cooling down, making it possible to create the desired shapes. Additive manufacturing via laser sintering was one of the first 3D printing processes to emerge, and today it produces good results for metals and certain plastics, specifically polyamides. However, it cannot be used for all available materials. Therefore, scientists have chosen to seek other processes, in order to expand the range of possibilities.

 

A wide range of stakeholderss

Jérémie Soulestin explains that the TPCIM department is “ahead of the game, particularly in terms of machines.” In support of this claim, he mentions the recent acquisition of the Arburg freeformer. Theoretically, this 3D printer is capable of using a large range of plastic materials used in plastics processes. “This tool uses an approach that is at odds with other manufacturers offering machines adapted to a limited range of associated materials,” the researcher explains. This approach is also better adapted to the work of Mines Douai scientists, which has traditionally focused on injection processes. Unlike laser sintering, this new additive manufacturing technique is within the researchers’ field of expertise. It is also a very popular field of expertise as reflected by the many industrial collaboration projects, which have continued to increase in line with the new work on additive manufacturing.

“We work with partners with a wide range of profiles,” explains Jérémie Soulestin. And for good reason, since the new processes interest industrial stakeholders at different levels of maturity, who all recognize the increasingly important role additive manufacturing will play in the industry of the future. “Some companies come to us for business development purposes: they know this is important, without truly understanding the issues,” admits the scientist. However, he adds, “Others, like major companies, come to us with very specific subjects.” All sectors are concerned, such as aeronautics for the small-series production of part.

 

La freeformer d'Arburg offre, en théorie, une palette de matériaux bien plus large que les autres imprimantes 3D.

The Arburg freeformer offers, in theory, a much wider range of materials than other 3D printers. Credits: Arburg.


Additive manufacturing: added value

The reluctance expressed in the past — particularly regarding durability — is no longer valid today. Companies see additive manufacturing as representing “real added value” in comparison with other traditional processes (such as machining). “We no longer have the technological barriers we had a few years ago,” confirms Jérémie Soulestin. The technology, with its layer-by-layer concept, does have its limitations, “but the choice of materials and certain optimization concepts have made it possible to overcome these limitations,” the researcher stresses.

Today, the prospects for improving the processes lie essentially in expanding the range of useable materials. In plastics processes, the key issue is to be able to use a larger range than for polyamides, which form a large percentage of the available polymers. Another opportunity for research is in semi-crystalline polymers, which present more challenges in terms of mastering the solidification. The target seems clear: in the future, it should be possible to manufacture every part using an additive manufacturing process.

 

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Conference on Polymer materials for additive manufacturing

What are the prospects for additive manufacturing technology in the field of polymer materials? This is the question researchers and industrial stakeholders will be trying to answer at the conference on “Polymer materials for additive manufacturing – reality and prospects.” The conference, organized by the French Society of Plastics Engineers (SFIP), Mines Douai, and the French Society of Automotive Engineers (SIA), will take place on March 23 and 24 in Villeurbanne on the INSA Lyon campus, which is also a partner of this event.

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When biology meets electronics

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Since starting at Mines Saint-Etienne in 2009, researcher Róisín Owens has created unusual devices: cell cultures coupled with electronic monitoring, able to give a real-time measurement of the state of health and reactions of cells when confronted with a certain type of medicine or pathogen. Particularly promising results in this new field, called bioelectronics, could change the face of toxicology in the future.

 

In science, discoveries sometimes come about because of who you meet. This was the case of Róisín Owens and her husband George Malliaras, when they entered this new field of research called bioelectronics. “I was a biologist specializing in infectious diseases, and he was an expert in physics and materials science” Róisín explains. “He would talk to me about his new technology, and I thought about how it could be applied to biology. This was how we came up with this new project together, combining biology and electronics”. The project became a reality in 2009 with the creation of the Bioelectronics department at the Provence Microelectronics Center of Mines Saint-Étienne, in Gardanne. While one part of the department, with the team led by George Malliaras, focused on neurosciences or, more recently, on electronics in fabrics through research led by Esma Ismailova, Róisín Owens set up the IONOSENSE program (see insert), designed to create a new in vitro diagnostic device.

 

Organic electronics at the heart of the system

Róisín and her team have centered their research on technology known as organic electronics. In contrast to traditional electronics, based on rigid materials like silicon and copper, organic electronics uses flexible polymers that offer a better interface with biology. “Furthermore, these materials are transparent, allowing direct observation of the cells in the device” notes the Irish researcher. These polymer structures are used in devices called “organic transistors” which have enhanced signal transduction and are thus extremely sensitive. “The cells between the electrodes of the polymer and the transistor act as a resistor by limiting ionic transfer, which is something that can be measured” she explains. “If the cells are in poor condition, for example if they are affected by a toxin, they have a lower resistance. In this way we can measure the state of health of the cell culture in real time”.

 

[box type=”shadow” align=”” class=”” width=””]IONOSENSE: a double grant-winning program

Róisín Owens’ work at Mines Saint-Etienne is closely linked to the IONOSENSE project, or Exploitation of Organic Electrochemical Transistors for Biological Ion sensing. Launched in 2011 thanks to a Starting Grant from the European Research Council (ERC) of €1.5 million, this program led to the development of the first bioelectronics devices. “We have shown that thanks to these devices, we can detect the presence of different pathogens: viruses, toxins and bacteria” explains Róisín. Working at the same time on other research themes (microfluidics, biofilms, etc.), the IONOSENSE program progressed towards its scheduled completion in 2015, but this was before another prestigious grant from the ERC was obtained at the end of 2014: the Proof of Concept grant for an additional year, for a sum of €150,000 which will be spent working on the potential commercialization of the technique. For Róisín these grants are not just good financial support. “It’s particularly gratifying from a personal point of view,” she continues. “It has built my career and allowed me to develop my ideas”.[/box]

 

Cell cultures in three dimensions

The validity of the results produced by these small devices had to be proved over the course of many months, and to this end the transparent nature of the polymers was of valuable assistance, allowing electronic measurements to be compared with direct observations. Róisín and her team then wanted to go one step further by exploring the possibilities of this new system in other fields, in particular no longer studying whole cells but focusing on lipid bilayers with integrated proteins, allowing observation of the interactions between the pathogens and the cell wall. Above all, however, the biologist is transitioning from the use of glass surfaces in favor of 3D structures. “In toxicology we know that there is a big difference between cells in vivo and cultures on two-dimensional substrates”. The team produces polymer conductors that build three-dimensional structures, onto which the cells are placed, and where the cell properties can still be studied in real time.

 

View of the detachement of a layer of kidney epithelial cells in a 3D model using fluorescence

View of the detachement of a layer of kidney epithelial cells in a 3D model using fluorescence

Imitating living matter in vitro

An in vitro kidney model is under development, with a structure that also incorporates microfluidics. “In the kidney there is blood and urine and between the two are the epithelial and endothelial cells” Róisín Owens tells us. “In order to obtain a realistic cell model for the toxicology of the kidney, we need to include these two components”. The team produced a device containing 12 wells, each made up of a transistor, a fluidic system representing the urine, a membrane with epithelial cells on one side and endothelial cells on the other, and a second fluidic for the blood. “We maintain the transparency so that biologists can observe the cells, as well as electronics for measuring cell conductivity, but we now also have microfluidics, which allows us to measure the presence of biomarkers secreted by the cells in the tubes” the biologist continues.

 

From invention to commercialization

Although the results are particularly promising, there is still a long way to go before these devices can be used in laboratories. “We would like to improve our technique with a view to commercial production, but first we need even more results to persuade people of the effectiveness of our system” Róisín Owens went on. “In addition to toxicology there is the fundamental research aspect: using optics and electronics at the same time could enable us to better understand cell movement and adhesion mechanisms, which are of particular interest to oncologists”. For the pharmaceutical industry this new process developed in the Provence Microelectronics Center also offers very interesting advantages. “Bringing out a new drug can cost more than a billion euros and take 12 years to develop, but 90% of these drugs don’t have the desired effect on human beings” she emphasizes. “This is due to the fact that these tests are carried out on animals, which are very different to humans: we therefore need to improve in vitro studies on human cells, with more predictive models that limit the number of false positives.” Róisín believes it will take just under ten years for her system to be commonly used in laboratories. In the meantime, she is already thinking of setting up a company to develop specific combinations for a particular application, on demand. The history of bioelectronics has only just begun.

 

Photo_portrait_rapprochéRóisín Owens’ career reflects her multilingual background: she speaks English, Gaelic, French, German and Greek. Culminating her studies in biochemistry in France, Ireland, she completed a PhD in England on proteins involved in infectious diseases, before taking off for the USA for her first postgraduate research at Cornell University, where she studied tuberculosis. In 2005, Róisín took time out from fundamental research and joined a New York start-up in order to develop technologies to improve the detection of pathogens. “At the time I wanted to go into something that was more applied”, she explained, but that was before realizing, two years later, that “[her] heart was in academic research”. She returned to Cornell University for two years for another postgraduate research project in an engineering department. “My husband is Greek and I’m Irish: after eight years in the USA we wanted to return to Europe”, Róisín recalls. In 2009 they both joined Mines Saint-Etienne, where their arrival led to the creation of the Bioelectronics department in the Provence Microelectronics Center. Today, the center is made up of around 30 people.
Biomécanique au service de la santé

Biomechanics serving healthcare

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Stéphane Avril, a researcher at Mines Saint-Étienne, describes himself as a “biomechanics” but would like to become a “mechanobiologist”, a switch from studying the mechanical properties of the body to decoding its biological mechanisms using engineering tools. Focused in particular on analysis of the behavior of normal and pathological vessels, his work should have significant consequences on treatment for various vascular illnesses, and has already led to several industrial partnerships.

 

“Research at Mines Saint-Étienne was originally organized around three main activities: mechanics and materials, manufacturing and processes engineering, and company performances. After adjustments and reorientation within the manufacturing industry in France, the idea emerged of setting up an ‘Engineering and health’ research center, which would develop the School’s three main activities but orientate them towards the fields of biology and medicine”, explained Stéphane Avril.

The researcher was hired in 2008 to develop biomechanics in health, a discipline that analyzes the mechanical behavior (movements, deformations) of tissue and organs (blood circulation, articulations etc.). He has been managing the ‘Engineering and health’ center at Mines Saint-Étienne, made up of sixty or so people, since 2010.

 

Two main themes: vessels and compression

The work of the biomechanics team led by Stéphane Avril, composed of twenty or so engineers and researchers, has a “double backbone”, he explains. “The first subject, more biologically-themed, tends towards predicting the development of certain cardiovascular illnesses, such as aneurysms (dilatations) of the aorta, thanks to studies on the resistance of the vascular wall”. The second focuses on the treatment offered by medical fabric in the general sense including, principally, compression stockings but also knee braces, lumbar belts etc. “This second field was developed at the request of certain industrial players. The region is the largest in Europe for manufacturing these textiles”, the researcher added. “The approach we have adopted entails working on an application, such as a piece of software, in order to see if it can resolve a medical problem. This translational research, driven by its practical benefits, is one of the school’s specialties.”

 

Biomécanique au service de la santé

Predicting the effects of elastic compression on a subject’s leg

A team recognized for its research in the treatment of aortic aneurisms

Since 2008 the biomechanics team has been working with vascular surgeons at Saint-Étienne who implant stent grafts (prostheses placed inside the diseased vessel) in patients with aortic aneurisms that are in danger of breaking, with the aim of protecting the aneurism sac from the blood flow. This operation rebuilds a solid aortic ‘wall’.

Stéphane Avril has started an important program that has received grants from the French National Research Agency (ANR). The program’s objective is to better adapt stent grafts to the characteristics of the aneurism through mechanical calculations and the use of industrial software. “These questions, which may seem applied research, have raised fundamental issues that have been acknowledged by the international community”, the researcher indicated. In particular the team is interested in enzymes (metalloproteases) and their participation in the weakening then dilation of the artery wall.

In December 2014 Pierre Badel, a researcher in the laboratory, was given a ‘starting grant’ by the prestigious European Research Council (ERC) for his work on the prevention of aneurism rupture as part of the AArteMIS (Aneurysmal Arterial Mechanics: Into the Structure) project. At the beginning of 2015 Stéphane Avril was also honored by the ERC with the ‘consolidator grant’ for the BIOLOCHANICS project. Through this project, the team of researchers aims to develop a new approach to treatment of aortic aneurisms. Mines Saint-Etienne will thus receive 3.5 million euros over 5 years for research into aneurism rupture. In addition, within 5 years Stéphane Avril’s team hope to identify the signs of arterial instability with the support of companies specializing in magnetic resonance imaging (MRI). Over time the research should lead to work on medication and regenerative cell treatments, in connection with industry.

All this work takes us from classical biomechanics (analysis of movements and deformations) to mechanobiology which aims to predict the changes in the microstructure of an organ, in this case vessels, taking into account the mechanical constraints acting on its location. We could even talk of cellular mechanobiology, inasmuch as the researchers at Mines Saint-Étienne attempt to understand better the influence of mechanical changes on the cellular working itself (protein constructions, chemical reactions etc.)

 

Atheromatous plaques in the carotid artery, coronary dilation complications: a better understanding

After starting at Mines Saint-Étienne, Stéphane Avril received funding from the ANR (French National Research Agency), using MRI to identify what may cause atherosclerotic plaques formed in the carotid arteries to break in patients.

Recently, the team’s biomechanics looked at complications of coronary angioplasty, work which consists of dilating the coronary arteries of the heart, shrunken by atheroma, in order to improve flow. One of these complications, called a dissection, occurs when part of the dilated coronary artery wall tears lengthways. Using simulations, Stéphane Avril and his researchers have identified the pathological processes that occur and have shown that some of these occurrences may be factors of secondary coronary obstruction.

A leader in medical compression

Within a few years Stéphane Avril’s team was a European leader in soft tissue biomechanics, “one of the cutting edge subjects at Mines Saint-Étienne”. The researchers are especially well-known for their work in the field of medical mechanical compression. Some of this research aims to better understand venous compression devices, associated with the wearing of contention stockings, and is carried out in collaboration with the companies Sigvaris and Thuasne which specialize in the manufacture of these fabrics. Thanks to a recent study using ultrasound by a young PhD student, in partnership with Sigvaris, it has been shown that elastic compression exercises a type of pressure on soft tissue that tends to reduce stagnant blood in venous microcirculation. This would explain the positive effect of contention on superficial varicose veins.

Other work, using magnetic resonance images, suggests that this compression has an effect on deep veins in the leg more through contraction of the leg muscles than by the passive transmission of pressure to the vein wall itself.

 

A good example of the importance of biomedical engineering

It is clear that Stéphane Avril’s work is an excellent illustration of the multiple possibilities made available by the development of biomedical engineering techniques, including a better understanding of physiological and pathological processes and an improvement of treatments.
Biomechanics and mechanobiology are necessarily multidisciplinary fields because they are situated at the interface of engineering, the health profession and industrial development, and should offer even more contributions in the years to come.

 

StéphanPortrait_Stéphane_Avrile Avril, cutting edge research
dedicated to health

Aged 38, he joined Mines-Saint-Étienne in 2008 as a professor and researcher. After a degree in math and studies in engineering followed by a PhD at Mines Saint-Étienne, he chose a career as a researcher in engineering sciences, first applied to the field of materials and then health. During his PhD thesis he applied new photomechanics technology to analysis of the properties of materials. Then in 2003 he worked in Châlons-en-Champagne in the mechanics and manufacturing laboratory, directed by Fabrice Pierron, at Arts et Métiers ParisTech, where he developed new mathematical tools for using photomechanical data. In 2006 a year spent in the laboratory directed by Jon Huntley at Loughborough University in Great Britain enabled him to better understand the advantages of MRI data for analyzing living tissue. Between May and August in 2014 Stéphane Avril completed his training with a sabbatical in the American laboratory directed by Jay Humphrey at Yale University in the USA, in order to start working on mechanobiology. In January 2015 he received the prestigious European research grant from the ERC.

Editor: Umaps, Corinne Tutin

Mines Douai, Concrete, sediments

Recycling concrete and sediment to create new materials

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How can we meet the needs for construction materials in an environmentally responsible manner? Recycling could be the solution, but it is not yet easy to create high-performance and eco-friendly materials using waste. At the conference on Natural Resources and Environment, which took place on November 5-6 2014 at Institut Mines-Télécom, Vincent Thiéry, a researcher at Mines Douai, presented two aspects of the research developed in the Civil and Environmental Engineering department on designing the concrete of the future.

 

It is increasingly difficult to find high-quality raw materials to make materials like concrete. At the same time, we are generating more and more waste that we do not know how to dispose of – industrial by-products, concrete from building renovations or demolitions, and sediments that block ports and canals. Vincent Thiéry and his colleagues are therefore working to design alternative materials, such as concrete and cements, using these new raw materials whose potential remains unexplored: “One the one hand, we could generate less waste, and on the other hand, we wouldn’t have to use as many natural resources.”

 

Recycling sediments and old concrete

“Our mission is to create high-performance materials that are environmentally friendly. This can be accomplished through recycling, by incorporating a certain amount of waste into these materials.” The sediments are retrieved by dredging ports and canals every 10 to 20 years, which produces large quantities of materials. The construction materials sector is has many uses for the recovered sediments: “We will try to integrate them into the construction of roads, prefabricated concrete (casting of concrete blocks or concrete for street furniture), landscaped mounds, embankments, and in artificial aggregates for reinforcing beaches.” Another possibility is recycled concrete aggregate. 300 million tonnes of construction and demolition waste are generated each year, which can be reused as aggregate for producing concrete, even though this type of aggregate requires much more water than traditional concrete. Better yet, “certain industrial by-products and waste – typically those generated by the steel industry – are resources used in the cement industry: the integration of these materials can produce attractive results, such as resistance to seawater and good mechanical strength.”

 

Vincent Thiéry, Mines Douai, concrete, sediments

Recycled concrete aggregate (diameter: approximately 1 cm). Black components: a natural aggregate. Gray components: cement paste. These two components behave differently when they are integrated into new concrete; they must be correctly characterized and quantified.

Recycling challenges: sustainable formulations

“Scientific and technical challenges arise in relation to durability.” The dredged sediments contain heavy metals and organic pollutants, which must not be released into the environment: therefore, the stabilization of the recycled materials must be ensured. “Concrete that is poorly made can develop certain pathologies — which appear in the form of swelling, flaking, or crumbling — and can no longer be used for its intended purpose.” A very well known pathology – the alkali-silica reaction – has been one of the Civil and Environmental Engineering (GCE) department’s areas of expertise for around fifteen years. Not all types of aggregate cause this pathology, yet for some of them, a specific mineralogy must undergo extensive analysis to ensure it will not react. “Eventually, we will no longer have a choice; we will have to find ways of using them anyway. Fortunately, several types of industrial waste allow for the recycling of aggregates that could generate pathologies.”

An example of microscopy applied to cementitious materials: a thin section of concrete. The colored components are the aggregates; the black part is the cement paste. The use of traditional optical microscopy (thin petrographic sections) makes it possible to compare the different components, thus facilitating their identification.

Prior research is required in order to find the right concrete formulation to match the intended use. “An extremely precise characterization of the recycled aggregate will be required before it can be integrated into new concrete.” Vincent Thiéry works on characterizing the materials, both natural and recycled. In other words, he uses microscopic observation to interpret the arrangement and properties of the minerals that compose the materials. “We know that in certain aggregates, we will need to look for a specific type of mineral, in a specific form, to determine if there is a risk of the concrete developing a pathology.”

The laboratory has also developed an experimental method based on the dissolution of the cement paste hardened in salicylic acid to measure the percentage of cement in the recycled concrete. The lab features a mechanical characterization center and a digital simulation center.

 

Partnerships to move from fundamental research to applied research

The EcoSed (Sediments in a Circular Economy) Industrial Chair, launched in April 2014 by Mines Douai, will carry out partnership-based research over a 5-year period on the management of dredging sediments (ports and canals). The tonnages are significant – around 50 million metric tonnes per year in France. “It involves more fundamental aspects, like sediment characterization, before moving towards extremely practical and applied aspects”: developing materials, improving knowledge of sediment-based concrete, and improving knowledge of their behavior in road geotechnics, etc. It is one of the Civil and Environmental Engineering (GCE) department’s flagship projects. It is also participating in the national Recybéton project, which studies the use of materials from concrete recycling sites through experiments in the laboratory and at experimental construction sites.