Category: Chemistry

Human sweat is a rich source of health information, offering insights into a person’s hydration level, electrolyte balance, and overall physiological state. For instance, lactate level in sweat is a useful biomarker of exercise intensity. Its measurement can help estimate the amount of lactic acid in the blood and, in turn, predict muscle fatigue.

Today, wearable sensors make it possible to continuously monitor biomarkers such as sweat lactate. Using the latest microfluidics technology, scientists have developed devices that convey minuscule amounts of sweat to tiny chemical sensors, which can transmit their measurements in real time wirelessly.

However, one common problem in such devices is that their microfluidic channels tend to trap air bubbles present in the sweat. If these bubbles cover the sensor’s electrodes, the measurements get interrupted, interfering with the continuous monitoring of the target biomarker.

To address this issue, a research team, led by Associate Professor Isao Shitanda from Tokyo University of Science (TUS) in Japan, has come up with a novel microfluidic sweat lactate sensor whose measurements remain unaffected by the air bubbles. Their study, published in ACS Sensors, was co-authored by Dr. Masahiro Motosuke, Dr. Tatsunori Suzuki, Dr. Shinya Yanagita, and Dr. Takahiro Mukaimoto from TUS.

The proposed wearable device consists of a relatively simple layered structure—a conventional lactate oxidase sensor attached via double-sided tape to a microfluidic system made of a silicone polymer. When the person wearing the device begins to perspire, the sweat enters the microfluidic channels via four inlets and flows toward a reservoir near which the electrodes are located. Old sweat exits the system through an outlet as new sweat enters, and a small wireless transmitter reports the measured lactate levels.

The key innovation in the proposed design was the use of a larger-than-usual sweat reservoir. “By increasing the length of the reservoir in the microfluidic channel, a space of approximately four microliters was created for trapping any air bubbles that infiltrate the device, thereby preventing them from contacting the electrodes of the sensor,” explains Dr. Shitanda.

The researchers tested their sensor in a series of laboratory experiments. They verified that the bubble-trapping region worked as intended by injecting bubbles into the device while measuring lactate levels in artificial sweat. In addition, the measurements were not affected by the sweat flow rate, and the response of the sensor remained stable for approximately two hours.

Lastly, the researchers tested the device on a male volunteer who exercised on a stationary bike for almost an hour. The sensor showed a lactate concentration correlation ranging from 1 to 50 mM as well as a correlation between sweat and blood lactate levels.

Overall, the results of this study hint at the potential of wearable microfluidic sensors for monitoring sweat biomarkers during exercise. “Since the microfluidic system of the proposed lactate sensor is fabricated from a soft, flexible, and non-irritating material, it could be used to continuously monitor lactate levels in sweat, especially in sports and medicine,” remarks Dr. Shitanda.

“Wearable lactate sensors may become useful condition management tools in sports such as soccer and basketball, allowing team managers to know when it’s best to replace a player.”

Only time will tell what training management and healthcare monitoring will look like in the future as wearable sensors become more capable and reliable.

More information: Isao Shitanda et al, Air-Bubble-Insensitive Microfluidic Lactate Biosensor for Continuous Monitoring of Lactate in Sweat, ACS Sensors (2023). DOI: 10.1021/acssensors.3c00490

Journal information: ACS Sensors 

Provided by Tokyo University of Science 

Wearable medical devices, such as the soft exoskeletons that provide support for stroke patients or controlled drug delivery patches, have to be made of materials that can adapt intelligently and autonomously to the wearer’s movements and to changing environmental conditions. These are precisely the type of autonomously switchable polymer materials that have recently been developed by materials scientists at the University of Stuttgart and pharmacists at the University of Tübingen, whose research findings have been reported in Advanced Materials Technologies.

The collaborating groups, which are headed up by Prof. Sabine Ludwigs (Institute of Polymer Chemistry) and Prof. Holger Steeb (Institute of Mechanics, MIB) at the University of Stuttgart and Prof. Dominique Lunter (at the University of Tübingen’s Department of Pharmaceutical Technology), have published a paper entitled “Autonomous Adaptation of Intelligent Humidity-Programmed Hydrogel Patches,” in which they demonstrate how intelligent polymer materials can be produced, whereby the word “intelligent” refers to the fact that the properties of the material can adapt autonomously to the environmental conditions in which they are used.

The rigidity of the materials in question can change by more than four orders of magnitude depending on humidity and temperature, and can undergo elastic changes even when subjected to major deformations, which enables the mechanical properties to adjust to the respective application.

Very high degree of adaptability

One of the authors of the paper, Sabine Ludwigs, refers to these materials as “intelligent rubber materials” and explains that “this high level of adaptability makes our polymers ideally suited for robots made of soft organic materials, such as those used in biomedicine or in search and rescue missions—the keyword here being ‘soft robotics.’ These polymers are also very well suited for use in smart skin applications, such as exoskeletons made of soft flexible fabrics.”

For both applications, the material needs to allow for both fast and slow movements, meaning it needs to have adjustable viscoelastic properties. “That is exactly what the material we have developed is able to do,” says Holger Steeb.

In addition, the material’s hydro-adaptability and reversible water absorption capacity make it suitable for use as a patch for the controlled release of drugs via the skin. The researchers specifically conducted experiments with the release of the painkiller diclofenac in a skin model. “The key mechanism is that it is the patch itself that controls the release of the active ingredient in response to the variable moisture levels of the wound, i.e., depending on the fluids that seep out of the wound,” says Dominique Lunter, a pharmaceutical expert based in Tübingen, Germany.

The relevant research was carried out as part of the recently established cross-faculty Functional Soft Materials Laboratory (FSM Lab) at the University of Stuttgart’s Data-integrated Simulation Science Cluster of Excellence (EXC 2075, SimTech). This is the result of a very successful collaboration between two research groups headed up by Sabine Ludwigs who specializes in polymer chemistry, and Holger Steeb, whose work is focused on the mechanics and function of smart polymer materials.

The vision: Materials that respond to active triggers

Going forward, the researchers are planning to investigate multifunctional material systems, which are able to autonomously adapt to their environment as well as react to active triggers, such as electrical stimuli. They are also planning to use simulations as a basis for modeling and predicting complex architectures.

As such, the polymer materials research results also benefit the studies being carried out by the university’s Data-Integrated Simulation Science (SimTech) cluster of excellence.

More information: Stephan Pflumm et al, Autonomous Adaption of Intelligent Humidity‐Programmed Hydrogel Patches for Tunable Stiffness and Drug Release, Advanced Materials Technologies (2023). DOI: 10.1002/admt.202300937

Journal information: Advanced Materials Technologies 

Provided by University of Stuttgart 

Polymers have become an indispensable part of everyday life. However, the current polymers represent only a small fraction of the huge number of polymers that theoretically exist.

Prof. Dr. Christopher Kuenneth at the University of Bayreuth, Germany, together with research partners in Atlanta, U.S., have now developed a digital system that promises extraordinarily high economical, technological and ecological benefits: from around 100 million theoretically possible polymers, their system can precisely select those materials that have an ideal property profile for targeted applications at unprecedented speed.

The new system is presented in Nature Communications.

Kuenneth, Professor of Computational Materials Science at the Faculty of Engineering at the University of Bayreuth, and Prof. Dr. Rampi Ramprasad at the Georgia Institute of Technology in Atlanta have named their new system “polyBERT.” The name comes from the interdisciplinarity from which polyBERT emerged: insights, concepts and techniques of polymer chemistry, linguistics and natural language processing, and the new artificial intelligence paradigm.

polyBERT is a system that treats the chemical structure of polymers like a chemical language: each word that can be formed in this language is a unique name for a theoretically possible polymer. The molecular building blocks and structures of respective polymers are reflected in these names. Building on new insights from linguistics and computer science, polyBERT has been trained and developed to a learning system by the research team in Bayreuth and Atlanta.

From polymer language to digital ‘fingerprints’

In a first step, polyBERT has learned the names of about 100 million theoretically possible polymers. These names are combinations of molecular units contained in approximately 13,000 polymers. The training of polyBERT makes it understand the polymer language, and correctly identify building blocks and structures of about 100 million polymers. The learning digital system can even use the polymer language on its own. This means that polyBERT can generate further names of previously unknown but theoretically possible polymers.

Linked to the chemical language expertise is another capability: polyBERT automatically translates polymer names that it knows into numerical representations, so-called “fingerprints.” Each fingerprint is a unique code word consisting of numbers from which the building blocks and structure of the respective polymer can be inferred. This automatic generation of digital fingerprints is far less error-prone and much faster than human-generated fingerprints for each chemical structure of polymers.

Rapid and precise prediction of polymer properties

polyBERT derives its enormous practical relevance from the teaching process, by the researchers in Bayreuth and Atlanta, about numerous characteristic polymer properties that are particularly relevant for technological applications. The system is therefore able to unambiguously correlate fingerprints and properties of polymers.

Novel techniques from the field of artificial intelligence enable polyBERT to precisely select, with high accuracy and at unprecedented speed, those polymers required for specific applications from the 100 million theoretically possible polymers.

“polyBERT is an exceptionally high-performance system for rapid and accurate prediction of polymer properties. Therefore, our research has the potential to significantly accelerate the design, synthesis and technological application of polymers,” says Kuenneth.

Past study identifies bioplastics

The importance of machine learning approaches to polymer research is already demonstrated by a past study that Kuenneth published in the journal Communications Materials in December 2022. Here, he and research partners at Atlanta and the Los Alamos National Laboratories in the United States present a similar artificial neural network-based system for predicting polymer properties.

This system is capable of countering global plastic waste pollution. About 75 percent of industrially produced plastics are based on fossil raw materials. The new system can significantly accelerate the search for biopolymers which can replace these plastics: The authors of the study identified 14 biologically producible and degradable polymers from 1.4 million possible candidates that can replace the current industrial plastics as soon as fast and cost-effective synthesis processes become available.

More information: Christopher Kuenneth et al, polyBERT: a chemical language model to enable fully machine-driven ultrafast polymer informatics, Nature Communications (2023). DOI: 10.1038/s41467-023-39868-6

Journal information: Nature Communications 

Provided by Bayreuth University

Plasma engineers and chemists at the University of Illinois have demonstrated a sustainable way of forming carbon-carbon bonds—the bedrock of all organic compounds—without expensive, rare metals that are typically required as catalysts in bond-forming organic reactions.

Through an interdisciplinary collaboration, Illinois researchers in Nuclear, Plasma, and Radiological Engineering, Bioengineering and Chemistry combined their expertise to develop this novel metal-catalyst-free approach that could lead organic chemistry in a new direction, according to the researchers.

In the study, “Plasma Electrochemistry for Carbon−Carbon Bond Formation via Pinacol Coupling,” published in the Journal of the American Chemical Society, the team explains how they used electricity and a plasma-liquid process to generate solvated electrons to form carbon-carbon bonds in a pinacol coupling reaction. C-C bond formation is widely used in the production of many man-made chemicals like pharmaceuticals and plastics.

According to researchers, this is the first example of plasma-generated solvated electrons for an organic redox coupling reaction and offers a sustainable solution for similar reductive organic reactions. Typically, such reactions require metal reagents or catalysts that are not only scarce and costly, but also present safety or environmental issues and sometimes require heat in the reactive process.

“Our process only really requires electricity—other than the reactor cell and equipment—and in the future hopefully this can come from renewable sources like wind or solar or nuclear, so the whole process is sustainable,” said study co-author R. Mohan Sankaran, Donald Biggar Willett Professor in Engineering in the Department of Nuclear, Plasma, and Radiological Engineering.

Sankaran said their process produces electrons from argon gas and then injects these electrons into solution to generate solvated electrons, a powerful chemical species typically generated by radiolysis, which requires complex equipment.

“In our case, the solvated electrons are generated with just a DC power supply and a relatively simple electrolysis reactor that houses our electrodes and the solution where we have the organic substrates,” said Sankaran, whose group has been developing atmospheric pressure plasmas for over a decade, and in previous work, has applied this type of plasma-liquid process to other applications—nanoparticle synthesis and nitrogen fixation. “We were curious about organic chemistry, but we had no expertise in either the methods or the characterization.”

Sankaran, who reached out to Jeffrey S. Moore, research professor in chemistry, for expertise, said this project would not have been possible without the collaboration.

“Most of this is chemistry—something that my group doesn’t do—and there is no way we would have succeeded without having someone with the requisite chemistry background,” Sankaran said.

Jian Wang, lead author of the study and a postdoctoral associate in the Moore group, brought his expertise in chemistry and materials science to the project and worked with plasma expert Scott Dubowsky, study co-author and research scientist in the Sankaran group, to learn the plasma-liquid process and then identify an organic reaction to study.

Wang experimented with different organic substrates, characterizing reactions using various analytical techniques, and ultimately chose pinacol coupling, because it is a well-established reaction for carbon-carbon bond formation and a reaction they believed could work with the plasma liquid process. Matthew Confer, another co-author and a postdoctoral researcher in the group of Rohit Bhargava, professor of bioengineering and faculty affiliate in chemistry, used his computational chemistry expertise to model how the pinacol product was formed from the solvated electron chemistry and radical reactions.

“This is an excellent illustration of the golden rule for a successful collaboration: the best collaborators share a common goal but bring different expertise,” said Moore, Stanley O. Ikenberry Research Professor, Professor Emeritus of Chemistry, and Howard Hughes Medical Institute Professor.

There have been a few studies where a plasma was used for an organic reaction, Sankaran explained, but the reactions and the mechanism were different.

“The plasma was typically used to oxidize a chemical and the chemical that was produced by the plasma was a reactive oxygen species. In our case, the reaction we studied was reduction which required electrons (or solvated electrons), and the reduction led to the formation of new carbon-carbon bonds,” Sankaran said.

Their next step will be applying their process to another organic chemistry reaction and showing that this approach is general and can be applied to different reactions.

“We also hope to find a reaction that is difficult to carry out, because it has a low yield, requires harsh conditions, or there is no active metal,” said Sankaran, who also explained that they hope to address one issue their study revealed—that yields can be limited by mass transfer limitations. “Our reaction occurs at the interface of a plasma and the solution, and for the substrate to reach the interface, it must diffuse. We can address this issue by incorporating liquid flow which will enhance mass transport by convection. Liquid flow will also potentially help us scale up the process whereby we can make a product continuously.”

Wang said one particular challenge for plasma electrochemistry as an alternative to more traditional organic synthesis is that the plasma is so energetic.

“Although we are able to achieve relatively good yield and selectivity, the control is still not as good as for example traditional chemistries with metal catalysts, or electro- or photocatalytic chemistries,” Wang said. “We are working on improving the controllability and selectivity right now.”

More information: Jian Wang et al, Plasma Electrochemistry for Carbon–Carbon Bond Formation via Pinacol Coupling, Journal of the American Chemical Society (2023). DOI: 10.1021/jacs.3c01779

Journal information: Journal of the American Chemical Society 

Provided by University of Illinois at Urbana-Champaign, College of Liberal Arts and Sciences

Scientists from the Radboud University have developed synthetic molecules that resemble real organic molecules. A collaboration of researchers, led by Alex Khajetoorians and Daniel Wegner, can now simulate the behavior of real molecules by using artificial molecules. In this way, they can tweak properties of molecules in ways that are normally difficult or unrealistic, and they can understand much better how molecules change.

Their paper is published in the journal Science.

Emil Sierda, who was in charge of conducting the experiments at Radboud University said, “A few years ago we had this crazy idea to build a quantum simulator. We wanted to create artificial molecules that resembled real molecules. So we developed a system in which we can trap electrons. Electrons surround a molecule like a cloud, and we used those trapped electrons to build an artificial molecule.” The results the team found were astonishing. Sierda says, “The resemblance between what we built and real molecules was uncanny.”

Changing molecules

Alex Khajetoorians, head of the Scanning Probe Microscopy (SPM) department at the Institute for Molecules and Materials of Radboud University said, “Making molecules is difficult enough. What is often harder, is to understand how certain molecules react, for example how they change when they are twisted or altered.”

How molecules change and react is the basis of chemistry, and leads to chemical reactions, like the formation of water from hydrogen and oxygen. “We wanted to simulate molecules, so we could have the ultimate toolkit to bend them and tune them in ways that are nearly impossible with real molecules. In that way we can say something about real molecules, without making them, or without having to deal with the challenges they present, like their constantly changing shape.”

Using this simulator, the researchers created an artificial version of one of the basic organic molecules in chemistry, benzene. Benzene is the first component for a number of chemicals, like styrene, which is used to make polystyrene. Khajetoorians says, “By making benzene, we simulated a textbook organic molecule, and built a molecule that is made up of elements that are not organic.” In addition, the molecules are 10 times bigger than their real counterparts, which makes them easier to work with.

Practical uses

The uses of this new technique are endless. Daniel Wegner, assistant professor within the SPM department says, “We have only begun to imagine what we can use this for. We have so many ideas that it is hard to decide where to start.” By using the simulator, scientists can understand molecules and their reactions much better, which will help in every scientific field imaginable.

Wegner adds, “New materials for future computer hardware are really hard to make, for instance. By making a simulated version, we can look for the novel properties and functionalities of certain molecules and evaluate whether it will be worth making the real material.”

In the far future, all kinds of things may be possible: understanding chemical reactions step by step like in a slow-motion video, or making artificial single-molecule electronic devices, like shrinking the size of a transistor on a computer chip. Quantum simulators are even suggested to perform as quantum computers. Sierda says, “But that’s a long way to go, for now we can start by beginning to understand molecules in a way we never understood before.”

More information: E. Sierda et al, Quantum simulator to emulate lower-dimensional molecular structure, Science (2023). DOI: 10.1126/science.adf2685. www.science.org/doi/10.1126/science.adf2685

Journal information: Science 

Provided by Radboud University Nijmegen 

by Leibniz-Institut für Polymerforschung Dresden e. V.

Living organisms use powerful physical principles to control interactions at their surfaces. Researchers at the Leibniz Institute of Polymer Research Dresden, Leipzig University and TU Dresden have now discovered why cholesterol-containing surfaces can exhibit greatly reduced attachment of proteins and bacteria.

The interdisciplinary team led by Carsten Werner had previously identified cholesterol as a component of the skin of widespread invertebrates (collembolae), which breathe through their skin and therefore need to protect it from contamination. In their paper published in Nature on June 22, 2023, the scientists have now elucidated a repulsive mechanism of cholesterol-containing surfaces.

Using experiments, simulations and thermodynamic analyses, they were able to show how the spontaneous change in the orientation of interfacial cholesterol molecules creates an “entropic barrier” that makes cholesterol-containing surfaces repellent.

The development of synthetic materials using the discovered principle is promising, as it is important for many products and technologies to effectively minimize the attachment of biomolecules and bacteria. However, such “translation” of the effect to scalable, robust surface functionalization requires further research.

More information: Jens Friedrichs et al, Entropic repulsion of cholesterol-containing layers counteracts bioadhesion, Nature (2023). DOI: 10.1038/s41586-023-06033-4

Journal information: Nature 

Provided by Leibniz-Institut für Polymerforschung Dresden e. V.

by Leibniz-Institut für Zoo- und Wildtierforschung (IZW) im Forschungsverbund Berlin e.V.

Mammalian seminal fluid contains a variety of proteins secreted by the accessory sex glands that are important for the processes involved in fertilization. One of these proteins, which is found in ungulates—and in particularly large quantities in boars—is the spermadhesin AQN-3.

A science team from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW), the Humboldt University of Berlin (HUB) and the Leibniz Institute for Molecular Pharmacology has studied the protein and discovered unexpected properties that could help sperm remain functional until they reach the egg. The findings are published in the scientific journal Chemistry and Physics of Lipids.

The proteins in seminal fluid are important for the survival of male germ cells and their species-specific interactions with the components of the female genital tract. There are five different spermadhesins in the seminal fluid of ungulates. Spermadhesins are found in particularly large quantities in porcine semen. In order to understand the function of these proteins, which—as the name suggests—attach themselves to the sperm surface, the spermadhesins AWN and AQN-3, named after the letter code of the first three amino acids of the protein sequence, have so far been artificially produced in bacteria.

In a previous study, the scientific team led by Karin Mueller and Beate Braun from the Leibniz-IZW showed that AWN binds specifically to negatively charged lipids. However, these are primarily found on the half of the cell membrane facing the inside of the sperm cell. This raises the question of how the spermadhesins attach to the surface of the sperm? Since it is known from work of other scientific groups that AWN forms aggregates with AQN-3, it was now investigated whether AQN-3 binds to typical lipids on the outside of the sperm membrane, such as phosphatidylcholine and sphingomyelin.

“Surprisingly, the applied model systems with lipid strips and vesicles showed that AQN-3 also binds selectively with negatively charged lipids, such as phosphatidic acid and various phosphatidylinositol phosphates,” explains Mueller. In addition, AQN-3 has a strong tendency to form aggregates with itself and other proteins.

Studies by other scientific groups describe yet another protein in the aggregates of native AWN and AQN-3 in seminal fluid, the protein pB1. “The pB1 protein belongs to a group of proteins that are known to bind to the phosphatidylcholine on the outside of the cell membrane in bovine sperm and thus have a stabilizing effect,” says Peter Müller from the Humboldt University in Berlin.

It is therefore assumed that pB1 anchors the protective protein envelope of AWN and AQN-3 in the cell membrane of sperm through aggregate formation. Negatively charged lipids such as phosphatidylinositol phosphates serve, among other things, as signaling molecules during fertilization. If they are formed and released prematurely, they could be “intercepted” by spermadhesins until the sperm have reached the egg at the site of fertilization.

Interestingly, the composition of the protein coat around the sperm is species-specific, so spermadhesins are the main component in seminal fluid only in porcine species. This raises the question of how their role is fulfilled in other species and whether their protective properties could be exploited in the application of assisted reproduction techniques in the context of species conservation.

More information: Karin Müller et al, Porcine spermadhesin AQN-3 binds to negatively charged phospholipids, Chemistry and Physics of Lipids (2023). DOI: 10.1016/j.chemphyslip.2023.105306

Provided by Leibniz-Institut für Zoo- und Wildtierforschung (IZW) im Forschungsverbund Berlin e.V.

by University of Vienna

To unveil the previously elusive behavior and stability of complex metal compounds found in aqueous solutions, researchers at the University of Vienna have created a speciation atlas now published in Science Advances. This achievement has the potential to drive new discoveries and advancements in fields like catalysis, medicine, and beyond.

Metal atoms can form tiny 3D structures with oxygen, intricate frameworks that look not unlike wire mandalas and that are called “polyoxometalates,” or “POMs.” These POMs are useful for controlling chemical reactions in chemistry, biology, or material science, but also are relevant for understanding natural processes in these fields.

However, like wire mandalas, their structure is highly variable and depends on minute changes in their environment, making it very difficult for researchers to predict their structure and thus their function for various applications, from medicine to environmental remediation.

Nadiia Gumerova and Annette Rompel from the Faculty of Chemistry at the University of Vienna have now developed a so-called speciation atlas, a cheat sheet that allows researchers to accurately ascertain the expected structure and behavior of 10 commonly used POMs for any given chemical condition.

More specifically, this atlas is a database including a predictive model that can be extended to other than the 10 selected POMs, that will yield POM species distributions, stability and catalytic activity considering the factors pH, temperature, incubation time, buffer solutions, reducing or chelating agents, and ionic strength.

To further support future research, Gumerova and Rompel have also developed a “roadmap” for other scientists conducting experiments with their own POMs: By selecting stable POM variants, listing the application system parameters and then conducting so-called “POM speciation studies”—experiments that reveal the change of POM structure under a change of conditions—researchers can ensure that they are getting the most accurate results and make the best use of POMs in their work.

“The speciation atlas for POMs represents a significant advancement in our understanding of these complex metal compounds. Its insights have the potential to drive new discoveries and advancements in catalysis, biology, medicine, and beyond,” says Annette Rompel.

More information: Nadiia I. Gumerova et al, Speciation atlas of polyoxometalates in aqueous solutions, Science Advances (2023). DOI: 10.1126/sciadv.adi0814

Journal information: Science Advances 

Provided by University of Vienna 

by University of Science and Technology of China

Recently, flexible and foldable devices have developed at a dramatic rate. More and more foldable devices appear in people’s lives. Long-term service requires the folded parts to endure repeated deformation which might cause fatigue damage to the devices. Consequently, the damage will affect the normal function of the devices.

Inspired by the hinge of bivalve Cristaria plicata, which experiences hundreds of thousands of repeating opening-and-closing valve motions throughout the bivalve’s lifetime, a research team led by Prof. Yu Shuhong collaborating with Prof. Wu Hengan from the University of Science and Technology of China (USTC) proposed their tactics to improve the fatigue resistance of structural materials. The work titled “Deformable hard tissue with high fatigue resistance in the hinge of bivalve Cristaria plicata” was published in Science on 23 June 2023.

The researchers illuminated the mechanism of fatigue resistance of deformable biomineral tissue in the hinge of bivalve C. plicata, a species of mollusk, and proposed a novel design strategy of fatigue-resistant structural materials by exploiting the inherent properties of each component through the multiscale structure.

They found that the folding fan-shaped region (FFR) in the hinge can sustain large deformation during repetitive opening-and-closing valve motions and maintain its structure and function for a long period. The tissue still functions well and shows no signs of fatigue behaviors even after 1,500,000 cycles.

The hinge is composed of two regions, the outer ligament (OL) and the folding fan-shaped region. Through observation and finite element analysis, the researchers uncovered the roles of each hinge region during the valves’ motion. When closing, the stretched OL undertakes the circumferential stress dominantly and stores most of the elastic strain energy, while the FFR is deformed circumferentially and provides strong radial support to fix the OL under the limited radial deformation.

They revealed that the hierarchical structures which span from the macroscale level down to the lattice level endow the FFR with notable deformability and load translation capability.

This work provides a novel biomimetic model for designing artificial materials with brittle components and brings a new perspective for elongating materials’ longevity. The multi-level design strategy sheds light on development of the future fatigue-resistant materials.

More information: Xiang-Sen Meng et al, Deformable hard tissue with high fatigue resistance in the hinge of bivalve Cristaria plicata, Science (2023). DOI: 10.1126/science.ade2038. www.science.org/doi/10.1126/science.ade2038

Journal information: Science 

Provided by University of Science and Technology of China

by Massachusetts Institute of Technology

A team of chemists from MIT and Duke University has discovered a counterintuitive way to make polymers stronger: introduce a few weaker bonds into the material.

Working with a type of polymer known as polyacrylate elastomers, the researchers found that they could increase the materials’ resistance to tearing up to tenfold, simply by using a weaker type of crosslinker to join some of the polymer building blocks.

These rubber-like polymers are commonly used in car parts, and they are also often used as the “ink” for 3D-printed objects. The researchers are now exploring the possible expansion of this approach to other types of materials, such as rubber tires.

“If you could make a rubber tire 10 times more resistant to tearing, that could have a dramatic impact on the lifetime of the tire and on the amount of microplastic waste that breaks off,” says Jeremiah Johnson, a professor of chemistry at MIT and one of the senior authors of the study, which appears in Science.

A significant advantage of this approach is that it doesn’t appear to alter any of the other physical properties of the polymers.

“Polymer engineers know how to make materials tougher, but it invariably involves changing some other property of the material that you don’t want to change. Here, the toughness enhancement comes without any other significant change in physical properties—at least that we can measure—and it is brought about through the replacement of only a small fraction of the overall material,” says Stephen Craig, a professor of chemistry at Duke University who is also a senior author of the paper.

This project grew out of a longstanding collaboration between Johnson, Craig, and Duke University Professor Michael Rubinstein, who is also a senior author of the paper. The paper’s lead author is Shu Wang, an MIT postdoc who earned his Ph.D. at Duke.

The weakest link

Polyacrylate elastomers are polymer networks made from strands of acrylate held together by linking molecules. These building blocks can be joined together in different ways to create materials with different properties.

One architecture often used for these polymers is a star polymer network. These polymers are made from two types of building blocks: one, a star with four identical arms, and the other a chain that acts as a linker. These linkers bind to the end of each arm of the stars, creating a network that resembles a volleyball net.

In a 2021 study, Craig, Rubinstein, and MIT Professor Bradley Olsen teamed up to measure the strength of these polymers. As they expected, they found that when weaker end-linkers were used to hold the polymer strands together, the material became weaker. Those weaker linkers, which contain cyclic molecules known as cyclobutane, can be broken with much less force than the linkers that are usually used to join these building blocks.

As a follow-up to that study, the researchers decided to investigate a different type of polymer network in which polymer strands are cross-linked to other strands in random locations, instead of being joined at the ends.

This time, when the researchers used weaker linkers to join the acrylate building blocks together, they found that the material became much more resistant to tearing.

This occurs, the researchers believe, because the weaker bonds are randomly distributed as junctions between otherwise strong strands throughout the material, instead of being part of the ultimate strands themselves. When this material is stretched to the breaking point, any cracks propagating through the material try to avoid the stronger bonds and go through the weaker bonds instead. This means the crack has to break more bonds than it would if all of the bonds were the same strength.

“Even though those bonds are weaker, more of them end up needing to be broken, because the crack takes a path through the weakest bonds, which ends up being a longer path,” Johnson says.

Tough materials

Using this approach, the researchers showed that polyacrylates that incorporated some weaker linkers were nine to 10 times harder to tear than polyacrylates made with stronger crosslinking molecules. This effect was achieved even when the weak crosslinkers made up only about 2% of the overall composition of the material.

The researchers also showed that this altered composition did not alter any of the other properties of the material, such as resistance to breaking down when heated.

“For two materials to have the same structure and same properties at the network level, but have an almost order of magnitude difference in tearing, is quite rare,” Johnson says.

The researchers are now investigating whether this approach could be used to improve the toughness of other materials, including rubber.

More information: Shu Wang et al, Facile mechanochemical cycloreversion of polymer cross-linkers enhances tear resistance, Science (2023). DOI: 10.1126/science.adg3229. www.science.org/doi/10.1126/science.adg3229

Journal information: Science 

Provided by Massachusetts Institute of Technology 

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.