The best way to stave off the worst effects of climate change is to reduce CO2 emissions around the world. And one way to do that, says Zhongwei Chen, a professor in the Department of Chemical Engineering at the University of Waterloo, is to capture the CO2 and convert it into other useful chemicals, such as methanol and methane for fuels.
Stopping emissions at the source, and further reducing future ones by replacing CO2-producing fuels with cleaner ones “…is a way to close the circle,” Chen says.
In order to turn CO2 into methanol, you need a catalyst to jump-start the electrochemical reaction. Traditionally, these catalysts have either been made out of precious metals like gold or palladium, or base metals like copper or tin. However, they are expensive and break down easily, hindering large-scale implementation.
“Right now we can’t meet industrial requirements,” says Chen. “So we are trying to design catalysts with better activity, selectivity, and durability.”
Chen and his team are focused on low-cost metal and metal-free catalysts. The metal-free catalysts, made from carbon, are cheaper and more durable but tend to have lower catalytic activity than metal ones. So the team tweaked the chemical composition and physical design of the catalyst to optimize its efficiency, combining the materials science of the catalyst design with the engineering of the electrode and reactor to improve the activity of the whole system.
“We want to make it as small as we can, but not too small to be a practical application,” says Chen. They combined nanometer-scale active sites within a micrometer-scale particle—like bubbles in a tiny sponge—to create a catalyst with a huge number of active sites in a particle that is easy and practical to fabricate.
The powerful light beams and expert technical teams at the Canadian Light Source (CLS) at the University of Saskatchewan were instrumental in helping to design an efficient catalyst, says Chen. “The advanced facilities at CLS are critical in helping us understand what was going on during the reaction, so we can continue to design and improve the next generation of catalysts.”
The paper is published in the journal ACS Catalysis.
More information: Zhen Zhang et al, Steering Carbon Hybridization State in Carbon-Based Metal-free Catalysts for Selective and Durable CO2 Electroreduction, ACS Catalysis (2022). DOI: 10.1021/acscatal.2c03055
In a study published in Analytical Methods, a research group led by Li Bei from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) proposed the rapid detection of beer spoilage bacteria based on label-free surface-enhanced Raman spectroscopy (SERS) technology.
Lactic acid bacteria are common spoilage bacteria in beer and need to be monitored and controlled at all stages of beer production. Traditional spoilage bacteria detection methods are time-consuming and cannot meet the demand for real-time, in-situ, rapid detection during the production process.
Raman spectroscopy has been widely used for microbial detection due to its fast, non-destructive and accurate properties, but conventional Raman spectroscopy has the disadvantage of poor signal-to-noise ratio, which affects the accuracy of microbial identification.
Compared with conventional Raman spectroscopy, the SERS technique has a stronger and more sensitive signal and is well suited to the detection of beer spoilage bacteria. Furthermore, the label-free SERS technique is ideal for commercialization due to its low cost and good results.
In this study, the researchers improved the existing process for the preparation of label-free SERS silver nanoparticles (AgNPs). The effect of the AgNPs@KCl agglomeration effect on SERS enhancement was investigated. Eight species of beer spoilage bacteria produced during the beer brewing process were identified by SERS.
The researchers further investigated the effect of the method on the final identification rate by combining the t-distributed stochastic neighbor embedding (t-SNE) dimensionality reduction analysis algorithm, Support Vector Machine (SVM), k-NearestNeighbor (KNN) and Linear Discriminant Analysis (LDA) machine learning algorithms. All three machine learning algorithms achieved an accuracy of around 90% and performed well in identifying beer spoilage bacteria.
In the stability analysis and mixing tests, two known spoilage bacteria were mixed with pure beer and incubated at constant temperature for a period of time to identify the bacteria in the beer. The two spoilage bacteria were successfully detected in the samples and had good spectral stability.
According to the final validation study, the technique can indeed identify the target spoilage bacteria from the simulated samples, which is of great significance to the rapid identification of spoilage bacteria in the beer brewing process.
More information: Lindong Shang et al, Rapid detection of beer spoilage bacteria based on label-free SERS technology, Analytical Methods (2022). DOI: 10.1039/D2AY01221A
Fabrication of PFM. (A) Preparation of PFM with laser puller and SI-ATRP. (B) SEM image of the 10-μm-diameter tip of a PFM. (C) Experimental setup for the electric measurement with the PFM. Credit: Science (2023). DOI: 10.1126/science.adc9150
Neuromorphic devices have attracted increasing attention because of their potential applications in neuromorphic computing, intelligence sensing, brain-machine interfaces and neuroprosthetics. However, most of the neuromorphic functions realized are based on the mimic of electric pulses with solid state devices. Mimicking the functions of chemical synapses, especially neurotransmitter-related functions, is still a challenge in this research area.
In a study published in Science, the research group led by Prof. Yu Ping and Mao Lanqun from the Institute of Chemistry of the Chinese Academy of Sciences developed a polyelectrolyte-confined fluidic memristor (PFM), which could emulate a diverse electric pulse with ultralow energy consumption. Moreover, benefitting from the fluidic nature of PFM, chemical-regulated electric pulses and chemical-electric signal transduction could also be emulated.
The researchers first fabricated the polyelectrolyte-confined fluidic channel by surface-initiated atomic transfer polymerization. By systematically studying the current-voltage relationship, they found that the fabricated fluidic channel could be identified as a memristor, defined as PFM. The origin of the ion memory came from the relatively slow diffusion dynamics of anions into and out of the polyelectrolyte brushes.
The PFM could emulate short-term plasticity patterns (STP), including paired-pulse facilitation and paired-pulse depression. These functions can be operated at a voltage and energy consumption as low as those biological systems, suggesting the potential application in bioinspired sensorimotor implementation, intelligent sensing and neuroprosthetics.
The PFM could also emulate the chemical-regulated STP electric pulses. Based on the interaction between polyelectrolyte and counterions, the retention time could be regulated in different electrolytes. More importantly, in a physiological electrolyte (i.e., phosphate-buffered saline solution, pH 7.4), the PFM could emulate the regulation of memory by adenosine triphosphate (ATP), demonstrating the possibility to regulate the synaptic plasticity by neurotransmitter.
Based on the interaction between polyelectrolytes and counterions, the chemical-electric signal transduction was accomplished with the PFM, which is a key step towards the fabrication of artificial chemical synapses.
With structural emulation to ion channels, PFM features versatility and easily interfaces with biological systems, paving a way to building neuromorphic devices with advanced functions by introducing rich chemical designs. This study provides a new way to interface chemistry with neuromorphic devices.
More information: Tianyi Xiong et al, Neuromorphic functions with a polyelectrolyte-confined fluidic memristor, Science (2023). DOI: 10.1126/science.adc9150
Graphical Abstract. Credit: Angewandte Chemie International Edition (2022). DOI: 10.1002/anie.202216512
The quantitative detection of specific antibodies in complex samples such as blood can provide information on many different diseases but usually requires a complicated laboratory procedure. A new method for the rapid, inexpensive, yet quantitative and specific point-of-care detection of antibodies has now been introduced in the journal Angewandte Chemie International Edition by an Italian research team. It uses an electrochemical cell-free biosensor that can directly detect antibodies against diseases such as influenza in blood serum.
Influenza is a severe, widespread, epidemic disease that can be fatal and may also have significant societal and economic consequences. The clinical evaluation of immune responses to flu vaccines and infections is thus correspondingly important. A simple, inexpensive, point-of-care diagnostic method would be preferable to current expensive and complex laboratory analysis.
A new method developed by Sara Bracaglia, Simona Ranallo, and Francesco Ricci (University of Rome) fulfills this wish. It is based on “programmable” gene circuits, cell-free transcription, and electrochemical detection.
In living cells, genes are read by RNA polymerases and transcribed into an RNA sequence, which then serves as a blueprint for building proteins (translation). This “machinery” can also be used by cell-free systems. To build their new detector, the team combined this type of machinery with specifically designed synthetic gene circuits that only get “switched on” when the antibody being tested for is present in the sample. As an example, they designed a test that detects anti-influenza antibodies, which are directed against a surface molecule on influenza viruses.
To do this, the team developed a synthetic gene with an incomplete promoter. The promoter is a DNA segment that controls the reading of the gene. If the promoter is incomplete RNA polymerase cannot start the transcription of RNA. The test solution also contains a pair of synthetic DNA strands that are bound to a protein portion (also called peptide) that is specifically recognized by anti-influenza antibodies.
Upon binding between the antibodies and the peptide, the two DNA strands are arranged in a way that completes the promoter and switches the synthetic gene on. The RNA polymerase can now dock on the synthetic gene and start transcribing RNA strands. These RNA strands in turn can bind specifically to a DNA probe fixed to a small disposable electrode and give a measurable current signal change. As long as no antibodies are present, no RNA will be transcribed and no change in current signal will be measured by the disposable electrode. If the sample contains influenza antibodies, the machinery synthesizes RNA, which binds to the electrode leading to a current signal.
The system requires only very small sample volumes, is very specific and sensitive, reliable, and inexpensive. Thus, it can be readily miniaturized to make a portable and easy-to-use diagnostic tool. It is also adaptable for the detection of a wide variety of other antibodies.
More information: Sara Bracaglia et al, Electrochemical Cell‐Free Biosensors for Antibody Detection, Angewandte Chemie International Edition (2022). DOI: 10.1002/anie.202216512
Just like a “dam burst”, the key bottleneck of MgH2 as hydrogen storage material is the first-layer dehydrogenation. Credit: Royal Society of Chemistry
A group of researchers has identified the key stumbling block of a common solid-state hydrogen material, paving the way for future design guidelines and widespread commercial use.
Details of their findings were published in the Journal of Materials Chemistry A, where the article was featured as a front cover article.
Hydrogen will play a significant role in powering our future. It’s abundant and produces no harmful emissions when burned. But the storage and transportation of hydrogen is both costly and risky.
Currently, hydrogen is stored by three methods: high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage, and solid-state hydrogen storage. Among solid-state hydrogen storage, solid-state materials are generally the safest and provide the most hydrogen storage density.
Metal hydrides have long been explored for their large hydrogen storage potentiality and their low cost. As these metals come into contact with gaseous hydrogen, hydrogen gets absorbed onto the surface. Further energy input leads to hydrogen atoms finding their way into the metal’s crystal lattices until the metal becomes saturated with hydrogen. From there, the material can absorb and desorb hydrogen in larger amounts.
Magnesium hydride (MgH2) has shown immense promise for superior hydrogen storage capacity. However, a high temperature is necessary for MgH2 to decompose and produce hydrogen. Furthermore, the material’s complex hydrogen migration and desorption, which result in sluggish dehydrogenation kinetics, have stymied its commercial application.
An interesting “burst effect” was found on the dehydrogenation of a typical solid-state hydrogen storage material, MgH2. After the sluggish dehydrogenation at the first layer, hydrogen desorption from the subsequent layers will be much easier. Credit: Hao Li et al.
For decades, scientists have debated why dehydrogenation within MgH2 is so difficult. But now, the research group has uncovered an answer.
Using calculations based on spin-polarized density functional theory with van der Waals corrections, they unearthed a “burst effect” during MgH2‘s dehydrogenation. The initial dehydrogenation barriers measured at 2.52 and 2.53 eV, whereas subsequent reaction barriers were 0.12–1.51 eV.
The group carried out further bond analysis with the crystal orbital Hamilton population method, where they confirmed the magnesium-hydride bond strength decreased as the dehydrogenation process continued.
“Hydrogen migration and hydrogen desorption is much easier following the initial burst effect,” points out Hao Li, associate professor at Tohoku University’s Advanced Institute for Materials Research (WPI-AIMR) and corresponding author of the paper. “Structural engineering tweaks that promote this desorption process could be the key to facilitating the hydrogen desorption of MgH2.”
Li and his colleagues demonstrated that hydrogen vacancies maintained a high degree of electronic localization when the first layer of atomic hydrogen exists. Analyses of the kinetic characteristics of MgH2 after surface dehydrogenation, performed by ab initiomolecular dynamics simulations, also provided additional evidence.
“Our findings provide a theoretical basis for the MgH2‘s dehydrogenation kinetics, providing important guidelines for modifying MgH2-based hydrogen storage materials,” adds Li.
More information: Shuai Dong et al, The “burst effect” of hydrogen desorption in MgH2 dehydrogenation, Journal of Materials Chemistry A (2022). DOI: 10.1039/D2TA06458H
Illustration of the new synthetic route for functionalised Z-alkenes. Idea: Dr. Sofiya Runikhina, University of Groningen. Credit: Stutpak Illustration and Animation, Deventer, the Netherlands
Chemists from the University of Groningen have found a simple way to produce previously inaccessible chiral Z-alkenes, molecules that offer a significant synthetic short-cut for the production of bioactive molecules.
Instead of eight to ten synthetic steps to produce these molecules, the new reaction can be done in three steps, without the need for any purification. The key lies in a phosphine molecule that is normally used to make metal-containing catalysts but that turns out to be the ideal starting point for this chemical reaction. The results were published in Science Advances on January 13.
Organic compounds are very versatile. Their carbon atoms can be connected by single, double, or triple bonds. Furthermore, many biologically important molecules contain chiral centers, parts of the molecule that can be in two mirror image positions, comparable to a left and a right hand. Molecules that have a double bond, a chiral center, and a reactive group for synthetic modifications all next to each other are also important, but chemists find that these are very difficult to make.
Unstable
Alkenes are compounds that contain two carbon atoms that are connected by a double bond. When picturing these two carbon atoms horizontally, we can distinguish Z-alkenes, whereby both carbon atoms are connected to another carbon on the same side (both pointing up), and E-alkenes, whereby the connected carbons are on opposite sides, (one up and one down). Z-alkenes are unstable because carbons that are connected on the same side are forced to be close to each other.
“The molecule doesn’t like this and if it gets a chance it will transform into the more stable E-alkene. That is why it is hard to make less stable Z-configured alkenes,” explains Syuzanna Harutyunyan, Professor of Homogeneous Catalysis at the University of Groningen. “Z-alkenes are very useful, but also difficult to make.”
The team needed to make the less stable Z-alkenes, where the double bond is connected to a chiral carbon center, further connect to a highly reactive carbon center, which is very tricky.
This picture shows the configuration of Z- and E-alkenes (upper panel) and the one-pot synthesis of functionalised Z-alkenes. Credit: Harutyunyan Lab, University of Groningen
Reactive salt
Using known synthetic methods, it would take about eight to ten separate steps to create such a structure. Harutyunyan and her team tried to simplify this by starting out with a molecule called phosphine. Co-author Roxana Postolache says, “This molecule is normally used to produce metal-containing catalysts. In previous work, we developed a way to make a chiral phosphine, which formed the basis for our new synthetic route to Z-alkenes.”
Harutyunyan states, “We took our phosphine and turned it into a salt. This would allow the creation of a double bond with Z-configuration.”
But this salt is very reactive and all the attempts to introduce a double bond resulted in a lot of products that the scientists did not want. “So, we had to find a way to tune the reactivity,” explains Postolache.
Blackboard
This step required a blackboard and chalk approach, which Harutyunyan and her team used to discuss options. A potential solution was found in adding a special group to the phosphine to make a different type of salt. Harutyunyan says, “We figured that this should pull electrons away from the phosphorus and would allow us to tune the reactivity.”
First author Luo Ge took the idea from the blackboard to the laboratory. “We tried to make this idea work and we got it right with our first attempt. It was a pleasant surprise to see that our idea really worked.” They subsequently optimized the reaction and then used their method to modify real bioactive compounds.
Possibilities
A big advantage of the new synthetic route is that it takes fewer steps and is essentially a one-pot reaction. It just requires room temperature for the first step, mild heating (50–70 °C) to make the salt, and –78 °C for the final step of making the double bond with a Z-configuration.
Joint first author Esther Sinnema says, “By using our phosphine as a synthetic tool, rather than a catalyst, we opened up all kinds of possibilities. We could make a large number of new chiral Z-alkenes and use the method to modify bioactive compounds. In the paper, we present 35 different molecules that were made with our method.”
“We expect that our study will pave the way for using commercially available, simple alkenes to make much more complex functionalized alkenes via phosphine and salt intermediates,” says Harutyunyan.
Could washing our clothes with detergent become a thing of the past? Even though the research is in its early stages, an investigation as to whether washing or cleaning can be done with purified water instead of detergent solution looks promising.
“Our goal is to develop a scientific model that explains what happens both chemically and physically when dirt is removed in purified water. When it comes to washing with detergents we already know what happens, but this is an unexplored area,” says Andriani Tsompou, Ph.D. candidate at Malmö University.
Professor Vitaly Kocherbitov adds, “In the long run, our research can solve environmental problems with water pollution caused by detergents. To succeed in this, we need to better understand the intermolecular forces that act in purified water.”
The hypothesis is that in purified water—water that has been filtered and deionised so that impurities and especially ions are removed—repulsive forces between charged objects become stronger. As a result, dirt particles easier detach from surfaces and form a finely dispersed colloidal system in water.
Tsompou explains, “When you have salt in the system, the dirt you want to remove will clump together more and make it harder for the water to remove the particles from the material.”
According to earlier results of a study published in the Journal of Colloid and Interface Science, Tsompou and her colleagues used water with different properties: tap water, water with added salt, and two grades of purified water. In a QCM-D measurement—a surface-sensitive real-time technique for analyzing surface interaction and layer properties in thin films—a 90% purification of Vaseline on a glass slide was achieved for both grades of purified water at 25-degres.
In later trials, they have been experimenting with several washing cycles and with different temperatures and achieved a degree of purification of 100% in purified water at 40 degrees in two washing cycles.
In these trials, however, the most favorable conditions have been assumed by choosing surfaces and dirts that form weak bonds. “We have used water-friendly surfaces such as glass and silicate which have a negative charges and then olive oil or Vaseline, which also can get negative charges, so that they release each other easily, explains Tsompou.
The idea is to gradually increase the bond strength and change the materials so that they finally approach real conditions.
“Because these are such complicated processes, we have to build up knowledge from less complicated areas. The next step will be oil on plastic which stronger attach to each other. The end goal is of course to test on real fabric,” says Tsompou.
These bio-based foams avoid the need for petroleum products. Credit: Srikanth Pilla, CC BY-ND
A new plant-based substitute for polyurethane foam eliminates the health risk of the material, commonly found in insulation, car seats and other types of cushioning, and it’s more environmentally sustainable, our new research shows.
Polyurethane foams are all around you, anywhere a lightweight material is needed for cushioning or structural support. But they’re typically made using chemicals that are suspected carcinogens.
Polyurethanes are typically produced in a very fast reaction between two chemicals made by the petrochemical industry: polyols and isocyanates. While much work has gone into finding replacements for the polyol component of polyurethane foams, the isocyanate component has largely remained, despite its consequences for human health. Bio-based foams can avoid that component.
We created a durable bio-based foam using lignin, a byproduct of the paper pulping industry, and a vegetable oil-based curing agent that introduces flexibility and toughness to the final material.
At the heart of the innovation is the ability to create a system that “gels,” both in the sense that the materials are compatible with one another and that they physically create a gel quickly so that the addition of a foaming agent can create the lightweight structure associated with polyurethane foams.
Lignin is a difficult material to convert into a usable chemical, given its complicated and heterogeneous structure. We used this structure to create a network of bonds that enabled what we believe is the world’s first lignin-based nonisocyanate foam.
The foam can also be recycled because it has bonds that can unzip the chemical network after it has formed. The main components used to produce the foam can then be extracted and used again.
How the chemicals in bio-based foams can be recycled and reused. Credit: Srikanth Pilla, CC BY-ND
Why it matters
Polyurethane foams are the world’s sixth-most-produced plastic yet among the least recycled materials. They are also designed for durability, meaning they will remain in the environment for several generations.
The fully bio-based origin of our foams addresses the issue of carbon neutrality, and the chemical recycling capability ensures that waste plastic has a value attached to it so it is less likely to be thrown away. Ensuring waste has value is a hallmark of the circular approach to manufacturing—attaching a monetary value to things tends to decrease the amount that is discarded.
We hope the nature of these foams inspires others to design plastics with the full life cycle in mind. Just as plastics need to be designed according to properties of their initial application, they also need to be designed to avoid the final destination of 90% of plastic waste: landfills and the environment.
What’s next
Our initial versions of bio-based foams produce a rigid material suitable for use in foam-core boards used in construction or for insulation in refrigerators. We have also created a lightweight and flexible version that can be used for cushioning and packaging applications. Initial testing of these materials showed good durability in wet conditions, increasing their chance of gaining commercial adoption.
Polyurethane foams are used so extensively because of their versatility. The formulation that we initially discovered is being translated to create a library of precursors that can be mixed to produce the desired properties, like strength and washability, in each application.
More information: James Sternberg et al, Chemical recycling of a lignin-based non-isocyanate polyurethane foam, Nature Sustainability (2023). DOI: 10.1038/s41893-022-01022-3
New research from Rohit Pappu’s lab shows that within condensates, the molecules are organized into a small-world structure that we readily recognize from the hub-and-spoke network structure of airports for commercial airlines. Credit: Pappu lab
Before mixing an oil-and-vinegar-based salad dressing, the individual drops of vinegar are easily seen suspended in the oil, each with a perfectly circular boundary that delineates the two liquids. In the same way, our cells contain condensed bundles of proteins and nucleic acids called condensates delineated by clear boundaries. The boundaries are known as interfaces and given that condensates talk to one another through their interfaces, the structural features of the interface are of significant interest.
New research has uncovered unique features of interfaces of model condensates. The findings are relevant because the features interfaces are relevant to the seeding of fibrillar conformations that are associated with neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS).
A team of researchers led by Rohit Pappu, the Gene K. Beare Distinguished Professor and Director of the Center for Biomolecular Condensates in the McKelvey School of Engineering at Washington University in St. Louis, recently focused on defining the molecular scale features of interfaces of condensates. The research, driven by Mina Farag, an MD/Ph.D. student in the Pappu lab and first author of the paper, were generated in collaboration with Tanja Mittag and her lab at St. Jude Children’s Research Hospital. The results were published in Nature Communications Dec. 13, 2022.
A surprising finding was that interfaces, which might seem to be uniform and infinitesimally thin from the vinegar in oil picture, are thick and defined by specific shape and size preferences at the molecular level, Pappu said. Within condensates, the molecules are organized into a small-world structure that we readily recognize from the hub-and-spoke network structure of airports for commercial airlines.
“There is a particular type of connectivity that defines the way these molecules are organized, and that is because they have viscoelastic properties that makes them either elastic on short timescales and viscous on long timescales, much like putty,” Pappu said.
As the protein molecules go through the interface, the shapes and sizes of the molecules change in a way that these are unique to the interface, the team’s research found.
“We made a very striking observation that the conformations, or the shapes, of these molecules were very distinctive as they go through the interface, and those types of conformations poise them to be reactive,” Pappu said. “That can be good for facilitating biochemical reactions inside a cell, or be deleterious in the context of ALS, whereby the interface catalyzes the fibrillar growth in motor neurons.”
In Pappu’s lab, Farag used data from Mittag’s lab to train a machine learning model that describes the interactions among the molecules. This allowed them to simulate condensate formation in a computer. The simulations reproduce condensation for 30 different variants of a specific protein domain that is associated with ALS. Importantly, the simulation paradigm affords a way to design proteins with bespoke condensate structures and interfacial properties.
“We think that the distinct conformational preferences in interfaces contribute to low interfacial tensions of condensates. However, the specific chemistries of different interfaces are likely to enable functional selectivity. This seems like a very happy medium between physics and chemistry, as gleaned using engineering-based methods.”
More information: Mina Farag et al, Condensates formed by prion-like low-complexity domains have small-world network structures and interfaces defined by expanded conformations, Nature Communications (2022). DOI: 10.1038/s41467-022-35370-7
Gut-on-a-chip integrated with sensors. a) Device fabrication process. b) Annotated device decomposition diagram. The top and bottom microchannels were separated by the porous membrane. Simultaneous integration of three-electrode sensors and an Ag/AgCl electrode for in situ detection of Hg(II) and TEER. c) Photograph of the gut-on-a-chip integrated with sensors. Credit: Microsystems & Nanoengineering (2023). DOI: 10.1038/s41378-022-00447-2
The transport of mercury ions across intestinal epithelial cells can be studied for toxicology assessments by using animal models and static cell cultures. However, the concepts do not reliably replicate conditions of the human gut microenvironment to monitor in situ cell physiology. As a result, the mechanism of mercury transport in the human intestine is still unknown.
They proposed to explore the dynamic concept to simulate the physical intestinal barrier and mirror biological transport and adsorption mechanisms of mercury ions. The scientists recreated the cellular microenvironment by applying fluid shear stress and cyclic mechanical strain.
Wang and the team studied mercury adsorption and the physical damage caused by the toxic element on epithelial cells via the performance of electrochemical sensors after exposing them to intestinal cells growing under diverse concentrations of mercury mixed in the cell culture medium. The team noted the corresponding expression and upregulation of Piezo1 and DMT1 (divalent metal transporter), both mechanosensory ion channels and iron transporters respectively on the cell surface.
While mercury adsorption occurs predominantly in the small intestine, high levels of mercury ingestion can cause internal bleeding and perforation in a short timeframe. The long-term intake of low concentrations of mercury ions can also lead to chronic intestinal diseases. Since the intestinal epithelium provides an initial barrier to limit the penetration of ingested mercury in the blood stream and reduce its harmful effects; a reasonable intestinal model is of great significance to explore transport mechanisms of mercury in the lab. Although animal models and static cell cultures are traditionally used to study intestinal adsorption and mercury transport, these models do not efficiently recapitulate the intestinal microenvironment to emulate the living intestine.
Quantification of physical properties in gut-on-a-chip. a) FEA results of fluid shear stress in a microchannel. b) Calibration relationship between the actual flow rate of the culture medium into the gut-on-a-chip and the input flow by the syringe pump. Inset (I): Calibration experimental platform. Inset (II): Microscopic image of fluid flow in the gut-on-a-chip (scale bar, 200 μm). c) The FEA results of shear stress in the gut-on-a-chip were compared with the actual results (n = 3). d Quantitation of the mechanical strain produced in the adherent gut epithelial cells as a function of pressure applied by the vacuum controller. Black lines represent linear fitting lines (y = 0.099 + 0.270x; R2 = 0.988). Inset (I): Comparison of cell masses on porous membranes before and after stretching by 3% (scale bar, 20 μm). e Variation in the pore diameter of the porous film within 10 days under 1% tensile strain. RSD = 1.81% (n = 3). f) The change in Young’s modulus of the porous membrane under 1% tensile strain within 10 days. RSD = 0.07% (n = 3). Credit: Microsystems & Nanoengineering (2023). DOI: 10.1038/s41378-022-00447-2
In this work, the researchers developed a gut-on-a-chip model integrated with label-free sensors, to non-invasively monitor changes in transepithelial electrical resistance (TEER) during cellular behavior of mercury absorption, in real time. The team identified key features of the gut via electrical measurements and immunohistochemistry studies, to assess the effect on mechanosensory ion channels.
Characteristics of the intestinal epithelium in the gut-on-a-chip. a) Tight junctional integrity of the epithelium quantified by measuring TEER (n = 3). b) AKP activity under static (3 days, 7 days and 21 days) and dynamic (3 days and 7 days) cultures (n = 3; *P < 0.05, **P < 0.01). c) (I) Confocal fluorescence view of a tight junction protein (ZO-1; red) and brush border protein (ezrin; green) in static (3 days; 21 days) and dynamic cultures (3 days) (scale bar 20 μm). (II) Confocal fluorescence view of vertical cross section of cell monolayer in static (3 days; 21 days) and dynamic culture (3 days) (scale bar 10 μm). d) Average fluorescence intensity analysis of ZO-1 and ezrin proteins in static and dynamic cultures (3 days) (n = 3; ***P < 0.001). e) Average cell height cultured in static and dynamic cultures (n = 3; *P < 0.05). f) Microscope top-down views of intestinal villi-like structures (scale bar 100 μm). g) An SEM image of intestinal villi-like structures. h) A fluorescence microscopic view highlighting the nuclei (DAPI) of intestinal villi-like structures (scale bar 100 μm). i) A photograph showing the proposed gut-on-a-chip with its monitoring and culturing component. Credit: Microsystems & Nanoengineering (2023). DOI: 10.1038/s41378-022-00447-2
Numerical analysis of the device
The research team developed a chip that showed mechanical behavior similar to the living intestine and introduced representative fluid flow and cyclic mechanical stretching. For instance, a shear stress approximating 0.02 dyne/cm2 produced a fluid flow required for intestinal epithelial morphogenesis. Based on additional calculations on the organ chip, the team obtained a flow rate of 160 μL/hour for the corresponding dimensions of shear stress.
They then simulated the tensile strain/stress dynamics via finite element analysis to understand the effects of the parameters on the physical properties of the instrument including its pore diameter and their impact on the cytodifferentiation by analyzing the catalytic activity of alkaline phosphatase; typically used as a marker of bone and liver damage. The team noted greater catalytic activity among cells under fluid flow and those undergoing mechanical strain on a chip after only seven days of cell culture.
Damage to cells caused by Hg(II). a) Immunofluorescence of cells exposed to different concentrations of Hg(II) for 5, 12, and 24 h in static culture (red: dead cells; green: living cells). b) Changes in cell activity under the treatment of different concentrations of Hg(II). The cell activity remained above 80% within 24 h under low concentrations of Hg(II) (1, 10 μM) (n = 3). c) Epithelial cells were exposed to 100 μM Hg(II), and LDH was detected at 5, 12′ and 24 h. Within 24 h, the results of LDH detection showed that the expression of LDH in static samples was 1.3-fold higher than that in dynamic samples (n = 3; *P < 0.05). d) The change rate of TEER in static and dynamic cultures of cells exposed to 100 μM Hg(II) within 24 h. The TEER under dynamic conditions was 4.4-fold higher than that under static conditions (n = 3; *P < 0.05). e) In the absence or presence of Hg(II) (100 μM), confocal immunofluorescence of ZO-1 (red) and ezrin (green) protein was observed (scale bar 20 μm). (f, g) Analysis of the average fluorescence intensity of ZO-1 and ezrin proteins after epithelial cell injury. Compared with the control group, the fluorescence intensity of ZO-1 and ezrin decreased by 1.8-fold (n = 3; ***P < 0.001). Credit: Microsystems & Nanoengineering (2023). DOI: 10.1038/s41378-022-00447-2
The outcomes highlighted the biomimetic approach and the capacity for growth and differentiation of the cell monolayer under mechanical stimulation. The gut-on-a-chip instrument provided biomimetic intestinal villus-like structures to maintain the integrity of the tissue barrier and represented a key physiologically relevant human intestine.
a) The TEER value of the cell monolayer on the 7th day under different mechanical stretching conditions (1%, 3%, 5%). The TEER values were 26.65 ± 1.17 kΩ cm2, 32.21 ± 1.05 kΩ cm2 and 34.10 ± 0.93 kΩ cm2, and the cell barrier ability was increased by 20.86% and 27.95% (1% mechanical stimulation as the control group) (n = 3). b) Changes in intestinal epithelial cell monolayer absorption of Hg(II) within three hours under different mechanical stretching conditions (1%, 3%, 5%). The concentrations of Hg(II) absorbed by cells under three mechanical stretching stimuli were 1.78 ± 0.11 μM, 1.98 ± 0.03 μM, and 2.20 ± 0.14 μM (n = 3). c) The change in the Papp value under different mechanical stretching (1%, 3%, 5%). Compared with 1% mechanical stimulation, the ability of cells to absorb Hg(II) increased by 11.65% and 17.96% under 3% and 5% mechanical stimulation, respectively (n = 3). d) The expression of Piezo1 protein and DMT1 protein under different mechanical stretching conditions (Piezo1: red; DMT1: green; nucleus: blue) (scale bar 20 μm). Credit: Microsystems & Nanoengineering (2023). DOI: 10.1038/s41378-022-00447-2
Functional assays
The research team next exposed the cells to mercury under static culture conditions to understand the process of cell death. And noted an increase to the process when upon increasing the mercury concentration and culture time. They noted that the activity of lactate dehydrogenase (LDH) increased with time in the assays to show equal effects of the toxin across both cell cultures. However, the degree of injury between the two cultures differed. For instance, the expression of LDH was greater in the static culture compared to the dynamic cell cultures after mercury treatment.
The scientists used an electrochemical sensor array integrated into a gut-on-a-chip device to observe epithelial cell interactions with mercury. They explored the transport mechanism of the element relative to its absorption on epithelial cells and investigated the expression of key proteins such as Piezo1 and DMT1 relative to mechanosensory ion channels and active iron transporters. They studied the effects of different tensile strains on the cell barrier and noted that an increase in mechanical stimulation led to increased adsorption of mercury via intestinal epithelial cells, where the mechanosensory ion channels too showed a positive correlation.
Outlook
In this way, Li Wang and colleagues developed a gut-on-a-chip device integrated with transepithelial electrical resistor sensors and multiple electrochemical sensors to stimulate mercury transport in the human intestine in vitro. The chip dynamics emulated a physical intestinal barrier and microenvironment to observe the transport of mercury in real-time. The team noted the cell monolayer on the gut-on-a-chip to differentiate to form a complete cellular barrier via imaging and immunohistochemistry. The team intends to further understand additional mechanisms underlying human intestinal diseases using organ chips to promote personalized drug development.
More information: Li Wang et al, Gut-on-a-chip for exploring the transport mechanism of Hg(II), Microsystems & Nanoengineering (2023). DOI: 10.1038/s41378-022-00447-2
Sangeeta N Bhatia et al, Microfluidic organs-on-chips, Nature Biotechnology (2014). DOI: 10.1038/nbt.2989
