Tag: Science

Princeton engineers have developed an easily scalable 3D printing technique to manufacture soft plastics with programmed stretchiness and flexibility that are also recyclable and inexpensive—qualities not typically combined in commercially manufactured materials.

In an article in the journal Advanced Functional Materials, a team led by Emily Davidson reported that they used a class of widely available polymers called thermoplastic elastomers to create soft 3D printed structures with tunable stiffness.

Engineers can design the print path used by the 3D printer to program the plastic’s physical properties so that a device can stretch and flex repeatedly in one direction while remaining rigid in another. Davidson, an assistant professor of chemical and biological engineering, said this approach to engineering soft architected materials could have many uses, such as soft robots, medical devices and prosthetics, strong lightweight helmets, and custom high-performance shoe soles.

The key to the material’s performance is its internal structure at the tiniest level. The research team used a type of block copolymer which forms stiff cylindrical structures that are 5-7 nanometers thick (for comparison, human hair measures about 90,000 nanometers) inside a stretchy polymer matrix.

The researchers used 3D printing to orient these nanoscale cylinders, which leads to a 3D printed material that is hard in one direction but soft and stretchy in nearly all others. Designers can orient these cylinders in different directions throughout a single object, leading to soft architectures which exhibit stiffness and stretchiness in different regions of an object.

“The elastomer we are using forms nanostructures that we are able to control,” Davidson said. This allows designers a great degree of control over finished products. “We can create materials that have tailored properties in different directions.”

The first step in developing this process was choosing the right polymer. The researchers chose a thermoplastic elastomer, which is a block copolymer that can be heated and processed as a polymer melt, but which solidifies into an elastic material when it cools.

At the molecular level, polymers are long chains of linked molecules. Traditional homopolymers are long chains of one repeating molecule, whereas block copolymers are made of different homopolymers connected to each other. These different regions of a block copolymer chain are like oil and water- they separate instead of mixing. The researchers used this property to produce material with stiff cylinders within a stretchy matrix.

The researchers used their knowledge of how these block copolymer nanostructures form and how they respond to flow to develop a 3D printing technique that effectively induces alignment of these stiff nanostructures. The researchers analyzed the way that printing rate and controlled under-extrusion could be used to control the physical properties of the printed material.

Alice Fergerson, a graduate student at Princeton and the article’s lead author, spoke about the technique and the key role played by thermal annealing—the controlled heating and cooling of a material.

“I think one of the coolest parts of this technique is the many roles that thermal annealing plays— it both drastically improves the properties after printing, and it allows the things we print to be reusable many times and even self-heal if the item gets damaged or broken.”

Davidson said that one of the goals of the project was to create soft materials with locally tunable mechanical properties in a way that is both affordable and scalable for industry. It is possible to create similar structures with locally controlled properties using materials such as liquid crystal elastomers.

But Davidson said those materials are both expensive (upwards of $2.50 per gram) and require multi-stage processing involving carefully controlled extrusion followed by exposure to ultraviolet light. The thermoplastic elastomers used in Davidson’s lab cost about a cent per gram and can be printed with a commercial 3D printer.

The researchers have shown their technique’s ability to incorporate functional additives into the thermoplastic elastomer without reducing the ability to control material properties. In one example, they added an organic molecule developed by Professor Lynn Loo’s group that makes the plastic glow red after exposure to ultraviolet light. They also demonstrated the printer’s ability to produce complex and multi-layered structures including a tiny plastic vase and printed text that used sharp turns to spell out PRINCETON.

Annealing plays a key role in their process by increasing the perfection of the order of internal nanostructures. Davidson said annealing also enables self-healing properties of the material. As part of the work, the researchers can cut a flexible sample of the printed plastic and reattached it by annealing the material. The repaired material demonstrated the same characteristics as the original sample. The researchers said they observed “no significant differences” between the original and the repaired material.

As a next step, the research team expects to being exploring new 3D printable architectures that will be compatible with applications such as wearable electronics and biomedical devices.

Microorganisms have long used hydrogen as an energy source. To do this, they rely on hydrogenases that contain metals in their catalytic center. In order to use these biocatalysts for hydrogen conversion, researchers are working to understand the catalysis process.

A team from three Max Planck Institutes (MPI), the Center for Biostructural Imaging of Neurodegeneration (BIN) at the University Medical Center Göttingen (UMG), the University of Kiel, and the FACCTs GmbH used a chemical peculiarity of hydrogen to amplify the signals of magnetic resonance spectroscopy. In this way, the scientists were able to visualize previously unknown intermediate steps in the conversion of hydrogen. The study is published in Nature Catalysis.

As a substitute for fossil fuels, energy source, or catalyst in chemical processes—hydrogen is considered a good candidate for a sustainable energy economy. On Earth, the element occurs mainly in bound form, in water, as hydrogen gas, or in fossil raw materials such as natural gas and crude oil. To obtain hydrogen in its pure form, it must be split from the chemical compound using energy.

The most common method of producing hydrogen today is the steam methane reforming of natural gas. However, this also produces climate-damaging carbon dioxide (CO₂). In the catalytic production of hydrogen from water, electrodes made of the precious metal platinum have mostly been used up to now. This makes hydrogen production by means of catalysis comparatively expensive.

Many microorganisms are a step ahead of these production processes. To split off hydrogen to generate energy, they use three different types of hydrogenases that function without precious metals and do not release CO₂: [NiFe] hydrogenases from archaea and bacteria, [FeFe] hydrogenases from bacteria, some algae, and some anaerobic archaea, as well as [Fe] hydrogenases found only in archaea.

The latter play a key role in methanogenesis, in which CO₂ is reduced to methane (CH₄). The homodimeric [Fe] hydrogenase contains one redox-inactive iron (Fe) per subunit, which is bound to a guanylylpyridinol cofactor.

While intermediates in the catalytic cycle of [NiFe] hydrogenases and [FeFe] hydrogenases have already been well studied, the catalytic intermediates of [Fe] hydrogenases were not observable—until now. A research team has now succeeded in detecting the intermediates in the [Fe]-hydrogenases catalysis cycle for the first time.

The team was led by Stefan Glöggler (Max Planck Institute for Multidisciplinary Sciences (MPI-NAT) and the Center for Biostructural Imaging of Neurodegeneration (BIN) at the University Medical Center Göttingen (UMG), Lukas Kaltschnee (MPI-NAT and BIN at UMG, currently at the TU Darmstadt), Christian Griesinger (MPI-NAT), and Seigo Shima (MPI for Terrestrial Microbiology), and included colleagues from the MPI für Kohlenforschung, Kiel University, and the FAccTs GmbH.

The researchers made use of the fact that hydrogen occurs as so-called parahydrogen and orthohydrogen, depending on its nuclear spin. The researchers showed that nuclear magnetic resonance spectroscopy results in signal amplification when the [Fe] hydrogenase reacts with parahydrogen. This so-called parahydrogen-induced polarization (PHIP) made it possible to identify the reaction intermediates and visualize how the [Fe] hydrogenase binds hydrogen during catalysis.

The scientists’ data indicate that a hydride is formed at the iron center during catalysis. The new method also made it possible to study the binding kinetics. Due to its high sensitivity, PHIP is particularly promising for application to living cells and for investigating hydrogen metabolism in vivo. The results could help to develop (bio)catalysts for hydrogen conversion with higher productivity in the future.

Over the last decade, the global market for plant-based beverages has seen remarkable growth, with oat, almond, soy and rice drinks emerging as popular alternatives to cow’s milk in coffee and oatmeal during this time.

One of the likely reasons for millions of liters of plant-based drinks ending up in the shopping baskets of consumers is that their climate footprint is often lower than that of cow’s milk. But consumers would be mistaken if they considered plant-based beverages healthier than cow’s milk. This is highlighted in a new study conducted by the University of Copenhagen in collaboration with the University of Brescia, Italy.

In the study, published in the journal Food Research International, researchers examined how chemical reactions during processing affect the nutritional quality of 10 different plant-based drinks, comparing them with cow’s milk. The overall picture is clear.

“We definitely need to consume more plant-based foods. But if you’re looking for proper nutrition and believe that plant-based drinks can replace cow’s milk, you’d be mistaken,” says Department of Food Science professor Marianne Nissen Lund, the study’s lead author.

Long shelf life at the expense of nutrition

While milk is essentially a finished product when it comes out of a cow, oats, rice, and almonds require extensive processing during their conversion to a drinkable beverage. Moreover, each of the plant-based drinks tested underwent “Ultra High Temperature” (UHT) treatment, a process that is widely used for long-life milks around the world. In Denmark, milk is typically found only in the refrigerated sections of supermarkets and is low-pasteurized, meaning that it receives a much gentler heat treatment.

“Despite increased plant-based drink sales, cow milk sales remain higher. Consequently, plant-based drinks undergo more intense heat treatments than the milk typically sold in Denmark, in order to extend their shelf life. But such treatment comes at a cost,” says Lund.

UHT treatment triggers a so-called “Maillard reaction,” a chemical reaction between protein and sugar that occurs when food is fried or roasted at high temperatures. Among other things, this reaction impacts the nutritional quality of the proteins in a given product.

“Most plant-based drinks already have significantly less protein than cow’s milk. And the protein, which is present in low content, is then additionally modified when heat treated. This leads to the loss of some essential amino acids, which are incredibly important for us. While the nutritional contents of plant-based drinks vary greatly, most of them have relatively low nutritional quality,” explains the professor.

For comparison, the UHT-treated cow’s milk used in the study contains 3.4 grams of protein per liter, whereas eight of the 10 plant-based drinks analyzed contained between 0.4 and 1.1 grams of protein. The levels of essential amino acids were lower in all plant-based drinks. Furthermore, seven out of 10 plant-based drinks contained more sugar than cow’s milk.

Heat treatment may produce carcinogens

Besides reducing nutritional value, heat treatment also generates new compounds in plant-based drinks. One such compound measured by the researchers in four of the plant-based drinks made from almonds and oats is acrylamide, a carcinogen that is also found in bread, cookies, coffee beans and fried potatoes, including French fries.

“We were surprised to find acrylamide because it isn’t typically found in liquid food. One likely source is the roasted almonds used in one of the products. The compound was measured at levels so low that it poses no danger. But, if you consume small amounts of this substance from various sources, it could add up to a level that does pose a health risk,” says Lund.

Additionally, the researchers detected α-dicarbonyl compounds and hydroxymethylfurfural (HMF) in several of the plant-based drinks. Both are reactive substances that could potentially be harmful to human health when present in high concentrations, although this is not the case here.

While professor of nutrition Lars Ove Dragsted is not particularly concerned about the findings either, he believes that the study highlights how little we know about the compounds formed during food processing:

“The chemical compounds that result from Maillard reactions are generally undesirable because they can increase inflammation in the body. Some of these compounds are also linked to a higher risk of diabetes and cardiovascular diseases. Although our gut bacteria break down some of them, there are many that we either do not know of or have yet to study,” says Dragsted of the Department of Nutrition, Exercise and Sports.

Professor Dragsted adds, “This study emphasizes why more attention should be paid to the consequences of Maillard reactions when developing plant-based foods and processed foods in general. The compounds identified in this study represent only a small fraction of those we know can arise from Maillard reactions.”

Make your own food

According to Professor Lund, the study highlights broader issues with ultra-processed foods: “Ideally, a green transition in the food sector shouldn’t be characterized by taking plant ingredients, ultra-process them, and then assuming a healthy outcome. Even though these products are neither dangerous nor explicitly unhealthy, they are often not particularly nutritious for us either.”

Her advice to consumers is to “generally opt for the least processed foods and beverages, and to try to prepare as much of your own food as possible. If you eat healthily to begin with, you can definitely include plant-based drinks in your diet—just make sure that you’re getting your nutrients from other foods.”

At the same time, Professor Lund hopes that the industry will do more to address these issues: “This is a call to manufacturers to further develop their products and reconsider the extent of processing. Perhaps they could rethink whether UHT treatment is necessary or whether shorter shelf lives for their products would be acceptable.”

In a study published in Nature Methods, a research group developed a highly sensitive proteomics method called peptide-centric local stability assay (PELSA), which enables the simultaneous identification of ligand-binding proteins and their binding sites in complex systems. PELSA is broadly applicable to diverse ligands including metabolites, drugs, and pollutants.

The biochemical functions of proteins invariably involve interactions with ligands of some type, which act as enzyme substrates or inhibitors, signaling molecules, allosteric modulators, structural anchors, etc. Monitoring protein-ligand interactions is thus essential for characterizing proteins with unknown functions, for investigating regulatory mechanisms in cell metabolism, and for elucidating drug mechanisms of action. Knowledge of the ligand-binding regions is also extremely valuable for structure-based drug design and biological hypothesis generation.

Traditional methods for determining binding sites and affinities typically require the purification of recombinant proteins, which can be both time-consuming and labor-intensive. In addition, purified proteins may not fully replicate their native cellular state, resulting in inaccurate affinity measurements.

Modification-based proteomics methods offer a powerful solution for identifying ligand-binding proteins and their sites directly in native cellular lysates. However, they often require ligand modification, which can affect ligand activity and cannot be applicable to ligands that cannot be modified.

In the method proposed in this study, the researchers led by Prof. Ye Mingliang from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences (CAS), collaborating with Prof. Luo Cheng’s group from the Shanghai Institute of Materia Medica of CAS, used a large amount of trypsin (E/S ratio of 1:2) to directly generate small peptides from native proteins.

As these peptides are generated under native conditions, their abundance represents a measurement of proteins’ local stability. The large amount of trypsin ensured that even protein segments in low energy states could be cleaved, resulting in the generation of a large number of peptides reflecting a protein’s local stability.

These peptides were separated from the partially-digested proteins, collected and directly analyzed by mass spectrometry. By measuring the peptide abundance in ligand-treated and vehicle-treated samples, the ligand-binding regions and the corresponding binding proteins can then be determined.

PELSA has showed superior sensitivity in target protein identifications. For example, in identifying the target proteins of a pan-kinase inhibitor staurosporine, PELSA showed a 12-fold increase in kinase target identification compared to the state-of-art modification-free method, LiP-MS.

Compared to the widely-used thermal proteome profiling (TPP) technique, which lacks binding site information, PELSA identified 2.4-fold more kinase targets. Dose-dependent PELSA experiments can measure local affinity, providing insights into the dynamic protein structural changes upon ligand binding under physiological conditions.

Metabolites, known for their structural diversity and often low-affinity binding to proteins, pose challenges. PELSA proved particularly effective for the systematic identification of metabolite-binding proteins.

For example, PELSA identified 40 candidate target proteins for alpha-ketoglutarate in HeLa cell lysates, 30 of which were well-known binding proteins of alpha-ketoglutarate, demonstrating the method’s high sensitivity and reliability. In addition, PELSA identified binding proteins for other metabolites, such as folate, leucine, fumarate, and succinate, showcasing its broad applicability.

PELSA can directly detect ligand-induced local stability shifts of proteins in total cell lysate without the need for chemical modification of ligands.

It is broadly applicable to diverse ligands, and allows for systematic analysis of ligand-binding proteins, their binding sites, and local binding affinities in cell lysate, where proteins carry physiological post-translational modifications and are associated with interacting proteins.