Physics of Complex Fluids: Ring Polymers Show Unexpected Motion Patterns Under Shear

Schematic of poly[2]catenane slip tumbling and bonded ring gradient tumbling.
Illustration Credit: Reyhaneh A. Farimani

An international research team is attracting the attention of experts in the field with computational results on the behavior of ring polymers under shear forces: Reyhaneh Farimani, University of Vienna, and her colleagues showed that for the simplest case of connected ring pairs, the type of linkage – chemically bonded vs. mechanically linked – has profound effects on the dynamic properties under continuous shear. In these cases, novel rheological patterns emerge. In addition to being recently published in the prestigious journal Physical Review Letters, the study received an "Editors' Suggestion" for its particular novelty.

The shearing of fluids – meaning the sliding of fluid layers over each other under shear forces – is an important concept in nature and in rheology, the science that studies the flow behavior of matter, including liquids and soft solids. Shear forces are lateral forces applied parallel to a material, inducing deformation or slippage between its layers. Fluid shear experiments allow the characterization of important rheological properties such as viscosity (resistance to deformation or flow) and thixotropy (decrease in viscosity under the influence of shear) which are important in applications ranging from industrial processes to medicine. Studies on the shear behavior of viscoelastic fluids, created by introducing polymers into Newtonian fluids, have already been conducted in recent years. However, a novel approach in the current research involves the consideration of polymer topology – the spatial arrangement and structure of molecules – by using ring polymers. Ring polymers are macromolecules composed of repeating units, forming closed loops without free ends. 

Autism and ADHD are linked to disturbed gut flora very early in life

The researchers have found links between the gut flora in babies first year of life and future diagnoses.
Photo Credit: Cheryl Holt

Disturbed gut flora during the first years of life is associated with diagnoses such as autism and ADHD later in life. This is according to a study led by researchers at the University of Florida and Linköping University and published in the journal Cell.

The study is the first forward-looking, or prospective, study to examine gut flora composition and a large variety of other factors in infants, in relation to the development of the children's nervous system. The researchers have found many biological markers that seem to be associated with future neurological development disorders, such as autism spectrum disorder, ADHD, communication disorder and intellectual disability.

“The remarkable aspect of the work is that these biomarkers are found at birth in cord blood or in the child’s stool at one year of age over a decade prior to the diagnosis,” says Eric W Triplett, professor at the Department of Microbiology and Cell Science at the University of Florida, USA, one of the researchers who led the study.

Discovery of how COVID-19 virus replicates opens door to new antiviral therapies

A new study, looking at the replication stage of the SARS-CoV-2 virus that causes COVID-19, discovered important mechanisms in its replication that could be the foundation for new antiviral therapies.
Image Credit: Gerd Altmann

The study, which sets out to investigate how the SARS-CoV-2 virus replicates once it enters the cells, has made surprising discoveries that could be the foundation for future antiviral therapies. It also has important theoretical implications as the replication of the SARS-CoV-2 virus has, so far, received less attention from researchers.

The viral life cycle can be broken down into two main stages: the first stage is where the virus enters the cell. The second stage is replication where the virus uses the molecular machinery of the cell it has infected to replicate itself by building its parts, assembling them into new viruses that can then exit to infect other cells.

The majority of research into SARS-CoV-2 – the causative agent of COVID-19 – has focused on the Spike protein that allows viral entry. This has led to a lack of understanding of how the virus replicates once it has entered the cell.

A new paper led by Dr Jeremy Carlton in collaboration with Dr David Bauer at the Francis Crick Institute, focuses on how the Envelope protein of SARS-CoV-2 controls late stages of viral replication.

Self-assembly of complex systems: hexagonal building blocks are better

Professor Erwin Frey
Photo Credit: © Benjamin Asher / Ludwig-Maximilians-Universität München

Complex systems in nature, like their synthetic counterparts in technology, comprise a large number of small components that assemble of their own accord through molecular interactions. Gaining a better understanding of the principles and mechanisms of this self-assembly is important for the development of new applications in domains such as nanotechnology and medicine.

Professor Erwin Frey, Chair of Statistical and Biological Physics at LMU and member of the ORIGINS Excellence Cluster, and his research fellow Dr. Florian Gartner has now investigated an aspect of self-assembly that has received little attention before now: What role do the shape and the number of possible bonds between particles play? As the researchers report in the journal Physical Review X, their results show that hexagonal morphologies – in other words, six-sided structures – such as molecules with six binding sites are ideal for self-assembly.

Drug shows promise for slowing progression of rare, painful genetic disease

A CT angiography scan of a person with ACDC disease showing abnormal calcification of the blood vessels in the legs and feet.
Image Credit: Courtesy of National Institutes of Health

A drug used to treat certain bone diseases shows promise for slowing the progression of a rare, painful genetic condition that causes excessive calcium buildup in the arteries, known as arterial calcification due to deficiency of CD73 (ACDC). These results are from a first-in-human clinical trial supported by the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health. The study, published in the journal Vascular Medicine, could lead to the first effective treatment for the rare disease.

ACDC, which has no known cure, often targets the arteries of the legs and can make walking painful and difficult. It can also affect the joints of the hands, causing pain and deformities. In severe cases, the condition can lead to potential limb loss. Symptoms of the disease often begin in the late teens and 20s. An extremely rare disease, it is believed to affect only about 20 people worldwide and has an estimated prevalence of less than 1 in 1 million. Previous studies have identified the gene for ACDC disease and the biochemical mechanism behind it. More recent studies by the NHLBI research team identified an existing drug, called etidronate, as a potential treatment for ACDC based on disease models in animals and human cells.

Pressure determines which embryonic cells become ‘organizers’

 Tooth epithelium (cell surface; yellow) and mesenchyme (cell surface; magenta). Proliferating cells (cyan) expand the tissue, generating a mechanical pressure at the tissue center that drives the formation of the main tooth signaling center or organizer, the enamel knot.
Photo Credit Neha Pincha Shroff and Pengfei Xu

A collaboration between research groups at the University of California, TU Dresden in Germany and Cedars-Sinai Guerin Children’s in Los Angeles has identified a mechanism by which embryonic cells organize themselves to send signals to surrounding cells, telling them where to go and what to do. While these signaling centers have been known to science for a while, how individual cells turn into organizers has been something of a mystery.

Until now. In a paper published in the journal Nature Cell Biology, the researchers find that cells are literally pressed into becoming organizers.

“We were able to use microdroplet techniques to figure out how the buildup of mechanical pressure affects organ formation,” said co-corresponding author Otger Campàs, former associate professor of mechanical engineering at UC Santa Barbara, who is currently managing director, professor and chair of tissue dynamics at the Physics of Life Excellence Cluster of TU Dresden.

Discovery could end global amphibian pandemic

Panamanian golden frog
Photo Credit: Brian Gratwicke/U.S. Fish & Wildlife Service

A fungus devastating frogs and toads on nearly every continent may have an Achilles heel. Scientists have discovered a virus that infects the fungus, and that could be engineered to save the amphibians.

The fungus, Batrachochytrium dendrobatidis or Bd, ravages the skin of frogs and toads, and eventually causes heart failure. To date it has contributed to the decline of over 500 amphibian species, and 90 possible extinctions including yellow-legged mountain frogs in the Sierras and the Panamanian golden frog. 

A new paper in the journal Current Biology documents the discovery of a virus that infects Bd, and which could be engineered to control the fungal disease.

The UC Riverside researchers who found the virus are excited about the implications of their discovery. In addition to helping them learn about how fungal pathogens rise and spread, it offers the hope of ending what they call a global amphibian pandemic. 

“Frogs control bad insects, crop pests, and mosquitoes. If their populations all over the world collapse, it could be devastating,” said UCR microbiology doctoral student and paper author Mark Yacoub. 

“They’re also the canary in the coal mine of climate change. As temperatures get warmer, UV light gets stronger, and water quality gets worse, frogs respond to that. If they get wiped out, we lose an important environmental signal,” Yacoub said. 

Pollen is a promising sustainable tool in the bone regeneration process

Scientists have used pollen to grow hydroxyapatite capsules, so the mineral can better support bone regeneration
Photo Credit: Alex Jones

A study has shown pollen grains can be used as green templates for producing biomaterials, showcasing their potential to support drug delivery and bone regeneration.

With an increasingly ageing population, bone fractures are becoming more common. Bone is generally able to self-repair but if the fracture is too big or the person affected too fragile, as for example people with osteoporosis, the use of bone fillers can help.

Hydroxyapatite (HAp) is an inorganic mineral present in human bone and teeth, which can be used to support bone regeneration. It makes up somewhere between 65 per cent and 70 per cent of the weight of human bone. Healthcare professionals often use synthetic and natural HAp when carrying out bone repair treatments.

A team at the University of Portsmouth has worked with international colleagues to explore sustainable ways to improve the process. 

They examined the feasibility of using pollen grains as bio-templates for growing calcium phosphate minerals in the lab - particularly hydroxyapatite (HAp) and β-tricalcium phosphate (TCP), which are types of calcium phosphate used for bone repair.

Kapitza-Dirac effect used to show temporal evolution of electron waves

Time dependent interference fringes from the ultrafast Kapitza Dirac Effect. An electron wave packet is exposed to two counterpropagating ultrashort laser pulses. The time span from back to front is 10 pico seconds.
Illustration Credit: © Goethe University Frankfurt

One of the most fundamental interactions in physics is that of electrons and light. In an experiment at Goethe University Frankfurt, scientists have now managed to observe what is known as the Kapitza-Dirac effect for the first time in full temporal resolution. This effect was first postulated over 90 years ago, but only now are its finest details coming to light. 

It was one of the biggest surprises in the history of science: In the early days of quantum physics around 100 years ago, scholars discovered that the particles which make up our matter always behave like waves. Just as light can scatter at a double slit and produce scattering patterns, electrons can also display interference effects. In 1933, the two theorists Piotr Kapitza and Paul Dirac proved that an electron beam is even diffracted from a standing light wave (due to the particles' properties) and that interference effects as a result of the wave properties are to be expected. 

A German-Chinese team led by Professor Reinhard Dörner from Goethe University Frankfurt has succeeded in using this Kapitza-Dirac effect to visualize even the temporal evolution of the electron waves, known as the electrons' quantum mechanical phase. The researchers have now presented their results in the journal Science. 

In the evolution of walking, the hip bone connected to the rib bones

New reconstruction of the skeleton of Tiktaalik roseae, a 375-million-year-old fossil fish. In a new study, researchers used micro-CT imaging to reveal vertebrae and ribs of the fish that were previously hidden beneath rock. The new reconstruction shows that the fish’s ribs likely attached to its pelvis, an innovation thought to be crucial to supporting the body and for the eventual evolution of walking.
Photo Credit: Thomas Stewart / Pennsylvania State University
(CC BY-NC-ND 4.0 DEED)

Before the evolution of legs from fins, the axial skeleton — including the bones of the head, neck, back and ribs — was already going through changes that would eventually help our ancestors support their bodies to walk on land. A research team including a Penn State biologist completed a new reconstruction of the skeleton of Tiktaalik, the 375-million-year-old fossil fish that is one of the closest relatives to limbed vertebrates. The new reconstruction shows that the fish’s ribs were likely attached to its pelvis, an innovation thought to be crucial to supporting the body and for the eventual evolution of walking.

A paper describing the new reconstruction, which used microcomputed tomography (micro-CT) to scan the fossil and reveal vertebrae and ribs of the fish that were previously hidden beneath rock, appeared in the journal Proceedings of the National Academy of Sciences.

“Tiktaalik was discovered in 2004, but key parts of its skeleton were unknown,” said Tom Stewart, assistant professor of biology in the Eberly College of Science at Penn State and one of the leaders of the research team. “These new high-resolution micro-CT scans show us the vertebrae and ribs of Tiktaalik and allow us to make a full reconstruction of its skeleton, which is vital to understanding how it moved through the world.”