June 08, 2020
Enjoy these interesting stories from the scientific community.
*-- World's most sensitive strain sensor can detect the weight of a feather --*
Scientists have unveiled the world's most sensitive strain sensor, capable of detecting the weight of a single feather.
The sensor is significantly more stretchable, capable of enduring 80 times greater strain than current commercial sensors, and is able to register resistance changes with 100 times the precision of current sensors, researchers said.
The new strain sensor -- described Thursday in the journal Advanced Functional Materials -- could be used to improve the sensitivity of a variety of medical and wearable devices.
"The next wave of strain sensing technology uses elastic materials like rubber imbued with conductive materials such as graphene or silver nanoparticles, and has been in development for over a decade now," lead study author Marcus O'Mara, researcher at the University of Sussex, said in a news release.
"We believe these sensors are a big step forward," O'Mara said. "When compared to both linear and non-linear strain sensors referenced in the scientific literature, our sensors exhibit the largest absolute change in resistance ever reported."
According to Alan Dalton, study co-author and professor of experimental physics at Sussex, the device could be used to measure joint movements of an athlete or the vital signs of a hospital patient.
"Multiple devices could be used across the body of a patient, connected wirelessly and communicating together to provide a live, mobile health diagnostics at a fraction of the current cost," Dalton said.
Researchers created the new strain sensor by carefully incorporating large amounts of graphene nanosheets into a matrix composed of the composite material polydimethylsiloxane, or PDMS.
According to the new study, PDMS is "biocompatible, elastic, transparent, durable, and has very minimal shrinkage on curing."
PDMS is normally resistant to mixing, but researchers developed a novel process for incorporating graphene into the composite material -- methods that researchers suggest could be used to develop other kinds of two-dimensional layered materials and polymer matrices.
Most strain sensors are limited in either their range or their sensitivity, but the latest strain sensor material is able to take on large amounts of strain while also registering tiny changes in strain.
"Nanocomposites are attractive candidates for next generation strain sensors due to their elasticity, but widespread adoption by industry has been hampered by non-linear effects such as hysteresis and creep due to the liquid like nature of polymers at the nanoscale which makes accurate, repeatable strain readouts an ongoing challenge," said Sean Ogilvie, researcher fellow at Sussex.
"Our sensors settle into a repeated, predictable pattern which means that we can still extract an accurate read-out of strain despite these effects," Ogilvie said.
*-- Neuroscientists find possible physical traces of short-term memories --*
 The brain must store memories to learn and acquire knowledge, but where do these memories go, and what do they look like? Finally, scientists have some answers.
In the early 20th century, the German scientist Richard Semon, a memory researcher and evolutionary biologist, coined the term "engram" for the physical substrate of a memory. Scientists have been looking for them ever since.
"Where are the engrams? This was one of the questions we asked," Peter Jonas, neuroscientist at the Institute of Science and Technology in Austria, said in a news release.
"Synaptic plasticity, the strengthening of communication between neurons, explains memory formation at the subcellular level," Jonas said. "To find the engram, we, therefore, explored structural correlates of synaptic plasticity."
Jonas and his colleagues precisely measured the activity of single synapses inside the hippocampus, the region of the brain responsible for learning and memory. Inside the hippocampus, pyramidal cells are linked with granule cells by synapses.
"We made simultaneous recordings of electrical signals from a small pre-synaptic terminal and its postsynaptic target neuron," said IST postdoctoral researcher David Vandael. "This is the perfect way to examine the synapse."
The observations showed that when a granule cell fires, it triggers a kind of plasticity called post-tetanic potentiation, which boosts the link between the granule and pyramidal cell for a few minutes.
Scientists hypothesized that plasticity arises when heightened neuronal activity primes vesicles to release neurotransmitters. Vesicles are cellular components that facilitate the uptake and release of communicative molecules.
"Instead, we found that after a granule cell is active, more vesicles containing neurotransmitter are stored at the pre-synaptic terminal," Vandael said. "Firing patterns induce plasticity through an increase of vesicles in this active zone, which can be stored for a few minutes."
In other words, plasticity allows for storage, not necessarily the release of neurotransmitters.
The new research showed that during learning, when granule cells are more active, vesicles flood the active zone. When activity tapers, these vesicles remain, and when activity picks back up, the vesicles are ready and in position to release neurotransmitters into the synapse.
"Short-term memory might be activity stored as vesicles that are released later," Vandael said.
It's possible, scientists surmise, that the activity observed by the IST research team -- and detailed Tuesday in the journal Neuron -- is, in fact, the elusive engram.
"By analyzing the biophysical and structural components of plasticity, David may have discovered the engram -- if we believe that synaptic plasticity underlies learning," Vandael said.
"It is fascinating to think of memories as numbers of neurotransmitter-containing quanta, and we truly believe it will be inspiring for the neuroscience research community," Vandael said. "We hope our work will contribute to solving part of the unresolved mysteries of learning and memory."
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