Tag Archives: Scuola Internazionale Superiore di Studi Avanzati

Neurons and graphene carpets

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I don’t entirely grasp the carpet analogy. Actually, I have no why they used a carpet analogy but here’s the June 12, 2018 ScienceDaily news item about the research,

A work led by SISSA [Scuola Internazionale Superiore di Studi Avanzati] and published on Nature Nanotechnology reports for the first time experimentally the phenomenon of ion ‘trapping’ by graphene carpets and its effect on the communication between neurons. The researchers have observed an increase in the activity of nerve cells grown on a single layer of graphene. Combining theoretical and experimental approaches they have shown that the phenomenon is due to the ability of the material to ‘trap’ several ions present in the surrounding environment on its surface, modulating its composition. Graphene is the thinnest bi-dimensional material available today, characterised by incredible properties of conductivity, flexibility and transparency. Although there are great expectations for its applications in the biomedical field, only very few works have analysed its interactions with neuronal tissue.

A June 12, 2018 SISSA press release (also on EurekAlert), which originated the news item, provides more detail,

A study conducted by SISSA – Scuola Internazionale Superiore di Studi Avanzati, in association with the University of Antwerp (Belgium), the University of Trieste and the Institute of Science and Technology of Barcelona (Spain), has analysed the behaviour of neurons grown on a single layer of graphene, observing a strengthening in their activity. Through theoretical and experimental approaches the researchers have shown that such behaviour is due to reduced ion mobility, in particular of potassium, to the neuron-graphene interface. This phenomenon is commonly called ‘ion trapping’, already known at theoretical level, but observed experimentally for the first time only now. “It is as if graphene behaves as an ultra-thin magnet on whose surface some of the potassium ions present in the extra cellular solution between the cells and the graphene remain trapped. It is this small variation that determines the increase in neuronal excitability” comments Denis Scaini, researcher at SISSA who has led the research alongside Laura Ballerini.

The study has also shown that this strengthening occurs when the graphene itself is supported by an insulator, like glass, or suspended in solution, while it disappears when lying on a conductor. “Graphene is a highly conductive material which could potentially be used to coat any surface. Understanding how its behaviour varies according to the substratum on which it is laid is essential for its future applications, above all in the neurological field” continues Scaini, “considering the unique properties of graphene it is natural to think for example about the development of innovative electrodes of cerebral stimulation or visual devices”.

It is a study with a double outcome. Laura Ballerini comments as follows: “This ‘ion trap’ effect was described only in theory. Studying the impact of the ‘technology of materials’ on biological systems, we have documented a mechanism to regulate membrane excitability, but at the same time we have also experimentally described a property of the material through the biology of neurons.”

Dexter Johnson in a June 13, 2018 posting, on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website), provides more context for the work (Note: Links have been removed),

While graphene has been tapped to deliver on everything from electronics to optoelectronics, it’s a bit harder to picture how it may offer a key tool for addressing neurological damage and disorders. But that’s exactly what researchers have been looking at lately because of the wonder material’s conductivity and transparency.

In the most recent development, a team from Europe has offered a deeper understanding of how graphene can be combined with neurological tissue and, in so doing, may have not only given us an additional tool for neurological medicine, but also provided a tool for gaining insights into other biological processes.

“The results demonstrate that, depending on how the interface with [single-layer graphene] is engineered, the material may tune neuronal activities by altering the ion mobility, in particular potassium, at the cell/substrate interface,” said Laura Ballerini, a researcher in neurons and nanomaterials at SISSA.

Ballerini provided some context for this most recent development by explaining that graphene-based nanomaterials have come to represent potential tools in neurology and neurosurgery.

“These materials are increasingly engineered as components of a variety of applications such as biosensors, interfaces, or drug-delivery platforms,” said Ballerini. “In particular, in neural electrode or interfaces, a precise requirement is the stable device/neuronal electrical coupling, which requires governing the interactions between the electrode surface and the cell membrane.”

This neuro-electrode hybrid is at the core of numerous studies, she explained, and graphene, thanks to its electrical properties, transparency, and flexibility represents an ideal material candidate.

In all of this work, the real challenge has been to investigate the ability of a single atomic layer to tune neuronal excitability and to demonstrate unequivocally that graphene selectively modifies membrane-associated neuronal functions.

…

I encourage you to read Dexter’s posting as it clarifies the work described in the SISSA press release for those of us (me) who may fail to grasp the implications.

Here’s a link to and a citation for the paper,

Single-layer graphene modulates neuronal communication and augments membrane ion currents by Niccolò Paolo Pampaloni, Martin Lottner, Michele Giugliano, Alessia Matruglio, Francesco D’Amico, Maurizio Prato, Josè Antonio Garrido, Laura Ballerini, & Denis Scaini. Nature Nanotechnology (2018) DOI: https://doi.org/10.1038/s41565-018-0163-6 Published online June 13, 2018

This paper is behind a paywall.

All this brings to mind a prediction made about the Graphene Flagship and the Human Brain Project shortly after the European Commission announced in January 2013 that each project had won funding of 1B Euros to be paid out over a period of 10 years. The prediction was that scientists would work on graphene/human brain research.

Babies have more general physics knowledge than experts realized

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A Feb. 10, 2016 news item on ScienceDaily sheds some light on babies and their knowledge of physics,

We are born with a basic grasp of physics, just enough not to be surprised when we interact with objects. Scientists discovered this in the past two decades. What they did not know yet was that, as early as five months of age, this ‘naive’ physics also extends to liquids and materials that do not behave like solids (for example, sand), as demonstrated by a new study.

A Feb. 10, 2016 SISSA (International School of Advanced Studies) press release (also on EurekAlert), which originated the news item, describes the conclusions and the research in more detail,

If we hold a ball and then let go of it and the ball remains suspended in mid-air, even a baby a few months old will be surprised. Just like an adult, the baby expects the ball to fall to the floor. Even at such a young age humans already have some rudimentary knowledge of the behaviour of solids. Now a new study extends this knowledge to add liquids and other non-solids to the “naïve physics” of infants.

“This new study developed out of previous experiments”, explains Alissa Ferry, SISSA research scientist and among the authors of the paper, “in which we observed that infants were surprised when a liquid failed to behave as a liquid (in those experiments we “cheated” by disguising solids as liquids)”. Their surprise, explains Ferry, demonstrates that their expectations for a liquid had not been met. “However, what we couldn’t establish was whether the infants knew how a liquid should behave or whether they just expected it to be different from a solid”.

Ferry and colleagues (the first author is Susan Hespos of Northwestern University in Illinois, USA, where the experiments were conducted) therefore devised a new set of tests with a greater range of materials and “interactions”. In a first “habituation” phase, the infants were shown the contents of a glass by tilting the glass in front of them. The glass either contained a solid (which, when not moving, had identical appearance to water) or some water. When the glass was tilted back and forth, the two materials behaved differently: the solid remained perfectly still whereas the water moved. This phase served to teach the infants whether they were looking at a solid or a liquid.

Next, the infants were shown an identical glass to the one seen in the previous phase (making them believe that it was the same glass) which contained either the material they had already seen or the other material. At this point, the infants watched the experimenter either pour the contents (liquid or solid) of the glass into another glass containing a grid or submerge the grid in the liquid (or rest it on top of the solid) inside the glass.

“In the previous experiments we merely poured the contents of the glass. This time we added a grid to find out whether the infants really understood the loose cohesiveness of liquids, which can pass through a perforated surface and recompose in the vessel unlike solids which, being highly cohesive, cannot pass through a grid” explains Ferry.

In the habituation phase, in fact, the infants could know how liquids change shape with movement, but it was unknown if they could use this knowledge to understand other properties of liquids, like loose cohesiveness. “If infants understand the properties of liquids, then they should be surprised when, what they think is a liquid gets trapped on a grid”.

And the analysis of the infants’ behaviour shows that when they expected a liquid they were surprised to see it blocked by the grid (or see the grid unable to penetrate the material). Conversely, if they thought they were looking at a solid, then they were surprised when they saw it pass through the grid.

The investigators also used other materials like sand and small glass spheres. “Even in these cases the infants showed that they knew the behaviour of substances”, concludes Ferry. “This is especially interesting because, while we can imagine that 5-month-old infants already have had extensive direct experience with liquids and especially water through meals, baths and 9 months in the amniotic liquid, it’s unlikely that they’ve had many encounters with sand or glass balls, suggesting that infants have a naïve understanding of the physics of nonsolid substances”.

Here’s a link to and a citation for the paper,

Five-Month-Old Infants Have General Knowledge of How Nonsolid Substances Behave and Interact by Susan J. Hespos, Alissa L. Ferry, Erin M. Anderson, Emily N. Hollenbeck, anb Lance J. Rips. Psychological Science February 2016 vol. 27 no. 2 244-256 doi: 10.1177/0956797615617897 Published online: January 7, 2016

This paper is behind a paywall.

Macramé and molecular entanglement at the nanoscale from Italy

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It’s all about the knots in Cristian Micheletti’s work on polymers in the June 10, 2013 news item on Nanowerk,

Timing and properties of spontaneous knotting in the macromolecular world. Courtesy: Sissa Medialab

Timing
and
properties
of spontaneous
knotting
in the macromolecular world. Courtesy: Sissa Medialab

From the news item (Note: A link has been removed),

Nanotechnologies require a detailed knowledge of the molecular state. For instance, it is useful to know when and how a generic polymer, a long chain of polymers (chain of beads), knots. The study of molecular entanglement is an important field of study as the presence of knots affects its physical properties, for instance the resistance to traction. Previous studies had mainly obtained “static” data on the knotting probability of such molecules. In other words, they focused on the likelihood that a polymer may knot. The novelty of the study (“Spontaneous Knotting and Unknotting of Flexible Linear Polymers: Equilibrium and Kinetic Aspects”) carried out by Micheletti and colleagues lies in the fact that this time the dynamic aspect of the phenomenon has been simulated.

Sissa (Scuola Internazionale Superiore di Studi Avanzati in Italy [my very rough translation: International School of Higher Learning and Advanced Studies]), has issued a June 10, 2013 press release which provides some insight into Micheletti’s perspective and more details about the work,

“It’s a little like the difference that lies between a disorganized collection of photographs and a
video. With the former we obtain statistical information (for instance, how many times a knot will appear), but we don’t know how that situation occurred and how it will evolve”, explained Micheletti. “Thanks to dynamic simulation we have found, for instance, that knots tend to form at the ends, where they are very frequent yet ephemeral, that is, they are short lived.”

According to the team’s observations, in fact, once formed the knot moves along the chain in an apparently casual manner, it may take a step to the left, then two to the right and so on, so that at the end of the chain it generally tends to disappear,“ falling ” outside the filament. Micheletti also explains that, although more infrequently, it has been observed that the knot moves towards the centre of the polymer: “When this occurs, the knots average lifetime is higher than when they remain trapped at the ends.”

At the center of the polymer also slip knots or pseudo knots, may form. “At first a loop is formed and this blocks another part of the filament. If thermal fluctuations pull to the correct side the knot disappears, while if they pull to the loop side, a proper knot may be created. These knots are very long lived,” explains Rosa [Angelo Rosa, a researcher at SISSA ].

“This research is useful since the data on simple knotting probability reveal nothing about knotting timing”, underlines Tubiana [Luca Tubianam a former SISSA student, now working at the Josef Stefan Institute of Ljubljana]. “If knots form and disappear very quickly, after a certain amount of time we may observe a given percentage of average knotting, yet we do not know whether the knots have remained the same or if they have changed through time. Researchers who carry out experiments of this kind need, instead, more detailed information.”

Micheletti was asked to present this latest work at Harvard University (US) today (June 10, 2013) at an Engineering and Physical Biology Symposium. For the curious who were not able to attend the symposium, here’s a link to and a citation for the team’s research paper,

Spontaneous Knotting and Unknotting of Flexible Linear Polymers: Equilibrium and Kinetic Aspects by L. Tubiana, A. Rosa, F. Fragiacomo, and C. Micheletti. Macromolecules, 2013, 46 (9), pp 3669–3678 DOI: 10.1021/ma4002963 Publication Date (Web): April 15, 2013
Copyright © 2013 American Chemical Society

This paper is behind a paywall.

I have a couple of extra comments. First, there’s a Sissa Medialab which seems to be the school’s  science communication initiative. You can go there to see more but you will need Italian language skills if you plan to do much more than look at the pictures. Second, I have referenced macramé (art of knotted textiles) before in a Nov. 10, 2011 posting about a synthetic molecular pentafoil knot