Tag Archives: CNTs

How small can a carbon nanotube get before it stops being ‘electrical’?

Research, which began as an attempt to get reproducible electronics (?) measurements, yielded some unexpected results according ta January 3, 2018 news item on phys.org,

Carbon nanotubes bound for electronics not only need to be as clean as possible to maximize their utility in next-generation nanoscale devices, but contact effects may limit how small a nano device can be, according to researchers at the Energy Safety Research Institute (ESRI) at Swansea University [UK] in collaboration with researchers at Rice University [US].

ESRI Director Andrew Barron, also a professor at Rice University in the USA, and his team have figured out how to get nanotubes clean enough to obtain reproducible electronic measurements and in the process not only explained why the electrical properties of nanotubes have historically been so difficult to measure consistently, but have shown that there may be a limit to how “nano” future electronic devices can be using carbon nanotubes.

Swansea University Issued a January 3, 2018 press release (also on EurekAlert), which originated the news item, explains the work in more detail,

Like any normal wire, semiconducting nanotubes are progressively more resistant to current along their length. But conductivity measurements of nanotubes over the years have been anything but consistent. The ESRI team wanted to know why.

“We are interested in the creation of nanotube based conductors, and while people have been able to make wires their conduction has not met expectations. We were interested in determining the basic sconce behind the variability observed by other researchers.”

They discovered that hard-to-remove contaminants — leftover iron catalyst, carbon and water — could easily skew the results of conductivity tests. Burning them away, Barron said, creates new possibilities for carbon nanotubes in nanoscale electronics.

The new study appears in the American Chemical Society journal Nano Letters.

The researchers first made multiwalled carbon nanotubes between 40 and 200 nanometers in diameter and up to 30 microns long. They then either heated the nanotubes in a vacuum or bombarded them with argon ions to clean their surfaces.

They tested individual nanotubes the same way one would test any electrical conductor: By touching them with two probes to see how much current passes through the material from one tip to the other. In this case, their tungsten probes were attached to a scanning tunneling microscope.

In clean nanotubes, resistance got progressively stronger as the distance increased, as it should. But the results were skewed when the probes encountered surface contaminants, which increased the electric field strength at the tip. And when measurements were taken within 4 microns of each other, regions of depleted conductivity caused by contaminants overlapped, further scrambling the results.

“We think this is why there’s such inconsistency in the literature,” Barron said.

“If nanotubes are to be the next generation lightweight conductor, then consistent results, batch-to-batch, and sample-to-sample, is needed for devices such as motors and generators as well as power systems.”

Annealing the nanotubes in a vacuum above 200 degrees Celsius (392 degrees Fahrenheit) reduced surface contamination, but not enough to eliminate inconsistent results, they found. Argon ion bombardment also cleaned the tubes, but led to an increase in defects that degrade conductivity.

Ultimately they discovered vacuum annealing nanotubes at 500 degrees Celsius (932 Fahrenheit) reduced contamination enough to accurately measure resistance, they reported.

To now, Barron said, engineers who use nanotube fibers or films in devices modify the material through doping or other means to get the conductive properties they require. But if the source nanotubes are sufficiently decontaminated, they should be able to get the right conductivity by simply putting their contacts in the right spot.

“A key result of our work was that if contacts on a nanotube are less than 1 micron apart, the electronic properties of the nanotube changes from conductor to semiconductor, due to the presence of overlapping depletion zones” said Barron, “this has a potential limiting factor on the size of nanotube based electronic devices – this would limit the application of Moore’s law to nanotube devices.”

Chris Barnett of Swansea is lead author of the paper. Co-authors are Cathren Gowenlock and Kathryn Welsby, and Rice alumnus Alvin Orbaek White of Swansea. Barron is the Sêr Cymru Chair of Low Carbon Energy and Environment at Swansea and the Charles W. Duncan Jr.–Welch Professor of Chemistry and a professor of materials science and nanoengineering at Rice.

The Welsh Government Sêr Cymru National Research Network in Advanced Engineering and Materials, the Sêr Cymru Chair Program, the Office of Naval Research and the Robert A. Welch Foundation supported the research.

Rice University has published a January 4, 2018 Rice University news release (also on EurekAlert), which is almost (95%) identical to the press release from Swansea. That’s a bit unusual as collaborating institutions usually like to focus on their unique contributions to the research, hence, multiple news/press releases.

Dexter Johnson, in a January 11, 2018 post on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website,  adds a detail or two while writing in an accessible style.

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

Spatial and Contamination-Dependent Electrical Properties of Carbon Nanotubes by Chris J. Barnett, Cathren E. Gowenlock, Kathryn Welsby, Alvin Orbaek White, and Andrew R. Barron. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.7b03390 Publication Date (Web): December 19, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Carbon nanotubes for enhanced wheat growth?

It’s been a long time (Oct. 22, 2009 posting; scroll down about 20% of the way) since I’ve written about carbon nanotubes and their possible use in agriculture but now a December 6, 2017 news item on ScienceDaily raises the topic again,

The introduction of purified carbon nanotubes appears to have a beneficial effect on the early growth of wheatgrass, according to Rice University scientists. But in the presence of contaminants, those same nanotubes could do great harm.

The Rice lab of chemist Andrew Barron grew wheatgrass in a hydroponic garden to test the potential toxicity of nanoparticles on the plant. To their surprise, they found one type of particle dispersed in water helped the plant grow bigger and faster.

They suspect the results spring from nanotubes’ natural hydrophobic (water-avoiding) nature that in one experiment apparently facilitated the plants’ enhanced uptake of water.

The research appears in the Royal Society of Chemistry journal Environmental Science: Nano.

A December 6, 2017 Rice University news release (also on EurekAlert), which originated the news item, expands on the theme,

The lab mounted the small-scale study with the knowledge that the industrial production of nanotubes will inevitably lead to their wider dispersal in the environment. The study cited rapid growth in the market for nanoparticles in drugs, cosmetic, fabrics, water filters and military weapons, with thousands of tons produced annually.

Despite their widespread use, Barron said few researchers have looked at the impact of environmental nanoparticles — whether natural or man-made — on plant growth.

The researchers planted wheatgrass seeds in multiple replicates in cotton wool and fed them with dispersions that contained raw single-walled or multi-walled nanotubes, purified single-walled nanotubes or iron oxide nanoparticles that mimicked leftover catalyst often attached to nanotubes. The solutions were either water or tetrahydrofuran (THF), an industrial solvent. Some of the seeds were fed pure water or THF as a control.

Rice University researchers tested the effects of carbon nanotubes on the growth of wheatgrass. While some showed no effect, purified single-walled nanotubes in water (5) enhanced the plants' growth, while the same nanotubes in a solvent (6) retarded their development. The photos at left show the plants after four days and at right after eight days, with odd-numbered plants growing in water and evens in a solvent. Numbers 1 and 2 are controls without nanotubes; 3-4 contain raw single-walled tubes; 5-6 purified single-walled tubes; 7-8 raw multi-walled tubes; 9-10 low-concentration iron-oxide nanoparticles and 11-12 high-concentration iron-oxide nanoparticles.

Rice University researchers tested the effects of carbon nanotubes on the growth of wheatgrass. While some showed no effect, purified single-walled nanotubes in water (5) enhanced the plants’ growth, while the same nanotubes in a solvent (6) retarded their development. The photos at left show the plants after four days and at right after eight days, with odd-numbered plants growing in water and evens in a solvent. Numbers 1 and 2 are controls without nanotubes; 3-4 contain raw single-walled tubes; 5-6 purified single-walled tubes; 7-8 raw multi-walled tubes; 9-10 low-concentration iron-oxide nanoparticles and 11-12 high-concentration iron-oxide nanoparticles. Click on the image for a larger version. Photos by Seung Mook Lee

After eight days, the plantings showed that purified single-walled nanotubes in water enhanced the germination rate and shoot growth of wheatgrass, which grew an average of 13 percent larger than plants in plain water. Raw single- and multi-walled nanotubes and particles in either solution had little effect on the plants’ growth, they found.

However, purified single-walled nanotubes in THF retarded plant development by 45 percent compared to single-walled nanotubes in water, suggesting the nanotubes act as a carrier for the toxic substance.

The concern, Barron said, is that if single-walled nanotubes combine with organic pollutants like pesticides, industrial chemicals or solvents in the environment, they may concentrate and immobilize the toxins and enhance their uptake by plants.

Nothing seen in the limited study indicated whether carbon nanotubes in the environment, and potentially in plants, will rise up the food chain and be harmful to humans, he said.

On the other hand, the researchers said it may be worth looking at whether hydrophobic substrates that mimic the positive effects observed in single-walled nanotubes could be used for high-efficiency channeling of water to seeds.

“Our work confirms the importance of thinking of nanomaterials as part of a system rather in isolation,” Barron said. “It is the combination with other compounds that is important to understand.”

Seung Mook Lee, a former visiting student research assistant from Memorial High School in Houston and now an undergraduate student at the University of California, Berkeley, is lead author of the paper. Co-authors are Rice research scientist Pavan Raja and graduate student Gibran Esquenazi. Barron is the Charles W. Duncan Jr.–Welch Professor of Chemistry and a professor of materials science and nanoengineering at Rice and the Sêr Cymru Chair of Low Carbon Energy and Environment at Swansea University, Wales (UK).

The Welsh Government Sêr Cymru Program and the Robert A. Welch Foundation supported the research.

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

Effect of raw and purified carbon nanotubes and iron oxide nanoparticles on the growth of wheatgrass prepared from the cotyledons of common wheat (triticum aestivum) by Seung Mook Lee, Pavan M. V. Raja, Gibran L. Esquenazi, and Andrew R. Barron. Environ. Sci.: Nano, 2018, Advance Article DOI: 10.1039/C7EN00680B First published on 09 Nov 2017

This paper appears to be behind a paywall.

Felted carbon nanotubes

Parachute (sculpted felt lantern). Artist and artisan felter: Chantal Cardinal. Studio: FELT à la main with LOVE

Scientists from Kiel University (Christian-Albrechts-Universität zu Kiel; Germany) and the University of Trento (Italy) claim to have developed a new method for integrating carbon nanotubes (CNTs) into new materials in a technique they describe as similar to felting according to a November 21, 2017 news item on Nanowerk,

Extremely lightweight, electrically highly conductive, and more stable than steel: due to their unique properties, carbon nanotubes would be ideal for numerous applications, from ultra-lightweight batteries to high-performance plastics, right through to medical implants. However, to date it has been difficult for science and industry to transfer the extraordinary characteristics at the nanoscale into a functional industrial application. The carbon nanotubes either cannot be combined adequately with other materials, or if they can be combined, they then lose their beneficial properties.

Scientists from the Functional Nanomaterials working group at Kiel University (CAU) and the University of Trento have now developed an alternative method, with which the tiny tubes can be combined with other materials, so that they retain their characteristic properties. As such, they “felt” the thread-like tubes into a stable 3D network that is able to withstand extreme forces.

In contrast to the ‘felted’ image which opened this posting, here’s an image of the ‘felted’ carbon nanotubes,

In this new process, the tiny, thread-like carbon nanotubes (CNTs) arrange themselves – almost like felting – to form a stable, tear-resistant layer. Photo/Copyright: Fabian Schütt Courtesy: Kiel University

A November 21, 2017 Kiel University press release (also on EurekAlert), which originated the news item, expands on the theme and adds another analogy,

Industry and science have been intensively researching the significantly less than one hundred nanometre wide carbon tubes (carbon nanotubes, CNTs), in order to make use of the extraordinary properties of rolled graphene. Yet much still remains just theory. “Although carbon nanotubes are flexible like fibre strands, they are also very sensitive to changes,” explained Professor Rainer Adelung, head of the Functional Nanomaterials working group at the CAU. “With previous attempts to chemically connect them with other materials, their molecular structure also changed. This, however, made their properties deteriorate – mostly drastically.”

In contrast, the approach of the research team from Kiel and Trento is based on a simple wet chemical infiltration process. The CNTs are mixed with water and dripped into an extremely porous ceramic material made of zinc oxide, which absorbs the liquid like a sponge. The dripped thread-like CNTs attach themselves to the ceramic scaffolding, and automatically form a stable layer together, similar to a felt. The ceramic scaffolding is coated with nanotubes, so to speak. This has fascinating effects, both for the scaffolding as well as for the coating of nanotubes.

On the one hand, the stability of the ceramic scaffold increases so massively that it can bear 100,000 times its own weight. “With the CNT coating, the ceramic material can hold around 7.5kg, and without it just 50g – as if we had fitted it with a close-fitting pullover made of carbon nanotubes, which provide mechanical support,” summarised first author Fabian Schütt. “The pressure on the material is absorbed by the tensile strength of the CNT felt. Compressive forces are transformed into tensile forces.”

The principle behind this is comparable with bamboo buildings [emphasis mine], such as those widespread in Asia. Here, bamboo stems are bound so tightly with a simple rope that the lightweight material can form extremely stable scaffolding, and even entire buildings. “We do the same at the nano-scale with the CNT threads, which wrap themselves around the ceramic material – only much, much smaller,” said Helge Krüger, co-author of the publication.

The materials scientists were able to demonstrate another major advantage of their process. In a second step, they dissolved the ceramic scaffolding by using a chemical etching process. All that remains is a fine 3D network of tubes, each of which consists of a layer of tiny CNT tubes. In this way, the researchers were able to greatly increase the felt surface, and thus create more opportunities for reactions. “We basically pack the surface of an entire beach volleyball field into a one centimetre cube,” explained Schütt. The huge hollow spaces inside the three-dimensional structure can then be filled with a polymer. As such, CNTs can be connected mechanically with plastics, without their molecular structure – and thus their properties – being modified. “We can specifically arrange the CNTs and manufacture an electrically conductive composite material. To do so only requires a fraction of the usual quantity of CNTs, in order to achieve the same conductivity,” said Schütt.

Applications for use range from battery and filter technology as a filling material for conductive plastics, implants for regenerative medicine, right through to sensors and electronic components at the nano-scale. The good electrical conductivity of the tear-resistant material could in future also be interesting for flexible electronics applications, in functional clothing or in the field of medical technology, for example. “Creating a plastic which, for example, stimulates bone or heart cells to grow is conceivable,” said Adelung. Due to its simplicity, the scientists agree that the process could also be transferred to network structures made of other nanomaterials – which will further expand the range of possible applications.

So, we have ‘felting’ and bamboo buildings. I can appreciate the temptation to use multiple analogies especially since I’ve given into it, on occasion.  But, it’s never considered good style, not even when I do it.

Getting back to the work at hand, here’s a link to and a citation for the paper,

Hierarchical self-entangled carbon nanotube tube networks by Fabian Schütt, Stefano Signetti, Helge Krüger, Sarah Röder, Daria Smazna, Sören Kaps, Stanislav N. Gorb, Yogendra Kumar Mishra, Nicola M. Pugno, & Rainer Adelung. Nature Communications 8, Article number: 1215 (2017) doi:10.1038/s41467-017-01324-7 Published online: 31 October 2017

This is an open access paper.

One final comment, I notice that one of the authors is Nicola Pugno who was last mentioned here in an August 30, 2017 posting titled: Making spider silk stronger by feeding graphene and carbon nanotubes to spiders.

Calligraphy ink and cancer treatment

Courtesy of ACS Omega and the researchers

Nice illustration! I wish I could credit the artist. For anyone who needs a little text to make sense of it, there’s a Sept. 27, 2017 news item on Nanowerk (Note: A link has been removed),

For hundreds of years, Chinese calligraphers have used a plant-based ink to create beautiful messages and art. Now, one group reports in ACS Omega (“New Application of Old Material: Chinese Traditional Ink for Photothermal Therapy of Metastatic Lymph Nodes”) that this ink could noninvasively and effectively treat cancer cells that spread, or metastasize, to lymph nodes.

A Sept. 27, 2017 American Chemical Society (ACS) news release, which originated the news item, reveals more about the research,

As cancer cells leave a tumor, they frequently make their way to lymph nodes, which are part of the immune system. In this case, the main treatment option is surgery, but this can result in complications. Photothermal therapy (PTT) is an emerging noninvasive treatment option in which nanomaterials are injected and accumulate in cancer cells. A laser heats up the nanomaterials, and this heat kills the cells. Many of these nanomaterials are expensive, difficult-to-make and toxic. However, a traditional Chinese ink called Hu-Kaiwen ink (Hu-ink) has similar properties to the nanomaterials used in PTT. For example, they are the same color, and are both carbon-based and stable in water. So Wuli Yang and colleagues wanted to see if Hu-ink could be a good alternative material for PTT.

The researchers analyzed Hu-ink and found that it consists of nanoparticles and thin layers of carbon. When Hu-ink was heated with a laser, its temperature rose by 131 degrees Fahrenheit, much higher than current nanomaterials. Under PPT conditions, the Hu-ink killed cancer cells in a laboratory dish, but under normal conditions, the ink was non-toxic. This was also the scenario observed in mice with tumors. The researchers also noted that Hu-ink could act as a probe to locate tumors and metastases because it absorbs near-infrared light, which goes through skin.

Being a little curious about Hu-ink’s similarity to nanomaterial, I looked for more detail in the the paper (Note: Links have been removed), From the: Introduction,

Photothermal therapy (PTT) is an emerging tumor treatment strategy, which utilizes hyperthermia generated from absorbed near-infrared (NIR) light energy by photoabsorbing agents to kill tumor cells.(7-13) Different from chemotherapy, surgical treatment, and radiotherapy, PTT is noninvasive and more efficient.(7, 14, 15) In the past decade, PTT with diverse nanomaterials to eliminate cancer metastases lymph nodes has attracted extensive attention by several groups, including our group.(3, 16-20) For instance, Liu and his co-workers developed a treatment method based on PEGylated single-walled carbon nanotubes for PTT of tumor sentinel lymph nodes and achieved remarkably improved treatment effect in an animal tumor model.(21) To meet the clinical practice, the potential metastasis of deeper lymph nodes was further ablated in our previous work, using magnetic graphene oxide as a theranostic agent.(22) However, preparation of these artificial nanomaterials usually requires high cost, complicated synthetic process, and unavoidably toxic catalyst or chemicals,(23, 24) which impede their future clinical application. For the clinical application, exploring an environment-friendly material with simple preparation procedure, good biocompatibility, and excellent therapeutic efficiency is still highly desired. [emphases mine]

From the: Preparation and Characterization of Hu-Ink

To obtain an applicable sample, the condensed Hu-ink was first diluted into aqueous dispersion with a lower concentration. The obtained Hu-ink dispersion without any further treatment was black in color and stable in physiological environment, including water, phosphate-buffered saline (PBS), and Roswell Park Memorial Institute (RPMI) 1640; furthermore, no aggregation was observed even after keeping undisturbed for 3 days (Figure 2a). The nanoscaled morphology of Hu-ink was examined by transmission electron microscopy (TEM) (Figure 2b), which demonstrates that Hu-ink mainly exist in the form of small aggregates. These small aggregates consist of a few nanoparticles with diameter of about 20–50 nm. Dynamic light scattering (DLS) measurement (Figure 2c) further shows that Hu-ink aqueous dispersion possesses a hydrodynamic diameter of about 186 nm (polydispersity index: 0.18), which was a crucial prerequisite for biomedical applications.(29) In the X-ray diffraction (XRD) pattern, no other characteristic peaks are found except carbon peak (Figure S1, Supporting Information), which confirms that the main component of Hu-ink is carbon.(25) Raman spectroscopy was a common tool to characterize graphene-related materials.(30) D band (∼1300 cm–1, corresponding to the defects) and G band (∼1600 cm–1, related to the sp2 carbon sites) peaks could be observed in Figure 2d with the ratio ID/IG = 0.96, which confirms the existence of graphene sheetlike structure in Hu-ink.(31) The UV–vis–NIR spectra (Figure 2e) also revealed that Hu-ink has high absorption in the NIR region around 650–900 nm, in which hemoglobin and water, the major absorbers of biological tissue, have their lowest absorption coefficient.(32) The high NIR absorption capability of Hu-ink encouraged us to investigate its photothermal properties.(33-35) Hu-ink dispersions with different concentrations were irradiated under an 808 nm laser (the commercial and widely used wavelength in photothermal therapy).(8-13) [emphases mine]

Curiosity satisfied! For those who’d like to investigate even further, here’s a link to and a citation for the paper,

New Application of Old Material: Chinese Traditional Ink for Photothermal Therapy of Metastatic Lymph Nodes by Sheng Wang, Yongbin Cao, Qin Zhang, Haibao Peng, Lei Liang, Qingguo Li, Shun Shen, Aimaier Tuerdi, Ye Xu, Sanjun Cai, and Wuli Yang. ACS Omega, 2017, 2 (8), pp 5170–5178 DOI: 10.1021/acsomega.7b00993 Publication Date (Web): August 30, 2017

Copyright © 2017 American Chemical Society

This paper appears to be open access.

Liquid circuitry, shape-shifting fluids and more

I’d have to see it to believe it but researchers at the US Dept. of Energy (DOE) Lawrence Berkeley National Laboratory (LBNL) have developed a new kind of ‘bijel’ which would allow for some pretty nifty robotics. From a Sept. 25, 2017 news item on ScienceDaily,

A new two-dimensional film, made of polymers and nanoparticles and developed by researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), can direct two different non-mixing liquids into a variety of exotic architectures. This finding could lead to soft robotics, liquid circuitry, shape-shifting fluids, and a host of new materials that use soft, rather than solid, substances.

The study, reported today in the journal Nature Nanotechnology, presents the newest entry in a class of substances known as bicontinuous jammed emulsion gels, or bijels, which hold promise as a malleable liquid that can support catalytic reactions, electrical conductivity, and energy conversion.

A Sept. 25, 2017 LBNL news release (also on EurekAlert), which originated the news item, expands on the theme,

Bijels are typically made of immiscible, or non-mixing, liquids. People who shake their bottle of vinaigrette before pouring the dressing on their salad are familiar with such liquids. As soon as the shaking stops, the liquids start to separate again, with the lower density liquid – often oil – rising to the top.

Trapping, or jamming, particles where these immiscible liquids meet can prevent the liquids from completely separating, stabilizing the substance into a bijel. What makes bijels remarkable is that, rather than just making the spherical droplets that we normally see when we try to mix oil and water, the particles at the interface shape the liquids into complex networks of interconnected fluid channels.

Bijels are notoriously difficult to make, however, involving exact temperatures at precisely timed stages. In addition, the liquid channels are normally more than 5 micrometers across, making them too large to be useful in energy conversion and catalysis.

“Bijels have long been of interest as next-generation materials for energy applications and chemical synthesis,” said study lead author Caili Huang. “The problem has been making enough of them, and with features of the right size. In this work, we crack that problem.”

Huang started the work as a graduate student with Thomas Russell, the study’s principal investigator, at Berkeley Lab’s Materials Sciences Division, and he continued the project as a postdoctoral researcher at DOE’s Oak Ridge National Laboratory.

Creating a new bijel recipe

The method described in this new study simplifies the bijel process by first using specially coated particles about 10-20 nanometers in diameter. The smaller-sized particles line the liquid interfaces much more quickly than the ones used in traditional bijels, making the smaller channels that are highly valued for applications.

Illustration shows key stages of bijel formation. Clockwise from top left, two non-mixing liquids are shown. Ligands (shown in yellow) with amine groups are dispersed throughout the oil or solvent, and nanoparticles coated with carboxylic acids (shown as blue dots) are scattered in the water. With vigorous shaking, the nanoparticles and ligands form a “supersoap” that gets trapped at the interface of the two liquids. The bottom panel is a magnified view of the jammed nanoparticle supersoap. (Credit: Caili Huang/ORNL)

“We’ve basically taken liquids like oil and water and given them a structure, and it’s a structure that can be changed,” said Russell, a visiting faculty scientist at Berkeley Lab. “If the nanoparticles are responsive to electrical, magnetic, or mechanical stimuli, the bijels can become reconfigurable and re-shaped on demand by an external field.”

The researchers were able to prepare new bijels from a variety of common organic, water-insoluble solvents, such as toluene, that had ligands dissolved in it, and deionized water, which contained the nanoparticles. To ensure thorough mixing of the liquids, they subjected the emulsion to a vortex spinning at 3,200 revolutions per minute.

“This extreme shaking creates a whole bunch of new places where these particles and polymers can meet each other,” said study co-author Joe Forth, a postdoctoral fellow at Berkeley Lab’s Materials Sciences Division. “You’re synthesizing a lot of this material, which is in effect a thin, 2-D coating of the liquid surfaces in the system.”

The liquids remained a bijel even after one week, a sign of the system’s stability.

Russell, who is also a professor of polymer science and engineering at the University of Massachusetts-Amherst, added that these shape-shifting characteristics would be valuable in microreactors, microfluidic devices, and soft actuators.

Nanoparticle supersoap

Nanoparticles had not been seriously considered in bijels before because their small size made them hard to trap in the liquid interface. To resolve that problem, the researchers coated nano-sized particles with carboxylic acids and put them in water. They then took polymers with an added amine group – a derivative of ammonia – and dissolved them in the toluene.

At left is a vial of bijel stabilized with nanoparticle surfactants. On the right is the same vial after a week of inversion, showing that the nanoparticle kept the liquids from moving. (Credit: Caili Huang/ORNL)

This configuration took advantage of the amine group’s affinity to water, a characteristic that is comparable to surfactants, like soap. Their nanoparticle “supersoap” was designed so that the nanoparticles join ligands, forming an octopus-like shape with a polar head and nonpolar legs that get jammed at the interface, the researchers said.

“Bijels are really a new material, and also excitingly weird in that they are kinetically arrested in these unusual configurations,” said study co-author Brett Helms, a staff scientist at Berkeley Lab’s Molecular Foundry. “The discovery that you can make these bijels with simple ingredients is a surprise. We all have access to oils and water and nanocrystals, allowing broad tunability in bijel properties. This platform also allows us to experiment with new ways to control their shape and function since they are both responsive and reconfigurable.”

The nanoparticles were made of silica, but the researchers noted that in previous studies they used graphene and carbon nanotubes to form nanoparticle surfactants.

“The key is that the nanoparticles can be made of many materials,” said Russell.  “The most important thing is what’s on the surface.”

This is an animation of the bijel

3-D rendering of the nanoparticle bijel taken by confocal microscope. (Credit: Caili Huang/ORNL [Oak Ridge National Laboratory] and Joe Forth/Berkeley Lab)

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

Bicontinuous structured liquids with sub-micrometre domains using nanoparticle surfactants by Caili Huang, Joe Forth, Weiyu Wang, Kunlun Hong, Gregory S. Smith, Brett A. Helms & Thomas P. Russell. Nature Nanotechnology (2017) doi:10.1038/nnano.2017.182 25 September 2017

This paper is behind a paywall.

Vampire nanogenerators: 2017

Researchers have been working on ways to harvest energy from bloodstreams. I last wrote about this type of research in an April 3, 2009 posting about ‘vampire batteries ‘(for use in pacemakers). The latest work according to a Sept. 8, 2017 news item on Nanowerk comes from China,

Men build dams and huge turbines to turn the energy of waterfalls and tides into electricity. To produce hydropower on a much smaller scale, Chinese scientists have now developed a lightweight power generator based on carbon nanotube fibers suitable to convert even the energy of flowing blood in blood vessels into electricity. They describe their innovation in the journal Angewandte Chemie (“A One-Dimensional Fluidic Nanogenerator with a High Power Conversion Efficiency”)

A Sept. 8, 2017 Wiley Publishing news release (also on EurekAlert), which originated the news item, expands on the theme,

For thousands of years, people have used the energy of flowing or falling water for their purposes, first to power mechanical engines such as watermills, then to generate electricity by exploiting height differences in the landscape or sea tides. Using naturally flowing water as a sustainable power source has the advantage that there are (almost) no dependencies on weather or daylight. Even flexible, minute power generators that make use of the flow of biological fluids are conceivable. How such a system could work is explained by a research team from Fudan University in Shanghai, China. Huisheng Peng and his co-workers have developed a fiber with a thickness of less than a millimeter that generates electrical power when surrounded by flowing saline solution—in a thin tube or even in a blood vessel.

The construction principle of the fiber is quite simple. An ordered array of carbon nanotubes was continuously wrapped around a polymeric core. Carbon nanotubes are well known to be electroactive and mechanically stable; they can be spun and aligned in sheets. In the as-prepared electroactive threads, the carbon nanotube sheets coated the fiber core with a thickness of less than half a micron. For power generation, the thread or “fiber-shaped fluidic nanogenerator” (FFNG), as the authors call it, was connected to electrodes and immersed into flowing water or simply repeatedly dipped into a saline solution. “The electricity was derived from the relative movement between the FFNG and the solution,” the scientists explained. According to the theory, an electrical double layer is created around the fiber, and then the flowing solution distorts the symmetrical charge distribution, generating an electricity gradient along the long axis.

The power output efficiency of this system was high. Compared with other types of miniature energy-harvesting devices, the FFNG was reported to show a superior power conversion efficiency of more than 20%. Other advantages are elasticity, tunability, lightweight, and one-dimensionality, thus offering prospects of exciting technological applications. The FFNG can be made stretchable just by spinning the sheets around an elastic fiber substrate. If woven into fabrics, wearable electronics become thus a very interesting option for FFNG application. Another exciting application is the harvesting of electrical energy from the bloodstream for medical applications. First tests with frog nerves proved to be successful.

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

A One-Dimensional Fluidic Nanogenerator with a High Power Conversion Efficiency by Yifan Xu, Dr. Peining Chen, Jing Zhang, Songlin Xie, Dr. Fang Wan, Jue Deng, Dr. Xunliang Cheng, Yajie Hu, Meng Liao, Dr. Bingjie Wang, Dr. Xuemei Sun, and Prof. Dr. Huisheng Peng. Angewandte Chemie International Edition DOI: 10.1002/anie.201706620 Version of Record online: 7 SEP 2017

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Carbon nanotubes for water desalination

In discussions about water desalination and carbon nanomaterials,  it’s graphene that’s usually mentioned these days. By contrast, scientists from the US Department of Energy’s Lawrence Livermore National Laboratory (LLNL) have turned to carbon nanotubes,

There are two news items about the work at LLNL on ScienceDaily, this first one originated by the American Association for the Advancement of Science (AAAS) offers a succinct summary of the work (from an August 24, 2017 news item on ScienceDaily,

At just the right size, carbon nanotubes can filter water with better efficiency than biological proteins, a new study reveals. The results could pave the way to new water filtration systems, at a time when demands for fresh water pose a global threat to sustainable development.

A class of biological proteins, called aquaporins, is able to effectively filter water, yet scientists have not been able to manufacture scalable systems that mimic this ability. Aquaporins usually exhibit channels for filtering water molecules at a narrow width of 0.3 nanometers, which forces the water molecules into a single-file chain.

Here, Ramya H. Tunuguntla and colleagues experimented with nanotubes of different widths to see which ones are best for filtering water. Intriguingly, they found that carbon nanotubes with a width of 0.8 nanometers outperformed aquaporins in filtering efficiency by a factor of six.

These narrow carbon nanotube porins (nCNTPs) were still slim enough to force the water molecules into a single-file chain. The researchers attribute the differences between aquaporins and nCNTPS to differences in hydrogen bonding — whereas pore-lining residues in aquaporins can donate or accept H bonds to incoming water molecules, the walls of CNTPs cannot form H bonds, permitting unimpeded water flow.

The nCNTPs in this study maintained permeability exceeding that of typical saltwater, only diminishing at very high salt concentrations. Lastly, the team found that by changing the charges at the mouth of the nanotube, they can alter the ion selectivity. This advancement is highlighted in a Perspective [in Science magazine] by Zuzanna Siwy and Francesco Fornasiero.

The second Aug. 24, 2017 news item on ScienceDaily offers a more technical  perspective,

Lawrence Livermore scientists, in collaboration with researchers at Northeastern University, have developed carbon nanotube pores that can exclude salt from seawater. The team also found that water permeability in carbon nanotubes (CNTs) with diameters smaller than a nanometer (0.8 nm) exceeds that of wider carbon nanotubes by an order of magnitude.

The nanotubes, hollow structures made of carbon atoms in a unique arrangement, are more than 50,000 times thinner than a human hair. The super smooth inner surface of the nanotube is responsible for their remarkably high water permeability, while the tiny pore size blocks larger salt ions.

There’s a rather lovely illustration for this work,

An artist’s depiction of the promise of carbon nanotube porins for desalination. The image depicts a stylized carbon nanotube pipe that delivers clean desalinated water from the ocean to a kitchen tap. Image by Ryan Chen/LLNL

An Aug. 24, 2017 LLNL news release (also on EurekAlert), which originated the second news item, proceeds

Increasing demands for fresh water pose a global threat to sustainable development, resulting in water scarcity for 4 billion people. Current water purification technologies can benefit from the development of membranes with specialized pores that mimic highly efficient and water selective biological proteins.

“We found that carbon nanotubes with diameters smaller than a nanometer bear a key structural feature that enables enhanced transport. The narrow hydrophobic channel forces water to translocate in a single-file arrangement, a phenomenon similar to that found in the most efficient biological water transporters,” said Ramya Tunuguntla, an LLNL postdoctoral researcher and co-author of the manuscript appearing in the Aug. 24 [2017]edition of Science.

Computer simulations and experimental studies of water transport through CNTs with diameters larger than 1 nm showed enhanced water flow, but did not match the transport efficiency of biological proteins and did not separate salt efficiently, especially at higher salinities. The key breakthrough achieved by the LLNL team was to use smaller-diameter nanotubes that delivered the required boost in performance.

“These studies revealed the details of the water transport mechanism and showed that rational manipulation of these parameters can enhance pore efficiency,” said Meni Wanunu, a physics professor at Northeastern University and co-author on the study.

“Carbon nanotubes are a unique platform for studying molecular transport and nanofluidics,” said Alex Noy, LLNL principal investigator on the CNT project and a senior author on the paper. “Their sub-nanometer size, atomically smooth surfaces and similarity to cellular water transport channels make them exceptionally suited for this purpose, and it is very exciting to make a synthetic water channel that performs better than nature’s own.”

This discovery by the LLNL scientists and their colleagues has clear implications for the next generation of water purification technologies and will spur a renewed interest in development of the next generation of high-flux membranes.

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

Enhanced water permeability and tunable ion selectivity in subnanometer carbon nanotube porins by Ramya H. Tunuguntla, Robert Y. Henley, Yun-Chiao Yao, Tuan Anh Pham, Meni Wanunu, Aleksandr Noy. Science 25 Aug 2017: Vol. 357, Issue 6353, pp. 792-796 DOI: 10.1126/science.aan2438

This paper is behind a paywall.

And, Northeastern University issued an August 25, 2017 news release (also on EurekAlert) by Allie Nicodemo,

Earth is 70 percent water, but only a tiny portion—0.007 percent—is available to drink.

As potable water sources dwindle, global population increases every year. One potential solution to quenching the planet’s thirst is through desalinization—the process of removing salt from seawater. While tantalizing, this approach has always been too expensive and energy intensive for large-scale feasibility.

Now, researchers from Northeastern have made a discovery that could change that, making desalinization easier, faster and cheaper than ever before. In a paper published Thursday [August 24, 2017] in Science, the group describes how carbon nanotubes of a certain size act as the perfect filter for salt—the smallest and most abundant water contaminant.

Filtering water is tricky because water molecules want to stick together. The “H” in H2O is hydrogen, and hydrogen bonds are strong, requiring a lot of energy to separate. Water tends to bulk up and resist being filtered. But nanotubes do it rapidly, with ease.

A carbon nanotube is like an impossibly small rolled up sheet of paper, about a nanometer in diameter. For comparison, the diameter of a human hair is 50 to 70 micrometers—50,000 times wider. The tube’s miniscule size, exactly 0.8 nm, only allows one water molecule to pass through at a time. This single-file lineup disrupts the hydrogen bonds, so water can be pushed through the tubes at an accelerated pace, with no bulking.

“You can imagine if you’re a group of people trying to run through the hallway holding hands, it’s going to be a lot slower than running through the hallway single-file,” said co-author Meni Wanunu, associate professor of physics at Northeastern. Wanunu and post doctoral student Robert Henley collaborated with scientists at the Lawrence Livermore National Laboratory in California to conduct the research.

Scientists led by Aleksandr Noy at Lawrence Livermore discovered last year [2016] that carbon nanotubes were an ideal channel for proton transport. For this new study, Henley brought expertise and technology from Wanunu’s Nanoscale Biophysics Lab to Noy’s lab, and together they took the research one step further.

In addition to being precisely the right size for passing single water molecules, carbon nanotubes have a negative electric charge. This causes them to reject anything with the same charge, like the negative ions in salt, as well as other unwanted particles.

“While salt has a hard time passing through because of the charge, water is a neutral molecule and passes through easily,” Wanunu said. Scientists in Noy’s lab had theorized that carbon nanotubes could be designed for specific ion selectivity, but they didn’t have a reliable system of measurement. Luckily, “That’s the bread and butter of what we do in Meni’s lab,” Henley said. “It created a nice symbiotic relationship.”

“Robert brought the cutting-edge measurement and design capabilities of Wanunu’s group to my lab, and he was indispensable in developing a new platform that we used to measure the ion selectivity of the nanotubes,” Noy said.

The result is a novel system that could have major implications for the future of water security. The study showed that carbon nanotubes are better at desalinization than any other existing method— natural or man-made.

To keep their momentum going, the two labs have partnered with a leading water purification organization based in Israel. And the group was recently awarded a National Science Foundation/Binational Science Foundation grant to conduct further studies and develop water filtration platforms based on their new method. As they continue the research, the researchers hope to start programs where students can learn the latest on water filtration technology—with the goal of increasing that 0.007 percent.

As is usual in these cases there’s a fair degree of repetition but there’s always at least one nugget of new information, in this case, a link to Israel. As I noted many times, the Middle East is experiencing serious water issues. My most recent ‘water and the Middle East’ piece is an August 21, 2017 post about rainmaking at the Masdar Institute in United Arab Emirates. Approximately 50% of the way down the posting, I mention Israel and Palestine’s conflict over water.

Yarns that harvest and generate energy

The researchers involved in this work are confident enough about their prospects that they will be  patenting their research into yarns. From an August 25, 2017 news item on Nanowerk,

An international research team led by scientists at The University of Texas at Dallas and Hanyang University in South Korea has developed high-tech yarns that generate electricity when they are stretched or twisted.

In a study published in the Aug. 25 [2017] issue of the journal Science (“Harvesting electrical energy from carbon nanotube yarn twist”), researchers describe “twistron” yarns and their possible applications, such as harvesting energy from the motion of ocean waves or from temperature fluctuations. When sewn into a shirt, these yarns served as a self-powered breathing monitor.

“The easiest way to think of twistron harvesters is, you have a piece of yarn, you stretch it, and out comes electricity,” said Dr. Carter Haines, associate research professor in the Alan G. MacDiarmid NanoTech Institute at UT Dallas and co-lead author of the article. The article also includes researchers from South Korea, Virginia Tech, Wright-Patterson Air Force Base and China.

An August 25, 2017 University of Texas at Dallas news release, which originated the news item, expands on the theme,

Yarns Based on Nanotechnology

The yarns are constructed from carbon nanotubes, which are hollow cylinders of carbon 10,000 times smaller in diameter than a human hair. The researchers first twist-spun the nanotubes into high-strength, lightweight yarns. To make the yarns highly elastic, they introduced so much twist that the yarns coiled like an over-twisted rubber band.

In order to generate electricity, the yarns must be either submerged in or coated with an ionically conducting material, or electrolyte, which can be as simple as a mixture of ordinary table salt and water.

“Fundamentally, these yarns are supercapacitors,” said Dr. Na Li, a research scientist at the NanoTech Institute and co-lead author of the study. “In a normal capacitor, you use energy — like from a battery — to add charges to the capacitor. But in our case, when you insert the carbon nanotube yarn into an electrolyte bath, the yarns are charged by the electrolyte itself. No external battery, or voltage, is needed.”

When a harvester yarn is twisted or stretched, the volume of the carbon nanotube yarn decreases, bringing the electric charges on the yarn closer together and increasing their energy, Haines said. This increases the voltage associated with the charge stored in the yarn, enabling the harvesting of electricity.

Stretching the coiled twistron yarns 30 times a second generated 250 watts per kilogram of peak electrical power when normalized to the harvester’s weight, said Dr. Ray Baughman, director of the NanoTech Institute and a corresponding author of the study.

“Although numerous alternative harvesters have been investigated for many decades, no other reported harvester provides such high electrical power or energy output per cycle as ours for stretching rates between a few cycles per second and 600 cycles per second.”

Lab Tests Show Potential Applications

In the lab, the researchers showed that a twistron yarn weighing less than a housefly could power a small LED, which lit up each time the yarn was stretched.

To show that twistrons can harvest waste thermal energy from the environment, Li connected a twistron yarn to a polymer artificial muscle that contracts and expands when heated and cooled. The twistron harvester converted the mechanical energy generated by the polymer muscle to electrical energy.

“There is a lot of interest in using waste energy to power the Internet of Things, such as arrays of distributed sensors,” Li said. “Twistron technology might be exploited for such applications where changing batteries is impractical.”

The researchers also sewed twistron harvesters into a shirt. Normal breathing stretched the yarn and generated an electrical signal, demonstrating its potential as a self-powered respiration sensor.

“Electronic textiles are of major commercial interest, but how are you going to power them?” Baughman said. “Harvesting electrical energy from human motion is one strategy for eliminating the need for batteries. Our yarns produced over a hundred times higher electrical power per weight when stretched compared to other weavable fibers reported in the literature.”

Electricity from Ocean Waves

“In the lab we showed that our energy harvesters worked using a solution of table salt as the electrolyte,” said Baughman, who holds the Robert A. Welch Distinguished Chair in Chemistry in the School of Natural Sciences and Mathematics. “But we wanted to show that they would also work in ocean water, which is chemically more complex.”

In a proof-of-concept demonstration, co-lead author Dr. Shi Hyeong Kim, a postdoctoral researcher at the NanoTech Institute, waded into the frigid surf off the east coast of South Korea to deploy a coiled twistron in the sea. He attached a 10 centimeter-long yarn, weighing only 1 milligram (about the weight of a mosquito), between a balloon and a sinker that rested on the seabed.

Every time an ocean wave arrived, the balloon would rise, stretching the yarn up to 25 percent, thereby generating measured electricity.

Even though the investigators used very small amounts of twistron yarn in the current study, they have shown that harvester performance is scalable, both by increasing twistron diameter and by operating many yarns in parallel.

“If our twistron harvesters could be made less expensively, they might ultimately be able to harvest the enormous amount of energy available from ocean waves,” Baughman said. “However, at present these harvesters are most suitable for powering sensors and sensor communications. Based on demonstrated average power output, just 31 milligrams of carbon nanotube yarn harvester could provide the electrical energy needed to transmit a 2-kilobyte packet of data over a 100-meter radius every 10 seconds for the Internet of Things.”

Researchers from the UT Dallas Erik Jonsson School of Engineering and Computer Science and Lintec of America’s Nano-Science & Technology Center also participated in the study.

The investigators have filed a patent on the technology.

In the U.S., the research was funded by the Air Force, the Air Force Office of Scientific Research, NASA, the Office of Naval Research and the Robert A. Welch Foundation. In Korea, the research was supported by the Korea-U.S. Air Force Cooperation Program and the Creative Research Initiative Center for Self-powered Actuation of the National Research Foundation and the Ministry of Science.

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

Harvesting electrical energy from carbon nanotube yarn twist by Shi Hyeong Kim, Carter S. Haines, Na Li, Keon Jung Kim, Tae Jin Mun, Changsoon Choi, Jiangtao Di, Young Jun Oh, Juan Pablo Oviedo, Julia Bykova, Shaoli Fang, Nan Jiang, Zunfeng Liu, Run Wang, Prashant Kumar, Rui Qiao, Shashank Priya, Kyeongjae Cho, Moon Kim, Matthew Steven Lucas, Lawrence F. Drummy, Benji Maruyama, Dong Youn Lee, Xavier Lepró, Enlai Gao, Dawood Albarq, Raquel Ovalle-Robles, Seon Jeong Kim, Ray H. Baughman. Science 25 Aug 2017: Vol. 357, Issue 6353, pp. 773-778 DOI: 10.1126/science.aam8771

This paper is behind a paywall.

Dexter Johnson in an Aug. 25, 2017 posting on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website) delves further into the research,

“Basically what’s happening is when we stretch the yarn, we’re getting a change in capacitance of the yarn. It’s that change that allows us to get energy out,” explains Carter Haines, associate research professor at UT Dallas and co-lead author of the paper describing the research, in an interview with IEEE Spectrum.

This makes it similar in many ways to other types of energy harvesters. For instance, in other research, it has been demonstrated—with sheets of rubber with coated electrodes on both sides—that you can increase the capacitance of a material when you stretch it and it becomes thinner. As a result, if you have charge on that capacitor, you can change the voltage associated with that charge.

“We’re more or less exploiting the same effect but what we’re doing differently is we’re using an electric chemical cell to do this,” says Haines. “So we’re not changing double layer capacitance in normal parallel plate capacitors. But we’re actually changing the electric chemical capacitance on the surface of a super capacitor yarn.”

While there are other capacitance-based energy harvesters, those other devices require extremely high voltages to work because they’re using parallel plate capacitors, according to Haines.

Dexter asks good questions and his post is very informative.

Making spider silk stronger by feeding graphene and carbon nanotubes to spiders

Spider silk is already considered a strong and tough material but now scientists have found a way to enhance those properties. From an August 15, 2017 Institute of Physics Publishing press release (also on EurekAlert),

…  researchers in Italy and the UK have found a way to make Spidey’s silk a lot stronger, using various different spider species and carbon nanotubes or graphene.

The research team, led by Professor Nicola Pugno at the University of Trento, Italy, succeeded in having their spiders produce silk with up to three times the strength and ten times the toughness of the regular material.

Their discovery, published today in the journal 2D Materials, could pave the way for a new class of bionicomposites, with a wide variety of uses.

Professor Pugno said: “Humans have used silkworm silks widely for thousands of years, but recently research has focussed on spider silk, as it has extremely promising mechanical properties. It is among the best spun polymer fibres in terms of tensile strength, ultimate strain, and especially toughness, even when compared to synthetic fibres such as Kevlar.

“We already know that there are biominerals present in in the protein matrices and hard tissues of insects, which gives them high strength and hardness in their jaws, mandibles and teeth, for example. So our study looked at whether spider silk’s properties could be ‘enhanced’ by artificially incorporating various different nanomaterials into the silk’s biological protein structures.”

To do this, the team exposed three different spider species to water dispersions containing carbon nanotubes or graphene.

After collecting the spiders’ silk, the team tested its tensile strength and toughness.

Professor Pugno said: “We found that the strongest silk the spiders spun had a fracture strength up to 5.4 gigapascals (GPa), and a toughness modulus up to 1,570 joules per gram (J/g). Normal spider silk, by comparison, has a fracture strength of around 1.5 GPa and a toughness modulus of around 150 J/g.

“This is the highest fibre toughness discovered to date, and a strength comparable to that of the strongest carbon fibres or limpet teeth. These are still early days, but our results are a proof of concept that paves the way to exploiting the naturally efficient spider spinning process to produce reinforced bionic silk fibres, thus further improving one of the most promising strong materials.

“These silks’ high toughness and resistance to ultimate strain could have applications such as parachutes.”

“Furthermore, this process of the natural integration of reinforcements in biological structural materials could also be applied to other animals and plants, leading to a new class of “bionicomposites” for innovative applications.”

Remember this? “You are what you eat.” If you’ve ever had doubts about that saying, these spiders should be laying them to rest.

Sadly, this news release doesn’t explain much about the decision to feed the spiders graphene or carbon nanotubes, which are identical other than in their respective shapes (sheet vs tube)  and whether those shapes did or did not affect the strength of the silk.

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

Spider silk reinforced by graphene or carbon nanotubes by Emiliano Lepore, Federico Bosia, Francesco Bonaccorso, Matteo Bruna, Simone Taioli, Giovanni Garberoglio, Andrea C Ferrari, and Nicola Maria Pugno. 2D Materials, Volume 4, Number 3 DOI: https://doi.org/10.1088/2053-1583/aa7cd3 Published 14 August 2017

© 2017 IOP Publishing Ltd

This paper is behind a paywall.

Pugno was most recently mentioned here in a May 29, 2015 posting where he was listed as an author for a paper on synthesizing spider silk. Prior to 2015 I was familiar with Pugno’s name due to his work on adhesiveness in geckos.

Carbon nanotubes to repair nerve fibres (cyborg brains?)

Can cyborg brains be far behind now that researchers are looking at ways to repair nerve fibers with carbon nanotubes (CNTs)? A June 26, 2017 news item on ScienceDaily describes the scheme using carbon nanotubes as a material for repairing nerve fibers,

Carbon nanotubes exhibit interesting characteristics rendering them particularly suited to the construction of special hybrid devices — consisting of biological issue and synthetic material — planned to re-establish connections between nerve cells, for instance at spinal level, lost on account of lesions or trauma. This is the result of a piece of research published on the scientific journal Nanomedicine: Nanotechnology, Biology, and Medicine conducted by a multi-disciplinary team comprising SISSA (International School for Advanced Studies), the University of Trieste, ELETTRA Sincrotrone and two Spanish institutions, Basque Foundation for Science and CIC BiomaGUNE. More specifically, researchers have investigated the possible effects on neurons of the interaction with carbon nanotubes. Scientists have proven that these nanomaterials may regulate the formation of synapses, specialized structures through which the nerve cells communicate, and modulate biological mechanisms, such as the growth of neurons, as part of a self-regulating process. This result, which shows the extent to which the integration between nerve cells and these synthetic structures is stable and efficient, highlights the great potentialities of carbon nanotubes as innovative materials capable of facilitating neuronal regeneration or in order to create a kind of artificial bridge between groups of neurons whose connection has been interrupted. In vivo testing has actually already begun.

The researchers have included a gorgeous image to illustrate their work,

Caption: Scientists have proven that these nanomaterials may regulate the formation of synapses, specialized structures through which the nerve cells communicate, and modulate biological mechanisms, such as the growth of neurons, as part of a self-regulating process. Credit: Pixabay

A June 26, 2017 SISSA press release (also on EurekAlert), which originated the news item, describes the work in more detail while explaining future research needs,

“Interface systems, or, more in general, neuronal prostheses, that enable an effective re-establishment of these connections are under active investigation” explain Laura Ballerini (SISSA) and Maurizio Prato (UniTS-CIC BiomaGUNE), coordinating the research project. “The perfect material to build these neural interfaces does not exist, yet the carbon nanotubes we are working on have already proved to have great potentialities. After all, nanomaterials currently represent our best hope for developing innovative strategies in the treatment of spinal cord injuries”. These nanomaterials are used both as scaffolds, a supportive framework for nerve cells, and as means of interfaces releasing those signals that empower nerve cells to communicate with each other.

Many aspects, however, still need to be addressed. Among them, the impact on neuronal physiology of the integration of these nanometric structures with the cell membrane. “Studying the interaction between these two elements is crucial, as it might also lead to some undesired effects, which we ought to exclude”. Laura Ballerini explains: “If, for example, the mere contact provoked a vertiginous rise in the number of synapses, these materials would be essentially unusable”. “This”, Maurizio Prato adds, “is precisely what we have investigated in this study where we used pure carbon nanotubes”.

The results of the research are extremely encouraging: “First of all we have proved that nanotubes do not interfere with the composition of lipids, of cholesterol in particular, which make up the cellular membrane in neurons. Membrane lipids play a very important role in the transmission of signals through the synapses. Nanotubes do not seem to influence this process, which is very important”.

There is more, however. The research has also highlighted the fact that the nerve cells growing on the substratum of nanotubes, thanks to this interaction, develop and reach maturity very quickly, eventually reaching a condition of biological homeostasis. “Nanotubes facilitate the full growth of neurons and the formation of new synapses. This growth, however, is not indiscriminate and unlimited since, as we proved, after a few weeks a physiological balance is attained. Having established the fact that this interaction is stable and efficient is an aspect of fundamental importance”. Maurizio Prato and Laura Ballerini conclude as follows: “We are proving that carbon nanotubes perform excellently in terms of duration, adaptability and mechanical compatibility with the tissue. Now we know that their interaction with the biological material, too, is efficient. Based on this evidence, we are already studying the in vivo application, and preliminary results appear to be quite promising also in terms of recovery of the lost neurological functions”.

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

Sculpting neurotransmission during synaptic development by 2D nanostructured interfaces by Niccolò Paolo Pampaloni, Denis Scaini, Fabio Perissinotto, Susanna Bosi, Maurizio Prato, Laura Ballerini. Nanomedicine: Nanotechnology, Biology and Medicine, DOI: http://dx.doi.org/10.1016/j.nano.2017.01.020 Published online: May 25, 2017

This paper is open access.