Tag Archives: mussels

Mussels to muscles for biocompatible fibres

Mussels and barnacles in the intertidal near Newquay, Cornwall, England.
Wilson44691 at English Wikipedia – Photograph taken by Mark A. Wilson (Department of Geology, The College of Wooster

I love puns and word play so I was happy to see this in a June 9, 2017 news item on ScienceDaily,

Rice University chemists can thank the mussel for putting the muscle into their new macroscale scaffold fibers.

A June 9, 2017 Rice University news release (also on EurekAlert), which originated the news item, provides more details about the research,

The Rice lab of chemist Jeffrey Hartgerink had already figured out how to make biocompatible nanofibers out of synthetic peptides. In new work, the lab is using an amino acid found in the sticky feet of mussels to make those fibers line up into strong hydrogel strings.

Hartgerink and Rice graduate student I-Che Li introduced their room-temperature method this month in an open-access paper in the Journal of the American Chemical Society.

The hydrogel strings can be picked up and moved with tweezers, and Li said he expects they will help labs gain better control over the growth of cell cultures.

“Usually when cells grow on a surface, they spread randomly,” he said. “There are a lot of biomaterials we want to grow in a specific direction. With the hydrogel scaffold aligned, we can expect cells to grow the way we want them to. One example would be neuron cells, which we want to grow head-to-tail to aid nerve regeneration.

“Basically, this could allow us to direct cell growth from here to there,” he said. “That’s why this material is so exciting.”

In previous research Hartgerink’s lab had developed synthetic hydrogels that could be injected into the body to serve as scaffolds for tissue growth. The hydrogels contained hydrophobic peptides that self-assembled into fibers about 6 nanometers wide and up to several microns long. However, because the fibers did not interact with one other, they generally appeared in microscope images as a tangled mass.

Experiments showed the fibers could be coaxed into alignment with the application of shear forces, in the same way that playing cards are aligned during shuffling by pushing on both the top and bottom of the deck.

Hartgerink and Li decided to try pushing the fibers through a needle to force them into alignment, a process that would be easier if the material was water soluble. So they added a chain of amino acids known as DOPA to the sides of the fibers to allow them to remain water-soluble in the syringe, Li said.

DOPA — short for 3,4-dihydroxyphenylalanine — is the compound that lets mussels stick to just about anything. Hartgerink and Li found that the combination of DOPA and shear stress from passing through the needle prompted the fibers to form visible, rope-like bundles.

They also found that DOPA promoted chemical cross-linking reactions that helped the bundles hold their shape. “DOPA is really sensitive to oxidizing agents,” Li said. “Even exposing DOPA to air oxidizes it, and that aids in cross-linking the fibers.”

As a bonus, the aligned fibers also proved to have a curious and useful optical property called “uniform birefringence,” or double-refraction. Li said this could allow researchers to use polarized light to see exactly where the aligned fibers are, even if they’re covered by cells.

“This will be an important technique for us to make sure of the long-range order of fiber alignment when we are testing directed cell growth,” he said.

The researchers expect the aligned fibers can be used for macroscale medical applications but with nanoscale control over the structures.

“Self-assembly is basically the ability of a molecule to make ordered structure from chaos, and what I-Che has done is push this organization to a new level with his aligned strings,” said Hartgerink, a professor of chemistry and of bioengineering. “With this material, we are excited to see if we can impose this organization onto the growth of cells that interact with it.”

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

Covalent Capture of Aligned Self-Assembling Nanofibers by I-Che Li and Jeffrey D. Hartgerink. J. Am. Chem. Soc., Article ASAP DOI: 10.1021/jacs.7b04655 Publication Date (Web): June 5, 2017

Copyright © 2017 American Chemical Society

This paper is open access.

Ocean-inspired coatings for organic electronics

An Oct. 19, 2016 news item on phys.org describes the advantages a new coating offers and the specific source of inspiration,

In a development beneficial for both industry and environment, UC Santa Barbara [University of California at Santa Barbara] researchers have created a high-quality coating for organic electronics that promises to decrease processing time as well as energy requirements.

“It’s faster, and it’s nontoxic,” said Kollbe Ahn, a research faculty member at UCSB’s Marine Science Institute and corresponding author of a paper published in Nano Letters.

In the manufacture of polymer (also known as “organic”) electronics—the technology behind flexible displays and solar cells—the material used to direct and move current is of supreme importance. Since defects reduce efficiency and functionality, special attention must be paid to quality, even down to the molecular level.

Often that can mean long processing times, or relatively inefficient processes. It can also mean the use of toxic substances. Alternatively, manufacturers can choose to speed up the process, which could cost energy or quality.

Fortunately, as it turns out, efficiency, performance and sustainability don’t always have to be traded against each other in the manufacture of these electronics. Looking no further than the campus beach, the UCSB researchers have found inspiration in the mollusks that live there. Mussels, which have perfected the art of clinging to virtually any surface in the intertidal zone, serve as the model for a molecularly smooth, self-assembled monolayer for high-mobility polymer field-effect transistors—in essence, a surface coating that can be used in the manufacture and processing of the conductive polymer that maintains its efficiency.

An Oct. 18, 2016 UCSB news release by Sonia Fernandez, which originated the news item, provides greater technical detail,

More specifically, according to Ahn, it was the mussel’s adhesion mechanism that stirred the researchers’ interest. “We’re inspired by the proteins at the interface between the plaque and substrate,” he said.

Before mussels attach themselves to the surfaces of rocks, pilings or other structures found in the inhospitable intertidal zone, they secrete proteins through the ventral grove of their feet, in an incremental fashion. In a step that enhances bonding performance, a thin priming layer of protein molecules is first generated as a bridge between the substrate and other adhesive proteins in the plaques that tip the byssus threads of their feet to overcome the barrier of water and other impurities.

That type of zwitterionic molecule — with both positive and negative charges — inspired by the mussel’s native proteins (polyampholytes), can self-assemble and form a sub-nano thin layer in water at ambient temperature in a few seconds. The defect-free monolayer provides a platform for conductive polymers in the appropriate direction on various dielectric surfaces.

Current methods to treat silicon surfaces (the most common dielectric surface), for the production of organic field-effect transistors, requires a batch processing method that is relatively impractical, said Ahn. Although heat can hasten this step, it involves the use of energy and increases the risk of defects.

With this bio-inspired coating mechanism, a continuous roll-to-roll dip coating method of producing organic electronic devices is possible, according to the researchers. It also avoids the use of toxic chemicals and their disposal, by replacing them with water.

“The environmental significance of this work is that these new bio-inspired primers allow for nanofabrication on silicone dioxide surfaces in the absence of organic solvents, high reaction temperatures and toxic reagents,” said co-author Roscoe Lindstadt, a graduate student researcher in UCSB chemistry professor Bruce Lipshutz’s lab. “In order for practitioners to switch to newer, more environmentally benign protocols, they need to be competitive with existing ones, and thankfully device performance is improved by using this ‘greener’ method.”

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

Molecularly Smooth Self-Assembled Monolayer for High-Mobility Organic Field-Effect Transistors by Saurabh Das, Byoung Hoon Lee, Roscoe T. H. Linstadt, Keila Cunha, Youli Li, Yair Kaufman, Zachary A. Levine, Bruce H. Lipshutz, Roberto D. Lins, Joan-Emma Shea, Alan J. Heeger, and B. Kollbe Ahn. Nano Lett., 2016, 16 (10), pp 6709–6715
DOI: 10.1021/acs.nanolett.6b03860 Publication Date (Web): September 27, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall but the scientists have made an illustration available,

An artist's concept of a zwitterionic molecule of the type secreted by mussels to prime surfaces for adhesion Photo Credit: Peter Allen

An artist’s concept of a zwitterionic molecule of the type secreted by mussels to prime surfaces for adhesion Photo Credit: Peter Allen

Inspiration from the sea for titanium implants (mussels) and adhesive panels for flexible sensors (octopuses/octopi/octopodes)

I have two sea-inspired news bits both of which concern adhesion.

Mussels and titanium implants

A July 8, 2016 news item on ScienceDaily features some mussel-inspired research from Japan into how to make better titanium implants,

Titanium is used medically in applications such as artificial joints and dental implants. While it is strong and is not harmful to tissues, the metal lacks some of the beneficial biological properties of natural tissues such as bones and natural teeth. Now, based on insights from mussels–which are able to attach themselves very tightly to even metallic surfaces due to special proteins found in their byssal threads–scientists from RIKEN have successfully attached a biologically active molecule to a titanium surface, paving the way for implants that can be more biologically beneficial.

A July 11, 2016 RIKEN press release (also on EurekAlert but dated July 8, 2016), which originated the news item, provides more information,

The work began from earlier discoveries that mussels can attach to smooth surfaces so effectively thanks to a protein, L-DOPA, which is known to be able to bind very strongly to smooth surfaces such as rocks, ceramics, or metals (…). Interestingly, the same protein functions in humans as a precursor to dopamine, and is used as a treatment for Parkinson’s disease.

According to Chen Zhang of the RIKEN Nano Medical Engineering Laboratory, the first author of the paper published in Angewandte Chemie, “We thought it would be interesting to try to use various techniques to attach a biologically active protein—in our case we chose insulin-like growth factor-1, a promoter of cell proliferation—to a titanium surface like those used in implants” (…).

Using a combination of recombinant DNA technology and treatment with tyrosinase, they were able to create a hybrid protein that contained active parts of both the growth factor and L-DOPA. Tests showed that the proteins were able to fold normally, and further experiments in cell cultures demonstrated that the IGF-1 was still functioning normally. Thanks to the incorporation of the L-DOPA, the team was able to confirm that the proteins bound strongly to the titanium surface, and remained attached even when the metal was washed with phosphate-buffered saline, a water-based solution. Zhang says, “This is similar to the powerful properties of mussel adhesive, which can remain fixed to metallic materials even underwater.”

According to Yoshihiro Ito, Team Leader of the Emergent Bioengineering Research Team of the RIKEN Center for Emergent Matter Science, “We are very excited by this finding, because the modification process is a universal one that could be used with other proteins. It could allow us to prepare new cell-growth enhancing materials, with potential applications in cell culture systems and regenerative medicine. And it is particularly interesting that this is an example of biomimetics, where nature can teach us new ways to do things. The mussel has given us insights that could be used to allow us to live healthier lives.”

The work was done by RIKEN researchers in collaboration with Professor Peibiao Zhang of the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, and Professor Yi Wang of the School of Pharmaceutical Sciences, Jilin University. The work was partially supported by the Japan Society for the Promotion of Science KAKENHI (Grant Number 15H01810 and 22220009), CAS-JSPS joint fund (GJHZ1519), and RIKEN MOST joint project.

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

A Bioorthogonal Approach for the Preparation of a Titanium-Binding Insulin-like Growth-Factor-1 Derivative by using Tyrosinase by Chen Zhang, Hideyuki Miyatake, Yu Wang, Takehiko Inaba, Yi Wang, Peibiao Zhang, and Prof. Yoshihiro Ito. Angewandte Chemie International Edition DOI: 10.1002/anie.201603155 Version of Record online: 6 JUL 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Octopuses/octopi/octopodes and adhesive panels

Before launching into the science part of this news bit, here’s some grammar (from the Octopus Wikipedia entry; Note: Links have been removed),

The standard pluralized form of “octopus” in the English language is “octopuses” /ˈɒktəpʊsɪz/,[10] although the Ancient Greek plural “octopodes” /ɒkˈtɒpədiːz/, has also been used historically.[9] The alternative plural “octopi” — which misguidedly assumes it is a Latin “-us”-word — is considered grammatically incorrect.[11][12][13][14] It is nevertheless used enough to make it notable, and was formally acknowledged by the descriptivist Merriam-Webster 11th Collegiate Dictionary and Webster’s New World College Dictionary. The Oxford English Dictionary (2008 Draft Revision)[15] lists “octopuses”, “octopi”, and “octopodes”, in that order, labelling “octopodes” as rare and noting that “octopi” derives from the apprehension that octōpus comes from Latin.[16] In contrast, New Oxford American Dictionary (3rd Edition 2010) lists “octopuses” as the only acceptable pluralization, with a usage note indicating “octopodes” as being still occasionally used but “octopi” as being incorrect.[17]

Now the news. A July 12, 2016 news item on Nanowerk highlights some research into adhesives and octopuses,

With increased study of bio-adhesives, a significant effort has been made in search for novel adhesives that will combine reversibility, repeated usage, stronger bonds and faster bonding time, non-toxic, and more importantly be effective in wet and other extreme conditions.

A team of Korean scientists-made up of scientists from Korea Institute of Science and Technology (KIST) and UNIST has recently found a way to make building flexible pressure sensors easier–by mimicking the suction cups on octopus’s tentacles.

A July 5, 2016 UNIST (Ulsan National Institute of Science and Technology) press release, which originated the news item, provides more information,

According to the research team, “Although flexible pressure sensors might give future prosthetics and robots a better sense of touch, building them requires a lot of laborious transferring of nano- and microribbons of inorganic semiconductor materials onto polymer sheets.”

In search of an easier way to process this transfer printing, Prof. Hyunhyub Ko (School of Energy and Chemical Engineering, UNIST) and his colleagues turned to the octopus suction cups for inspiration.

An octopus uses its tentacles to move to a new location and uses suction cups underneath each tentacle to grab onto something. Each suction cup contains a cavity whose pressure is controlled by surrounding muscles. These can be made thinner or thicker on demand, increasing or decreasing air pressure inside the cup, allowing for sucking and releasing as desired.

By mimicking muscle actuation to control cavity-pressure-induced adhesion of octopus suckers, Prof. Ko and his team engineered octopus-inspired smart adhesive pads. They used the rubbery material polydimethylsiloxane (PDMS) to create an array of microscale suckers, which included pores that are coated with a thermally responsive polymer to create sucker-like walls.

The team discovered that the best way to replicate organic nature of muscle contractions would be through applied heat. Indeed, at room temperature, the walls of each pit sit in an ‘open’ state, but when the mat is heated to 32°C, the walls contract, creating suction, therby allowing the entire mate to adhere to a material (mimicking the suction function of an octopus). The adhesive strength also spiked from .32 kilopascals to 94 kilopascals at high temperature.

The team reports that the mat worked as envisioned—they made some indium gallium arsenide transistors that sat on a flexible substrate and also used it to move some nanomaterials to a different type of flexible material.

Prof. Ko and his team expect that their smart adhesive pads can be used as the substrate for wearable health sensors, such as Band-Aids or sensors that stick to the skin at normal body temperatures but fall off when rinsed under cold water.

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

Octopus-Inspired Smart Adhesive Pads for Transfer Printing of Semiconducting Nanomembranes by Hochan Lee, Doo-Seung Um, Youngsu Lee, Seongdong Lim, Hyung-jun Kim,  and Hyunhyub Ko. Advanced Materials DOI: 10.1002/adma.201601407 Version of Record online: 20 JUN 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

The challenges of wet adhesion and how nature solves the problem

I usually post about dry adhesion, that is, sticking to dry surfaces in the way a gecko might. This particular piece concerns wet adhesion, a matter of particular interest in medicine where you want bandages and such to stick to a wet surface and in marine circles where they want barnacles and such to stop adhering to boat and ship hulls.

An Aug. 6, 2015 news item on ScienceDaily touts ‘wet adhesion’ research focused on medicinal matters,

Wet adhesion is a true engineering challenge. Marine animals such as mussels, oysters and barnacles are naturally equipped with the means to adhere to rock, buoys and other underwater structures and remain in place no matter how strong the waves and currents.

Synthetic wet adhesive materials, on the other hand, are a different story.

Taking their cue from Mother Nature and the chemical composition of mussel foot proteins, the Alison Butler Lab at UC [University of California] Santa Barbara [UCSB] decided to improve a small molecule called the siderophore cyclic trichrysobactin (CTC) that they had previously discovered. They modified the molecule and then tested its adhesive strength in aqueous environments. The result: a compound that rivals the staying power of mussel glue.

An Aug. 6, 2015 UCSB news release by Julie Cohen, which originated the news item, describes some of the reasons for the research, the interdisciplinary aspect of the collaboration, and technical details of the work (Note: Links have been removed),

“There’s real need in a lot of environments, including medicine, to be able to have glues that would work in an aqueous environment,” said co-author Butler, a professor in UCSB’s Department of Chemistry and Biochemistry. “So now we have the basis of what we might try to develop from here.”

Also part of the interdisciplinary effort were Jacob Israelachvili’s Interfacial Sciences Lab in UCSB’s Department of Chemical Engineering and J. Herbert Waite, a professor in the Department of Molecular, Cellular and Developmental Biology, whose own work focuses on wet adhesion.

“We just happened to see a visual similarity between compounds in the siderophore CTC and in mussel foot proteins,” Butler explained. Siderophores are molecules that bind and transport iron in microorganisms such as bacteria. “We specifically looked at the synergy between the role of the amino acid lysine and catechol,” she added. “Both are present in mussel foot proteins and in CTC.”
Mussel foot proteins contain similar amounts of lysine and the catechol dopa. Catechols are chemical compounds used in such biological functions as neurotransmission. However, certain proteins have adopted dopa for adhesive purposes.

From discussions with Waite, Butler realized that CTC contained not only lysine but also a compound similar to dopa. Further, CTC paired its catechol with lysine, just like mussel foot proteins do.

“We developed a better, more stable molecule than the actual CTC,” Butler explained. “Then we modified it to tease out the importance of the contributions from either lysine or the catechol.”

Co-lead author Greg Maier, a graduate student in the Butler Lab, created six different compounds with varying amounts of lysine and catechol. The Israelachvili lab tested each compound for its surface and adhesion characteristics. Co-lead author Michael Rapp used a surface force apparatus developed in the lab to measure the interactions between mica surfaces in a saline solution.

Only the two compounds containing a cationic amine, such as lysine, and catechol exhibited adhesive strength and a reduced intervening film thickness, which measures the amount two surfaces can be squeezed together. Compounds without catechol had greatly diminished adhesion levels but a similarly reduced film thickness. Without lysine, the compounds displayed neither characteristic. “Our tests showed that lysine was key, helping to remove salt ions from the surface to allow the glue to get to the underlying surface,” Maier said.

“By looking at a different biosystem that has similar characteristics to some of the best-performing mussel glues, we were able to deduce that these two small components work together synergistically to create a favorable environment at surfaces to promote adherence,” explained Rapp, a chemical engineering graduate student. “Our results demonstrate that these two molecular groups not only prime the surface but also work collectively to build better adhesives that stick to surfaces.”

“In a nutshell, our discovery is that you need lysine and you need the catechol,” Butler concluded. “There’s a one-two punch: the lysine clears and primes the surface and the catechol comes down and hydrogen bonds to the mica surface. This is an unprecedented insight about what needs to happen during wet adhesion.”

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

Adaptive synergy between catechol and lysine promotes wet adhesion by surface salt displacement by Greg P. Maier, Michael V. Rapp, J. Herbert Waite, Jacob N. Israelachvili, and Alison Butler. Science 7 August 2015: Vol. 349 no. 6248 pp. 628-632 DOI: 10.1126/science.aab055

This paper is behind a paywall.

I have previously written about mussels and wet adhesion in a Dec. 13, 2012 posting regarding some research at the University of British Columbia (Canada). As for dry adhesion, there’s my June 11, 2014 posting titled: Climb like a gecko (in DARPA’s [US Defense Advanced Research Projects Agency] Z-Man program) amongst others.

Gluing blood vessels with mussel goo

The University of British Columbia [UBC] Dec. 11, 2012 news release states,

A University of British Columbia researcher has helped create a gel – based on the mussel’s knack for clinging to rocks, piers and boat hulls – that can be painted onto the walls of blood vessels and stay put, forming a protective barrier with potentially life-saving implications.

Co-invented by Assistant Professor Christian Kastrup while a postdoctoral student at the Massachusetts Institute of Technology, the gel is similar to the amino acid that enables mussels to resist the power of churning water. The variant that Kastrup and his collaborators created, described in the current issue of the online journal PNAS [Proceeings of the National Academy of Sciences of the US] Early Edition, can withstand the flow of blood through arteries and veins.

Here’s the citation and a link to the article (which is behind a paywall),

Painting blood vessels and atherosclerotic plaques with an adhesive drug depot by Christian J. Kastrup, Matthias Nahrendorf, Jose Luiz Figueiredo, Haeshin Lee, Swetha Kambhampati, Timothy Lee, Seung-Woo Cho, Rostic Gorbatov, Yoshiko Iwamoto, Tram T. Dang, Partha Dutta, Ju Hun Yeon, Hao Cheng, Christopher D. Pritchard, Arturo J. Vegas, Cory D. Siegel, Samantha MacDougall, Michael Okonkwo, Anh Thai, James R. Stone, Arthur J. Coury, Ralph Weissleder, Robert Langer, and Daniel G. Anderson.  PNAS, December 11, 2012 DOI: 10.1073/pnas.1217972110

For those of a more technical turn of mind, here’s the abstract (from PNAS),

The treatment of diseased vasculature remains challenging, in part because of the difficulty in implanting drug-eluting devices without subjecting vessels to damaging mechanical forces. Implanting materials using adhesive forces could overcome this challenge, but materials have previously not been shown to durably adhere to intact endothelium under blood flow. Marine mussels secrete strong underwater adhesives that have been mimicked in synthetic systems. Here we develop a drug-eluting bioadhesive gel that can be locally and durably glued onto the inside surface of blood vessels. In a mouse model of atherosclerosis, inflamed plaques treated with steroid-eluting adhesive gels had reduced macrophage content and developed protective fibrous caps covering the plaque core. Treatment also lowered plasma cytokine levels and biomarkers of inflammation in the plaque. The drug-eluting devices developed here provide a general strategy for implanting therapeutics in the vasculature using adhesive forces and could potentially be used to stabilize rupture-prone plaques.

The news release describes the work layperson’s terms,

The gel’s “sheer strength” could shore up weakened vessel walls at risk of rupturing – much like the way putty can fill in dents in a wall, says Kastrup, a member of the Department of Biochemistry and Molecular Biology and the Michael Smith Laboratories.

By forming a stable barrier between blood and the vessel walls, the gel could also prevent the inflammation that typically occurs when a stent is inserted to widen a narrowed artery or vein; that inflammation often counteracts the opening of the vessel that the stent was intended to achieve.

The widest potential application would be preventing the rupture of blood vessel plaque. When a plaque ruptures, the resulting clot can block blood flow to the heart (triggering a heart attack) or the brain (triggering a stroke). Mice treated with a combination of the gel and an anti-inflammatory steroid had more stable plaque than a control group of untreated mice.

“By mimicking the mussel’s ability to cling to objects, we created a substance that stays in place in a very dynamic environment with high flow velocities,” says Kastrup, a member of UBC’s Centre for Blood Research.

Robert Langer, one of the paper’s co-authors, was mentioned here in an Aug. 27, 2012 posting about nanoelectronics, tissue engineering, and medicine.

University of Missouri and the US Geological survey study carbon nanotubes in aquatic environments

The University of Missouri’s Aug. 22, 2012 news release (by Timothy Wall) announces the result of a carbon nanotube study in aquatic environments,

A joint study by the University of Missouri and United States Geological Survey found that they [carbon nanotubes or CNTs] can be toxic to aquatic animals. The researchers urge that care be taken to prevent the release of CNTs into the environment as the materials enter mass production.

“The great promise of carbon nanotubes must be balanced with caution and preparation,” said Baolin Deng, professor and chair of chemical engineering at the University of Missouri. “We don’t know enough about their effects on the environment and human health. The EPA and other regulatory groups need more studies like ours to provide information on the safety of CNTs.”

CNTs are microscopically thin cylinders of carbon atoms that can be hundreds of millions of times longer than they are wide, but they are not pure carbon. Nickel, chromium and other metals used in the manufacturing process can remain as impurities. Deng and his colleagues found that these metals and the CNTs themselves can reduce the growth rates or even kill some species of aquatic organisms. The four species used in the experiment were mussels (Villosa iris), small flies’ larvae (Chironomus dilutus), worms (Lumbriculus variegatus) and crustaceans (Hyalella azteca).

“One of the greatest possibilities of contamination of the environment by CNTs comes during the manufacture of composite materials,” said Hao Li, associate professor of mechanical and aerospace engineering at MU. “Good waste management and handling procedures can minimize this risk. Also, to control long-term risks, we need to understand what happens when these composite materials break down.”

I found the abstract for the team’s paper gave a good overview of how the research was conducted,

Carbon nanotubes (CNTs) are hydrophobic in nature and thus tend to accumulate in sediments if released into aquatic environments. As part of our overall effort to examine the toxicity of carbon-based nanomaterials to sediment-dwelling invertebrates, we have evaluated the toxicity of different types of CNTs in 14-d water-only exposures to an amphipod (Hyalella azteca), a midge (Chironomus dilutus), an oligochaete (Lumbriculus variegatus), and a mussel (Villosa iris) in advance of conducting whole-sediment toxicity tests with CNTs. The results of these toxicity tests conducted with CNTs added to water showed that 1.00 g/L (dry wt) of commercial sources of CNTs significantly reduced the survival or growth of the invertebrates. Toxicity was influenced by the type and source of the CNTs, by whether the materials were precleaned by acid, by whether sonication was used to disperse the materials, and by species of the test organisms. Light and electron microscope imaging of the surviving test organisms showed the presence of CNTs in the gut as well as on the outer surface of the test organisms, although no evidence was observed to show penetration of CNTs through cell membranes. The present study demonstrated that both the metals solubilized from CNTs such as nickel and the “metal-free” CNTs contributed to the toxicity.

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

Toxicity of carbon nanotubes to freshwater aquatic invertebrates by Joseph N. Mwangi, Ning Wang, Christopher G. Ingersoll, Doug K. Hardesty, Eric L. Brunson, Hao Li, and Baolin Deng in Environmental Toxicology and Chemistry, Volume 31, Issue 8, pages 1823–1830, August 2012

For anyone who’s curious about what carbon nanotubes look like, here’s an image provided by the University of MIssouri,

Carbon Nanotubes Credit: Shaddack, Wikimedia Commons
Multi-walled carbon nanotubes. 3-15 walls, mean inner diameter 4nm, mean outer diameter 13-16 nm, length 1-10+ micrometers. Black clumpy powder, grains shown, partially smeared on paper. Scale in centimeters.

I could have included a larger version of the image but, given that we’re talking about the nanoscale, the smaller image seems more appropriate.