Tag Archives: mussels

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.