Tag Archives: sea stars

Spider glue

Caption: An orb spider, glue-maker extraordinaire, at work on a web. Credit: The University of Akron

Scientists are taking inspiration from spiders in their quest to develop better adhesives. (Are they abandoning the gecko? Usually when scientists study adhesiveness, there’s talk of geckos. From a June 5, 2018 news item on ScienceDaily,

Ever wonder why paint peels off the wall during summer’s high humidity? It’s the same reason that bandages separate from skin when we bathe or swim.

Interfacial water, as it’s known, forms a slippery and non-adhesive layer between the glue and the surface to which it is meant to stick, interfering with the formation of adhesive bonds between the two.

Overcoming the effects of interfacial water is one of the challenges facing developers of commercial adhesives.

To find a solution, researchers at The University of Akron (UA) are looking to one of the strongest materials found in nature: spider silk.

The sticky glue that coats the silk threads of spider webs is a hydrogel, meaning it is full of water. One would think, then, that spiders would have difficulty catching prey, especially in humid conditions — but they do not. In fact, their sticky glue, which has been a subject of intensive research for years, is one of the most effective biological glues in all of nature.

A June 4, 2018 University of Akron news release (also on EurekAlert published on June 5, 2018), which originated the news item, provides more detail,

So how is spider glue able to stick in highly humid conditions?

That question was the subject of investigation by UA graduate students Saranshu Singla, Gaurav Amarpuri and Nishad Dhopatkar, who have been working with Dr. Ali Dhinojwala, interim dean of the College of Polymer Science and Polymer Engineering, and Dr. Todd Blackledge, professor of biology in the Integrated Bioscience program. Both professors are principal investigators in UA’s Biomimicry Research Innovation Center [BRIC], which specializes in emulating biological forms, processes, patterns and systems to solve technical challenges.

The team’s findings, which may provide the clue to developing stronger commercial adhesives, can be read in a paper recently published in the journal Nature Communications.

Singla and her colleagues set out to examine the secret behind the success of the common orb spider (Larinioides cornutus) glue and uncover how it overcomes the primary obstacle of achieving good adhesion in the humid conditions where water could be present between the glue and the target surface.

To investigate the processes involved, the team took orb spider glue, set it on sapphire substrate, then examined it using a combination of interface-sensitive spectroscopy and infrared spectroscopy.

Spider glue is made of three elements: two specialized glycoproteins, a collection of low molecular mass organic and inorganic compounds (LMMCs), and water. The LMMCs are hygroscopic (water-attracting), which keeps the glue soft and tacky to stick.

Singla and her team discovered that these glycoproteins act as primary binding agents to the surface. Glycoprotein-based glues have been identified in several other biological glues, such as fungi, algae, diatoms, sea stars, sticklebacks and English ivy.

But why doesn’t the water present in the spider glue interfere with the adhesive contact the way it does with most synthetic adhesives?

The LMMCs, the team concluded, perform a previously unknown function of sequestering interfacial water, preventing adhesive failure.

Singla and colleagues determined that it is the interaction of glycoproteins and LMMCs that governs the adhesive quality of the glue produced, with the respective proportions varying across species, thus optimizing adhesive strength to match the relative humidity of spider habitat.

“The hygroscopic compounds – known as water-absorbers – in spider glue play a previously unknown role in moving water away from the boundary, thereby preventing failure of spider glue at high humidity,” explained Singla.

The ability of the spider glue to overcome the problem of interfacial water by effectively absorbing it is the key finding of the research, and the one with perhaps the strongest prospect for commercial development.

“Imagine a paint that is guaranteed for life, come rain or shine,” Singla remarked.

All thanks to your friendly neighborhood spider glue.

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

Hygroscopic compounds in spider aggregate glue remove interfacial water to maintain adhesion in humid conditions by Saranshu Singla, Gaurav Amarpuri, Nishad Dhopatkar, Todd A. Blackledge, & Ali Dhinojwala. Nature Communicationsvolume 9, Article number: 1890 (2018) Published 22 May 2018 DOI: https://doi.org/10.1038/s41467-018-04263-z

This paper is open access.

Like a starfish shell, facetless crystals

Made by accident, these facetless crystals could prove useful in applications for cells, medications, and more according to researchers at the University of Michigan in an Oct. 20, 2014 news item on Nanowerk,

In a design that mimics a hard-to-duplicate texture of starfish shells, University of Michigan engineers have made rounded crystals that have no facets.

“We call them nanolobes. They look like little hot air balloons that are rising from the surface,” said Olga Shalev, a doctoral student in materials science and engineering who worked on the project.

There is a video with the researcher, Olga Shalev, describing the nanolobes in more detail,

An Oct. 17, 2014 University of Michigan news release (also on EurekAlert*), which originated the news item, offers text for those who prefer to read about the science rather than receive it by video,

Both the nanolobes’ shape and the way they’re made have promising applications, the researchers say. The geometry could potentially be useful to guide light in advanced LEDs, solar cells and nonreflective surfaces. A layer might help a material repel water or dirt. And the process used to manufacture them – organic vapor jet printing – might lend itself to 3D-printing medications that absorb better into the body and make personalized dosing possible.

The nanoscale shapes are made out of boron subphthalocyanine chloride, a material often used in organic solar cells. It’s in a family of small molecular compounds that tend to make either flat films or faceted crystals with sharp edges, says Max Shtein, an associate professor of materials science and engineering, macromolecular science and engineering, chemical engineering, and art and design.

“In my years of working with these kinds of materials, I’ve never seen shapes that looked like these. They’re reminiscent of what you get from biological processes,” Shtein said. “Nature can sometimes produce crystals that are smooth, but engineers haven’t been able to do it reliably.”

Echinoderm sea creatures such as brittle stars have ordered rounded structures on their bodies that work as lenses to gather light into their rudimentary eyes. But in a lab, crystals composed of the same minerals tend either to be faceted with flat faces and sharp angles, or smooth, but lacking molecular order.

The U-M researchers made the curved crystals by accident several years ago. They’ve since traced their steps and figured out how to do it on purpose.

In 2010, Shaurjo Biswas, then a doctoral student at U-M, was making solar cells with the organic vapor jet printer. He was recalibrating the machine after switching between materials. Part of the recalibration process involves taking a close look at the fresh layers of material, of films, printed on a plate. Biswas X-rayed several films of different thicknesses to observe the crystal structure. He noticed that the boron subphthalocyanine chloride, which typically does not form ordered shapes, started to do so once the film got thicker than 600 nanometers. He made some thicker films to see what would happen.

“At first, we wondered if our apparatus was functioning properly,” Shtein said.

At 800 nanometers thick, the repeating nanolobe pattern emerged every time.

For a long while, the blobs were lab curiosities. Researchers were focused on other things. Then doctoral student Shalev got involved. She was fascinated by the structures and wanted to understand the reason for the phenomenon. She repeated the experiments in a modified apparatus that gave more control over the conditions to vary them systematically. She collaborated with physics professor Roy Clarke to gain a better understanding of the crystallization, and mechanical engineering professor Wei Lu to simulate the evolution of the surface.. She’s first author of a paper on the findings published in the current edition of Nature Communications.

“As far as we know, no other technology can do this,” Shalev said.

The organic vapor jet printing process the researchers use is a technique Shtein helped to develop when he was in graduate school. He describes it as spray painting, but with a gas rather than with a liquid. It’s cheaper and easier to do for certain applications than competing approaches that involve stencils or can only be done in a vacuum, Shtein says. He’s especially hopeful about the prospects for this technique to advance emerging 3D-printed pharmaceutical concepts.

For example, Shtein and Shalev believe this method offers a precise way to control the size and shape of the medicine particles, for easier absorption into the body. It could also allow drugs to be attached directly to other materials and it doesn’t require solvents that might introduce impurities.

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

Growth and modelling of spherical crystalline morphologies of molecular materials by O. Shalev, S. Biswas, Y. Yang, T. Eddir, W. Lu, R. Clarke,  & M. Shtein. Nature Communications 5, Article number: 5204 doi:10.1038/ncomms6204 Published 16 October 2014

This paper is behind a paywall.

* EurekAlert link added on Oct. 20, 2014 at 1035 hours PDT.