Tag Archives: dragline silk

Spider silk as a bio super-lens

Bangor University (Wales, UK) is making quite the impact these days. I’d never heard of the institution until their breakthrough with nanobeads (Sept. 7, 2016 posting) to break through a resolution barrier and now there’s a second breakthrough with their partners at Oxford University (England, UK). From an Aug. 19, 2016 news item on ScienceDaily (Note: A link has been removed),

Scientists at the UK’s Bangor and Oxford universities have achieved a world first: using spider-silk as a superlens to increase the microscope’s potential.

Extending the limit of classical microscope’s resolution has been the ‘El Dorado’ or ‘Holy Grail’ of microscopy for over a century. Physical laws of light make it impossible to view objects smaller than 200 nm — the smallest size of bacteria, using a normal microscope alone. However, superlenses which enable us to see beyond the current magnification have been the goal since the turn of the millennium.

Hot on the heels of a paper (Sci. Adv. 2 e1600901,2016) revealing that a team at Bangor University’s School of Electronic Engineering has used a nanobead-derived superlens to break the perceived resolution barrier, the same team has achieved another world first.

Now the team, led by Dr Zengbo Wang and in colloboration with Prof. Fritz Vollrath’s silk group at Oxford University’s Department of Zoology, has used a naturally occurring material — dragline silk of the golden web spider, as an additional superlens, applied to the surface of the material to be viewed, to provide an additional 2-3 times magnification.

This is the first time that a naturally occurring biological material has been used as a superlens.

An Aug. 19, 2016 Bangor University press release (also on EurekAlert), which originated the news item, provides more information about the new work,

In the paper in Nano Letters (DOI: 10.1021/acs.nanolett.6b02641, Aug 17 2016), the joint team reveals how they used a cylindrical piece of spider silk from the thumb sized Nephila spider as a lens.

Dr Zengbo Wang said:

“We have proved that the resolution barrier of microscope can be broken using a superlens, but production of manufactured superlenses invovles some complex engineering processes which are not widely accessible to other reserchers. This is why we have been interested in looking for naturally occurring superlenses provided by ‘Mother Nature’, which may exist around us, so that everyone can access superlenses.”

Prof Fritz Vollrath adds:

“It is very exciting to find yet another cutting edge and totally novel use for a spider silk, which we have been studying for over two decades in my laboratory.”

These lenses could be used for seeing and viewing previously ‘invisible’ structures, including engineered nano-structures and biological micro-structures as well as, potentially, native germs and viruses.

The natural cylindrical structure at a micron- and submicron-scale make silks ideal candidates, in this case, the individual filaments had diameters of one tenth of a thin human hair.

The spider filament enabled the group to view details on a micro-chip and a blue- ray disk which would be invisible using the unmodified optical microscope.

In much the same was as when you look through a cylindrical glass or bottle, the clearest image only runs along the narrow strip directly opposite your line of vision, or resting on the surface being viewed, the single filament provides a one dimensional viewing image along its length.

Wang explains:

“The cylindrical silk lens has advantages in the larger field-of-view when compared to a microsphere superlens. Importantly for potential commercial applications, a spider silk nanoscope would be robust and economical, which in turn could provide excellent manufacturing platforms for a wide range of applications.”

James Monks, a co-author on the paper comments: “it has been an exciting time to be able to develop this project as part of my honours degree in electronic engineering at Bangor University and I am now very much looking forward to joining Dr Wang’s team as a PhD student in nano-photonics.”

The researchers have provided a close up image with details,

Caption: (a) Nephila edulis spider in its web. (b) Schematic drawing of reflection mode silk biosuperlens imaging. The spider silk was placed directly on top of the sample surface by using a soft tape, which magnify underlying nano objects 2-3 times (c) SEM image of Blu-ray disk with 200/100 nm groove and lines (d) Clear magnified image (2.1x) of Blu-ray disk under spider silk superlens. Credit: Bangor University/ University of Oxford

Caption: (a) Nephila edulis spider in its web. (b) Schematic drawing of reflection mode silk biosuperlens imaging. The spider silk was placed directly on top of the sample surface by using a soft tape, which magnify underlying nano objects 2-3 times (c) SEM image of Blu-ray disk with 200/100 nm groove and lines (d) Clear magnified image (2.1x) of Blu-ray disk under spider silk superlens. Credit: Bangor University/ University of Oxford

Here’s a link to and a citation for the ‘spider silk’ superlens paper,

Spider Silk: Mother Nature’s Bio-Superlens by James N. Monks, Bing Yan, Nicholas Hawkins, Fritz Vollrath, and Zengbo Wang. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.6b02641 Publication Date (Web): August 17, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Gossamer silk that withstands hurricane force winds

I’ve written about spiderwebs before (mostly recently in my Dec. 9, 2011 posting titled, Music, math, and spiderwebs. Researcher, Markus J. Buehler, was featured in the Dec. 2011 posting and he is featured in this one too. I imagine he’s the ‘go to’ spiderweb researcher at MIT (Massachusetts Institute of Technology).

The most discussed characteristic of spiderwebs is their strength, a topic of endless fascination. The Feb. 1, 2012 news item on physorg.com offers a new take on this phenomenon,

While researchers have long known of the incredible strength of spider silk, the robust nature of the tiny filaments cannot alone explain how webs survive multiple tears and winds that exceed hurricane strength.

Now, a study that combines experimental observations of spider webs with complex computer simulations has shown that web durability depends not only on silk strength, but on how the overall web design compensates for damage and the response of individual strands to continuously varying stresses.

Reporting in the cover story of the Feb. 2, 2012, issue of Nature, researchers from the Massachusetts Institute of Technology (MIT) [team leader Markus Buehler, associate professor of civil and environmental engineering at MIT] and the Politecnico di Torino [team leader Nicola Pugno, Professor of Solid and Structural Mechanics at the Politecnico di Torino] in Italy show how spider web-design localizes strain and damage, preserving the web as a whole.

Very simply, two of the types of spider silk that give the webs their strength were examined separately and together. From the news item,

Viscid silk is stretchy, wet and sticky, and it is the silk that winds out in increasing spirals from the web center. Its primary function is to capture prey. Dragline silk is stiff and dry, and it serves as the threads that radiate out from a web’s center, providing structural support. Dragline silk is crucial to the mechanical behavior of the web.

If you’re a weaver, that description will like remind you of warp and weft. The warp threads provide the strength and remain immobile while the the weft threads are the ones you weave in and out and use to create patterns, etc. if you are so inclined.

These observations about viscid and dragline silk have practical applications (from the news item),

The concept of selective, localized failure for spider webs is interesting since it is a distinct departure from the structural principles that seem to be in play for many biological materials and components,” adds Dennis Carter, the NSF program director for biomechanics and mechanobiology who helped support the study. [emphasis mine]

“For example, the distributed material components in bone spread stress broadly, adding strength. There is no ‘wasted’ material, minimizing the weight of the structure. While all of the bone is being used to resist force, bone everywhere along the structure tends to be damaged prior to failure.”

In contrast, a spider’s web is organized to sacrifice local areas so that failure will not prevent the remaining web from functioning, even if in a diminished capacity, says Carter. “This is a clever strategy when the alternative is having to make an entire, new web!,” he adds. “As Buehler suggests, engineers can learn from nature and adapt the design strategies that are most appropriate for specific applications.”

According to David Kaplan’s Feb. 2, 2012 article for MIT News, the spiderweb’s localized failure was a considered a sign of weakness,

It turns out that a key property of spider silk that helps make webs robust is something previously considered a weakness: the way it can stretch and soften at first when pulled, and then stiffen again as the force of the pulling increases.

This stiffening response is crucial to the way spider silk resists damage. Buehler and his team analyzed how materials with different properties, arranged in the same web pattern, respond to localized stresses. They found that materials with other responses — those that either behave as a simple linear spring as they’re pulled, or start out stretchy and then become more “plastic” — perform much less effectively.

Spider webs, it turns out, can take quite a beating without failing. Damage tends to be localized, affecting just a few threads — the place where a bug got caught in the web and flailed around, for example. This localized damage can simply be repaired, rather than replaced, or even left alone if the web continues to function as before. “Even if it has a lot of defects, the web actually still functions mechanically virtually the same way,” Buehler says. “It’s a very flaw-tolerant system.”

Here’s an image that illustrates how spiderwebs react to stress,

Images show the successive deformation states as loading is increased on a spider web, with red marking high stresses. Simulation picture by S. Cranford & M.J. Buehler/MIT, photographic image by Francesco Tomasinelli & Emanuele Biggi.

The researchers’ article in Nature, Nonlinear material behaviour of spider silk yields robust webs by Steven W. Cranford, Anna Tarakanova, Nicola M. Pugno & Markus J. Buehler is available behind a paywall.

Note: I’m pretty sure I searched to find out if it should be spiderwebs or spider webs. I will investigate further but do not have time now. Meanwhile, I committed to spiderwebs in Dec. 2011.