Tag Archives: Emiliano Lepore

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.

Synthesizing spider silk

Most of the research on spider silk and spider webs that’s featured here is usually from the Massachusetts Institute of Technology (MIT) and, more specifically, from professor Markus J. Buehler. This May 28, 2015 news item on ScienceDaily, which heralds the development of synthetic spider silk, is no exception,

After years of research decoding the complex structure and production of spider silk, researchers have now succeeded in producing samples of this exceptionally strong and resilient material in the laboratory. The new development could lead to a variety of biomedical materials — from sutures to scaffolding for organ replacements — made from synthesized silk with properties specifically tuned for their intended uses.

The findings are published this week in the journal Nature Communications by MIT professor of civil and environmental engineering (CEE) Markus Buehler, postdocs Shangchao Lin and Seunghwa Ryu, and others at MIT, Tufts University, Boston University, and in Germany, Italy, and the U.K.

The research, which involved a combination of simulations and experiments, paves the way for “creating new fibers with improved characteristics” beyond those of natural silk, says Buehler, who is also the department head in CEE. The work, he says, should make it possible to design fibers with specific characteristics of strength, elasticity, and toughness.

The new synthetic fibers’ proteins — the basic building blocks of the material — were created by genetically modifying bacteria to make the proteins normally produced by spiders. These proteins were then extruded through microfluidic channels designed to mimic the effect of an organ, called a spinneret, that spiders use to produce natural silk fibers.

A May 28, 2015 MIT news release (also on EurekAlert), which originated the news item, describes the work in more detail,

While spider silk has long been recognized as among the strongest known materials, spiders cannot practically be bred to produce harvestable fibers — so this new approach to producing a synthetic, yet spider-like, silk could make such strong and flexible fibers available for biomedical applications. By their nature, spider silks are fully biocompatible and can be used in the body without risk of adverse reactions; they are ultimately simply absorbed by the body.

The researchers’ “spinning” process, in which the constituent proteins dissolved in water are extruded through a tiny opening at a controlled rate, causes the molecules to line up in a way that produces strong fibers. The molecules themselves are a mixture of hydrophobic and hydrophilic compounds, blended so as to naturally align to form fibers much stronger than their constituent parts. “When you spin it, you create very strong bonds in one direction,” Buehler says.

The team found that getting the blend of proteins right was crucial. “We found out that when there was a high proportion of hydrophobic proteins, it would not spin any fibers, it would just make an ugly mass,” says Ryu, who worked on the project as a postdoc at MIT and is now an assistant professor at the Korea Advanced Institute of Science and Technology. “We had to find the right mix” in order to produce strong fibers, he says.

The researchers made use of computational modelling to speed up the process of synthesizing proteins for synthetic spider silk, from the news release,

This project represents the first use of simulations to understand silk production at the molecular level. “Simulation is critical,” Buehler explains: Actually synthesizing a protein can take several months; if that protein doesn’t turn out to have exactly the right properties, the process would have to start all over.

Using simulations makes it possible to “scan through a large range of proteins until we see changes in the fiber stiffness,” and then home in on those compounds, says Lin, who worked on the project as a postdoc at MIT and is now an assistant professor at Florida State University.

Controlling the properties directly could ultimately make it possible to create fibers that are even stronger than natural ones, because engineers can choose characteristics for a particular use. For example, while spiders may need elasticity so their webs can capture insects without breaking, those designing fibers for use as surgical sutures would need more strength and less stretchiness. “Silk doesn’t give us that choice,” Buehler says.

The processing of the material can be done at room temperature using water-based solutions, so scaling up manufacturing should be relatively easy, team members say. So far, the fibers they have made in the lab are not as strong as natural spider silk, but now that the basic process has been established, it should be possible to fine-tune the materials and improve its strength, they say.

“Our goal is to improve the strength, elasticity, and toughness of artificially spun fibers by borrowing bright ideas from nature,” Lin says. This study could inspire the development of new synthetic fibers — or any materials requiring enhanced properties, such as in electrical and thermal transport, in a certain direction.

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

Predictive modelling-based design and experiments for synthesis and spinning of bioinspired silk fibres by Shangchao Lin, Seunghwa Ryu, Olena Tokareva, Greta Gronau, Matthew M. Jacobsen, Wenwen Huang, Daniel J. Rizzo, David Li, Cristian Staii, Nicola M. Pugno, Joyce Y. Wong, David L. Kaplan, & Markus J. Buehler. Nature Communications 6, Article number: 6892 doi:10.1038/ncomms7892 Published 28 May 2015

This paper is behind a paywall.

My two most recent (before this one) postings about Buehler’s work are an August 5, 2014 piece about structural failures and a June 4, 2014 piece about spiderwebs and music.

Finally, I recognized one of the authors, Nicola Pugno from Italy. He’s been mentioned here more than once in regard to his biomimicry work which has often been focused on geckos and their adhesive qualities as per this April 3, 2014 post announcing his book ‘An Experimental Study on Adhesive or Anti-Adhesive, Bio-Inspired Experimental Nanomaterials‘ (co-authored with Emiliano Lepore).

Biomimicry book focusses on adhesive and non-adhesive properties

While I’m not familiar with Emiliano Lepore’s work, his co-author’s name, Nicola Pugno, rang a bell; he’s mentioned in my Feb. 3, 2012 posting about spiderwebs and strength and in my Nanotech Mysteries wiki entry, ‘Scientists read comics, watch tv, and more‘ about adhesive properties at the nanoscale. The two men have authored a book, ‘An Experimental Study on Adhesive or Anti-Adhesive, Bio-Inspired Experimental Nanomaterials‘ (print version) according to an April 2, 2014 news item on Nanowerk (Note: A link has been removed),

While recognising that bio-inspiration for technological development is already an established concept, “An Experimental Study on Adhesive or Anti-Adhesive, Bio-Inspired Experimental Nanomaterials” by Italian scientists Emiliano Lepore and Nicola Pugno, released in Open Access by De Gruyter Open, sets out to explore the potential of three categories of bio-inspired materials, namely, adhesives, anti-adhesives, and materials designed to offer exceptional characteristics – particularly in terms of their strength-to-weight ratio. In each of these areas, the technologies, which are currently at the forefront of scientific research, are described in relation to how they have been inspired by nature in an attempt to optimise their physical characteristics and performance in operation, with an aim to design and develop new innovative products.

Lepore and Pugno investigate a wide range of natural systems and employ original experimental procedures, the book additionally stands out for its rigorous and innovative approach to biomaterials. For example, the challenge of creating strong, reliable and affordable adhesives appears in numerous areas of engineering, such as the development of aircrafts, and all types of vehicles for transportation on land or water, where the need to save energy consumption by reducing weight is of paramount importance. There is also a specific interest in bonding dissimilar materials, which due to their physical properties prohibit the application of more conventional joining techniques. In this field, inspiration has been sought by investigating the adhesive abilities of insects, spiders, and reptiles.

The book published by De Gruyter is available in a free PDF format in addition to the print version which can be purchased through Amazon.