An Interesting Visitor

In the span of three months since the Yellow Five blog's conception, we have received visitors from around the world. While we would like to believe our blog is being enjoyed in places like Finland and China, we know that these foreign views are most likely the result of random clicking. However, about one month ago, we received a very special visitor to our blog named Fiorenzo Omenetto. He has been featured on our blog here. Omenetto primarily does research with silk and its effectiveness as a nanomaterial. He has been named an Oppenheimer Fellow and a Guggenheim Fellow in 2011. About our blog, Omenetto commented saying:

"Yes, of course – there are so many interesting things out there and it's really nice to see you review these things and select the ones that you think are important or that strike your imagination. Keep going and put more!"

We are very thankful to Omenetto for taking the time to view our blog, and we wish him the best in his future research. To get more of Omenetto's research, check out his website here and his twitter over here. We interviewed him, and the contents of this interview can be viewed below. Once again, thanks for viewing our blog, and we hope to have another post up and running next week. See you soon!

The Interview:

Q: Can you introduce yourself?

Hi YellowFive! I'm Fio Omenetto a professor of Biomedical Engineering and a Prof. of Physics at Tufts University in Boston.

Q: What made you so interested in researching silk?

A chance conversation in the hallway with Dave Kaplan, who is now one of my closest collaborators. I didn't even know what silk was before coming to Tufts (OK, I did, but had not remotely thought about it as a photonics or electronic material, much less on the nanoscale. )

Q: What is the most exciting result of your research so far?

I think for me just the discovery of silk and the things that it can do at multiple scales, the favorable properties of the material, and how it can reinvent technology as we know it.

Q: Do you feel that the silk optics that you recently created and that we mentioned in our blog is a big accomplishment?

I think it is, but I'm biased… I think being mentioned in your blog is quite flattering! (thanks)

Q: What is the most interesting thing about being a researcher?

The fact that you have endless puzzles to solve, that you get to work with great people solving them, and that you get to imagine new things all the time (because, in fact, not all the things that you imagine or that you research work!).

Q: What do you think is the most interesting aspect about nanomaterials?

My first research love (and background) is in optics and physics – I have always liked the structural interaction of materials on the nanoscale with electromagnetic radiation – structural color, photonics band gaps and related things. I like how structure affects function, and specifically how nanostructures affect light propagation (and electromagnetic waves in general).

Q: What inspired you to look into silk and nanomaterials?

I was just trying to connect the dots between what I liked and something new.

Wood and Cellulose: Natural Nanomaterials

In our past few posts, we have primarily looked at naturally-occuring nanomaterial sources, such as a crab's claw and silk. Today, for a change, we present to you a potential source of nanomaterials that can easily be found in one's backyard - wood pulp. Before looking into the actual properties and benefits of the nanocellulose, we need to understand the physical properties of cellulose itself.

Cellulose, pictured to the right, with chemical formula (C6H10O5)n, is one of the main components of cell walls in plants. Its primary use in the industry is the manufacturing of paper; the cellulose obtained for this process can be extracted from wood pulp. Cellulose is a polar molecule, as evidenced from its various OH groups, which contribute a dipole movement. It has a high melting point of 773 K, which is a result of its IMF's. Cellulose also is a highly viscous fluid as a result; this poses a problem for manufacturers, as pulp flow is highly difficult. Despite its polarity, cellulose is insoluble in water, meaning that it does not dissociate at all.

Nanocellulose, on the other hand, has physical properties antithetic to those of cellulose. The wood pulp is taken, and gently beaten to reduce to cellulose to thin fibers. The cellulose then takes on a needle like crystalline structure, pictured to the left. The nanocellulose has its most impressive properties once it dries. It has eight times the tensile strength of steel, and is almost as stiff as Kelvar. The US Forest Service, which opened the first nanocellulose lab in the United States at Madison, WI, reports that nanocellulose can sell for just a few dollars per kilo. This has extreme economic implications; if nanocellulose is stronger and cheaper than steel, it could one day replace steel in the industry.

For more information about nanocellulose, check out the embed video right below this post. A few posts later, we will be publishing an interview we had with Fiorenzo Omenetto, Guggenheim Fellow, who worked with silk and its applications as a potential nanomaterial. Stay tuned for more posts.

Self-Healing Electronic Skin

Zhenan Bao and her team of researchers at Stanford University are striving to create electronic skin that can both register touch and heal itself the way natural skin can. Many materials scientist have worked on created flexible circuits while chemists have tackled the problem of self-healing polymers. Yet despite all the effort, no material has be discovered or created that can combine these two attractive properties. This is a big problem for prosthetics as many of these devices do not have a sense of touch, which makes many of its users complain about the clumsiness and clunkiness of current devices.  

Last year Bao's team was able to solve half of the puzzle, creating a flexible electronic skin that can sense pressure (video below), and this November, the team announced that they have come one step closer to a self-healing polymer.

In a paper published in Nature, Bao showcases her recent breakthrough regarding a self-healing electronic skin. By incorporating nickel atoms into a self-healing polymer, the Stanford team was able to arrive at a material that achieves both of the qualities needed for a self-healing electronic skin. The polymer is able to gain the electrical properties because through forces like pressure or twisting, the distance between adjacent nickel atoms changes. This affects how easily electrons can move from atom to atom, which changes the electronic resistance of the material. 

To demonstrate the effectiveness of the healing properties of the material, the researchers cut the material with a scalpel  They then help the two pieces together at the edges and after 15 seconds, electrical conductivity was restored with about 90% efficiency, and after a mere 10 minutes, the break was fully repaired and the material was once again flexible. 

John Boland of the Center for Research on Adaptive Nanostructures and Nanodevices (CRANN) at Trinity College Dublin called the development a breakthrough in an article on ScienceNOW, though he notes that scalpel cuts are very neat and the tearing and stretching of the material may affect its self-healing properties.  

Smart Materials have SMARTS

In the July 12 issue of Nature, a Harvard-led research team showcased a strategy for building self-thermoregulating nanomaterials that can be tailored to maintain a determined temperature, pressure, or any other measure by meeting the environmental changes with a compensatory chemical feedback response. 

This group of materials is called Self-regulated Mechano-chemical Adaptively Reconfigurable Tunable System, or SMARTS for short. As the name suggests, this group of innovative materials has offers a customizable way to automatically turn on and turn off chemical reactions in a way that mimics how biological systems naturally adjust to the dynamics of their surroundings. 

This development greatly benefits medical implants because it allow for more intelligent and efficient medical implants. In terms of its structure, SMARTS looks like a microscopic toothbrush with tiny fibers capable of either standing up or lying down, which results in creating or breaking contact with the later of the material that contains chemical 'nutrients'. Joanna Aizenberg, a lead author of the research, explains the structure of SMARTS as something similar to the hair on a person's arms. “When it is cold out, tiny muscles at the base of each hair on your arm cause the hairs to stand up in an insulating layer. As your skin warms up, the muscles contract and the hairs lie back down to keep you from overheating. SMARTS works in a similar way.”

At first glance, SMARTS may not seem like a big deal; there already exist glasses that dim and brighten depending on the intensity of light and piezocrystals that can convert vibrations into electrical signals, but one major downfall of these two examples is that they response to one specific stimuli and cannot self-regulate. 

A demonstration of the material can be seen in the video below. 

In the video, the stimuli used is temperature and a hydrogel is embedded with an array of tiny nanofibers, which cause the hydrogel to either expand or contract in response to the temperature changes. When the temperature drops, the gel swells, and the hairs stand upright and make contact with the ‘nutrient’ layer; when it warms up, the gel contracts, and the hairs lie down. The key aspect is that molecular catalysts placed on the tips of the nanofibers can trigger heat-generating chemical reactions in the ‘nutrient’ layer. 

Figure 1: Process of a homeostatic material maintaing constant temperature.

Aizenberg likens the process to homeostasis, saying, "The bilayer system effectively creates a self-regulated on-and-off switch controlled by the motion of the hairs, turning the reaction on and generating heat when it is cold. Once the temperature has achieved a pre-determined level, the hydrogel contracts, causing the hairs to lie down, interrupting further generation of heat. When it cools again below the set-point the cycle restarts autonomously. It’s homeostasis, right down at the materials level." 

Through additional refinement, the technique could eventually be incorporated into the material of medical implants to help stabilize bodily functions. Some examples include sensing and adjusting glucose or carbon dioxide levels in the blood.