Category Archives: biomimcry

Chinese scientists develop a novel 3D fabrication technique for bio-inspired hierarchical structures

An April 14, 2016 news item on phys.org describes a new 3D fabrication technique devised by Chinese scientists,

Nature is no doubt the world’s best biological engineer, whose simple, exquisite but powerful designs have inspired scientists and engineers to tackle the challenges of technologies for centuries. Scientists recently mimicked the surface structure of a moth’s eye, a unique structure with an antireflective property, to develop a highly light-absorbent graphene material. This is breakthrough [sic] in solar cell technology. Rice leaves and butterfly wings also have unique self-cleaning surface characteristics, which inspire scientists to develop novel materials resistant to biofouling. The bio-inspired periodic multi-scale structures, called hierarchical structures, have recently caught broad attention among scientists in various applications such as solar cells, Light-emitting diodes (LEDs), biomaterials and anti-bacterial surfaces.

An April 14, 2016 Optical Society of American news release (also on EurekAlert), which originated the news item, provides more detail,

Although a number of techniques for fabricating bio-inspired hierarchical structures already exist, most conventional methods either involve complicated processes or are highly time-consuming and low cost-efficiency for industrial applications. Now, a team of researchers from Changchun University of Science and Technology, China, have developed a novel method for the rapid and maskless fabrication of bio-inspired hierarchical structures, using a technique called laser interference lithography.

Specifically, the researchers use the interference pattern of three-and four-beam lasers to fabricate ordered multi-scale surface structures on silicon substrates, with the pattern of hierarchical structures controllable by adjusting the parameters of incident light. In accordance with the theoretical and computer analysis, the researchers have experimentally demonstrated the novel technique’s potential in large-area, low-cost and high-volume 3D fabrication of micro and nanostructures. …

“We presented a flexible and direct method for fabricating ordered multi-scale 3D structures using three- and four-beam interference lithography,” said Zuobin Wang, the primary author and a professor of International Research Centre for Nano Handling and Manufacturing of China at the Changchun University of Science and Technology, China. “Compared with other patterning technologies, our method is simple and efficient in terms of obtaining bio-inspired hierarchical structures.”

Wang mentioned that for certain complicated surface structures, conventional techniques such as electron beam lithography may take several hours or a day to fabricate the pattern, while the laser interference approach only takes several minutes to generate the structure, which makes the technique suitable for high-volume industrial production.

“Laser interference lithography is a maskless patterning technique that uses the interference patterns generated from two or several coherent laser beams to fabricate micro and nanometer periodic patterns over large areas,” Wang said. Different from conventional patterning techniques like electron beam lithography, the laser interference technique enables fabricating the entire substrate surface with one single exposure or one-step lithography.

For example, in Wang’s experiment, the one-dimension multi-scale structure, that is, one-dimension oriented arrangement with the sinusoidal grooves covered with periodic line-like structures was fabricated by exposing the silicon substrate to three or four interfered beams for one time. The resultant surface pattern, though arranged in one direction, has three-dimension spatial structure. To obtain more complicated structures such as two-dimension oriented multi-scale structures, the researchers simply rotated the substrate by 90 degrees in the plane and applied second laser exposure to the surface.

“Laser interference lithography is capable of fabricating homogeneous micro and nanometer structured patterns over areas more than one square meter, which is either impossible or highly time or cost consuming for conventional techniques,” Wang said. These features make laser interference lithography superior to other techniques in terms of efficiency and high-volume production.

According to Wang, their experimental process is simple: a high power laser beam was split into three or four equal beams, which then were directed by mirrors to generate interference patterns to fabricate the surface structures. The laser parameters such as incident angle and azimuthal angle of each beam were adjusted by beam splitters and mirror positions. Other optical devices such as quarter-wave plates and polarizers were used to select the polarization mode and control the energy of laser beams.

“The laser beam parameters are selected according to the desired surface structure and corresponding interference energy distribution calculated from theoretical simulation. In other words, the shapes or patterns of hierarchical structures in our method are controllable by adjusting the parameters of each incident beams,” Wang noted.

According to Wang, the proposed technique could be used to fabricate optical or medical devices such as solar cells, antireflective coatings, self-cleaning and antibacterial surfaces and long-life artificial hip joints.

The researchers’ next step is to develop functional surface structures with controllable wettability, adhesion and reflectivity properties for optical, medical and mechanical applications.

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

Bio-inspired hierarchical patterning of silicon by laser interference lithography by Yaowei Hu, Zuobin Wang, Zhankun Weng, Miao Yu, and Dapeng Wang. Applied Optics Vol. 55, Issue 12, pp. 3226-3232 (2016) doi: 10.1364/AO.55.003226

I believe this paper is behind a paywall.

The researchers have provided this image as an illustration of their concept,

 Caption: This is a Scanning Electron Microscope (SEM) image of a moth eye. Credit: Zuobin Wang/Changchun University of Science and Technology, China


Caption: This is a Scanning Electron Microscope (SEM) image of a moth eye. Credit: Zuobin Wang/Changchun University of Science and Technology, China

Drone fly larvae avoid bacterial contamination due to their nanopillars

This is some fascinating bug research. From an April 6, 2016 news item on phys.org,

The immature stage of the drone fly (Eristalis tenax) is known as a “rat-tailed maggot” because it resembles a hairless baby rodent with a “tail” that is actually used as a breathing tube. Rat-tailed maggots are known to live in stagnant, fetid water that is rich in bacteria, fungi, and algae. However, despite this dirty environment, they are able to avoid infection by these microorganisms.

An April 6, 2016 Entomological Society of America news release on EurekAlert, which originated the news item, describes the findings,

Recently, Matthew Hayes, a cell biologist at the Institute of Ophthalmology at University College London in England, discovered never-before-seen structures that appear to keep the maggot mostly free of bacteria, despite living where microorganisms flourish. …

With scanning and transmission electron microscopes, Hayes carefully examined the larva and saw that much of its body is covered with thin spines, or “nanopillars,” that narrow to sharp points. Once he confirmed the spiky structures were indeed part of the maggot, he noticed a direct relationship between the presence of the spines and the absence of bacteria on the surface of the larva. He speculated that the carpet of spines simply makes it impossible for the bacteria to find enough room to adhere to the larva’s body surface.

Here’s an image of the nanopillars,

Caption: This electron-microscope image expose the spines, or "nanopillars," that poke up from the body of the rat-tailed maggot. The length and density of the spines vary as shown in this cross-section image of the cuticle. Credit: Matthew Hayes

Caption: This electron-microscope image expose the spines, or “nanopillars,” that poke up from the body of the rat-tailed maggot. The length and density of the spines vary as shown in this cross-section image of the cuticle. Credit: Matthew Hayes

Back to the news release,

“They’re much like anti-pigeon spikes that keep the birds away because they can’t find a nice surface to land on,” he said.

Hayes also ventured that the spines could possibly have superoleophobic properties (the ability to repel oils), which would also impede the bacteria from colonizing and forming a biofilm that could ultimately harm or kill the maggot. The composition of the spines is as unique as the structures themselves, Hayes said. Each spine appears to consist of a stack of hollow-cored disks, the largest at the bottom and the smallest at the top.

“What I really think they look like is the baby’s toy with the stack of rings of decreasing size, but on a very small scale,” he said. “I’ve worked in many different fields and looked at lots of different things, and I’ve never seen anything that looks like it.”

This work with the rat-tailed maggot is leading him to examine other insects as well, including the ability of another aquatic invertebrate — the mosquito larva — to thwart bacteria. Such antibacterial properties have applications in many different fields, including ophthalmology and other medical fields where biofilms can foul surgical instruments or implanted devices.

For now, though, he’s thrilled about shedding light on the underappreciated rat-tailed maggot and revealing its spiny armor.

“I’ve loved insects since I was a child, when I would breed butterflies and moths,” he said. “I’m just so chuffed to have discovered something a bit new about insects!”

I am charmed by Hayes’s admission of being “chuffed.”

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

Identification of Nanopillars on the Cuticle of the Aquatic Larvae of the Drone Fly (Diptera: Syrphidae) by Matthew J. Hayes, Timothy P. Levine, Roger H. Wilson. DOI: http://dx.doi.org/10.1093/jisesa/iew019 36 First published online: 30 March 2016

This is an open access paper.

Split some water molecules and save solar and wind (energy) for a future day

Professor Ted Sargent’s research team at the University of Toronto has a developed a new technique for saving the energy harvested by sun and wind farms according to a March 28, 2016 news item on Nanotechnology Now,

We can’t control when the wind blows and when the sun shines, so finding efficient ways to store energy from alternative sources remains an urgent research problem. Now, a group of researchers led by Professor Ted Sargent at the University of Toronto’s Faculty of Applied Science & Engineering may have a solution inspired by nature.

The team has designed the most efficient catalyst for storing energy in chemical form, by splitting water into hydrogen and oxygen, just like plants do during photosynthesis. Oxygen is released harmlessly into the atmosphere, and hydrogen, as H2, can be converted back into energy using hydrogen fuel cells.

Discovering a better way of storing energy from solar and wind farms is “one of the grand challenges in this field,” Ted Sargent says (photo above by Megan Rosenbloom via flickr) Courtesy: University of Toronto

Discovering a better way of storing energy from solar and wind farms is “one of the grand challenges in this field,” Ted Sargent says (photo above by Megan Rosenbloom via flickr) Courtesy: University of Toronto

A March 24, 2016 University of Toronto news release by Marit Mitchell, which originated the news item, expands on the theme,

“Today on a solar farm or a wind farm, storage is typically provided with batteries. But batteries are expensive, and can typically only store a fixed amount of energy,” says Sargent. “That’s why discovering a more efficient and highly scalable means of storing energy generated by renewables is one of the grand challenges in this field.”

You may have seen the popular high-school science demonstration where the teacher splits water into its component elements, hydrogen and oxygen, by running electricity through it. Today this requires so much electrical input that it’s impractical to store energy this way — too great proportion of the energy generated is lost in the process of storing it.

This new catalyst facilitates the oxygen-evolution portion of the chemical reaction, making the conversion from H2O into O2 and H2 more energy-efficient than ever before. The intrinsic efficiency of the new catalyst material is over three times more efficient than the best state-of-the-art catalyst.

Details are offered in the news release,

The new catalyst is made of abundant and low-cost metals tungsten, iron and cobalt, which are much less expensive than state-of-the-art catalysts based on precious metals. It showed no signs of degradation over more than 500 hours of continuous activity, unlike other efficient but short-lived catalysts. …

“With the aid of theoretical predictions, we became convinced that including tungsten could lead to a better oxygen-evolving catalyst. Unfortunately, prior work did not show how to mix tungsten homogeneously with the active metals such as iron and cobalt,” says one of the study’s lead authors, Dr. Bo Zhang … .

“We invented a new way to distribute the catalyst homogenously in a gel, and as a result built a device that works incredibly efficiently and robustly.”

This research united engineers, chemists, materials scientists, mathematicians, physicists, and computer scientists across three countries. A chief partner in this joint theoretical-experimental studies was a leading team of theorists at Stanford University and SLAC National Accelerator Laboratory under the leadership of Dr. Aleksandra Vojvodic. The international collaboration included researchers at East China University of Science & Technology, Tianjin University, Brookhaven National Laboratory, Canadian Light Source and the Beijing Synchrotron Radiation Facility.

“The team developed a new materials synthesis strategy to mix multiple metals homogeneously — thereby overcoming the propensity of multi-metal mixtures to separate into distinct phases,” said Jeffrey C. Grossman, the Morton and Claire Goulder and Family Professor in Environmental Systems at Massachusetts Institute of Technology. “This work impressively highlights the power of tightly coupled computational materials science with advanced experimental techniques, and sets a high bar for such a combined approach. It opens new avenues to speed progress in efficient materials for energy conversion and storage.”

“This work demonstrates the utility of using theory to guide the development of improved water-oxidation catalysts for further advances in the field of solar fuels,” said Gary Brudvig, a professor in the Department of Chemistry at Yale University and director of the Yale Energy Sciences Institute.

“The intensive research by the Sargent group in the University of Toronto led to the discovery of oxy-hydroxide materials that exhibit electrochemically induced oxygen evolution at the lowest overpotential and show no degradation,” said University Professor Gabor A. Somorjai of the University of California, Berkeley, a leader in this field. “The authors should be complimented on the combined experimental and theoretical studies that led to this very important finding.”

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

Homogeneously dispersed, multimetal oxygen-evolving catalysts by Bo Zhang, Xueli Zheng, Oleksandr Voznyy, Riccardo Comin, Michal Bajdich, Max García-Melchor, Lili Han, Jixian Xu, Min Liu, Lirong Zheng, F. Pelayo García de Arquer, Cao Thang Dinh, Fengjia Fan, Mingjian Yuan, Emre Yassitepe, Ning Chen, Tom Regier, Pengfei Liu, Yuhang Li, Phil De Luna, Alyf Janmohamed, Huolin L. Xin, Huagui Yang, Aleksandra Vojvodic, Edward H. Sargent. Science  24 Mar 2016: DOI: 10.1126/science.aaf1525

This paper is behind a paywall.

Namib beetles, cacti, and pitcher plants teach scientists at Harvard University (US)

In this latest work from Harvard University’s Wyss Institute for Biologically Inspired Engineering, scientists have looked at three desert dwellers for survival strategies in water-poor areas. From a Feb. 25, 2015 news item on Nanowerk,

Organisms such as cacti and desert beetles can survive in arid environments because they’ve evolved mechanisms to collect water from thin air. The Namib desert beetle, for example, collects water droplets on the bumps of its shell while V-shaped cactus spines guide droplets to the plant’s body.

As the planet grows drier, researchers are looking to nature for more effective ways to pull water from air. Now, a team of researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering at Harvard University have drawn inspiration from these organisms to develop a better way to promote and transport condensed water droplets.

A Feb. 24, 2016 Harvard University press release by Leah Burrows (also on EurekAlert), which originated the news item, expands on the theme,

“Everybody is excited about bioinspired materials research,” said Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science at SEAS and core faculty member of the Wyss Institute. “However, so far, we tend to mimic one inspirational natural system at a time. Our research shows that a complex bio-inspired approach, in which we marry multiple biological species to come up with non-trivial designs for highly efficient materials with unprecedented properties, is a new, promising direction in biomimetics.”

The new system, described in Nature, is inspired by the bumpy shell of desert beetles, the asymmetric structure of cactus spines and slippery surfaces of pitcher plants. The material harnesses the power of these natural systems, plus Slippery Liquid-Infused Porous Surfaces technology (SLIPS) developed in Aizenberg’s lab, to collect and direct the flow of condensed water droplets.

This approach is promising not only for harvesting water but also for industrial heat exchangers.

“Thermal power plants, for example, rely on condensers to quickly convert steam to liquid water,” said Philseok Kim, co-author of the paper and co-founder and vice president of technology at SEAS spin-off SLIPS Technologies, Inc. “This design could help speed up that process and even allow for operation at a higher temperature, significantly improving the overall energy efficiency.”

The major challenges in harvesting atmospheric water are controlling the size of the droplets, speed in which they form and the direction in which they flow.

For years, researchers focused on the hybrid chemistry of the beetle’s bumps — a hydrophilic top with hydrophobic surroundings — to explain how the beetle attracted water. However, Aizenberg and her team took inspiration from a different possibility – that convex bumps themselves also might be able to harvest water.

“We experimentally found that the geometry of bumps alone could facilitate condensation,” said Kyoo-Chul Park, a postdoctoral researcher and the first author of the paper. “By optimizing that bump shape through detailed theoretical modeling and combining it with the asymmetry of cactus spines and the nearly friction-free coatings of pitcher plants, we were able to design a material that can collect and transport a greater volume of water in a short time compared to other surfaces.”

“Without one of those parameters, the whole system would not work synergistically to promote both the growth and accelerated directional transport of even small, fast condensing droplets,” said Park.

“This research is an exciting first step towards developing a passive system that can efficiently collect water and guide it to a reservoir,” said Kim.

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

Condensation on slippery asymmetric bumps by Kyoo-Chul Park, Philseok Kim, Alison Grinthal, Neil He, David Fox, James C. Weaver, & Joanna Aizenberg. Nature (2016) doi:10.1038/nature16956 Published online 24 February 2016

This paper is behind a paywall.

I have featured the Namib beetle and its water harvesting capabilities most recently in a July 29, 2014 posting and the most recent story I have about SLIPS is in an Oct. 14, 2014 posting.

Nanotech Security Corp. stock declining but Cantor Fitzgerald Canada analyst Ralph Garcea gives the stock a buy rating

Linda Rogers has written a Feb. 29, 2016 article about a Vancouver-based company rather perturbingly titled ‘What’s Propelling Nanotech Security Corp to Decline So Much?‘ for Small Cap Wired,

The stock of Nanotech Security Corp (CVE:NTS) is a huge mover today! The stock is down 3.23% or $0.04 after the news [Nanotech Security announced its first quarter fiscal 2016 results in a Feb. 29, 2016 news release], hitting $1.2 per share. … The move comes after 7 months negative chart setup for the $68.48M company. It was reported on Feb, 29 [2016] by Barchart.com. We have $1.06 PT which if reached, will make CVE:NTS worth $8.22 million less.

The Feb. 29, 2016 Nanotech Security news release (summary version) highlights the good news first,

  • Revenue of $1.5 million consistent with the same period last year.  Security Features contributed revenues of $569,000 largely from development contracts and Surveillance delivered $940,000.
  • Gross margin improved to 50% up from 34% in the same period last year.  The improvement reflects the increased mix of higher margin Security Features revenue.
  • Renewed a $1.0 million banknote security feature development contract. The Company successfully renewed the third and final phase of a banknote development contract with a top ten issuing authority to develop a unique Optically Variable Device (“OVD”) security feature for incorporation into future banknotes.  The final phase is expected to generate revenues of approximately $1.0 million.
  • Signed new $3.0 million KolourOptik banknote development contract. The Company signed a new three phase development contract to use the KolourOptik™ nanotechnology to develop a unique OVD security features with another G8 country for incorporation into future banknotes.
  • Strategic meetings with large international banknote issuing authority.  The Company continues to work with a large international banknote issuing authority to deliver a significant volume of colour shifting Optical Thin Film (“OTF”), and partner with our KolourOptik™ technology.  Management continues to devote a significant amount of time and resources in advancing these opportunities.
  • Signed a Memorandum of Understanding (“MOU”) with Hueck Folien, a European manufacturer to supply OTF to the banknote market.  The MOU contemplates an operational agreement to collaborate in the volume production of a colour shifting OTF security feature.  The OTF product is anticipated to initially be used in banknotes as threads and then expand into other markets in the future.

Doug Blakeway, Nanotech’s Chairman and CEO commented, “These two development contracts are material achievements.  Issuing authorities are paying us – something not common in the industry – to design unique banknote security features with our OTF and KolourOptik™ technologies.”  He further added, “Nanotech’s team has scaled the Hueck Folien production facility to where we believe together we can provide the initial volumes demanded by a top-ten issuing authority.  Our relationship with Hueck Folien continues to funnel security feature opportunities to Nanotech.”

The company’s sadder news can be found in their seven-page Feb. 29, 2016 news release (PDF). Their net earnings for the final quarter of 2015 and 2014 were both losses but in 2014 their loss was (931,271) and in 2015 it was (1,746,335). Still, the company’s gross profit from revenue for the same time periods was 50% in 2015 as opposed to 34% in 2014 despite slightly less revenue in 2015.

Assuming I’ve read this information correctly, Nanotech Security does seem to be in a fragile situation but that can change. After all, IBM was in serious trouble for a number of years during the 1990s when there was even talk the company might go bankrupt. As far as I’m aware, IBM is no longer in imminent danger of disappearing from the scene. *ETA March 9, 2016: It seems I used the wrong example if Robert X. Cringley’s March 9, 2016 article ‘What’s happening at IBM? (It’s dying)‘ for Beta News is to be believed.)* Getting back to my point, companies do go through cycles and it can be difficult to determine exactly what’s happening at some of the earlier stages.

Certainly, Cantor Fitzgerald Canada analyst Ralph Garcea has an optimistic view of Nanotech Security’s prospects according to a March 1, 2016 article by Nick Waddell for cantech letter,

Nanotech Security (TSXV:NTS) offers a better and more secure solution in multiple market segments that together are worth billions of dollars per year, says Cantor Fitzgerald Canada analyst Ralph Garcea.

This morning [March 1, 2016], Garcea initiated coverage of Nanotech with a “Buy” rating and a one-year price target of $2.50, implying a return of 110 per cent at the time of publication.

Garcea notes that Nanotech has already created solutions for the consumer electronics, brand identification and currency segments. He points out that one of the company’s biggest differentiators is that its solution can be embedded onto almost any material. This is important, he says, because it means that security can be embedded into places it previously could not go, such as directly onto a pharmaceutical pill.

Shares of Nanotech Security closed today [March 1, 2016] up 2.5 per cent to $1.22.

I have written about Nanotech Security frequently and believe the most recent is a Dec. 29, 2015 posting. For those unfamiliar with the company’s technology, it’s based on the structures found on the blue morpho butterfly. The holes in the butterfly’s wings lend it certain optical properties which the company mimics for its anti-counterfeiting technology.

One final comment, I am not endorsing the company or any of the analysis of the company’s financial situation and prospects.

Ice-free materials courtesy of penguins

The Humboldt penguin’s feathers don’t allow ice to form and a team of scientists have figured out why according to a Feb. 24, 2016 news item on Nanotechnology Now,

Humboldt penguins live in places that dip below freezing in the winter, and despite getting wet, their feathers stay sleek and free of ice. Scientists have now figured out what could make that possible. They report in ACS’ Journal of Physical Chemistry C that the key is in the microstructure of penguins’ feathers. Based on their findings, the scientists replicated the architecture in a nanofiber membrane that could be developed into an ice-proof material.

A Feb. 24, 2016 American Chemical Society (ACS) news release on EurekAlert, which originated the news item, provides a bit more detail,

The range of Humboldt penguins extends from coastal Peru to the tip of southern Chile. Some of these areas can get frigid, and the water the birds swim in is part of a cold ocean current that sweeps up the coast from the Antarctic. Their feathers keep them both warm and ice-free. Scientists had suspected that penguin feathers’ ability to easily repel water explained why ice doesn’t accumulate on them: Water would slide off before freezing. But research has found that under high humidity or ultra-low temperatures, ice can stick to even superhydrophobic surfaces. So Jingming Wang and colleagues sought another explanation.

The researchers closely examined Humboldt penguin feathers using a scanning electron microscope. They found that the feathers were comprised of a network of barbs, wrinkled barbules and tiny interlocking hooks. In addition to being hydrophobic, this hierarchical architecture with grooved structures is anti-adhesive. Testing showed ice wouldn’t stick to it. Mimicking the feathers’ microstructure, the researchers developed an icephobic polyimide fiber membrane. They say it could potentially be used in applications such as electrical insulation.

The researchers have provided an image illustrating their work,

[downloaded from http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b12298]

[downloaded from http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b12298]

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

Icephobicity of Penguins Spheniscus Humboldti and an Artificial Replica of Penguin Feather with Air-Infused Hierarchical Rough Structures by Shuying Wang, Zhongjia Yang, Guangming Gong, Jingming Wang, Juntao Wu, Shunkun Yang, and Lei Jiang. J. Phys. Chem. C, Article ASAP DOI: 10.1021/acs.jpcc.5b12298 Publication Date (Web): February 3, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Turning sunlight into hydrogen (a Korean project)

A Feb. 17, 2016 news item on Nanowerk describes a new technique for solar water-splitting (turning sunlight into hydrogen),

A team of Korean researchers, affiliated with UNIST [Ulsan National Institute of Science and Technology] has recently pioneered in developing a new type of multilayered (Au NPs/TiO2/Au) photoelectrode that boosts the ability of solar water-splitting to produce hydrogen. According to the research team, this special photoelectrode, inspired by the way plants convert sunlight into energy is capable of absorbing visible light from the sun, and then using it to split water molecules (H2O) into hydrogen and oxygen.

A Feb. 1, 2016 UNIST news release, which originated the news item, expands on the theme,

This multilayered photoelectrode takes the form of two-dimensional hybrid metal-dielectric structure, which mainly consists of three layers of gold (Au) film, ultrathin TiO2 layer (20 nm), and gold nanoparticles (Au NPs). In a study, reported in the January 21, 2016 issue of Nano Energy, the team reported that this promising photoelectrode shows high light absorption of about 90% in the visible range 380–700 nm, as well as significant enhancement in photo-catalytic applications.

The researchers have made an image illustrating their work available,

Two-dimensional metastructured film with Titanium Oxide is fabricated as a photo-catalytic photoanode with exceptional visible light absorption. Courtesy: UNIST

Two-dimensional metastructured film with Titanium Oxide is fabricated as a photo-catalytic photoanode with exceptional visible light absorption. Courtesy: UNIST

Back to the news release,

Many structural designs, such as hierarchical and branched assemblies of nanoscale materials have been suggested to increase the UV-visible absorption and to enhance water-splitting efficiency. However, through incorporation of plasmonic metal nanoparticles (i.e. Au) to TiO2 structures, their photoelectrodes have shown to enhance the photoactivity in the entire UV-visible region of solar spectrum when compared with the existing ones, the team reports.

Prof. Jeong Min Baik of UNIST (School of Materials Science and Engineering) states, “Several attemps have been made to use UV-based photoelectrodes for hydrogen production, but this is the first time to use the metal-dielectric hybrid-structured film with TiO2 for oxygen production.” Moreover, according to Prof. Baik, this special type of photoelectrode uses approximately 95% of the visible spectrum of sunlight, which makes up a substantial portion (40%) of full sunlight. He adds, “The developed technology is expected to improve hydrogen production efficiency.”

Prof. Heon Lee (Korean University) states, “This metal-dielectric hybrid-structured film is expected to further reduce the overall cost of producing hydrogen, as it doesn’t require complex operation processes.” He continues by saying, “Using nanoimprint lithography, mass production of hydrogen will be soon possible.”

Prof. Baik adds, “This simple system may serve as an efficient platform for solar energy conversion, utilizing the whole UV-visible range of solar spectrum based on two-dimensional plasmonic photoelectrodes.”

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

Two-dimensional metal-dielectric hybrid-structured film with titanium oxide for enhanced visible light absorption and photo-catalytic application by Joonmo Park, Hee Jun Kim, SangHyeon Nam, Hyowook Kim, Hak-Jong Choi, Youn Jeong Jang, Jae Sung Lee, Jonghwa Shin, Heon Lee, Jeong Min Baik. Nano Energy Volume 21, March 2016, Pages 115–122 doi:10.1016/j.nanoen.2016.01.004

This paper is behind a paywall.

Cambridge University researchers tell us why Spiderman can’t exist while Stanford University proves otherwise

A team of zoology researchers at Cambridge University (UK) find themselves in the unenviable position of having their peer-reviewed study used as a source of unintentional humour. I gather zoologists (Cambridge) and engineers (Stanford) don’t have much opportunity to share information.

A Jan. 18, 2016 news item on ScienceDaily announces the Cambridge research findings,

Latest research reveals why geckos are the largest animals able to scale smooth vertical walls — even larger climbers would require unmanageably large sticky footpads. Scientists estimate that a human would need adhesive pads covering 40% of their body surface in order to walk up a wall like Spiderman, and believe their insights have implications for the feasibility of large-scale, gecko-like adhesives.

A Jan. 18, 2016 Cambridge University press release (also on EurekAlert), which originated the news item, describes the research and the thinking that led to the researchers’ conclusions,

Dr David Labonte and his colleagues in the University of Cambridge’s Department of Zoology found that tiny mites use approximately 200 times less of their total body area for adhesive pads than geckos, nature’s largest adhesion-based climbers. And humans? We’d need about 40% of our total body surface, or roughly 80% of our front, to be covered in sticky footpads if we wanted to do a convincing Spiderman impression.

Once an animal is big enough to need a substantial fraction of its body surface to be covered in sticky footpads, the necessary morphological changes would make the evolution of this trait impractical, suggests Labonte.

“If a human, for example, wanted to walk up a wall the way a gecko does, we’d need impractically large sticky feet – our shoes would need to be a European size 145 or a US size 114,” says Walter Federle, senior author also from Cambridge’s Department of Zoology.

The researchers say that these insights into the size limits of sticky footpads could have profound implications for developing large-scale bio-inspired adhesives, which are currently only effective on very small areas.

“As animals increase in size, the amount of body surface area per volume decreases – an ant has a lot of surface area and very little volume, and a blue whale is mostly volume with not much surface area” explains Labonte.

“This poses a problem for larger climbing species because, when they are bigger and heavier, they need more sticking power to be able to adhere to vertical or inverted surfaces, but they have comparatively less body surface available to cover with sticky footpads. This implies that there is a size limit to sticky footpads as an evolutionary solution to climbing – and that turns out to be about the size of a gecko.”

Larger animals have evolved alternative strategies to help them climb, such as claws and toes to grip with.

The researchers compared the weight and footpad size of 225 climbing animal species including insects, frogs, spiders, lizards and even a mammal.

“We compared animals covering more than seven orders of magnitude in weight, which is roughly the same as comparing a cockroach to the weight of Big Ben, for example,” says Labonte.

These investigations also gave the researchers greater insights into how the size of adhesive footpads is influenced and constrained by the animals’ evolutionary history.

“We were looking at vastly different animals – a spider and a gecko are about as different as a human is to an ant- but if you look at their feet, they have remarkably similar footpads,” says Labonte.

“Adhesive pads of climbing animals are a prime example of convergent evolution – where multiple species have independently, through very different evolutionary histories, arrived at the same solution to a problem. When this happens, it’s a clear sign that it must be a very good solution.”

The researchers believe we can learn from these evolutionary solutions in the development of large-scale manmade adhesives.

“Our study emphasises the importance of scaling for animal adhesion, and scaling is also essential for improving the performance of adhesives over much larger areas. There is a lot of interesting work still to do looking into the strategies that animals have developed in order to maintain the ability to scale smooth walls, which would likely also have very useful applications in the development of large-scale, powerful yet controllable adhesives,” says Labonte.

There is one other possible solution to the problem of how to stick when you’re a large animal, and that’s to make your sticky footpads even stickier.

“We noticed that within closely related species pad size was not increasing fast enough to match body size, probably a result of evolutionary constraints. Yet these animals can still stick to walls,” says Christofer Clemente, a co-author from the University of the Sunshine Coast [Australia].

“Within frogs, we found that they have switched to this second option of making pads stickier rather than bigger. It’s remarkable that we see two different evolutionary solutions to the problem of getting big and sticking to walls,” says Clemente.

“Across all species the problem is solved by evolving relatively bigger pads, but this does not seem possible within closely related species, probably since there is not enough morphological diversity to allow it. Instead, within these closely related groups, pads get stickier. This is a great example of evolutionary constraint and innovation.”

A researcher at Stanford University (US) took strong exception to the Cambridge team’s conclusions , from a Jan. 28, 2016 article by Michael Grothaus for Fast Company (Note: A link has been removed),

It seems the dreams of the web-slinger’s fans were crushed forever—that is until a rival university swooped in and saved the day. A team of engineers working with mechanical engineering graduate student Elliot Hawkes at Stanford University have announced [in 2014] that they’ve invented a device called “gecko gloves” that proves the Cambridge researchers wrong.

Hawkes has created a video outlining the nature of his dispute with Cambridge University and US tv talk show host, Stephen Colbert who featured the Cambridge University research in one of his monologues,

To be fair to Hawkes, he does prove his point. A Nov. 21, 2014 Stanford University report by Bjorn Carey describes Hawke’s ingenious ‘sticky pads,

Each handheld gecko pad is covered with 24 adhesive tiles, and each of these is covered with sawtooth-shape polymer structures each 100 micrometers long (about the width of a human hair).

The pads are connected to special degressive springs, which become less stiff the further they are stretched. This characteristic means that when the springs are pulled upon, they apply an identical force to each adhesive tile and cause the sawtooth-like structures to flatten.

“When the pad first touches the surface, only the tips touch, so it’s not sticky,” said co-author Eric Eason, a graduate student in applied physics. “But when the load is applied, and the wedges turn over and come into contact with the surface, that creates the adhesion force.”

As with actual geckos, the adhesives can be “turned” on and off. Simply release the load tension, and the pad loses its stickiness. “It can attach and detach with very little wasted energy,” Eason said.

The ability of the device to scale up controllable adhesion to support large loads makes it attractive for several applications beyond human climbing, said Mark Cutkosky, the Fletcher Jones Chair in the School of Engineering and senior author on the paper.

“Some of the applications we’re thinking of involve manufacturing robots that lift large glass panels or liquid-crystal displays,” Cutkosky said. “We’re also working on a project with NASA’s Jet Propulsion Laboratory to apply these to the robotic arms of spacecraft that could gently latch on to orbital space debris, such as fuel tanks and solar panels, and move it to an orbital graveyard or pitch it toward Earth to burn up.”

Previous work on synthetic and gecko adhesives showed that adhesive strength decreased as the size increased. In contrast, the engineers have shown that the special springs in their device make it possible to maintain the same adhesive strength at all sizes from a square millimeter to the size of a human hand.

The current version of the device can support about 200 pounds, Hawkes said, but, theoretically, increasing its size by 10 times would allow it to carry almost 2,000 pounds.

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

Human climbing with efficiently scaled gecko-inspired dry adhesives by Elliot W. Hawkes, Eric V. Eason, David L. Christensen, Mark R. Cutkosky. Jurnal of the Royal Society Interface DOI: 10.1098/rsif.2014.0675 Published 19 November 2014

This paper is open access.

To be fair to the Cambridge researchers, It’s stretching it a bit to say that Hawke’s gecko gloves allow someone to be like Spiderman. That’s a very careful, slow climb achieved in a relatively short period of time. Can the human body remain suspended that way for more than a few minutes? How big do your sticky pads have to be if you’re going to have the same wall-climbing ease of movement and staying power of either a gecko or Spiderman?

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

Extreme positive allometry of animal adhesive pads and the size limits of adhesion-based climbing by David Labonte, Christofer J. Clemente, Alex Dittrich, Chi-Yun Kuo, Alfred J. Crosby, Duncan J. Irschick, and Walter Federle. PNAS doi: 10.1073/pnas.1519459113

This paper is behind a paywall but there is an open access preprint version, which may differ from the PNAS version, available,

Extreme positive allometry of animal adhesive pads and the size limits of adhesion-based climbing by David Labonte, Christofer J Clemente, Alex Dittrich, Chi-Yun Kuo, Alfred J Crosby, Duncan J Irschick, Walter Federle. bioRxiv
doi: http://dx.doi.org/10.1101/033845

I hope that if the Cambridge researchers respond, they will be witty rather than huffy. Finally, there’s this gecko image (which I love) from the Cambridge researchers,

 Caption: This image shows a gecko and ant. Credit: Image courtesy of A Hackmann and D Labonte

Caption: This image shows a gecko and ant. Credit: Image courtesy of A Hackmann and D Labonte

4D printing: a hydrogel orchid

In 2013, the 4th dimension for printing was self-assembly according to a March 1, 2013 article by Tuan Nguyen for ZDNET. A Jan. 25, 2016 Wyss Institute for Biologically Inspired Engineering at Harvard University news release (also on EurekAlert) points to time as the fourth dimension in a description of the Wyss Institute’s latest 4D printed object,

A team of scientists at the Wyss Institute for Biologically Inspired Engineering at Harvard University and the Harvard John A. Paulson School of Engineering and Applied Sciences has evolved their microscale 3D printing technology to the fourth dimension, time. Inspired by natural structures like plants, which respond and change their form over time according to environmental stimuli, the team has unveiled 4D-printed hydrogel composite structures that change shape upon immersion in water.

“This work represents an elegant advance in programmable materials assembly, made possible by a multidisciplinary approach,” said Jennifer Lewis, Sc.D., senior author on the new study. “We have now gone beyond integrating form and function to create transformable architectures.”

In nature, flowers and plants have tissue composition and microstructures that result in dynamic morphologies that change according to their environments. Mimicking the variety of shape changes undergone by plant organs such as tendrils, leaves, and flowers in response to environmental stimuli like humidity and/or temperature, the 4D-printed hydrogel composites developed by Lewis and her team are programmed to contain precise, localized swelling behaviors. Importantly, the hydrogel composites contain cellulose fibrils that are derived from wood and are similar to the microstructures that enable shape changes in plants.

By aligning cellulose fibrils (also known as, cellulose nanofibrils or nanofibrillated cellulose) during printing, the hydrogel composite ink is encoded with anisotropic swelling and stiffness, which can be patterned to produce intricate shape changes. The anisotropic nature of the cellulose fibrils gives rise to varied directional properties that can be predicted and controlled. Just like wood, which can be split easier along the grain rather than across it. Likewise, when immersed in water, the hydrogel-cellulose fibril ink undergoes differential swelling behavior along and orthogonal to the printing path. Combined with a proprietary mathematical model developed by the team that predicts how a 4D object must be printed to achieve prescribed transformable shapes, the new method opens up many new and exciting potential applications for 4D printing technology including smart textiles, soft electronics, biomedical devices, and tissue engineering.

“Using one composite ink printed in a single step, we can achieve shape-changing hydrogel geometries containing more complexity than any other technique, and we can do so simply by modifying the print path,” said Gladman [A. Sydney Gladman, Wyss Institute a graduate research assistant]. “What’s more, we can interchange different materials to tune for properties such as conductivity or biocompatibility.”

The composite ink that the team uses flows like liquid through the printhead, yet rapidly solidifies once printed. A variety of hydrogel materials can be used interchangeably resulting in different stimuli-responsive behavior, while the cellulose fibrils can be replaced with other anisotropic fillers of choice, including conductive fillers.

“Our mathematical model prescribes the printing pathways required to achieve the desired shape-transforming response,” said Matsumoto [Elisabetta Matsumoto, Ph.D., a postdoctoral fellow at the Wyss]. “We can control the curvature both discretely and continuously using our entirely tunable and programmable method.”

Specifically, the mathematical modeling solves the “inverse problem”, which is the challenge of being able to predict what the printing toolpath must be in order to encode swelling behaviors toward achieving a specific desired target shape.

“It is wonderful to be able to design and realize, in an engineered structure, some of nature’s solutions,” said Mahadevan [L. Mahadevan, Ph.D., a Wyss Core Faculty member] , who has studied phenomena such as how botanical tendrils coil, how flowers bloom, and how pine cones open and close. “By solving the inverse problem, we are now able to reverse-engineer the problem and determine how to vary local inhomogeneity, i.e. the spacing between the printed ink filaments, and the anisotropy, i.e. the direction of these filaments, to control the spatiotemporal response of these shapeshifting sheets. ”

“What’s remarkable about this 4D printing advance made by Jennifer and her team is that it enables the design of almost any arbitrary, transformable shape from a wide range of available materials with different properties and potential applications, truly establishing a new platform for printing self-assembling, dynamic microscale structures that could be applied to a broad range of industrial and medical applications,” said Wyss Institute Founding Director Donald Ingber, M.D., Ph.D., who is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and the Vascular Biology Program at Boston Children’s Hospital and Professor of Bioengineering at Harvard SEAS [School of Engineering and Applied Science’.

Here’s an animation from the Wyss Institute illustrating the process,

And, here’s a link to and a citation for the paper,

Biomimetic 4D printing by A. Sydney Gladman, Elisabetta A. Matsumoto, Ralph G. Nuzzo, L. Mahadevan, & Jennifer A. Lewis. Nature Materials (2016) doi:10.1038/nmat4544 Published online 25 January 2016

This paper is behind a paywall.

Revolutionary ‘smart’ windows from the UK

This is the first time I’ve seen self-cleaning and temperature control features mentioned together with regard to a ‘smart’ window, which makes this very exciting news. From a Jan. 20, 2016 UK Engineering and Physical Sciences Research Council (EPSRC) press release (also on EurekAlert),

A revolutionary new type of smart window could cut window-cleaning costs in tall buildings while reducing heating bills and boosting worker productivity. Developed by University College London (UCL) with support from EPSRC, prototype samples confirm that the glass can deliver three key benefits:

Self-cleaning: The window is ultra-resistant to water, so rain hitting the outside forms spherical droplets that roll easily over the surface – picking up dirt, dust and other contaminants and carrying them away. This is due to the pencil-like, conical design of nanostructures engraved onto the glass, trapping air and ensuring only a tiny amount of water comes into contact with the surface. This is different from normal glass, where raindrops cling to the surface, slide down more slowly and leave marks behind.
Energy-saving: The glass is coated with a very thin (5-10nm) film of vanadium dioxide which during cold periods stops thermal radiation escaping and so prevents heat loss; during hot periods it prevents infrared radiation from the sun entering the building. Vanadium dioxide is a cheap and abundant material, combining with the thinness of the coating to offer real cost and sustainability advantages over silver/gold-based and other coatings used by current energy-saving windows.
Anti-glare: The design of the nanostructures also gives the windows the same anti-reflective properties found in the eyes of moths and other creatures that have evolved to hide from predators. It cuts the amount of light reflected internally in a room to less than 5 per cent – compared with the 20-30 per cent achieved by other prototype vanadium dioxide coated, energy-saving windows – with this reduction in ‘glare’ providing a big boost to occupant comfort.

This is the first time that a nanostructure has been combined with a thermochromic coating. The bio-inspired nanostructure amplifies the thermochromics properties of the coating and the net result is a self-cleaning, highly performing smart window, said Dr Ioannis Papakonstantinou of UCL.

The UCL team calculate that the windows could result in a reduction in heating bills of up to 40 per cent, with the precise amount in any particular case depending on the exact latitude of the building where they are incorporated. Windows made of the ground-breaking glass could be especially well-suited to use in high-rise office buildings.

Dr Ioannis Papakonstantinou of UCL, project leader, explains: It’s currently estimated that, because of the obvious difficulties involved, the cost of cleaning a skyscraper’s windows in its first 5 years is the same as the original cost of installing them. Our glass could drastically cut this expenditure, quite apart from the appeal of lower energy bills and improved occupant productivity thanks to less glare. As the trend in architecture continues towards the inclusion of more glass, it’s vital that windows are as low-maintenance as possible.

So, when can I buy these windows? (from the press release; Note: Links have been removed)

Discussions are now under way with UK glass manufacturers with a view to driving this new window concept towards commercialisation. The key is to develop ways of scaling up the nano-manufacturing methods that the UCL team have specially developed to produce the glass, as well as scaling up the vanadium dioxide coating process. Smart windows could begin to reach the market within around 3-5 years [emphasis mine], depending on the team’s success in securing industrial interest.

Dr Papakonstantinou says: We also hope to develop a ‘smart’ film that incorporates our nanostructures and can easily be added to conventional domestic, office, factory and other windows on a DIY [do-it-yourself] basis to deliver the triple benefit of lower energy use, less light reflection and self-cleaning, without significantly affecting aesthetics.

Professor Philip Nelson, Chief Executive of EPSRC said: This project is an example of how investing in excellent research drives innovation to produce tangible benefits. In this case the new technique could deliver both energy savings and cost reductions.

A 5-year European Research Council (ERC) starting grant (IntelGlazing) has been awarded to fabricate smart windows on a large scale and test them under realistic, outdoor environmental conditions.

The UCL team that developed the prototype smart window includes Mr Alaric Taylor, a PhD student in Dr Papakonstantinou’s group, and Professor Ivan Parkin from UCL’s Department of Chemistry.

I wish them good luck.

One last note, these new windows are the outcome of a 2.5 year EPSRC funded project: Biologically Inspired Nanostructures for Smart Windows with Antireflection and Self-Cleaning Properties, which ended in Sept.  2015.