Tag Archives: Alison Grinthal

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

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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.

A bioinspired approach to self-healing materials

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Scientists have been working to develop self-healing materials for a while now and a Jan. 8, 2016 news item on Nanowerk chronicles a relatively recent attempt,

Inspired by healing wounds in skin, a new approach protects and heals surfaces using a fluid secretion process. In response to damage, dispersed liquid-storage droplets are controllably secreted. The stored liquid replenishes the surface and completes the repair of the polymer in seconds to hours …

The fluid secretion approach to repair the material has also been demonstrated in fibers and microbeads. This bioinspired approach could be extended to create highly desired adaptive, resilient materials with possible uses in heat transfer, humidity control, slippery surfaces, and fluid delivery.

A December ??, 2015 US Department of Energy (DOE) news release, which originated the news item, expands on the theme,

A polymer that secretes stored liquid in response to damage has been designed and created to function as a self-healing material. While human-made material systems can trigger the release of stored contents, the ability to continuously self-adjust and monitor liquid supply in these compartments is a challenge. In contrast, biological systems manage complex protection and healing functions by having individual components work in concert to initiate and self-regulate a coordinated response. Inspired by biological wound-healing, this new process, developed by researchers at Harvard University, involves trapping and dispersing liquid-storage droplets within a reversibly crosslinked polymer gel network topped with a thin liquid overlayer. This novel approach allows storage of the liquid, yet is reconfigurable to induce finely controlled secretion in response to polymer damage. When the gel was damaged by slicing, the ruptured droplets in the immediate vicinity of the damage released oil and the gel network was squeezed. This squeezing allowed oil to be pushed out from neighboring droplets and the polymer network linkages to unzip and rezip rapidly, allowing just enough oil to flow to the damaged region. Healing occurred at ambient temperature within seconds to hours as fluid was secreted into the crack, severed polymer ends diffused across the gap, and new network linkages were created. Droplet-embedded polymers repaired faster or at lower temperatures than polymers without oil droplets. Also, the repaired droplet-embedded materials were much stronger than the repaired networks that did not contain the droplets. This dynamic liquid exchange to repair the material has also been demonstrated in other forms, showing the potential to extend this bioinspired approach for fabricating highly desired adaptive, resilient materials to a wide range of polymeric structures.

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

Dynamic polymer systems with self-regulated secretion for the control of surface properties and material healing by Jiaxi Cui, Daniel Daniel, Alison Grinthal, Kaixiang Lin, & Joanna Aizenberg. Nature Materials 14,  790–795 (2015) doi:10.1038/nmat4325 Published online 22 June 2015

I’m not sure what occasioned a late push to promote this particular piece of research but if you are interested, the paper is behind a paywall.

“Spring is like a perhaps hand,” E. E. Cummings, Harvard, and nano flowers

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It’s always a treat to read a news/press/media release that starts with poetry. From the May 16, 2013 Harvard University press release,

“Spring is like a perhaps hand,” wrote the poet E. E. Cummings: “carefully / moving a perhaps / fraction of flower here placing / an inch of air there… / without breaking anything.”

This was written to celebrate the publication of a paper by Wim L. Noorduin and others, from the press release (Note: Links have been removed),

By simply manipulating chemical gradients in a beaker of fluid, Wim L. Noorduin, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS) and lead author of a paper appearing on the cover of the May 17 issue of Science, has found that he can control the growth behavior of these crystals to create precisely tailored structures.

“For at least 200 years, people have been intrigued by how complex shapes could have evolved in nature. This work helps to demonstrate what’s possible just through environmental, chemical changes,” says Noorduin.

The precipitation of the crystals depends on a reaction of compounds that are diffusing through a liquid solution. The crystals grow toward or away from certain chemical gradients as the pH of the reaction shifts back and forth. The conditions of the reaction dictate whether the structure resembles broad, radiating leaves, a thin stem, or a rosette of petals.

…

Replicating this type of effect in the laboratory was a matter of identifying a suitable chemical reaction and testing, again and again, how variables like the pH, temperature, and exposure to air might affect the nanoscale structures.

The project fits right in with the work of Joanna Aizenberg, an expert in biologically inspired materials science, biomineralization, and self-assembly, and principal investigator for this research.

Aizenberg is the Amy Smith Berylson Professor of Materials Science at Harvard SEAS, Professor of Chemistry and Chemical Biology in the Harvard Department of Chemistry and Chemical Biology, and a Core Faculty Member of the Wyss Institute for Biologically Inspired Engineering at Harvard.

Here are some details about how the scientists created their ‘flowers, from the press release,

To create the flower structures, Noorduin and his colleagues dissolve barium chloride (a salt) and sodium silicate (also known as waterglass) into a beaker of water. Carbon dioxide from air naturally dissolves in the water, setting off a reaction which precipitates barium carbonate crystals. As a byproduct, it also lowers the pH of the solution immediately surrounding the crystals, which then triggers a reaction with the dissolved waterglass. This second reaction adds a layer of silica to the growing structures, uses up the acid from the solution, and allows the formation of barium carbonate crystals to continue.

“You can really collaborate with the self-assembly process,” says Noorduin. “The precipitation happens spontaneously, but if you want to change something then you can just manipulate the conditions of the reaction and sculpt the forms while they’re growing.”

Increasing the concentration of carbon dioxide, for instance, helps to create ‘broad-leafed’ structures. Reversing the pH gradient at the right moment can create curved, ruffled structures.

Noorduin and his colleagues have grown the crystals on glass slides and metal blades; they’ve even grown a field of flowers in front of President Lincoln’s seat on a one-cent coin.

“When you look through the electron microscope, it really feels a bit like you’re diving in the ocean, seeing huge fields of coral and sponges,” describes Noorduin. “Sometimes I forget to take images because it’s so nice to explore.”

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

Rationally Designed Complex, Hierarchical Microarchitectures by Wim L. Noorduin, Alison Grinthal, L. Mahadevan, and Joanna Aizenberg. Science 17 May 2013: Vol. 340 no. 6134 pp. 832-837 DOI: 10.1126/science.1234621

H/T to the May 17, 2013 news item on Azonano.