Tag Archives: self-healing materials

Use kombucha to produce bacterial cellulose

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The combination of the US Army, bacterial cellulose, and kombucha seems a little unusual. However, this January 26, 2021 U.S. Army Research Laboratory news release (also on EurekAlert) provides some clues as to how this combination makes sense,

Kombucha tea, a trendy fermented beverage, inspired researchers to develop a new way to generate tough, functional materials using a mixture of bacteria and yeast similar to the kombucha mother used to ferment tea.

With Army funding, using this mixture, also called a SCOBY, or symbiotic culture of bacteria and yeast, engineers at MIT [Massachusetts Institute of Technology] and Imperial College London produced cellulose embedded with enzymes that can perform a variety of functions, such as sensing environmental pollutants and self-healing materials.

The team also showed that they could incorporate yeast directly into the cellulose, creating living materials that could be used to purify water for Soldiers in the field or make smart packaging materials that can detect damage.

“This work provides insights into how synthetic biology approaches can harness the design of biotic-abiotic interfaces with biological organization over multiple length scales,” said Dr. Dawanne Poree, program manager, Army Research Office, an element of the U.S. Army Combat Capabilities Development Command, now known as DEVCOM, Army Research Laboratory. “This is important to the Army as this can lead to new materials with potential applications in microbial fuel cells, sense and respond systems, and self-reporting and self-repairing materials.”

The research, published in Nature Materials was funded by ARO [Army Research Office] and the Army’s Institute for Soldier Nanotechnologies [ISN] at the Massachusetts Institute of Technology. The U.S. Army established the ISN in 2002 as an interdisciplinary research center devoted to dramatically improving the protection, survivability, and mission capabilities of the Soldier and Soldier-supporting platforms and systems.

“We foresee a future where diverse materials could be grown at home or in local production facilities, using biology rather than resource-intensive centralized manufacturing,” said Timothy Lu, an MIT associate professor of electrical engineering and computer science and of biological engineering.

Researchers produced cellulose embedded with enzymes, creating living materials that could be used to purify water for Soldiers in the field or make smart packaging materials that can detect damage. These fermentation factories, which usually contain one species of bacteria and one or more yeast species, produce ethanol, cellulose, and acetic acid that gives kombucha tea its distinctive flavor.

Most of the wild yeast strains used for fermentation are difficult to genetically modify, so the researchers replaced them with a strain of laboratory yeast called Saccharomyces cerevisiae. They combined the yeast with a type of bacteria called Komagataeibacter rhaeticus that their collaborators at Imperial College London had previously isolated from a kombucha mother. This species can produce large quantities of cellulose.

Because the researchers used a laboratory strain of yeast, they could engineer the cells to do any of the things that lab yeast can do, such as producing enzymes that glow in the dark, or sensing pollutants or pathogens in the environment. The yeast can also be programmed so that they can break down pollutants/pathogens after detecting them, which is highly relevant to Army for chem/bio defense applications.

“Our community believes that living materials could provide the most effective sensing of chem/bio warfare agents, especially those of unknown genetics and chemistry,” said Dr. Jim Burgess ISN program manager for ARO.

The bacteria in the culture produced large-scale quantities of tough cellulose that served as a scaffold. The researchers designed their system so that they can control whether the yeast themselves, or just the enzymes that they produce, are incorporated into the cellulose structure. It takes only a few days to grow the material, and if left long enough, it can thicken to occupy a space as large as a bathtub.

“We think this is a good system that is very cheap and very easy to make in very large quantities,” said MIT graduate student and the paper’s lead author, Tzu-Chieh Tang. To demonstrate the potential of their microbe culture, which they call Syn-SCOBY, the researchers created a material incorporating yeast that senses estradiol, which is sometimes found as an environmental pollutant. In another version, they used a strain of yeast that produces a glowing protein called luciferase when exposed to blue light. These yeasts could be swapped out for other strains that detect other pollutants, metals, or pathogens.

The researchers are now looking into using the Syn-SCOBY system for biomedical or food applications. For example, engineering the yeast cells to produce antimicrobials or proteins that could benefit human health.

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

Living materials with programmable functionalities grown from engineered microbial co-cultures by Charlie Gilbert, Tzu-Chieh Tang, Wolfgang Ott, Brandon A. Dorr, William M. Shaw, George L. Sun, Timothy K. Lu & Tom Ellis. Nature Materials (2021) DOI: https://doi.org/10.1038/s41563-020-00857-5 Published: 11 January 2021

This paper is behind a paywall.

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.

Pancake bounce

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What impact does a droplet make on a solid surface? It’s not the first question that comes to my mind but scientists have been studying it for over a century. From an Aug. 5, 2015 news item on Nanowerk (Note: A link has been removed),

Studies of the impact a droplet makes on solid surfaces hark back more than a century. And until now, it was generally believed that a droplet’s impact on a solid surface could always be separated into two phases: spreading and retracting. But it’s much more complex than that, as a team of researchers from City University of Hong Kong, Ariel University in Israel, and Dalian University of Technology in China report in the journal Applied Physics Letters, from AIP Publishing (“Controlling drop bouncing using surfaces with gradient features”).

An Aug. 4, 2015 American Institute of Physics news release (also on EurekAlert), which originated the news item, describes the impact in detail,

“During the spreading phase, the droplet undergoes an inertia-dominant acceleration and spreads into a ‘pancake’ shape,” explained Zuankai Wang, an associate professor within the Department of Mechanical and Biomedical Engineering at the City University of Hong Kong. “And during the retraction phase, the drop minimizes its surface energy and pulls back inward.”

Remarkably, on gold standard superhydrophobic–a.k.a. repellant–surfaces such as lotus leaves, droplets jump off at the end of the retraction stage due to the minimal energy dissipation during the impact process. This is attributed to the presence of an air cushion within the rough surface.

There exists, however, a classical limit in terms of the contact time between droplets and the gold standard superhydrophobic materials inspired by lotus leaves.

As the team previously reported in the journal Nature Physics, it’s possible to shape the droplet to bounce from the surface in a pancake shape directly at the end of the spreading stage without going through the receding process. As a result, the droplet can be shed away much faster.

“Interestingly, the contact time is constant under a wide range of impact velocities,” said Wang. “In other words: the contact time reduction is very efficient and robust, so the novel surface behaves like an elastic spring. But the real magic lies within the surface texture itself.”

To prevent the air cushion from collapsing or water from penetrating into the surface, conventional wisdom suggests the use of nanoscale posts with small inter-post spacings. “The smaller the inter-post spacings, the greater the impact velocity the small inter-post can withstand,” he elaborated. “By contrast, designing a surface with macrostructures–tapered sub-millimeter post arrays with a wide spacing–means that a droplet will shed from it much faster than any previously engineered materials.”

What the New Results Show

Despite exciting progress, rationally controlling the contact time and quantitatively predicting the critical Weber number–a number used in fluid mechanics to describe the ratio between deforming inertial forces and stabilizing cohesive forces for liquids flowing through a fluid medium–for the occurrence of pancake bouncing remained elusive.

So the team experimentally demonstrated that the drop bouncing is intricately influenced by the surface morphology. “Under the same center-to-center post spacing, surfaces with a larger apex angle can give rise to more pancake bouncing, which is characterized by a significant contact time reduction, smaller critical Weber number, and a wider Weber number range,” according to co-authors Gene Whyman and Edward Bormashenko, both professors at Ariel University.

Wang and colleagues went on to develop simple harmonic spring models to theoretically reveal the dependence of timescales associated with the impinging drop and the critical Weber number for pancake bouncing on the surface morphology. “The insights gained from this work will allow us to rationally design various surfaces for many practical applications,” he added.

The team’s novel surfaces feature a shortened contact time that prevents or slows ice formation. “Ice formation and its subsequent buildup hinder the operation of modern infrastructures–including aircraft, offshore oil platforms, air conditioning systems, wind turbines, power lines, and telecommunications equipment,” Wang said.

At supercooled temperatures, which involves lowering the temperature of a liquid or gas below its freezing point without it solidifying, the longer a droplet remains in contact with a surface before bouncing off the greater the chances are of it freezing in place. “Our new surface structure can be used to help prevent aircraft wings and engines from icing,” he said.

This is highly desirable, because a very light coating of snow or ice–light enough to be barely visible–is known to reduce the performance of airplanes and even cause crashes. One such disaster occurred in 2009, and called attention to the dangers of in-flight icing after it caused Air France Flight 447 flying from Rio de Janeiro to Paris to crash into the Atlantic Ocean.

Beyond anti-icing for aircraft, “turbine blades in power stations and wind farms can also benefit from an anti-icing surface by gaining a boost in efficiency,” he added.

As you can imagine, this type of nature-inspired surface shows potential for a tremendous range of other applications as well–everything from water and oil separation to disease transmission prevention.

The next step for the team? To “develop bioinspired ‘active’ materials that are adaptive to their environments and capable of self-healing,” said Wang.

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

Controlling drop bouncing using surfaces with gradient features by Yahua Liu, Gene Whyman, Edward Bormashenko, Chonglei Hao, and Zuankai Wang. Appl. Phys. Lett. 107, 051604 (2015); http://dx.doi.org/10.1063/1.4927055

This paper appears to be open access.

Finally, here’s an illustration of the pancake bounce,

Droplet hitting tapered posts shows “pancake” bouncing characterized by lifting off the surface of the end of spreading without retraction. Credit- Z.Wang/HKU

Droplet hitting tapered posts shows “pancake” bouncing characterized by lifting off the surface of the end of spreading without retraction. Credit- Z.Wang/HKU

There is also a pancake bounce video which you can view here on EurekAlert.

Global Agenda Council on Emerging Technologies announces its 2013 list of top 10 emerging technologies

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On Feb. 18, 2012 I published a list of technologies with life and globe changing impacts supplied by the World Economic Forum’s (WEF) Global Agenda Council on Emerging Technologies and, coincidentally, I’m publishing another such list from the Global Agenda Council on exactly the same day in 2013.  Although I’m not alone, Nanowerk has published a Feb. 18, 2013 news item featuring this year’s list, others published the list last week.

From a Feb. 14, 2013 post by Tim Harper (a member of the Global Agenda Council) on his Cientifica company’s Insight blog,

OnLine Electric Vehicles (OLEV)

Already widely used to exchange digital information, wireless technology can now also deliver electric power to moving vehicles. In next-generation electric cars, pick-up coil sets under the vehicle floor receive power remotely via an electromagnetic field broadcast from cables installed under the road surface. The current also charges an onboard battery used to power the vehicle when it is out of range. As electricity is supplied externally, these vehicles require only a fifth the battery capacity of a standard electric car, and can achieve transmission efficiencies of over 80 percent. Online electric vehicles are currently undergoing road tests in Seoul, South Korea.

3-D printing and remote manufacturing

Three-dimensional printing allows the creation of solid structures from a digital computer file, potentially revolutionising the economics of manufacturing if objects can be printed remotely in the home or office rather than requiring time and energy for transportation. The process involves layers of material being deposited on top of each other in order to create free-standing structures from the bottom up. Blueprints from computer-aided design are sliced into cross-section for print templates, allowing virtually-created objects to be used as models for ‘hard copies’ made from plastics, metal alloys or other materials.

Self-healing materials

One of the defining characteristics of living organisms is the inherent ability to repair physical damage done to them. A growing trend in biomimicry is the creation of non-living structural materials that also have the capacity to heal themselves when cut, torn or cracked. Self-healing materials which can repair damage without external human intervention could give manufactured goods longer lifetimes and reduce the demand for raw materials, as well as improving the inherent safety of structural materials used in construction or to form the bodies of aircraft.

Energy-efficient water purification

Water scarcity is a worsening ecological problem in many parts of the world due to competing demands from agriculture, cities and other human uses. Where freshwater systems are over-used or exhausted, desalination from the sea offers near-unlimited water but at the expense of considerable use of energy – mostly from fossil fuels – to drive evaporation or reverse osmosis systems. Emerging technologies offer the potential for significantly higher energy efficiency in desalination or purification of wastewater, potentially reducing energy consumption by 50 percent or more. Techniques such as forward osmosis can additionally improve efficiency by utilising low-grade heat from thermal power production or renewable heat produced by solar-thermal geothermal installations.

Carbon dioxide (CO2) conversion and use

Long-promised technologies for the capture and underground sequestration of carbon dioxide have yet to be proven commercially viable, even at the scale of a single large power station. New technologies that convert the unwanted CO2 into saleable goods can potentially address both the economic and energetic shortcomings of conventional CCS strategies. One of the most promising approaches uses biologically-engineered photosynthetic bacteria to turn waste CO2 into liquid fuels or chemicals, in low-cost, modular solar converter systems. Whilst only operational today at the acre scale, individual systems are expected to reach hundreds of acres within as little as two years. Being 10 to 100 times as productive per unit of land area, these systems address one of the main environmental constraints on biofuels from agricultural or algal feedstock, and could supply lower carbon fuels for automobiles, aviation or other large-scale liquid fuel users.

Enhanced nutrition to drive health at the molecular level

Even in developed countries millions of people suffer from malnutrition due to nutrient deficiencies in their diets. Efforts to improve the situation by changing diets have met with limited success.  Now modern genomic techniques have been applied to determine at the gene sequence level the vast number of naturally-consumed proteins which are important in the human diet. The proteins identified may have advantages over standard protein supplements in that they can supply a greater percentage of essential amino acids, and have improved solubility, taste, texture and nutritional characteristics. The large-scale production of pure human dietary proteins based on the application of biotechnology to molecular nutrition can deliver health benefits such as in muscle development, managing diabetes or reducing obesity.

Remote sensing

The increasingly widespread use of sensors that allow often passive responses to external stimulae will continue to change the way we respond to the environment, particularly in the area of health. Examples include sensors that continually monitor bodily function – such as heart rate, blood oxygen and blood sugar levels – and if necessary trigger a medical response such as insulin provision. Advances rely on wireless communication between devices, low power sensing technologies and, sometimes, active energy harvesting.  Other examples include vehicle-to-vehicle sensing for improved safety on the road.

Precise drug delivery through nanoscale engineering

Pharmaceuticals which can be precisely delivered at the molecular level within or around the cell offer unprecedented opportunities for more effectively treatments while reducing unwanted side effects. Targeted nanoparticles that adhere to diseased tissue allow for the micro-scale delivery of potent therapeutic compounds while minimizing their impact on healthy tissue, and are now advancing in medical trials. After almost a decade of research, these new approaches are now finally showing signs of clinical utility, through increasing the local concentration and exposure time of the required drug and thereby increasing its effectiveness. As well as improving the effects of current drugs, these advances in nanomedicine promise to rescue other drugs, which would otherwise be rejected due to their dose-limiting toxicity.

Organic electronics and photovoltaics

Organic electronics – a type of printed electronics – is the use of organic materials such as polymers to create electronic circuits and devices. In contrast to traditional (silicon based) semiconductors that are fabricated with expensive photolithographic techniques, organic electronics can be printed using low-cost, scalable processes such as ink jet printing- making them extremely cheap compared with traditional electronics devices, both in terms of the cost per device and the capital equipment required to produce them. While organic electronics are currently unlikely to compete with silicon in terms of speed and density, they have the potential to provide a significant edge in terms of cost and versatility. The cost implications of printed mass-produced solar photovoltaic collectors for example could accelerate the transition to renewable energy.

Fourth-generation reactors and nuclear waste recycling

Current once-through nuclear power reactors only utilise 1% of the potential energy available in uranium, leaving the rest radioactively contaminated as nuclear ‘waste’. Whilst the technical challenge of geological disposal is manageable, the political challenge of nuclear waste seriously limits the appeal of this zero-carbon and highly scaleable energy technology. Spent-fuel recycling and breeding uranium-238 into new fissile material – known as ‘Nuclear 2.0’ – would extend already-mined uranium resources for centuries while dramatically reducing the volume and long-term toxicity of wastes, whose radioactivity will drop below the level of the original uranium ore on a timescale of centuries rather millennia. This makes geological disposal much less of a challenge (and arguably even unnecessary) and nuclear waste a minor environmental issue compared to hazardous wastes produced by other industries. Fourth-generation technologies, including liquid metal-cooled fast reactors, are now being deployed in several countries and are offered by established nuclear engineering companies.

You can also find the list in the World Economic Forum’s Feb. 14, 2013 posting by David King (currently the chair of the Global Agenda Council on Emerging Technologies). There’s also more information about the Global Agenda Council here.