UCLA School of Dentistry: New membrane class shown to regenerate tissue and bone, viable solution for periodontitis


newmembranecA multifunctional periodontal membrane is surgically inserted into the pocket between affected gums and tooth. This new membrane has shown to protect the site from further infection as well as to help regrow bone. Credit: UCLA School of Dentistry

Periodontitis affects nearly half of Americans ages 30 and older, and in its advanced stages, it could lead to early tooth loss or worse. Recent studies have shown that periodontitis could also increase risk of heart disease and Alzheimer’s disease.

A team of UCLA researchers has developed methods that may lead to more effective and reliable therapy for periodontal disease—ones that promote gum tissue and bone regeneration with biological and mechanical features that can be adjusted based on treatment needs. The study is published online in ACS Nano.

Periodontitis is a chronic, destructive disease that inflames the gums surrounding the tooth and eventually degrades the structure holding the tooth in place, forming infected pockets leading to bone and tooth loss. Current treatments include infection-fighting methods; application of molecules that promote tissue growth, also known as growth factors; and guided tissue regeneration, which is considered the optimal standard of care for the treatment of periodontitis.

Guided tissue regeneration, in the case of periodontitis, involves the use of a membrane or thin film that is surgically placed between the inflamed gum and the tooth. Membranes, which come in non-biodegradable and biodegradable forms, are meant to act not only as barriers between the infection and the gums, but also as a delivery system for drugs, antibiotics and growth factors to the gum tissue.

Unfortunately, results from guided tissue regeneration are inconsistent. Current membranes lack the ability to regenerate gum tissue directly and aren’t able to maintain their structure and stability when placed in the mouth. The membrane also can’t support prolonged drug delivery, which is necessary to help heal infected gum tissue. For non-biodegradable membranes, multiple surgeries are needed to remove the membrane after any drugs have been released—compromising the healing process.

“Given the current disadvantages with guided tissue regeneration, we saw the need to develop a new class of membranes, which have tissue and bone regeneration properties along with a flexible coating that can adhere to a range of biological surfaces,” said Dr. Alireza Moshaverinia, lead author of the study and assistant professor of prosthodontics at the UCLA School of Dentistry. “We’ve also figured out a way to prolong the drug delivery timeline, which is key for effective wound healing.”

The team started with an FDA-approved polymer—a large-scale synthetic molecule commonly used in biomedical applications. Because the polymer’s surface isn’t suitable for cell adhesion in periodontal treatment, the researchers introduced a polydopamine coating—a polymer that has excellent adhesive properties and can attach to surfaces in wet conditions. The other benefit of using such a coating is that it speeds up bone regeneration by promoting mineralization of hydroxyapatite, which is the mineral that makes up tooth enamel and bone.

After identifying an optimal combination for their new membrane, the researchers used electrospinning to bond the polymer with the polydopamine coating. Electrospinning is a production method that simultaneously spins two substances at a rapid speed with positive and negative charges, and fuses them together to create one substance. To improve their new membrane’s surface and structural characteristics, the researchers used metal mesh templates in conjunction with the electrospinning to create different patterns, or micro-patterning, similar to the surface of gauze or a waffle.

“By creating a micro pattern on the surface of the membrane, we are now able to localize cell adhesion and to manipulate the membrane’s structure,” said co-lead author Paul Weiss, UC presidential chair and distinguished professor of chemistry and biochemistry, bioengineering, and materials science and engineering at UCLA. “We were able to mimic the complex structure of periodontal tissue and, when placed, our membrane complements the correct biological function on each side.”

To test the safety and efficiency of their new membrane, the researchers injected rat models with gingival-derived human stem cells and human periodontal ligament stem cells. After eight weeks of evaluating the degradation of the membranes and the tissue’s response, they observed that the patterned, polydopamine-coated polymer membrane had higher levels of bone gain when compared to models with no membrane or a membrane with no coating.

In order to suit a wide range of medical and dental applications, the researchers also figured out a way to adjust the speed at which their membranes degraded when inserted in their models. They did this by adding and subtracting different oxidative agents or using lighter polymer bases before going through the electrospinning process. The ability to turn the degradation rates up or down helped the researchers control the timing of the delivery of drugs to the desired areas.

“We’ve determined that our membranes were able to slow down periodontal infection, promote bone and tissue regeneration, and stay in place long enough to prolong the delivery of useful drugs,” Moshaverinia said. “We see this application expanding beyond periodontitis treatment to other areas needing expedited wound healing and prolonged drug delivery therapeutics.”

The researchers’ next steps are to evaluate whether their membranes can deliver cells with growth factors in the presence or absence of stem cells.

 Explore further: Microscopic membrane could fight gum disease

More information: Mohammad Mahdi Hasani-Sadrabadi et al. Hierarchically Patterned Polydopamine-Containing Membranes for Periodontal Tissue Engineering, ACS Nano (2019). DOI: 10.1021/acsnano.8b09623

 

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Sprayable gel could help the body fight off cancer … after surgery


sprayablegelA scanning electron microscope image of a gel developed by UCLA researchers that could help prevent cancer from recurring after surgery. Credit: University of California, Los Angeles

Many people who are diagnosed with cancer will undergo some type of surgery to treat their disease—almost 95 percent of people with early-diagnosed breast cancer will require surgery and it’s often the first line of treatment for people with brain tumors, for example. But despite improvements in surgical techniques over the past decade, the cancer often comes back after the procedure.

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Now, a UCLA-led  has developed a spray gel embedded with immune-boosting drugs that could help. In a peer-reviewed study, the substance was successful half of the time in awakening lab animals’ immune systems to stop the cancer from recurring and inhibit it from spreading to other parts of the body.

A paper describing the work is published online in the journal Nature Nanotechnology.

The researchers, led by Zhen Gu, a professor of bioengineering at the UCLA Samueli School of Engineering and member of the UCLA Jonsson Comprehensive Cancer Center, tested the biodegradable spray gel in mice that had advanced melanoma tumors surgically removed. They found that the gel reduced the growth of the tumor cells that remained after surgery, which helped prevent recurrences of the cancer: After receiving the treatment, 50 percent of the mice survived for at least 60 days without their tumors regrowing.

The spray not only inhibited the recurrence of tumors from the area on the body where it was removed, but it also controlled the development of tumors in other parts of the body, said Gu, who is also a member of the California NanoSystems Institute at UCLA.

Cancer-treatment-655x353The substance will have to go through further testing and approvals before it could be used in humans. But Gu said that the scientists envision the gel being applied to the tumor resection site by surgeons immediately after the tumor is removed during surgery.

“This sprayable gel shows promise against one of the greatest obstacles in curing cancer,” Gu said. “One of the trademarks of cancers is that it spreads. In fact, around 90 percent of people with cancerous tumors end up dying because of  recurrence or metastasis. Being able to develop something that helps lower this risk for this to occur and has low toxicity is especially gratifying.”

The researchers loaded nanoparticles with an antibody specifically targeted to block CD47, a protein that cancer cells release as a “don’t-eat-me” signal. By blocking CD47, the antibody enables the immune system to find and ultimately destroy the cancer cells.

The nanoparticles are made of calcium carbonate, a substance that is the main component of egg shells and is often found in rocks. Researchers chose  because it can be gradually dissolved in surgical wound sites, which are slightly acidic, and because it boosts the activity of a type of macrophage that helps rid the body of foreign objects, said Qian Chen, the study’s lead author and a  in Gu’s lab.

“We also learned that the gel could activate T cells in the immune system to get them to work together as another line of attack against lingering  cells,” Chen said.

Once the solution is sprayed on the surgical site, it quickly forms a gel embedded with the nanoparticles. The gel helps stop at the surgical site and promotes would healing; the nanoparticles gradually dissolve and release the anti-CD47 antibodies into the body.

The  will continue testing the approach in animals to learn the optimal dose, best mix of nanoparticles and ideal treatment frequency, before testing the gel on human patients.

 Explore further: Gradual release of immunotherapy at site of tumor surgery prevents tumors from returning

More information: Qian Chen et al. In situ sprayed bioresponsive immunotherapeutic gel for post-surgical cancer treatment, Nature Nanotechnology (2018). DOI: 10.1038/s41565-018-0319-4

 

Design for new electrode could boost supercapacitors’ performance – UCLA Researchers Design Super-efficient and Long-lasting electrode for Supercapacitors – 10X Efficiency


UCLA SC Boost 163903_webIMAGE: THE BRANCH-AND-LEAVES DESIGN IS MADE UP OF ARRAYS OF HOLLOW, CYLINDRICAL CARBON NANOTUBES (THE ‘BRANCHES’) AND SHARP-EDGED PETAL-LIKE STRUCTURES (THE ‘LEAVES’) MADE OF GRAPHENE. view more  CREDIT: UCLA ENGINEERING

Engineers from UCLA, 4 other universities produce nanoscale device that mimics the structure of tree branches

UCLA HENRY SAMUELI SCHOOL OF ENGINEERING OF APPLIED SCIENCE

Mechanical engineers from the UCLA Henry Samueli School of Engineering and Applied Science and four other institutions have designed a super-efficient and long-lasting electrode for supercapacitors. The device’s design was inspired by the structure and function of leaves on tree branches, and it is more than 10 times more efficient than other designs.

 

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The branch-and-leaves design is made up of arrays of hollow, cylindrical carbon nanotubes (the “branches”) and sharp-edged petal-like structures (the “leaves”) made of graphene.

The electrode design provides the same amount of energy storage, and delivers as much power, as similar electrodes, despite being much smaller and lighter. In experiments it produced 30 percent better capacitance — a device’s ability to store an electric charge — for its mass compared to the best available electrode made from similar carbon materials, and 30 times better capacitance per area. It also produced 10 times more power than other designs and retained 95 percent of its initial capacitance after more than 10,000 charging cycles.

Their work is described in the journal Nature Communications.

Supercapacitors are rechargeable energy storage devices that deliver more power for their size than similar-sized batteries. They also recharge quickly, and they last for hundreds to thousands of recharging cycles. Today, they’re used in hybrid cars’ regenerative braking systems and for other applications. Advances in supercapacitor technology could make their use widespread as a complement to, or even replacement for, the more familiar batteries consumers buy every day for household electronics.

Engineers have known that supercapacitors could be made more powerful than today’s models, but one challenge has been producing more efficient and durable electrodes. Electrodes attract ions, which store energy, to the surface of the supercapacitor, where that energy becomes available to use. Ions in supercapacitors are stored in an electrolyte solution. An electrode’s ability to deliver stored power quickly is determined in large part by how many ions it can exchange with that solution: The more ions it can exchange, the faster it can deliver power.

Knowing that, the researchers designed their electrode to maximize its surface area, creating the most possible space for it to attract electrons. They drew inspiration from the structure of trees, which are able to absorb ample amounts of carbon dioxide for photosynthesis because of the surface area of their leaves.

“We often find inspiration in nature, and plants have discovered the best way to absorb chemicals such as carbon dioxide from their environment,” said Tim Fisher, the study’s principal investigator and a UCLA professor of mechanical and aerospace engineering. “In this case, we used that idea but at a much, much smaller scale — about one-millionth the size, in fact.”

To create the branch-and-leaves design, the researchers used two nanoscale structures composed of carbon atoms. The “branches” are arrays of hollow, cylindrical carbon nanotubes, about 20 to 30 nanometers in diameter; and the “leaves” are sharp-edged petal-like structures, about 100 nanometers wide, that are made of graphene — ultra thin sheets of carbon. The leaves are then arranged on the perimeter of the nanotube stems. The leaf-like graphene petals also give the electrode stability.

The engineers then formed the structures into tunnel-shaped arrays, which the ions that transport the stored energy flow through with much less resistance between the electrolyte and the surface to deliver energy than they would if the electrode surfaces were flat.

The electrode also performs well in acidic conditions and high temperatures, both environments in which supercapacitors could be used.

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Fisher directs UCLA’s Nanoscale Transport Research Group and is a member of the California NanoSystems Institute at UCLA. Lei Chen, a professor at Mississippi State, was the project’s other principal investigator. The first authors are Guoping Xiong of the University of Nevada, Reno, and Pingge He of Central South University. The research was supported by the Air Force Office of Scientific Research.

 

Chemists synthesize Nano-Ribbons of Graphene for the Next Generation of Semiconductors: Applications for Electronic Devices


UCLA 2-chemistssyntAn illustration of the molecular structure of graphene nanoribbons produced by UCLA scientists. Credit: Yves Rubin

Silicon—the shiny, brittle metal commonly used to make semiconductors—is an essential ingredient of modern-day electronics. But as electronic devices have become smaller and smaller, creating tiny silicon components that fit inside them has become more challenging and more expensive.

Now, UCLA chemists have developed a new method to produce nanoribbons of graphene, next-generation structures that many scientists believe will one day power .

This research is published online in the Journal of the American Chemical Society.

The nanoribbons are extremely narrow strips of graphene, the width of just a few carbon . They’re useful because they possess a bandgap, which means that electrons must be “pushed” to flow through them to create electrical current, said Yves Rubin, a professor of chemistry in the UCLA College and the lead author of the research.

“A material that has no bandgap lets electrons flow through unhindered and cannot be used to build logic circuits,” he said.

Rubin and his research team constructed graphene nanoribbons molecule by molecule using a simple reaction based on ultraviolet light and exposure to 600-degree heat.

“Nobody else has been able to do that, but it will be important if one wants to build these molecules on an industrial scale,” said Rubin, who also is a member of the California NanoSystems Institute at UCLA.

The process improves upon other existing methods for creating graphene nanoribbons, one of which involves snipping open tubes of  known as carbon nanotubes. That particular approach is imprecise and produces ribbons of inconsistent sizes—a problem because the value of a nanoribbon’s bandgap depends on its width, Rubin said.

To create the nanoribbons, the scientists started by growing crystals of four different colorless molecules. The crystals locked the molecules into the perfect orientation to react, and the team then used light to stitch the  into polymers, which are large structures made of repeating units of carbon and .

The scientists then placed the shiny, deep blue polymers in an oven containing only argon gas and heated them to 600 degrees Celsius. The heat provided the necessary boost of energy for the polymers to form the final bonds that gave the nanoribbons their final shape: hexagonal rings composed of carbon atoms, and hydrogen atoms along the edges of the ribbons.

“We’re essentially charring the polymers, but we’re doing it in a controlled way,” Rubin said.

The process, which took about an hour, yielded  just eight  wide but thousands of atoms long. The scientists verified the molecular structure of the nanoribbons, which were deep black in color and lustrous, by shining light of different wavelengths at them.

“We looked at what wavelengths of light were absorbed,” Rubin said. “This reveals signatures of the structure and composition of the ribbons.”

The researchers have filed a patent application for the process.

Rubin said the team now is studying how to better manipulate the nanoribbons—a challenge because they tend to stick together.

“Right now, they are bundles of fibers,” Rubin said. “The next step will be able to handle each nanoribbon one by one.”

 Explore further: A nanotransistor made of graphene nanoribbons

More information: Robert S. Jordan et al. Synthesis of N = 8 Armchair Graphene Nanoribbons from Four Distinct Polydiacetylenes, Journal of the American Chemical Society (2017). DOI: 10.1021/jacs.7b08800

 

UCLA: Solar supercapacitor creates electricity and hydrogen fuel on the cheap


Hydrogen-powered vehicles are slowly hitting the streets, but although it’s a clean and plentiful fuel source, a lack of infrastructure for mass producing, distributing and storing hydrogen is still a major roadblock.

But new work out of the University of California, Los Angeles (UCLA) could help lower the barrier to entry for consumers, with a device that uses sunlight to produce both hydrogen and electricity.

The UCLA device is a hybrid unit that combines a supercapacitor with a hydrogen fuel cell, and runs the whole shebang on solar power.

Along with the usual positive and negative electrodes, the device has a third electrode that can either store energy electrically or use it to split water into its constituent hydrogen and oxygen atoms – a process called water electrolysis.

To make the electrodes as efficient as possible, the team maximized the amount of surface area that comes into contact with water, right down to the nanoscale. That increases the amount of hydrogen the system can produce, as well as how much energy the supercapacitor can store.

“People need fuel to run their vehicles and electricity to run their devices,” says Richard Kaner, senior author of the study. “Now you can make both fuel and electricity with a single device.”

Hydrogen itself may be clean, but producing it on a commercial scale might not be. It’s often created by converting natural gas, which not only results in a lot of carbon dioxide emissions but can be costly.

Using renewable sources like solar can help solve both of those problems at once. And it helps that the UCLA device uses materials like nickel, iron and cobalt, which are much more abundant than the precious metals like platinum that are currently used to produce hydrogen.

“Hydrogen is a great fuel for vehicles: It is the cleanest fuel known, it’s cheap and it puts no pollutants into the air – just water,” says Kaner. “And this could dramatically lower the cost of hydrogen cars.”

The new system could also help solve some of the infrastructure woes as well. Hydrogen vehicles can’t really take off until consumers can easily find places to fill up, and while strides are being made in that department, with the UCLA device users can hook into the sun almost anywhere to produce their own fuel, which could be particularly handy for those living in rural or remote areas.

As an added bonus, the supercapacitor part of the system can chemically store the harvested solar energy as hydrogen. Doing so could help bolster energy storage for the grid. Although the current device is palm-sized, the researchers say that it should be relatively easy to scale up for those applications.

The research was published in the journal Energy Storage Materials.

Source: UCLA

Chasing the ‘Holey’ Grail of Batteries ~ Will Porous Graphene Provide the Next ‘Quantum Leap’?


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A porous form of graphene, the world’s thinnest and lightest nanomaterial, could help bring about the quantum leap in battery efficiency that’s needed to better harness renewable energy

The future, we’re told, will run on batteries. Fully electric vehicles will become the industry standard, running fast and far on a single charge. Our phone and laptop batteries will last for days and recharge in minutes. Our homes may even power themselves, storing energy from rooftop solar panels in lightweight and long-lasting battery packs.

One thing’s clear, though: If this battery-powered future is going to happen, we need a quantum leap in battery technology. Current lithium-ion batteries have hit a wall. For the past decade, researchers have been experimenting with new materials and novel designs to build batteries that are more powerful, last longer, and charge faster. energy_storage_2013 042216 _11-13-1 LARGE

This week, a team of researchers from the United States, China, and Saudi Arabia unveiled a new type of battery electrode made with “holey” graphene. In a paper published in Science, the researchers describe a porous form of graphene — the world’s thinnest and lightest nanomaterial — that overcomes some key challenges in creating next-generation batteries.

To understand how the porous graphene helps, first you need to know how today’s lithium-ion batteries work. Like all batteries, lithium-ion cells contain a positive electrode (cathode) and a negative electrode (anode) separated by a chemical medium called an electrolyte and a semi-permeable barrier called a separator.

RELATED: Fern-Like Sheets of Graphene Could Boost Solar Panel Efficiency

When the battery is charged, lithium ions flow to the anode, which is made of graphite. The lithium ions stick to the surface of the graphite and also bury themselves deep in its layers, which is how the energy is stored. When the battery goes to work powering a device, the ions flow from the anode to the cathode, passing through the separator at a steady rate. At the same time, electrons are released at the anode, flow out into the external circuit, and eventually return to the cathode.

To recap, there are two processes that make batteries work, the transport and storage of ions between electrodes, and the release of electrons into the external circuit. To build a battery that stores more energy and recharges faster, you need to optimize the flow of both ions and electrons.

That’s where nanomaterials come in.

Graphene Anodes 1 id35611Nanomaterials are named for their impossibly small dimensions, measured in nanometers (one millionth of a millimeter). A number of nanoscale materials have been explored as potential electrode materials that could promise far higher performance than today’s batteries. However, those extraordinary results have only been achieved in the lab using research devices with ultrathin electrodes, not the thicker electrodes required for real-world devices.

Graphene is a nanomaterial with some very unique properties. A single sheet of graphene is only one atom thick and consists of a 2D lattice of tightly bonded carbon atoms. Its structure makes it one of the best conductors of electricity on the planet. So if you incorporate graphene into a battery, you can greatly speed up the flow of electrons.

The problem with graphene is that while it’s terrific at moving electrons, it’s impenetrable to ions. If you tried to make an electrode purely out of graphene, the charge/discharge rate of the battery would be slowed by ions having to take detours around the broken edges of the graphene. That’s why researchers decided to punch holes straight through the graphene. Graphene Anodes 2images

Xiangfeng Duan from the UCLA, one of the authors of the Science paper, explained that the “holey” graphene is used as a conductive scaffold to speed the flow of electrons and direct the transport of ions with maximum efficiency. The graphene scaffold has a three-dimensional “hierarchical” structure with large holes feeding into smaller holes, ensuring that ions are funneled to every available nanometer of the electrode.

“It’s like a transportation network in a city,” said Duan. “You start with wide highways and then you move to narrow local roads to access every home. In the battery, the scaffold allows for the efficient transport of ions across a porous network to directly deliver charge to all of the electrode material.”

RELATED: Seaweed Could Provide a Powerful Boost to Next-Gen Batteries

In their experiments, Duan and his team placed the graphene as a conductive scaffold on niobia (Nb2O5) nanoparticles, a material known for its fast charge/discharge rate. Other labs have experimented with building electrodes solely from materials like niobia in super-thin sheets weighing almost nothing. But Duan said that the performance of the active material in such tiny amounts is canceled out by the bulkier inactive components of an electrode, like the current collectors. In other words, what works in the lab won’t cut it in real-world devices.

By loading the niobia on a graphene scaffold, Duan and his team achieved performance results that were several times greater than with a thin nanomaterial alone. Duan pointed out that the same porous scaffold design they used with niobia could be used with other active materials like silicon or tin oxide, which boast high energy density, the ability to store lots of ions for longer-lasting batteries.

It will still be a while before we see “holey” graphene batteries in real-world devices, said Duan, who calls this paper “a critical step, but just a starting point toward commercialization.” Looking ahead, he could easily see niobia-based batteries that charge up to five or 10 times faster than today’s lithium-ion cells. And batteries made with energy-dense materials like silicon could power laptops for 20 or 30 hours on a single charge, and triple the driving range of an electric vehicle.

“I think this really gives us a pathway toward using these high-performance materials in real-world devices,” Duan said.

Battery-free implantable medical device powered by human body – A biological supercapacitor


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Researchers from UCLA and the University of Connecticut have designed a new biofriendly energy storage system called a biological supercapacitor, which operates using charged particles, or ions, from fluids in the human body. The device is harmless to the body’s biological systems, and it could lead to longer-lasting cardiac pacemakers and other implantable medical devices.   The UCLA team was led by Richard Kaner, a distinguished professor of chemistry and biochemistry, and of materials science and engineering, and the Connecticut researchers were led by James Rusling, a professor of chemistry and cell biology.

A paper about their design was published this week in the journal Advanced Energy Materials.   Pacemakers — which help regulate abnormal heart rhythms — and other implantable devices have saved countless lives. But they’re powered by traditional batteries that eventually run out of power and must be replaced, meaning another painful surgery and the accompanying risk of infection. In addition, batteries contain toxic materials that could endanger the patient if they leak.

The researchers propose storing energy in those devices without a battery. The supercapacitor they invented charges using electrolytes from biological fluids like blood serum and urine, and it would work with another device called an energy harvester, which converts heat and motion from the human body into electricity — in much the same way that self-winding watches are powered by the wearer’s body movements. That electricity is then captured by the supercapacitor.   “Combining energy harvesters with supercapacitors can provide endless power for lifelong implantable devices that may never need to be replaced,” said Maher El-Kady, a UCLA postdoctoral researcher and a co-author of the study.

Modern pacemakers are typically about 6 to 8 millimeters thick, and about the same diameter as a 50-cent coin; about half of that space is usually occupied by the battery. The new supercapacitor is only 1 micrometer thick — much smaller than the thickness of a human hair — meaning that it could improve implantable devices’ energy efficiency. It also can maintain its performance for a long time, bend and twist inside the body without any mechanical damage, and store more charge than the energy lithium film batteries of comparable size that are currently used in pacemakers.   “Unlike batteries that use chemical reactions that involve toxic chemicals and electrolytes to store energy, this new class of biosupercapacitors stores energy by utilizing readily available ions, or charged molecules, from the blood serum,” said Islam Mosa, a Connecticut graduate student and first author of the study.

The new biosupercapacitor comprises a carbon nanomaterial called graphene layered with modified human proteins as an electrode, a conductor through which electricity from the energy harvester can enter or leave. The new platform could eventually also be used to develop next-generation implantable devices to speed up bone growth, promote healing or stimulate the brain, Kaner said.

Although supercapacitors have not yet been widely used in medical devices, the study shows that they may be viable for that purpose.   “In order to be effective, battery-free pacemakers must have supercapacitors that can capture, store and transport energy, and commercial supercapacitors are too slow to make it work,” El-Kady said. “Our research focused on custom-designing our supercapacitor to capture energy effectively, and finding a way to make it compatible with the human body.”   Among the paper’s other authors are the University of Connecticut’s Challa Kumar, Ashis Basu and Karteek Kadimisetty. The research was supported by the National Institute of Health’s National Institute of Biomedical Imaging and Bioengineering, the NIH’s National Institute of Environmental Health Sciences, and a National Science Foundation EAGER grant.   Source and top image: UCLA Engineering

 

UCLA: Chemists Devise Technology that could Transform Solar Energy Storage


Energy Storage 061915 chemistsdeviThe materials in most of today’s residential rooftop solar panels can store energy from the sun for only a few microseconds at a time. A new technology developed by chemists at UCLA is capable of storing solar energy for up to several weeks—an advance that could change the way scientists think about designing solar cells.

The findings are published June 19 in the journal Science.

The new design is inspired by the way that plants generate energy through photosynthesis.

“Biology does a very good job of creating energy from sunlight,” said Sarah Tolbert, a UCLA professor of chemistry and one of the senior authors of the research. “Plants do this through photosynthesis with extremely high efficiency.”

“In photosynthesis, plants that are exposed to sunlight use carefully organized nanoscale structures within their cells to rapidly separate charges—pulling electrons away from the positively charged molecule that is left behind, and keeping positive and negative charges separated,” Tolbert said. “That separation is the key to making the process so efficient.”

Energy Storage 061915 chemistsdevi

The scientists devised a new arrangement of solar cell ingredients, with bundles of polymer donors (green rods) and neatly organized fullerene acceptors (purple, tan). Credit: UCLA Chemistry 

To capture energy from sunlight, conventional rooftop solar cells use silicon, a fairly expensive material. There is currently a big push to make lower-cost solar cells using plastics, rather than silicon, but today’s are relatively inefficient, in large part because the separated positive and negative electric charges often recombine before they can become electrical energy.

“Modern plastic solar cells don’t have well-defined structures like plants do because we never knew how to make them before,” Tolbert said. “But this new system pulls charges apart and keeps them separated for days, or even weeks. Once you make the right structure, you can vastly improve the retention of energy.”

The two components that make the UCLA-developed system work are a polymer donor and a nano-scale acceptor. The polymer donor absorbs sunlight and passes electrons to the fullerene acceptor; the process generates electrical energy.

The plastic materials, called organic photovoltaics, are typically organized like a plate of cooked pasta—a disorganized mass of long, skinny polymer “spaghetti” with random fullerene “meatballs.” But this arrangement makes it difficult to get current out of the cell because the electrons sometimes hop back to the polymer spaghetti and are lost.

The UCLA technology arranges the elements more neatly—like small bundles of uncooked spaghetti with precisely placed meatballs. Some fullerene meatballs are designed to sit inside the spaghetti bundles, but others are forced to stay on the outside. The fullerenes inside the structure take electrons from the polymers and toss them to the outside fullerene, which can effectively keep the electrons away from the polymer for weeks.

“When the charges never come back together, the system works far better,” said Benjamin Schwartz, a UCLA professor of chemistry and another senior co-author. “This is the first time this has been shown using modern synthetic organic photovoltaic materials.”

In the new system, the materials self-assemble just by being placed in close proximity.

“We worked really hard to design something so we don’t have to work very hard,” Tolbert said.

The new design is also more environmentally friendly than current technology, because the materials can assemble in water instead of more toxic organic solutions that are widely used today.

“Once you make the materials, you can dump them into water and they assemble into the appropriate structure because of the way the materials are designed,” Schwartz said. “So there’s no additional work.”

The researchers are already working on how to incorporate the technology into actual .

Yves Rubin, a UCLA professor of chemistry and another senior co-author of the study, led the team that created the uniquely designed molecules. “We don’t have these materials in a real device yet; this is all in solution,” he said. “When we can put them together and make a closed circuit, then we will really be somewhere.”

For now, though, the UCLA research has proven that inexpensive photovoltaic can be organized in a way that greatly improves their ability to retain from sunlight.

Explore further: Improving the efficiency of solar energy cells

More information: Long-lived photoinduced polaron formation in conjugated polyelectrolyte-fullerene assemblies Science 19 June 2015: Vol. 348 no. 6241 pp. 1340-1343. DOI: 10.1126/science.aaa6850

Self-assembly fabricating method for graphene nanoribbons brings scientists a step closer to revolutionizing electronics


1-Self Assembling NP id37769First characterized in 2004, graphene is a two-dimensional material with extraordinary properties. The thickness of just one carbon atom, and hundreds of times faster at conducting heat and charge than silicon, graphene is expected to revolutionize high-speed transistors in the near future.
Graphene’s exotic electronic and magnetic properties can be tailored by cutting large sheets of the material down to ribbons of specific lengths and edge configurations — scientists have theorized that nanoribbons with zigzag edges are the most magnetic, making them suitable for spintronics applications. (Spintronics devices, unlike conventional electronics, use electrons’ spins rather than their charge.) But this “top-down” fabrication approach is not yet practical, because current lithographic techniques for tailoring the ribbons always produce defects.
Graphene nanoribbons
Graphene nanoribbons imaged by scanning tunneling microscopy. The zigzag edges are highlighted by the red structure. (Image: Patrick Han)
Now, scientists from UCLA and Tohoku University have discovered a new self-assembly method for producing defect-free graphene nanoribbons with periodic zigzag-edge regions. In this “bottom-up” technique, researchers use a copper substrate’s unique properties to change the way the precursor molecules react to one another as they assemble into graphene nanoribbons. This allows the scientists to control the nanoribbons’ length, edge configuration and location on the substrate.
This new method of graphene fabrication by self-assembly is a stepping stone toward the production of self-assembled graphene devices that will vastly improve the performance of data storage circuits, batteries and electronics.
Paul Weiss, distinguished professor of chemistry and biochemistry and a member of UCLA’s California NanoSystems Institute, developed the method for producing the nanoribbons with Patrick Han and Taro Hitosugi, professors at the Advanced Institute of Materials Research at Tohoku University in Sendai, Japan, of which Weiss is also a member. The study was published recently in the journal ACS Nano (“Bottom-Up Graphene-Nanoribbon Fabrication Reveals Chiral Edges and Enantioselectivity”).
“To make devices out of graphene, we need to control its geometric and electronic structures,” Weiss said. “Making zigzag edges does both of these simultaneously, as there are some special properties of graphene nanoribbons with zigzag edges. Having these in hand will enable us to test theoretical predictions about them, such as magnetic properties.”
Other bottom-up methods of fabricating graphene have been attempted, but they have produced bundles of ribbons that need to be subsequently isolated and positioned for use in devices.
“Previous strategies in bottom-up molecular assemblies used inert substrates, such as gold or silver, to give molecules a lot of freedom to diffuse and react on the surface,” Han said. “But this also means that the way these molecules assemble is completely determined by the intermolecular forces and by the molecular chemistry. Our method opens the possibility for self-assembling single-graphene devices at desired locations, because of the length and the direction control.”
Source: UCLA

Liquid Inks Used by Researchers at UCLA & California NanoSystems to Create Better Solar Cells


Solar Inks 41-researchersuThe basic function of solar cells is to harvest sunlight and turn it into electricity. Thus, it is critically important that the film that collects the light on the surface of the cell is designed for the best energy absorption. The quest to develop more efficient solar cells has resulted in a fierce competition among scientists to find the lowest cost and highest energy materials.

Toward that goal, a diverse team of UCLA scientists from the California NanoSystems Institute is improving the efficiency of new film materials that are revolutionizing . Researchers led by Professor Yang Yang, the Carol and Lawrence E. Tannas Jr. Professor of Engineering at the UCLA Henry Samueli School of Engineering and Applied Science, recently published two studies in which they increased the efficiency of the materials kesterite and perovskite for making highly efficient and low-cost .

Kesterite

Kesterite is an inorganic substance (not derived from plants or animals) that is made from abundant materials, such as copper, zinc, tin and sulfur. The UCLA team has developed a way to increase the conversion of sunlight to electricity by controlling the composition and dispersion of kesterite nanocrystals in an ink that’s used to create the film used in solar cells.

Solar Inks 41-researchersu

Diagram showing elemental layers of kesterite (CZTS, left) and perovskite. Credit: UCLA

In a paper published online Aug. 8 in the journal ACS Nano, the Yang group showed that their ability to control and improve the spatial composition and distribution of nanocrystals in the kesterite ink improved its power to 8.6 percent with a consistent and repeatable technique.

“The device uses copper, zinc and tin, and we were able to control the ratio of the elements to make the nanocrystals better,” said Huanping Zhou, a postdoctoral scholar and first author of the study. “One problem in the past was too many defects in the film due to the element distribution problem. We are now synthesizing the nanocrystals in a way to precisely control the spatial elements and distribution in the film. This allows us to maximize .”

Yang said that the team was able to do a full solution process with the material. “That means that all the solar cell element layers needed—the adsorbent, the electrode, etc., are liquid that can be sprayed or painted on a surface to make that surface a solar cell,” he said. “That could be the roof of an electric car, or a building’s outer walls, windows or roof.”

Yang also pointed out that kesterite is very stable, and that copper, zinc and tin are inexpensive and widely available.

Perovskite

Perovskite is an organic and inorganic hybrid material that combines carbon and lead. Since it was first used as five years ago, improvements have advanced its to nearly 20 percent, as shown in a study published in the journal Science on Aug. 1.

“We have developed a technique for controlling the formation of the perovskite to make a solar cell with just under 20 percent efficiency,” said Qi Chen, post-doctoral scholar and first author on the study with Zhou, “Perovskite is a very low cost material to produce and is very thin, one one-thousandth of the thickness of a normal silicon solar cell. It can be made flexible, hung on the wall, or could be used to build a solar farm.”

Perovskite also begins as a liquid ink, and the UCLA researchers delicately controlled the dynamics of the material during its growth, which is done in air at low temperatures. This makes manufacture of large-area perovskite devices with high performance levels inexpensive. The improved technique can be used in perovskite-based devices of such differing applications as light-emitting diodes, field-effect transistors, and sensors.

Chen said that because currently perovskite is unstable in air and deteriorates over time, the researchers are working on long-term stability to make it more stable. And because lead is a toxic element, environmentally friendly lead-free perovskite materials would be an attractive topic in the future.

Yang said that with the competition in low-cost, high-efficiency solar cells being so hot, his team pursues as many avenues as they can toward the goal of having the most efficient, lowest-cost solar cells.

Explore further: Scientists develop pioneering new spray-on solar cells

More information: “Spatial Element Distribution Control in a Fully Solution-Processed Nanocrystals-Based 8.6% Cu2ZnSn(S,Se)4” Device Wan-Ching Hsu, Huanping Zhou, Song Luo, Tze-Bin Song, Yao-Tsung Hsieh, Hsin-Sheng Duan, Shenglin Ye, Wenbing Yang, Chia-Jung Hsu, Chengyang Jiang, Brion Bob, and Yang Yang. ACS Nano Article ASAP DOI: 10.1021/nn503992e

“Interface engineering of highly efficient perovskite solar cells” is available online: yylab.seas.ucla.edu/papers/Sci… -2014-Zhou-542-6.pdf