wired.com– For years, scientists have known that Mars has ice locked away within its rusty exterior. More elusive, though, is figuring out how much of that water is actually sloshing around in liquid form. No…
29 Sep 2015
Consumers aren’t embracing electric cars and trucks, partly due to the dearth of charging stations required to keep them moving. Even the conservation-minded are hesitant to go electric in some states because, studies show, if fossil fuels generate the electricity, the car is no greener than one powered with an efficient gasoline.
Charging cars by solar cell would appear to be the answer. But most cells fail to meet the power requirements needed to directly charge lithium-ion batteries used in today’s all-electric and plug-in hybrid electric vehicles.
Researchers at Case Western Reserve University, however, have wired four perovskite solar cells in series to enhance the voltage and directly photo-charged lithium batteries with 7.8 percent efficiency–the most efficient reported to date, the researchers believe.
The research, published in the Aug. 27 issue of Nature Communications, holds promise for cleaner transportation, home power sources and more.
“We found the right match between the solar cell and battery,” said Liming Dai, the Kent Hale Smith Professor of macromolecular science and engineering and leader of the research. “Others have used polymer solar cells to charge lithium batteries, but not with this efficiency.”
In fact, the researchers say their overall photoelectric conversion and storage outperformed all other reported couplings of a photo-charging component with lithium-ion batteries, flow batteries or super-capacitors.
Perovskite solar cells have active materials with a crystalline structure identical to the mineral perovskite and are considered a promising new design for capturing solar energy. Compared to silicon-based cells, they convert a broader spectrum of sunlight into electricity.
In short order, they have matched the energy conversion of silicon cells, and researchers around the world are pursuing further advances.
Dai’s lab made multilayer solar cells, which increases their energy density, performance and stability. Testing showed that, as desired, the three layers convert into a single perovskite film.
By wiring four lab-sized cells, about 0.1 centimeter square each, in series, the researchers further increased the open circuit voltage. The solar-to-electric power conversion efficiency was 12.65 percent.
To charge button-sized lithium-ion batteries, they used a lithium-ion-phosphate cathode and a lithium-titanium-oxide anode. The photoelectric conversion and storage efficiency was 7.8 percent. Through 10 photo-charge/galvanostatic (steady current) discharge cycles lasting nearly 18 hours, the technology maintained almost identical discharge/charge curves over all cycles, showing high cycling stability and compatibility of the components.
“We envision, in the not too distant future, this is a system that you could have at home to refuel your car and, eventually, because perovskite solar cells can be made as a flexible film, they would be on the car itself,” said Jiantie Xu, who, with Yonghua Chen, is an equally contributing first author of the study. Both are macromolecular science and engineering research associates in Case School of Engineering.
The researchers are developing small-scale prototypes and working to further improve the perovskite cell’s stability and optimize the system.
- Jiantie Xu, Yonghua Chen, Liming Dai. Efficiently photo-charging lithium-ion battery by perovskite solar cell. Nature Communications, 2015; 6: 8103 DOI: 10.1038/ncomms9103
29 Sep 2015
|Some of the 300 million tires discarded each year in the United States alone could be used in supercapacitors for vehicles and the electric grid using a technology developed at the Department of Energy’s Oak Ridge National Laboratory and Drexel University.|
|By employing proprietary pretreatment and processing, a team led by Parans Paranthaman has created flexible polymer carbon composite films as electrodes for supercapacitors. These devices are useful in applications for cars, buses and forklifts that require rapid charge and discharge cycles with high power and high energy density. Supercapacitors with this technology in electrodes saw just a 2 percent drop after 10,000 charge/discharge cycles.|
|Instead of ending up in landfills, old tires can supply a key ingredient for supercapacitors. (Image: ORNL)|
|The technology, described in a paper published in ChemSusChem(“Waste Tire Derived Carbon–Polymer Composite Paper as Pseudocapacitive Electrode with Long Cycle Life”), follows an ORNL discovery of a method to use scrap tires for batteries. Together, these approaches could provide some relief to the problems associated with the 1.5 billion tires manufacturers expect to produce annually by 2035.|
|“Those tires will eventually need to be discarded, and our supercapacitor applications can consume several tons of this waste,” Paranthaman said. “Combined with the technology we’ve licensed to two companies to convert scrap tires into carbon powders for batteries, we estimate consuming about 50 tons per day.”|
|While that amount represents just a fraction of the 8,000 tons that need to be recycled every day, co-author Yury Gogotsi of Drexel noted that other recycling companies could contribute to that goal.|
|“Each tire can produce carbon with a yield of about 50 percent with the ORNL process,” Gogotsi said. “If we were to recycle all of the scrap tires, that would translate into 1.5 million tons of carbon, which is half of the annual global production of graphite.”|
|To produce the carbon composite papers, the researchers soaked crumbs of irregularly shaped tire rubber in concentrated sulfuric acid. They then washed the rubber and put it into a tubular furnace under a flowing nitrogen gas atmosphere. They gradually increased the temperature from 400 degrees Celsius to 1,100 degrees.|
|After several additional steps, including mixing the material with potassium hydroxide and additional baking and washing with deionized water and oven drying, researchers have a material they could mix with polyaniline, an electrically conductive polymer, until they have a finished product.|
|“We anticipate that the same strategy can be applied to deposit other pseudocapacitive materials with low-cost tire-derived activated carbon to achieve even higher electrochemical performance and longer cycle life, a key challenge for electrochemically active polymers,” Gogotsi said.|
|Source: Oak Ridge National Laboratory|
In a broad new assessment of the status and prospects of solar photovoltaic technology, MIT researchers say that it is “one of the few renewable, low-carbon resources with both the scalability and the technological maturity to meet ever-growing global demand for electricity.”
Use of solar photovoltaics has been growing at a phenomenal rate: Worldwide installed capacity has seen sustained growth averaging 43 percent per year since 2000. To evaluate the prospects for sustaining such growth, the MIT researchers look at possible constraints on materials availability, and propose a system for evaluating the many competing approaches to improved solar-cell performance.
The analysis is presented in the journal Energy & Environmental Science; a broader analysis of solar technology, economics, and policy will be incorporated in a forthcoming assessment of the future of solar energy by the MIT Energy Initiative.
The team comprised MIT professors Vladimir Bulović, Tonio Buonassisi, and Robert Jaffe, and graduate students Joel Jean and Patrick Brown. One useful factor in making meaningful comparisons among new photovoltaic technologies, they conclude, is the complexity of the light-absorbing material.
The report divides the many technologies under development into three broad classes: wafer-based cells, which include traditional crystalline silicon, as well as alternatives such as gallium arsenide; commercial thin-film cells, including cadmium telluride and amorphous silicon; and emerging thin-film technologies, which include perovskites, organic materials, dye-sensitized solar cells, and quantum dots.
With the recent evolution of solar technology, says Jean, the paper’s lead author, it’s important to have a uniform framework for assessment. It may be time, he says, to re-examine the traditional classification of these technologies, generally into three areas: silicon wafer-based cells, thin-film cells, and “exotic” technologies with high theoretical efficiencies.
“We’d like to build on the conventional framework,” says Jean, a doctoral student in MIT’s Department of Electrical Engineering and Computer Science. “We’re seeking a more consistent way to think about the wide range of current photovoltaic technologies and to evaluate them for potential applications. In this study, we chose to evaluate all relevant technologies based on their material complexity.”
Under this scheme, traditional silicon — a single-element crystalline material — is the simplest material. While crystalline silicon is a mature technology with advantages including high efficiency, proven reliability, and no material scarcity constraints, it also has inherent limitations: Silicon is not especially efficient at absorbing light, and solar panels based on silicon cells tend to be rigid and heavy. At the other end of the spectrum are perovskites, organics, and colloidal quantum dots, which are “highly complex materials, but can be much simpler to process,” Jean says.
Courtesy of the researchers
The authors make clear that their definition of material complexity as a key parameter for comparison does not imply any equivalency with complexity of manufacturing. On the contrary, while silicon is the simplest solar-cell material, silicon wafer and cell production is complex and expensive, requiring extraordinary purity and high temperatures.
By contrast, while some complex nanomaterials involve intricate molecular structures, such materials can be deposited quickly and at low temperatures onto flexible substrates. Nanomaterial-based cells could even be transparent to visible light, which could open up new applications and enable seamless integration into windows and other surfaces. The authors caution, however, that the conversion efficiency and long-term stability of these complex emerging technologies is still relatively low. As they write in the paper: “The road to broad acceptance of these new technologies in conventional solar markets is inevitably long, although the unique qualities of these evolving solar technologies — lightweight, paper-thin, transparent — could open entirely new markets, accelerating their adoption.”
The study does caution that the large-scale deployment of some of today’s thin-film technologies, such as cadmium telluride and copper indium gallium diselenide, may be severely constrained by the amount of rare materials that they require. The study highlights the need for novel thin-film technologies that are based on Earth-abundant materials.
The study identifies three themes for future research and development. The first is increasing the power-conversion efficiency of emerging photovoltaic technologies and commercial modules.
A second research theme is reducing the amount of material needed per cell. Thinner, more flexible films and substrates could reduce cell weight and cost, potentially opening the door to new approaches to photovoltaic module design.
A third important research theme is reducing the complexity and cost of manufacturing. Here the researchers emphasize the importance of eliminating expensive, high-temperature processing, and encouraging the adoption of roll-to-roll coating processes for rapid, large-scale manufacturing of emerging thin-film technologies.
“We’ve looked at a number of key metrics for different applications,” Jean says. “We don’t want to rule out any of the technologies,” he says — but by providing a unified framework for comparison, he says, the researchers hope to make it easier for people to make decisions about the best technologies for a given application.
Martin Green, a professor at the Australian Centre for Advanced Photovoltaics at the University of New South Wales who was not involved in this work, says the MIT team has produced “some interesting new insights and observations.” He says the paper’s main significance “lies in the attempt to take a unifying look at the issues involved in choosing between PV technologies.”
“The issues involved are complex,” Green adds, “and the authors abstain from betting on any particular PV technology.”
28 Sep 2015
A new study out of St. Mary’s College of Maryland puts us closer to do-it-yourself spray-on solar cell technology — promising third-generation solar cells utilizing a nanocrystal ink deposition that could make traditional expensive silicon-based solar panels a thing of the past.
In a 2014 study, published in the journal Physical Chemistry Chemical Physics, St. Mary’s College of Maryland energy expert Professor Troy Townsend introduced the first fully solution-processed all-inorganic photovoltaic technology.
While progress on organic thin-film photovoltaics is rapidly growing, inorganic devices still hold the record for highest efficiencies which is in part due to their broad spectral absorption and excellent electronic properties. Considering the recorded higher efficiencies and lower cost per watt compared to organic devices, combined with the enhanced thermal and photo stability of bulk-scale inorganic materials, Townsend, in his 2014 study, focused on an all-inorganic based structure for fabrication of a top to bottom fully solution-based solar cell.
A major disadvantage compared to organics, however, is that inorganic materials are difficult to deposit from solution. To overcome this, Townsend synthesized materials on the nanoscale. Inorganic nanocrystals encased in an organic ligand shell are soluble in organic solvents and can be deposited from solution (i.e., spin-, dip-, spray-coat) whereas traditional inorganic materials require a high temperature vacuum chamber. The solar devices are fabricated from nanoscale particle inks of the light absorbing layers, cadmium telluride/cadmium selenide, and metallic inks above and below. This way, the entire electronic device can be built on non-conductive glass substrates using equipment you can find in your kitchen.
The outstanding challenge facing the (3-5 nm) inorganic nanocrystals is that they must be annealed or heated to form larger ‘bulk scale’ grains (100 nm to 1 μm) in order to produce working devices. Townsend recently teamed with Navy researchers to explore this process.
“When you spray on these nanocrystals, you have to heat them to make them work,” explained Townsend, “but you can’t just heat the crystals by themselves, you have to add a sintering agent and that, for the last 40 years, has been cadmium chloride, a toxic salt used in commercial thin-film devices. No one has tested non-toxic alternatives for nanoscale ink devices, and we wanted to explore the mechanism of the sintering process to be able to implement safer salts.”
In his latest study, published this year in the Journal of Materials Chemistry A, Townsend, along with Navy researchers, found that ammonium chloride is a non-toxic, inexpensive viable alternative to cadmium chloride for nanocrystal solar cells. This discovery came after testing several different salts. Devices made using ammonium chloride (which is commonly used in bread making) had comparable device characteristics to those made with cadmium chloride, and the move away from cadmium salt treatments alleviates concerns about the environmental health and safety of current processing methods.
The team also discovered that the role of the salt treatment involves crucial ligand removal reactions. This is unique to inorganic nanocrystals and is not observed for bulk-scale vacuum deposition methods. “A lot of exciting work has been done on nanocrystal ligand exchange, but, for the first time, we elucidated the dual role of the salt as a ligand exchange agent and a simultaneous sintering agent. This is an important distinction for these devices, because nanocrystals are typically synthesized with a native organic ligand shell. This shell needs to be removed before heating in order to improve the electronic properties of the film,” said Townsend about the discovery. Because nanomaterials are at the forefront of emerging new properties compared to their bulk counterpart, the study is important to the future of electronic device fabrication.
The research comes in the wake of the Obama Administration’s announcement in July to put more solar panels on low-income housing and expand access to solar power for renters, and recent pledge to get 20 percent of the U.S. total electricity from renewable sources by the year 2030.
“Right now, solar technology is somewhat unattainable for the average person,” said Townsend. “The dream is to make the assembly and installation process so cheap and simple that you can go to your local home improvement store and buy a kit and then spray it on your own roof. That is why we we’re working on spray-on solar cells.” Townsend plans for further research to increase the efficiency of the all-inorganic nanocrystal solar cells (currently reaching five percent), while building them with completely non-toxic components.
- Troy K. Townsend, William B. Heuer, Edward E. Foos, Eric Kowalski, Woojun Yoon, Joseph G. Tischler. Safer salts for CdTe nanocrystal solution processed solar cells: the dual roles of ligand exchange and grain growth. J. Mater. Chem. A, 2015; 3 (24): 13057 DOI: 10.1039/C5TA02488A
- Troy K. Townsend, Edward E. Foos. Fully solution processed all inorganic nanocrystal solar cells. Physical Chemistry Chemical Physics, 2014; 16 (31): 16458 DOI: 10.1039/C4CP02403F
28 Sep 2015
Though applied since the 1940s, hydraulic fracturing boomed in the 1990s, according to The Geological Society of America. New technology allowed the practice to be applied to horizontal wells for extracting shale gas. Unprecedented growth followed. According to a 2014 report by FracTracker Alliance, over 1.1 million active oil and gas wells exist in the U.S.
“The rapid pace of shale gas development in the U.S. has naturally led to several gaps in knowledge about environmental impacts,” said Douglas Arent, executive director of the Joint Institute for Strategic Energy Analysis at the U.S. Dept. of Energy’s National Renewable Energy Laboratory.
Arent and colleagues recently published a paper in MRS Energy & Sustainability overviewing the developments of unconventional gas in the U.S., particularly focusing on trends in water and greenhouse gas emissions.
“If unconventional natural gas is produced and distributed responsibly, and incorporated into resilient energy systems with increasing levels of renewables, then gas can likely play a significant role in realizing a more sustainable energy future,” said Arent.
With many U.S. states experiencing droughts—the west coast especially—water resources are stressed. Fresh water is a valuable resource. Even if one removes hydraulic fracturing from the equation, other domestic, agricultural and industrial water needs abound.
A recent Stanford Univ. study found that regardless how deep a well was, amounts of water used to frack were indistinguishable. The average volume used to frack, according to the study, was 2.4 million gallons.
“Groundwater depletion—a situation in which water is withdrawn from aquifers faster than it can be replenished—is occurring in many areas where there are shale plays,” Arent et al. write. “Depletion not only reduces the quantity of available water, it can also result in an overall deterioration of water quality.”
Water quality degradation can occur in a myriad of ways, from leaking wells and poor wastewater treatment practices, to spills and toxic element accumulation in soil. Clarity regarding the sources and mechanisms of contamination are needed, followed by an examination of effective practices to eliminate risks, according to the researchers.
“Currently, best management practices to mitigate (water) quantity and quality related risks have not been established by industry and stakeholder groups,” the researchers write. Further, no uniformity exists across the country. Individual states are responsible for regulations regarding well construction, and mitigating potential risks to water quality. Often separate state regulations don’t mesh due to each state’s geological makeup.
An “analysis will be critical to establishing those (best management practices) and government regulations, where needed, which will ensure that shale gas can be responsibly and sustainably produced,” write the researchers.
Greenhouse gas emissions
Natural gas production, compared to coal production, results in half the carbon emissions per unit of energy. The researchers contend natural gas can offer greenhouse gas mitigation benefits relative to coal, if methane emissions are small.
In 2014, the Environmental Protection Agency reported methane gas emissions from fractured natural gas wells decreased by 73% since 2011.
“Significant work is needed to measure and verify methane emissions across the full production, transportation and distribution value chain,” the researchers write. “If natural gas is to help mitigate climate change, it will do so primarily by displacing coal. However, in the long term, natural gas itself…will not significantly alter long-range climate projections.”
While natural gas, according to the researchers, will play an important role in the U.S.’s energy future, renewable energies or carbon capture and storage will be needed to meet carbon mitigation goals.
“More transparent and accessible data related to water use and emissions from shale gas development and use…are essential to providing a more complete understanding of all the pathways to a decarbonized energy future,” said Arent.
23 Sep 2015
|Researchers from the Institute for Advanced Chemistry of Catalonia (IQAC-CSIC), with support from the Nuclear Magnetic Resonance Service of the Universitat Autònoma de Barcelona (UAB) have developed a method for synthesising organic molecules very selectively, by assembling simple molecules and using an enzyme from E. coli (FSA: D-fructose-6-phosphate aldolase), which acts as a biocatalyst. This is a significant step forward since it replicates the formation of carbohydrates in conditions resembling those that presumably initiated life on the Earth (prebiotic conditions) and because it allows relatively large organic molecules to be obtained very selectively and efficiently.|
|Furthermore, it is a process with few steps, that does not use organic solvents and generates no waste, and it has great potential in chemistry, especially for obtaining molecules and active ingredients of interest (drugs, supplements, etc.).|
|This is an E.coli FSA enzyme. (Image: CSIC)|
|Pere Clapés, a research professor with the CSIC who led this project, explains that in the synthesis of organic molecules “…it is not only important for them to have the correct structure, but also the right angle and position in space, because this affects their function”.|
|In fact, this is one of the main problems that can limit the effectiveness of compounds like drugs. In the case of pentoses and hexoses, these are simple sugars (monosaccharides) with five and six carbon atoms, respectively: crucial for life thanks to their function in energy production, structuring, communication and cell-cell recognition.|
|The results presented in the journal Nature Chemistry (“Asymmetric assembly of aldose carbohydrates from formaldehyde and glycolaldehyde by tandem biocatalytic aldol reactions”) show that the scientists obtained pentoses and hexoses by assembling formaldehyde and glycolaldehyde, with a minimal modification to the FSA enzyme sequence.|
|A very malleable enzyme|
|The enzyme FSA was discovered in 2001 and its physiological function in E. coli is still unknown. It is thought to be an ancestral enzyme, and that it is active before a broad range of compounds. What surprised the researchers is that it is a very malleable enzyme, much more so than others. As a result, with only a small number of genetic mutations in the enzyme, its catalytic capacity can be modulated and increased significantly. This is what allows the enzyme to be carefully adapted in order to synthesise several molecules at will.|
|The metabolism of carbohydrates in living organisms is a complex process, forged over millions of years of evolution. It is no easy task to carry out these processes in a flask, whether by assembling the enzymes involved in the process or by manipulating the metabolic pathways of living organisms. Nor is it simple to obtain carbohydrates with conventional chemical methods, which require several stages and the use of organic solvents.|
|The procedure was developed by scientists in the Biotransformation and Active Molecules Group of the Spanish National Research Council (CSIC), with support from the Nuclear Magnetic Resonance Service of the UAB. Pere Clapés explains: “we want to prove that the tools of biocatalysis allow complex molecules to be obtained from simpler ones, which are in fact the same ones used in nature”. He goes on: “Over millions of years, living organisms have forged these metabolic strategies to obtain the carbohydrates they need to survive.”|
|“The process is a simple one, mimicking the prebiotic formation of carbohydrates from compounds that were probably around in the world before life began”, adds Teodor Parella, of the UAB.|
|For these researchers, the engineering of proteins, in particular of biocatalysts, has enormous potential for the sustainable synthesis of natural molecules and their derived products.|
|Source: Universitat Autonoma de Barcelona|
Posted: Sep 23, 2015
Semiconductor nanocrystals, or quantum dots, are tiny, nanometer-sized particles with the ability to absorb light and re-emit it with well-defined colors.
With low-cost fabrication, long-term stability and a wide palette of colors, they have become a building blocks of the display technology, improving the image quality of TV-sets, tablets, and mobile phones.
Exciting quantum dot applications are also emerging in the fields of green energy, optical sensing, and bio-imaging.
Prospects have become even more appealing after a publication was published in the journal Nature Communications last July (“Band structure engineering via piezoelectric fields in strained anisotropic CdSe/CdS nanocrystals”).
An international team, formed by scientists at the Italian Institute of Technology (Italy), the University Jaume I (Spain), the IBM research lab Zurich (Switzerland) and the University of Milano-Bicocca (Italy) demonstrated a radically new approach to manipulate the light emission of quantum dots.
The traditional operating principle of quantum dots is based on the so-called quantum confinement effect, where the particle size determines the color of the emitted light. The new strategy relies on a completely different physical mechanism; a strain induced electrical field inside the quantum dots. It is created by growing a thick shell around the dots. This way, researchers were able to compress the inner core, creating the intense internal electric field. This field now becomes the dominating factor in determining the emission properties.
The result is a new generation of quantum dots whose properties are beyond those enabled by quantum confinement alone. This not only broadens the application scope of the well-known CdSe/CdS material set but also of other materials. “Our findings add an important new degree of freedom to the development of quantum dot-based technological devices,” the researchers say.
“For example, the elapsed time between light absorption and emission can be extended to be more than 100 times longer compared to conventional quantum dots, which opens the way towards optical memories and smart pixel new devices. The new material could also lead to optical sensors that are highly sensitive to the electrical field in the environment on the nanometer scale”.
Source: Asociación RUVID
University of Vermont: Building the Electron Superhighway: Scientists Invent New Approach in quest for Organic Solar Panels and Flexible Electronics
genesisnanotech.wordpress.com – But the basic science of how to get electrons to move quickly and easily in these organic materials remains murky. To help, Furis and a team of UVM materials scientists have invented a new way to c…
genesisnanotech.wordpress.com – Solar energy is an important source of renewable energy, in which solar cell will be used to convert light energy directly into electricity by photovoltaic effect. The first generation crystalline …
Nanoparticles disguised as human platelets could greatly enhance the healing power of drug treatments for cardiovascular disease and systemic bacterial infections. These platelet-mimicking nanoparticles, developed by engineers at the University of California, San Diego, are capable of delivering drugs to targeted sites in the body — particularly injured blood vessels, as well as organs infected by harmful bacteria. Engineers demonstrated that by delivering the drugs just to the areas where the drugs were needed, these platelet copycats greatly increased the therapeutic effects of drugs that were administered to diseased rats and mice.
The research, led by nanoengineers at the UC San Diego Jacobs School of Engineering, was published online Sept. 16 in Nature.
“This work addresses a major challenge in the field of nanomedicine: targeted drug delivery with nanoparticles,” said Liangfang Zhang, a nanoengineering professor at UC San Diego and the senior author of the study. “Because of their targeting ability, platelet-mimicking nanoparticles can directly provide a much higher dose of medication specifically to diseased areas without saturating the entire body with drugs.”
The study is an excellent example of using engineering principles and technology to achieve “precision medicine,” said Shu Chien, a professor of bioengineering and medicine, director of the Institute of Engineering in Medicine at UC San Diego, and a corresponding author on the study. “While this proof of principle study demonstrates specific delivery of therapeutic agents to treat cardiovascular disease and bacterial infections, it also has broad implications for targeted therapy for other diseases such as cancer and neurological disorders,” said Chien.
The ins and outs of the platelet copycats
On the outside, platelet-mimicking nanoparticles are cloaked with human platelet membranes, which enable the nanoparticles to circulate throughout the bloodstream without being attacked by the immune system. The platelet membrane coating has another beneficial feature: it preferentially binds to damaged blood vessels and certain pathogens such as MRSA bacteria, allowing the nanoparticles to deliver and release their drug payloads specifically to these sites in the body.
Enclosed within the platelet membranes are nanoparticle cores made of a biodegradable polymer that can be safely metabolized by the body. The nanoparticles can be packed with many small drug molecules that diffuse out of the polymer core and through the platelet membrane onto their targets.
To make the platelet-membrane-coated nanoparticles, engineers first separated platelets from whole blood samples using a centrifuge. The platelets were then processed to isolate the platelet membranes from the platelet cells. Next, the platelet membranes were broken up into much smaller pieces and fused to the surface of nanoparticle cores. The resulting platelet-membrane-coated nanoparticles are approximately 100 nanometers in diameter, which is one thousand times thinner than an average sheet of paper.
This cloaking technology is based on the strategy that Zhang’s research group had developed to cloak nanoparticles in red blood cell membranes. The researchers previously demonstrated that nanoparticles disguised as red blood cells are capable of removing dangerous pore-forming toxins produced by MRSA, poisonous snake bites and bee stings from the bloodstream.
By using the body’s own platelet membranes, the researchers were able to produce platelet mimics that contain the complete set of surface receptors, antigens and proteins naturally present on platelet membranes. This is unlike other efforts, which synthesize platelet mimics that replicate one or two surface proteins of the platelet membrane.
“Our technique takes advantage of the unique natural properties of human platelet membranes, which have a natural preference to bind to certain tissues and organisms in the body,” said Zhang. This targeting ability, which red blood cell membranes do not have, makes platelet membranes extremely useful for targeted drug delivery, researchers said.
Platelet copycats at work
In one part of this study, researchers packed platelet-mimicking nanoparticles with docetaxel, a drug used to prevent scar tissue formation in the lining of damaged blood vessels, and administered them to rats afflicted with injured arteries. Researchers observed that the docetaxel-containing nanoparticles selectively collected onto the damaged sites of arteries and healed them.
When packed with a small dose of antibiotics, platelet-mimicking nanoparticles can also greatly minimize bacterial infections that have entered the bloodstream and spread to various organs in the body. Researchers injected nanoparticles containing just one-sixth the clinical dose of the antibiotic vancomycin into one of group of mice systemically infected with MRSA bacteria. The organs of these mice ended up with bacterial counts up to one thousand times lower than mice treated with the clinical dose of vancomycin alone.
“Our platelet-mimicking nanoparticles can increase the therapeutic efficacy of antibiotics because they can focus treatment on the bacteria locally without spreading drugs to healthy tissues and organs throughout the rest of the body,” said Zhang. “We hope to develop platelet-mimicking nanoparticles into new treatments for systemic bacterial infections and cardiovascular disease.”
- Che-Ming J. Hu, Ronnie H. Fang, Kuei-Chun Wang, Brian T. Luk, Soracha Thamphiwatana, Diana Dehaini, Phu Nguyen, Pavimol Angsantikul, Cindy H. Wen, Ashley V. Kroll, Cody Carpenter, Manikantan Ramesh, Vivian Qu, Sherrina H. Patel, Jie Zhu, William Shi, Florence M. Hofman, Thomas C. Chen, Weiwei Gao, Kang Zhang, Shu Chien, Liangfang Zhang. Nanoparticle biointerfacing by platelet membrane cloaking. Nature, 2015; DOI: 10.1038/nature15373