jueves, 29 de marzo de 2012

Silicon-Carbon Electrodes Snap, Swell, Don't Pop

A study that examines a new type of silicon-carbon nanocomposite electrode reveals details of how they function and how repeated use could wear them down. The study also provides clues to why this material performs better than silicon alone. With an electrical capacity five times higher than conventional lithium battery electrodes, silicon-carbon nanocomposite electrodes could lead to longer-lasting, cheaper rechargeable batteries for electric vehicles.

Published online in the journal Nano Letters last week, the study includes videos of the electrodes being charged at nanometer-scale resolution. Watching them in use can help researchers understand the strengths and weaknesses of the material.

"The electrodes expand as they get charged, and that shortens the lifespan of the battery," said lead researcher Chongmin Wang at the Department of Energy's Pacific Northwest National Laboratory. "We want to learn how to improve their lifespan, because silicon-carbon nanofiber electrodes have great potential for rechargeable batteries."

Complete article in here

Chong-Min Wang, Xiaolin Li, Zhiguo Wang, Wu Xu, Jun Liu, Fei Gao, Libor Kovarik, Ji-Guang Zhang, Jane Howe, David J. Burton, Zhongyi Liu, Xingcheng Xiao, Suntharampillai Thevuthasan, Donald R. Baer. In Situ TEM Investigation of Congruent Phase Transition and Structural Evolution of Nanostructured Silicon/Carbon Anode for Lithium Ion Batteries. Nano Letters, 2012; 12 (3): 1624 DOI: 10.1021/nl204559u

lunes, 26 de marzo de 2012

Nanopower: Avoiding Electrolyte Failure in Nanoscale Lithum Batteries

Researchers from the National Institute of Standards and Technology (NIST), the University of Maryland, College Park, and Sandia National Laboratories built a series of nanowire batteries to demonstrate that the thickness of the electrolyte layer can dramatically affect the performance of the battery, effectively setting a lower limit to the size of the tiny power sources. The results are important because battery size and performance are key to the development of autonomous MEMS -- microelectromechanical machines -- which have potentially revolutionary applications in a wide range of fields.

NIST researcher Alec Talin and his colleagues created a veritable forest of tiny -- about 7 micrometers tall and 800 nanometers wide -- solid-state lithium ion batteries to see just how small they could be made with existing materials and to test their performance.
Starting with silicon nanowires, the researchers deposited layers of metal (for a contact), cathode material, electrolyte, and anode materials with various thicknesses to form the miniature batteries. They used a transmission electron microscope (TEM) to observe the flow of current throughout the batteries and watch the materials inside them change as they charged and discharged.
The team found that when the thickness of the electrolyte film falls below a threshold of about 200 nanometers, the electrons can jump the electrolyte border instead of flowing through the wire to the device and on to the cathode. Electrons taking the short way through the electrolyte cause the electrolyte to break down and the battery to quickly discharge.

Dmitry Ruzmetov, Vladimir P. Oleshko, Paul M. Haney, Henri J. Lezec, Khim Karki, Kamal H. Baloch, Amit K. Agrawal, Albert V. Davydov, Sergiy Krylyuk, Yang Liu, JianY. Huang, Mihaela Tanase, John Cumings, A. Alec Talin. Electrolyte Stability Determines Scaling Limits for Solid-State 3D Li Ion Batteries. Nano Letters, 2012; 12 (1): 505 DOI: 10.1021/nl204047z

sábado, 24 de marzo de 2012

Super Piel : Celdas Solares Flexibles.

The "super skin" developed by Stanford University researcher Zhenan Bio is self-powering, using polymer solar cells to generate electricity. The solar cells are not just flexible, but stretchable -- they can be stretched up to 30 percent beyond their original length and snap back without any damage or loss of power.

"With artificial skin, we can basically incorporate any function we desire," says Bao, a professor of chemical engineering, who presented her work on Feb. 20 at the AAAS annual meeting in Washington, D.C. "That is why I call our skin 'super skin.' It is much more than what we think of as normal skin."

The foundation for the artificial skin is a flexible organic transistor, made with flexible polymers and carbon-based materials. To allow touch sensing, the transistor contains a thin, highly elastic rubber layer, molded into a grid of tiny inverted pyramids. When pressed, this layer changes thickness, which changes the current flow through the transistor. The sensors have from several hundred thousand to 25 million pyramids per square centimeter, corresponding to the desired level of sensitivity.

To sense a particular biological molecule, the surface of the transistor has to be coated with another molecule to which the first one will bind when it comes into contact. The coating layer only needs to be a nanometer or two thick.

"Depending on what kind of material we put on the sensors and how we modify the semiconducting material in the transistor, we can adjust the sensors to sense chemicals or biological material," she says.

Bao's team has successfully demonstrated the concept by detecting a certain kind of DNA. The researchers are now working on extending the technique to detect proteins, which could prove useful for medical diagnostics purposes.

"For any particular disease, there are usually one or more specific proteins associated with it -- called biomarkers -- that are akin to a 'smoking gun,' and detecting those protein biomarkers will allow us to diagnose the disease," Bao says.

The same approach would allow the sensors to detect chemicals, she said. By adjusting aspects of the transistor structure, the super skin can detect chemical substances in either vapor or liquid environments.

Regardless of what the sensors are detecting, they have to transmit electronic signals to get their data to the processing center, whether it is a human brain or a computer.

Having the sensors run on the sun's energy makes generating the needed power simpler than using batteries or hooking up to the electrical grid, allowing the sensors to be lighter and more mobile. And having solar cells that are stretchable opens up other applications.

A recent research paper by Bao, describing the stretchable solar cells, will appear in an upcoming issue of Advanced Materials. The paper details the ability of the cells to be stretched in one direction, but she said her group has since demonstrated that the cells can be designed to stretch along two axes.

The cells have a wavy microstructure that extends like an accordion when stretched. A liquid metal electrode conforms to the wavy surface of the device in both its relaxed and stretched states.

"One of the applications where stretchable solar cells would be useful is in fabrics for uniforms and other clothes," says Darren Lipomi, a graduate student in chemical engineering in Bao's lab and lead author of the paper.

"There are parts of the body, at the elbow for example, where movement stretches the skin and clothes," he adds. "A device that was only flexible, not stretchable, would crack if bonded to parts of machines or of the body that extend when moved."

Stretchability would be useful in bonding solar cells to curved surfaces without cracking or wrinkling, such as the exteriors of cars, lenses and architectural elements.

The solar cells continue to generate electricity while they are stretched out, producing a continuous flow of electricity for data transmission from the sensors.

Bao says she sees the super skin as much more than a super mimic of human skin; it could allow robots or other devices to perform functions beyond what human skin can do.

"You can imagine a robot hand that can be used to touch some liquid and detect certain markers or a certain protein that is associated with some kind of disease and the robot will be able to effectively say, 'Oh, this person has that disease,'" she says. "Or the robot might touch the sweat from somebody and be able to say, 'Oh, this person is drunk.'"

Finally, Bao has figured out how to replace the materials used in earlier versions of the transistor with biodegradable materials. Now, not only will the super skin be more versatile and powerful, it will also be more eco-friendly.

An educated public needs access to clear, reliable research news. Futurity finds all that really promising good stuff—fresh from the lab—and funnels it directly to you. Think of it as a snapshot of where science is today and where it just might take us tomorrow.

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FUTURITY STAFF. (2011, February 22). Stretchy solar cells power "super skin". Retrieved from http://www.stumbleupon.com/su/2BrK9Q/www.fastcompany.com/1730687/stretchy-solar-cells-power-super-skin?hpt=Sbin/

miércoles, 21 de marzo de 2012

Cell Therapy for Skin Wound Using Fibroblast Encapsulated Poly(ethylene glycol)-poly(L-alanine) Thermogel

Thermogels that undergo sol-to-gel transition with increasing temperature have been extensively investigated, focusing on the new materials development, transition mechanisms, and new biomedical applications. Polyesters, chitosan, polyphosphazenes, polycarbonates, polycyanoacrylates, polyorthoesters, and polypeptides have been developed as a thermogel.
A simple procedure for encapsulating pharmaceuticals agents including drugs and cells makes the thermogel a promising material for drug delivery and tissue engineering and postsurgical adhesion prevention.
In particular, a thermogel has the advantages of filling irregular-shaped defects and providing a three-dimensional cell growth matrix. Therefore, thermogels have been suggested as a promising platform for an injectable tissue engineering scaffold.The wound healing process in skin includes inflammation, proliferation, and remodeling of the skin tissue. All three phases can overlap during the healing process.

As a new application of a thermogel, a poly-(ethylene glycol)-b-poly(L-alanine) (PEG-L-PA) gel encapsulating fibroblasts was investigated for wound healing. The fibroblasts were encapsulated by the temperature sensitive sol-to-gel transition of the polymer aqueous solution. Under the in vitro three-dimensional (3D) cell culture condition, the PEG-L-PA thermogel was comparable with Matrigel for cell proliferation and was significantly better than Matrigel for collagen types I and III formation. After confirming the excellent 3D microenvironment of the PEG-L-PA thermogel for fibroblasts, in vivo wound healing was investigated by injecting the cell-suspended polymer, aqueous solution on incisions of rat skin, where the cell-encapsulated gel was formed in situ. Compared with the phosphate buffered saline treated system and the cell-free PEG-L-PA thermogel, the cell-encapsulated PEG-L-PA thermogel not only accelerated the wound closure but also improved epithelialization and the formation of skin appendages such as keratinocyte layer (epidermis), hair follicles, and sebaceous glands. The results demonstrate the potential of thermogels for cell therapy as an injectable tissue-engineering scaffold.

Cell Therapy for Skin Wound Using Fibroblast Encapsulated Poly(ethylene glycol)-poly(L-alanine) Thermogel

Eun Jung Yun, Bora Yon, Min Kyung Joo, and Byeongmoon Jeong
Department of Bioinspired Science and Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 120-750,

Find more information here.

Large-Scale Fabrication of 4-nm-Channel Vertical Protein-Based Ambipolar Transistors

The increasing demand for smaller and faster complementary transistors (in which both n- and p-type devices exist on one wafer) arranged in dense arrays requires the development of new methods for the parallel fabrication of nanometer- sized transistors. However, because of limitations in current technology, the achievement of these goals is very challeng- ing. Although, some isolated examples of such devices and architectures have been demonstrated, they exhibit only moderate or limited performance, or are constructed via sophisticated multistep methodologies. In this publication Mentovich and his team suggest and demonstrate a universal method in which a new type of nanometer-sized, ambipolar, vertical molecular transistor is fabricated in parallel fashion. This centralgate molecular vertical transistor (C-Gate MolVeT) is fabricated by a combination of conventional microlithography techniques and self-assembly methods. The general fabrication methodology of the C-Gate MolVeT allows the process to be adapted for various materials and systems.

Protein used to fabricate the transistor

In this design, the nanometer channel length is determined by a protein-based self-assembled monolayer composed of bovine serum albumin protein, that is sandwiched between source and drain electrodes inside a microcavity, while a centered oxidized-metal-electrode column inside the cavity serves as the gate electrode. The results showed a transistor fully operational, that can be made with lithography thechniques, they messured the gate effect, and demonstrated the characteristic transistor curves when variating the voltage in the drain terminal.

Transference Curve

The full article can be found in nanoletters:

Large-Scale Fabrication of 4-nm-Channel Vertical Protein-Based Ambipolar Transistors

Elad D. Mentovich, Bogdan Belgorodsky, Itsik Kalifa, Hagai Cohen, and Shachar Richter

Nano Letters