Tag Archives: flexible electronics

‘Green’, flexible electronics with nanocellulose materials

Bendable or flexible electronics based on nanocellulose paper present a ‘green’ alternative to other solutions according to a May 20, 2015 American Chemical Society (ACS) news release (also on EurekAlert),

Technology experts have long predicted the coming age of flexible electronics, and researchers have been working on multiple fronts to reach that goal. But many of the advances rely on petroleum-based plastics and toxic materials. Yu-Zhong Wang, Fei Song and colleagues wanted to seek a “greener” way forward.

The researchers developed a thin, clear nanocellulose paper made out of wood flour and infused it with biocompatible quantum dots — tiny, semiconducting crystals — made out of zinc and selenium. The paper glowed at room temperature and could be rolled and unrolled without cracking.

(h’t Nanotechnology Now, May 20, 2015)

There’s no mention in the news release or abstract as to what material (wood, carrot, banana, etc.) was used to derive the nanocellulose. Regardless, here’s a link to and a citation for the paper,

Let It Shine: A Transparent and Photoluminescent Foldable Nanocellulose/Quantum Dot Paper by Juan Xue, Fei Song, Xue-wu Yin, Xiu-li Wang, and Yu-zhong Wang. ACS Appl. Mater. Interfaces, 2015, 7 (19), pp 10076–10079 DOI: 10.1021/acsami.5b02011 Publication Date (Web): May 4, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Fully textile-embedded transparent and flexible technology?

There are a lot of research teams jockeying for position in the transparent, flexible electrodes stakes (for anyone unfamiliar with the slang, I’m comparing the competition between various research teams to a horse race). A May 11, 2015 news item on Nanowerk describes work from an international collaboration at the University of Exeter (UK), Note: A link has been removed,

An international team of scientists, including Professor Monica Craciun from the University of Exeter, have pioneered a new technique to embed transparent, flexible graphene electrodes into fibres commonly associated with the textile industry.

The discovery could revolutionise the creation of wearable electronic devices, such as clothing containing computers, phones and MP3 players, which are lightweight, durable and easily transportable.

The international collaborative research, which includes experts from the Centre for Graphene Science at the University of Exeter, the Institute for Systems Engineering and Computers, Microsystems and Nanotechnology (INESC-MN) in Lisbon, the Universities of Lisbon and Aveiro in Portugal and the Belgian Textile Research Centre (CenTexBel), is published in the leading scientific journal Scientific Reports (“Transparent conductive graphene textile fibers”).

A May 11, 2015 University of Exeter press release (also on EurekAlert*), which originated the news item,  describes the current situation regarding transparent and flexible electrodes in textiles and how the research at Exeter improves the situation,

Professor Craciun, co-author of the research said: “This is a pivotal point in the future of wearable electronic devices. The potential has been there for a number of years, and transparent and flexible electrodes are already widely used in plastics and glass, for example. But this is the first example of a textile electrode being truly embedded in a yarn. The possibilities for its use are endless, including textile GPS systems, to biomedical monitoring, personal security or even communication tools for those who are sensory impaired.  The only limits are really within our own imagination.”

At just one atom thick, graphene is the thinnest substance capable of conducting electricity. It is very flexible and is one of the strongest known materials. The race has been on for scientists and engineers to adapt graphene for the use in wearable electronic devices in recent years.

This new research has identified that ‘monolayer graphene’, which has exceptional electrical, mechanical and optical properties, make it a highly attractive proposition as a transparent electrode for applications in wearable electronics. In this work graphene was created by a growth method called chemical vapour deposition (CVD) onto copper foil, using a state-of-the-art nanoCVD system recently developed by Moorfield.

The collaborative team established a technique to transfer graphene from the copper foils to a polypropylene fibre already commonly used in the textile industry.

Dr Helena Alves who led the research team from INESC-MN and the University of Aveiro said: “The concept of wearable technology is emerging, but so far having fully textile-embedded transparent and flexible technology is currently non-existing. Therefore, the development of processes and engineering for the integration of graphene in textiles would give rise to a new universe of commercial applications. “

Dr Ana Neves, Associate Research Fellow in Prof Craciun’s team from Exeter’s Engineering Department and former postdoctoral researcher at INESC added: “We are surrounded by fabrics, the carpet floors in our homes or offices, the seats in our cars, and obviously all our garments and clothing accessories. The incorporation of electronic devices on fabrics would certainly be a game-changer in modern technology.

“All electronic devices need wiring, so the first issue to be address in this strategy is the development of conducting textile fibres while keeping the same aspect, comfort and lightness. The methodology that we have developed to prepare transparent and conductive textile fibres by coating them with graphene will now open way to the integration of electronic devices on these textile fibres.”

Dr Isabel De Schrijver,an expert of smart textiles from CenTexBel said: “Successful manufacturing of wearable electronics has the potential for a disruptive technology with a wide array of potential new applications. We are very excited about the potential of this breakthrough and look forward to seeing where it can take the electronics industry in the future.”

Professor Saverio Russo, co-author and also from the University of Exeter, added: “This breakthrough will also nurture the birth of novel and transformative research directions benefitting a wide range of sectors ranging from defence to health care. “

In 2012 Professor Craciun and Professor Russo, from the University of Exeter’s Centre for Graphene Science, discovered GraphExeter – sandwiched molecules of ferric chloride between two graphene layers which makes a whole new system that is the best known transparent material able to conduct electricity.  The same team recently discovered that GraphExeter is also more stable than many transparent conductors commonly used by, for example, the display industry.

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

Electron transport of WS2 transistors in a hexagonal boron nitride dielectric environment by Freddie Withers, Thomas Hardisty Bointon, David Christopher Hudson, Monica Felicia Craciun, & Saverio Russo. Scientific Reports 4, Article number: 4967 doi:10.1038/srep04967 Published 15 May 2014

Did they wait a year to announce the research or is this a second-go-round? In any event, it is an open access paper.

* Added EurekAlert link 1120 hours PDT on May 12, 2015.

Just how bendy are the new organic semiconductors?

In all the excitement about flexible electronics, an interesting question about performance, which seems to have been overlooked until now (how bendy are they?), is being answered by scientists, according to a May 5, 2015 University of Massachusetts at Amherst news release (also on EurekAlert),

A revolution is coming in flexible electronic technologies as cheaper, more flexible, organic transistors come on the scene to replace expensive, rigid, silicone-based semiconductors, but not enough is known about how bending in these new thin-film electronic devices will affect their performance, say materials scientists at the University of Massachusetts Amherst.

They are the first to apply inhomogeneous deformations, that is strain, to the conducting channel of an organic transistor and to understand the observed effects, says Reyes-Martinez [Marcos Reyes-Martinez], who conducted the series of experiments as part of his doctoral work.

As he explains, “This is relevant to today’s tech industry because transistors drive the logic of all the consumer electronics we use. In the screen on your smart phone, for example, every little pixel that makes up the image is turned on and off by hundreds of thousands or even millions of miniaturized transistors.”

“Traditionally, the transistors are rigid, made of an inorganic material such as silicon,” he adds. “We’re working with a crystalline semiconductorcalled rubrene, which is an organic, carbon-based material that has performance factors, such as charge-carrier mobility, surpassing those measured in amorphous silicon. Organic semiconductors are an interesting alternative to silicon because their properties can be tuned to make them easily processed, allowing them to coat a variety of surfaces, including soft substrates at relatively low temperatures. As a result, devices based on organic semiconductors are projected to be cheaper since they do not require high temperatures, clean rooms and expensive processing steps like silicon does.”

Until now, Reyes-Martinez notes, most researchers have focused on controlling the detrimental effects of mechanical deformation to atransistor’s electrical properties. But in their series of systematic experiments, the UMass Amherst team discovered that mechanical deformations only decrease performance under certain conditions, and actually can enhance or have no effect in other instances.

“Our goal was not only to show these effects, but to explain and understand them. What we’ve done istake advantage of the ordered structure of ultra-thin organic single crystals of rubrene to fabricate high-perfomance, thin-film transistors,” he says. “This is the first time that anyone has carried out detailed fundamental work at these length scales with a single crystal.”

Though single crystals were once thought to be too fragile for flexible applications, the UMass Amherst team found that crystals ranging in thickness from about 150 nanometers to 1 micrometer were thin enough to be wrinkled and applied to any elastomer substrate. Reyes-Martinez also notes, “Our experiments are especially important because they help scientists working on flexible electronic devices to determine performance limitations of new materials under extreme mechanical deformations, such as when electronic devices conform to skin.”

They developed an analytical model based on plate bending theoryto quantifythe different local strains imposed on the transistor structure by the wrinkle deformations. Using their model they are able to predict how different deformations modulate charge mobility, which no one had quantified before, Reyes-Martinez notes.

These contributions “represent a significant step forward in structure-function relationships in organic semiconductors, critical for the development of the next generation of flexible electronic devices,” the authors point out.

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

Rubrene crystal field-effect mobility modulation via conducting channel wrinkling by Marcos A. Reyes-Martinez, Alfred J. Crosby,  & Alejandro L. Briseno. Nature Communications 6, Article number: 6948 doi:10.1038/ncomms7948 Published 05 May 2015

This is an open access paper.

Hyper stretchable nanogenerator

There’s a lot of talk about flexibility, stretchability and bendability in electronics and the latest is coming from Korea. An April 13, 2015 Korea Advanced Institute for Science and Technology (KAIST) news release on EurekAlert describes the situation and the Korean scientists’ most recent research into stretchable electronics,

A research team led by Professor Keon Jae Lee of the Department of Materials Science and Engineering at the Korea Advanced Institute of Science and Technology (KAIST) has developed a hyper-stretchable elastic-composite energy harvesting device called a nanogenerator.

Flexible electronics have come into the market and are enabling new technologies like flexible displays in mobile phone, wearable electronics, and the Internet of Things (IoTs). However, is the degree of flexibility enough for most applications? For many flexible devices, elasticity is a very important issue. For example, wearable/biomedical devices and electronic skins (e-skins) should stretch to conform to arbitrarily curved surfaces and moving body parts such as joints, diaphragms, and tendons. They must be able to withstand the repeated and prolonged mechanical stresses of stretching. In particular, the development of elastic energy devices is regarded as critical to establish power supplies in stretchable applications. Although several researchers have explored diverse stretchable electronics, due to the absence of the appropriate device structures and correspondingly electrodes, researchers have not developed ultra-stretchable and fully-reversible energy conversion devices properly.

Recently, researchers from KAIST and Seoul National University (SNU) have collaborated and demonstrated a facile methodology to obtain a high-performance and hyper-stretchable elastic-composite generator (SEG) using very long silver nanowire-based stretchable electrodes. Their stretchable piezoelectric generator can harvest mechanical energy to produce high power output (~4 V) with large elasticity (~250%) and excellent durability (over 104 cycles). These noteworthy results were achieved by the non-destructive stress- relaxation ability of the unique electrodes as well as the good piezoelectricity of the device components. The new SEG can be applied to a wide-variety of wearable energy-harvesters to transduce biomechanical-stretching energy from the body (or machines) to electrical energy.

Professor Lee said, “This exciting approach introduces an ultra-stretchable piezoelectric generator. It can open avenues for power supplies in universal wearable and biomedical applications as well as self-powered ultra-stretchable electronics.”

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

A Hyper-Stretchable Elastic-Composite Energy Harvester by Chang Kyu Jeong, Jinhwan Lee, Seungyong Han, Jungho Ryu, Geon-Tae Hwang, Dae Yong Park, Jung Hwan Park, Seung Seob Lee, Mynghwan Byun, Seung Hwan Ko, and Keon Jae Lee. Advanced Materials DOI: 10.1002/adma.201500367 30 March 2015Full

This paper is behind a paywall.

The researchers have prepared a short video (22 secs. and silent),

3D printing soft robots and flexible electronics with metal alloys

This research comes from Purdue University (Indiana, US) which seems to be on a publishing binge these days. From an April 7, 2015 news item on Nanowerk,

New research shows how inkjet-printing technology can be used to mass-produce electronic circuits made of liquid-metal alloys for “soft robots” and flexible electronics.

Elastic technologies could make possible a new class of pliable robots and stretchable garments that people might wear to interact with computers or for therapeutic purposes. However, new manufacturing techniques must be developed before soft machines become commercially feasible, said Rebecca Kramer, an assistant professor of mechanical engineering at Purdue University.

“We want to create stretchable electronics that might be compatible with soft machines, such as robots that need to squeeze through small spaces, or wearable technologies that aren’t restrictive of motion,” she said. “Conductors made from liquid metal can stretch and deform without breaking.”

A new potential manufacturing approach focuses on harnessing inkjet printing to create devices made of liquid alloys.

“This process now allows us to print flexible and stretchable conductors onto anything, including elastic materials and fabrics,” Kramer said.

An April 7, 2015 Purdue University news release (also on EurekAlert) by Emil Venere, which originated the news item, expands on the theme,

A research paper about the method will appear on April 18 [2015] in the journal Advanced Materials. The paper generally introduces the method, called mechanically sintered gallium-indium nanoparticles, and describes research leading up to the project. It was authored by postdoctoral researcher John William Boley, graduate student Edward L. White and Kramer.

A printable ink is made by dispersing the liquid metal in a non-metallic solvent using ultrasound, which breaks up the bulk liquid metal into nanoparticles. This nanoparticle-filled ink is compatible with inkjet printing.

“Liquid metal in its native form is not inkjet-able,” Kramer said. “So what we do is create liquid metal nanoparticles that are small enough to pass through an inkjet nozzle. Sonicating liquid metal in a carrier solvent, such as ethanol, both creates the nanoparticles and disperses them in the solvent. Then we can print the ink onto any substrate. The ethanol evaporates away so we are just left with liquid metal nanoparticles on a surface.”

After printing, the nanoparticles must be rejoined by applying light pressure, which renders the material conductive. This step is necessary because the liquid-metal nanoparticles are initially coated with oxidized gallium, which acts as a skin that prevents electrical conductivity.

“But it’s a fragile skin, so when you apply pressure it breaks the skin and everything coalesces into one uniform film,” Kramer said. “We can do this either by stamping or by dragging something across the surface, such as the sharp edge of a silicon tip.”

The approach makes it possible to select which portions to activate depending on particular designs, suggesting that a blank film might be manufactured for a multitude of potential applications.

“We selectively activate what electronics we want to turn on by applying pressure to just those areas,” said Kramer, who this year was awarded an Early Career Development award from the National Science Foundation, which supports research to determine how to best develop the liquid-metal ink.

The process could make it possible to rapidly mass-produce large quantities of the film.

Future research will explore how the interaction between the ink and the surface being printed on might be conducive to the production of specific types of devices.

“For example, how do the nanoparticles orient themselves on hydrophobic versus hydrophilic surfaces? How can we formulate the ink and exploit its interaction with a surface to enable self-assembly of the particles?” she said.

The researchers also will study and model how individual particles rupture when pressure is applied, providing information that could allow the manufacture of ultrathin traces and new types of sensors.

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

Nanoparticles: Mechanically Sintered Gallium–Indium Nanoparticles by John William Boley, Edward L. White and Rebecca K. Kramer. Advanced Materials Volume 27, Issue 14, page 2270, April 8, 2015 DOI: 10.1002/adma.201570094 Article first published online: 7 APR 2015

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

Spinal cords, brains, implants, and remote control

I have two items about implants and brains and an item about being able to exert remote control of the brain, all of which hint at a cyborg future for at least a few of us.

e-Dura, the spinal column, and the brain

The first item concerns some research, at the École Polytechnique de Lausanne (EPFL) which features flexible electronics. From a March 24, 2015 article by Ben Schiller for Fast Company (Note: Links have been removed),

Researchers at the Swiss Federal Institute of Technology, in Lausanne, have developed the e-Dura—a tiny skinlike device that attaches directly to damaged spinal cords. By sending out small electrical pulses, it stimulates the cord as if it were receiving signals from the brain, thus allowing movement.

“The purpose of the neuro-prosthesis is to excite the neurons that are on the spinal cord below the site of the injury and activate them, just like if they were receiving information from the brain,” says Stéphanie Lacour, a professor at the institute.

A January 8, 2015 (?) EPFL press release provides more information about the research,

EPFL scientists have managed to get rats walking on their own again using a combination of electrical and chemical stimulation. But applying this method to humans would require multifunctional implants that could be installed for long periods of time on the spinal cord without causing any tissue damage. This is precisely what the teams of professors Stéphanie Lacour and Grégoire Courtine have developed. Their e-Dura implant is designed specifically for implantation on the surface of the brain or spinal cord. The small device closely imitates the mechanical properties of living tissue, and can simultaneously deliver electric impulses and pharmacological substances. The risks of rejection and/or damage to the spinal cord have been drastically reduced. An article about the implant will appear in early January [2015] in Science Magazine.

So-called “surface implants” have reached a roadblock; they cannot be applied long term to the spinal cord or brain, beneath the nervous system’s protective envelope, otherwise known as the “dura mater,” because when nerve tissues move or stretch, they rub against these rigid devices. After a while, this repeated friction causes inflammation, scar tissue buildup, and rejection.

Here’s what the implant looks like,

Courtesy: EPFL

Courtesy: EPFL

The press release describes how the implant is placed (Note: A link has been removed),

Flexible and stretchy, the implant developed at EPFL is placed beneath the dura mater, directly onto the spinal cord. Its elasticity and its potential for deformation are almost identical to the living tissue surrounding it. This reduces friction and inflammation to a minimum. When implanted into rats, the e-Dura prototype caused neither damage nor rejection, even after two months. More rigid traditional implants would have caused significant nerve tissue damage during this period of time.

The researchers tested the device prototype by applying their rehabilitation protocol — which combines electrical and chemical stimulation – to paralyzed rats. Not only did the implant prove its biocompatibility, but it also did its job perfectly, allowing the rats to regain the ability to walk on their own again after a few weeks of training.

“Our e-Dura implant can remain for a long period of time on the spinal cord or the cortex, precisely because it has the same mechanical properties as the dura mater itself. This opens up new therapeutic possibilities for patients suffering from neurological trauma or disorders, particularly individuals who have become paralyzed following spinal cord injury,” explains Lacour, co-author of the paper, and holder of EPFL’s Bertarelli Chair in Neuroprosthetic Technology.

The press release goes on to describe the engineering achievements,

Developing the e-Dura implant was quite a feat of engineering. As flexible and stretchable as living tissue, it nonetheless includes electronic elements that stimulate the spinal cord at the point of injury. The silicon substrate is covered with cracked gold electric conducting tracks that can be pulled and stretched. The electrodes are made of an innovative composite of silicon and platinum microbeads. They can be deformed in any direction, while still ensuring optimal electrical conductivity. Finally, a fluidic microchannel enables the delivery of pharmacological substances – neurotransmitters in this case – that will reanimate the nerve cells beneath the injured tissue.

The implant can also be used to monitor electrical impulses from the brain in real time. When they did this, the scientists were able to extract with precision the animal’s motor intention before it was translated into movement.

“It’s the first neuronal surface implant designed from the start for long-term application. In order to build it, we had to combine expertise from a considerable number of areas,” explains Courtine, co-author and holder of EPFL’s IRP Chair in Spinal Cord Repair. “These include materials science, electronics, neuroscience, medicine, and algorithm programming. I don’t think there are many places in the world where one finds the level of interdisciplinary cooperation that exists in our Center for Neuroprosthetics.”

For the time being, the e-Dura implant has been primarily tested in cases of spinal cord injury in paralyzed rats. But the potential for applying these surface implants is huge – for example in epilepsy, Parkinson’s disease and pain management. The scientists are planning to move towards clinical trials in humans, and to develop their prototype in preparation for commercialization.

EPFL has provided a video of researcher Stéphanie Lacour describing e-Dura and expressing hopes for its commercialization,

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

Electronic dura mater for long-term multimodal neural interfaces by Ivan R. Minev, Pavel Musienko, Arthur Hirsch, Quentin Barraud, Nikolaus Wenger, Eduardo Martin Moraud, Jérôme Gandar, Marco Capogrosso, Tomislav Milekovic, Léonie Asboth, Rafael Fajardo Torres, Nicolas Vachicouras, Qihan Liu, Natalia Pavlova, Simone Duis, Alexandre Larmagnac, Janos Vörös, Silvestro Micera, Zhigang Suo, Grégoire Courtine, Stéphanie P. Lacour. Science 9 January 2015: Vol. 347 no. 6218 pp. 159-163 DOI: 10.1126/science.1260318

This paper is behind a paywall.

Carbon nanotube fibres could connect to the brain

Researchers at Rice University (Texas, US) are excited about the possibilities that carbon nanotube fibres offer in the field of implantable electronics for the brain. From a March 25, 2015 news item on Nanowerk,

Carbon nanotube fibers invented at Rice University may provide the best way to communicate directly with the brain.

The fibers have proven superior to metal electrodes for deep brain stimulation and to read signals from a neuronal network. Because they provide a two-way connection, they show promise for treating patients with neurological disorders while monitoring the real-time response of neural circuits in areas that control movement, mood and bodily functions.

New experiments at Rice demonstrated the biocompatible fibers are ideal candidates for small, safe electrodes that interact with the brain’s neuronal system, according to the researchers. They could replace much larger electrodes currently used in devices for deep brain stimulation therapies in Parkinson’s disease patients.

They may also advance technologies to restore sensory or motor functions and brain-machine interfaces as well as deep brain stimulation therapies for other neurological disorders, including dystonia and depression, the researchers wrote.

A March 25, 2015 Rice University news release (also on EurekAlert*), which originated the news item, provides more details,

The fibers created by the Rice lab of chemist and chemical engineer Matteo Pasquali consist of bundles of long nanotubes originally intended for aerospace applications where strength, weight and conductivity are paramount.

The individual nanotubes measure only a few nanometers across, but when millions are bundled in a process called wet spinning, they become thread-like fibers about a quarter the width of a human hair.

“We developed these fibers as high-strength, high-conductivity materials,” Pasquali said. “Yet, once we had them in our hand, we realized that they had an unexpected property: They are really soft, much like a thread of silk. Their unique combination of strength, conductivity and softness makes them ideal for interfacing with the electrical function of the human body.”

The simultaneous arrival in 2012 of Caleb Kemere, a Rice assistant professor who brought expertise in animal models of Parkinson’s disease, and lead author Flavia Vitale, a research scientist in Pasquali’s lab with degrees in chemical and biomedical engineering, prompted the investigation.

“The brain is basically the consistency of pudding and doesn’t interact well with stiff metal electrodes,” Kemere said. “The dream is to have electrodes with the same consistency, and that’s why we’re really excited about these flexible carbon nanotube fibers and their long-term biocompatibility.”

Weeks-long tests on cells and then in rats with Parkinson’s symptoms proved the fibers are stable and as efficient as commercial platinum electrodes at only a fraction of the size. The soft fibers caused little inflammation, which helped maintain strong electrical connections to neurons by preventing the body’s defenses from scarring and encapsulating the site of the injury.

The highly conductive carbon nanotube fibers also show much more favorable impedance – the quality of the electrical connection — than state-of-the-art metal electrodes, making for better contact at lower voltages over long periods, Kemere said.

The working end of the fiber is the exposed tip, which is about the width of a neuron. The rest is encased with a three-micron layer of a flexible, biocompatible polymer with excellent insulating properties.

The challenge is in placing the tips. “That’s really just a matter of having a brain atlas, and during the experiment adjusting the electrodes very delicately and putting them into the right place,” said Kemere, whose lab studies ways to connect signal-processing systems and the brain’s memory and cognitive centers.

Doctors who implant deep brain stimulation devices start with a recording probe able to “listen” to neurons that emit characteristic signals depending on their functions, Kemere said. Once a surgeon finds the right spot, the probe is removed and the stimulating electrode gently inserted. Rice carbon nanotube fibers that send and receive signals would simplify implantation, Vitale said.

The fibers could lead to self-regulating therapeutic devices for Parkinson’s and other patients. Current devices include an implant that sends electrical signals to the brain to calm the tremors that afflict Parkinson’s patients.

“But our technology enables the ability to record while stimulating,” Vitale said. “Current electrodes can only stimulate tissue. They’re too big to detect any spiking activity, so basically the clinical devices send continuous pulses regardless of the response of the brain.”

Kemere foresees a closed-loop system that can read neuronal signals and adapt stimulation therapy in real time. He anticipates building a device with many electrodes that can be addressed individually to gain fine control over stimulation and monitoring from a small, implantable device.

“Interestingly, conductivity is not the most important electrical property of the nanotube fibers,” Pasquali said. “These fibers are intrinsically porous and extremely stable, which are both great advantages over metal electrodes for sensing electrochemical signals and maintaining performance over long periods of time.”

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

Neural Stimulation and Recording with Bidirectional, Soft Carbon Nanotube Fiber Microelectrodes by Flavia Vitale, Samantha R. Summerson, Behnaam Aazhang, Caleb Kemere, and Matteo Pasquali. ACS Nano, Just Accepted Manuscript DOI: 10.1021/acsnano.5b01060 Publication Date (Web): March 24, 2015

Copyright © 2015 American Chemical Society

The paper is open access provided you register on the website.

Remote control for stimulation of the brain

Mo Costandi, neuroscientist and freelance science writer, has written a March 24, 2015 post for the Guardian science blog network focusing on neuronal remote control,

Two teams of scientists have developed new ways of stimulating neurons with nanoparticles, allowing them to activate brain cells remotely using light or magnetic fields. The new methods are quicker and far less invasive than other hi-tech methods available, so could be more suitable for potential new treatments for human diseases.

Researchers have various methods for manipulating brain cell activity, arguably the most powerful being optogenetics, which enables them to switch specific brain cells on or off with unprecedented precision, and simultaneously record their behaviour, using pulses of light.

This is very useful for probing neural circuits and behaviour, but involves first creating genetically engineered mice with light-sensitive neurons, and then inserting the optical fibres that deliver light into the brain, so there are major technical and ethical barriers to its use in humans.

Nanomedicine could get around this. Francisco Bezanilla of the University of Chicago and his colleagues knew that gold nanoparticles can absorb light and convert it into heat, and several years ago they discovered that infrared light can make neurons fire nervous impulses by heating up their cell membranes.

Polina Anikeeva’s team at the Massachusetts Institute of Technology adopted a slightly different approach, using spherical iron oxide particles that give off heat when exposed to an alternating magnetic field.

Although still in the experimental stages, research like this may eventually allow for wireless and minimally invasive deep brain stimulation of the human brain. Bezanilla’s group aim to apply their method to develop treatments for macular degeneration and other conditions that kill off light-sensitive cells in the retina. This would involve injecting nanoparticles into the eye so that they bind to other retinal cells, allowing natural light to excite them into firing impulses to the optic nerve.

Costandi’s article is intended for an audience that either understands the science or can deal with the uncertainty of not understanding absolutely everything. Provided you fall into either of those categories, the article is well written and it provides links and citations to the papers for both research teams being featured.

Taken together, the research at EPFL, Rice University, University of Chicago, and Massachusetts Institute of Technology provides a clue as to how much money and intellectual power is being directed at the brain.

* EurekAlert link added on March 26, 2015.

Think of your skin as a smartphone

A March 5, 2015 news item on Azonano highlights work on flexible, transparent electronics designed to adhere to your skin,

Someone wearing a smartwatch can look at a calendar or receive e-mails without having to reach further than their wrist. However, the interaction area offered by the watch face is both fixed and small, making it difficult to actually hit individual buttons with adequate precision. A method currently being developed by a team of computer scientists from Saarbrücken in collaboration with researchers from Carnegie Mellon University in the USA may provide a solution to this problem. They have developed touch-sensitive stickers made from flexible silicone and electrically conducting sensors that can be worn on the skin.

Here’s what the sticker looks like,

Caption: The stickers are skin-friendly and are attached to the skin with a biocompatible, medical-grade adhesive. Credit: Oliver Dietze

Caption: The stickers are skin-friendly and are attached to the skin with a biocompatible, medical-grade adhesive. Credit: Oliver Dietze Courtesy: Saarland University

A March 4, 2015 University of Saarland press release on EurekAlert, which originated the news item, expands on the theme on connecting technology to the body,

… The stickers can act as an input space that receives and executes commands and thus controls mobile devices. Depending on the type of skin sticker used, applying pressure to the sticker could, for example, answer an incoming call or adjust the volume of a music player. ‘The stickers allow us to enlarge the input space accessible to the user as they can be attached practically anywhere on the body,’ explains Martin Weigel, a PhD student in the team led by Jürgen Steimle at the Cluster of Excellence at Saarland University. The ‘iSkin’ approach enables the human body to become more closely connected to technology. [emphasis mine]

Users can also design their iSkin patches on a computer beforehand to suit their individual tastes. ‘A simple graphics program is all you need,’ says Weigel. One sticker, for instance, is based on musical notation, another is circular in shape like an LP. The silicone used to fabricate the sensor patches makes them flexible and stretchable. ‘This makes them easier to use in an everyday environment. The music player can simply be rolled up and put in a pocket,’ explains Jürgen Steimle, who heads the ‘Embodied Interaction Group’ in which Weigel is doing his research. ‘They are also skin-friendly, as they are attached to the skin with a biocompatible, medical-grade adhesive. Users can therefore decide where they want to position the sensor patch and how long they want to wear it.’

In addition to controlling music or phone calls, the iSkin technology could be used for many other applications. For example, a keyboard sticker could be used to type and send messages. Currently the sensor stickers are connected via cable to a computer system. According to Steimle, in-built microchips may in future allow the skin-worn sensor patches to communicate wirelessly with other mobile devices.

The publication about ‘iSkin’ won the ‘Best Paper Award’ at the SIGCHI conference, which ranks among the most important conferences within the research area of human computer interaction. The researchers will present their project at the SIGCHI conference in April [2015] in Seoul, Korea, and beforehand at the computer expo Cebit, which takes place from the 16th until the 20th of March [2015] in Hannover (hall 9, booth E13).

Hopefully, you’ll have a chance to catch researchers’ presentation at the SIGCHI or Cebit events.

That quote about enabling “the human body to become more closely connected to technology” reminds me of a tag (machine/flesh) I created to categorize research of this nature. I explained the idea being explored in a May 9, 2012 posting titled: Everything becomes part machine,

Machine/flesh. That’s what I’ve taken to calling this process of integrating machinery into our and, as I newly realized, other animals’ flesh.

I think my latest previous post on this topic was a Jan. 10, 2014 post titled: Chemistry of Cyborgs: review of the state of the art by German researchers.

Silver nanowires have a surprising ability to self-heal

It seems there could be a new member of the flexible electronics materials community, silver nanowires, according to a Jan. 23, 2015 news item on ScienceDaily,

Wth its high electrical conductivity and optical transparency, indium tin oxide is one of the most widely used materials for touchscreens, plasma displays, and flexible electronics. But its rapidly escalating price has forced the electronics industry to search for other alternatives.

One potential and more cost-effective alternative is a film made with silver nanowires–wires so extremely thin that they are one-dimensional–embedded in flexible polymers. Like indium tin oxide, this material is transparent and conductive. But development has stalled because scientists lack a fundamental understanding of its mechanical properties.

A Jan. 23, 2015 Northwestern University news release (also on EurekAlert), which originated the news item, explains what makes silver nanowires a candidate as an alternative to indium tin oxide for use in flexible electronics,

… Horacio Espinosa, the James N. and Nancy J. Farley Professor in Manufacturing and Entrepreneurship at Northwestern University’s McCormick School of Engineering, has led research that expands the understanding of silver nanowires’ behavior in electronics.

Espinosa and his team investigated the material’s cyclic loading, which is an important part of fatigue analysis because it shows how the material reacts to fluctuating loads of stress.

“Cyclic loading is an important material behavior that must be investigated for realizing the potential applications of using silver nanowires in electronics,” Espinosa said. “Knowledge of such behavior allows designers to understand how these conductive films fail and how to improve their durability.”

By varying the tension on silver nanowires thinner than 120 nanometers and monitoring their deformation with electron microscopy, the research team characterized the cyclic mechanical behavior. They found that permanent deformation was partially recoverable in the studied nanowires, meaning that some of the material’s defects actually self-healed and disappeared upon cyclic loading. These results indicate that silver nanowires could potentially withstand strong cyclic loads for long periods of time, which is a key attribute needed for flexible electronics.

“These silver nanowires show mechanical properties that are quite unexpected,” Espinosa said. “We had to develop new experimental techniques to be able to measure this novel material property.”

The findings were recently featured on the cover of the journal Nano Letters. Other Northwestern coauthors on the paper are Rodrigo Bernal, a recently graduated PhD student in Espinosa’s lab, and Jiaxing Huang, associate professor of materials science and engineering in McCormick.

“The next step is to understand how this recovery influences the behavior of these materials when they are flexed millions of times,” said Bernal, first author of the paper.

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

Intrinsic Bauschinger Effect and Recoverable Plasticity in Pentatwinned Silver Nanowires Tested in Tension by Rodrigo A. Bernal, Amin Aghaei, Sangjun Lee, Seunghwa Ryu, Kwonnam Sohn, Jiaxing Huang, Wei Cai, and Horacio Espinosa. Nano Lett., 2015, 15 (1), pp 139–146 DOI: 10.1021/nl503237t Publication Date (Web): October 3, 2014
Copyright © 2014 American Chemical Society

This particular version of the paper is behind a paywall. However, access to the paper is possible although I make no claims as to which version it is or whether it will continue to be freely accessible.

Flexible electronics and Inorganic-based Laser Lift-off (ILLO) in Korea

Korean scientists are trying to make the process of creating flexible electronics easier according to a Nov. 25, 2014 news item on ScienceDaily,

Flexible electronics have been touted as the next generation in electronics in various areas, ranging from consumer electronics to bio-integrated medical devices. In spite of their merits, insufficient performance of organic materials arising from inherent material properties and processing limitations in scalability have posed big challenges to developing all-in-one flexible electronics systems in which display, processor, memory, and energy devices are integrated. The high temperature processes, essential for high performance electronic devices, have severely restricted the development of flexible electronics because of the fundamental thermal instabilities of polymer materials.

A research team headed by Professor Keon Jae Lee of the Department of Materials Science and Engineering at KAIST provides an easier methodology to realize high performance flexible electronics by using the Inorganic-based Laser Lift-off (ILLO).

The process is described in a Nov. 26, 2014 KAIST news release on ResearchSEA, which originated the news item (despite the confusion of the date, probably due to timezone differentials), provides more detail about the technique for ILLO,

The ILLO process involves depositing a laser-reactive exfoliation layer on rigid substrates, and then fabricating ultrathin inorganic electronic devices, e.g., high density crossbar memristive memory on top of the exfoliation layer. By laser irradiation through the back of the substrate, only the ultrathin inorganic device layers are exfoliated from the substrate as a result of the reaction between laser and exfoliation layer, and then subsequently transferred onto any kind of receiver substrate such as plastic, paper, and even fabric.

This ILLO process can enable not only nanoscale processes for high density flexible devices but also the high temperature process that was previously difficult to achieve on plastic substrates. The transferred device successfully demonstrates fully-functional random access memory operation on flexible substrates even under severe bending.

Professor Lee said, “By selecting an optimized set of inorganic exfoliation layer and substrate, a nanoscale process at a high temperature of over 1000 °C can be utilized for high performance flexible electronics. The ILLO process can be applied to diverse flexible electronics, such as driving circuits for displays and inorganic-based energy devices such as battery, solar cell, and self-powered devices that require high temperature processes.”

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

Flexible Crossbar-Structured Resistive Memory Arrays on Plastic Substrates via Inorganic-Based Laser Lift-Off by Seungjun Kim, Jung Hwan Son, Seung Hyun Lee, Byoung Kuk You, Kwi-Il Park, Hwan Keon Lee, Myunghwan Byun and Keon Jae Lee. Advanced Materials Volume 26, Issue 44, pages 7480–7487, November 26, 2014 Article first published online: 8 SEP 2014 DOI: 10.1002/adma.201402472

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Here’s an image the researchers have made available,

This photo shows the flexible RRAM device on a plastic substrate. Courtesy: KAIST

This photo shows the flexible RRAM device on a plastic substrate. Courtesy: KAIST

Finally, the research paper is behind a paywall.

Bend it, twist it, any way you want to—a foldable lithium-ion battery

Feb. 26, 2013 news item on ScienceDaily features an extraordinary lithium-ion battery,

Northwestern University’s Yonggang Huang and the University of Illinois’ John A. Rogers are the first to demonstrate a stretchable lithium-ion battery — a flexible device capable of powering their innovative stretchable electronics.

No longer needing to be connected by a cord to an electrical outlet, the stretchable electronic devices now could be used anywhere, including inside the human body. The implantable electronics could monitor anything from brain waves to heart activity, succeeding where flat, rigid batteries would fail.

Huang and Rogers have demonstrated a battery that continues to work — powering a commercial light-emitting diode (LED) — even when stretched, folded, twisted and mounted on a human elbow. The battery can work for eight to nine hours before it needs recharging, which can be done wirelessly.

The researchers at Northwestern have produced a video where they demonstrate the battery’s ‘stretchability’,

The Northwestern University Feb. 26, 2013 news release by Megan Fellman, which originated the news item, offers this detail,

“We start with a lot of battery components side by side in a very small space, and we connect them with tightly packed, long wavy lines,” said Huang, a corresponding author of the paper. “These wires provide the flexibility. When we stretch the battery, the wavy interconnecting lines unfurl, much like yarn unspooling. And we can stretch the device a great deal and still have a working battery.”

The power and voltage of the stretchable battery are similar to a conventional lithium-ion battery of the same size, but the flexible battery can stretch up to 300 percent of its original size and still function.

Huang and Rogers have been working together for the last six years on stretchable electronics, and designing a cordless power supply has been a major challenge. Now they have solved the problem with their clever “space filling technique,” which delivers a small, high-powered battery.

For their stretchable electronic circuits, the two developed “pop-up” technology that allows circuits to bend, stretch and twist. They created an array of tiny circuit elements connected by metal wire “pop-up bridges.” When the array is stretched, the wires — not the rigid circuits — pop up.

This approach works for circuits but not for a stretchable battery. A lot of space is needed in between components for the “pop-up” interconnect to work. Circuits can be spaced out enough in an array, but battery components must be packed tightly to produce a powerful but small battery. There is not enough space between battery components for the “pop-up” technology to work.

Huang’s design solution is to use metal wire interconnects that are long, wavy lines, filling the small space between battery components. (The power travels through the interconnects.)

The unique mechanism is a “spring within a spring”: The line connecting the components is a large “S” shape and within that “S” are many smaller “S’s.” When the battery is stretched, the large “S” first stretches out and disappears, leaving a line of small squiggles. The stretching continues, with the small squiggles disappearing as the interconnect between electrodes becomes taut.

“We call this ordered unraveling,” Huang said. “And this is how we can produce a battery that stretches up to 300 percent of its original size.”

The stretching process is reversible, and the battery can be recharged wirelessly. The battery’s design allows for the integration of stretchable, inductive coils to enable charging through an external source but without the need for a physical connection.

Huang, Rogers and their teams found the battery capable of 20 cycles of recharging with little loss in capacity. The system they report in the paper consists of a square array of 100 electrode disks, electrically connected in parallel.

I’d like to see this battery actually powering a device even though the stretching is quite alluring in its way. For those who are interested here’s a citation and a link to the research paper,

Stretchable batteries with self-similar serpentine interconnects and integrated wireless recharging systems by Sheng Xu, Yihui Zhang, Jiung Cho, Juhwan Lee, Xian Huang, Lin Jia, Jonathan A. Fan, Yewang Su, Jessica Su, Huigang Zhang, Huanyu Cheng, Bingwei Lu,           Cunjiang Yu, Chi Chuang, Tae-il Kim, Taeseup Song, Kazuyo Shigeta, Sen Kang, Canan Dagdeviren, Ivan Petrov  et al.   Nature Communications 4, Article number: 1543 doi: 10.1038/ncomms2553  Published 26 February 2013

The article is behind a paywall.