Transparent Artificial Muscle Plays Music to Prove a Point

Aug. 29, 2013 — In a materials science laboratory at Harvard University, a transparent disk connected to a laptop fills the room with music -- it's the "Morning" prelude from Peer Gynt, played on an ionic speaker.

As Jeong-Yun Sun and Christoph Keplinger, Harvard University, demonstrate here, two major advantages of ionic conductors are that they can be very stretchy and completely transparent, two properties difficult to achieve with electronics. (Credit: Photo by Eliza Grinnell, SEAS Communications.)

No ordinary speaker, it consists of a thin sheet of rubber sandwiched between two layers of a saltwater gel, and it's as clear as a window. A high-voltage signal that runs across the surfaces and through the layers forces the rubber to rapidly contract and vibrate, producing sounds that span the entire audible spectrum, 20 hertz to 20 kilohertz.

But this is not an electronic device, nor has it ever been seen before. Published in the August 30 issue of Science, it represents the first demonstration that electrical charges carried by ions, rather than electrons, can be put to meaningful use in fast-moving, high-voltage devices.

"Ionic conductors could replace certain electronic systems; they even offer several advantages," says co-lead author Jeong-Yun Sun, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS).

For example, ionic conductors can be stretched to many times their normal area without an increase in resistivity -- a problem common in stretchable electronic devices. Secondly, they can be transparent, making them well suited for optical applications. Thirdly, the gels used as electrolytes are biocompatible, so it would be relatively easy to incorporate ionic devices -- such as artificial muscles or skin -- into biological systems.

After all, signals carried by charged ions are the electricity of the human body, allowing neurons to share knowledge and spurring the heart to beat. Bioengineers would dearly love to mesh artificial organs and limbs with that system.

"The big vision is soft machines," says co-lead author Christoph Keplinger, who worked on the project as a postdoctoral fellow at Harvard SEAS and in the Department of Chemistry and Chemical Biology. "Engineered ionic systems can achieve a lot of functions that our body has: they can sense, they can conduct a signal, and they can actuate movement. We're really approaching the type of soft machine that biology has to offer."

The audio speaker represents a robust proof of concept for ionic conductors because producing sounds across the entire audible spectrum requires both high voltage (to squeeze hard on the rubber layer) and high-speed actuation (to vibrate quickly) -- two criteria which are important for applications but which would have ruled out the use of ionic conductors in the past.

The traditional constraints are well known: high voltages can set off electrochemical reactions in ionic materials, producing gases and burning up the materials. Ions are also much larger and heavier than electrons, so physically moving them through a circuit is typically slow. The system invented at Harvard overcomes both of these problems, opening up a vast number of potential applications including not just biomedical devices, but also fast-moving robotics and adaptive optics.

"It must seem counterintuitive to many people, that ionic conductors could be used in a system that requires very fast actuation, like our speaker," says Sun. "Yet by exploiting the rubber layer as an insulator, we're able to control the voltage at the interfaces where the gel connects to the electrodes, so we don't have to worry about unwanted chemical reactions. The input signal is an alternating current (AC), and we use the rubber sheet as a capacitor, which blocks the flow of charge carriers through the circuit. As a result, we don't have to continuously move the ions in one direction, which would be slow; we simply redistribute them, which we can do thousands of times per second."

Sun works in a research group led by Zhigang Suo, the Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials at Harvard SEAS. An expert in the mechanical behaviors of materials, Suo is also a Kavli Scholar at the Kavli Institute for Bionano Science & Technology, which is based at SEAS.

Suo teamed up with George M. Whitesides, a prominent chemist who specializes in soft machines, among many other topics. Whitesides is the Woodford L. and Ann A. Flowers University Professor in the Department of Chemistry and Chemical Biology, co-director of the Kavli Institute at Harvard, and a Core Faculty Member at the Wyss Institute for Biologically Inspired Engineering at Harvard.

"We'd like to change people's attitudes about where ionics can be used," says Keplinger, who now works in Whitesides' research group. "Our system doesn't need a lot of power, and you can integrate it anywhere you would need a soft, transparent layer that deforms in response to electrical stimuli -- for example, on the screen of a TV, laptop, or smartphone to generate sound or provide localized haptic feedback -- and people are even thinking about smart windows. You could potentially place this speaker on a window and achieve active noise cancellation, with complete silence inside."

Sam Liss, Director of Business Development in Harvard's Office of Technology Development, is working closely with the Suo and Whitesides labs to commercialize the technology. Their plan is to work with companies in a range of product categories, including tablet computing, smartphones, wearable electronics, consumer audio devices, and adaptive optics.

"With wearable computing devices becoming a reality, you could imagine eventually having a pair of glasses that toggles between wide-angle, telephoto, or reading modes based on voice commands or gestures," suggests Liss.

For now, there is much more engineering and chemistry work to be done. The Harvard team chose to make its audio speaker out of very simple materials -- the electrolyte is a polyacrylamide gel swollen with salt water -- but they emphasize that an entire class of ionically conductive materials is available for experimentation. Future work will focus on identifying the best combinations of materials for compatibility, long life, and adhesion between the layers.

In addition to Keplinger, Sun, Whitesides, and Suo, coauthors included Keith Choon Chiang Foo, a former postdoctoral fellow at Harvard SEAS, now at the Institute of High Performance Computing in Singapore; and Philipp Rothemund, a graduate student at Harvard SEAS.

This research was supported by the National Science Foundation through a grant to the Materials Research Science and Engineering Center at Harvard University (DMR-0820484) and by the Army Research Office (W911NF-09-1-0476). It was also enabled in part by the Department of Energy (ER45852) and the Agency for Science, Technology, and Research (A*STAR), Singapore.

'Trojan' Asteroids in Far Reaches of Solar System More Common Than Previously Thought

Aug. 29, 2013 — UBC astronomers have discovered the first Trojan asteroid sharing the orbit of Uranus, and believe 2011 QF99 is part of a larger-than-expected population of transient objects temporarily trapped by the gravitational pull of the Solar System's giant planets.

This image shows the motion of 2011 QF99 over the next 59 kyr. Shown here is the trajectory of 2011 QF99, according to the best fit to the observations. The current position is marked by a red square, and the black line shows the trajectory 59 kyr into the future. L4 and L5 are the triangular Lagrange points, the points in space which (Credit: UBC Astronomy)

Trojans are asteroids that share the orbit of a planet, occupying stable positions known as Lagrangian points. Astronomers considered their presence at Uranus unlikely because the gravitational pull of larger neighbouring planets would destabilize and expel any Uranian Trojans over the age of the Solar System.

To determine how the 60 kilometre-wide ball of rock and ice ended up sharing an orbit with Uranus the astronomers created a simulation of the Solar System and its co-orbital objects, including Trojans.

"Surprisingly, our model predicts that at any given time three per cent of scattered objects between Jupiter and Neptune should be co-orbitals of Uranus or Neptune," says Mike Alexandersen, lead author of the study to be published tomorrow in the journalScience. This percentage had never before been computed, and is much higher than previous estimates.

Several temporary Trojans and co-orbitals have been discovered in the Solar System during the past decade. QF99 is one of those temporary objects, only recently (within the last few hundred thousand years) ensnared by Uranus and set to escape the planet's gravitational pull in about a million years.

"This tells us something about the current evolution of the Solar System," says Alexandersen. "By studying the process by which Trojans become temporarily captured, one can better understand how objects migrate into the planetary region of the Solar System."

UBC astronomers Brett Gladman, Sarah Greenstreet and colleagues at the National Research Council of Canada and Observatoire de Besancon in France were part of the research team.

Scientist controls colleague's hand in first human brain-to-brain interface

University of Washington researcher Rajesh Rao sends a brain signal to Andrea Stocco via the Internet, causing Stocco's right hand to move on a keyboard.

University of Washington researcher Rajesh Rao, left, plays a computer game with his mind, while across campus, researcher Andrea Stocco wears a magnetic stimulation coil over the left motor cortex region of his brain.

(Credit: University of Washington)

The telepathic cyborg lives, sort of. University of Washington scientists Rajesh Rao and Andrea Stocco claim that they are the first to demonstrate human brain-to-brain communication. Rao sent a signal into a Stocco's brain via the Internet that caused him to move his right hand. Brain-to-brain communication has previously been demonstrated between rats and from humans to rats.

"The experiment is a proof in concept. We have tech to reverse engineer the brain signal and transmit it from one brain to another via computer," said Chantel Prat, an assistant professor of psychology who worked on the project.

In a press release, the experiment was described as follows:

The team had a Skype connection set up so the two labs could coordinate, though neither Rao nor Stocco could see the Skype screens. Rao looked at a computer screen and played a simple video game with his mind. When he was supposed to fire a cannon at a target, he imagined moving his right hand (being careful not to actually move his hand), causing a cursor to hit the "fire" button. Almost instantaneously, Stocco, who wore noise-canceling earbuds and wasn't looking at a computer screen, involuntarily moved his right index finger to push the space bar on the keyboard in front of him, as if firing the cannon. Stocco compared the feeling of his hand moving involuntarily to that of a nervous tic.

The mind-meld between the researchers wasn't seamless. Rao spent time training his mind, with feedback from the computer, to emit the brainwave for moving the right hand so that it could be detected by the computer. "The intention can be as detectable as the movement itself," Prat said. "Brain-computer interfaces have been capturing this with increasing accuracy over the last decade."

When the software sees the right signal it is sent via the Internet to a computer connected to a transcranial magnetic stimulation device, which is positioned on the exact spot of the brain that controls the right hand. "It uses simple physics," Prat said. "When the magnetic field changes, it induces an electrical current, so a signal is sent through the cortex of the brain and excites the neurons, simulating what happens naturally."

The schematic diagram shows how the brainwave signal was transferred from one brain to another.

(Credit: University of Washington)

Where does human brain-to-brain communication go from this simple experiment? "It's very much a first step, but it shows what is possible," Prat said.

"Right now the only way to transfer information from one brain to another is with words," she said. With advances in computer science and neuroscience, people could eventually perform complicated tasks, such as flying an airplane, and dancing the tango, by transferring information in a noninvasive way from one brain to another. "You can imagine all complex motor skills, which are difficult to verbalize, are just chains of procedures," Prat said.

More complex cognitive skills, such as understanding algebra and physics could also benefit from the technology. "Ultimately, it's important education and training, especially when knowledge cannot be easily translatable into words." she said.

Prat noted that some people might be nervous about this technology being used to control minds against their will. "The signal is being transmitted remotely through the Internet, but the humans are connected to physical equipment and must be trained to create the right signals. There is no way to control minds without their willingness," Prat said.

At least for now, your mind is safe, but who knows where technology leads.