Giving Prosthetics a Sense of Touch

Monkey see: In an experiment, monkeys implanted with two interfaces—one that reads their intended movements and another that responds to touch sensations—learned to operate the arm of a virtual monkey.
Courtesy of the Nicolelis Lab at Duke University

BIOMEDICINE

Giving Prosthetics a Sense of Touch

A study gives a first demonstration that brain-machine interfaces can include touch feedback.

• BY COURTNEY HUMPHRIES

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Brain-machine interfaces have made it possible for monkeys and some humans to control robotic limbs using just their thoughts. But ideally, a person using an artificial limb or other device would not only be able to control the device, but also feel what it's touching.

A new study from the lab of Miguel Nicolelis at Duke University Medical Center takes a first step toward such an interface. In a paper published today in Nature, his team reports that monkeys can learn to operate a virtual-reality hand that incorporates tactile feedback.

Nicolelis says that brain-machine interfaces will only be clinically useful if they use bidirectional signals, with both sensory feedback from the device and motor commands from the user. "It's not enough to just provide motion," he says. "You need to sense what you're touching."

As a first experiment, monkeys used a joystick to control a virtual "avatar" (a monkey arm and hand) on a computer screen, and were encouraged to use the avatar to grab objects on the screen. The virtual objects had textures, and this was conveyed using stimulation through microwave arrays implanted in a part of the brain's cortex responsible for sensing touch. The monkeys learned to hold the avatar's hand over objects with a particular texture—conveyed by the frequency of stimulation—in order to be rewarded with food.

In another experiment, the monkeys received the same tactile feedback but controlled the virtual hand using just their thoughts, via microwire arrays implanted in the motor cortex. Although their performance on the task was less accurate, the monkeys improved over time.

Nicolelis says the successful use of a "brain-machine-brain interface" demonstrates that the processes of sensing and responding to tactile sensations can be combined. "We are decoding motor intentions and tactile messages simultaneously," he says. "That's never been done before." Although the stimulation the monkeys receive is artificial, he says, they seem to learn to associate it with tactile information.

The next step is to incorporate the sense of touch into real prosthetics, using pressure sensors that will generate similar tactile feedback about real-world objects. Nicolelis says his group hopes to build a simulator that would test this approach in humans, then incorporate touch sensation in prosthetics it's creating for people with reduced mobility.

NitishThakor, a biomedical engineer at Johns Hopkins University, says that adding sensory information "is absolutely the next logical step" in brain-machine interface design. Thakor says the experiment not only demonstrates the feasibility of adding touch, but shows that the monkeys can learn a task using these coupled signals. The caveat, he adds, is that textures in the real world are much more complex, as are body movements, and "whether this is scalable remains to be seen."

Dipping May Improve Ultracapacitors and Batteries

Wrap up: Scanning electron microscope images show the surface of nanostructured graphene-manganese oxide electrodes covered with conductive carbon nanotubes (top) and a polymer (bottom).
Nano Letters

ENERGY

Dipping May Improve Ultracapacitors and Batteries

A sheath of carbon nanotubes or conductive polymer improves the charge-storage capacity of electrodes.

• BY PRACHI PATEL

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A simple trick could improve the ability of advanced ultracapacitors, or supercapacitors, to store charge. The technique, developed by Stanford University researchers, could enable the use of new types of nanostructured electrode materials that store more energy.

While ultracapacitors provide quick bursts of power and can be recharged many more times than batteries without losing their storage capacity, they can store only a tenth as much energy as batteries, which limits their applications. To improve their energy density, researchers have focused on the use of electrode materials withgreater surface area—such as graphene and carbon nanotubes—which can hold more charge-carrying ions.

The Stanford team, led by Yi Cui and Zhenan Bao, used composite electrodes made of graphene and manganese oxide. Manganese oxide is considered an attractive electrode material because, "one, manganese is abundant so it's very low cost," Cui says. "It also has high theoretical capacity to store ions for supercapacitors." However, in the past its use has been hindered by its low conductivity, which makes conveying ions in and out of the material difficult.

The researchers dipped the composite electrodes into either a carbon nanotube solution or a conductive polymer solution. The coating improves the electrodes' conductivity and hence their capacitance—their ability to store charge—by 20 percent and 45 percent respectively. The researchers report their work in a paper that appeared online in the journal Nano Letters.

"This is an important advancement," says Lu-Chang Qin, a physics professor at the University of North Carolina at Chapel Hill, who has recently developed similar graphene–manganese oxide electrodes. These results "promise hopes for a new generation of supercapacitors," Qin says. However, he points out that the Stanford team has yet to measure the energy density of its new electrodes. Qin has collaborated with Japanese researchers to make electrodes from carbon nanotube graphene. These have an energy density of 155 watt-hours per kilogram, comparable with that of nickel–

Bor Jang, cofounder of Nanotek Instruments in Dayton, Ohio, which makes graphene electrodes for supercapacitors, says the new electrodes may lack energy density. Besides, he says, "a combination of graphene, MnO2, and a conductive polymer or carbon nanotubes might be overkill."

Others have obtained much higher capacitance numbers with graphene–metal oxide or conductive polymer electrodes. However, Cui says what's most exciting about the new work is that such a simple dipping technique can enhance capacitance. He says the technique might be used to improve the conductivity of other electrode materials such as sulfur, silicon, and lithium manganese phosphate, thereby enhancing the performance of lithium-ion batteries. Cui and his colleagues are now working on improving battery electrodes using the new method.

Modified iPhone Can Detect Blood Disorders

COMMUNICATIONS

Modified iPhone Can Detect Blood Disorders

The device could mean better and faster diagnoses for patients in poor countries.

• BY STEPHEN CASS

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A cheap lens that enables a cell phone's camera to discern the shapes of cells in a blood sample could make it easier to diagnose conditions such as sickle-cell anemia in places without medical infrastructure.

The system was developed at the University of California, Davis, and is designed to allow field workers to photograph blood samples from patients, and then send the micrographs to doctors via the cellular network for interpretation.

Although others have coupled microscopes to cell phone cameras, the Davis group aimed to make its device inexpensive. It did this by using a very simple lens that is made from a single ball of glass about one millimeter in diameter and held in position in front of the camera with a small piece of rubber. That small size results in a high curvature that provides good magnification, says Sebastian Wachsmann-Hogiu, a physicist with Davis's Center for Biophotonics, Science, and Technology, and the leader of the research team. Because a cell phone camera also uses lenses with a short focal length and a miniaturized sensor with very small pixels, it's optically compatible with the small ball lens. "You couldn't do this with a regular camera, the distances there are too big," says Wachsmann-Hogiu.

The downside of using a ball lens is that the resulting image is significantly distorted, except for in one very small area directly behind the lens. The Davis team solved this problem with software. To take an image using its system, the software takes multiple photos of a blood sample as either the camera or the sample is moved about; the software then combines the images into a larger, undistorted image. The current prototype can resolve features about 1.5 micrometers across.

While the system was developed using a relatively expensive iPhone 4 with a five-megapixel camera, Wachsmann-Hogiu says it could be adapted to cheaper phones with one or two megapixel cameras, which are more likely to be found in poor countries. Wachsmann-Hogiu believes that with mass production, an accessory based on a plastic, rather than glass, lens design could be produced for around $2, cheap enough to be broadly adopted in poor countries. 

Ramesh Raskar, a professor at MIT's Media Lab, agrees that leveraging ubiquitous technologies is the key to improving health in poor countries. "There are more than four billion phones out there," he says. "I can't imagine more than one million microscopes are sold per year." Raskar's own Netra project is developing cell phone attachments that can be used for eye exams. He says work like that of his own and the Davis group is part of a "beautiful" trend that lets global health initiatives "piggyback on scalable platforms like cell phones."

The Davis team, which will present its research to the Optical Society of America's annual meeting next Wednesday, is planning a series of field tests and is in discussions with manufacturing partners to commercialize the technology. Wachsmann-Hogiu estimates the system could reach the market within two or three years. His team is also working on an accessory that lets a cell phone act as a spectrometer, built by stretching electrical tape with a narrow slit over the ends of a plastic tube. Light from a sample is diffracted by passing through the slits before falling on the phone's camera, creating a spectrum that could be used to perform basic analyses of blood chemistry.