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Medical Product Manufacturing News, September/October 2015

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q m e d . c o m / m p m n M e d i c a l P r o d u c t M a n u f a c t u r i n g n e w s s e P t e M b e r / o c t o b e r 2 0 1 5 7 A dIY optogenetics device That costs $10 one of the hottest research topics in neuroscience, optogenetics has given scientists unprecedented control of the brain. in mice studies, researchers have used the technology to beam light at targeted neurons to activate or deactivate them, potentially altering how the mice behave or feel in near real time. researchers have used optogenetics to help numb mice in pain and to even reshape their memories of fearful events. optogenetics has also led to breakthroughs in understanding diseases in humans, adding to our understanding of diseases ranging from depression to Parkinson's. now, ada Poon, Phd, a stanford professor of electrical engineering, has announced that her research team has developed the first miniature, completely implantable, optogenetic device. "when turned off, you don't see any implant unlike the current solution. when switched on, light can be seen leaking out of the mouse's skull." the wireless stimulator costs a mere $10 to make and enables mice be tracked within a 16-cm radiofrequency cavity. Poon's entire optogenetic system costs roughly $5000 to build. "People ask us if they can mass produce them and we say: 'just hire some undergraduates and have them follow this video here," Poon says. "we want any school with a limited budget to be able to do optogenetic research." the new device is completely implantable, allowing the mice to roam freely. "it does not affect the behavior of the mouse," Poon says. up until recently, mice studies have tethered mice to a fiber optic strand plugged into a brain implant or used bulky head- mounted devices. in the first case, the fiber optic cable attached to a mouse's head can get tangled and can disrupt its ability to navigate. the researchers wanted to make a simple technology that could support a relatively large coverage area for the miniature device. inspired by quantum tunnelling, they came up with an elegant solution power the technology: power the device wirelessly, using the mouse itself as a dielectric resonator. "because it has a high concentration of water, a mouse is a good dielectric resonator," Poon says. the researchers built a radiofrequency cavity with holes in the top. "when there is no animal inside it, all of the energy retracts. but when there is an animal inside, because it very dense, the energy will be automatically extracted," Poon. "this enables self tracking. i don't need any more electronics to track where the animal is, which would require localized power." the approach is much simpler compared with others that have come before it. for instance, one approach investigated the use of a network of coil's beneath the mouse's cage. determining where the mouse was in the cage, a coil would turn on or off. "that system is like a cellphone tower for humans. i couldn't convince myself to make something so complicated for a mouse," Poon says. but treating the mouse as a dielectric resonator was not without its own challenges. "it seemed like the most ridiculous thing we have done in our academic career—studying the resonant electromagnetic modes of a mouse in different orientations," Poon jokes. in one study, the researchers implanted the stimulator in the right motor cortex. when the unit was switched on, the mouse moved counterclockwise in a circular cage. Poon jokes that adding a second stimulator to the left motor cortex would enable them to make the mouse remote-controllable. However, the small size of the device does open up numerous potential applications, enabling custom versions of the stimulators to be implanted at various points throughout the body, Poon says. "we can stimulate the spinal cord or peripheral nerves," she says. already, the stanford team has used the technology in a pain study. "current, researchers use a reflexive measure for pain studies for drug testing. in this approach, a pain stimulus is administered to mice and the reaction time is measured," Poon says. Measuring sedated and non-sedated mice this way provides a determination for the efficacy of an analgesic drug. "but a lot of drugs that pass in an animal model don't work in humans. genetically modifying mice to feel pain when light is optogenetically administered to the brain provides a new mechanism for studying painkillers. inspired by the open source movement, Poon has not only released instructions for the system, but her team has produced a Youtube video demonstrating how to show potential optogenetic researchers how to build their own systems. —brian buntz Move Over Graphene, Meet the Next Wonder Material credit: brian buntz Te optogenetic stimulators recently developed at Stanford are the frst that are completely implantable. when it comes to enhancing transistor technology, thinner is theoretically better. this is why graphene — a material one-atom thick — could potentially be an ideal replacement material for silicon transistors. Yet graphene lacks a critical property: in its natural state, it doesn't have a band gap, which causes it to continuously work as a conductor. researchers at berkeley have succeeded in making the material work as a semiconductor by making it thicker—stacking two sheets of graphene on top of the other. but perhaps another material, black phosphorus, is better suited for replacing silicon in electronics. for one thing, the material works as a semiconductor out of the gate. its ability to have its conductivity, meaning it can be readily switched on and off would enable the binary encoding of 1s and 0s in computer languages. the key to integrating the material into transistor technology is keeping it thin, constraining electrons to move in only two dimensions. these traits open up a world of possibilities when it comes to applications, specifically in nanoelectronics and wearable sensors. recent research out of Mcgill university and Pohang university of science and technology (PostecH) indicate that the versatile material could be potentially used for an array of applications, including medical sensors. "one thing that quickly comes up in my mind is [the use of black phosphorus in] the flexible nanoscale sensors that can be attached directly to human skin, monitoring [a person's] medical status," said Kim Keun su, a professor in physics at PostecH, where he's been working with a team of scientists to create the first semiconductor from black phosphorus. "for applications in such nano- medical sensors, developments of devices composed of 2-d semiconductors would be very important." the integration of enhanced transistor technologies into electronics will also have a significant impact on speed and performance. since the development of graphene, scientists have been exploring various other two-dimensional materials that could be easily separated into single atomic layers. black phosphorus quickly emerged as a candidate given its similarities to graphene. "black phosphorus has a very similar honeycomb lattice with graphene, but it is strongly puckered," Kim Keun su said. "the electronic state of black phosphorus could be tuned from a semiconductor to an efficient conductor, depending on the strength of electric field applied." deji akinwande, an associate professor of electrical and computer engineering at the university of texas in austin, believes that the largest obstacle for using the material in electronics is manufacturing it on a large scale. but researchers, convinced of its great potential to advance semiconductor technology, are currently working on doing this, he says. "black phosphorus is arguably the most outstanding of the 2-d atomic materials so far. it has a high bandgap, a property needed to make electronic switches, unlike graphene which cannot offer this." researchers continue to work to fine tune graphene for electronics applications, exploring not only how the material could be woven into devices, but also experiment with new methods of giving the material a band gap and shaping the material for integration into flexible electronics and microelectromechanical systems. — Kristopher sturgis

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