Seeing a Bionic Eye on Medicine’s Horizon
A More Sensitive Sensor. Tel Aviv University pioneers sensor technology for industry using nano-sized carbon tubes more..Electro-mechanical sensors tell the airbag in your car to inflate and rotate your iPhone screen to match your position on the couch. Now a research group of Tel Aviv University’s Faculty of Engineering is making the technology even more useful. Prof. Yael Hanein, Dr. Slava Krylov and their doctoral student Assaf Ya`akobovitz have set out to make sensors for microelectromechanical systems (MEMS) significantly more sensitive and reliable than they are today. And they’re shrinking their work to nano-size to do it. More sensitive sensors means more thrilling videogames, better functioning prosthetic limbs, cars that can detect collisions and dangerous turns before they occur, and ― in the defense industry ― missiles that can reach a target far more precisely. Miniscule earthquakes. Able to “feel” and sense the movement of individual atoms, the researchers’ new MEMS sensing device uses small carbon tubes, nano in size ― about one-billionth of a meter long. Creating these tiny tubes using a
process involving methane gas and a furnace, Prof. Hanein has developed a method whereby they arrange themselves on a surface of a silicon chip to accurately sense tiny movements and changes in gravity. In the device developed by Prof. Hanein’s and Dr. Krylov’s team, a very tiny nanometer scale tube is added onto much larger micrometer-scale MEMS devices. Small deformities in the crystal structure of the tubes register a change in the movement of the nano object, and deliver the amplitude of the movement through an electrical impulse. “It’s such a tiny thing,” she says. “But at our resolution, we are able to feel the motion of objects as small as a few atoms.” “Originally developed mainly for the car industry, miniature sensors are all around us,” says Prof. Hanein. “We’ve been able to fabricate a new device where the nano structures are put onto a big surface ― and they can be arranged in a process that doesn’t require human intervention, so they’re easier to manufacture. We can drive these nano-sensing tubes to wherever we need them to go, which could be very convenient and cost-effective across a broad spectrum of industries.” Until now, Prof. Hanein explains, the field of creating sensors for nanotechnology has been primarily based on manual operation requiring time-consuming techniques. Prof. Hanein and her team have developed a sensitive but abundant and cost-effective material that can be coated onto prosthetic limbs, inserted into new video games for more exciting play, and used by the
auto industry to detect a potential collision before it becomes fatal. The technology has been presented in a number of peer-reviewed journals including the Journal of Micromechanics and Micro-engineering; at a MEMS conference in Hong Kong; and at a nano conference in Tirol, Austria in March. Markets in motion. The market for MEMS devices, which take mechanical signals and convert them into electrical impulses, is estimated to be worth billions. “The main challenge facing the industry today is to make these basic sensors a lot more sensitive, to recognize minute changes in motion and position. Obviously there is a huge interest from the military, which recognizes the navigation potential of such technologies, but there are also humanitarian and recreational uses that can come out of such military developments,” Prof. Hanein stresses. More sensitive MEMS could play a role in guided surgery, for example. The TAU team is working on optimizing the system, hoping to make it at least 100 times more sensitive than any sensor device on the market today. Dr. Yael Hanein received the B.Sc. degree in physics from Tel-Aviv University, Israel, and the M.Sc. and Ph.D. degrees in physics from the Weizmann Institute of Science, Israel. In 2003, she completed a Postdoctoral Fellowship at the Electrical Engineering Department and a
research associate position at the physics department at the University of Washington, Seattle and joined the faculty of Tel-Aviv University, at Tel-Aviv, Israel. She is currently a lecturer at the school of electrical engineering at Tel-Aviv University. Her current interests include BioMEMS, micro-self-assembly, and carbon nanotube electronic devices for biological applications. news from tau.ac.il ~ A visual prosthesis or bionic eye is a form of neural prosthesis intended to partially restore lost vision or amplify existing vision. It usually takes the form of an externally-worn camera that is attached to a stimulator on the retina, optic nerve, or in the visual cortex, in order to produce perceptions in the visual cortex. These experimental visual devices are modeled on the cochlear implant or bionic ear devices, a type of neural prosthesis in use since the mid 1980s. These are an externally-worn microphone and processor that is attached to a stimulator in the cochlea, auditory nerve, in order to produce sound perception in the auditory cortex.Scientific research since at least the 1950s has investigated interfacing electronics at the level of the retina, optic nerve, thalamus, and cortex. Visual prosthetics, which have been implanted in patients around the world both acutely and chronically, have demonstrated proof of principle, but do
not yet offer the visual acuity of a normally sighted eye. After the accidental death of a human volunteer in the late nineties, caused by a massive infection after they pulled on wires attached to electrodes implanted in their brain, much research on visual prostheses has been halted.The ability to give sight to a blind person via a bionic eye depends on the circumstances surrounding the loss of sight. For retinal prostheses, which are the most prevalent visual prosthetic under development (due to ease of access to the retina among other considerations), vision loss due to degeneration of photoreceptors (retinitis pigmentosa, choroideremia, geographic atrophy macular degeneration) is the best candidate for treatment. Candidates for visual prosthetic implants find the procedure most successful if the optic nerve was developed prior to the onset of blindness. Persons born with blindness may lack a fully developed optical nerve, which typically develops prior to birth. Visual prosthetics are being developed as a potentially valuable aide for individuals with visual degradation. The visual prosthetic in humans remains investigational. Eyes are organs that detect light, and send electrical impulses along the optic nerve to the visual and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally
different forms, and 96% of animal species possess a complex optical system.Image-resolving eyes are present in cnidaria, molluscs, chordates, annelids and arthropods. The simplest “eyes”, such as those in unicellular organisms, do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment. Complex eyes can distinguish shapes and colors. The visual fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception; in other organisms, eyes are located so as to maximise the field of view, such as in rabbits and horses, which have monocular vision.The first proto-eyes evolved among animals 600 million years ago, about the time of the Cambrian explosion. The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the thirty-plus main phyla. In most vertebrates and some molluscs, the eye works by allowing light to enter it and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for color) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals
for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye, and reducing aberrations when there is enough light. The eyes of cephalopods, fish, amphibians and snakes usually have fixed lens shapes, and focusing vision is achieved by telescoping the lens — similar to how a camera focuses. Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360-degree field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images. Possessing detailed hyperspectral color vision, the
Mantis shrimp has been reported to have the world’s most complex color vision system. Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in one eye.In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which gives a rough image. Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot actually “see” in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight. In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and adapted to spot the infra-red light produced by the hot vents – in this way the bearers can spot hot springs and avoid being boiled alive. ~ GoodNews International Edition
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