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Presentation Nanotech 2


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MEMS in retinal prosthesis

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Presentation Nanotech 2

  1. 1. ‘ MEMS in visual prosthesis’<br />Nanotecnologias 2009/2010<br />David Conceição<br />Nº 64405 MBioNano<br />
  2. 2. Introduction ...<br /><ul><li> A photoreceptor does not have an axon – it does not generate action potentials.
  3. 3. Ganglion cells generate action potentials. </li></ul>Retina<br /><ul><li> External – pigmented layer – reduces light dispersion
  4. 4. Internal, it responds to light – Neural layer (sensorial retina) – PHOTORECEPTORES! – Cones and rods</li></li></ul><li>Retinal phototransduction<br />Retinal – Light absorving molecule<br />The retinal molecule absorbs different wavelenghts. <br />Different kinds of opsin molecules! <br />
  5. 5. Retinitis pigmentosa<br />A type of progressive retinal dystrophy<br />Causes the loss of up to 95% of the photoreceptor layer, but spares up to 80% of the inner nuclear layer and ~<br />30% of the ganglion celllayer<br />Macular degeneration<br />Patients with age-related macular degeneration (AMD) can lose up to<br />70% of photoreceptors with no loss of other retinal cell types<br />Medical condition which usually affects older adults that results in a loss of vision in the center of the visual field (the macula) because of damage to the retina<br />
  6. 6. Previousstudies ...<br />Epiretinal implants sit on top of the retina, directly stimulating ganglia using signals sent from the external camera and power sent from an external transmitter<br />Subretinalimplantssit under the retina, stimulating bipolar or ganglion cells from underneath<br />It has been demonstrated that electrical stimulation of the retina can produce visual percepts in blind patients suffering from macular degeneration and retinitis pigmentosa.<br />
  7. 7. A videocameratransmits640 × 480 pixel images at 25–50 Hz to a pocket PC.<br />The computer processes the data and displays the resulting video on an LCD matrix mounted on goggles worn by the patient<br />The LCD screen is illuminated with pulsed near-infrared (NIR, 800–900 nm) light, projecting each video image through the eye optics onto the retina<br />The NIR light is then received by a photodiode array on a ∼3 mm implanted chip<br />
  8. 8. Effect of cellular migration !!<br />Two basic geometries of sub-retinal implants presented: perforated membranes and protruding electrode arrays<br />Photodiodes convert light into pulsed electric<br />current<br />Electrodes must inject enough charge to stimulate nerve cells, within electrochemically safe voltage limits<br />
  9. 9. Lithographically fabricated 10 μm wide pillars penetrating into the inner plexiform layer in the retina of RCS rat 15 days after the implantation.<br />Rat retina grown on the three-layered structure for 7 days in vitro. <br />Common problems include biocompatibility and electrochemical stability<br />- Electrodes height: 70 µm;<br />
  10. 10. Carbon Nanotubes as na alternative ...<br />Superior electrochemical properties<br />Robust<br />Flexible<br />Biocompatible?<br />CNT protruding electrodes may be able to provide a safer solution for long-term retinal stimulation and implantation<br />They could also act as recording units to sense electrical and chemical activities in neural systems for fundamental neuroscience research <br />
  11. 11. - Their usage may be limited by their potential toxicity;<br />- A large number of variables has considerable impact on the reactivity of carbon nanotubes.<br />Carbon nanotubes<br />Insulating layer<br />Silicon wafer <br />
  12. 12. Several considerations...<br />- For functional restoration of sight a retinal implant should ideally cover a larger field of view, up to 10◦ (3 mm in diameter), and support a visual acuity of at least 20/80 (corresponding to a pixel size of 20 μm) – 18 000 pixels – Tissue hyperthermia!<br />-Minimal distance between electrodes and target cells (for visual acuity of 20/80): 7 µm;<br />- The optimal size of the electrode designed for selective stimulation of a single cell should be comparable to the cellular size (L ≈ 10 μm)<br />