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California startup Tactus Technology prototype touchscreen presented featured buttons that can rise out of the flat surface of the screen at the user’s whim, disappearing completely once they are no longer needed.
Beneath the surface of the screen are a number of microscopic channels that can be prearranged by the manufacturer, and a small amount of a clear oily substance. When the 
physical buttons are “switched on” by the user, the clear substance is pumped through the channels and the solid buttons magically rise out of the display. When the keyboard is switched off, the buttons disappear completely, leaving the user with a full-sized touchscreen device.
For more information :http://tactustechnology.com/technology/
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