In my book, Getting To Zero Waste, I discuss a number of promising research directions for making paper reusable. One of them involves a scheme for embedding tiny spheres into paper, which are white on one side and black on the other. Then the printing process would consist of turning certain spheres to black side up while the rest are left white side up. Reusing would consist of changing the locations of the black and white spheres.
I was therefore intrigued to read that this approach is now being used in an electronic device, the Kindle Paperwhite. See article.
Here is an explanatory paragraph from the story:
How Electronic Ink Works
The display is made up of millions of microscopic spheres sandwiched between electrodes. Within each sphere are positively charged white ink particles and negatively charged black ones. Applying a negative charge to the bottom electrode repels the black spheres to the top, making the screen appear black at that pixel. A positive charge moves the white ones to the top.
While this is being used on a screen, perhaps the technology could take us a bit closer to rewritable paper by using the same approach. The pixel by pixel control would not be built in to fixed spheres but would be controlled by an outside signal, much the way that a dot matrix printer hovers over every pixel of paper and performs an operation. Today’s printer deposits a microdrop of ink but another kind of printer could apply a local electrical signal.