We have been hearing a lot about the use of Carbon nanotubes within 3D printing. Although in general, carbon nanotubes do not typically lead to stronger prints, and such technology is used more as a way to turn the plastic into a conductor of electricity, one engineer named Brandon Sweeney has figured out a way to used CNT's to create strength within a 3D printed object. What he does, is coat the filament with CNTs and then expose the printed object to microwave radiation, causing the CNT to become extremely hot. This fuses the plastic and creates a layer of CNTs between each layer of filament. More details on just what has been done can be see here: http://3dprint.com/4517/carbon-nanot...print-filament

Below is a TED talk that Brandon gave in February on this new approach: