coatings for implantable electrodes consisting of single - or multi - walled nanotubes , nanotube ropes , carbon whiskers , and a combination of these are described . the nanotubes can be carbon or other conductive nanotube - forming materials such as a carbon - doped boron nitride . the nanotube coatings are grown “ in situ ” on a catalytic substrate surface from thermal decomposition , or they are bonded to the substrate using a metal or conductive metal oxide thin film binder deposited by means of a metal compound precursor in liquid form . in the latter case , the precursor / nanotube coating is then converted to a pure metal or conductive metal oxide , resulting in the desired surface coating with imbedded nanotubes .