Nanotube inside a cell, illustration. Nanotubes are a type of fullerene molecule, a structural form (allotrope) of carbon whose atoms are arranged into interlinking hexagonal and pentagonal rings. Theoretically, a wide range of shapes can be engineered at the molecular level using fullerenes. Such structures could have a wide range of technological and medical uses. Nanotube structures have been designed for medical research including cancer treatments. Here, a nanotube wrapped in RNA (ribonucleic acid) is shown inside a cell, with the cell membrane at upper right.