[nihila]

Carbon Nanotubes (CNTs) are allotropes of carbon. They are cylindrical tubes made with a diameter ranging in nanometers. They are made up of graphene sheets (carbon atoms) rolled like a cylinder. These graphene sheets can be rolled in different ways and the angle of rolling gives different CNTs different properties. CNTs with a single cylindrical carbon layer is known as single walled carbon nanotubes (SWCNTs) which have a diameter of 0.4 – 2 nm and those containing multi layers is known as multi walled carbon nanotubes (MWCNTs) with inner tubes pertaining to a diameter of 1 -3 nm and outer tubes to 2- 100nm. They belong to fullerene family. They can be open at both side or can contain cap at one end

CNTs are the most dynamic and most promising nanomaterials for variety of fields. In medicine they can be used for drug delivery, cancer treatment, biosensors, etc. Because of their unique physical, chemical and biological properties they have various therapeutic uses. They are the strongest materials found till now. They sp2 bonds between the carbon atoms make them the strongest materials. They are highly conductive.

CNTs can be designed to function as carrier systems for nanoparticles that are used in and are mentioned as Nano carrier drug delivery systems. With different type of rolling they acquire different properties and their functions vary. Variety of biological molecules or drugs can be attached onto the surface of the CNTs or they can be filled inside them and injected into the body.

The main aspect here is how these CNTs reach the target cells. For this the surface of CNTs with the anti-cancer drug is coated with specific antibody that can identify the target cell and then released into the body. To track the CNTs, they are loaded with quantum dots which generate fluorescence when subjected to certain radiation. The Nano needle shape of these CNTs, the hollow monolithic structure and their ability to bind with different functional groups provide delivery of drugs directly to target tissue preventing harm to normal tissues. CNTs are introduced into the body with a Nano injector.

There are two main routes of CNTs to enter the cell, one is through passive diffusion through lipid bilayer and the other is by endocytosis where the CNT attaches to the external cell membrane and then absorbed by cell using energy dependent process. SWCNTs and MWCNTs have different cell penetration mechanism. SWCNTs internalize into cells, long SWCNTs localize into cytoplasm and short SWCNTs can enter nucleus. MWCNTs cannot enter the cells, they are excluded.

The release of drug into the target tissue is also an important aspect. CNTs loaded with drugs are sealed at both ends with molecules which can be cleaved intracellularly or the drugs can be attached to the walls of CNTs and can be cleaved by various conditions in the cell like acidic environment, pH, etc. They can also be released when subjected to heat.

The combination of CNTs with radiofrequency or radiation can be a potential treatment for cancer that is harmless to normal cells and is highly efficient. When CNTs are exposed to laser heat is generated from these CNTs and it increases the surface temperature of the cells. This causes coagulative necrosis and as a result of this heat shock protein induction is observed in deeper tissues indicating that CNTs can be used to extend the depth of radiation therapy.

Despite the biological advantages of CNTs, there are limitations to their use as medicines because their surfaces of CNTs are highly contaminated with metal catalysts and amorphous carbon, various factors like size of the nanoparticles, their surface chemistry, dosage, morphology and chemical components are also responsible for the magnitude of their toxicity. Several studies have stated that when appropriate molecules are attached to the surface of CNTs they become less toxic and more biocompatible. This attachment of molecules is called functionalization and studies have observed that a high degree of functionalization reduces the toxicity of CNTs.

The unique and dynamic properties of CNTs make them interesting to be multifunctional therapeutic agents in cancer treatment. The major drawback is its toxicity. It is a relief that functionalizing CNTs would allow them to be biocompatible for clinical applications. Despite this, the advances made by CNTs are of great significance in for us.