Regenerative medicine refers to the use of technology to directly or indirectly regenerate or grow and replace cells, tissues, or organs. This may be achieved by stimulating the repair mechanisms that are naturally present in the body. Most recently, CNTs have been tested for regenerative medicine purposes.
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What are carbon nanotubes?
Carbon nanotubes (CNTs) are single or multi-walled tubular structures made from graphene sheets that have been rolled and bonded to themselves. Recently, biocompatible CNTs have been created by coating their surface with protective polar molecules. This increases their solubility for biological applications.
The all-carbon structure of CNTs allows for a wide variety of chemical functionalization, providing a platform that can be customized to a range of functions related to regenerative medicine.
What are the Uses of CNTs in Regenerative Medicine?
CNTs for the purpose of bone regeneration are being developed, which use negatively charged functional groups with calcium bonded to them. This can provide a scaffold to which hydroxyapatite, the most common inorganic component of bone, can attach. CNTs are very strong, stiff, and flexible which makes them an excellent alternative to the titanium or ceramic bone scaffolds.
Regeneration of neurons
Graphene sheets, and by extension CNTs, are excellent conductors of electricity, and thus are highly useful in the regeneration of neurons. Neurons can grow successfully on CNT beds, and modifying the surface with 4-hydroxyonoenal, known to be involved with neuron growth, can improve the neuron length and degree of branching over CNTs.
Neuronal circuit activity can also improve through the improvement of electron transfer over connections between neurons. Thick glial scar tissue often forms around traditional implanted probes made from metal and silicon composites, rendering them useless.
Similarly, implanted electrodes are currently used to stimulate the nervous system in the treatment of multiple health problems, including chronic pain, Parkinson’s, and epilepsy. CNTs provide a promising alternative to such electrodes.
Carbon nanotubes make potentially excellent drug delivery vehicles as they enter cells through endocytosis. Applications of carbon nanotubes include gene and protein delivery which can be employed to encourage the production of proteins using the cells own biological machinery. This can promote the activity of the body’s healing mechanisms.
Are CNTs Toxic?
Studies have found that uncoated CNTs can destroy cells by disrupting the protein signalling in extracellular matrix, causing changes to the cytoskeleton and displacement of organelles and the cell membrane. This is due to the highly electrostatic nature of CNTs which can interfere with various biomolecules.
Short CNTs display this effect more prominently than longer ones as they possess a larger surface area, providing a larger surface to interact with proteins and other molecules. It is for this purpose that CNTs are coated with non-toxic ligands, though ligand displacement may prove to overcome this protective measure.
The similarity in structure between CNTs and asbestos fibers is also a concern for those working with them regularly. If CNTs enter the lungs they have been shown in mouse models to increase the rate of cell death and encourage the formation of granulomas, which may lead to lung cancer.