Nanotechnology is currently being utilized for tissue engineering and regenerative medicine. Nanostructures can mimic tissue-specific bio-environments by designing constructs with particular biochemical, mechanical and electrical properties.
Therefore, tissue can be engineered by employing these nanostructures for enhanced cell adhesion, growth and differentiation. As the range of tissues being proposed for engineering increases, there is also a proportional increase in demand for new scaffold properties.
The Use of Nanostructures for Tissue Engineering Scaffolds
Tissue engineering requires a porous scaffold that will serve as both substrate and support for tissue growth. The scaffold forms the necessary spatial composition for directing cells to grow into the correct anatomical shape. The nanostructures developed for use as tissue engineering scaffolds can have variable functionality dependent on their design. For example, neural tissue requires electrical conductivity whilst bone and cartilage cells necessitate enhanced mechanical properties.
The main requirement for a tissue engineering scaffold is biocompatibility to avoid inhibition of cell growth. The scaffold must also be fabricated into a three dimensional porous structure for tissue formation, along with the ability to transport nutrients and waste. Nanotechnology is being employed for the development of these scaffolds at the requisite nanoscale.
Why Carbon Nanotubes are Suitable for Tissue Engineering
The properties of nanostructures vary dependent on the nanomaterial used. Carbon nanotubes have been proposed for use in tissue engineering because they can conduct electricity, are chemically stable and are strong enough for use as scaffolds. Moreover, filamentous carbon nanotubes have a structural composition that is comparable to the extracellular matrix which supports surrounding cells. This means that carbon nanotubes may have the ability to stimulate cell function in the same way as the extracellular matrix.
Early carbon nanotube biocompatibility tests analyzed both loose carbon nanotubes in suspension and carbon nanotubes contained in a structure. Loose carbon nanotubes suspended in a cell culture were found to decrease cell viability. However, cells attached directly onto carbon nanotube-containing structures produced good cell growth and proved the general biocompatibility of carbon nanotubes with living cells.
Carbon Nanotubes for Bone Tissue Engineering
Bone tissue engineering requires the complex formation of cell types such as osteoblasts, osteoclasts and osteocytes within a non-cellular mineral component. Previously, nanomaterials chosen for bone tissue engineering were limited due to their low mechanical strength. Studies in the last decade have shown that high-strength carbon nanotubes are fully compatible with bone cells. Multi-walled carbon nanotubes have also been proven to produce bone repair that can be fully integrated into new bone. In the future, bone tissue engineering could be applied during hard tissue surgery, particularly for reinforcing artificial bone implants.
Carbon Nanotubes for Neural Tissue Engineering
In comparison to bone tissue repair, the regeneration of neural tissue has proved more challenging and the ability to re-grow nerves for paraplegic patients has not yet been reached. Nanotechnology may provide a promising new strategy for treatment. This is because nanotubes are especially suited for neural tissue engineering as their structure mimics the natural tubular forms of microtubules and axons.
Carbon nanotubes are characterized by relatively high conductivity which is necessary for maintaining electrical signals between neuronal cells. Studies have found that neuronal cells can grow neurites onto carbon nanotube substrates. Furthermore, by changing the orientation of the carbon nanotubes, the direction of neurite growth can be controlled.
Carbon Nanotubes for Cardiac Tissue Engineering
The electrical conducting property of carbon nanotubes is also being put to use in cardiac tissue engineering. Regenerating cardiac tissue would improve the prognosis of heart pathologies such as cardiovascular defects and heart failure. Carbon nanotubes are being used to develop devices for functional regenerative purposes. Through embedding carbon nanotubes into gelatin methacrylate hydrogels, a two-dimension patch was formed which allowed for the engineering of cardiomyocytes. The cells produced displayed synchronous beating as the carbon nanotubes promoted cell-cell adhesion and improved cell-cell electrical coupling.
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