Nanotechnology refers to the use man-made of nano-sized (typically 1-100 billionths of a meter) particles for industrial or medical applications suited to their unique properties. Physical properties of known elements and materials can change as their surface to area ratio is dramatically increased, i.e. when nanoscale sizes are achieved. These changes do not take place when going from macro to micro scale. Changes in physical properties such as colloidal properties, solubility and catalytic capacity have been found very useful in areas of biotechnology, such as bioremediation and drug delivery.
The very different properties of the different types of nanoparticles have resulted in novel applications. For example, compounds known to be generally inert materials, may become catalysts. The extremely small size of nanoparticles allows them to penetrate cells and interact with cellular molecules. Nanoparticles often also have unique electrical properties and make excellent semiconductors and imaging agents. Because of these qualities, the science of nanotechnology has taken off in recent years, with testing and documentation of a broad spectrum of novel uses for nanoparticles, particularly in nanomedicine.
The development of nanotechnologies for nanomedical applications has become a priority of the National Institutes of Health (NIH). Between 2004 and 2006, the NIH established a network of eight Nanomedicine Development Centers, as part of the NIH Nanomedicine Roadmap Initiative. In 2005, The National Cancer Institute (NCI) committed 144.3 million over 5 years for its “Alliance for Nanotechnology in Cancer” program which funds seven Centres of Excellence for Cancer Nanotechnology (Kim, 2007). The funding supports various research projects in areas of diagnostics, devices, biosensors, microfluidics and therapeutics.
Among the long term objectives of the NIH initiative are goals such as being able to use nanoparticles to seek out cancer cells before tumors grow, remove and/ or replace “broken” parts of cells or cell mechanisms with miniature, molecular-sized biological “machines”, and use similar “machines” as pumps or robots to deliver medicines when and where needed within the body. All of these ideas are feasible based on present technology. However, we don’t know enough about the physical properties of intracellular structures and interactions between cells and nanoparticles, to currently reach all of these objectives. The primary goal of the NIH is to add to current knowledge of these interactions and cellular mechanisms, such that precisely-built nanoparticles can be integrated without adverse side-effects.
Many different types of nanoparticles currently being studied for applications in nanomedicine. They can be carbon-based skeletal-type structures, such as the fullerenes, or micelle-like, lipid-based liposomes, which are already in use for numerous applications in drug delivery and the cosmetic industry. Colloids, typically liposome nanoparticles, selected for their solubility and suspension properties are used in cosmetics, creams, protective coatings and stain-resistant clothing. Other examples of carbon-based nanoparticles are chitosan and alginate-based nanoparticles described in the literature for oral delivery of proteins, and various polymers under study for insulin delivery.
Additional nanoparticles can be made from metals and other inorganic materials, such as phosphates. Nanoparticle contrast agents are compounds that enhance MRI and ultrasound results in biomedical applications of in vivo imaging. These particles typically contain metals whose properties are dramatically altered at the nano-scale. Gold “nanoshells” are useful in the fight against cancer, particularly soft-tissue tumors, because of their ability to absorb radiation at certain wavelengths. Once the nanoshells enter tumor cells and radiation treatment is applied, they absorb the energy and heat up enough to kill the cancer cells. Positively-charged silver nanoparticles adsorb onto single-stranded DNA and are used for its detection. Many other tools and devices for in vivo imaging (fluorescence detection systems), and to improve contrast in ultrasound and MRI images, are being developed.
There are numerous examples of disease-fighting strategies in the literature, using nanoparticles. Often, particularly in the case of cancer therapies, drug delivery properties are combined with imaging technologies, so that cancer cells can be visually located while undergoing treatment. The predominant strategy is to target specific cells by linking antigens or other biosensors (e.g. RNA strands) to the surface of the nanoparticles that detect specialized properties of the cell walls. Once the target cell has been identified, the nanoparticles will adhere to the cell surface, or enter the cell, via a specially designed mechanism, and deliver its payload.
One the drug is delivered, if the nanoparticle is also an imaging agent, doctors can follow its progress and the distribution of the cancer cell is known. Such specific targeting and detection will aid in treating late-phase metastasized cancers and hard-to-reach tumors and give indications of the spread of those and other diseases. It also prolongs the life of certain drugs that have been found to last longer inside a nanoparticle than when the tumor was directly injected, since often drugs that have been injected into a tumor diffuse away before effectively killing the tumor cells.