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Over the last years, nanotechnology has been introduced in our daily routine. This revolutionary technology has been applied in multiple fields, several scientific areas have benefited significantly from this. An increasing number of applications and products containing nanomaterials or at least with Nano-based claims have become available.

According to the EC recommendation, nanomaterial refers to a natural, incidental, or manufactured material comprising particles, either in an unbound state or as an aggregate wherein one or more external dimensions is in the size range of 1–100 nm for ≥50% of the particles, according to the number size distribution should be considered as nanomaterials.

However, the definition of nanomaterial has been controversial among the various scientific and international regulatory corporations.

Some efforts have been made in order to find a consensual definition due to the fact that nanomaterials possess novel physicochemical properties, different from those of their conventional bulk chemical equivalents, due to their small size.

Nanotechnology is a rapidly advancing field that is expected to have a revolutionary impact on many industries, including medicine.

The application of nanotechnology for medical purposes has been termed nanomedicine and is defined as the use of nanomaterials for diagnosis, monitoring, control, prevention and treatment of diseases.

Size

The most important feature to take into account is size, because it is applicable to a huge range of materials. The conventional range is from 1 to 100 nm.To this extent, it is assumed that other properties should be taken in account.

Particle Size Distribution

The PSD is a parameter widely used in the nanomaterial identification, reflecting the range of variation of sizes. It is important to set the PSD, because a nanomaterial is usually polydisperse, which means, it is commonly composed by particles with different sizes.

Permeability

If NPs are properly designed, their small size can enable them to cross physiological barriers to deliver drugs to sites that are not normally accessible by traditional means. The increased permeability of NPs may also allow them to cross the blood–brain barrier through the use of different uptake mechanisms.

Nanoparticle Functionalization

One of the most interesting capabilities in nanomedicine is the functionalization of NPs. Functionalization involves altering properties of an NP through chemical or physical modifications that are applied to achieve a desired effect. This process can provide local or directed delivery, prolong drug effects, facilitate transport into target cells, locate a tumour or area of infection, provide feedback regarding efficacy or drug delivery, or reduce blood flow shear effects.

Advantages

Due to their small size, nanomaterials have a high specific surface area in relation to the volume. Consequently, the particle surface energy is increased, making the nanomaterials much more reactive. Nanomaterials have a tendency to adsorb biomolecules, e.g., proteins, lipids, among others, when in contact with the biological fluids.

Its composition is dependent on the portal of entry into the body and on the particular fluid that the nanoparticles come across with (e.g., blood, lung fluid, gastro-intestinal fluid, etc.). Additional dynamic changes can influence the “corona” constitution as the nanoparticle crosses from one biological compartment to another one.

Applications

Nanomaterials can be applied in nanomedicine for medical purposes in three different areas: diagnosis (nanodiagnosis), controlled drug delivery (nanotherapy), and regenerative medicine.

Nanomedicine is holding promising changes in clinical practice by the introduction of novel medicines for both diagnosis and treatment, having enabled to address unmet medical needs, by

· Integrating effective molecules that otherwise could not be used because of their high toxicity (e.g., Mepact)

· Exploiting multiple mechanisms of action (e.g., Nanomag, multifunctional gels)

· Maximizing efficacy (e.g., by increasing bioavailability) and reducing dose and toxicity

· Providing drug targeting, controlled and site specific release, favoring a preferential distribution within the body (e.g., in areas with cancer lesions) and improved transport across biological barriers.

Challenges for Nanomedicine

Despite the benefits that nanomedicine has to offer, much research is still required to evaluate the safety and toxicity associated with many NPs.

Studies are also needed to assess the immunogenicity of NPs

The most frequently reported side effect after injection of a Nano therapeutic agent seems to be a hypersensitivity reaction, which may be caused by activation of the immune complement system.

Research to evaluate the size and surface properties of NPs may also help to identify the critical dimensions at which they tend to significantly accumulate in the body. The possible tissue accumulation, storage, and slow clearance of these potentially free radical–producing particles, as well as the prevalence of numerous phagocytes in the RES, may make organs such as the liver and spleen the main targets of oxidative stress.

Even though Nanomedicines potentially offers a means of earlier diagnosis; more effective, safer, and personalized treatments; as well as reduced health care costs, for significant progress to be made toward this goal, much more work is needed to establish testing.