Nanoparticles (NPs) come in many different varieties: Gold NPs, Liposomes, Polymeric NPs, dendrimers, and Micelles to name a few. The differences between these microscopic particles lie in the materials used to make them.

Polymeric nanoparticles are made of natural or synthetic polymers – repeating units of covalently attached small molecules (monomers) – that are often hydrophobic in character and necessarily biocompatible. Synthetic polymers, PLGA, PLA, and PGA, are commonly used in drug delivery due to their special characteristics.

Due to their unique degradation profiles, these materials, when used in drug delivery, allow small molecule medicines to be gradually released into the bloodstream over periods of weeks, months or years. The ability to continually release medication into the bloodstream for weeks or months on end eliminates the need to constantly take pills or endure daily injection in order to deliver therapy. Polymers breakdown in one of two ways – Bulk degradation –   whereby the entire polymer diminishes over time or – Surface erosion – in which the surface of the polymer is gradually eroded to release the encapsulated medicines.

Polymeric NPs are made using oil and water emulsion techniques, similar to the one pictured below. Polymers are dissolved in organic solvents and combined with a drug and other chemicals in water such that the hydrophobicity of the polymer and drug together cause the formation of spheres of drug encapsulated by polymer. The shape of a polymeric NP is directly influenced by the way in which it is made. More interesting shapes, like rods, cubes or discs, can be made using microfluidic techniques.

Once a polymeric NP is made, its surface can be modified to increase its survivability in the bloodstream. Surface charge and PEGylation (addition of Polyethylene glycol to the NP surface) can make the NP last longer in circulation. PEG specifically makes NPs more water-soluble, more stable, and less susceptible to attack by immune cells or clearance by the liver or kidney.

Polymeric nanoparticles are fast becoming the standard for drug delivery systems throughout the world due to their ability to deliver medication over long periods of time and to stay in circulation by evading capture or excretion. The next step in improving their effectiveness would be to increase their ability to target diseased tissue. Attempts to do this have been made many times over the past decade, mainly by attaching specific antibodies to NP surfaces so that they will bind to specific epitopes characteristic of diseased tissue. This approach, however, has not produced significant increases in targeting specificity and as such is an area of NP drug delivery in need of further improvement and study.