About the Nanoprecipitation Method of Preparation of Nanoparticles

It's no news that owing to their phenomenally small size and other impressive qualities, nanoparticles have found applications in a wide variety of domains including biotechnology, photonics and electronics. In fact, these nanoparticles are changing the way we lead our everyday lives even as we speak and discuss their preparation!

The preparation of nanoparticles can be done in several different ways. Here in this article, we'll focus specifically on the nanoprecipitation method of preparation of nanoparticles.

Preparation of nanoparticles using the nanoprecipitation method

Also commonly referred to as the solvent displacement method, the nanoprecipitation method of preparation of nanoparticles was developed around late 1980s by Fessi et al (Fessi H, Benita S, Devissaguet JP, Ammoury N and Puisieux F).

This is by far the most economical and easiest reproducible routes for production of nanospheres or nanoparticles using the preformed polymers in place of monomers. Quite similar to the spontaneous emulsification method, the nanoprecipitation method has its basis in a polymer's interfacial deposition post the displacement of a semi-polar solvent that's mixable in water, from a lipophilic solution.

Ingredients required in the nanoprecipitation method of preparation of nanoparticles

The process requires three different ingredients for its successful completion:

The polymer - The used polymer for this process can be natural, semisynthetic or synthetic.

The polymer solvent - The most commonly used polymer solvents are dioxane, hexane, ethanol, methylene chloride or acetone. The selection of the exact polymer solvent to be used for the process is determined by two different factors:

• Easy removal through evaporation and
• High solubility in water

Acetone is the most preferred choice considering these conditions, however, a binary blend of acetone with small quantity of water, or an ethanol/methanol and acetone blend can even be employed.

A non-solvent of the polymer - Coming to the non-solvent phase, it's composed of either one or a mixture of different polymer non-solvents, followed by the eventual addition of surfactants.

The generation or preparation of nanoparticles happens through the rapid diffusion of the polymer solvent inside the non-solvent through constant mixing of the polymer with the non-solvent phase. The process leads to a reduction in the interfacial tension between two phases, resulting in an increase in the surface area, apart from instant precipitation of the polymeric nanoparticles.

The addition of lipophilic polymer solution to the non-polymer solvent is done rather slowly, however, nanoparticles can be produced even in the reverse order.

This method of preparation of nanoparticles provides a more narrower and well-defined distribution of the sizes of the nanoparticles, falling in the range of 75 to 900 nm, when compared to the nanoparticles prepared through the emulsification solvent evaporation method.

There are several parameters that can condition the eventual properties of these nanoparticles, for instance, agitation while adding the polymer solution, the speed of the organic phase injection, the kind of polymer and solvent interactions and the mixing ability of the polymer solvent in the non-solvent phase.

The process is also influenced by the exact concentration and type of the added surfactants because the surface active agents play a key role in stabilising the nanoparticles that are prevented from aggregation. This is highly useful in situations where you need to store the suspensions for longer time periods.

The nanoprecipitation method of preparation of nanoparticles can be performed using various formulations, including several polymers like poly(hydroxyl butyrate), poly(e-caprolactone), poly(lactide-co-glycolide), poly lactide or even peptides. What more, the process can even be applied to the non-polymeric compounds like cyclodextrin and drug.

The widespread use of the nanoprecipitation method for producing non-polymeric or polymeric nanoparticles (nanospheres) is primarily because of its reproducibility, quickness and simplicity, despite the fact that the nanoparticles' yield is limited by the requirement of low polymer concentration.