Electrospraying Technique

Nowadays there are numerous techniques to produce special polymers (large chain-like molecules made of small molecules known as monomers) with different properties, suitable for many applications. One of those techniques that has emerged as a promising method of synthesis and encapsulation is electrospraying. This technique allows to obtain small particles (micro or nano size) that are useful in many applications such as drug delivery, flavor or repellent encapsulation, tissue engineering, composites, etc.

The Electrospraying technique is basically a synthesis method which consists in the atomization of a polymer solution passing through a capillary by means of the application of high voltage. This method can be used for obtaining polymeric particles derived from the corresponding solution. The process begins at the tip of the capillary, where a droplet of the polymer solution is subjected to high voltage. The electric charges generate an electrostatic force inside the droplet, which is deformed into a cone (known as Taylor cone) from which smaller droplets will be ejected as soon as the surface tension is overcome. These droplets are accelerated toward the grounded collector, and the solvent is simultaneously evaporated through the process.

Some advantages of the electrospraying technique are attributed to:

• The versatility that this technique has, which allows to work with many solvents, drugs, polymers, monomers, etc.
• The droplet size is smaller than that obtained with other conventional techniques e.g., mechanical atomizers.
• The size distribution of the droplets is usually narrow, with small standard deviation that allows to produce particles of uniform size.
• The motion of charged droplets can be easily controlled by varying electric fields and/or the flow rate.

The morphological characteristics of the particles are affected by different parameters. Some of them are listed below:

• Process conditions (electrical conductivity, flow rate, voltage): generally, an increment in electrical conductivity or in higher applied voltage results in smaller particles. In addition, the flow rate should be low enough to allow complete solvent evaporation.
• Solution properties (viscosity, polymer concentration, polymer-drug rate, drug characteristics, etc.): solution viscosity should be sufficiently low to allow for the formation of droplets. A high polymer concentration conduces to the formation of fibers instead of particles.
• Equipment (capillary diameter, capillary-collector distance): smaller capillary diameter produces smaller particles. Also, a shorter distance between capillary-collector generates a higher electrical field that produces smaller particles.

The applications of the Electrospraying technique, as mentioned before, covers many fields. For example, Perez-Masía et al. have used this technique to encapsulate folic acid with high efficiency  ; Wulong Li et al. obtained microspheres to produce superhydrophobic coatings on textiles via electrospraying  ; Faridi and Jafari showed that encapsulation by electrospraying is an effective technique for the protection and delivery of phenolic compounds .

In conclusion, the Electrospraying technique is a simple, versatile, useful, economic and scale-up method to obtained micro or nano particles that could be used in important fields such as medicine, pharmacology, food industry, agro-industry among others.