# Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone
## 2 Electrospraying Technology
### Experimental Apparatus
have used this nozzle to fabricate QD605/Cy5-G3139-loaded lipoplexes with high compatibility, high encapsulation efficiency, highly uniform and fine size [90]. Besides, in order to improve the throughputs and productivity of electrospraying, some special nozzles (Figure 2f,g) are also used in electrospraying to achieve the stable multi-jet [65; 91]. Using grooved inner nozzle can not only strengthen the electric field at the groove but also promote the formation of Taylor cone at each groove. Therefore, the stable multi-jet that ensures the desired size and uniform dispersion of electrospray particles can be successfully achieved, and the throughputs, as well as the productivity of electrospraying, also enhance significantly. Meanwhile, the interactions between inner and outer liquids and its interference in the formation of cone-jet can be optimized and minimized when the inner capillary is extended some distance out from the outer capillary. Similar results are also obtained using multiplexed electrospray device with several electrospraying sources operating in parallel and an extractor. The extractor not only minimizes interference between sources but also localizes the electric field. A grounded metal plate (usually an aluminum foil) is mainly used to collect electrospraying particles, and sometimes a glass slide is also placed on the metal plate. Although these collection methods are convenient and straightforward, there are still some drawbacks. For example, the solvent with a high boiling point is challenging to be removed out when droplets reach the surface of the collector. These particles with residual solvents trace tend to aggregate together to form large droplets. Meanwhile, the collection efficiency of metal plate or glass slide is relatively low due to the airflow and long flight distance. The majority of the electrosprayed particles is carried away by the airflow and cannot reach the surface of the collector, then finally deposited on the other place of working cupboard. In order to prevent the aggregation among electrosprayed particles and improve the collection efficiency, a grounded bath containing liquid media (Figure 2i) and an enclosed chamber with air/nitrogen flow and filters (Figure 2h) are applied to collect electrosprayed particles. The selection of collection liquid media mainly depends on its chemical interactions with the particles (including core and shell material), compatibility to solvent systems in electrospraying solution, and surface tension [95]. Thus, this system requires a poor chemical affinity between the liquid media to the polymeric shell and core substance, to achieve complete entrapment of it under microsphere or microcapsule form. The compatibility between collection media and solvent system in electrospraying solutions need to be higher than that between polymeric matrix and solvent system. The residual solvent in particles diffuses into collection media and is effectively removed from particles due to the existence of a concentration gradient. The aggregation of electrosprayed particles can be further prevented with the use of a low surface tension collection solution. The main disadvantages of this collection method are that (1) the drug or active substance absorbed on the surface of particles may diffuse into the collection media, and (2) these collected particles tend to form a film at the surface, which hampers their further dispersion. In addition, some researchers also put some aqueous solution containing a polyelectrolyte into the bath [96; 97]. The use of air/nitrogen flow with vacuum aspiration as well as filters in a chamber allows to increase the collection yield and to obtain particles with a smooth surface state and low mean diameter, due to sufficient evaporation time of solvent [94]. In some cases, ring-shaped grounded copper wire was also applied to collect the electrosprayed particles, having a uniform size and a smooth surface. This method has a higher collection efficiency compared with other collection methods [98].