# Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone
## 1 Introduction
Secondly, the size, size distribution, and morphology of electrosprayed particles are also determined by these solution properties and operating parameters. For instance, increasing electrical conductivity of electrospraying solution or applied voltage not only decrease particles size significantly but also broaden the particle size distribution [44]. The entanglement among polymeric chains and the solution viscosity determine the final morphology of electrospraying object, i.e., fibers or spheres. In general, electrolytically sprayed microspheres are manufactured with a low viscosity and a lower polymer chain entanglement, unlike electrospun fibers, which require the use of a solution with a higher viscosity and a higher entanglement amount [45; 46]. Besides, the phase separations and the solidification processes of electrosprayed droplets play a primary role in the shape on the morphology of the obtained particles. They are also affected by the physico-chemical properties of electrospraying solution and more especially the system solvent choice used to solubilize the polymer [47; 48]. For example, the non-porous and filled PCL particles change into cup-shaped porous particles when acetone is added into the PCL/chloroform electrospraying solution [49]. Meanwhile, the electrosprayed particles with porous structure are easily obtained when the binary solvent system is used. The different evaporation rates, as well as compatibility among non-solvent, solvent and polymeric matrix, lead to the phase separation and result in the synthesis of highly porous particles [50]. Furthermore, the formation of a core-shell structure for PCL capsules and the encapsulation efficiency of active substance are also closely related to the selection of solvents systems [38]. According to these above mentioned, investigating these effects coming from different solvent systems and selecting a desirable solvent system for electrospraying are crucial for designing and obtaining an ideal structure as well as the morphology of electrosprayed PCL particles. However, the understanding of the effect of selecting solvent systems on electrospraying is still limited even though it is widely used to prepare polymeric particles. The selection of a suitable solvent system used in the electrospraying process according to the required structure, properties, and applications of final particles is still unclear. This paper aims to present a comprehensive review of the current state of the art in preparing micro- or nanoscale PCL particles via electrospraying technology. PCL was selected as a suitable polymeric system due to its biocompatibility, biodegradability, and non-toxicity, and can be considered as one of the main candidates in drug control release and delivery, tissue engineering, and food packaging. Furthermore, the study and the use of the kind of polymer also meet the requirements for green, non-toxic and environmentally friendly production processes as well as technology development. Taking into account its thermal properties, such as its low glass transition and melting temperatures, its solubility characteristics, the design of the microencapsulation process can be optimized. Therefore, the review focuses on the use of different solvent systems and describes the effects of varying solution properties and the operating parameters in electrospraying process, on the formation of Taylor cone and the final structure as well as the morphology. Meanwhile, some relationships among the operating parameters, the formation of cone jetting and final structure as well as the morphology of electrospray particles are also summarized. Finally, this review provides detailed guidance about the selection of a suitable solvent system concerning the desired morphology and structure of PCL particles and their applications in some fields.