# Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone
## 1 Introduction  
Polycaprolactone (PCL), a semi-crystalline polyester, is prepared from ring-opening polymerization of \(\varepsilon\)-caprolactone monomer under the catalysis of metal anion complex catalyst [1]. Due to its relatively low melting temperature (Tm = 60 \({}^{\circ}\)C) and glass transition temperature (Tg = \(-\)60 \({}^{\circ}\)C), PCL has excellent viscoelastic properties and processability [2; 3]. Moreover, PCL is regarded as a green environmental and non-toxic polymer material due to its prominent biocompatibility and biodegradation. Thus, PCL is widely used in medical tissue engineering, drug delivery, and control release systems, food packaging industry, antibacterial study, protective clothing fabrication, and biosensors [4; 5; 6; 7; 8; 9]. Particularly, micro- or nanoscale PCL particles with a wide specific surface area, a small pore size, high encapsulation efficiency, and a high porosity are considered to be the main candidates in these fields [10; 11]. For instance, the release profiles of active drug encapsulated in polymer microspheres are controlled by the size, distribution, and porous structure of microcapsules [12; 13; 14; 15; 16]. Meanwhile, the drug-loaded nanoparticles with small size and narrow distribution have an enhanced ability to reach their target [17]. The degradation process of these particles with a huge surface to volume ratio also occurs at a relatively faster rate [18; 19]. Apart from the chemical and physical nature of particles, the properties and applications of polymeric particles are mainly determined by their structure and morphology. However, the perfect design as well as control of the structure and morphology of PCL particles and achieving their high encapsulation efficiency according to requirements during their preparation process is still a hot spot and difficult for scientificresearchers. In literature, various techniques are reported for the fabrication of micro- or nanoscale PCL particles or capsules with versatile structure and morphology. Conventional methods include emulsification, spray drying, enhanced solution dispersion, phase separation, solvent evaporation, and hot melt techniques [20; 21; 22; 23; 24; 25]. Although PCL particles with micro- or nanoscale structure and specific morphology can be obtained successfully via these methods, there are still some limitations and drawbacks, including the use and removal of surfactant, complexity of the process, low encapsulation efficiency, time-consuming, wide particle size distribution, particles agglomeration, use and removal organic solvent and the degradation of protein [26; 27; 28]. Therefore, the applications and developments of these methods in the biomedical field are inefficient and limited. Electrospraying, a rapidly emerging electrohydrodynamic atomization process, has great potential to overcome these above limitations and drawbacks [29]. In the process of electrospraying, the polymeric solution is polarized firstly due to the applied electric field and then charged droplets is stretched and accelerated into the charged jet by the electrostatic force generated on the surface of droplets. Next, charged jet breakups into smaller charged droplets via Coulomb repulsion forces. After evaporation of the solvent, micro- or nanoscale particles are collected [30]. On the one hand, its experimental device is operational and straightforward steps are easy to carry out. It can avoid the operation of vigorous stirring, the use of chemical additives (i.e., surfactant, electrolyte and catalyst) as well as large quantities of organic solvents. Therefore, the activity and structure of active substance will not be destroyed during the process of electrospray [31]. At the same time, electrospraying carries out under room temperature and atmospheric pressure, and there is no further drying step required since the solidification of particles occurs instantaneously during electrospraying process.