## 3 Results and Discussions
### Significance of Factors
During the electrospraying process, the polymeric solution ejected from the nozzle was stretched and broken into tiny droplets by the electrical fields. With a shorter distance, the electrical force applied to the droplets is higher. It is thus easier for the droplets to break into tiny particles. The empirical data in Figure 3 (factor level A1) suggested that one should use the lowest PLGA concentration (3%) to spray microspheres of smallest diameters. This is due to the fact that to produce smaller droplets and uniform microparticles and, it is necessary to limit chain entanglements [20; 21]. During the electrospraying process, solvent evaporation and polymer chain diffusion occur during the travel of solution droplets to the collector, and chain entanglement is responsible for the final morphology of particles [22]. It has been reported that, to prepare particles by electrospraying technique, the best polymeric solution is a semi-dilute moderately entangled regime, which takes place at the critical entanglement concentration (Ce) [23]. This stage is the crossover point from \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Factor** & **Degree of Freedom** & **Sum of Squares** & **Mean Square** & **F** \\ \hline A-Polymer concentration (\%) & 2 & 8.08 & 4.04 & 1.62 \\ B-Flow rate (mL/h) & 2 & 13.75 & 6.87 & 2.76 \\ C-Travel distance (cm) & 2 & 12.24 & 6.12 & 2.46 \\ D-Voltage (kV) & 2 & 7.43 & 3.71 & 1.49 \\ E-Needle size (mm) & 2 & 10.48 & 5.24 & 2.10 \\ F-Solvent type & 2 & 244.07 & 122.03 & 49.02 \\ Error & 36 & 89.61 & 2.48 & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Standard analysis of variance (ANOVA) table for the size distribution of electrosprayed particles. the semi-dilute unentangled regime to the semi-dilute moderately entangled regime. Within this range, there is enough entanglement, and dense, solid, and reproducible particles can be prepared. [PERSON] et al. [24] studied the effect of solution on the morphology and size of electrospray PLGA particles, and proposed that polymeric concentration of 2-4 wt. % falls into the range of a semi-dilute, moderately entangled regime and chain entanglement can easily occur for the electrospray of microparticles. Nevertheless, as the concentration increased to 6-8%, the semi-dilute highly entangled regime was formed and a variety of tailed particles and fibers started to appear along with the particles. The optimum PLGA concentration obtained in this study was 3%, which matches well with the results of the literature [24]. A polymeric concentration that is too high in the solution leads to major chain entanglements in the polymeric materials. The solution thus possesses higher strengths to resist the electric field from breaking into tiny drops. Electrosprayed microspheres thus possess a greater size distribution, and may sometime exhibit tailed geometries. Finally, despite the applied voltage required component in achieving sustainable solution-jet mode during electrospraying, it showed a relatively insignificant influence on the particle size distribution of electrosprayed PLGA microspheres, as suggested by the result in Table 4.  
This study has successfully employed the Taguchi experimental design to minimize the particle size of electrosprayed PLGA microspheres. The same scheme can also be applied to optimize the electrospraying of other materials. Furthermore, if a specific desired particle size is desired, the \"nominal-the-best\" formulation [17] can also be adopted to optimize the desired size distribution easily. This further demonstrates the feasibility of the experimental design in manufacturing microspheres for various applications.