## 6 Mechanical Properties of Electrospun PCL and Its Composites  
The intrinsic mechanical properties of synthetic PCL thermoplastic can be improved by the incorporation of foreign nanoparticles to form the PCL/fiber composites that can be utilized in various applications of biomedical practices. In addition, the preparation of PCL/fiber composites by electrospinning technique provides an added enhancement on the ultimate mechanical properties due to its facile preparatory set-up and the formation of well-dispersed nanofibers with uniform average diameter throughout the PCL matrix. Electrospun PCL/filler composites have shown exclusive improvement in various mechanical properties, namely: flexural strain, tensile strain, tensile stress, Young's modulus and thermomechanical strength [56; 58; 70; 79]. These mechanical properties are closely associated with the biomedical treatments, particularly in the implantation of artificial bone and muscle tissues regeneration, on the account that the stiffness of the electrospun PCL/fiber composites is relatively appropriate for in-vivo applications [72]. Different fillers of disparate properties can be treated, prior to incorporation into the synthetic PCL matrix in order to obtain the resultant PCL/filler composites with outstanding mechanical properties in which the horizon of applicability of PCL composites is vastly widened [57; 82]. In addition, the blending of PCL with other synthetic polymers with different properties for the preparation of polymer blends, after which the fabricated fillers can be introduced to the blends to afford PCL/blends composites with tremendous enhancement of the mechanical properties [79; 83; 84]. Table 4 summarizes the different solvent systems for electrospinning of PCL/filler nanocomposites and their mechanical properties [84; 85; 86; 87; 82; 88; 89; 27; 56; 52; 57; 58; 59; 62; 27; 55; 56; 58; 63; 64; 67; 72; 80; 82; 84; 85; 86; 87; 88; 89]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Solvent System** & **PCI/Filler Nanocomposites** & **Mechanical Properties and Observations** & **Refs.** \\ \hline \hline \multirow{6}{*}{Dimethylformamide/chloroform} & & Ultimate tensile strength and Young’s modulus show the \\  & & increasing trend with the increase in the chitosan \\  & & nanofibrils content to the highest values of 32.9 MPa \(\pm\) 4.4 \\  & & and 6.03 MPa \(\pm\) 0.65 at 10\(\%\), respectively. The increase in \\ \cline{1-1}  & & Young’s modulus is due to the interaction between the \\ \cline{1-1}  & & inter-molecular chains of CN and PCL. Elongation at break \\ \cline{1-1}  & & presented a general decrease with the incorporation of \\ \cline{1-1}  & & chiasm nanofluids reaching the minimal value of 44 MPa \\ \cline{1-1}  & & \(\pm\) 15 at 7.5\(\%\). This observable decrease is explained by the \\ \cline{1-1}  & & stiffening effect arising from the intrinsic structure of CN. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Different solvent systems, mechanical properties of the electrospun PCL/fiber composites. Figure 5: The effect of applied voltage on the control of the gene immobilization efficiency for electrospun PCL/alginate scaffolds [74]. Coyrights Elsevier. _Appl. Sci._**2019**, \(9\), 2205  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Solvent System** & \begin{tabular}{c} **PCL/Filler** \\ **Nanocomposites** \\ \end{tabular}  & \multicolumn{1}{c}{**Mechanical Properties and Observations**} & **Refs. ** \\ \hline Acetic acid & PCL/Cellulose & \
\begin{tabular}{c} The Young’s modulus increased significantly from 23 MPa \\ \(\pm\) 3.9 to 43 \(\pm\) 2.3 MPa pristine PCL to 1\% of cellulose \\ nanocrystals (CNCs) but decreased to 39.0 \(\pm\) 5.9, 39.6 \(\pm\) 1 \\ and 27.8 \(\pm\) 3.9 for 1.5\%, 2.5 and 4\% contents, respectively. \\ This is due to the agglomeration of the CNCs at higher \\ contents within the PCL nanofiber creating the stress \\ abetting areas.