## 5 Additives in Melt Electrospinning
### Pharmaceutical Additives
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Polymer** & **Additive** & **Effects in the Process \({}^{*}\)** & \begin{tabular}{c} **Fibers** \\ **Diameter** \\ \end{tabular} & **Ref.** \\ \hline \multirow{7}{*}{PP} & Sodium oleate (7 wt.\%) & \(\uparrow\) electrical conductivity, & \multirow{2}{*}{371 nm} & [43] \\  & & \(\downarrow\) hydrophobicity & & \\ \cline{2-5}  & NaCl (5 wt.\%) & \(\uparrow\) electrical conductivity & 310 nm & [43] \\ \cline{2-5}  & Poly(ethylene glycol) (PEG) & \(\downarrow\) melt viscosity & & [66] \\ \cline{2-5}  & Poly(dimethyl siloxane) (PDMS) & \(\downarrow\) melt viscosity & & [66] \\ \cline{2-5}  & Calcium stearate (5 wt.\%), Zinc stearate (5 wt.\%), & \(\downarrow\) melt viscosity, & \multirow{2}{*}{1–5 \(\upmu\)m} & [67] \\  & Magnesium stearate (5 wt.\%) & \(\uparrow\) electrical conductivity & & \\ \cline{2-5}  & Sodium stearate (5 wt.\%) & \(\downarrow\) melt viscosity & 1.3 \(\upmu\)m & [67] \\ \cline{2-5}  & Sodium stearate, Stearic acid & Plasticizer & & [69] \\ \cline{2-5}  & IrgastaR(r) P16 (6 wt.\%), Sodium stearate (2 wt.\%) & \begin{tabular}{c} Antistiate (insulator character), \\ \(\uparrow\) electrical conductivity \\ \end{tabular} & 210 nm & [40; 68] \\ \cline{2-5}  & \(\beta\)-Nucleating agent (La\({}^{+3}\) and Ca\({}^{+2}\)) crystallization in & \(\downarrow\) shear stress, \(\uparrow\) tensile strength, \(\beta\) form & \(\uparrow\) toughness, \(\uparrow\) fluidity & \(<\)5 \(\upmu\)m & [66] \\ \hline PMMA & Di-2-ethylhexyl terephthalate (DOTP) (40 wt.\%) & \begin{tabular}{c} Plasticizer, \(\downarrow\) melt viscosity \\ (facilitate the jet formation) \\ \end{tabular} & 4 \(\upmu\)m & [38] \\ \hline PA6 & Sodium stearate, sodium oleate, sodium myristate & \(\downarrow\) melt viscosity, & \multirow{2}{*}{\(<\)1.5 \(\upmu\)m} & [76] \\  & (10 wt.\%) & \(\uparrow\) electrical conductivity & & \\ \hline \multirow{7}{*}{PCL} & NaCl (8 wt.\%) & \(\downarrow\) melt viscosity, & \multirow{2}{*}{\(\sim\)3 \(\upmu\)m} & [80] \\  & NaCl (25 wt.\%) & \(\downarrow\) melt viscosity, & & \\ \cline{2-5}  & NaCl (25 wt.\%) & \(\downarrow\) electrical conductivity & & \\ \hline \multirow{7}{*}{PLA} & Sodium stearate (2–4 wt.\%) & \(\downarrow\) melt viscosity & 16–20 \(\upmu\)m & [82] \\ \cline{2-5}  & Polyethylene succinate (PES) & Plasticizer, \(\downarrow\) melt viscosity & & [82] \\ \cline{2-5}  & Haematoxylin (2 wt.\%) & \
\begin{tabular}{c} Plasticizer, \(\uparrow\) polymer degradation, \\ \(\downarrow\) electrical resistance \\ \end{tabular} & 16.04 \(\upmu\)m & [83] \\ \cline{2-5}  & Acetyl tributyl citrate (ATBC) &
\begin{tabular}{c} Plasticizer, \(\downarrow\) melt viscosity \\ (6 wt.\%) \\ \end{tabular} & \(<\)236 nm & [85] \\ \hline \hline \end{tabular}  
* The arrows \(\uparrow\) and \(\downarrow\) indicate increase and decrease, respectively.  
\end{table} 
Table 1: Salt, viscosity modifiers, stabilizers and dyes as additives in melt electrospinning. to its superhydrophobicity [112]. [PERSON] and [PERSON] [90] compared the behavior of solution and melt electrospun scaffolds loaded with curcumin, an anticancer agent, which was selected due to its green fluorescence [113] that facilitates observation of its dispersion inside the matrix, and for its high thermal stability [114]. Different concentrations were tested and, whilst it did not affect the morphology of melt electrospun fibers, the drug load was limited in solution electrospinningning. Another advantage of the melt electrospun fibers was the lack of a burst release and the low drug release rate. [PERSON] and [PERSON] created a PCL membrane for localized tumour therapy [115], in this case, daunorubicin hydrochloride was selected as the therapeutic agent. Again, different drug concentrations were tested, although some aggregation occurred with increasing drug contents, fiber diameters barely fluctuated and smooth surfaces were always observed. No burst release was detected and the release rate of the drug was again slow.