## 5 Additives in Melt Electrospinning
### Pharmaceutical Additives
Thus, PCL melt electrospun scaffolds become good candidates for long-term drug delivery systems for tumour therapy. Among bioactive molecules, antibiotics have also been evaluated in melt electrospun scaffolds. Fabrication of nanocomposite blends based on PCL, with different content of PEG and loaded with ciprofloxacin was performed for wound dressing applications [116]. These fiber mats were successfully fabricated by direct-writing melt electrospinningning (Figure 8). PEG properties are excellent for biological applications; hence it is suitable for different functions other than plasticizing. Opposite to PCL, PEG is highly hydrophilic, which enhanced the hydrophilic properties of the fiber mat. It also changed the release mechanism of the drug, making drug diffusion from the mat the main factor in the release. Moreover, release behaviour was observed to change according to the different geometric structures that were tested with the same composition. This means that, as mentioned above, the drug dissolution and release depend on several parameters, including the geometry of the final product and the hydrophilicity, and so this behaviour could be controlled by modifying these two. Triclosan (TCS) is a synthetic antimicrobial agent that has been largely employed in health and personal care products including deodorants, soaps, toothpaste, mouthwash, and preparations for skin protection [117; 118]. TCS has also been loaded in melt electrospun scaffolds of nanocomposite blends composed of PLA, starch, PCL and nanohydroxyapatite (nHAp) [82] taking into consideration previous works concerning the optimization of processing parameters [119; 120; 121]. Very abundant in nature, starch is a biodegradable material with high water absorption and weak mechanical properties. In blends, it enhances PLA hydrophilicity [122] and prolongs PCL biodegradation rate [108]. Nanohydroxyapatite (nHAp) is a calcium phosphate similar to natural bone [123] with bioactive properties that is used as bone substitutes and coating for implants because of its osteoconductivity and strong bonding with bone tissue both in vitro [124] and in vivo [125]. Compared to micron-sized ceramics, nHAp shows a greater protein adsorption and osteoblast adhesion [126; 127]. nHAp is also a brittle material. This property might limit its applications although its incorporation in polymer matrices could overcome this hindrance. The function of nHAp in this study was to eliminate the adverse effects of triclosan through its encapsulation and increasing the cell attachment. The resulting nanocomposite blend shows improved properties (hydrolytic degradation, hydrophilicity, antibacterial activity, and drug release) with the addition of 3% nHAp with respect to their previous works. Therefore, this could have potential applications in the medical field both in hard and soft tissue [81]. Triclosan was also used in another drug-delivery system developed by [PERSON] et al. [128]. The antibiotic was loaded in PLA nanoparticles that were in turn added to a PCL matrix to obtain a bionanocomposite that provides a slow and controlled release of the drug. PLA could efficiently encapsulate triclosan particles, burst release was diminished, and the antibacterial property of the sample was extended to up to two years by virtue of the polymer's higher glass transition temperature and more rigidity compared to PCL. A good dispersion of the nanoparticles was also achieved in the PCL matrix by setting the melt mixing temperature below than the melting point of the nanoparticles and fiberswith a diameter between 40-60 \(\upmu\)m were obtained, making them a good candidate for soft connective tissue engineering and long-term drug delivery. Antimicrobial drugs have not only been studied in polyesters. Recently, there has been an increasing interest in polyolefin fibrous membranes containing antibacterial agents for their high efficiency in air and water filtration. Polyolefins are hydrophobic polymers that can be colonized by harmful bacteria [129; 130; 131]. [PERSON], et al.