# Electrospinning of Essential Oils
## 3 Electrospun Fibres Containing EOs and Their Applications
### Peppermint Essential Oil  
_Mentha pipertia_ is a _Lamiaceae_ herb native of the Mediterranean region but cultivated worldwide for its uses in cookery and pharmaceutics [48]. Its essential oil, peppermint EO, is rich in menthol and menthone, and possesses antibacterial, antiviral, fungicidal and anti-inflammatory properties [48; 83; 84; 85]. The efficiency of peppermint EO against microorganisms has been evaluated in both liquid and vapour phase, concluding that the concentration of monoterenes in the oil vapours, such as \(\alpha\)-pinene, \(\beta\)-pinene, and limonene, plays a role in inhibiting bacteria growth by inducing extensive damages to the cell membrane [48]. Peppermint EO has been electrospun from PCL [49], cellulose acetate [44], gelatine [50], polyurethane [51], and PEO [52] matrices, and in combination with other bioactive compounds, such as chamomile EO [50], copper sulphate [51], and cerium oxide [52]. Gelatine fibres with an average diameter of \(\sim\)500 nm were electrospun from acetic acid/water solutions containing 0%, 3%, 6%, and 9% v/v of peppermint EO and 1:1 blends of peppermint and chamomile EOs [50]. The following experimental parameters were used: voltage of 15 kV, flow rate of 0.3 mL/hour and working distance of 10 cm. The fibres containing only peppermint EO (9% v/v) showed the highest inhibitory effect against _E. coli_ and _S. aureus_, whereas the addition of chamomile EO enhanced their antioxidant properties. Gelatine fibres with 9% v/v of peppermint EO exhibited a DPPH radical scavenging activity of 50%; while values higher than 60% were collected for fibres with 9% v/v of peppermint/chamomile  
Figure 2: (**a**) Schematic representation of the structure of a cyclodextrin molecule, with indication of the hydrophilic external surface and hydrophobic cavity. Adapted from Ref. [76]. (**b**) Illustration of the formation of cinnamon EO/\(\beta\)-CD proteoliposomes contained in poly(ethylene oxide) (PEO) nanofibers, and release of the essential oil (EO) when the fibres are in contact with _B. cereus_. Reproduced from Ref. [43] with permission from Elsevier. EOs (Figure 3a), due to the combined action of the two EOs (chamazulen and bisabolene are the main components of chamomile EO) [86]. In another study, the synergistic effect of peppermint EO and copper sulphate was investigated for wound healing applications [51]. Fibres of thermoplastic polyurethane (TPU, medical grade Tecoflex EG 80A) were electrospun from DMF solutions at 8:1 v/v ratio of TPU:peppermint EO, and 8.0:0.5:0.5 v/v ratio of TPU:peppermint EO:CuSO4, using a voltage of 11 kV, a flow rate of 0.3 mL/hour and a working distance of 20 cm. Fibres with peppermint EO were characterised by an average diameter of (99 7\(\pm\) 134) nm, while the presence of copper sulphate reduced the size of the fibres to (359 \(\pm\) 166) nm, possibly due to changes of the electrical conductivity of the polymer solution. Blood coagulation assays were conducted with thromboplastin and prothrombin to assess the anti-coagulant properties of the fibres. The release of the EO determined a 1.2-fold increase of the time needed for blood clot formation, and reduced toxicity toward red blood cells, while no significant effect was reported for copper sulphate. On the other hand, the combined action of peppermint EO and CuSO4 increased the viability of Human Dermal Fibroblasts (HDFs), giving cell viability of 144%, compared with 133% and 130% for TPU/peppermint EO and TPU fibres, respectively. The high cytocompatibility was attributed to the small diameter and low hydrophobicity (water contact angle of 82\({}^{\circ}\)) of the composite fibres that promoted cell proliferation, while the phenolic components of peppermint EO protected HDFs against oxidative stresses. Nowadays, electrospinning is regarded as a key technology for the production of biomimetic membranes for tissue engineering and particularly for the treatment of skin wounds [87].