# Electrospinning of Essential Oils
## 3 Electrospun Fibres Containing EOs and Their Applications
### Oregono Essential Oil  
Recent studies have reported on electrospun fibres containing oregano essential oils, extracted from _Origanum vulgare_[45; 46; 47] and _Origanum minutiforum_[48], which are plants belonging to the _Lamiaceae_family and predominantly distributed in the Mediterranean, Euro-Siberian and Iran-Siberian areas. The major constituents of oregano EO are carvacrol and thymol, which have inhibitory effect on diverse microorganisms, including Methicillin-resistant _S. aureus_ (MRSA), _E. coli_, _Bacillus subtilis_ (_B. subtilis_), and _Saccharomyces cerevisiae_[79; 80; 81]. As other EOs, oregano EO acts on the bacteria cell membrane by disrupting its functions, inducing loss of cytosolic material and leakage of potassium ions, with eventual cell necrosis. Oregano EO has been proposed to inactivate biofilms, which are sessile colonies of bacterial cells strongly adherent to surfaces and poorly permeable to antibacterial agents and antibiotics [82]. Concentrations of this EO in the range of 0.3-1.0 mg/mL have been proved effective in completely eradicating 24-h old biofilms of _Acinetobacter baumannnii_, _Pseudomonas aeruginosa_ (_P. aeruginosa_) and MRSA within 1 h. Oregano EO permeated the biofilms and led to physical and morphological damages to the bacteria organisation. Oregano EO has been embedded in biodegradable fibres of chitosan and poly(caprolactone) (PCL) that have been electrospun from formic acid/acetic acid (1:1 volume ratio) solutions, using a voltage of 18 kV, a flow rate of 0.1 mL/h and a needle-collector distance of 15 cm [46]. The resulting mats (210-320 nm average fibre diameter), containing 1%, 3%, and 5% w/w of EO, induced a decrease of bacteria population in the range of 40-53% after 3 h of incubation. They were tested against four pathogens relevant to food packaging: _S. aureus_, _L. monocytogenes_, _E. coli_ and _Salmonella enteritidis_ (_S. enteritidis_). The release of the EO was investigated in-vitro in a buffer solution at 37 \({}^{\circ}\)C and pH 7.4. A burst release was recorded in the first 12 h, with values of \(\sim\)10% for the lowest EO concentration, and \(\sim\)32% for the highest concentration. This was attributed to oil present on the surface of the chitosan/PCL fibres. Then, the release gradually increased till reaching a plateau after 48 h, with values of 15-45% after 96 h, due to oil entrapped within the fibre volume. A similar biphasic release profile has been reported for poly (L-lactic acid-_co_-caprolactone)/silk fibroin (PLCL/SF) fibres that were electrospun from 1,1,1,3,3,3-hexafluoro-2-isopropanol (HFIP) solutions containing 2.5%, 5.0%, and 7.5% v/v of oregano EO [47]. The fibrous mats had an average fibre diameter of \(\sim\)500 nm obtained by electrospinning at a voltage of 12-15 kV, a flow rate of 1 mL/hour and a needle-collector distance of 12-14 cm. They showed an initial burst release in vitro in the first 3 h (77% oil released from fibres with 5% v/v EO) and a steady release after 48 h (89% oil released from fibres with 5% v/v EO). The antioxidant and antitumor activity of the encapsulated oregano EO was investigated, instead of the antibacterial properties. The electrospun samples with 5.0% and 7.5% v/v of oregano EO exhibited the ability of scavenging 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) free radicals in 30 min, with values (\(\sim\)90%) comparable to those of pure ascorbic acid (standard antioxidant agent) and higher than those of pure, non-encapsulated oregano EO (\(\sim\)65%). The excellent DPPH radical scavenging activity indicates that the high surface-to-volume ratio of the nanofibres facilitates the release of the antioxidant agent and enhances its therapeutic potential.