Physical, Thermal, and Antibacterial Effects of Active Essential Oils with Potential for Biomedical Applications Loaded onto Cellulose Acetate/Polycaprolactone Wet-Spun Microfibers

Abstract

New approaches to deal with the growing concern associated with antibiotic-resistant bacteria are emerging daily. Essential oils (EOs) are natural antimicrobial substances with great potential to mitigate this situation. However, their volatile nature, in their liquid-free form, has restricted their generalized application in biomedicine. Here, we propose the use of cellulose acetate (CA)/polycaprolactone (PCL) wet-spun fibers as potential delivery platforms of selected EOs to fight infections caused by Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Twenty EOs were selected and screened for their minimal inhibitory concentration (MIC), using the antibiotic ampicillin as positive control. The cinnamon leaf oil (CLO), cajeput oil (CJO), and the clove oil (CO) were the most effective EOs, against the Gram-positive (MIC < 22.38 mg/mL) and the Gram-negative (MIC < 11.19 mg/mL) bacteria. Uniform microfibers were successfully wet-spun from CA/PCL with an averaged diameter of 53.9 ± 4.5 µm, and then modified by immersion with CLO, CJO and CO at 2 × MIC value. EOs incorporation was confirmed by UV-visible spectroscopy, Fourier-transformed infrared spectroscopy, and thermal gravimetric analysis. However, while microfibers contained ampicillin at MIC (control) after the 72 h modification, the CLO, CO and CJO-loaded fibers registered ≈ 14%, 66%, and 76% of their MIC value, respectively. Data showed that even at small amounts the EO-modified microfibers were effective against the tested bacteria, both by killing bacteria more quickly or by disrupting more easily their cytoplasmic membrane than ampicillin. Considering the amount immobilized, CLO-modified fibers were deemed the most effective from the EOs group. These results indicate that CA/PCL microfibers loaded with EOs can be easily produced with increased antibacterial action, envisioning their use as scaffolding materials for the treatment of infections.

Eugenol-Containing Essential Oils Loaded onto Chitosan/Polyvinyl Alcohol Blended Films and Their Ability to Eradicate Staphylococcus aureus or Pseudomonas aeruginosa from Infected Microenvironments

“…Bacteria were supplied from American Type Culture Collection (ATCC), encompassing Gram-positive bacteria, S. aureus (ATCC 6538, grown in TSB/TSA) and Gram-negative bacteria, P. aeruginosa (ATCC 25853, grown in NB/NA). EOs were selected based on results obtained elsewhere by the team [ 20 , 28 ], apart from the minimum inhibitory concentration (MIC) value of CO while incubated with P. aeruginosa that was here determined. In brief, the MICs of the chosen EOs–CLO and CO–against S. aureus and P. aeruginosa were determined using the broth microdilution procedure described by Wiegand et al [ 50 ], which adapts the standard published by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) [ 51 ].…”

“…Essential oils (EOs), in particular, are aromatic, volatile, lipophilic biomolecules, extracted from different regions of plants, in which they work as secondary metabolites, defending the host from microbial invasion [ 17 , 20 , 27 ]. These complex mixtures contain hydrophobic molecules such as thymol, carvacrol, and eugenol (among others) that exhibit a broad spectrum of AM activity against bacteria, fungi, and viruses [ 20 , 28 ]. Eugenol, in particular, is an amphipathic hydroxyphenyl propene ( Figure 1 b), highly bactericidal towards S. aureus and P. aeruginosa [ 20 , 29 ].…”

“…CLO can be obtained through the bark and leaves of the cut trees of Cinnamomum zeylanicum [ 30 ], whereas CO can be obtained by distilling different parts of the plant, namely flowers, stems, and leaves of the clove tree ( Eugenia caryophyllus ) [ 31 ]. These EOs are increasingly studied for applications in the pharmaceutical and biomedical fields [ 19 , 20 , 28 , 32 ], due to their powerful antioxidant, anti-inflammatory, and AM properties [ 31 , 33 , 34 ], either encapsulated and/or incorporated in nanoparticles, hydrogels, films, or fibers to facilitate their delivery [ 19 , 28 , 35 , 36 , 37 , 38 ]. Both EOs show a promising inhibitory action on the growth of S. aureus and P. aeruginosa [ 19 , 20 , 39 , 40 ].…”

“…Both EOs show a promising inhibitory action on the growth of S. aureus and P. aeruginosa [ 19 , 20 , 39 , 40 ]. Still, their cytotoxicity at increased concentrations, their low resistance to degradation by external factors (e.g., temperature, light, moisture), and volatility in their free, liquid form hinder their expanded use [ 28 , 41 ].…”

“…Ergo, the main goal of the present study is to explore the potential of CS and EO’s synergistic effect over microbial growth inhibition within a matrix containing the flexible and hydrophilic PVA for prospective CW treatments. Recent studies have shown that the volatile nature of EO can be protected by combining it with polymeric matrices [ 28 ]. Yet, very few have explored CS/PVA blended films as EO delivery platforms and none, to the author’s knowledge, has used the proposed approach [ 48 , 49 ].…”