INTRODUCTION: Wound complications, including surgical site infections, are among the most common issues in spine surgery (wound infection follows >10% of spine surgeries), causing patient discomfort, need for prolonged antibiotic treatment, hospitalization, and frequent readmission[1,2]. Percutaneous implants and prolonged wear of orthotic devices (i.e. corsets) can also cause wounds formation. To promote their healing, dressings are needed, capable of absorbing the exudate and promoting tissue regeneration. Electrospun patches have shown promising in addressing these needs and can adapt to complex shapes, so they can be easily coupled with prostheses/orthoses[3,4]. However, prevention of infection remains unmet and the applicability of antibiotics-based strategies is limited, as it favors the raise of bacterial resistance.
Here, we propose new antimicrobial electrospun dressings, based on essential oils, natural compounds showing broad spectrum antibacterial efficacy and high biocompatibility. We start from the encapsulation of tea tree oil (TTO) in poly(ethylene oxide), PEO, for immediate and burst release (post-surgical patch), and in polycaprolactone, PCL, to achieve a longer release profile and stability (for prolonged use in transcutaneous implants and orthoses). After optimization of the electrospun patch characteristics, we explore a library of antimicrobial oils (i.e., thymol, carvacrol, lavender and citronella), to target the devices to different microbial communities.
METHODS: PEO-TTO patches are developed with TTO concentrations (3, 5, 7.5 and 10 w/w). Optimized electrospinning parameters are selected based on patch morphology (fibers characteristics, defects, SEM), the amount of TTO effectively embedded in the electrospun patch and its stability over time (>14 days, UV-VIS spectrophotometry). After optimization, PCL-TTO (18% w/v solution) is electrospun, using optimized parameters, then the other oils are electrospun in PEO and PCL, keeping the same procedure/concentrations. For all combinations (single oils and their combinations in the two polymers), release profile is studied and antibacterial efficacy is tested on Escherichia coli ATCC® 8739™ and Staphylococcus aureus ATCC® 6538P™ (n=3), by evaluating their planktonic growth (4h, 8h) and adhesion to the substrate (statistical significance by one-way Anova test).
RESULTS: Upon optimization of the electrospinning parameters, PEO and PCL patches (w/wo oils) show negligible defects and a suitable morphology. In spite of their volatility, oils can be efficiently incorporated in PEO and PCL and have high stability. All TTO-patches show high inhibition of the planktonic growth of S. aureus (% reduction vs patch without oil: 98% PEO, 96% PCL) and a moderate effect on E. coli (72% PEO, 81% PCL), consistently with the different capability to permeate the membrane of gram-positive and gram-negative bacteria[5]. TTO-patches also significantly inhibit bacterial adhesion, for both strains, due to the TTO capability to modify proteins determining bacterial binding to the substrate[6]. These results are oil-dependent, as different oils exert different efficacy against gram + and gram – strains, paving the way for personalized medicine in infection.
DISCUSSION: Electrospun essential oils-loaded antibacterial patches are successfully developed, obtaining high stability over time and antimicrobial efficacy, thus appearing promising for application in wounds healing. Further studies will investigate their capability to support skin regeneration and influence of oil release on cells adhesion and viability.