2.3.2. Antimicrobial Activity

The antibacterial properties of SE and subsequently of the films were ascertained in triplicate against *Staphylococcus aureus* (ATCC 6538P) and *Escherichia coli* (ATCC 25922). The bacterial strains were obtained from the Spanish Type Culture Collection (CECT, Valencia, Spain) and stored in PBS with 10% MHB and 10% glycerol at −80 ◦C. To prepare fresh inoculum, a loopful of the bacteria was cultivated in MHB at optimal growth conditions overnight and an aliquot was again transferred to MHB and grown at 37 ◦C to the mid-exponential phase of growth. Suspensions containing approximately 5 × 10<sup>5</sup> CFU/mL were used for antimicrobial activity assays. Previously to each assay, the samples were sterilized by UV radiation for 30 min in a Biostar cabinet (Telstar S.A., Madrid, Spain).

The antibacterial potential of SE was evaluated by the broth microdilution method [29]. 90 μL of the bacterial suspension was added into a 96-well microtiter plate (Thermo Fischer Scientific, Roskilde, Denmark) containing 10 μL of two-fold serially diluted extract (concentration range from 0.31 to 80 mg/mL). Wells containing only MHB and wells with the bacterial suspension in MHB were used as positive and negative controls, respectively. The plates were incubated at 37 ◦C for 24 h. Afterward, 10 μL of resazurin, a metabolic indicator, was added into each well and incubated at 37 ◦C for 3 h. Minimum inhibitory concentration (MIC) was considered as the lowest extract concentration that inhibited bacterial growth according to a resazurin color. The contents from the wells containing dilutions designated as MIC were sub-cultured on MHA. Minimum bactericidal concentration (MBC) was established as the lowest extract concentration for which no bacterial growth was observed after incubation at 37 ◦C for 24 h.

#### *2.4. Preparation of Poly(ε-caprolactone) Based Films*

#### 2.4.1. Preparation of Solutions for Electrospinning

Plain PCL solution (10% *<sup>w</sup>*/*<sup>w</sup>*, designated as PCL) was prepared by dissolving PCL pellets in a solvent comprising chloroform and butanol (chloroform:butanol = 3:1, *v*/*v*) under magnetic stirring at room temperature. Three PCL-based active systems containing different contents of the sage extract (5%, 10%, and 20% *w*/*w* with respect to the polymer content) were formulated. These formulations were designated as PCL-SE5, PCL-SE10, and PCL-SE20, respectively. The solutions were prepared by dissolving the required amount of the sage extract in the chloroform-butanol mixture and stirring overnight. Subsequently, the solutions were centrifuged at 10,000 rpm for 10 min. Supernatants were collected, filtered through 0.22 μm polytetrafluoroethylene (PTFE) filters, and filled up to the initial weight. Afterwards, polymer was added to the solutions and stirred until it was completely dissolved.

#### 2.4.2. Characterization of the Solutions

The viscosity was measured using a rotational viscometer Visco Basic Plus L (Fungilab S.A., Sane Feliu de Llobregat, Spain). The surface tension was determined applying the Wilhemy plate method an Easy Dyne K20 tensiometer (Krüss GmbH, Hamburg, Germany). The conductivity was measured using a conductivity meter (HI98192 portable meter HANNA Instruments, Gothenburg, Sweden). The measurements were made in triplicate at room temperature.
