Mylar

The gelatin film forming solution was prepared by dissolving 5 wt.% of bovine gelatin powder (Sigma-Aldrich, Taufkirchen, Germany) in distilled water at 60 °C for 30 min. Then, 60-µm thick films were obtained by casting the gelatin film forming solution over a covered Mylar® (DuPont Teijin Films^TM, Cotern, Luxembourg) mold. The evaporation of water was carried out at 22 ± 2 °C and at 50 ± 10% relative humidity. Dehydrothermal (DHT) crosslinking [16 (link)] of the gelatin films was achieved by drying the films at 100 °C for 1 h, then heating them to 150 °C for 8 h in a Memmert UFE500 oven (Memmert GmbH, Schwabach, Germany). This DHT treatment time was chosen as the compromise between the fabrication convenience and the achieved performance properties of the films (see Appendix A). The treatment formed crosslinks through a condensation reaction between the carboxyl and amino groups in the gelatin. The samples were stored for 1–2 days at room temperature in a vacuum desiccator before being cut into 20 cm long strips using an infrared laser machine (Laser solution LS100, Gravotech Marking, La Chapelle Saint-Luc, France) and making the capsules.

Medium molecular weight chitosan powder (94% purity) was obtained from Huantai Goldenlake Carapace Products Co., Ltd. (Qingdao, China) and used as the base material to form the test films. Glycerol was obtained from Fisher Scientific (Fisher Scientific, Fair Lawn, NJ, USA) and used in the film as a plasticizer. Glacial acetic acid was purchased from J.T. Baker (Phillipsburg, NJ, USA) and used as a solvent for the film-forming compounds. The green tea extract (GTE), soluble in water, with an EGCG content of 50% was purchased from Herb Store USA (Walnut, CA, USA) and used in this study.
To make the films, chitosan (2% w/w) was dissolved in a 1% acetic acid solution with glycerol (Figure 1). Green tea powder at different concentrations (0-15%) was then added to chitosan film-forming solutions (FFS) as depicted in Table 1. The solutions were stirred using a magnetic stirrer for 30 min to dissolve the powdered extracts. The film-forming solutions were then degassed in a water bath sonicator. To form a film, a 20 g aliquot of the FFS was poured onto a Mylar (DuPont Inc., Kinston, NC, USA) polyethylene terephthalate (PET) sheet attached to a glass plate and a drawbar used to spread the solution into a thin film. After drying in an oven at 45°C for 2 h, the film was peeled off from the Mylar backing and stored in an air-tight container at 23°C for further testing.