Nisin–biogel was prepared as described elsewhere [3 (link),19 (link),20 (link),26 (link),51 (link)]. Briefly, a nisin solution of 1000 μg/mL was obtained by dissolving 1 g of nisin powder (2.5% purity, 1000 IU/mg, Sigma-Aldrich, St. Louis, MO, USA) in 25 mL of HCl (0.02 M) (Merck, Alges, Portugal). A 1.5% guar-gum biogel (w/v) solution was obtained by dissolving 0.75 g of guar gum (Sigma-Aldrich, St. Louis, MO, USA) in 50 mL of sterile distilled water, which was then heat sterilized via an autoclave. Afterwards, nisin was incorporated within the biogel in a proportion of 1:1, in order to obtain a gel with a final concentration of 200 µg/mL to be used in the clinical trial [26 (link),31 (link)]. The nisin–biogel concentration was selected based on previous reports regarding its cytotoxicity [20 (link)]. For posology establishment, standard procedures for PD prevention were considered [52 (link),53 (link)].
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