Chlorhexidine dihydrochloride chx

The pellet form of poly(lactic acid) (PLA) 4032 D was obtained from Nature Works (Blair, NE) to use as a substrate. The reagents of N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDAC), N-Hydroxysuccinimide (NHs) and Chlorhexidine dihydrochloride (CHx) were purchased from Sigma-Aldrich and their chemical compositions are given in Figure 1. PLA pellets were first dried in an oven at 60 C overnight, then pressed into the shape of sheets in 150 µm thickness by compression molding at 180 C. PLA sheets were then cut into the square form of 50 × 50 mm, gently washed with distilled water, and subsequently dried at room temperature; hereafter referred to as PLA. The solutions of 0.1% (w/v) EDAC and NHs were prepared in distilled water and CHx in 70% (v/v) isopropanol.

The cationic biocides BAC (Sigma Aldrich, Steinheim, Germany), chlorhexidine dihydrochloride (CHX; Sigma Aldrich), cetylpyridinium chloride (CTP; TCI, Eschborn, Germany), didecyldimethylammonium chloride (DDAC; Sigma Aldrich), and octenidine dihydrochloride (OCT; Alfa Aesar by Thermo Fisher, Kandel, Germany) were tested including the following concentrations in doubling dilution steps: 256 to 0.5 mg/L (BAC), 128 to 0.25 mg/L (CHX), 256 to 1 mg/L (CTP), 128 to 0.5 mg/L (DDAC), and 32 to 0.125 mg/L (OCT).