2.2. Preparation WPUn Emulsions and Coatings

A series of self-polishing WPUn emulsions based on IPDI, PCL, PEG, lysine, and EG12 were synthesized by two-step polymerization. The feed ratios were shown in Table 1. The content of GQAS in WPUn structure was regulated by changing the ratio of two chain extenders. PEG and PCL were dehydrated under vacuum at 80–90 °C for 2 h first. Then, IPDI and 0.1% stannous octoate were added under N₂ environment. After continuous reaction for another 2 h at 70–75 °C, the reaction prepolymer was cooled down. Then, different content of chain extender EG12 in acetone was added in the mixture for 0.5 h. Afterward, the polyurethane prepolymer was poured into L-lysine aqueous solution under stirring (600 rpm) and ultrasound (200 W) simultaneously for 1 h. An amount of 1 M NaOH was added dropwise to neutralize L-lysine and accelerate the secondary chain extension. WPU0 without GQAS was prepared as a control with a similar process.

The theoretical composition, molecular weight, Zeta potential, and glass transition temperature (Tgs) of WPUn samples.

WPUn coatings were prepared with a similar process to our previous work [32] by casting these WPUn emulsions siliconized culture dishes and dried at room temperature for 2 days, 60 °C for 2 days, and then 60 °C under vacuum for 2 days. The films were cut in sheets (1 × 1 cm², 0.5 mm thickness) and used directly for tests unless mentioned otherwise. To eliminate the influences of unreacted PEG and GQAS moieties onto WPUn films of their anti-fouling activities, all the films were immersed in water (110 rpm, 37 °C) for 6 h, then put into an oven at 60 °C for 2 days before testing, including antibacterial, anti-biofilm activity, protein adsorption assay, and cell cytotoxicity.