*2.1. Materials*

Gelatin (type B, basic-processed, prepared by bones, with a molecular weight of 100,000, viscosity value of 4.9 MPa·s−1) was obtained from Dongbao Bio-Tech Co., Ltd. (Baotou, China). 2,2,2-trifluoroethanol, formaldehyde solution (37–40 wt %), zinc acetate dihydrate (Zn(CH3COO)2·2H2O), diethylene glycol and ethanol absolute were purchased from Titan Scientific Co., Ltd. (Shanghai, China). The human lung fibroblast cell lines (MRC-5) were purchased from the Cell Bank of Chinese Academy of Sciences (Shanghai, China). *Staphylococcus aureus* (*S. aureus*) and *Escherichia coli* (*E. coli*) were obtained from the China General Microbiological Culture Collection Center (Beijing, China). The deionized water had a resistivity of 18.2 MΩ·cm in the process of the experiments. All chemical reagents were of analytical grade and required no post-treatment.
