*2.4. Characterization*

The microstructure and chemical composition of the gelatin/ZnO fibers were characterized by a S-4300 scanning electron microscope (SEM, Hitachi, Tokyo, Japan) and energy dispersive X-ray spectroscopy (EDX, Hitachi, Tokyo, Japan). The size of ZnO particles was analyzed by the dynamic light scattering (DLS) method (litesizerTM 500, Anton Paar GmbH, Graz, Austria). Samples were dispersed in the ethanol, the concentration of the sample was 1 mg·mL<sup>−</sup>1, and the pH value was 6.5. The functional groups in the fibers were characterized by Fourier transform infrared spectroscopy (FTIR) (Bruker Tensor II, Karlsruhe, Germany), and the scanning range of the samples was 4000–400 cm<sup>−</sup>1. The crystal structures of the samples were determined by X-ray diffraction (XRD, ARL XTRA, Zurich, Switzerland). The scanning rate was 0.1 s·step−<sup>1</sup> and the scanning range was 10–80◦. The thermal stability of the samples was analyzed by thermogravimetry (TGA, NETZSCH, Selb, Germany) in nitrogen atmosphere, and the heating rate was 10 ◦C·min<sup>−</sup>1. The IncucyteTM Zoom system (EssenBio, Ann Arbor, MI, USA)

was used to observe effect of the extraction on MRC-5 cells in real time. The extraction and 10% FBS were placed in 96-well plates. Each well was inoculated with 2000 cells and cultured in an atmosphere of 5% CO2 at 37 ◦C for seven days. Phase contrast images were acquired every 3 h.
