3.2.1. Cell Activity

The proliferation of GZ0, GZ1 and GZ2 were analyzed by real-time monitoring of MRC-5 cells using an IncucyteTM Zoom microscope. In Figure 8, time-lapse imaging of the control exhibits a standard growth curve up to 55.5% cell confluence level by day 7, and the GZ0, GZ1 and GZ2 reach 45.6, 43.1 and 41.8% cell confluence level by day 7, respectively. The growth curve trends for GZ0, GZ1 and GZ2 are basically the same, and lower than that of the control. The results indicate that the GZ0, GZ1 and GZ2 have certain inhibiting effects on cell proliferation. Relative growth rate (RGR, %) was used to express the cytotoxicity. Table 1 shows that all the relative growth rates are more than 75%, corresponding to the cytotoxicity level of 0 or 1 per the standard in Table 2. This indicates that the gelatin/ZnO fibers (GZ0, GZ1 and GZ2) have no cytotoxicity. In addition, as shown in Figure 9, MRC-5 cells cultured in extraction from GZ0, GZ1 and GZ2 are marked by a green phase object mask via the software of IncucyteTM Zoom. It can be seen that the cells display healthy spindle-like or star-like shape, and the number of cells rose with the extension of culture time, which suggests that GZ1 and GZ2 impose no suppression on the growth of cells.

**Figure 8.** Real-time cell confluence study MRC-5 cells. The cell population was monitored for 168 h using an Incucyte™ Zoom system in an incubator (5% CO2 and 37 ◦C).


**Table 1.** The relative growth rate (RGR) and cytotoxicity level of GZ0, GZ1 and GZ1.

**Table 2.** The standard of cytotoxicity determined from RGR. **Cytotoxicity Level 0 1 2 3 4 5 RGR (%)** >100 75–99 50–74 25–49 1–24 0

**Figure 9.** Cell morphology of (**a**–**e**) Control, (**f**–**j**) GZ0, (**k**–**o**) GZ1 and (**p**–**t**) GZ2 at point of day 0, 1, 3, 5 and 7, respectively. Scale bar: 500 μm.
