*3.3. Effect of Mechanical Stimulus on Electrical Performances*

To study the dependence of the electrical outputs of NGs on the degree of polarization, two kinds of NGs processed by different poling electrical fields were measured. Figure 5a shows the illustrative diagram of the experiment setup for imitating the real scene of the electrical stimulation of the cells in vitro during the dynamic mechanical vibration. The NG was deformed periodically via a self-designed setup driven with an amplitude of 4 V (peak-to-peak value). The resulting curve exhibited a periodic alternation of negative and positive responses corresponding to the deformed and

released states of a piezoelectric nanofiber NG, respectively (Figure 5b). As the frequency increases from 2 Hz to 5 Hz, the generated peak-to-peak piezoelectric current increased from 18.1 nA to 39.7 nA in the P80-NG sample (Figure 5c upper); the P100-NG sample was modulated from 23.1 nA to 41.5 nA (Figure 5c lower). These results confirm that the charge transfer is kept equal at different vibration frequencies, but the output is due to rapid electron flow.

**Figure 5.** Effect of mechanical stimulus on electrical performances of different NGs. (**a**) Schematic diagram of the home-designed experimental shaker for providing periodic mechanical vibrations. (**b**) Piezoelectric output currents recorded during bending and releasing. The insets are the schematics of NG under mechanical bending deformation and releasing state, respectively, (P100-NG at a frequency of 3 Hz). (**c**) Current outputs of P80-NG (above) and P100-NG (below) in the frequency range of 2 to 5 Hz. (**d**) Comparison of measured current of P80-NG and P100-NG under different frequency from 2 to 5 Hz. (**e**) Voltage outputs of P80-NG and P100-NG at a frequency of 2 Hz.

Figure 5d shows that the measured current increased with increasing vibration frequency in both P80-NG and P100-NG. The slope of the P100-NG sample was 1.2-fold higher than that of P80-NG sample under the same vibration force. Figure 5e shows the results of induced voltage under a frequency of 2 Hz. The output voltage of P80-NG and P100-NG reached −1.3 V and −1.75 V, respectively. These results indicate that the electrical performance of the piezoelectric nanofiber NG are affected by poling treatment and the outputs can be modulated and optimized by adjusting the polarization treatment. In the following in vitro assay, piezoelectric nanofiber NG as an electrical stimulator can provide an exact stimulation to cells in real time during the dynamic status.
