**4. Conclusions**

In conclusion, we introduced a promising strategy of a self-powered well-aligned P(VDF-TrFE) piezoelectric nanofiber nanogenerator as an exact piezoelectric stimulator for bone tissue engineering. We investigated the specific effects of post-treatments on the properties of NG. Poling post-treatment could effectively improve the mechanical, piezoelectric, and sensing performances of NG. We also measured the accurate piezoelectric response of NG and emulated the real scene of the electrical stimulation of the cells in vitro during the dynamic status. The well-aligned piezoelectric P(VDF-TrFE) NGs with different encouraged the MC3T3-E1 cells to proliferate in vitro under a sustainable piezoelectric stimulus. To clarify the effect of the exact electrical stimulation on the proliferation fate of preosteoblasts, two different output voltages of NG as stimulators were compared. Our work provides additional insights into the application of P(VDF-TrFE) piezoelectric nanofiber NG as self-powered electrical stimulation system for assisting tissue repair and regeneration.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-4991/9/3/349/s1, Figure S1: The diameter distribution and morphology, Figure S2: The strain-stress plots of the different NFMs, Figure S3: The cell viability of MC3T3-E1 on P80-NG, P100-NG and control.

**Author Contributions:** Conceptualization, A.W. and M.H.; methodology, A.W., L.Z.; software, A.W.; validation, A.W.; formal analysis, A.W.; investigation, A.W.; resources, M.H.; data curation, A.W.; writing—original draft preparation, A.W.; writing—review and editing, L.Z. and X.Q.; visualization, X.Q.; supervision, M.H.; project administration, M.H.; funding acquisition, M.H.

**Funding:** This work was supported by the National Natural Science Foundation of China (grant Nos. 61271070 and 60771019).

**Acknowledgments:** We would like to thank LetPub (for providing linguistic assistance during the preparation of this manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
