Funding for this research was provided by:
the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (17XNF029)
Received: 24 May 2019
Accepted: 3 March 2020
First Online: 26 March 2020
Ethics approval and consent to participate
: The objective of the study and the experimental procedure was explained to the subjects and written consent forms were obtained. The study has been approved by the Ethical Review Board of Renmin University of China (ref. no. 2018007).
: All study participants gave consent for their identifying image in Fig. InternalRef removed to be published in this study.
: The authors declare that they have no competing interests.