1. Department of Surgical Research, General Hospital, Ningxia Medical University, Ningxia 750004, China
2. Graduate School, Ningxia Medical University, Ningxia 750004, China
3. Institute for Regenerative Medicine, Wake Forest University Health Sciences, Winston-Salem, NC 27157, U.S.A.
4. Department of Obstetrics and Gynecology, General Hospital, Ningxia Medical University, Ningxia 750004, China