1. Shaanxi Key Laboratory of Degradable Biomedical Materials Shaanxi R&D Center of Biomaterials and Fermentation Engineering Biotech. & Biomed. Research Institute Northwest University Taibai North Road 229 Xi'an Shaanxi 710069 China
2. Department of Dermatology Peking University First Hospital Xishiku Street No.8 Beijing 100034 China