Wei Wu1, Tonglei Li2. 1. Key Laboratory of Smart Drug Delivery of MOE, School of Pharmacy, Fudan University, Shanghai 201203, China.. Electronic address: wuwei@shmu.edu.cn. 2. Department of Industrial and Physical Pharmacy, College of Pharmacy, Purdue University, West Lafayette, IN 47907, United States of America.. Electronic address: tonglei@purdue.edu.