1. Soft Active Materials Laboratory, Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708;
2. School of Engineering and Applied Sciences and Wyss Institute, Harvard University, Cambridge, MA 02139;
3. Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology, Cambridge, MA 02139; and
4. Department of Chemistry, American University of Beirut, Beirut 11-0236, Lebanon