1. Department of Mechanical Engineering and Materials Science, Duke University, 144 Hudson Hall, Box 90300, Durham, North Carolina 27708-09300, Center for Biologically Inspired Materials and Material Systems, Duke University, Durham, North Carolina 27708-09300, Department of Chemistry, Southern Illinois University, Carbondale, Illinois 62901-4409, and Army Research Office, P.O. Box 12211, Research Triangle Park, North Carolina 27709-2211