1. Department of Mechanical Engineering, Department of Biophysics, Department of Chemical and Biomolecular Engineering, Department of Material Science and Engineering, Howard Hughes Medical Institute Graduate Training Program and Institute for NanoBioTechnology, and Whitaker Biomedical Engineering Institute, Johns Hopkins University, Baltimore Maryland 21218, and Departamento de Ingeniería Mecánica y Metalúrgica, Pontificia Universidad Católica de Chile, Santiago, Chile