1. Biomechanics Group, Department of Bioengineering, Politecnico di Milano, Via Golgi 39, 20133 Milan, Italy, Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Room 1-235A&B, Cambridge, Massachusetts, and Center for Computational Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts