1. Department of Mechanical Engineering, Massachusetts Institute of Technology, 500 Technology Square, MIT Building, Room NE47-321, Cambridge, Massachusetts 02139, USA
2. Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Turin, Italy
3. Department of Biological Engineering, Massachusetts Institute of Technology, 500 Technology Square, MIT Building, Room NE47-321, Cambridge, Massachusetts 02139, USA
4. Singapore-MIT Alliance for Research and Technology (SMART), BioSystems and Micromechanics (BioSym), Singapore, Singapore