1. Department of Biomedical Engineering University of Michigan Ann Arbor MI 48109 USA
2. Department of Chemical Engineering University of Michigan Ann Arbor MI 48109 USA
3. Institute of Materials École Polytechnique Fédérale de Lausanne 1015 Lausanne Switzerland
4. Interfaculty Institute of Bioengineering École Polytechnique Fédérale de Lausanne 1015 Lausanne Switzerland
5. Dipartimento di Fisica “Ettore Pancini” Università di Napoli “Federico II” 80138 Napoli NA Italy
6. Institute for Functional Interfaces Karlsruhe Institute of Technology 76131 Karlsruhe Germany