[1] Univ Zurich, Inst Biomed Engn, CH-8044 Zurich, Switzerland
[2] Univ Zurich, Dept Mat Sci, CH-8044 Zurich, Switzerland
[3] Swiss Fed Inst Technol, Surface Sci & Technol Lab, CH-8044 Zurich, Schlieren, Switzerland
[4] Ecole Polytech Fed Lausanne, Inst Biomol Sci, CH-1015 Lausanne, Switzerland