1. Institute of Microsystems Engineering IMTEK, University of Freiburg, 79110 Freiburg, Germany
2. Freiburg Center for Interactive Materials and Bioinspired Technologies FIT, University of Freiburg, 79110 Freiburg, Germany
3. Freiburg Materials Research Center FMF, University of Freiburg, 79104 Freiburg, Germany
4. Ingénierie des Matériaux Polymères (IMP), Université Claude Bernard Lyon 1, INSA de Lyon, Université Jean Monnet, CNRS, UMR 5223, 69622 Villeurbanne CEDEX, France