aInstitute of Polymer Materials, Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Martensstrasse 7, 91058 Erlangen, Germany
bInstitute of Biomaterials, Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Cauerstrasse 6, 91058 Erlangen, Germany
Received 9 December 2013, Revised 12 March 2014, Accepted 16 March 2014, Available online 22 March 2014.