Klein, D
Schmitz, T
Verhelst, V
Panic, A
Schenck, M
Reis, H
Drab, M
Sak, A
Herskind, C
Maier, P
Jendrossek, V
Article History
Received: 31 December 2014
Revised: 24 February 2015
Accepted: 20 March 2015
First Online: 18 May 2015
Competing interests
: The authors declare no conflicts of interest.