Received: 2 July 2020
Accepted: 25 August 2020
First Online: 15 September 2020
Ethics approval and consent to participate
: The need for ethics approval was waived by the institutional review board RWTH Aachen University (EK 137/15). All the participants voluntarily participated in this study and provided written informed consent.
: Not applicable in general.
: The authors declare that they have no competing interests.