Background and experimental approachA main challenge in cell therapies and other tissueregeneration approaches is to produce a therapeuticallysignificant cell number. For expansion of mesenchymalstem cells (MSC) the cultivation on 2D plastic surfacesis still the conventional procedure, even though theculture conditions differ significantly from the 3Denvironment in vivo. Additionally, static amplificationof MSC is a labour-intensive procedure. We thereforeused a specialized rotating bed bioreactor in order tomaximize ex vivo expansion of MSC. MSC were iso-lated from umbilical cord (UC) by explant methodapproach under xeno-free conditions. UC-MSC werethereafter expanded under dynamic conditions in anovel rotating bed bioreactor. The bioreactor systemwas designed to enable integration of sensors for onlinemonitoring of various parameters (e.g. pH, pO