Susanne Staehlke

Electrical stimulation (ES) and its effects on biological systems is an area of research in regenerative medicine. The focus here is on the mechanism of action of ES on cell membrane-related components. A short alternating current (AC) stimulation (10 min) was applied on suspended human MG-63 osteoblasts via a commercially available multi-channel system (IonOptix). The pulsed ES with 1 V or 5 V and frequencies of 20 Hz on cells was performed immediately after cell seeding. The in vitro investigations were conducted by microscopy, flow cytometry, and particle analysis via a Litesizer within 24 h. The short-time ES with the parameter 1 V and 20 Hz was beneficial for the process of cell attachment, which could be related to an enhanced deposition of fibronectin on the glass bottom from the protein-containing medium (10% FBS). The MG-63 cells’ spherical coat hyaluronan remained constant and did not contribute to this AC-triggered adhesion. In this context, the cells’ zeta potential also did not play a role. The membrane potential analyzed via DiBAC4(3) was unchanged. Only the aquaporin channel AQP 8 in the cell membrane was significantly enhanced. Suspended cells in an AC electric field were activated during their settlement, and the fibronectin adsorption on the bottom contributed to this effect but not the membrane-related components.

Mesenchymal stem/stromal cells (MSC) are capable of progenitor cell fraction renewal or tissue-specific differentiation. These properties are maintained during in vitro cultivation, making them an interesting model system for testing biological and pharmacological compounds. Cell cultivation in 2D is commonly used to study cellular responses, but the 2D environment does not reflect the structural situation of most cell types. Therefore, 3D culture systems have been developed to provide a more accurate physiological environment in terms of cell–cell interactions. Since knowledge about the effects of 3D culture on specific differentiation processes is limited, we studied the effects on osteogenic differentiation and the release of factors affecting bone metabolism for up to 35 days and compared them with the effects in 2D culture. We demonstrated that the selected 3D model allowed the rapid and reliable formation of spheroids that were stable over several weeks and both accelerated and enhanced osteogenic differentiation compared with the 2D culture. Thus, our experiments provide new insights into the effects of cell arrangement of MSC in 2D and 3D. However, due to the different culture dimensions, various detection methods had to be chosen, which in principle limits the explanatory power of the comparison between 2D and 3D cultures.