## 1 Introduction  
As the average age of the German population has risen significantly in recent years, the importance of measures to maintain quality of life continues to increase. The aging process of the musculoskeletal system and the brain plays a key role here, which is why electrically active implants are becoming a focus of research. Electrical signals are the basis for many processes in the human body. In bone tissue, electrical activity also seems relevant for regeneration processes [1]. The bone constituents collagen and hydroxyapatite could be defined as causative for the emission of electrical signals according to past research [1]. The application of external electrical stimulation (ES) is used to enhance fracture healing and bone formation in delayed unions and non-unions [2, 3]. The underlying mechanisms are not yet completely understood. In in vitro experiments, electrically stimulated stem cells showed increased osteogenic differentiation compared to non-stimulated controls [4,5]. The stimulation of osteoblasts led to enhanced survival and proliferation as well as increased mineralization and collagen production [6,7]. Osteoblasts are significantly involved in bone tissue formation, and the osteoblast-like MG-63 cells are widely used internationally as model cells for in vitro experiments in biomaterials research [8, 9, 10, 11]. If MG-63 osteoblasts in suspension were electrically stimulated (ES) with an alternating current (AC) for only 10 min, initial adhesion was increased, and cells were more active. The boost in adhesion was impressively seen in a higher basal Ca\({}^{2+}\) level in the cytoplasm, and the prompt cell reaction was due to an additional adenosine triphosphate (ATP) stimulus with a prolonged steady state [12]. In addition, the production of reactive oxygen species (ROS) was also increased 4 h after AC using the IonOptix multi-channel system [12,13]. ROS have long been considered a toxic by-product of metabolism, as they have the potential to damage DNA and inhibit growth when they exceed the capacity of antioxidant enzymes. However, physiological concentrations also involve various regulatory signaling pathways [14], such as activating the mitogen-activated protein kinase (MAPK) signaling pathway [15]. Since the generation of ROS, such as hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)), is one of the effects of AC with certain parameters, the impact of H\({}_{2}\)O\({}_{2}\) on physiologic processes combined with other electrical stimulation effects needs to be investigated. H\({}_{2}\)O\({}_{2}\) is transported into cells mainly by aquaporins (AQPs) 1, 3, 5, 7, 8, and 9 [16]. AQPs are membrane-bound channels that mediate the bidirectional passive transport of water and play an essential role in water and osmolyte homeostasis [17]. However, AQPs are also partially found in intracellular compartments, which can be transported into the membrane in response to various stimuli [16]. Currently, 13 classes have already been detected in multiple cells and tissues [18]. In human tissue microarrays, e.g., AQP 3 was found to be moderately expressed not only in articular chondrocytes but also in subchondoral osteoblasts and synovium [17]. In addition to their transport function, AQPs also play a role in cellular signaling pathways, migration, proliferation, and the regulation of cell-cell adhesions [19]. For example, AQP 1 regulates the expression of cell-cell adhesion proteins, such as \(\upbeta\)-catenin and \(\upgamma\)-catenin [19]. We discovered earlier that a short-time biphasic electrical stimulation improved initial adhesion processes. Still, we did not find an explanation for why cells adhere better. One possible mechanism is an altered hyaluron synthesis by cells, because earlier findings indicated a crucial role of the pericellular matrix substance hyaluron (HA) in the initial adhesion processes of osteoblasts and chondrocytes [20,21]. Research to date has not yet been able to fully explain the mechanism of action of ES.