For many years electromagnetic fields (EMFs) have been used clinically with various settings as an exogenous stimulation method to promote fracture healing. However, underlying mechanisms of action and EMF parameters responsible for certain effects remain unclear. Our aim was to investigate the influence of defined EMFs on human osteoblasts' and osteoclasts' viability and function. Primary human osteoblasts and osteoclasts were treated 3 times weekly for 21 days during their maturation process using the Somagen® device (Sachtleben GmbH, Hamburg, Germany), generating defined extremely low-frequency pulsed electromagnetic fields (ELF-PEMFs). Certain ELF-PEMF treatment significantly increased the total protein content (up to 66%), mitochondrial activity (up to 91.1%) and alkaline phosphatase (AP) activity (up to 129.9%) of human osteoblasts during the entire differentiation process. Furthermore, ELF-PEMF treatment enhanced formation of mineralized matrix (up to 276%). Interestingly, ELF-PEMF dependent induction of AP activity and matrix mineralization was strongly donor dependent — only osteoblasts with a poor initial osteoblast function responded to the ELF-PEMF treatment. As a possible regulatory mechanism, activation of the ERK1/2 signaling pathway was identified. Maturation of osteoclasts from human monocytes was not affected by the ELF-PEMF treatment. In summary the results indicate that a specific ELF-PEMF treatment with the Somagen® device improves viability and maturation of osteoblasts, while osteoclast viability and maturation was not affected. Hence, ELF-PEMF might represent an interesting adjunct to conventional therapy supporting bone formation during fracture healing or even for the treatment of osteoporosis.

The finding that alterations in electrical potential play an important role in the mechanical stimulation of the bone provoked hype that noninvasive extremely low frequency pulsed electromagnetic fields (ELF-PEMF) can be used to support healing of bone and osteochondral defects. This resulted in the development of many ELF-PEMF devices for clinical use. Due to the resulting diversity of the ELF-PEMF characteristics regarding treatment regimen, and reported results, exposure to ELF-PEMFs is generally not among the guidelines to treat bone and osteochondral defects. Notwithstanding, here we show that there is strong evidence for ELF-PEMF treatment. We give a short, confined overview of in vitro studies investigating effects of ELF-PEMF treatment on bone cells, highlighting likely mechanisms. Subsequently, we summarize prospective and blinded studies, investigating the effect of ELF-PEMF treatment on acute bone fractures and bone fracture non-unions, osteotomies, spinal fusion, osteoporosis, and osteoarthritis. Although these studies favor the use of ELF-PEMF treatment, they likewise demonstrate the need for more defined and better controlled/monitored treatment modalities. However, to establish indication-oriented treatment regimen, profound knowledge of the underlying mechanisms in the sense of cellular pathways/events triggered is required, highlighting the need for more systematic studies to unravel optimal treatment conditions.

Cigarette smoking (CS) is one of the main factors related to avoidable diseases and death across the world. Cigarette smoke consists of numerous toxic compounds that contribute to the development of osteoporosis and fracture nonunion. Exposure to pulsed electromagnetic fields (PEMF) was proven to be a safe and effective therapy to support bone fracture healing. The aims of this study were to investigate if extremely low frequency (ELF-) PEMFs may be beneficial to treat CS-related bone disease, and which effect the duration of the exposure has. In this study, immortalized human mesenchymal stem cells (SCP-1 cells) impaired by 5% cigarette smoke extract (CSE) were exposed to ELF-PEMFs (16 Hz) with daily exposure ranging from 7 min to 90 min. Cell viability, adhesion, and spreading were evaluated by Sulforhodamine B, Calcein-AM staining, and Phalloidin-TRITC/Hoechst 33342 staining. A migration assay kit was used to determine cell migration. Changes in TGF-β signaling were evaluated with an adenoviral Smad2/3 reporter assay, RT-PCR, and Western blot. The structure and distribution of primary cilia were analyzed with immunofluorescent staining. Our data indicate that 30 min daily exposure to a specific ELF-PEMF most effectively promoted cell viability, enhanced cell adhesion and spreading, accelerated migration, and protected TGF-β signaling from CSE-induced harm. In summary, the current results provide evidence that ELF-PEMF can be used to support early bone healing in patients who smoke.

Delayed fracture healing and fracture non-unions impose an enormous burden on individuals and society. Successful healing requires tight communication between immune cells and bone cells. Macrophages can be found in all healing phases. Due to their high plasticity and long life span, they represent good target cells for modulation. In the past, extremely low frequency pulsed electromagnet fields (ELF-PEMFs) have been shown to exert cell-specific effects depending on the field conditions. Thus, the aim was to identify the specific ELF-PEMFs able to modulate macrophage activity to indirectly promote mesenchymal stem/stromal cell (SCP-1 cells) function. After a blinded screening of 22 different ELF-PEMF, two fields (termed A and B) were further characterized as they diversely affected macrophage function. These two fields have similar fundamental frequencies (51.8 Hz and 52.3 Hz) but are emitted in different groups of pulses or rather send–pause intervals. Macrophages exposed to field A showed a pro-inflammatory function, represented by increased levels of phospho-Stat1 and CD86, the accumulation of ROS, and increased secretion of pro-inflammatory cytokines. In contrast, macrophages exposed to field B showed anti-inflammatory and pro-healing functions, represented by increased levels of Arginase I, increased secretion of anti-inflammatory cytokines, and growth factors are known to induce healing processes. The conditioned medium from macrophages exposed to both ELF-PEMFs favored the migration of SCP-1 cells, but the effect was stronger for field B. Furthermore, the conditioned medium from macrophages exposed to field B, but not to field A, stimulated the expression of extracellular matrix genes in SCP-1 cells, i.e., COL1A1, FN1, and BGN. In summary, our data show that specific ELF-PEMFs may affect immune cell function. Thus, knowing the specific ELF-PEMFs conditions and the underlying mechanisms bears great potential as an adjuvant treatment to modulate immune responses during pathologies, e.g., fracture healing.

Exposure to extremely low frequency pulsed electromagnetic fields (ELF-PEMF) is supposed to simulate local EMF generated during mechanical stimulation of bone and may therefore be used to improve bone regeneration. This study aimed at optimizing the exposure strategy and investigating the underlying mechanisms of a 16 Hz ELF-PEMF, previously reported to boost osteoblast function. Comparing influences of daily continuous (30 min every 24 h) and intermittent (10 min every 8 h) exposure to the 16 Hz ELF-PEMF on osteoprogenitor cells revealed that the intermittent exposure strategy enhanced the 16 Hz ELF-PEMF effects regarding cell numbers and osteogenic function. Gene expression of piezo 1 and related Ca2+ influx were significantly increased in SCP-1 cells with the daily intermittent exposure. Pharmacological inhibition of piezo 1 with Dooku 1 largely abolished the positive effect of the 16 Hz ELF-PEMF exposure on osteogenic maturation of SCP-1 cells. In summary, the intermittent exposure strategy enhanced the positive effects of 16 Hz continuous ELF-PEMF exposure in terms of cell viability and osteogenesis. This effect was shown to be mediated by an increased expression of piezo 1 and related Ca2+ influx. Thus, the intermittent exposure strategy is a promising way to further optimize the therapeutic effects of the 16 Hz ELF-PEMF regarding fracture healing or osteoporosis.