# Evaluation of Pulsed Electromagnetic Field Effects: A Systematic Review and Meta-Analysis on Highlights of Two Decades of Research In Vitro Studies

Authors: Mahsa Mansourian; Ahmad Shanei
Journal: BioMed Research International
 (2021)

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## Abstract

Pulsed electromagnetic field (PEMF) therapy is a type of physical stimulation that affects biological systems by producing interfering or coherent fields. Given that cell types are significantly distinct, which represents an important factor in stimulation, and that PEMFs can have different effects in terms of frequency and intensity, time of exposure, and waveform. This study is aimed at investigating if distinct positive and negative responses would correspond to specific characteristics of cells, frequency and flux density, time of exposure, and waveform. Necessary data were abstracted from the experimental observations of cell-based in vitro models. The observations were obtained from 92 publications between the years 1999 and 2019, which are available on PubMed and Web of Science databases. From each of the included studies, type of cells, pulse frequency of exposure, exposure flux density, and assayed cell responses were extracted. According to the obtained data, most of the experiments were carried out on human cells, and out of 2421 human cell experiments, cell changes were observed only in 51.05% of the data. In addition, the results pointed out the potential effects of PEMFs on some human cell types such as MG-63 human osteosarcoma cells (p value < 0.001) and bone marrow mesenchymal stem cells. However, human osteogenic sarcoma SaOS-2 (p<0.001) and human adipose-derived mesenchymal stem cells (AD-MSCs) showed less sensitivity to PEMFs. Nevertheless, the evidence suggests that frequencies higher than 100 Hz, flux densities between 1 and 10 mT, and chronic exposure more than 10 days would be more effective in establishing a cellular response. This study successfully reported useful information about the role of cell type and signal characteristic parameters, which were of high importance for targeted therapies using PEMFs. Our findings would provide a deeper understanding about the effect of PEMFs in vitro, which could be useful as a reference for many in vivo experiments or preclinical trials.


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## 1. Introduction

Electromagnetic fields (EMFs) are composed of magnetic and electric fields that influence each other [1]. There are many EMF subtypes with varying frequency rates, and they can cause either positive or detrimental biological effects. For medical purposes, they can be used in diagnostic modality and be considered as a potential therapeutic option as well. On the other hand, EMFs can penetrate tissues without experiencing intensity decrement [2], pass through the cell membrane, and affect cell responses. Consequently, cells may experience diverse pathophysiological disorders like cancer, thus, elevating one’s concern during the course of using EMFs for therapeutic purposes [3]. However, despite many findings, the carcinogenic role of EMF is still unclear.Among subtypes of EMFs, low-frequency fields with specific amplitudes and waveforms are referred to as pulsed EMFs (PEMFs) [4]. Being a promising strategy and a type of the noninvasive and inexpensive physical approaches, PEMFs have exhibited therapeutic potential for treating various diseases [5]. It has already been shown that they can make changes to cell cycle, apoptosis, cell proliferation, and differentiation. Indeed, they are able to affect and alter the cell function by inducing forced vibration for free ions on the cell membrane surfaces due to an external oscillating field [6]. Irregular gating of ion channels triggered by this situation can certainly disturb the balance of transmembrane proteins and, consequently, disrupt cell function [7]. It has also been proposed that the effect of PEMFs may be propagated and amplified along the whole signal transduction pathway, thereby changing cell behavior [8]. In some studies, it has been reported that PEMFs can modulate both downstream signal transduction pathway and cell surface receptor expression/activation [8, 9]. As a result, homeostatic cell functions such as differentiation, viability, proliferation, interaction with components of extracellular matrix (ECM), and communication with neighboring cells could be restored [10]. In addition, PEMFs could enhance both the neurogenic differentiation of mesenchymal stem cells (MSCs) and osteogenic differentiation. Because EMFs easily permeate through cells [4] and change the electric field of the inner cell membrane, they can induce biological changes. In particular, they can induce changes in the Ca2+ efflux and, consequently, modulate various biological effects such as nitric oxide signaling, growth factor secretion, and Mitogen-Activated Protein Kinase (MAPK)/Extracellular Signal-Regulated Kinase (ERK) [11]. It has been hypothesized that the production of second messengers is stimulated by the direct effect of PEMF on phospholipids within the plasma membrane, and subsequently, multiple intracellular signal transduction pathways are initiated [12].There are many factors affecting the biological responses. To clarify PEMF impacts, studies have reported that signal characteristics play a crucial role in determining the type of biological responses including amplitude and frequency of exposure to the applied PEMF [13]. Indeed, to deliver a therapeutic PEMF, it is necessary to optimize these important parameters [6]. In addition, a large volume of evidence has revealed that some kinds of cells appear exquisitely sensitive to PEMF, while other types appear relatively unresponsive. For instance, undifferentiated PC12 cells are more sensitive to PEMF exposure, while differentiated PC12 cells are more resistant to stress [14]. Consequently, cell properties are of vital importance in establishing a biological response to PEMF in vitro.Despite a relatively long history of using PEMFs in medicine, little is known about the biological mechanism of such therapies. To develop a reliable working principle of PEMF therapies, it is worth investigating the experimentally observed biological effects caused by these fields alone. Thus, in this study, a meta-analysis was performed using 3249 in vitro experimental observations available in 92 scientific journals (1999-2019) in order to determine the potential effects of PEMF on different cell types of both human and rat/mouse. Our analysis scrutinized the published experiments that had considered the effects of exposure to PEMFs (cytogenetic, gene, and protein expression analysis) on cell types from rats, mice, and humans to gain a more explicit and evidence-based conclusion on the association between PEMFs and cell responses.


## 2. Material and Methods

In Tables1–15, the characteristics of experimental protocols and variables are presented. In this paper, cellular response (presence or absence) in human, mouse, or rat cells is defined as changes due to exposure to PEMFs. We analyzed the reported studies based on the different experimental readouts/endpoints which they used for their studies and the physiological variables they measured. These studies are shown in Figures 1–3, (human cells), Figure 4 (rat/mouse cells), and Figure 5 (other species), separately.Table 1
Statistically significant difference cell groups from Figures1–3.
Exposure detailTotalStudies with statistical significant cellular responsePresenceAbsenceHuman143 (21.43%)11 (78.57%)Rat/mouse52 (40%)3 (60%)Other species000Total cells195 (23.81%)14 (76.19%)Table 2
Human cell studies: PEMFs exposure conditions used in in vitro studies.
No.Cell lineFrequencies and intensitiesCell responseResultYearFirst author1Retinal pigment epithelial (RPE) cellsFrequency of 50 HzIntensity of 1 mTCell proliferation, cell death, and gene expressionTranscript levels of proangiogenic genes (HIF-1α, VEGFA, VEGFR-2, CTGF, cathepsin D TIMP-1, E2F3, MMP-2, and MMP-9) increased2019Oladnabi et al. [56]2Adipose-derived mesenchymal stem cells (AD-MSCs)Frequency of 5 HzIntensity of 1.1 mTCell proliferationPEMF can be beneficial to tissue-derived stem cell proliferation2018Daish et al. [16]3Adipose-derived stem cells (ASCs)Frequency of 50 HzIntensity of 1 mTCell proliferation, cell differentiationGene expressionProtein expressionPEMF could promote cell proliferation and osteogenic differentiation.Bone-related gene expression and protein expression of OPN, OCN, and RUNX-2 increased2018Yin et al. [17]4Human adipose-derived mesenchymal stromal cells (hAMSC)Frequencies:10, 16, 20.6, 23.8, 26, 33, 49.9, 52.3, 75.6, and 90.6 HzCell proliferation, gene expressionProtein expressionPEMF showed significant upregulations of collagen I, alkaline phosphatase, and osteocalcin2018Poh et al. [18]5H4 glioma cellsFrequency of 7 HzIntensity of 30 mTCell apoptosisLFPEMF stimulation of H4 glioma cell cultures induced apoptosis in exposed cells.2018Kaszuba-Zwoińska et al. [38]6Mesenchymal stem cells (hMSCs)Frequency of 75 Hz, the intensity peak of 1.5 mTGene expressionThe exposure to PEMFs did not produce any change on notch-related genes2017Bagheri et al. [20]7Human umbilical vein endothelial cells (HUVECs)The frequency of 50 HzIntensity of 2.25 mTCell proliferationGene expressionProtein expressionProteins and mRNA expression levels of Akt, mTOR, and TGF-β1 were elevated2017Cheng et al. [59]8Human mesenchymal stem cells (MSCs)Frequency of 15 HzFlux densities between 1–4 mT.Gene expressionBrief and single exposures to low amplitude PEMFs were most effective at stimulating MSC chondrogenesis.2017Parate et al. [21]Table 3
Human cell studies: PEMF exposure conditions used in in vitro studies.
No.Cell lineFrequencies and intensitiesCell response analysisResultYearFirst author9MCF-7Frequencies of 2122.24, 1970.56, 2072.32, and 2648.64 HzCell viabilityThere was a significant effect on MCF-7 cells after treatment with PEMF at the resonant frequencies of the genes of RICTOR, PPARG, and NBN CHEK22017Alcantara et al. [43]10U937 cells (leukemia cell line)Frequency of 50 HzIntensity of 45 mTCell viability protein expressionThere were no significant differences in the expression level of calmodulin between control- and only MF-treated samples2017Wojcik-Piotrowicz et al. [46]11Human bone marrow stromal cells (hBMSCs)Pulse frequency of 3.8 kHzEnzyme activitySignal transductionPathwayGene expressionPEMF regulated preosteoblast gene expression, and notably, the transforming growth factor-beta (TGF-β) signaling pathway and microRNA 21 (miR21) were the most highly regulated2017Selvamurugan et al. [25]25Peripheral blood mononuclear cells (PBMCs)Frequency of 75 HzIntensity of 3 mTGene expressionLF-PEMF modulated gene expression.2017Capelli et al. [57]12Human bone marrow mesenchymal stem cells (hBM-MSCs)Frequency of 60 HzIntensity of 10 mTProtein expressionAfter exposure to only PEMF, the expression of proteins slightly increased, but there was no significant difference when compared to the nonexposed groups.2016Choi et al. [26]13Human glioblastoma U87 cell lineFrequencies of 50 Hz and 100 Hz intensities of 10 mT and 5 mTCell viabilityCell morphologyProtein expressionA significant increase in the number of cells after 24 h exposure to 50 Hz, 100 G.A dramatic decrease in cells exposed to 100 Hz, 100 G, and 10 Hz, 50 G EMFs compared with controls2016Akbarnejad et al. [3]14Human glioblastoma cell line (T98G).Frequency of 75 HzIntensity of 2 mTCell proliferation, cell apoptosismiR-421 expression significantly increased over the control after PEMF alone.2016Pasi et al. [39]Table 4
Human cell studies: PEMF exposure conditions used in in vitro studies.
No.Cell lineFrequencies and intensitiesCell response analysisResultYearFirst author15Periodontal ligament stem cells (PDLSCs)Pulsed burst frequency of 15 HzIntensities of 0.6, 1.2, 1.8, 2.4, and 3.0 mTCell proliferationCell differentiationGene expressionProtein expressionNo influence on cell proliferation.PEMF appeared to stimulate the earlier onset of osteogenic differentiation of PDLSCs and upregulated the gene expression of Runx2, ALP, and OPN compared with the sham group.2016Wang et al. [32]16Human mesenchymal stem cells (MSCs)Frequency of 50 HzIntensity of 0.6 mTCell viabilityCell differentiationGene expressionPEMFs upregulated genes related to Ca2+ signaling, proliferation, and neurogenic differentiation2016Lim et al. [11]17Human tendon stem cells (hTSCs)Frequency of 10–30 HzIntensity of 0.5–1.5 mTCell morphologyCell viabilityCell proliferationCell apoptosisGene expressionPEMF did not cause any significant changes in proliferation, viability, and morphology.2016Randelli et al. [33]18Human dental pulp stem cells (hDPSCs)Schwann-like cellsFrequency of 50 HzIntensity of 1 mTGene expressionGroup treated to PEMF showed significantly greater P75NTR mRNA expression than the control group2016Hei et al. [34]19HeLa, HEK293, MCF7, and AGSFrequency of 75 HzIntensities of 2, 4, and 6 mTCell proliferationCell proliferations of all four different cell lines also showed an increase in PEMF exposure until 4 mT, but not at 6 mT.2016Cho et al. [44]20Human annulus fibrosus (AF) cellsNucleus pulposus (NP) cellsFrequency of 3,850 HzIntensity of 1.19 mTGene expressionPEMF alone had no effect on gene expression.2016Miller et al. [62]Table 5
Human cell studies: PEMF exposure conditions used in in vitro studies.
No.Cell lineFrequencies and intensitiesCell response analysisResultYearFirst author21Human dermal fibroblasts (HDF), human epidermal keratinocytes (HEK), and human mononuclear cells (HMNC)Pulse frequency of 1 kHz, intensity of 6.7 A/mGene expressionPEMF treatment changed the relative amount of messenger (m) RNA encoding enzymes involved in heme catabolism and removal of reactive oxygen species.2015Kubat et al. [60]22Acute lymphoblastic leukemia (CEM/C2), B-cell lymphoma (SU-DHL-4), colorectal adenocarcinoma (COLO-320DM), breast adenocarcinoma (MDABM-468), and ductal carcinoma (ZR-75-1)Frequencies of 15 Hz, 125 Hz, and 625 Hz intensity of 5 mTCell morphology, cell viability, and cell apoptosisA PEMF of 125 Hz and 625 Hz for 24 h–48 h increased proliferation activity in the 2 types of cancer cell lines used2015Loja et al. [48]23Human neuroblastoma SH-SY5Y cellsFrequency of 75 HzIntensity of 2 mTEnzymatic activity, cell proliferation, cell viability, and cell apoptosisBasal MnSOD specific activity was higher in PEMF stimulated cells when compared to cells not treated with PEMF2015Osera et al. [42]24Human bone marrow stromal cells (hBMSCs)Frequency of 200 HzIntensities of 0.6, 1 teslaCell proliferationCell differentiationProliferation and the osteogenic differentiation of hBMSCs were increased2014Fu et al. [31]25Human amniotic epithelial cells (AECs)Frequency of 50 HzIntensity of 1 mTCell differentiationGene expressionProtein expressionThe PEMF stimulation could induce osteogenic differentiation, as shown by the expression of osteoblast-specific genes and proteins including alkaline phosphatase and osteocalcin2014Wang et al. [35]Table 6
Human cell studies: PEMF exposure conditions used in in vitro studies.
No.Cell lineFrequencies and intensitiesCell response analysisResultYearFirst author26Human tendon cells (hTCs)Intensities of 1.5 and 3 mTCell viabilityCell proliferationGene expressionProliferation and the viability of hTCs were enhanced by PEMF2014de Girolamo et al. [61]27Human umbilical cord-derivedMesenchymal stem cellsFrequency of 75 Hz, intensity of 1.8-3 mTCell morphologyGene expressionMorphological data showed that the treatment with PMEF reduced the time to obtain cell differentiation.2013Esposito et al. [36]28Human disc cellsFrequency of 15 Hz. Intensity of 1.6 mTGene expressionProtein expressionBMP-7 and BMP-2 were upregulated by PEMF2013Okada et al. [63]29Tendon cells (TCs) (human)Frequency of 75 Hz, intensity of 1.5 mTCell morphology, cell viability, cell apoptosis, and gene expressionPEMF exposure is not cytotoxic and is able to stimulate TCs’ proliferation2013de Girolamo et al. [15]30Human disc cells (intervertebral disc (IVD))Frequency of 15 HzIntensity of 1.6 mTGene expressionProtein expressionmRNA expression of BMP-2 was upregulated by PEMF alone2013Okada et al. [64]31MCF7, MCF10Frequencies of 20 and 50 HzIntensities of 2.0, 3.0, and 5.0 mTCell apoptosisMCF7 cancer cells were particularly vulnerable to 3 mT PEMFs.2013Crocetti et al. [45]32Bone marrow MSCs (BM-MSCs)Adipose tissue mesenchymal stem cells (ASC)Frequency of 75 Hz, intensity of 2 mTCell viabilityCell proliferationCell morphologyCell apoptosisGene expressionCell differentiationAfter PEMF exposure, in comparison with ASCs, BM-MSCs showed an increase in cell proliferation2013Ceccarelli et al. [19]33Human osteogenic sarcoma SaOS-2Bone marrow-derived human MSCsFrequency of 15 Hz, intensity of 0.1 mTCell proliferationGene expressionPEMF caused a minor increase in expression of osteogenic markers of MSCs2012Kaivosoja et al. [50]Table 7
Human cell studies: PEMF exposure conditions used in in vitro studies.
No.Cell lineFrequencies and intensitiesCell response analysisResultYearFirst author34Human mesenchymal stem cell osteoblastFrequencies of 5, 25, 50, 75, 100, and 150 Hz, intensity of 1.1 mT,Cell differentiationLevels of human mesenchymal stem cell differentiation changed by PEMF2012Luo et al. [37]35Stromal cells of human bone marrow (BMSC)Frequency of 75 Hz, intensity of 1.8-3 mTGene expression, cell differentiationThe cells treated with PEMF began differentiation earlier than untreated cells.2012Esposito et al. [24]36Human breast carcinoma cells (T47D)Frequencies of 100, 217 Hz intensity of 0.1 mTCell proliferation, cell viability, cell morphology, protein expression, and ROS productionPEMF induced a time-dependent decrease in cell growth after 72 h2012Sadeghipour et al. [49]37Human peripheral blood mononuclear cell (PBMC)Frequency of 7 Hz flux density of 30 mTCell apoptosisPEMF induced apoptosis in PBMC2011Kaszuba-Zwoińska et al. [58]38Bone marrow mesenchymal stem cells (BMMSCs)Frequency of 15 Hz flux density of 1.8 mTCell proliferationCell apoptosisGene expressionProtein expressionPEMF treated cells also showed greater MMP-2 expression compared to unstimulated cells.2011Griffin et al. [27]39Human bone marrow-derived stromal cell (BMSC)Human fetal preosteoblasts (SVHFO)Frequency of 15 HzFlux density of 0.1 mTCell proliferationCell differentiationGene expressionSignal pathwayPEMF treatment increased mRNA levels of bone morphogenetic protein 2, transforming growth factor-beta 1, osteoprotegerin, matrix metalloproteinase-1 and -3, osteocalcin, and bone sialoprotein2010Jansen et al. [28]40Osteoblast-like cell cultures (MG-63)Frequency of 75 HzFlux density of 3 mTGene expressionPEMFs induced the upregulation of important genes related to bone formation genes, however, PEMF induced downregulation of genes related to the degradation of extracellular matrixSollazzo et al. [53]Table 8
Human cell studies: PEMF exposure conditions used in in vitro studies.
No.Cell lineFrequencies and intensitiesCell response analysisResultYearFirst author41Human osteoblast-like Saos-2 cellsFrequency of 15 Hz flux density of 2 mTGene expressionProtein expressionPEMF induced increase in RANKL mRNA expression2010Borsje et al. [51]42Bone marrow mesenchymal stem cells (BMMSCs)Frequency of 15 Hz flux density of 1.8 mTCell proliferationGene expressionExposure of BMMSCs to PEMFs increased cell proliferation2010Sun et al. [29]43Human mesenchymal stem cells (hMSCs)Frequency of 7.5 Hz flux density of 0.13 mTCell proliferationCell differentiationGene expressionThe expressions of osteogenic genes, including Runx2/Cbfa1 and ALP, were modulated by PEMF exposure.2009Tsai et al. [22]44Human bone marrow mesenchymal stem cells (BMMSC)Frequency of 15 Hz flux density of 1.8 mTCell morphologyCell proliferationCell differentiationPEMF exposure could enhance the BMMSC cell proliferation2009Sun et al. [30]45SaOS-2 osteoblast-like cellsFrequency of 15 HzCell viabilityCell proliferationCell differentiationPEMF stimulation did not affect cell number, however, increased ALP activity2008Martino et al. [7]46Human chondrocyteFrequency of 21.2 MHzCell viabilityPEMF exposure increase cell viability2007Štolfa et al. [66]47Primary human mesenchymal stem cells (MSCs), human chondrocyteFrequency of 30 Hz, intensity of 35μTGene expressionPEMF altered the gene expression of a limited number of gene products in human mesenchymal stem cells and human chondrocytes.2007Walther et al. [23]48Human promyelocytic leukemia HL-60 cellsFrequency of 0.25 Hz 0.25–4.5 T peak magnetic field strengthCell viability signal transductionPEMF did not alter the cell viability or content of cAMP2006Sontag and Kalka [47]49A human osteosarcoma (cell line) SaOS-2Frequency of 15 HzIntensity of 1.6 mTCell ProliferationCell differentiationPEMF reduced proliferation and increased differentiation in SaOS-2 cell line2005Hannay et al. [52]50MG-63 human osteosarcoma cellsFrequency of 75 Hz, intensity of 2.3 mTCell proliferationGene expressionThe PEMF increased [3H]-thymidine incorporation2005Mattei et al. [54]Table 9
Human cell studies: PEMF exposure conditions used in in vitro studies.
No.Cell lineFrequencies and intensitiesCell response analysisResultYearFirst author51Human astrocytoma cell line U-373 MGFrequency of 50 Hz, intensity of 3 mTCell proliferationPEMF did not cause cell proliferation or cell death2001Pessina et al. [40]52Sympathetic neuronal-like PC6 cellsFrequency of 2 Hz, intensity of 0.3 mTCell proliferation, cell differentiationProliferation was unaffected by PEMF2001Shah et al. [67]53Human atrophic nonunion cell cultureHypertrophic nonunion cell cultureFrequency of 15 Hz, intensity of 1.8 mTCell morphologyCell proliferationCell differentiationPEMF resulted in a change in morphologic features of cells.2001Guerkov et al. [65]54Human astrocytoma cell lineU-373 MG cellsFrequency of 50 Hz, intensity of 3 mTCell proliferationCa2+ concentrationAfter the cells were exposed to EMFs, the basal [Ca2+]i levels increased2000Aldinucci et al. [41]55TE-85 human osteosarcoma cellsMG-63 human osteosarcoma cellsHuman normal osteoblast cells (NHOC)Frequency of 15 Hz, intensity of 1.8 mTCell proliferationThe cells increase their proliferation when exposed to PEMF1999De Mattei et al. [55]56MG63 human osteoblast-like cellsFrequency of 75 Hz, intensity of 2.3 mTCell proliferation, cell differentiationPEMF caused a reduction in cell proliferation and an increase ALP activity1999Lohmann et al. [4]Table 10
Rat/mouse cells: cellular response (presence or absence) for cultured rat/mouse cells.
No.Cell lineFrequency and intensityCell response analysisResultYearAuthors57MC3T3-E1Flux density of either 0.1 or 0.4 mT. Frequency of 10 Hz.Signal transduction pathway, cell proliferation, cell differentiationThe activation of mTOR, increased, BrdU uptake was increased, and ALPase activity was not observed.2019Miyamoto et al. [91]58RAW264.7Frequency of 75 Hz, flux density of 1 mT.Cell viability, cell differentiation, gene expression, protein expressionThe results revealed no significant difference between groups stimulated by PEMF alone and control group.2019Pi et al. [78]59Oligodendrocyte precursor cells (OPCs)Frequency of 50 Hz, intensity of 1.8 mT.Cell differentiation, protein expression, gene expressionPEMF promoted the differentiation of OPCs. PEMF upregulated the expression level of miR-219-5p and downregulated the expression level of Lingo1 during the differentiation of OPCs.2019Yao et al. [5]60Tendon stem and progenitor cells (TDSPCs)Frequency of 125 kHz, intensity of 82 mTCell viability, cell apoptosisThe exposure to PEMF alone did not effect on the viability and apoptosis of cells2019Gehwolf et al. [70]61MC3T3-E1 subclone 4 cellsFrequency of 50 Hz, intensity of 0.60 mTCell morphology, cell viability, cell proliferation, Ca2+ concentration, gene expressionPEMF influenced cell proliferation, did not significantly influence cellular viability, and affected osteogenic differentiation on mRNA level2019Suryani et al. [92]62Bone marrow-derived mesenchymal stem cells (BMSCs) (rat)50 Hz, 1 mTCell proliferation, gene expressionS100, GFAP, and NGF mRNA expression levels were higher on days 5, 7, and 10 of culture.Seo et al. [73]63C3H10T1/2 mesenchymal cellsFrequency of 30 Hz, intensities of 0.1, 1, 2, or 10 mTCell proliferation, cell differentiation, Ca2+ concentration, gene expression, protein expressionCell proliferation was promoted, and intracellular Ca2+ during the process of cell differentiation was increased. The expression of ALP, OSX, Wnt1, phospho-Lrp6, and b-catenin was increased2018Wu et al. [71]Table 11
Rat/mouse cells: cellular response (presence or absence) for cultured rat/mouse cells.
No.Cell lineFrequency and intensityCell response analysisResultYearAuthors64RAW264.7 cellsFrequency of 15 Hz intensities of 0.5, 1, 2, and 3 mTCell apoptosis, gene expressionGene expression of RANK, NFATc1, TRAP, CTSK, BAX, and BAX/BCL was significantly decreased by 0.5 mT PEMF, but increased by 3 mT2017Wang et al. [79]65Spermatogonia germ cell line, (GC-1), spermatocyte cell line (GC-2)Frequencies of 2, 50, and 120 Hz, intensity of 2.5 mTCell proliferation, cell morphology, cellular oxidative stress, protein expression, cell viabilityPEMF resulted in elongated and fibroblast-like shapes in GC-1 spg cells. PEMF increased the total p53 protein level in GC-2 spd cells.2017Solek et al. [83]66Adipose-derived stem cells (ADSCs) isolatedFrequency of 7 Hz, flux density of 30 mTCell apoptosisExposure to PEMF resulted in a significant increase in the proportion of apoptotic cells2017Baranowska et al. [69]67Primary rat nucleus pulposus cellsFrequency of 2 Hz, intensities of 0.5, 1.0, 2.0, and 3.0 A/mCell morphology, cell viability, protein expressionStimulation of nucleus pulposus cells with LF-PEMFs did not appear to affect cell morphology or nucleus pulposus cell IL-1β and TNF-α expression levels.2017Zou et al. [84]68Mouse osteosarcoma cell line (LM8 cells)Frequency of 200 Hz, flux density of 5 mTCa2+ concentration, cell apoptosisThe level of intracellular Ca2+ after PEMF treatment was significantly higher.2017Muramatsu et al. [85]69C2C12 myoblastsFrequency of 100 Hz, flux density of 1 mTCell proliferation, cell apoptosis, signal transduction, pathway, protein expressionIncrease of proliferation, no influence on the apoptosis the phosphorylation level of extracellular, signal-regulated kinase (ERK) was significantly increased, while p38 MAPK and c-Jun N-terminal kinase (JNK) pathways were not affected.2016Xu et al. [96]70Bone marrow stem cells (BMSCs)Frequency of 20 Hz, flux density of 2 mTGene expression, cell differentiationPEMFs significantly promoted the activity of ALP in the BMSCs and mRNA expression of osteogenic proteins2015Lu et al. [74]Table 12
Rat/mouse cells: cellular response (presence or absence) for cultured rat/mouse cells.
No.Cell lineFrequency and intensityCell response analysisResultYearAuthors71Rat bone marrow-derived stem cellsFrequency of 75 HzIntensities of 1, 2, or 5 mTCell proliferationPEMF stimulation did not cause significant changes in rat BMSC proliferation2015Wang et al. [75]72The murine MN9D dopaminergic cell lineFrequency of 5 HzCell morphologyPEMF signals increased cell body width2014Lekhraj et al. [68]73Primary culture osteoblastic cellsIntensities of 0.06 and 0.2 mTCell proliferationCell viabilityCell differentiationCell morphologyControl group had a higher cell proliferation than 0.06 and 0.2 mT PEMF groups2013Emes et al. [86]74RAW 264.7 macrophage-like cells (murine)Frequencies of 5.1 Hz, 7.8 Hz, 10.8 Hz, 15.6 Hz, 20.8 Hz, 23.4 Hz, or 30 Hz.Intensity of 4 mTSignaling pathwaysGene expressionCells exposed to PEMF demonstrated changes in the downregulation of NFkB2013Ross and Harrison [80]75PC12 and NR8383 rat alveolar macrophagesFrequency of 0.172 HzIntensity of 700 mTSignal pathwayEnzyme activityPEMF induced activation of ERK1/2 in PC12 cells2013Tada-Aki et al. [81]76Rat brain cortical neurons, PC12, U87MG cellsFrequency of 75 Hz, intensity of 1.5 mTGene expressionCell apoptosisPEMF treatment induced an upregulation of A3ARs, A2ARs2012Vincenzi et al. [82]77C3H10T1/2 cellsImmortalized calvarial cellsiCALsFrequency of 1000 HzCell differentiationCell proliferationGene expressionProtein expressionPEMF stimulation augmented osteopontin and osteocalcin expression2012Teven et al. [72]78Mesenchymal stem cells (MSCs)Frequency of 50 Hz, intensity of 10 mTCell viability, cell proliferationPEMF increases the proliferation of MSC cells.2012Li et al. [76]Table 13
Rat/mouse cells: cellular response (presence or absence) for cultured rat/mouse cells.
No.Cell lineFrequency and intensityCell response analysisResultYearAuthors79The murine osteoblast-like cell line MC3T3-E1Frequency of 0.5 Hz, intensities of 0.17 mT and 1.33 mTCell proliferationCell differentiationGene expressionProtein expressionThe proliferation and differentiation of cells in PEMF exposure groups changed, COL-I and Cbfa1 mRNA expression and BMP2/4 and Smad1/5/8 protein expression did not change.2011Li et al. [93]80Rat basophilic leukemia cells (RBL-2H3)Frequency of 8 kHz, intensity of 200 mTCell morphologyCell proliferationGene expressionPEMFStimulation led to increased cell proliferation2010Choi et al. [97]81Rat bone marrow cellsFrequency of 8 Hz, intensity of 3.8 mTGene expressionNo statistically significant difference was found between the PEMF group and the control group2010Chen et al. [98]82Neural stem cells (NSCs)Frequency of 0.1 Hz, intensities of 0.5, 1.0, 3.0, 4.0, 5.0, 6.0, 8.0, and 10.0 TCell proliferationCell differentiationExposure of NSCs to PEMFs changed cell proliferation2009Meng et al. [77]83Osteoblast-like MC3T3-E1 cellsPrimary osteoblast cellsFrequency of 48 HzIntensity of 1.55 mTCell proliferationCell differentiationPEMF treatment accelerated the cell proliferation and promoted cell differentiation of the primary osteoblast cell.2008Wei et al. [87]84Rat primary osteoblastic cellsFrequency of 3.8 kHzCell proliferationGene expressionContinuous daily 4 h treatment with PEMF alone increased expression of osteoblast marker genes2007Selvamurugan et al. [88]85A rat osteogenic cell linePhysio-stim® PEMF signalsSignal pathwayPEMF induced rapid phosphorylation reactions of Intracellular signaling molecules2006Schnoke and Midura [89]86MurinePreosteoblastsMC3T3-E1Fibroblast cell linesFrequency of 3850 HzIntensity of 0.4 mTSignal transduction pathwaymTOR pathway was activated within minutes of PEMF exposure2006Patterson et al. [95]Table 14
Rat/mouse cells: cellular response analysis for cultured rat/mouse cells.
No.Cell lineFrequency and intensityCell response analysisResultYearAuthors87Pheochromocytoma cells (PC12)Frequency of 0.25 HzIntensity of 0.25–4.5 TCell viabilitySignal transductionPEMF did not alter the cell viability or content of cAMP2006Sontag and Kalka [47]88Osteoblast-like cellsFrequency of 15 Hz, intensity of 0.1 mTCell proliferationCell differentiationGene expressionPEMF of osteoblasts accelerated cellular proliferation, but did not affect the cellular differentiation2004Chang et al. [90]89MLO-Y4 osteocyte-like cellsROS 17/2.8 cellsFrequency of 15 Hz, intensity of 1.6 mTCell proliferation, cell differentiationProtein expressionEnzyme activityPEMF did not affect cell number, osteocalcin mRNA, or osteocalcin protein2003Lohmann et al. [101]90Osteoblast-like MC3T3-E1 cell lineFrequency of 15 Hz, intensity of 7 mTCell proliferationCell differentiationPEMF treatment accelerated cellular proliferation and enhanced cellular differentiation.2002Diniz et al. [94]Table 15
Other species cell studies.
No.Cell lineFrequency and intensityCell response analysisResultYearAuthors91Intervertebral discs (IVDs) from bovine caudal spinesPulse frequency of 3850 HzProtein expression, signal pathwayOverall p65 expression was increased, and P38 expression was not influenced.2019Tang et al. [99]92Rabbit adipose-derived mesenchymal stem cells (AD-MSCs)Frequencies of 25 Hz and 50 Hz, intensity of 1.6 mTCell proliferationGene expressionPEMF did not cause any significant increase in SOX9 mRNA productions2016Kavand et al. [100]Figure 1
Human cells (stem cells): cellular response (presence or absence) for cultured human cells (3249 in vitro exposures) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Statistical significant cell groups are highlighted. Heterogeneity results:I2=92.03, p value < 0.001.Figure 2
Human cells (cancer cells): cellular response (presence or absence) for cultured human cells (3249 in vitro exposures) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Statistical significant cell groups are highlighted.Figure 3
Human cells (other normal cells): cellular response (presence or absence) for cultured human cells (3249 in vitro exposures) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Statistical significant cell groups are highlighted. Heterogeneity results:I2=92.03, p value < 0.001.Figure 4
Rat/mouse cells: cellular response (presence or absence) for cultured rat/mouse cells (3249 in vitro experiments) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Statistical significant cell groups are highlighted. Heterogeneity results:I2=56.25, p value < 0.001.Figure 5
Other species cells: cellular response (presence or absence) for cultured species cells (3249 in vitro experiments) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Heterogeneity results:I2=70.90, p value = 0.064.


### 2.1. Collection of Raw Data

An electronic literature search of databases including Web of Sciences and PubMed was conducted for publications in English from 1999 up to 2019. The key terms introduced in the search engines included “pulsed electromagnetic fields” and “cell.” The process of selecting the papers was carried out by reading the titles and abstracts of the studies as well as the full article when necessary. Upon omitting duplicate titles, full-text versions of the selected papers were obtained.We excluded those experiments that (1) targeted direct animal or human exposure followed by the analysis of individual cells and (2) applied the combination of PEMFs and other effective treatments, e.g., chemotherapy. After screening many research studies, 92 papers with different designs were eligible for meta-analysis.For data analysis, the cell responses were classified as “presence” (PEMF exposure changed the cell response statistically significantly in comparison to the control group regardless of direction) and “absence” (no significant PEMF effect).For each included study, the following data were extracted: type of cells, pulse frequency of exposure, exposure flux density, time of exposure, waveform, and assayed cell responses (cells, cell function, and DNA). Bibliographic details of the studies including the first author and year of publication were also retrieved.


### 2.2. Analysis of Raw Data

According to the above explanations, given that the frequency and intensity of the mentioned exposure differ across studies, achieving different biological responses would not be unexpected. In this respect, we pooled the retrieved experimental data based on used pulse frequencies and flux densities. Our analysis considered the effect of several subgroups of pulse frequency and flux density as follows: (a)0.1<ƒ≤10Hz, (b) 10<ƒ≤100Hz, (c) 100<ƒHz, (d) I<1mT, (e) 1≤I<10mT, (f) 10≤I<100mT, and (g) 100mT≤I. Also, subgroups of exposure time and waveform were considered as follows: (H) acuteexposure≤24h, (I) acuteexposure>24h, (J) chronicexposure≤10days, (K) chronicexposure>10days, (L) square wave, (M) the bursts consisted of a series of consecutive, (N) triangle wave, and (O) other waveforms.


### 2.3. Statistical Analysis

Microsoft Excel was used to organize the initial data and build a database. Meta-analysis combined the results obtained from separate studies with a similar outcome. The pooled results were obtained based on cell type, frequency, and intensity. A random-effect model was used to facilitate conducting the analysis, through whichI2 value was calculated as the indicator of heterogeneity. I2 values greater than 50% could imply significant heterogeneity between the related studies. Also, the random-effect model could account for the above variation between studies, and thus, it achieved more conservative results than a fixed-effect model. Sensitivity analysis was performed to determine the effect of a particular study on the overall effect size. The presence of publication bias was tested using Begg’s and Egger’s regression asymmetry tests [9]. Statistical analyses were conducted using STATA version 14.0. A p value less than 0.05 was considered significant for all tests.


## 2.1. Collection of Raw Data

An electronic literature search of databases including Web of Sciences and PubMed was conducted for publications in English from 1999 up to 2019. The key terms introduced in the search engines included “pulsed electromagnetic fields” and “cell.” The process of selecting the papers was carried out by reading the titles and abstracts of the studies as well as the full article when necessary. Upon omitting duplicate titles, full-text versions of the selected papers were obtained.We excluded those experiments that (1) targeted direct animal or human exposure followed by the analysis of individual cells and (2) applied the combination of PEMFs and other effective treatments, e.g., chemotherapy. After screening many research studies, 92 papers with different designs were eligible for meta-analysis.For data analysis, the cell responses were classified as “presence” (PEMF exposure changed the cell response statistically significantly in comparison to the control group regardless of direction) and “absence” (no significant PEMF effect).For each included study, the following data were extracted: type of cells, pulse frequency of exposure, exposure flux density, time of exposure, waveform, and assayed cell responses (cells, cell function, and DNA). Bibliographic details of the studies including the first author and year of publication were also retrieved.


## 2.2. Analysis of Raw Data

According to the above explanations, given that the frequency and intensity of the mentioned exposure differ across studies, achieving different biological responses would not be unexpected. In this respect, we pooled the retrieved experimental data based on used pulse frequencies and flux densities. Our analysis considered the effect of several subgroups of pulse frequency and flux density as follows: (a)0.1<ƒ≤10Hz, (b) 10<ƒ≤100Hz, (c) 100<ƒHz, (d) I<1mT, (e) 1≤I<10mT, (f) 10≤I<100mT, and (g) 100mT≤I. Also, subgroups of exposure time and waveform were considered as follows: (H) acuteexposure≤24h, (I) acuteexposure>24h, (J) chronicexposure≤10days, (K) chronicexposure>10days, (L) square wave, (M) the bursts consisted of a series of consecutive, (N) triangle wave, and (O) other waveforms.


## 2.3. Statistical Analysis

Microsoft Excel was used to organize the initial data and build a database. Meta-analysis combined the results obtained from separate studies with a similar outcome. The pooled results were obtained based on cell type, frequency, and intensity. A random-effect model was used to facilitate conducting the analysis, through whichI2 value was calculated as the indicator of heterogeneity. I2 values greater than 50% could imply significant heterogeneity between the related studies. Also, the random-effect model could account for the above variation between studies, and thus, it achieved more conservative results than a fixed-effect model. Sensitivity analysis was performed to determine the effect of a particular study on the overall effect size. The presence of publication bias was tested using Begg’s and Egger’s regression asymmetry tests [9]. Statistical analyses were conducted using STATA version 14.0. A p value less than 0.05 was considered significant for all tests.


## 3. Results

A number of publications are analyzed in Figure6, which provides an overview of the years of publication. Cellular response (presence or absence) was observed in human cells (2441 experiments in Figures 1–3), rat or mouse cells (854 experiments in Figure 4), and other species (11 experiments in Figure 5). The results indicated that most of the experiments were carried out on human cells, among which stem cells drew greater experimental attention. Of not, in case the analysis incorporated such parameters as exposure to PEMFs and individual cell types, the potential effects of PEMFs on cell types, such as bone marrow mesenchymal stem cells (BM-MSCs) (based on 559 reported experiments, p value < 0.001), would become clear. However, based on the reported evidence, no such effect was observed for human adipose-derived mesenchymal stem cells (AD-MSCs) and human osteogenic sarcoma SaOS-2 (p<0.001). As a result, despite the higher susceptibility of cancer cells to PEMFS than that of other cell types, various cancer cells respond differently to PEMF stimulation.Figure 6
Overview of the published year: cellular response (presence or absence) for cultured human, rat/mouse, and other species cells (3249 in vitro exposures) pooling data from 92 peer-reviewed scientific articles. Heterogeneity results:I2=36.12, p value = 0.049.We categorized different experimental techniques as follows: (a) cell structure (cell viability, cell morphology, apoptosis, cell proliferation, and cell differentiation), (b) cell functions (calcium concentration, signal transductions, enzyme activity, membrane potential, and membrane stability), and (c) DNA (gene expression, protein expression, ROS production, chromosome aberration, micronucleus assay, DNA damage, oxidative stress, DNA single-strand breaks, DNA double-strand breaks, and genotoxicity) in Figure7. Our analysis of the reported results (Figure 8) suggests that most of the experiments used experimental techniques for DNA including gene expression, protein expression, and ROS production for assaying the effect of PEMFs on cells.Figure 7
Different experimental techniques: cellular response (presence or absence) for cultured human, rat/mouse, and other species cells (3249 in vitro experiments) pooling data from 92 peer-reviewed scientific articles. Heterogeneity results:I2=98.49, p value < 0.001.Figure 8
Classification of experimental techniques observed from 3306 experiments from 92 peer-reviewed scientific publications (1999-2019). Cells exposed to PEMFs in vitro experiments that reported results (cellular response (presence or absence)) for different exposure conditions (frequency and intensity). These experimental techniques are classified as (i) cells (cell proliferation, cell differentiation, cell viability, cell morphology, and apoptosis), (ii) cell functions (enzyme activity, calcium concentration, signal transductions, membrane potential, and membrane stability), and (iii) DNA (chromosome aberration, micronucleus assay, DNA damage, oxidative stress, DNA single-strand breaks, DNA double-strand breaks, genotoxicity, gene expression, protein expression, and ROS production).We also considered the effects of different pulse frequencies of PEMFs and intensity. To do so, we pooled experimental data based on the frequencies (Figure9), intensity levels (Figure 10), time of exposure (Figure 11), and waveforms (Figure 12) used in each experiment of the 92 publications Among subgroups of frequencies, significant effects were observed at 100Hz<ƒ (p<0.001). However, at frequencies smaller than or equal to 10 Hz, no statistically significant effects were observed. Among subgroups of intensities, the presence of response as a result of PEMFs was seen significantly in intensities between 1 and 10 mT (p<0.05) Analysis of different times of exposure in the studies indicated on effectiveness of PEMFs in chronicexposure>10 days (p<0.001) and absence of cell response in acuteexposure>24h (p<0.001).Figure 9
Different frequency levels: cellular response (presence or absence) for cultured human, rat/mouse, and other species cells (3249 in vitro experiments) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Please note that frequency values were not given in 85 experiments/exposures. Heterogeneity results:I2=96.7, p value < 0.001.Figure 10
Different intensity levels: cellular response (presence or absence) for cultured human, rat/mouse, and other species cells (3249 in vitro experiments) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Please note that intensity values were not given in 624 experiments/exposures. Heterogeneity results:I2=92.36, p value < 0.001.Figure 11
Different time of exposure: cellular response (presence or absence) for cultured human, rat/mouse, and other species cells (3249 in vitro experiments) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Please note that intensity values were not given in 624 experiments/exposures. (a) Heterogeneity results:I2=0.3, p value = 0.765.Figure 12
Different waveforms: cellular response (presence or absence) for cultured human, rat/mouse, and other species cells (3249 in vitro experiments) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Please note that intensity values were not given in 624 experiments/exposures. (b) Heterogeneity results:I2=0.45, p value = 0.87.The cells exposed to PEMFs in in vitro experiments, which reported results (cellular response, either presence, or absence Table1) under different exposure conditions, are shown as follows: (a) classification of experimental techniques in Figure 8, (b) frequency of PEMFs in Figure 13, (c) intensity levels in Figure 14, (d) time of exposure in Figure 15, and (e) waveform in Figure 16. It should be noted that our statistical test only reports the presence or absence of cellular responses in the literature, and it is not concerned with the increased or reduced effect of the mentioned responses.Figure 13
Frequency range observed from 3306 experiments studies from 92 peer-reviewed scientific publications (1999-2019). Cells exposed to PEMFs in vitro experiments that reported results (cellular response (presence or absence)) for different exposure conditions (frequency and intensity). Frequency values are shown in Hz.Figure 14
Intensity observed from 3306 experiments from 92 peer-reviewed scientific publications (1999-2019). Cells exposed to PEMFs in vitro experiments that reported results (cellular response (presence or absence)) for different exposure conditions. Intensity values are shown in mT.Figure 15
Time of exposure observed from 3306 experiments from 92 peer-reviewed scientific publications (1999-2019). Cells exposed to PEMFs in vitro experiments that reported results (cellular response (presence or absence)) for different exposure conditions.Figure 16
Waveforms observed from 3306 experiments from 92 peer-reviewed scientific publications (1999-2019). Cells exposed to PEMFs in vitro experiments that reported results (cellular response (presence or absence)) for different exposure conditions.


## 4. Publication Bias and Sensitivity Analysis

The results of Egger’s and Begg’s test demonstrated no publication bias in the meta-analysis of cellular response (presence or absence) in human cells, rat or mouse cells, and other species according to different frequencies and intensity levels (p values for Begg’s test and Egger’s test for all categorizes were >0.05). To evaluate the effect of each single study on the pooled effect size, we removed each study, one by one. We found no significant effects of any individual study on the combined effect sizes in different meta-analysis presentation.


## 5. Discussion

This study scrutinized the related scientific literature for the association between PEMFs and cell responses in vitro. Realizing that there were distinctions between cell types in terms of apoptosis, rate of proliferation and age, and other characteristics and that PEMFs parameters can be characterized in terms of frequency, intensity, time of exposure, and waveform, we investigated if there were distinct properties of positive and negative findings associated with these characteristics. The results showed that there was no significant difference between the presence and absence of the cell response to PEMF stimulation in human cells, rat/mouse cells, and other species (Figure17 for each row (p>0.05)). However, several aspects of our results are notable, which are given below.Figure 17
Cellular response (presence or absence) for cultured human, rat/mouse, and other species cells (3249 in vitro exposures) pooling data from 92 peer-reviewed scientific articles published in 1999-2019. Heterogeneity results:I2=88.92, p value < 0.001.Our findings demonstrated that in in vitro studies, nearly 50% of human cells (Figure17) would undergo changes due to PEMFs, whereas fewer number of cells in rats/mice (44.61%) and other species (18.18%) were influenced by PEMFs. Thus, a large number of experiments on cells in rats/mice and other species pointed out the absence of any effect caused by PEMFs. Among the studies conducted on human cells, most of them were performed on stem cells. According to the results, it seems that the type of stem cell plays as an effective factor in intracellular processes affected by PEMFs. Especially, in the field of bone tissue engineering in which mesenchymal stem cells are activated by EMF, this finding would be considerable.Another significant finding of our study was among osteoblast-like cells, MG-63 human osteosarcoma cells seem to be very sensitive to PEMFs (86.1%). The studies have shown that these fields could alter activity through changes in local factor production [4]. However, in human osteogenic sarcoma SaOS-2, the absence of cell response to PEMFs alone was greater in degree than the presence of cell response (75%). PEMFs appeared to have little effect on the phenotype and number of SaOS-2 cells [7].The potential effects of PEMFs on tendon cells showed that these fields (87.74%), focusing on the potential applicability of this cell source for regenerative medicine purpose, could be effective in the treatment of tendon disorders. In fact, these fields could influence the proliferation, release of anti-inflammatory cytokines, tendon-specific marker expression, and angiogenic factor in healthy human TCs culture models [15].Analysis of the results of other related studies concerning the effect of PEMFs on the cells of blood cancers like leukemia and lymphoma in human (and on basophilic leukemia cells in rats/mice) showed that these cells were not affected to PEMFs. Thus, it seems that these fields alone are not an effective treatment for blood cancers. Further investigations are required to examine the responsiveness of different types of blood cancer cells to PEMFs. Evaluation of different experimental techniques used in the studies showed that most of the experiments were carried out on the expression of genes and proteins, because PEMFs could verifiably promote bone fracture healing and enhance the maturation of osteoblastic cells. Also, most of studies have examined the effect of osteogenic differentiation of these fields on mRNA level.Another part of this study focused on evaluating the role of intensity and frequency of PEMFs in stimulating cellular responses in the subgroups. This research was subject to some constraints; first, some of the related experimental studies did not provide sufficient descriptions of exposure signal characteristics, especially in expressing waveform, which in turn made us unable to interpret the results fully. Nevertheless, analysis of frequencies of PEMFs used in the studies showed that different frequencies corresponded to different levels of cellular response. In the subgroups, frequencies higher than 100 Hz and intensities between 1 and 10 mT seemed to be more effective in establishing a cellular response. In addition, the analysis of times of exposure showed that in chronic exposure to PEMF more than 10 days may observe the effect of these fields (presence: 57.66%, absence: 42.34%;p<0.01), while acute exposure more than 24 h may cause to less effect (presence: 17.87%, absence: 82.13%, p<0.01).It is worth noting that we may be able to find optimal parameters of PEMF in future studies in the effective ranges obtained from the present study to achieve the most effective response, depending on the desired effect.Basically, in vitro studies use cells to investigate the interaction mechanisms better by breaking down the complexity of a whole organism into a controllable system. Indeed, each cell with a model system of its own could be suitable for a specific biological aspect. Therefore, although it cannot be expected that humans respond to PEMFs, studies of simple biological systems can advance our understanding about which systems in the body are more susceptible to PEMFs. Therefore, conducting an analysis similar to the present meta-analysis could be useful as a reference for many epidemiological studies or in vivo experiments using the whole organism animal models.


## 6. Conclusion

To the best of our knowledge, no other meta-analysis has investigated the effects of PEMF on cell responses in vitro. The findings of this study provided us insight into that which cell types could be more responsive to PEMFs. Additionally, we determined the range of frequencies and intensities which PEMFs appeared more effective. Future research would need to explore the effects of other variables on cell response in vitro and to investigate the effectiveness of PEMFs in vivo.



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*Source: 6647497-2021-07-29.xml*