Effects of Static Magnetic Fields on Bone Formation in Rat Osteoblast Cultures

Comprehensive Review of Adipose Stem Cells and Their Implication in Distraction Osteogenesis and Bone Regeneration

Bone is one of the most dynamic tissues in the human body that can heal following injury without leaving a scar. However, in instances of extensive bone loss, this intrinsic capacity of bone to heal may not be sufficient and external intervention becomes necessary. Several techniques are available to address this problem, including autogenous bone grafts and allografts. However, all these techniques have their own limitations. An alternative method is the technique of distraction osteogenesis, where gradual and controlled distraction of two bony segments after osteotomy leads to induction of new bone formation. Although distraction osteogenesis usually gives satisfactory results, its major limitation is the prolonged duration of time required before the external fixator is removed, which may lead to numerous complications. Numerous methods to accelerate bone formation in the context of distraction osteogenesis have been reported. A viable alternative to autogenous bone grafts for a source of osteogenic cells is mesenchymal stem cells from bone marrow. However, there are certain problems with bone marrow aspirate. Hence, scientists have investigated other sources for mesenchymal stem cells, specifically adipose tissue, which has been shown to be an excellent source of mesenchymal stem cells. In this paper, the potential use of adipose stem cells to stimulate bone formation is discussed.

Cytotoxic and genotoxic effects on gingival fibroblasts from static magnetic fields produced by dental magnetic attachments

OBJECTIVE

To investigate cytotoxic and genotoxic effects of static magnetic field (SMF) produced by dental magnetic attachments on human gingival fibroblasts in vitro.

BACKGROUND

Magnetic attachments have numerous roles in dental prosthesis fixation, but few reports evaluate possible biological effects of static magnetic field (SMF) on human gingival tissues, particular genotoxic effects.

MATERIALS AND METHODS

The Dyna (500-gr breakaway force) and Steco (173-gr breakaway force) dental magnetic attachments were embedded into autopolymerising acrylic resin in four different configurations each, including single and double magnets. Gingival biopsy was performed on 28 individuals during third molar extraction, and each sample was divided into two pieces for culture under SMF exposure or as a control. In total, seven test and seven control gingival fibroblast cultures were performed for each group resulting in 56 gingival fibroblast cultures. The test culture flasks were placed atop the magnet-embedded resin blocks. After cultures were terminated, mitotic index (MI) and micronucleus (MN) rates were analysed at a p = 0.05 significance level by Wilcoxon's test; intergroup differences were analysed with a Kruskal-Wallis test.

RESULTS

There was no significant difference in intragroup or intergroup MI rates. The double Dyna (p = 0.023) and double Steco (p = 0.016) groups had statistically significant intragroup differences in the MN rates. There were no statistically significant differences in MN rates in intergroup analyses.

CONCLUSION

In particular, higher magnetic fields from dental magnetic attachments might be toxic genetically to human gingival fibroblasts. However, there is need for further investigations from different aspects to detect any genotoxicity.

Novel magnetic nanocomposite injectables: calcium phosphate cements impregnated with ultrafine magnetic nanoparticles for bone regeneration

Novel magnetic nanocomposite injectables made of calcium phosphate cements and magnetite nanoparticles demonstrated excellent physico-chemical and biological properties effective for bone regeneration.

A hypomagnetic field aggravates bone loss induced by hindlimb unloading in rat femurs

A hypomagnetic field is an extremely weak magnetic field--it is considerably weaker than the geomagnetic field. In deep-space exploration missions, such as those involving extended stays on the moon and interplanetary travel, astronauts will experience abnormal space environments involving hypomagnetic fields and microgravity. It is known that microgravity in space causes bone loss, which results in decreased bone mineral density. However, it is unclear whether hypomagnetic fields affect the skeletal system. In the present study, we aimed to investigate the complex effects of a hypomagnetic field and microgravity on bone loss. To study the effects of hypomagnetic fields on the femoral characteristics of rats in simulated weightlessness, we established a rat model of hindlimb unloading that was exposed to a hypomagnetic field. We used a geomagnetic field-shielding chamber to generate a hypomagnetic field of <300 nT. The results show that hypomagnetic fields can exacerbate bone mineral density loss and alter femoral biomechanical characteristics in hindlimb-unloaded rats. The underlying mechanism might involve changes in biological rhythms and the concentrations of trace elements due to the hypomagnetic field, which would result in the generation of oxidative stress responses in the rat. Excessive levels of reactive oxygen species would stimulate osteoblasts to secrete receptor activator of nuclear factor-κB ligand and promote the maturation and activation of osteoclasts and thus eventually cause bone resorption.

Moderate-intensity rotating magnetic fields do not affect bone quality and bone remodeling in hindlimb suspended rats

Abundant evidence has substantiated the positive effects of pulsed electromagnetic fields (PEMF) and static magnetic fields (SMF) on inhibiting osteopenia and promoting fracture healing. However, the osteogenic potential of rotating magnetic fields (RMF), another common electromagnetic application modality, remains poorly characterized thus far, although numerous commercial RMF treatment devices have been available on the market. Herein the impacts of RMF on osteoporotic bone microarchitecture, bone strength and bone metabolism were systematically investigated in hindlimb-unloaded (HU) rats. Thirty two 3-month-old male Sprague-Dawley rats were randomly assigned to the Control (n = 10), HU (n = 10) and HU with RMF exposure (HU+RMF, n = 12) groups. Rats in the HU+RMF group were subjected to daily 2-hour exposure to moderate-intensity RMF (ranging from 0.60 T to 0.38 T) at 7 Hz for 4 weeks. HU caused significant decreases in body mass and soleus muscle mass of rats, which were not obviously altered by RMF. Three-point bending test showed that the mechanical properties of femurs in HU rats, including maximum load, stiffness, energy absorption and elastic modulus were not markedly affected by RMF. µCT analysis demonstrated that 4-week RMF did not significantly prevent HU-induced deterioration of femoral trabecular and cortical bone microarchitecture. Serum biochemical analysis showed that RMF did not significantly change HU-induced decrease in serum bone formation markers and increase in bone resorption markers. Bone histomorphometric analysis further confirmed that RMF showed no impacts on bone remodeling in HU rats, as evidenced by unchanged mineral apposition rate, bone formation rate, osteoblast numbers and osteoclast numbers in cancellous bone. Together, our findings reveal that RMF do not significantly affect bone microstructure, bone mechanical strength and bone remodeling in HU-induced disuse osteoporotic rats. Our study indicates potentially obvious waveform-dependent effects of electromagnetic fields-stimulated osteogenesis, suggesting that RMF, at least in the present form, might not be an optimal modality for inhibiting disuse osteopenia/osteoporosis.

Study of biocompatibility of medical grade high nitrogen nickel-free austenitic stainless steel in vitro

Adverse effects of nickel ions being released into the living organism have resulted in development of high nitrogen nickel-free austenitic stainless steels for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also improves steel properties. The cell cytocompatibility, blood compatibility and cell response of high nitrogen nickel-free austenitic stainless steel were studied in vitro. The mechanical properties and microstructure of this stainless steel were compared to the currently used 316L stainless steel. It was shown that the new steel material had comparable basic mechanical properties to 316L stainless steel and preserved the single austenite organization. The cell toxicity test showed no significant toxic side effects for MC3T3-E1 cells compared to nitinol alloy. Cell adhesion testing showed that the number of MC3T3-E1 cells was more than that on nitinol alloy and the cells grew in good condition. The hemolysis rate was lower than the national standard of 5% without influence on platelets. The total intracellular protein content and ALP activity and quantification of mineralization showed good cell response. We conclude that the high nitrogen nickel-free austenitic stainless steel is a promising new biomedical material for coronary stent development.

Fabrication and magnetic testing of a poly-L-lactide biocomposite incorporating magnetite nanoparticles

Polylactic acid (PLA)-based composite has been widely used in tissue engineering. To modify the material’s properties, inorganic substances have been used to form nanoparticle-PLA composites. The aim of this study is to develop a novel magnetic biodegradable composite. Nanoscale magnetite (Fe3O4) was incorporated into a poly-L-lactide (PLLA) matrix with proportions of 0%, 5%, 10%, and 15% (w/w). Injection molding was carried out to produce the nano-magnetite-PLLA composite samples. X-ray diffraction (XRD), differential scanning calorimetry (DSC), superconducting quantum device (SQUID), and three-point bending were performed to test the physical properties of the magnetite-PLLA composite. The results showed that the magnetite-PLLA composite exhibited typical ferromagnetic hysteresis loops. The addition of nanoscale magnetite significantly increased the magnetic flux density of the PLLA composite. These results suggest that the magnetite-PLLA composite has the potential to be used for future applications in tissue engineering.

Development and biocompatibility tests of electrospun poly-l-lactide nanofibrous membranes incorporating oleic acid-coated Fe3O4

The aim of this study was to develop an electrospun poly-l-lactide (PLLA) nanofibrous membrane incorporating oleic acid-coated Fe3O4. The Fe3O4 nanoparticles were prepared using the chemical co-precipitation method, and particle diameters were analyzed using transmission electron microscopy. After mixing the oleic acid-coated Fe3O4 nanoparticles and PLLA, a membrane with nanofibers was manufactured using the electrospinning technique. Our results showed that Fe3O4 nanoparticle diameters fabricated in this study were concentrated at 2–8 nm (84.2%). After magnetizing, there exists an approximately linear relationship between magnetic flux density and membrane thickness (R2=0.7, p<0.05). NIH-3T3 fibroblast cells cultured on the magnetized Fe3O4/PLLA nanomembranes exhibited a more spreading and attached phenotype. These results can serve as a reference for future advanced studies.

Osteogenic activity of titanium surfaces with nanonetwork structures

Background

Titanium surfaces play an important role in affecting osseointegration of dental implants. Previous studies have shown that the titania nanotube promotes osseointegration by enhancing osteogenic differentiation. Only relatively recently have the effects of titanium surfaces with other nanostructures on osteogenic differentiation been investigated.

Methods

In this study, we used NaOH solutions with concentrations of 2.5, 5.0, 7.5, 10.0, and 12.5 M to develop a simple and useful titanium surface modification that introduces the nanonetwork structures with titania nanosheet (TNS) nanofeatures to the surface of titanium disks. The effects of such a modified nanonetwork structure, with different alkaline concentrations on the osteogenic differentiation of rat bone marrow mesenchymal stem cells (BMMSCs), were evaluated.

Results

The nanonetwork structures with TNS nanofeatures induced by alkali etching markedly enhanced BMMSC functions of cell adhesion and osteogenesis-related gene expression, and other cell behaviors such as proliferation, alkaline phosphatase activity, extracellular matrix deposition, and mineralization were also significantly increased. These effects were most pronounced when the concentration of NaOH was 10.0 M.

Conclusion

The results suggest that nanonetwork structures with TNS nanofeatures improved BMMSC proliferation and induced BMMSC osteogenic differentiation. In addition, the surfaces formed with 10.0 M NaOH suggest the potential to improve the clinical performance of dental implants.

The effects of static magnetic fields on bone

All the living beings live and evolve under geomagnetic field (25-65 μT). Besides, opportunities for human exposed to different intensities of static magnetic fields (SMF) in the workplace have increased progressively, such SMF range from weak magnetic field (<1 mT), moderate SMF (1 mT-1 T) to high SMF (>1 T). Given this, numerous scientific studies focus on the health effects and have demonstrated that certain magnetic fields have positive influence on our skeleton systems. Therefore, SMF is considered as a potential physical therapy to improve bone healing and keep bones healthy nowadays. Here, we review the mechanisms of effects of SMF on bone tissue, ranging from physical interactions, animal studies to cellular studies.

The influence of static magnetic fields on canine and equine mesenchymal stem cells derived from adipose tissue

The aim of this study was to evaluate the proliferation rate and morphological changes of adipose-derived mesenchymal stem cells of canine and equine origin (Eq- and CaAdMSC). Investigated cells were exposed to a static magnetic field (MF) with the intensity of 0.5 T. Proliferation activity of cells was determined with the Alamar Blue assay. Obtained results, normalized in respect to the control culture, showed that EqAdMSC exposed to MF maintained a high proliferation status, whereas proliferation activity of CaAdMSC cultured in the presence of MF was decreased. Estimations of population doubling time (PDT) also revealed that EqAdMSCs exposed to static MF achieved a twofold increase in the total number of cells in a shorter amount of time than the control culture. The PDT value obtained for investigated CaAdMSCs indicated that MF exposure resulted in the prolongation of population doubling time. Morphology of cells and cellular composition was investigated using a light inverted microscope and a fluorescent microscope. A scanning electron microscope was used for microvesicles (MVs) imaging. Obtained results showed that both cell types maintained fibroblastic morphology and did not reveal signs of apoptosis or necrosis. However, the MF had an influence on the MVs secretion. While EqAdMSCs propagated in the presence of MF were characterized by the abundant MVs presence, CaAdMSCs revealed poor secretory activity. The approach presented provides complex analysis, which enables one to determine changes in equine and canine cytophysiology.

Examination of extremely low frequency electromagnetic fields on orthodontic tooth movement in rats

The purpose of this study was to evaluate whether 50 Hz extremely low frequency electromagnetic fields (ELF-EMFs) affect the amount of orthodontic tooth movement in rats. The experiments were performed on 18 male Sprague-Dawley rats. The rats were randomly divided into three groups (n = 6): cage-control (Cg-Cnt) group (n = 6); sinusoidal electromagnetic field (SEMF) group (n = 6); and pulsed electromagnetic field (PEMF) group (n = 6). In SEMF and PEMF groups, rats were subjected to 1.5 mT EMF exposure eight hours per day for eight days. In order to obtain tooth movement, holes were drilled on the right and left maxillary central incisors of the rats at a distance 1.5-2 mm away from the gingiva and 20 g of orthodontic forces were applied to the teeth. Generated linear model for repeated measures and Bonferroni tests were used to evaluate the differences between the groups. Interactions among groups by days were found by using Pillai's trace multivariate test. The results showed that significant differences were present among the groups (F = 5.035; p = 0.03) according to the extent of tooth movement. Significant differences between the amount of tooth movements were determined especially after the fifth day and the following days six, seven and eight (p < 0.001). Within the limitations, according to the results of the present study, the application of ELF-EMF accelerated the orthodontic tooth movement in rats.

Modifying bone scaffold architecture in vivo with permanent magnets to facilitate fixation of magnetic scaffolds

The fundamental elements of tissue regeneration are cells, biochemical signals and the three-dimensional microenvironment. In the described approach, biomineralized-collagen biomaterial functions as a scaffold and provides biochemical stimuli for tissue regeneration. In addition superparamagnetic nanoparticles were used to magnetize the biomaterials with direct nucleation on collagen fibres or impregnation techniques. Minimally invasive surgery was performed on 12 rabbits to implant cylindrical NdFeB magnets in close proximity to magnetic scaffolds within the lateral condyles of the distal femoral epiphyses. Under this static magnetic field we demonstrated, for the first time in vivo, that the ability to modify the scaffold architecture could influence tissue regeneration obtaining a well-ordered tissue. Moreover, the association between NdFeB magnet and magnetic scaffolds represents a potential technique to ensure scaffold fixation avoiding micromotion at the tissue/biomaterial interface.

Cell behaviors on magnetic electrospun poly-D, L-lactide nanofibers

It is widely accepted that magnetic fields have an influence on cell behaviors, but the effects are still not very clear since the magnetic field's type, intensity and exposure time are different. In this study, a static magnetic field (SMF) in moderate intensity (10mT) was employed to investigate its effect on osteoblast and 3T3 fibroblast cell behaviors cultured respectively with magnetic polymer nanofiber mats. The magnetic mats composed of random oriented or aligned polymer nanofibers were fabricated by electrospinning the mixed solution of poly-d, l-lactide (PLA) and iron oxide nanoparticles. The fiber morphology was characterized by scanning electron microscopy (SEM), the nanoparticle distribution in fiber matrix was measured with transmission electron microscope (TEM). Mechanical properties of nanofiber mats are studied by uniaxial tensile test. The results showed the nanofibers loaded with magnetic nanoparticles displayed excellent magnetic responsibility and biodegradability. In vitro cytotoxicity analysis demonstrated that the osteoblast proliferation of all fiber mats stimulated with or without SMF was increased with the increase of the culturing days. Furthermore, in the horizontal SMFs, cell orientation tended to deviate from nanofiber orientation to field direction while the nanofiber orientation is perpendicular to the field direction, while the horizonal direction of SMFs could also direct the cell growth orientation. The magnetic nanofiber mats provide a potential platform to explore the cell behaviors under the stimulation of external magnetic field.

Enhancement of differentiation and mineralisation of osteoblast-like cells by degenerate electrical waveform in an in vitro electrical stimulation model compared to capacitive coupling

Electrical stimulation (ES) is effective in enhancing bone healing, however the best electrical waveform, mode of application and mechanisms remains unclear. We recently reported the in vitro differential healing response of a novel electrical waveform called degenerate sine wave (DW) compared to other forms of ES. This study further explores this original observation on osteoblast cells. Here, we electrically stimulated SaOS-2 osteoblast-like cells with DW in an in vitro ES chamber (referred to as ‘DW stimulation’) and compared the intracellular effects to capacitive coupling (CC) stimulation. ES lasted for 4 h, followed by an incubation period of 20 h and subsequent ES for 4 additional hours. Cytotoxicity, proliferation, differentiation and mineralisation of the osteoblast-like cells were evaluated to determine the cell maturation process. DW significantly enhanced the differentiation of cells when compared to CC stimulation with increased alkaline phosphatase and collagen I gene expression by quantitative real time- polymerase chain reaction analysis (p<0.01). Moreover, DW significantly increased the mineralisation of cells compared to CC stimulation. Furthermore the transcription of osteocalcin, osteonectin, osteopontin and bone sialoprotein (p<0.05) was also up regulated by DW. However, ES did not augment the proliferation of cells. Translational analysis by immunocytochemistry and Western blotting showed increased collagen I, osteocalcin and osteonectin expression after DW than CC stimulation. In summary, we have demonstrated for the first time that DW stimulation in an in vitro ES chamber has a significant effect on maturation of osteoblast-like cells compared to CC stimulation of the same magnitude.

Construction of microenvironment onto titanium substrates to regulate the osteoblastic differentiation of bone marrow stromal cells in vitro and osteogenesis in vivo

To mimic the extracellular matrix of natural bone, apatite/gelatin composite was deposited onto nanostructured titanium substrates via a coprecipitation method, which was pretreated by potassium hydroxide and heat treatment to generate an anticorrosive nanostructured layer. The successful formation of the apatite/gelatin nanocomposite onto titanium surfaces was revealed by Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, atomic force microscopy (AFM), and thin film X-ray diffraction (TF-XRD) measurements, respectively. The immunofluorescence staining of vinculin revealed that the apatite/gelatin nanocomposite deposited titanium substrate was favorable for cell adhesion. More importantly, bone marrow stromal cells cultured onto the apatite/gelatin nanocomposite deposited titanium substrates displayed significantly higher (p < 0.05 or p < 0.01) proliferation and differentiation levels of alkaline phosphatase, mRNA expressions of osteocalcin (OC), osteopontin (OPN), and collagen type I (Col I), and OC content after culture for 7, 14, and 21 days, respectively, which was also revealed by the immunofluorescence analysis of OC and OPN expression. The deposition of apatite/gelatin nanocomposite improved bone density (p < 0.05) and bone-implant contact rate (p < 0.05), which was reflected by microcomputed tomography analysis and histological evaluation in vivo using a rabbit model. This work provides an approach to fabricate high-performance titanium-based implants with enhanced bone osseointegration.

Regulation of the behaviors of mesenchymal stem cells by surface nanostructured titanium

The study describes the influence of surface nanostructured titanium substrates on the growth behaviors of mesenchymal stem cells. Surface nanostructures of titanium were produced with surface mechanical attrition treatment (SMAT) technique. The morphologies of native titanium and surface nanostructured titanium substrates were characterized by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and contact-angle measurements, respectively. A thin nanostructured layer was formed onto the surfaces of titanium substrates after SMAT treatment. The effects of the surface nanostructured titanium substrates on the adhesion, spreading, proliferation and differentiation of mesenchymal stem cells (MSCs) was examined at cellular and molecular levels in vitro. The results suggest that the surface nanostructured substrates were beneficial for the growth of MSCs, including adhesion, filament orientation, proliferation and gene expression. This approach for the fabrication of surface nanostructured titanium may be exploited in the development of high performance titanium-based implants.

Synthesis and spectroscopic characterization of magnetic hydroxyapatite nanocomposite using ultrasonic irradiation

Nowadays magnetic hydroxyapatite (m-HAP) has potential applications in biomedicine more especially for bone cancer treatment. In this paper the functionalization of the hydroxyapatite (HAP) with magnetite nanoparticle (MNP) through ultrasonic irradiation technique is reported and its spectral investigation has been carried out. The ultrasonic irradiation with two different frequencies of 28kHz and 35kHz at the power of 150 and 320W, respectively, was employed for the synthesis of m-HAP. The ultrasound irradiation of 35kHz at 320W shows the efficient diffusion of MNP to the HAP host matrix leads to the formation of m-HAP. The ultrasonic irradiation technique does not require stabilizers as in the case of coprecipitation method hence the final product of pure m-HAP is obtained. The X-ray diffraction pattern shows the formation of magnetite nanoparticles which are functionalized with hydroxyapatite host matrix. The vibrating sample magnetometer curve exhibits the super paramagnetic property of the samples and the saturation magnetization (M(s)) value of the functionalized magnetic hydroxyapatite. The M(s) value is found to be much less than that of pure magnetite nanoparticle and this decrement in M(s) is due to the hindrance of magnetic domain of the particles with HAP. The portrayed Raman spectra discriminate between the m-HAP and MNP with corresponding vibrational modes of frequencies. The transmission electron micrograph shows excellent morphology of functionalized m-HAP in nanometer range. The atomic force microscopic investigation shows the 3-dimensional view of crust and trench shape of m-HAP. All these results confirm the formation of magnetic hydroxyapatite nanocomposite with typical magnetic property for biological applications.

TiO2 nanotubes as drug nanoreservoirs for the regulation of mobility and differentiation of mesenchymal stem cells

The extracellular microenvironment plays a key role in the regulation of cellular behavior. To mimic the natural extracellular microenvironment, TiO(2) nanotube (TNT) arrays as drug nanoreservoirs for loading of bone morphogenetic protein 2 (BMP2) were constructed on titanium substrates and then covered with multilayered coatings of gelatin/chitosan (Gel/Chi) for controlled drug release. The multilayered coatings were constructed via a spin-assisted layer-by-layer assembly technique. The successful fabrication of this system was monitored by field emission scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and contact angle measurements. Multilayered coating with Gel/Chi retained the drug bioactivity and release properties, which were revealed by superoxide dismutase activity measurement. In addition, cytoskeleton observation and wound healing assay confirmed that BMP2-loaded and multilayer-coated TNT arrays were able to stimulate motogenic responses of mesenchymal stem cells (MSCs). More importantly, the system demonstrated that it was capable of promoting the osteoblastic differentiation of MSCs. This study may have potential impact on the development of bone implants for enhanced bone osseointegration.

Effects of 50 Hz sinusoidal electromagnetic fields of different intensities on proliferation, differentiation and mineralization potentials of rat osteoblasts

Electromagnetic fields (EMFs) have been used clinically to slow down osteoporosis and promote fracture healing for many years. However, the underlying action mechanisms and optimal parameters of the EMF applications are unclear. In this study, we investigated the effects of treatment for different durations with 50 Hz sinusoidal electromagnetic fields (SEMFs) at different intensities on proliferation, differentiation and mineralization potentials of rat osteoblasts. Osteoblasts isolated from neonatal rats were treated with SEMFs (50 Hz at 0.9 mT-4.8 mT, 0.3 mT interval, 30 min/day up to 15 days). Compared to untreated control, SEMFs inhibited osteoblast proliferation (after 3 days' treatment) but increased alkaline phosphatase (ALP) activity (after treatment for 9 days) from 0.9 mT to 1.8 mT, declined from 1.8 mT until 3.0 mT, and then increased again from 3.0 mT to 3.6 mT and decreased once again from 3.6 mT to 4.8 mT. Numbers of colonies stained positive for ALP after 8 days and mineralized nodules stained by Alizarin red after 10 days showed the same bimodal tendency as with the ALP activity, with two peaks at 1.8 mT and 3.6 mT. SEMFs also bimodally increased Runx-2, Col1α2 and Bmp-2 mRNA expression levels in osteoblasts at 12, 24 and 96 h after exposure. The results indicated that while exposure to 50 Hz SEMFs inhibits the osteoblast proliferation, it significantly promotes differentiation and mineralization potentials of osteoblasts in an intensity-dependent manner with peak activity at 1.8 mT and 3.6 mT.

Recovery Effects of a 180 mT Static Magnetic Field on Bone Mineral Density of Osteoporotic Lumbar Vertebrae in Ovariectomized Rats

The effects of a moderate-intensity static magnetic field (SMF) on osteoporosis of the lumbar vertebrae were studied in ovariectomized rats. A small disc magnet (maximum magnetic flux density 180 mT) was implanted to the right side of spinous process of the third lumbar vertebra. Female rats in the growth stage (10 weeks old) were randomly divided into 4 groups: (i) ovariectomized and implanted with a disc magnet (SMF); (ii) ovariectomized and implanted with a nonmagnetized disc (sham); (iii) ovariectomized alone (OVX) and (vi) intact, nonoperated cage control (CTL). The blood serum 17-β-estradiol (E₂) concentrations were measured by radioimmunoassay, and the bone mineral density (BMD) values of the femurs and the lumbar vertebrae were assessed by dual energy X-ray absorptiometry. The E₂ concentrations were statistically significantly lower for all three operated groups than those of the CTL group at the 6th week. Although there was no statistical significant difference in the E₂ concentrations between the SMF-exposed and sham-exposed groups, the BMD values of the lumbar vertebrae proximal to the SMF-exposed area statistically significantly increased in the SMF-exposed group than in the sham-exposed group. These results suggest that the SMF increased the BMD values of osteoporotic lumbar vertebrae in the ovariectomized rats.

The role of the calmodulin-dependent pathway in static magnetic field-induced mechanotransduction

While the effects of static magnetic fields (SMFs) on osteoblastic differentiation are well demonstrated, the mechanotransduction pathways of SMFs are still unclear. The aim of this study was to explore the role of calmodulin in the biophysical effects of SMFs on osteoblastic cells. MG63 cells were exposed to a 0.4 T SMF. The expression of phosphodiesterase RNA in the cytoplasm was tested using real-time polymerase chain reaction. The differentiation of the cells was assessed by detecting changes in alkaline phosphatase activity. The role of calmodulin antagonist W-7 was used to evaluate alterations in osteoblastic proliferation and differentiation after the SMF simulations. Our results showed that SMF exposure increased alkaline phosphatase activity and phosphodiesterase 1C gene expression in MG63 cells. Addition of W-7 significantly inhibited the SMF-induced cellular response. We suggest that one possible mechanism by which SMFs affects osteoblastic maturation is through a calmodulin-dependent mechanotransduction pathway.

Surface engineering of titanium with potassium hydroxide and its effects on the growth behavior of mesenchymal stem cells

To improve the corrosion resistance and biological performance of commercially pure titanium (cp-Ti) substrates, potassium hydroxide was employed to modify the surfaces of titanium substrates, followed by biomimetic deposition of apatite on the substrates in a simulated body fluid. The morphologies of native and treated titanium substrates were characterized by field emission scanning electron microscopy (FE-SEM). Treatment with potassium hydroxide led to the formation of intermediate layers of potassium titanate on the surfaces of titanium substrates, while apatite was subsequently deposited onto the intermediate layer. The formation of potassium titanate and apatite was confirmed by thin-film X-ray diffraction and FE-SEM equipped with energy dispersive spectroscopy, respectively. Electrochemical impedance spectroscopy showed that the formed potassium titanate layer improved the corrosion-resistance properties of titanium substrates. The influence of modified titanium substrates on the biological behavior of mesenchymal stem cells (MSCs), including osteogenic differentiation, was investigated in vitro. Compared with cp-Ti substrates, MSCs cultured onto alkali- and heat-treated titanium substrates and apatite-deposited titanium substrates displayed significantly higher (P<0.05 or P<0.01) proliferation and differentiation levels of alkaline phosphatase and osteocalcin in 7 and 14day cultures, respectively. More importantly, our results suggest that the modified titanium substrates have great potential for inducing MSCs to differentiate into osteoblasts. The approach presented here may be exploited to fabricate titanium-based implants.

The static magnetic field accelerates the osteogenic differentiation and mineralization of dental pulp cells

Dental pulp cells (DPCs) can differentiate into osteoblasts and are deemed a promising cell source for bone regeneration. Static magnetic field (SMF) stimulates osteoblast differentiation but the effect in DPCs remains unknown. The aim of this study was to investigate the effect of SMF exposure on the osteogenic differentiation and mineralization of rat DPCs in vitro. Cells were continuously exposed to SMF at 290 mT in the presence/absence of osteogenic induction [dexamethasone (Dex)/beta-glycerophosphate (beta-GP)]. Results showed that SMF alone did not impair the cell cycle and proliferation. On the other hand, obvious condensation in the metachromatic staining of the extracellular matrix with toluidine blue was observed for SMF-exposed cells as well as the Dex/beta-GP treated cells. SMF in combination with Dex/beta-GP significantly increased the mRNA expression of osteogenic genes, as well as the ALP activity and extracellular calcium concentration at the early stage, followed by obvious calcium deposits later. Besides, SMF exposure increased the activity of extracellular signal-regulated kinase 1/2 (ERK1/2) at 3 h and accelerated the mRNA expression of osteogenic transcription factor, Cbfa1, advancing its activation time from 168 to 72 h under osteogenic induction. In summary, SMF exposure in combination of Dex/beta-GP induction could significantly accelerate the osteogenic differentiation and mineralization of DPCs.

A novel calcium phosphate ceramic-magnetic nanoparticle composite as a potential bone substitute

A magnetic field has been applied to accelerate bone healing for a long time. In this study, in order to combine the bone repair capability of calcium phosphate (CaP) ceramics with the magnetic field, a novel CaP ceramic-magnetic nanoparticle (CaP-MNP) composite was fabricated through integrating the superparamagnetic nanoparticles into the CaP ceramics. Two kinds of CaP ceramics were chosen: hydroxyapatite (HA) and HA/tricalcium phosphate (65/35, HT). The samples were cultured with Ros17/2.8 and MG63 cells respectively in vitro to evaluate the cell proliferation and differentiation via MTT and alkaline phosphatase activity tests. In order to find the influence of the magnetic materials on the expression of the bone morphological protein (BMP), the samples composited with BMP-2 were implanted subcutaneously in the fasciae of rat back muscles for 30 days. Compared with ordinary CaP ceramics, the results indicated that the CaP-MNP composite had good biocompatibility and was able to promote cell proliferation and differentiation significantly. The in vivo test showed that the expression of BMP-2 would be accelerated by HT composited with MNPs, and new bone-like tissue formation could be observed. Accordingly, it might be expected that this CaP-MNP composite could become a potential bone substitute or bone tissue engineering scaffold.

Magnetic Field Therapy: A Review

There is increasing interest in using permanent magnets for therapeutic purposes encouraged by basic science publications and clinical reports. Magnetotherapy provides a non invasive, safe, and easy method to directly treat the site of injury, the source of pain and inflammation, and other types of disease. The physiological bases for the use of magnetic fields for tissue repair as well as physical principles of dosimetry and application of various magnetic fields are subjects of this review. Analysis of the magnetic and electromagnetic stimulation is followed by a discussion of the advantage of magnetic field stimulation compared with electric current and electric field stimulation.

Surface mediated in situ differentiation of mesenchymal stem cells on gene-functionalized titanium films fabricated by layer-by-layer technique

In this work, multilayered and gene-functionalized titanium films composed of chitosan (Chi) and plasmid DNA (pEGFP-hBMP2, pGB) were employed to investigate the surface mediated in situ differentiation of mesenchymal stem cells (MSCs). The Chi/pGB multilayered structures were fabricated by layer-by-layer (LbL) assembly technique and degraded to release plasmid DNA complexes depending on bilayer numbers over 7 days. Therefore, the differentiation behaviors of MSCs cultured onto Chi/pGB multilayered titanium films surface were investigated. Chi/pGB LbL-modified titanium films show significant higher (p<0.01) transfection efficiency than those of other groups transfected by lipofectamine 2000 regarding the expression of green fluorescent protein (GFP). Reverse transcription-polymerase chain reaction (RT-PCR) assay revealed that MSCs adhered onto Chi/pGB LbL-modified titanium films could still express hBMP2 mRNA over 7 days culture. Compared with control groups, MSCs cultured onto Chi/pGB LbL-modified titanium films display significantly higher (p<0.01 or p<0.05) production levels of alkaline phosphatase (ALP) and osteocalcin over 7 days and 14 days culture, respectively. These results demonstrate that Chi/pGB LbL-modified titanium films are beneficial for sustained in situ inducing osteoprogenitor cells to differentiate into mature osteoblasts over long time. The approach presented here has potential applications in the development of gene-stimulating biomaterials and implant technology.

Effects of extremely low-frequency-pulsed electromagnetic field on different-derived osteoblast-like cells

The aim of this study is to investigate the effects of extremely low-frequency pulsed electromagnetic field (PEMF) on osteoblast-like cells. PEMF with a magnetic flux density of 1.55 mT at 48 Hz was employed to stimulate the MC3T3-E1 cell and the primary osteoblast cell derived from 2-day-old Sprague Dawley (SD) rat calvaria for different time. MTS method was applied to analyze cell proliferation and flow cytometry to detect cell cycle. The intracellular alkaline phosphatase (ALP) activity was measured by colorimetry. Our results demonstrated that PEMF of 1.55 mT at 48 Hz did not affect cell number of MC3T3-E1 cell, whereas the cell percentage of S and G(2)M phase decreased significantly. Although the cell number of the primary osteoblast cell did not alter by MTS assay after being exposed to PEMF for 24 h continuously, the cell percentage of S and G(2)M phase increased significantly. When culture time extended to 48 h, the cell number increased greatly and the cell percentage of S and G(2)M phase decreased significantly despite of the exposure type. After the primary osteoblast cell was exposed to PEMF for 24 h continuously, the ALP activity decreased significantly, whereas it increased significantly when being exposed to PEMF for 48 h continuously. From the results we concluded that PEMF of 1.55 mT at 48 Hz did not affect proliferation and differentiation of MC3T3-E1 cell, but it promoted proliferation, inhibited differentiation at proliferation stage, and promoted differentiation at differentiation stage of primary osteoblast cells.

Mature adipocyte-derived dedifferentiated fat cells can trans-differentiate into osteoblasts in vitro and in vivo only by all-trans retinoic acid

We investigated whether de-differentiated fat (DFAT) cells, a mature adipocyte-derived preadipocyte cell line, can be induced to trans-differentiate into osteoblasts in vitro and in vivo. All-trans retinoic acid (RA) induced expression of osteoblast-specific mRNAs encoding Cbfa1/Runx2, osterix, alkaline phosphatase, osteopontin, parathyroid hormone receptor, and osteocalcin in the DFAT cells, but did not induce the expression of adipocyte-specific mRNAs encoding PPARgamma2, C/EBPalpha, and GLUT4. Moreover, alkaline phosphatase activity was expressed in DFAT cells and the cells underwent mineralization of the bone matrix in vitro. Furthermore, when DFAT cells were transplanted subcutaneously into C57BL/6N mice in diffusion chambers, these cells formed ectopic osteoid tissue without any host cell-invasion of the chambers. These results indicate that DFAT cells derived from mature adipocytes can be converted into fully differentiated osteoblasts in vitro and in vivo using RA. DFAT cells provide a unique model for studying the lineage commitment of the adipocytes and osteoblasts derived from mesenchymal stem cells. Identification of the pathways that regulate these processes could lead to the development of new therapeutic strategies for control of unwarranted growth of bone and adipose tissue.

Static magnetic field combined with functional appliances: a new approach to enhance mandibular growth in Class II malocclusion

Class II malocclusion is one of the most common orthodontic problems. The main aetiology of Class II malocclusion is mandibular retrognathia. A variety of functional appliances have been used to stimulate mandibular growth in adolescence, however, the effects remain unsatisfactory. Therefore, new approaches are in need to strengthen the effects of functional appliances. Static magnetic field (SMF), created by permanent magnets, has long been proven to be clinically safe and is well accepted as a practical and non-invasive therapy. Numerous experimental and clinical data suggest that exogenous SMF can make profound effects on a large variety of biological systems. There has been increasing interest in curing bone injuries with SMF. More recently, literatures shed light on the chondrogenic and osteogenic effects of SMF. SMF and functional appliances may well have a synergistic effect in mandibular growth promotion. Based on experimental results and theoretical analysis, it is hypothesized that SMF combined with functional appliances can enhance mandibular growth in Class II malocclusion. A practical clinical design is also put forward.

Pulsed electromagnetic fields enhance BMP-2 dependent osteoblastic differentiation of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) express an osteoblastic phenotype when treated with BMP-2, and BMP-2 is used clinically to induce bone formation although high doses are required. Pulsed electromagnetic fields (PEMF) also promote osteogenesis in vivo, in part through direct action on osteoblasts. We tested the hypothesis that PEMF enhances osteogenesis of MSCs in the presence of an inductive stimulus like BMP-2. Confluent cultures of human MSCs were grown on calcium phosphate disks and were treated with osteogenic media (OM), OM containing 40 ng/mL rhBMP-2, OM + PEMF (8 h/day), or OM + BMP-2 + PEMF. MSCs demonstrated minor increases in alkaline phosphatase (ALP) during 24 days in culture and no change in osteocalcin. OM increased ALP and osteocalcin by day 6, but PEMF had no additional effect at any time. BMP-2 was stimulatory over OM, and PEMF + BMP-2 synergistically increased ALP and osteocalcin. PEMF also enhanced the effects of BMP-2 on PGE2, latent and active TGF-beta1, and osteoprotegerin. Effects of PEMF on BMP-2-treated cells were greatest at days 12 to 20. These results demonstrate that PEMF enhances osteogenic effects of BMP-2 on MSCs cultured on calcium phosphate substrates, suggesting that PEMF will improve MSC response to BMP-2 in vivo in a bone environment.

Static electromagnetic fields generated by corrosion currents inhibit human osteoblast differentiation

STUDY DESIGN

Human osteoblast cultures were exposed to a very low intensity static magnetic fields (SMF) to investigate its effects on osteoblast growth and differentiation.

OBJECTIVE

Analysis of the effects of periprosthetic SMF on the growth and differentiation of human osteoblast cell cultures in vitro.

SUMMARY OF BACKGROUND DATA

The effects of pulsed electromagnetic fields (PEMF) on cell proliferation, especially in human osteoblast-like cells is well described, whereas few data are available on the effects of SMF on osteoblast cell culture. We previously demonstrated that the proliferation of human osteoblast cultures is reduced when cells are exposed to a continuous low intensity SMF comparable to the one that occurs around metal devices (Ti spinal implant) because of the generation of electric currents between the screw (Ti6Al4V) and the rod (Ti).

METHODS

Primary osteoblastic cells were isolated from a human femoral head. Osteoblast cultures were exposed to SMF and alkaline phosphatase activity was evaluated in the osteoblast cell cultures at different time points. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed to evaluate mRNA expression levels of osteocalcin, Runx2, and collagen I genes.

RESULTS

The SMF-treated cells showed a progressive increase in the alkaline phosphatase activity which, however, remained always lower than the one observed in the control group at each observation time (72 hours, 7 and 14 days). RT-PCR demonstrated that Runx2 and collagen I mRNA were downregulated following SMF stimulation, whereas no change in osteocalcin mRNA was observed.

CONCLUSION

Continuous low-intensity electromagnetic field comparable to the one that generates around metal devices because of the generation of corrosion currents inhibits osteoblasts differentiation pattern and might contribute at least in part to a decrease in periprosthetic bone formation occurring in vivo.

Deleterious effects of MRI on chondrocytes

OBJECTIVE

To assess how magnetic fields (MFs), with or without concurrent radio frequency (RF), influence chondrocytes and knee joint repair, we applied an MF strength via magnetic resonance imaging (MRI) slightly greater than the frequently used dosage in the clinics and examined the effects of these treatments in vitro on human chondrocytes and in vivo in pigs.

METHODS

Human chondrocytes were directly exposed to a 3-tesla (T) magnetic field (MF group) or a 3-T static magnetic field plus 125.3 MHz radio frequency (MF+RF group), and cell proliferation, apoptosis, cytosolic Ca2+ ([Ca2+]i) fluxes and expression of the apoptosis-related proteins of the treated cells were examined to assess the effects of the treatments. In the pig study, we examined the effects of the treatments on the recovery of surgically damaged pig knees.

RESULTS

A 3-T static MF and RF suppressed cell growth and induced apoptosis through p53, p21, p27 and Bax protein expression. In the pig model, we found that MRI surveillance had a deleterious effect on the recovery of the damaged knee cartilage.

CONCLUSION

Magnetic strength, with or without concurrent RF, suppressed chondrocyte growth in vitro and affected recovery of damaged knee cartilage in vivo in the pig model. These results may be specific to the parameters used in this study and may not apply to other situations, field strengths, forms of cartilage injury, or animal species.

Transient down-regulation of cbfa1/Runx2 by RNA interference in murine C3H10T1/2 mesenchymal stromal cells delays in vitro and in vivo osteogenesis, but does not overtly affect chondrogenesis

In order to ensure that MSCs designed for in vivo cartilage repair do not untowardly differentiate into osteoblasts and mineralize in situ, we tested whether siRNA-induced suppression of cbfa1/Runx2 affected the osteogenic and chondrogenic differentiation potential of the murine cell line C3H10T1/2. Anti-cbfa1/Runx2 siRNA decreased the levels of cbfa1/Runx2 mRNA and protein by 65-80%, and also markedly reduced the expression of osteoblast-related genes such as Dlx5, osterix, collagen type I, alkaline phosphatase (AP), osteocalcin, SPARC/osteonectin and osteopontin, leading to a temporal expression of AP enzyme activity and mineralization potential delayed by at least some 7-9 days. Furthermore, siRNA-transfected cells, grown under chondrogenic conditions did not display biologically significant changes in the expression of aggrecan, collagen type II or type X, or histology when grown in micropellets or monolayer cultures. Finally, when cells were propagated in osteogenic medium and injected into the tibial muscles of SCID mice, no overtly mineralized bone tissue emerged. These experiments indicate that a major transient reduction of cbfa1/Runx2 expression in MSCs is sufficient to delay osteoblastic differentiation, both in vitro and in vivo, while chondrogenesis seemed to be sustained.

Static Magnetic Fields Promote Osteoblast-Like Cells Differentiation Via Increasing the Membrane Rigidity

The aim of this study was to test the differentiative effects of osteoblasts after treatment with a static magnetic field (SMF). MG63 osteoblast-like cells were exposed to a 0.4-T SMF. The differentiation markers were assessed by observing the changes in alkaline phosphatase activity and electron microscopy images. Membrane fluidity was used to evaluate alterations in the biophysical properties of the cellular membranes after the SMF simulation. Our results show that SMF exposure increases alkaline phosphatase activity and extracellular matrix release in MG63 cells. On the other hand, MG63 cells exposed to a 0.4-T SMF exhibited a significant increase in fluorescence anisotropy at 6 h, with a significant reduction in the proliferation effects of growth factors noted at 24 h. Based on these findings, the authors suggest that one of the possible mechanisms that SMF affects osteoblastic maturation is by increasing the membrane rigidity and reducing the proliferation-promoting effects of growth factors at the membrane domain.