Plasma Treatment Duration Research Articles

Enhanced interfacial shear strength in ultra-high molecular weight polyethylene epoxy composites through a zinc oxide nanowire interphase

The mechanical properties of fiber-reinforced composites are largely dictated by fiber-matrix interactions, where a well-adhered interface is desired. Ultra-high molecular weight polyethylene (UHMWPE) fibers suffer from poor interfacial properties due to their smooth and inert surface. Therefore, enhancing the interfacial properties of such composites will lead to an increased use in structural applications where high modulus, tenacity, low density, high impact and abrasion resistance properties are needed. In this work, an interfacial modification process consisting of an oxygen plasma surface functionalization followed by the grafting of zinc oxide nanowires (ZnO NWs) onto the UHMWPE fiber surface is investigated to improve the fiber-matrix interaction in UHMWPE composites. The UHMWPE fiber surface is subjected to varying oxygen plasma treatment durations such that the surface oxygen content can be increased to improve ZnO NW adhesion. Through single fiber pullout testing, the interfacial shear strength (IFSS) of oxygen plasma functionalized and ZnO NW coated UHMWPE fibers was shown a maximum increase of 135% with a 30 s plasma treatment prior to ZnO NWs. This increase in IFSS is attributed to an increased surface area interaction and mechanical interlocking between the fiber and matrix. The results detailed in this work demonstrate a benign, simple, and effective way to significantly improve the interfacial properties of UHMWPE fiber reinforced composites.

Decontamination of infected plant seeds utilizing atmospheric gliding arc discharge plasma treatment

In agriculture production, plant health is threatened by pathogens parasitic on seeds; hence, it is necessary to disinfect harvested seeds before germination. In this study, a technique of gliding arc plasma treatment was proposed and investigated. The experiment was conducted to treat Astragalus membranaceus (A. membranaceus) seeds that were artificially infected with Fusarium oxysporum (F. oxysporum). The plasma treatment duration varied from 30 s to 270 s. Direct and indirect treatments were compared to evaluate the inactivation efficiency of the F. oxysporum spores on the surface of seeds. The results indicated that the direct treatment behaved significantly better in disinfection than the indirect way. Meanwhile, experiments of the quantitative assessment of seed germination were also conducted, including the germination rate, the germination potential, and the germination index. The results showed that the inactivation efficiency increased as the plasma treatment time was extended. When the treatment time was 90 s, the inactivation efficiency reached more than 98%. The plasma treatment of 270 s had a complete devitalization of F. oxysporum spores on the surface of the seeds. After the treatment of 30 s and 90 s, the seed germination parameters improved significantly. This study verified the inactivation efficacy of gliding arc discharge plasma under atmospheric pressure. The technique of gliding arc treatment shows advantages of energy saving and adaptation and has the potential to be utilized in industry.

Cold Atmospheric Plasma Changes the Amino Acid Composition of Solutions and Influences the Anti-Tumor Effect on Melanoma Cells.

Cold Atmospheric Plasma (CAP) is an ionized gas near room temperature. Its anti-tumor effect can be transmitted either by direct treatment or mediated by a plasma-treated solution (PTS), such as treated standard cell culture medium, which contains different amino acids, inorganic salts, vitamins and other substances. Despite extensive research, the active components in PTS and its molecular or cellular mechanisms are not yet fully understood. The purpose of this study was the measurement of the reactive species in PTS and their effect on tumor cells using different plasma modes and treatment durations. The PTS analysis yielded mode- and dose-dependent differences in the production of reactive oxygen and nitrogen species (RONS), and in the decomposition and modification of the amino acids Tyrosine (Tyr) and Tryptophan (Trp). The Trp metabolites Formylkynurenine (FKyn) and Kynurenine (Kyn) were produced in PTS with the 4 kHz (oxygen) mode, inducing apoptosis in Mel Im melanoma cells. Nitrated derivatives of Trp and Tyr were formed in the 8 kHz (nitrogen) mode, elevating the p16 mRNA expression and senescence-associated ß-Galactosidase staining. In conclusion, the plasma mode has a strong impact on the composition of the active components in PTS and affects its anti-tumor mechanism. These findings are of decisive importance for the development of plasma devices and the effectiveness of tumor treatment.

Tuning the Surface Wettability of Cyclic Olefin Copolymer by Plasma Treatment and Graphene Oxide Deposition and Reduction.

Selective altering of surface wettability in microfluidic channels provides a suitable platform for a large range of processes, such as the phase separation of multiphase systems, synthesis of reaction controlled, nanoliter sized droplet reactors, and catalyst impregnation. Herein we study the feasibility to tune the wettability of a flexible cyclic olefin copolymer (COC). Two methods were considered for enhancing the surface hydrophilicity. The first is argon/oxygen plasma treatment, where the effect of treatment duration on water contact angle and COC surface morphology and chemistry were investigated, and the second is coating COC with GO dispersions of different concentrations. For enhancing the hydrophobicity of GO-coated COC surfaces, three reduction methods were considered: chemical reduction by Hydroiodic acid (HI), thermal reduction, and photo reduction by exposure of GO-coated COC to UV light. The results show that as the GO concentration and plasma treatment duration increased, a significant decrease in contact angle was observed, which confirmed the ability to enhance the wettability of the COC surface. The increase in hydrophilicity during plasma treatment was associated with the increase in surface roughness on the treated surfaces, while the increase during GO coating was associated with introducing oxygen-containing groups on the GO-coated COC surfaces. The results also show that the different reduction methods considered can increase the contact angle and improve the hydrophobicity of a GO-coated COC surface. It was found that the significant improvement in hydrophobicity was related to the reduction of oxygen-containing groups on the GO-coated COC modified surface.

Design and characterisation of jet cold atmospheric pressure plasma and its effect on Escherichia coli, colour, pH, and bioactive compounds of sour cherry juice

SummaryA new system for cold atmospheric pressure plasma (CAPP) generation was designed and characterised. The effects of voltage (10, 15, 20 kV), frequency (10, 15, 20 kHz), gas flow rate (3, 5, 7 L min−1) and percentage of oxygen (0%, 0.5%, 1%) on the plasma jet length (PJL) were investigated. Then, different volumes (5, 10, 15 mL) of sour cherry juice were treated by CAPP to compare their physicochemical properties (colour and pH), Escherichia coli count, and bioactive compounds with samples treated by the conventional process. According to the results, PJL was increased by increasing the voltage and frequency and then remained constant. Also, PJL increases and then decreases by increasing the gas flow rate. Furthermore, CAPP treatment reduced E. coli count but did not alter the colour and pH of samples. Moreover, increasing the voltage, plasma treatment duration, and oxygen percentage enhanced the inactivation of E. coli. The best sterilisation effect was 6‐log cycle decrease in E. coli count which was achieved at a voltage of 19.6 kV, an oxygen concentration of 1%, and a gas flow rate of 4.5 L min−1. Besides, the total phenol content of juice was 277 GAE/100 g and was changed to 279 and 359 after plasma treatment and conventional process, respectively.

Cold Atmospheric Plasma Promotes the Immunoreactivity of Granulocytes In Vitro.

Cold atmospheric plasma (CAP) reduces bacteria and interacts with tissues and cells, thus improving wound healing. The CAP-related induction of neutrophils was recently described in stained sections of wound tissue in mice. Consequently, this study aimed to examine the functionality of human polymorphonuclear cells (PMN)/granulocytes through either a plasma-treated solution (PTS) or the direct CAP treatment with different plasma modes and treatment durations. PTS analysis yielded mode-dependent differences in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) after CAP treatment. Live-cell imaging did not show any chemo-attractive or NETosis-inducing effect on PMNs treated with PTS. The time to maximum ROS production (TmaxROS) in PMNs was reduced by PTS and direct CAP treatment. PMNs directly treated with CAP showed an altered cell migration dependent on the treatment duration as well as decreased TmaxROS without inducing apoptosis. Additionally, flow cytometry showed enhanced integrin and selectin expression, as a marker of activation, on PMN surfaces. In conclusion, the modification of PMN immunoreactivity may be a main supporting mechanism for CAP-induced improvement in wound healing.

Elimination of Aspergillus flavus from Pistachio Nuts with Dielectric Barrier Discharge (DBD) Cold Plasma and Its Impacts on Biochemical Indices

In the present research, the effects of different durations (0, 15, 30, 60, 90, 120, 150, and 180 sec) of dielectric barrier discharge (DBD) cold plasma on decontaminating Aspergillus flavus, detoxifying pure aflatoxin B1 (AFB1), and the quality attributes of pistachio nuts (total phenolic content, antioxidant activity, chlorophylls, total carotenoids, instrumental color, total soluble protein, and malondialdehyde determination) were studied. The results showed that the viable spore population reduced with the increase of plasma treatment duration, so that after 180 s of the treatment, a decrease by 4 logs was observed in the spore population. Chlorophyll a and b, as well as total carotenoid levels and color parameters, decreased, which led to darker pistachio samples and intensity reduction in soluble protein content and protein bands. Plasma treatment did not alter the total phenolic content but slightly increased the antioxidant activity of pistachio nuts samples. The malondialdehyde values significantly increased all the plasma treatment durations. The maximum reduction of AFB1 was observed after 180 s of the treatment, which was 64.63% and 52.42% for glass slides and pistachio nut samples, respectively. The present findings demonstrated that cold plasma could be used as an efficient decontamination method of food products without inducing undesirable quality changes in nuts.

Potential application of non-thermal atmospheric plasma in reducing the activity of Pseudomonas-secreted proteases in milk

Application of non-thermal atmospheric plasma was examined against the activity of Pseudomonas-secreted proteases in milk. UHT milk samples were inoculated with crude extract of Pseudomonas-secreted proteases and treated in atmospheric plasma discharge system. Evaluation of the progress in protein hydrolysis of plasma-treated and non-treated milk samples revealed that the degree of hydrolysis was lower in plasma-treated milk samples. The longer the plasma treatment time, the lower the degree of hydrolysis during storage. Furthermore, plasma-induced changes in milk proteins and volatile compounds were also evaluated. Caseins, whey proteins, aldehydes, ketones, free fatty acids and hydrocarbons were all affected by plasma discharge. The amount of increase or decrease in these components was dependent on the duration of plasma treatment. Overall, this method is a promising approach that could be used to inactivate bacterial hydrolytic enzymes in milk.

Effect of Glow and Dielectric Barrier Discharges Plasma on Volatile and Non-volatile Chemical Profiling of Camu-Camu Juice

Nuclear magnetic resonance (NMR) is a powerful technique to characterization of taste profile based on organic compounds from foods. Likely, gas chromatography coupled to mass spectrometry (GC-MS) enables the detection of aroma profile of foodstuff. Therefore, the present study aimed to evaluate the influence of two different cold plasma processes (dielectric barrier discharge atmospheric plasma (ACP) and glow discharge plasma (GP)), as well as the effect of different processing conditions on taste and aroma profiles from camu-camu juice. Both ACP and GP processing resulted in modifications on taste and aroma, which were strongly dependent of the frequency of plasma generation, flow rate, and treatment duration. The GP processing resulted in higher influence on camu-camu composition than ACP, which decreased the contents of important flavor compounds while increasing vitamin C and ethanol contents. Moreover, GP during 10 min at 10 mL/min and 20 min at 20 mL/min of plasma flow rate did not present significant effect on the juices composition as a whole (taste and aroma related compounds). The ACP processing presented significant influence on the juices composition at 420 and 530 Hz, while 200 and 960 Hz maintained the overall organic composition. Therefore, the use of NMR and GC-MS coupled to advanced chemometric analysis (data fusion) allowed a deep understand the camu-camu chemical variability submitted to plasma technologies based on taste and aroma compounds. This information indicates that appropriate treatment conditions are important for decontamination while preserving and improving the food characteristics in order to match the consumer demands.

Rapid and eco-friendly technique for surface modification of TFC RO membrane for improved filtration performance

In this work, an environmentally friendly plasma enhanced chemical vapor deposition (PECVD) technique was employed to rapidly alter the surface properties of commercial thin film composite extra-low energy (XLE) reverse osmosis (RO) membrane to improve its fouling resistance and desalination performance. Hereafter, two different hydrophilic precursors, i.e., aniline monomer and oxygen (O2) gas were respectively introduced to the membrane’s polyamide surface at different plasma treatment duration (15 s and 60 s). At 15-s plasma treatment, our results revealed that the O2-modified membrane outperformed the polyaniline (PANI)-modified membrane and unmodified membrane, attributed to the polar functional groups presented on the polyamide surface. Compared to plasma polymerization of aniline, O2 plasma etching can lower polyamide densification degree which potentially reduce membrane resistance. Evidently, the O2-modified membrane exhibited higher pure water permeability (6.64 L/m2.h.bar) compared to the PANI-modified membrane (5.57 L/m2.h.bar). The enhanced surface hydrophilicity of O2-modified membrane could be noticed when its water contact angle was reduced from 88.39⁰ (unmodified) to 79.46⁰ in just 15-s plasma treatment. Furthermore, this O2-modified membrane achieved an outstanding NaCl and Na2SO4 rejection with an increment of 4.2% and 2.6%, respectively compared to the unmodified membrane. However, prolonged gas plasma treatment (60 s) should be avoided as it can damage polyamide selective layer. With respect to fouling resistance, the best O2-modified membrane demonstrated higher flux recovery rate (96%) than that of unmodified membrane (76.5%) after being used to filter 1000-ppm sodium alginate solution. These results highlighted the versatility of O2 plasma treatment to improve RO membrane performance.

Synthesis and pressure study of bubbles in hexagonal boron nitride interlayer

Hexagonal boron nitride (h-BN) is considered as an ideal substrate material for new electronic devices and nano-electromechanical (NEMS) devices, owing to its hexagonal network lattice structure and high chemical and mechanical stability. It can be used to seal gas with a long-term stability, and then has a big potential in further applications in electronics and NEMS. Recently, researchers have discovered that hydrogen atoms can penetrate multiple layers of h-BN non-destructively, forming the bubbles between layers, which can be used as NEMS devices. In this article, we investigate the effect of hydrogen plasma treatment duration on the size of h-BN bubbles. It is found that the size of bubbles becomes larger with the increase of treatment time while their distribution density decreases. It is also observed that the prepared h-BN bubbles have similar morphological characteristics, which are related to Young’s modulus of h-BN and interlayer van der Waals interaction. With the help of force-displacement curve measurement, it is obtained that the internal pressure is about 1—2 MPa for micro-sized bubbles, while the internal pressure of nano-sized bubbles can reach a value of GPa.

Surface modification of electrospun silk/AMOX/PVA nanofibers by dielectric barrier discharge plasma: physiochemical properties, drug delivery and in-vitro biocompatibility.

The naturally obtained protein Bombyxmori silk is a biocompatible polymer with excellent mechanical properties and have the potential in controlled drug delivery applications. In this work, we have demonstrated dielectric barrier discharge (DBD) oxygen (O2) plasma surface modified electrospun Bombyxmori silk/Amoxicillin hydrochloride trihydrate (AMOX)/polyvinyl alcohol (PVA) nanofibers for drug release applications with controlled plasma treatment duration (1-10min). The findings indicate that plasma treated electrospun nanofibers for 1-3min exhibited significant enhancement in tensile strength, Young's modulus, wettability and surface energy. The plasma treated electrospun nanofibers for 1-5min showed remarkable increase in AMOX released rate, whereas the electrospun nanofibers treated with plasma irradiation beyond 5min showed only marginal increase. Moreover, the plasma treated nanofibers also exhibited good antibacterial activity against both E. coli (gram negative) and S. aureus (gram positive) bacteria. The untreated and the plasma treated silk/AMOX/PVA electrospun nanofibers for 1-3min showed enhanced viability of primary adipose derived mesenchymal stem cells (ADMSCs) growth on them and much less hemolysis activity (< 5%). The in vitro biocompatibility of various electrospun nanofibers were further corroborated by live/dead imaging and cytoskeletal architecture assessment demonstrating enhanced cell adhesion and spreading on the plasma treated nanofibers for 1-3min. The findings of the present study suggest that the silk/AMOX/PVA electrospun nanofibers with plasma treatment (1-3min) due to their enhanced drug release ability and biocompatibility can be used as potential wound dressing applications.

ДОСЛІДЖЕННЯ ВПЛИВУ ПАРАМЕТРІВ СИНТЕЗУ НА МАГНІТНІ ВЛАСТИВОСТІ CoNi ФЕРИТІВ

The influence of synthesis conditions on saturation magnetization and coercive force of NiCo ferrites, which were obtained under the action of low-temperature contact nonequilibrium plasma (PNP), is investigated. The main influencing factors were the initial pH of the solution, the treatment temperature and the duration of plasma treatment. Mathematical equations adequately describe the obtained dependences. The results showed that the pH of the reaction medium is the parameter that most affects the magnetic hysteresis for samples obtained by processing KNP. Increasing the initial pH leads to an increase in coercive force.

Textile wastewater treatment by underwater parallel-multi-tube air discharge plasma jet

Textile wastewaters (WW) as released from textile industries damage aquatic environment and thereby create threat to plants and animals. To overcome the problems associated with wastewaters, the plasma technology can be an alternative approach for the reduction of effluents dissolved in textile WWs. In this present study, the degradation of textile dye model WWs is carried out using underwater parallel-multi-tube atmospheric pressure air discharge plasma jet. The investigation reveals that: pH is decreased, while electrical conductivity (EC) is increased in the deionized (DI) waters and model WWs with increasing plasma treatment duration. The Concentrations of O3, H2O2 and NO3- in model WWs are decreased compared to that of DI water with treatment duration, but NO2- is increased. The decrease in O3, H2O2 and NO3- suggest that they participate in the dissociation processes of textile dyes. UV–vis spectroscopic measurements show that almost 70 % of dyes were degraded within 10 min of treatments but the remaining 30 % was taken a longer time. FTIR spectroscopic measurements reveal that the amines and alkynes are likely to be produced through oxidative processes of azo-bonds and nitrogen containing functional groups with the interactions of O3 and OH radical. A fraction of organic nitrogen can be converted to nitrites through oxidation for which the concentration of nitrite is increasing with treatment duration. The proposed environment friendly plasma technology can alternatively be adapted to the reduction of effluents as dissolve in textile WW.

Changes in the Surface Morphology, Microhardness, and Physicochemical Properties of Natural Minerals under the Influence of a Dielectric Barrier Discharge

Analytical electron (SEM-EDX) and confocal laser scanning microscopy (CLSM), microhardness testing, determining the contact angle of wetting, and other means are used to study the mechanism behind changes in the structural state of surfaces, and the mechanical, physicochemical, and technological properties of semiconductor ore minerals (sulfides) and natural quartz under conditions of a pulsed dielectric barrier discharge at atmospheric pressure in air. Due to the action of the products of low-temperature plasma and other effective factors resulting from a discharge, the minerals soften (general maximum relative reduction in microhardness ~7–30%), and the morphology, roughness, contact angle of wetting of the surfaces of mineral polished sections, and the flotation activity of sulfide minerals change with respect to the duration of plasma treatment.

The effect of nitrogen plasma treatment on adhesive properties of PEEK

The purpose of this study is to investigate the effect of nitrogen plasma treatment on the shear bonding strength (SBS) of polyetheretherketone (PEEK) to resin cements. A total of 240 PEEK specimens were subjected to different duration of nitrogen plasma treatment for 0 min, 15 min, 25 min, 35 min respectively. The surface topography was observed by a scanning electron microscope (SEM). In addition, X-ray photoelectron spectroscopy (XPS) was applied to study the surface element content changes before and after treatment. The adhesive specimens were bonded with Variolink in all groups. Afterwards, each group was divided into three subgroups (n = 20/group), (a) water storage for 56 h at 37 °C, (b) thermal cycling for 5000 times, (c) thermal cycling for 10000 times. Following storage shear bond strength (SBS) was tested in a universal testing machine and the failure modes were observed by stereoscopic microscope. After plasma treatment, the bonding strength between PEEK and Variolink was significantly increased. Among them, the 25 min group achieved the highest bonding strength. After thermal cycling, the SBS values were significantly decreased, compared with the group in water storage. Nitrogen low temperature plasma treatment improves SBS between PEEK and resin, and a duration of 25 min treatment group seems to be the best.

Influence of the Nitrogen exposure time to the plasma treatment on the wettability of polystyrene surfaces

The wettability of material can change from hydrophobic to hydrophilic when treated using plasma nitrogen. The present work investigated the influence of the plasma treatment duration on the modification of polystyrene’s surface coating on a glass surface. The polystyrene layer was produced by means of spin coating method with the rotational speed of 3000 RPM for 1 minute. The plasma was established by a 2 MHz RF generator at the power of 40 watts, pressure of 0.3 Torr, flow rate 40 mL/min. The samples were treated at various exposure time which were 2 min, 5 min, 10 min, and 15 min. The wettability of the polystyrene was measured using a contact angle measurement before and after the nitrogen plasma treatment. Polar functional groups related to the wettability were observed by a Fourier Transform Infrared (FTIR). The longer the treatment duration, the smaller the contact angle was observed. A very low contact angle of 6.42° was achieved at a power of 40 watt at 0.3 torr for the exposure time of 15 min. This means that the surface of the polystyrene changed to super hydrophilic or super wetting. The FTIR results show the spectra of NH2 and C-H functional group at the wavenumber of 3485 cm1 and 2962 cm1, respectively. These functional groups indicate the existence of the polar groups, which contribute to the change of surface hydrophobicity into hydrophilicity.

Plasma treatment as an effective tool for crosslinking of electrospun fibers

Electrospinning is a versatile method for the preparation of polymer fiber networks. From the medical application point of view, the stability of the fibrous structure in water is crucial. The aim of this research was to explore the possibility to induce crosslinking by treatment with non-equilibrium low pressure plasma to give structural stability to fibrous meshes. Low pressure plasma treatment was studied to induce crosslinking in allylamine-modified polysuccinimide nanofibers. Polysuccinimide was first modified with allylamine (PSI-AA) to attach the reactive allyl groups to the polymer chain. Allylamine-modification degrees varied between 10 and 100%. Then PSI-AA meshes were created by electrospinning followed by low pressure plasma treatment to allow the allylamine groups to establish crosslinks in the meshes. The crosslinked structure was confirmed by immersing both the plasma-treated, and untreated PSI-AA meshes in dimethyl sulfoxide, which is a good solvent of the non-crosslinked PSI-AA. Plasma-treated meshes kept their integrity, while the untreated samples dissolved almost immediately, which proved the formation of crosslinks due to plasma treatment. Structural changes in the meshes were studied with infrared spectroscopy (IR). X-ray photoelectron spectroscopy (XPS) investigates the structural changes on the surface of the samples and proved the presence of crosslinks. PSI-AA meshes were then hydrolyzed into poly(aspartic acid) (PASP) meshes and with the right choice of synthesis parameters (allylamine grafting degree, plasma treatment duration and power) PASP hydrogel meshes retained their fibrous structure, which was observed in SEM images of PSI-AA meshes.

Study of the effect of duration of non-thermal plasma treatment on the surface properties of polymers

One of the factors affecting the electric charge acquired through friction between the polymers is their surface roughness. The dielectric barrier discharge (DBD) treatment is known to modify the surface characteristics of polymers. The aim of this study is to quantify the effect of atmospheric DBD exposure, in a well-defined configuration on the triboelectric behavior of polymers. Thus, Polytetrafluoroethylene (PTFE) plate samples characterized by different surface roughness were rubbed against bronze plate samples in a triboelectric test bench and then the electric potential at their surface was measured. The results were compared with those obtained for surfaces previously exposed to DBD treatment duration of which did not bring any change in their roughness. It was found that the roughness of the surface of the treated polymers hardly changed for rather short DBD exposure time (a few minutes). Significant changes were noticed for longer treatment duration (30 minutes and more). The samples that had undergone a longer treatment period modification acquired higher levels of electric charge by triboelectric effect.

Surface modification of UHMWPE using ECR plasma for osteoblast and osteoclast differentiation

The work presented in this study, elucidates the change in surface properties of UHMWPE polymer, as a result of microwave assisted Electron Cyclotron Resonance (ECR) plasma. The ECR plasma was found to be suitable to enhance the surface energy and generate CN/CO related functional groups that were found to be associated with enhancement of cellular adhesion. In order to investigate its application in bone tissue engineering, interactions of modified UHMWPE with two major classes of bone cells: osteoblasts and osteoclasts, has been elaborated. The results clearly indicate a positive cellular interaction of the polymers treated for 1 min with O2 plasma as compared to their HN plasma treated counterparts. However, we also emphasize that the type of plasma and the duration of treatment, play a major role in governing the proliferation and differentiation of a particular cell type. This means that the duration of plasma treatment governs whether the polymer surface would support osteoblast or osteoclast differentiation. The present study is first of its kind to highlight the culture of two types of bone cells on modified polymer surfaces. The results provide an overview that 1 min O2 treatment support osteogenesis whereas 2 min O2 treatment favors osteoclast.