High Methylene Blue Concentration Research Articles

A novel bimetallic Fe-Cu-CNT catalyst for effective catalytic wet peroxide oxidation: reaction optimization and mechanism investigation

Treatment of organic wastewater is of great importance and can be carried out by catalysis technologies such as catalytic wet peroxide oxidation (CWPO). A novel bimetallic Fe-Cu-CNT catalyst was first developed by a facile hydrothermal method; Fe species (Fe (Ⅱ) and Fe (Ⅲ)) and Cu species (Cu (Ⅰ) and Cu (Ⅱ)) were used to fabricate the catalyst with the CNTs, which was stable during testing. Methylene blue (MB) was chosen as model compound for the study; the optimization for treatment by the Box-Behnken design indicated that a combination of low pH, high MB concentration and intermediate temperature led to better treatment performance. The CWPO reaction obeyed the 2nd-order kinetic equation and the catalyst activity increased with an increase in the Cu content. The reaction induction period was shortened with decreasing Fe:Cu ratio. The cycling reaction between Fe3+/Fe2+ and Cu2+/Cu+ pairs generated a large number of oxidative radicals and improved the pollutant degradation efficiency. Finally, the reaction rate equation of CWPO over Fe-Cu-CNT was derived, and it was experimentally illustrated that hydroxyl radicals played a crucial role in the treatment. This study demonstrates that the optimized Fe-Cu-CNT has great potentials for treatment of organic wastewater with higher efficiency and lower cost.

Copper Selenide (CuSe) Monolith Fabricated by Facile Copper Foam Selenization for Efficient Photocatalytic Degradation of Methylene Blue

A critical challenge that impedes the application of photocatalytic techniques for organic dye degradation from polluted industrial effluents is that traditional powdery photocatalysts exposed limited photo-absorption sites and exhibited inefficient recyclability. To overcome these challenges, this study designed a one-step process to synthesize a monolithic copper selenide (CuSe)-based photocatalyst. The characterization results fully supported that the maintenance of the copper foam during the selenization process was the prerequisite for the monolithic photocatalyst to keep its structural integrity in photocatalytic reactions. The surface of the monolithic photocatalyst fully covered by active CuSe is crucial for the exposure of photocatalytically active sites and the efficient degradation of methylene blue (MB). It was found that the CuSe-based monolithic photocatalyst exhibited excellent MB degradation performances under harsh pH conditions and high MB concentrations. From these perspectives, it is reasonable to conclude that the CuSe-based monolithic photocatalyst as prepared is a promising alternative to traditional powdery photocatalysts for organic dye degradation and industrial effluent cleaning.

Highly Active Carbon Material Derived from Carica papaya Fruit Juice: Access to Efficient Photocatalytic Degradation of Methylene Blue in Aqueous Solution under the Illumination of Ultraviolet Light

Herein, we describe a cost-effective, efficient, sustainable, and environmentally friendly pyrolytic method for the synthesis of highly active carbon materials from Carica papaya fruit juice for the photodegradation of various pollutants, such as methylene blue (MB), in aqueous solutions using ultraviolet (UV) light. Various analytical techniques were used to examine the morphology, crystal quality, functional group chemistry, particle size distribution, and optical properties of the materials. For evaluating the performance of the newly prepared carbon material, various photocatalyst parameters were investigated, including initial dye concentration, catalyst dose, pH of dye solution, cyclic stability, and scavenger studies. The obtained findings attest that the optimal degradation efficiency of carbon material for high MB concentrations (2.3 × 10−5 M) is around 98.08%, whereas at low concentrations of MB (1.5 × 10−5 M) it reaches 99.67%. Degradation kinetics indicate that MB degrades in a first-order manner. Importantly, as the pH of the dye solution was adjusted to ~11, the degradation rate increased significantly. The scavenger study indicated that hydroxyl radicals were the predominant species involved in the degradation of MB. In addition, active surface site exposure and charge transfer were strongly associated with efficient MB degradation. On the basis of its performance, this newly developed carbon material may prove to be an excellent alternative and promising photocatalyst for wastewater treatment. Furthermore, the synthetic approach used to produce carbon material from Carica papaya fruit juice may prove useful for the development of a new generation of photoactive materials for environmentally friendly applications, as well as for the production of hydrogen from solar energy.

Bismuth oxychloride microcrystals decorated carbon foams based on waste polyurethane elastomer for enhanced removal of methylene blue

Multicomponent materials containing nanoscale structures, the so-called “nanocomposites” are one of the fastest-growing areas of photocatalytic research. In this study, the nanocomposites of bismuth oxychloride (BiOCl) with porous carbon foam (CF) derived from waste polyurethane (PU) elastomers were developed by a simple hydrothermal method, and the photocatalytic performance of the as-prepared materials was investigated. The structure, morphology and optical properties of the composites were characterized in detail. The photocatalytic activity of the samples was evaluated by studying the degradation of methylene blue (MB) under UV-A irradiation. Even at a high MB concentration (0.5 mmol/L), excellent photocatalytic activity was observed, with an overall removal efficiency of 99.0% in 100 min of irradiation. Kinetic studies were also carried out for the degradation of MB by pristine BiOCl and CF-BiOCl. The photodegradation rate constants were evaluated by fitting the kinetic data with a pseudo-first-order model, and the rate constants of CF-BiOCl composites were higher than that of pristine BiOCl. The enhanced activity of the composites was due to the well-connected heterojunction interface, improved hydrophilicity, more reactive sites, and effective separation of photo-generated charges. Thus, our work combines the valuable waste PU-derived CFs with BiOCl, which provides a strategy to achieve circular economy and environmental remediation objectives.

Modeling Electropolymerization of Methylene Blue in the Presence of Pillar[6]arene and DNA

For the first time, cumulative effect of the changes in the concentration of methylene blue (MB), pillar[6]arene (P6) and DNA in the MB electropolymerization performed by repeated cycling of the potential of the glassy carbon electrode (GCE) modified with carbon black (CB) was described by construction of generalized linear models within the full factor experiment design. The proposed models of the currents and potentials of the peaks attributed to the monomeric and polymeric MB forms fully describe synergistic effect of the reaction mixture components and their contribution to the efficiency of electropolymerization and accumulation of the redox active layer on the electrode. The MB concentration exerted the biggest effect on the redox peak currents of the coating. DNA addition decreased the redox peak currents to a degree mostly pronounced for the high MB concentrations. The P6 addition significantly improved the conditions of the electron exchange and increased the redox peak currents, especially at low MB concentrations. The results obtained can find application for the optimization of the assembling conditions in the DNA sensors design.

Highly efficient removal of organic contaminant with wide concentration range by a novel self-cleaning hydrogel: Mechanism, degradation pathway and DFT calculation

A novel carbon nitride based self-cleaning hydrogel photocatalyst (KI-PCN gel, potassium and iodine co-doped carbon nitride confined in alginate) has been successfully constructed by a facile method. Fabricated photocatalyst showed enhanced synergistic adsorption-photocatalytic degradation property on a high concentration of methylene blue (HMB) because of enhanced carrier separation efficiency and improved light adsorption capacity of KI-PCN. As expected, the KI-PCN gel showed the highest apparent rate constant value (Kapp =0.0310 min−1), which was about 38.8 and 5.8 times as that of blank hydrogel (Kapp=0.0008 min−1) and PCN gel (Kapp=0.0053 min−1), respectively. Meanwhile, KI-PCN gel can continuously adsorb low concentration of MB (LMB), and the MB-adsorbed KI-PCN gel can self-clean under light irradiation. The bench-scale experiments simulating real river showed that KI-PCN gel can effectively and continuously remove LMB (0.1–20 ppm), indicating the possibility for the removal of contaminants in natural rivers. Furthermore, the possible degradation pathways were proposed by combining the density functional calculations (DFT) and intermediates identified by liquid chromatography-mass spectrometry (LC-MS). This work proposed a new perspective to acquire a novel self-cleaning and easily recyclable photocatalyst for treatment of wide concentration range organic wastewater as well as remediation of natural waterbody.

The potential of transforming rice straw (Oryza sativa) and golden shower (Cassia fistula) seed waste into high-efficiency biochar by atmospheric pressure microwave plasma

Biochars were successfully produced from rice straw and golden shower seed wastes and used to obtain agricultural waste-derived and low-cost adsorbents to remove methylene blue (MB) dye pollutants. The biochars were prepared using atmospheric pressure microwave plasma in a nitrogen environment at three individual flow rates of 7, 9, and 11 L/min for 5 min via pyrolysis. After pyrolysis, RS biochar’s surface area and pore volume increased from 1.224 m2/g to 13.796 m2/g, 11.995 m2/g, 6.865 m2/g, and 0.006 cm3/g to 0.804 cm3/g, 0.168 cm3/g, 0.08 cm3/g, respectively, then GS increased from 11.874 m2/g to 40.423 m2/g, 45.731 m2/g, 73.067 m2/g, and 0.006 cm3/g to 0.181 cm3/g, 0.277 cm3/g, 4.227 cm3/g, respectively. FTIR results showed O–H stretching in hydroxyl groups, CO functional group, C-H bending of CH3, and C-H vibration aromatic compounds, essential for MB adsorption. The golden shower seed biochar activated by plasma gas flowrate 11 l/m (GS-11) and rice straw biochar activated by plasma gas flowrate 7 l/m (RS-7) had the highest adsorption capacity among all biochars, 344.82 mg/g, and 188.32 mg/g, respectively, which was 10.6 and 2.07 times higher than other golden shower and rice straw biochar from the previous research by much shorter pyrolysis duration of 24 and 48 times, respectively. In addition, both biochars had higher adsorption capacity than previous biochars from different biomass and pyrolysis methods even though they applied 5 times lower in dosage, 3 times higher on initial MB concentration, and 36–144 times shorter pyrolysis time. The equilibrium data fit well with the Langmuir model, and the adsorption kinetics followed pseudo-second-order kinetics. According to the current study, the atmospheric pressure microwave plasma can generate high-quality biochars quickly and be promoted as a recycling technology method. Then, the product biochars can reach high adsorption capacity with a low dosage, high initial MB concentration, low energy consumption, and no chemical added. Furthermore, the product can enhance the value of rice straw and golden shower seed waste, support a circular economy approach, reduce the waste released to the environment, and reduce air pollution generated.

A hybrid mesoporous CuO@barley straw-derived SiO2 nanocomposite for adsorption and photocatalytic degradation of methylene blue from real wastewater

In this article, we have reported synthesizing a novel mesoporous CuO@barley straw derived SiO2 (CuO@BSS) as a photocatalyst and adsorbent for methylene blue (MB) removal from aqueous media. Silica nanoparticle as a platform was prepared from barley straw, then modified by grafting of CuO nanoparticles. Our strategy represents a significant development in recycling agricultural waste, such as barley straw, offering a cost for effective photocatalyst and adsorbent. The as-prepared CuO@BSS nanocomposite was characterized using FE-SEM, EDX, TEM, XRD, FT-IR, TGA, and N2 adsorption-desorption. The effect of the pH, CuO@BSS dosage, temperature, time, and initial MB-concentration was systematically investigated. Furthermore, isotherm, kinetic and thermodynamic of MB-removal were also studied. The obtained results indicated that MB-photodegradation is a more convenient method in removing MB than the adsorption process onto mesoporous CuO@BSS nanocomposite at pH 10, where 90% and 99% of MB-dye were removed through adsorption and photodegradation techniques, respectively. The calculated values of ∆G°, ∆H°, and ∆So indicate adsorption's spontaneous and endothermic behavior. The prepared CuO@BSS nanocomposite is a promising candidate for removing MB from real water samples even at high MB concentrations or even after multi-reuse cycles.

Efficient reduction of methylene blue in aqueous solution using a Fenton-like catalyst of Fe3O4/Cu

This work aimed to investigate the efficient reduction of methylene blue (MB) by a heterogeneous magnetic nanoparticles/copper (MNs/Cu) Fenton-like catalyst. The MNs/Cu was successfully synthesized in the presence of Citrus aurantifolia extract. The characterizations showed an effective fabrication of Cu onto the surface of MNs. The reduction of MB by the MNs/Cu Fenton-like catalyst presented an efficiency of 99.5% at the optimum conditions, including MNs/Cu dose of 0.1 mg, temperature of 25°C, contact time of 75 min, pH 4.0, and 20 mL H2O2 30%, MB initial concentration of 25 mg/L. The reduction kinetics was well fitted to pseudo-second-order with reaction rate constant of 0.0029 g/mg.min. The main mechanism of the MB reduction due to active oxygen species was pointed out. The decrease of reduction yield at high pH, catalyst dose and MB concentration was elucidated in this study.

B/N-doped carbon sheets from a new ionic liquid with excellent sorption properties for methylene blue

The pyrolytic treatment of the novel ionic liquid 1-ethyl-3-methyl-imidazolium tetrakis-(1-imidazolyl)borate ([EMIM][BIm4]) allowed the preparation of B/N-doped carbonaceous materials with an exceptional performance in the adsorptive removal of the cationic dye methylene blue (MB) from wastewater. [EMIM][BIm4] was prepared via an easy and scalable synthesis protocol in very good yield. The carbon materials obtained after salt templated pyrolysis of the IL displayed high degrees of heteroatom doping (up to 22 wt% N, 3 wt% B) and high surface areas of up to 1860 m2 g−1. The materials were tested for their performance in the adsorptive removal of MB from contaminated water. Adsorption equilibrium experiments revealed an adsorption capacity exceeding500 mg g−1, which is, to the best of our knowledge, the highest value reported so far. Time-resolved adsorption experiments showed that the materials not only exhibit high capacity but also very fast adsorption kinetics. Complete decolorization of MB solutions in only 5 min at high MB concentrations of 100 mg L−1 was observed. These results demonstrate that [EMIM][BIm4] is an excellent precursor for the preparation of IL-derived B/N-doped carbon sorbents.

Effect of long-term methylene blue treatment on the composition of mouse gut microbiome and its relationship with the cognitive abilities of mice.

In recent years, methylene blue (MB) has attracted considerable interest as a potential drug for the treatment of methemoglobinemia and neurodegenerative diseases. MB is active against microorganisms from various taxonomic groups. However, no studies have yet been conducted on the effect of MB on the intestinal microbiome of model animals. The aim of this work was to study the effect of different concentrations of MB on the mouse gut microbiome and its relationship with the cognitive abilities of mice. We showed that a low MB concentration (15 mg/kg/day) did not cause significant changes in the microbiome composition. The Bacteroidetes/Firmicutes ratio decreased relative to the control on the 2nd and 3rd weeks. A slight decrease in the levels Actinobacteria was detected on the 3rd week of the experiment. Changes in the content of Delta, Gamma, and Epsilonproteobacteria have been also observed. We did not find significant alterations in the composition of intestinal microbiome, which could be an indication of the development of dysbiosis or other gut dysfunction. At the same time, a high concentration of MB (50 mg/kg/day) led to pronounced changes, primarily an increase in the levels of Delta, Gamma and Epsilonproteobacteria. Over 4 weeks of therapy, the treatment with high MB concentration has led to an increase in the median content of Proteobacteria to 7.49% vs. 1.61% in the control group. Finally, we found that MB at a concentration of 15 mg/kg/day improved the cognitive abilities of mice, while negative correlation between the content of Deferribacteres and cognitive parameters was revealed. Our data expand the understanding of the relationship between MB, cognitive abilities, and gut microbiome in respect to the antibacterial properties of MB.

Visible Light Spectroscopic Analysis of Methylene Blue in Water; What Comes after Dimer?

As in our previous work, most attempts to study the self-aggregation of methylene blue (MB) in water have been limited to the dimer. In the present work, we have analyzed the self-aggregation of MB in water beyond the dimeric form. For this purpose, the visible light absorption spectra of a large number of aqueous solutions of MB (1.1 × 10–6 to 3.4 × 10–3 M) and NaCl (0.0–0.15 M) at different temperatures (282–333 K) have been fed to a mathematical routine in order to determine the potential existence of a unique higher-order aggregate without any preconception about the aggregation order or about the need of counterions, such as chloride, for compensating the positive charge of the aggregates. Contrary to the common belief that the trimer is the dominant aggregate at high MB concentration, to our surprise we found that the tetramer acting alone, and without any counterion, is the higher-order aggregate that yields the best fitting to all the experimental absorbance spectra, with a very low average relative error of 0.04 ± 0.34%. Also contrary to previous assumptions, it has emerged quite evidently that this aggregate is present in the solution at MB concentrations below 3.4 × 10–5 M (11 ppm), though to a rather low extent. This has brought the need for the recalculation of the visible light absorption spectrum and the thermodynamic parameters for the dimer, which along with those for the tetramer are the main contributions of the present work.

Flax Biomass Conversion via Controlled Oxidation: Facile Tuning of Physicochemical Properties.

The role of chemical modification of pristine linen fiber (LF) on its physicochemical and adsorption properties is reported in this contribution. The surface and textural properties of the pristine LF and its peroxyacetic acid- (PAF) and chlorite-treated (CF) fiber forms were characterized by several complementary methods: spectroscopy (SEM, TEM, FT-IR, and XPS), thermal analysis (DSC and TGA), gas/water adsorption isotherms, and zeta potential (ξ). The results obtained reveal that the surface charge and textural properties (surface area and pore structure) of the LF material was modified upon chemical treatment, as indicated by changes in the biomass composition, morphology, ξ-values, and water/dye uptake properties of the fiber samples. Particularly, the pristine LF sample displays preferential removal efficiency (ER) of methylene blue (MB) dye with ER ~3-fold greater (ER~62%) as compared to the modified materials (CF or PAF; ER~21%), due to the role of surface charge of pectins and lignins present in pristine LF. At higher MB concentration, the relative ER values for LF (~19%) relative to CF or PAF (~16%) reveal the greater role of micropore adsorption sites due to the contributing effect of the textural porosity observed for the modified flax biomass at these conditions. Similar trends occur for the adsorption of water in the liquid vs. vapour phases. The chemical treatment of LF alters the polarity/charge of the surface functional groups, and pore structure properties of the chemically treated fibers, according to the variable hydration properties. The surface and textural properties of LF are altered upon chemical modification, according to the variable adsorption properties with liquid water (l) vs. water vapor (g) due to the role of surface- vs. pore-sites. This study contributes to an understanding of the structure-adsorption properties for pristine and oxidized flax fiber biomass. The chemical conversion of such biomass yields biomaterials with tunable surface and textural properties, as evidenced by the unique adsorption properties observed for pristine LF and its modified forms (CF and PAF). This study addresses knowledge gaps in the field by contributing insight on the relationship between structure and adsorption properties of such LF biomass in its pristine and chemically modified forms.

Supported TiO2 on Kaolin, Cordierite, and Calcite for Photocatalytic Removal of Dyes from Wastewater

AbstractKaolin, cordierite, and calcite are investigated as supports for TiO2. The prepared TiO2/support samples are examined for the removal of organic dyes from wastewater. The samples are preliminarily investigated to identify the optimal loaded system using synthetic wastewater containing methylene blue (MB). Data indicate that the investigated support significantly affects the photocatalytic activity of the supported TiO2. Low photocatalytic activity toward MB degradation is observed upon using TiO2/calcite when compared to the unsupported TiO2. Interaction between calcite and titania species probably occurrs to produce the less photoactive CaTiO3 amorphous species. Anatase TiO2 is obtained upon using kaolin and cordierite as supports. The low photocatalytic performance of the TiO2/kaolin sample is also observed. A high concentration of MB on TiO2/kaolin surfaces blocks the photoactive sites. TiO2/cordierite shows the highest photocatalytic activity compared to the unsupported TiO2 as well as the other TiO2/support samples. Rigid cordierite particles suppress the agglomeration of TiO2 particles during the preparation, leading to a high exposed surface of TiO2 towards light illumination. TiO2/cordierite is investigated for the removal of organic dye from real wastewater collected from a textile dyeing factory. Color removal of up to 46% is achieved upon UV irradiation.

Unravelling the distinct surface interactions of modified graphene nanostructures with methylene blue dye through experimental and computational approaches

Nanoscopic modifications leading to multi-dimensional graphene structures are known to significantly influence their candidature for several applications including catalysis, energy storage, molecular sensing and most significantly adsorption and remediation of harmful materials such as dyes. The present work attempts to identify the key trajectories that connect the structural qualification with a chosen application, viz., the interactive forces in dye remediation. Various physico-chemically Modified Graphene Nanostructures (MGNs) such as 2 dimensional Graphite, Graphene Oxide (GO), reduced GO (rGO), holey rGO, and 3 dimensional GO hydrogel and Holey GO hydrogel are chosen and synthesised herein. These represent varieties of physicochemical features with respect to their dimensionality, surface features such as oxygen functionality, nanoscopic holes etc., that contribute to their characteristic overall surface interactions. Methylene Blue (MB), a popular industrial effluent posing major environmental concern is chosen to be a probe adsorbate in this case study. An exclusive real time in-situ UV visible spectral experiment provides the revealing reasons behind the outstanding performance of 2D GO sheets with an adsorption capacity of greater than 92 % even at high MB concentrations (>2000 ppm). A complex dependency of various factors such as surface oxygen, morphology, nanoporosity etc. on the unique overall interaction with an adsorbent such as MB by all these adsorbates is demonstrated using experimental and DFT based computational studies. Electrostatics and hydrogen bonding are understood to be the two dominant forces driving the MB adsorption on the best performing GO here.

Facile Synthesis of Co3O4 Nanoparticle-Functionalized Mesoporous SiO2 for Catalytic Degradation of Methylene Blue from Aqueous Solutions

In this study, a series of Co3O4 nanoparticle-functionalized mesoporous SiO2 (Co–SiO2) were successfully synthesized via a spontaneous infiltration route. Co species were firstly infiltrated into the confined spaces between the surfactant and silica walls, with the assistance of grinding CoCl3·6H2O and the as-prepared mesoporous SiO2. Then, Co3O4 nanoparticles (NPs) were formed and grown in the limited space of the mesopores, after calcination. Structures, morphologies, and compositions of the materials were characterized by X-ray diffraction, transmission electron microscopy, energy dispersion spectrum, N2 adsorption, and Fourier transform infrared spectra. Results showed that the high content of Co (rCo:Si = 0.17) can be efficiently dispersed into the mesoporous SiO2 as forms of Co3O4 NPs, and the structural ordering of the mesoporous SiO2 was well-preserved at the same time. The Co3O4 NP functionalized mesoporous SiO2 materials were used as Fenton-like catalysts for removing methylene blue (MB) from aqueous solutions. The catalyst prepared at rCo:Si = 0.17 could completely remove the high-concentration of MB (120 mg·L−1), and also showed an excellent performance with a removal capacity of 138 mg·g−1 to 180 mg·L−1 of MB. Catalytic mechanisms were further revealed, based on the degradation results.

Comparative study of the adsorption of micropollutant contained in aqueous phase using coal fly ash and activated coal fly ash: Kinetic and isotherm studies

Abstract The removal of methylene blue (MB) from aqueous solution with the help of fly ash (FA) and activated FA was investigated by kinetics and isotherms modeling studies. The results of physical and chemical analyses of the FA after activation process indicate the formation of new geo-adsorbent. The adsorption kinetics behavior of MB onto fly ash and activated fly ash were studied and compeered using pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The equilibrium adsorption data were evaluated by Langmuir, Freundlich and Temkin isotherm equations. The investigation of adsorption isotherms data were fitted well to Langmuir isotherm model and the adsorption kinetic was better expressed by pseudo-second-order equation. Based on the Langmuir model, the maximum monolayer adsorption capacity of MB using FA and activated fly ash were 2.88 and 37.08 mg/g, respectively. The results indicate that the activated FA is an efficient and low-cost adsorbent for decontamination of dye containing water. In addition, the other results suggested that the formation of new stable material for encapsulation of aqueous solution contaminated by high concentration of methylene blue.

Enhancing osteoblast functions on biofilm-contaminated titanium alloy by concentration-dependent use of methylene blue-mediated antimicrobial photodynamic therapy.

The concentration of methylene blue (MB) photosensitizer could affect the eradication efficacy of antimicrobial photodynamic therapy (aPDT) in the treatment of contaminated implants, which is linked to the osseointegration of the implant. We evaluated osteoblast functions on the contaminated SLA (sandblasting, large-grit and acid-etching) Ti alloy surfaces after the concentration-dependent use of MB-aPDT. Totally 1164 SLA discs were randomly distributed for the analyses of antibacterial efficacy and osteoblast functions. Gram-negative (Aggregatibacter actinomycetemcomitans; A. actinomycetemcomitans) or Gram-positive (Streptococcus mutans; S. mutans) adhered on disc samples was subjected to aPDT with different MB concentrations (200, 250, 300, 350, and 400 μg/mL) using 660 nm diode laser with maximum output 80 mW for 1 min irradiation (4.8 J/cm2). Bactericidal effect was examined by viability, morphology, and lipopolysaccharide (LPS) assays. The disinfected disc surfaces by MB-aPDT to support osteoblast-like MG63 attachment, proliferation, differentiation, and mineralization were assessed for the predetermined culture time intervals. The statistical differences between the means were performed using a one-way analysis of variance (ANOVA) with a post hoc Scheffe test. The results of the morphology observation and bacterial survival examination consistently indicated a remarkably lower quantity of bacterial colonies on biofilm-contaminated surfaces after the aPDT treatment with higher MB concentration. Similarly, the higher MB concentration in aPDT resulted in the lower LPS amounts remaining on the A. actinomycetemcomitans-contaminated surfaces. Intriguingly, the expression of osteoblast cultured on disinfected surfaces using aPDT with higher MB concentration was comparable to the control without contamination. Within the limits of this in vitro model, this formulation of 400 μg/mL MB used in aPDT may be not only the lethal concentration against the 2 bacteria-contaminated implants, but it could also enhance the osteoblast functions on the contaminated implants. Nevertheless, the efficacy in the clinical practice for peri-implantitis therapy remains to be studied.

Toxicity Effects of Methylene Blue on Rat Intervertebral Disc Annulus Fibrosus Cells

Background: There is an increasing local application of methylene blue (MB) in the treatment of discogenic low back pain (LBP) and percutaneous transforaminal endoscopic discectomy (PTED) procedures. MB could generate DNA damage and induce apoptosis in different cell types; however, the effects of MB on intervertebral disc (IVD) annulus fibrosus (AF) cells are not clearly understood. Objective: The objective of this study was to investigate the effects of different concentrations of MB on rat AF cells in vitro. Study Design: This study used an experimental design. Setting: This research was conducted at the Orthopaedic Institute of the Clinical Medical College of Yangzhou University. Methods: AF cells were isolated and cultured with different concentrations of MB (0, 2, 20, and 200 μg/mL) and assessed to determine the possible cytotoxic effects of MB. The cell proliferation was detected by Cell Counting Kit-8 (CCK-8) assay. The inverted phase-contrast microscopy was used to perform morphological observation of apoptotic cells, and flow cytometry was used to measure the incidence of cell apoptosis. The mRNA and protein expression levels of apoptosis-associated genes (caspase-3, Bcl-2, and Bax) and other related genes (collagen type I, transforming growth factor β1 [TGF-β1], fibroblast growth factor [bFGF], and tissue inhibitor of metalloproteinase-1 [TIMP-1]) were analyzed by quantitative real-time PCR (RT-PCR) and Western blotting. Results: Our results indicated that MB reduced cell viability in a concentration- and timedependent manner. MB also induced marked AF cell apoptosis in a concentration-dependent manner observed by inverted phase-contrast microscopy, flow cytometry, and indicated by the increased expression of caspase-3. Both RT-PCR and Western blotting revealed significant upregulation of Bax and caspase-3 expression levels accompanied by decreased expression of Bcl2 in a concentration-dependent manner. Moreover, collagen type I, TGF-β1, bFGF, and TIMP-1 mRNA and protein levels were also found to be decreased by MB in a concentration-dependent manner. Limitations: Limitations of this study were the in vitro study design and lack of in vivo validation of the observed effects of MB on human IVD cells. Conclusions: Our results indicate that a high concentration of MB can not only inhibit proliferation and paracrine function of AF cells, but can also induce cell apoptosis in a concentration-dependent manner, suggesting that it is necessary to choose low concentrations of MB in practical application and limit the use of MB in the treatment of discogenic LBP to research protocols. Key words: Methylene blue, annulus fibrosus cell, proliferation, apoptosis, paracrine

Antimicrobial efficacy of methylene blue-mediated photodynamic therapy on titanium alloy surfaces in vitro.

Bacterial elimination using antimicrobial photodynamic therapy (aPDT) has been considered an alternative therapeutic modality in peri-implantitis treatment. The present in vitro study evaluated the dose-dependent and pH-dependent bactericidal effects of methylene blue (MB)-mediated aPDT at eliminating Gram-negative (P. gingivalis and A. actinomycetemcomitans) and Gram-positive (S. mutans) bacteria on sandblasting, large-grit and acid-etching (SLA)-pretreated titanium alloy. The effects of different MB concentrations (50, 100, and 200 μg/mL), the pH of the MB (4, 7, and 10), and irradiation time (0, 30, and 60 s) on the bacterial viability and residual lipopolysaccharide (LPS) levels were examined. The variations in the pH of the MB solution after aPDT for 60 s on the uncontaminated and contaminated specimens were also detected. The experimental results indicated that MB-mediated PDT could effectively kill the majority of bacteria on the titanium alloy surfaces of biofilm-contaminated implants compared with the MB alone. Of note, aPDT exhibited better antibacterial efficacy with increase in the MB concentration and irradiation time. While treated in an acidic solution on the biofilm-contaminated specimens, aPDT caused the pH to increase. By contrast, the initially high alkaline pH decreased to a value of about pH 8.5 after aPDT. Intriguingly, the neutral pH had minor changes, independent of the MB concentration and bacterial species. As expected, aPDT with higher MB concentration at higher pH environment significantly lowered the LPS concentration of A. actinomycetemcomitans and P. gingivalis. On the basis of the data, the aPDT with 200 μg/mL MB at pH 10 for 60 s of irradiation time might be an effectively treatment to eliminate bacteria and LPS adherent to titanium surface, however, the use of the multispecies biofilm model and the evaluation of in vitro osteogenesis needed to be further evaluated.