Cytotoxicity of dental disclosing solution on gingival epithelial cells in vitro.

OBJECTIVE: Coloring dental biofilm and plaque with a dental disclosing solution is visually effective in dental treatment and oral hygiene education. Despite continuous reports of the risk of the product ingredients, dental disclosing solution are widely used in dentistry. However, the cytotoxic mechanism of dental disclosing solution is not known. Here we elucidated the tissue dyeing range and investigated the cytotoxic mechanism of dental disclosing solution. MATERIALS AND METHODS: Gingival epithelial cells and mouse head and neck tissue were stained with dental disclosing solution. Changes in the cell cycle distribution by the dental disclosing solution treatment were analyzed. A deoxynucleotidyl transferase dUTP nick and labeling (TUNEL) assay was performed to examine the apoptotic features of the gingival epithelial cells. RESULTS: Dental disclosing solution stained the chromosome strongly, as well as both the hard and soft tissue of the mouse head and neck. The results of flow cytometric analysis and TUNEL analyses revealed that the cytotoxicity associated with dental disclosing solution was related to the induction of apoptosis. However, the staining of porcine skin by dental disclosing solution was not easily removed, even with a wide range of pH solutions. CONCLUSIONS: These results suggest that dental disclosing solution had strong cytotoxicity and safer alternatives are needed.

Surface modification and use of polymer complex agents to mitigate metal crossover of anion-exchange membranes.

The facile surface modification of a commercial anion-exchange membrane (i.e., Neosepta-AFX, Astom Corp., Japan) was investigated with brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO), which had non-charged polar groups, and its quaternized form (QPPO) to improve the acid recovery efficiency in diffusion dialysis (DD). By coating a thin layer of BPPO on the membrane surface, the significant changes in the surface compactness and charge density were observed while the electrochemical properties were mostly maintained. From the DD experiments, it was revealed that the membrane modified with 1 wt% BPPO exhibited the moderate acid permeability as well as the highest acid selectivity (KAcid/KFe3+=48.81), which is more than double compared with that of the pristine membrane (KAcid/KFe3+=22.48) among the tested membranes. The electron-rich polar groups contained in BPPO are believed to provide moderate proton transport while the reduced swelling property of the membrane surface can effectively mitigate the crossover of metal cations. In addition, the acid selectivity (KAcid/KFe3+=30.69) was largely improved by using small molecular weight poly(ethyleneimine) (PEI, Mn=1800) with a small content (in the range of 1-5 wt%) as a solution additive for the growing size of metal species by the formation of polymer-metal complexes.

An approach to fouling characterization of an ion-exchange membrane using current-voltage relation and electrical impedance spectroscopy.

Fouling phenomena of an anion-exchange membrane by bovine serum albumin (BSA) were investigated using current-voltage relation and electrical impedance spectroscopy (EIS) in this study. Electrochemical parameters of the Neosepta CMX cation- and AMX anion-exchange membrane (Tokuyama Corp., Japan) such as limiting current density (LCD), transport number, plateau length, and fraction of the conducting phase were measured. Fraction of the conducting phase of the ion-exchange membranes, calculated from the modified Sand equation, played an important role in determining the electrochemical parameters in the presence of foulants such as BSA. Fraction of the conducting phase of the AMX membrane significantly decreased in the presence of BSA. Two distinguishable slopes were observed in the over-LCD region of the current-voltage (I-V) curve, indicating the change of resistance. To further elucidate the phenomena, the electrical impedance spectroscopic study was carried out using the offset alternating current. It was found that the negatively charged loose fouling layer changed to the dense deposited BSA on the surface of the AMX membrane occurring along with enhanced water dissociation phenomena at the surface of the fouled AMX membrane at a higher current density. This result was confirmed by water dissociation experiments in a six-compartment electrodialysis cell.

A study on stack configuration of continuous electrodeionization for removal of heavy metal ions from the primary coolant of a nuclear power plant.

This study investigated the production of high-purity water in the primary coolant of a nuclear power plant via the continuous electrodeionization (CEDI) process, using ion exchange resins as ion-conducting media between ion exchange membranes. The effectiveness of this method was examined with respect to the removal of heavy metals. The study was carried out on a laboratory scale with an effective area of 20 cm(2). The CEDI system was operated with a layered bed of cation exchange resins, anion exchange resins, and mixed-bed ion exchange resins. The stack configuration was designed to prevent a reaction between metal ions and hydroxide ions. The CEDI operation with the layered bed removed more than 99% of the ions at 30% of the current efficiency. The results showed that, with an inlet conductivity of 40 microScm(-1), a linear velocity of 4.17 cms(-1), and an applied current density of 17 mAcm(-2), the CEDI process yielded an outlet conductivity of 0.5 microScm(-1), thereby preventing the precipitation of metal ions. This study therefore successfully demonstrated the feasibility of the CEDI operation for the removal of heavy metals at a very low concentration.

Studies on adsorptive removal of Co(II), Cr(III) and Ni(II) by IRN77 cation-exchange resin.

The adsorption of cobalt, chromium and nickel from aqueous solutions on IRN77 cation-exchange resin has been studied comparatively. The percentage removal of cobalt, chromium and nickel was examined by varying experimental conditions, viz. dosage of adsorbent, pH of the solution and contact time. It was found that more than 95% removal was achieved under optimal conditions. The adsorption capacity (k) for cobalt, chromium and nickel were calculated from the Freundlich adsorption isotherm. The adsorption of cobalt, chromium and nickel on this cation-exchange resin followed the Lagergren kinetic model. Also the competitive adsorption of multi-metals onto the IRN77 resin was studied. The studies showed that this cation-exchange resin can be used as an efficient adsorbent material for the removal of cobalt, chromium and nickel from water and nuclear power plant coolant water.