Vigilancia Tecnológica
Información de la temática del proyectoAntibacterial and antiviral activities of transparent PVA coating films prepared by using solutions containing eluted ions from rare earth iodates
AbstractAfter powders of three rare earth iodates (Ce(IO3)4, Ce(IO3)3, ?-La(IO3)3) were dispersed in water, the constituent ions were eluted. After filtration, polyvinyl alcohol was dissolved in the filtrated solution. Then the solution was flow-coated to form coating films on glass substrates. The obtained coating films exhibited high transmittance in the visible wavelength range. IO3? was confirmed from the IR spectra measured using the ATR method. Fine precipitates were observed in the coating. The amount was greater on the surface than inside. The coating films prepared from Ce(IO3)3 and ?-La(IO3)3 possessed high antibacterial and antiviral activities against Escherichia coli, Staphylococcus aureus, bacteriophage Q?, and bacteriophage ?6 in the dark. Moreover, they inactivated viruses adsorbed from the gas phase.
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IntroductionRecently, antibacterial and antiviral materials are attracting attention as a technology for preventing infectious diseases without reliance on vaccinations or antibiotics. During the long history of humanity, many organic antibacterial and antiviral materials have been developed. However, in recent years, the development of inorganic antibacterial and antiviral materials has become particularly active because they are less likely to lead to the emergence of resistant bacteria and viruses. Conventional inorganic antibacterial and antiviral materials include metallic materials such as Ag and Cu,1,2,3,4 photocatalysts such as TiO2,5,6 and materials such as ZnO and alkaline earth oxides.7,8 However, metallic systems present issues such as degradation of activity caused by oxidation, toxicity to the human body,9 coloration, and cost (Ag). Photocatalysts and alkaline earth oxides present challenges because of limitations in the environments in which they can be used (e.g., lighting requirements, alkaline soils). The performance of ZnO is not necessarily higher than that of other materials.
In response to these challenges, we have reported very recently that amorphous Ce(IO3)4 and crystalline Ce(IO3)3 and ?-La(IO3)3 are low-toxicity, low-cost inorganic materials with high antibacterial and antiviral activity in the dark.10 Careful study has revealed that the antibacterial and antiviral activities of these materials are manifested when bacteria and viruses come into contact with a powder surface or with ions eluted from the sample powder into water.
When coating various industrial products with inorganic antibacterial and antiviral materials, the material particles are generally added and dispersed in a solvent in which an organic substance that acts as a binder is dissolved.11,12,13 However, in this case, if the material particles are buried in the binder material of the coating, then they are unable to exhibit antibacterial and antiviral activities.14 For a coating with inorganic antibacterial and antiviral materials, the key factor is how to expose the material to the surface.
In this study, we focused on the characteristic that elements constituting rare earth iodates elute to a certain amount as ions in water. Then we investigated preparation of coatings by dissolving an organic binder substance in an aqueous solution containing these eluted ions after filtration of particles. Using this method, the ions effective to antibacterial and antiviral activity are concentrated near the surface of the coating during evaporation, allowing the rare earth iodates to be distributed effectively over a wide area of the surface. Then thereby overcoming difficulties of conventional inorganic antibacterial and antiviral materials coatings described above may be feasible. For this study, polyvinyl alcohol (PVA) was used as the organic binder material. Coating film samples were prepared from aqueous solutions prepared using this process. Their structures and antibacterial and antiviral activities were evaluated.
ExperimentalSample powdersThe samples of Ce(IO3)4, Ce(IO3)3, and ?-La(IO3)3 used for this study were the same as those prepared for our earlier study.10 The method for synthesis and detailed characteristics of these samples can be referred from a report of that study.10
Preparation and evaluation of coatingsAfter powders of rare earth iodates (Ce(IO3)4, Ce(IO3)3, and ?-La(IO3)3) were added each to 20 mL of distilled water to a concentration of 5.76 g/L, they were stirred in the dark at room temperature for 2 h. The suspensions were then filtered to make ion extraction solutions. The concentrations of Ce, La, and I in each ionic extract solution were measured using ICP (ICP-OES, 5100 VDV; Agilent Technologies Japan Ltd., Tokyo, Japan). The pH was also measured. To 20 mL of each ionic extract solution, 2 g of PVA ((C2H4O)x, partially saponified, 900–1100 degrees of polymerization; Fujifilm Wako Pure Chemical Corp., Tokyo, Japan) was added and stirred at 80°C for approximately 1 h to prepare a coating solution. After cooling to room temperature, 100 ?L was taken from this coating solution, and was flow-coated onto a 2.5 cm?×?2.5 cm soda-lime glass (30° tilt angle). The resulting coating was dried overnight at room temperature to prepare PVA coating films containing ions eluted from the rare earth iodates.
The transmittance of the obtained coating films in the visible light region was evaluated using an ultraviolet visible spectrophotometer (UV–Vis, V-750; Jasco Corp., Tokyo, Japan). Atomic bonds present in the samples were evaluated using the attenuated total reflection (ATR) method with Fourier transform infrared spectroscopy (FTIR, FT/IR6100; Jasco Corp., Tokyo, Japan). Surface and cross-sectional microstructures were observed using a field emission scanning electron microscope (FE-SEM, JSM7500 F; JEOL, Tokyo, Japan) with an energy dispersive X-ray microanalyzer (EDX; Genesis, EDAX Co., Pleasanton, CA, USA). The crystalline phase of the coating films was evaluated using X-ray diffraction (XRD, XRD-6100; Shimadzu Corp., Tokyo, Japan).
The antiviral activities of the prepared coating films were evaluated using the film adhesion method based on ISO 18061. For this experiment, bacteriophage Q? (hereinafter Q?, NBRC 20012) was used as a non-enveloped virus and bacteriophage ?6 (hereinafter ?6, NBRC 105899) as an enveloped virus. Escherichia coli (E. coli, NBRC 106373) was used for Q? and Pseudomonas syringae (NBRC 14084) for ?6 as host bacteria for antiviral activity evaluation. Experiment procedures and conditions were the same as those used for earlier studies.15,16 Antibacterial activity was also evaluated using the film adhesion method based on ISO 27447. For this experiment, E. coli (NBRC3972) was used as the Gram-negative bacteria. Staphylococcus aureus (S. aureus, NBRC12732) was used as the Gram-positive bacteria. The antibacterial and antiviral activities were evaluated by calculating the ratio of the number of colonies or plaques (N) at each time relative to the initial number of bacterial or viral colonies or plaques (N0). Following the same procedure, a control sample was measured using a PVA coating film with no eluted ions (no particle addition). Furthermore, the antiviral activity of PVA coating films was also assessed on several samples using a gas phase using spray method assuming droplet infection. The test procedure is described in Supporting Information (Fig. SI-1).
Results and discussionThe concentrations and pH of the ions in the ion extraction solutions are presented in Table 1. These values are similar to those reported earlier 10 on the 1/500NB solution (a solution in which bacteria and viruses are suspended when evaluating antibacterial and antiviral activity tests), with Ce(IO3)4 showing less Ce leakage than Ce(IO3)3. This finding might be attributable to the higher solubility of Ce3+ than that of Ce4+.17
Table 1 Results of eluted ion concentration in distilled waterFull size tableFigure 1 presents the UV–visible transmission spectra of the prepared samples. The prepared coating films were transparent to some degree, allowing the underlying characteristics to show through (Fig. 2). Figure 3 depicts the IR absorption spectra of various PVA coating films measured using the ATR method. The figure background is the PVA coating film without ions. The presence of IO3? in the coated films was confirmed by the detection of an IO3? derived peak at about 780 cm?1.18 The other few broad peaks at about 3000–3400 cm?1 were OH stretching vibrations. The peak at 2920 cm?1 was an asymmetric stretching vibration of CH2. In addition, the peak at 1630 cm?1 was a C=C stretching vibration. All of these peaks are from PVA.19
Fig. 1
Explore related subjects Discover the latest articles, news and stories from top researchers in related subjects. Use our pre-submission checklist Avoid common mistakes on your manuscript.
IntroductionRecently, antibacterial and antiviral materials are attracting attention as a technology for preventing infectious diseases without reliance on vaccinations or antibiotics. During the long history of humanity, many organic antibacterial and antiviral materials have been developed. However, in recent years, the development of inorganic antibacterial and antiviral materials has become particularly active because they are less likely to lead to the emergence of resistant bacteria and viruses. Conventional inorganic antibacterial and antiviral materials include metallic materials such as Ag and Cu,1,2,3,4 photocatalysts such as TiO2,5,6 and materials such as ZnO and alkaline earth oxides.7,8 However, metallic systems present issues such as degradation of activity caused by oxidation, toxicity to the human body,9 coloration, and cost (Ag). Photocatalysts and alkaline earth oxides present challenges because of limitations in the environments in which they can be used (e.g., lighting requirements, alkaline soils). The performance of ZnO is not necessarily higher than that of other materials.
In response to these challenges, we have reported very recently that amorphous Ce(IO3)4 and crystalline Ce(IO3)3 and ?-La(IO3)3 are low-toxicity, low-cost inorganic materials with high antibacterial and antiviral activity in the dark.10 Careful study has revealed that the antibacterial and antiviral activities of these materials are manifested when bacteria and viruses come into contact with a powder surface or with ions eluted from the sample powder into water.
When coating various industrial products with inorganic antibacterial and antiviral materials, the material particles are generally added and dispersed in a solvent in which an organic substance that acts as a binder is dissolved.11,12,13 However, in this case, if the material particles are buried in the binder material of the coating, then they are unable to exhibit antibacterial and antiviral activities.14 For a coating with inorganic antibacterial and antiviral materials, the key factor is how to expose the material to the surface.
In this study, we focused on the characteristic that elements constituting rare earth iodates elute to a certain amount as ions in water. Then we investigated preparation of coatings by dissolving an organic binder substance in an aqueous solution containing these eluted ions after filtration of particles. Using this method, the ions effective to antibacterial and antiviral activity are concentrated near the surface of the coating during evaporation, allowing the rare earth iodates to be distributed effectively over a wide area of the surface. Then thereby overcoming difficulties of conventional inorganic antibacterial and antiviral materials coatings described above may be feasible. For this study, polyvinyl alcohol (PVA) was used as the organic binder material. Coating film samples were prepared from aqueous solutions prepared using this process. Their structures and antibacterial and antiviral activities were evaluated.
ExperimentalSample powdersThe samples of Ce(IO3)4, Ce(IO3)3, and ?-La(IO3)3 used for this study were the same as those prepared for our earlier study.10 The method for synthesis and detailed characteristics of these samples can be referred from a report of that study.10
Preparation and evaluation of coatingsAfter powders of rare earth iodates (Ce(IO3)4, Ce(IO3)3, and ?-La(IO3)3) were added each to 20 mL of distilled water to a concentration of 5.76 g/L, they were stirred in the dark at room temperature for 2 h. The suspensions were then filtered to make ion extraction solutions. The concentrations of Ce, La, and I in each ionic extract solution were measured using ICP (ICP-OES, 5100 VDV; Agilent Technologies Japan Ltd., Tokyo, Japan). The pH was also measured. To 20 mL of each ionic extract solution, 2 g of PVA ((C2H4O)x, partially saponified, 900–1100 degrees of polymerization; Fujifilm Wako Pure Chemical Corp., Tokyo, Japan) was added and stirred at 80°C for approximately 1 h to prepare a coating solution. After cooling to room temperature, 100 ?L was taken from this coating solution, and was flow-coated onto a 2.5 cm?×?2.5 cm soda-lime glass (30° tilt angle). The resulting coating was dried overnight at room temperature to prepare PVA coating films containing ions eluted from the rare earth iodates.
The transmittance of the obtained coating films in the visible light region was evaluated using an ultraviolet visible spectrophotometer (UV–Vis, V-750; Jasco Corp., Tokyo, Japan). Atomic bonds present in the samples were evaluated using the attenuated total reflection (ATR) method with Fourier transform infrared spectroscopy (FTIR, FT/IR6100; Jasco Corp., Tokyo, Japan). Surface and cross-sectional microstructures were observed using a field emission scanning electron microscope (FE-SEM, JSM7500 F; JEOL, Tokyo, Japan) with an energy dispersive X-ray microanalyzer (EDX; Genesis, EDAX Co., Pleasanton, CA, USA). The crystalline phase of the coating films was evaluated using X-ray diffraction (XRD, XRD-6100; Shimadzu Corp., Tokyo, Japan).
The antiviral activities of the prepared coating films were evaluated using the film adhesion method based on ISO 18061. For this experiment, bacteriophage Q? (hereinafter Q?, NBRC 20012) was used as a non-enveloped virus and bacteriophage ?6 (hereinafter ?6, NBRC 105899) as an enveloped virus. Escherichia coli (E. coli, NBRC 106373) was used for Q? and Pseudomonas syringae (NBRC 14084) for ?6 as host bacteria for antiviral activity evaluation. Experiment procedures and conditions were the same as those used for earlier studies.15,16 Antibacterial activity was also evaluated using the film adhesion method based on ISO 27447. For this experiment, E. coli (NBRC3972) was used as the Gram-negative bacteria. Staphylococcus aureus (S. aureus, NBRC12732) was used as the Gram-positive bacteria. The antibacterial and antiviral activities were evaluated by calculating the ratio of the number of colonies or plaques (N) at each time relative to the initial number of bacterial or viral colonies or plaques (N0). Following the same procedure, a control sample was measured using a PVA coating film with no eluted ions (no particle addition). Furthermore, the antiviral activity of PVA coating films was also assessed on several samples using a gas phase using spray method assuming droplet infection. The test procedure is described in Supporting Information (Fig. SI-1).
Results and discussionThe concentrations and pH of the ions in the ion extraction solutions are presented in Table 1. These values are similar to those reported earlier 10 on the 1/500NB solution (a solution in which bacteria and viruses are suspended when evaluating antibacterial and antiviral activity tests), with Ce(IO3)4 showing less Ce leakage than Ce(IO3)3. This finding might be attributable to the higher solubility of Ce3+ than that of Ce4+.17
Table 1 Results of eluted ion concentration in distilled waterFull size tableFigure 1 presents the UV–visible transmission spectra of the prepared samples. The prepared coating films were transparent to some degree, allowing the underlying characteristics to show through (Fig. 2). Figure 3 depicts the IR absorption spectra of various PVA coating films measured using the ATR method. The figure background is the PVA coating film without ions. The presence of IO3? in the coated films was confirmed by the detection of an IO3? derived peak at about 780 cm?1.18 The other few broad peaks at about 3000–3400 cm?1 were OH stretching vibrations. The peak at 2920 cm?1 was an asymmetric stretching vibration of CH2. In addition, the peak at 1630 cm?1 was a C=C stretching vibration. All of these peaks are from PVA.19
Fig. 1