Emerson R. Camargo

The growing importance of materials that prevent microbial adhesion: antimicrobial effect of medical devices containing silver

Research has clarified the properties required for polymers that resist bacterial colonisation for use in medical devices. The increase in antibiotic-resistant microorganisms has prompted interest in the use of silver as an antimicrobial agent. Silver-based polymers can protect the inner and outer surfaces of devices against the attachment of microorganisms. Thus, this review focuses on the mechanisms of various silver forms as antimicrobial agents against different microorganisms and biofilms as well as the dissociation of silver ions and the resulting reduction in antimicrobial efficacy for medical devices. This work suggests that the characteristics of released silver ions depend on the nature of the silver antimicrobial used and the polymer matrix. In addition, the elementary silver, silver zeolite and silver nanoparticles, used in polymers or as coatings could be used as antimicrobial biomaterials for a variety of promising applications.

Moderating effect of ammonia on particle growth and stability of quasi-monodisperse silver nanoparticles synthesized by the Turkevich method

A new method to stabilize silver nanoparticles by the addition of ammonia is proposed. Colloidal dispersions of silver nanoparticles were synthesized by the Turkevich method using sodium citrate to reduce silver nitrate at high pH and at 90 °C. After approximately 12 min, a diluted ammonia solution was added to the reaction flask to form soluble diamine silver (I) complexes that played an important growth moderating role, making it possible to stabilize metallic silver nanoparticles with sizes as small as 1.6 nm after 17 min of reaction. Colloidal dispersions were characterized by UV-visible absorption spectroscopy, X-ray diffraction, and transmission electronic microscopy.

A novel aqueous solution route to the low-temperature synthesis of SrBi2Nb2O9 by use of water-soluble Bi and Nb complexes

Abstract Powders of SrBi 2 Nb 2 O 9 (SBN) were synthesized using an aqueous solution method from mixtures of all water-soluble compounds including Sr–EDTA, Bi–EDTA and Nb–citrate. Heating of a mixed aqueous solution with the molar ratio of Sr:Bi:Nb:citric acid=1:2:2:10 produced a pale-yellow gelatinous viscous matter without any precipitation, which was subsequently pyrolyzed at 300°C to give a powder precursor for SBN. The formation of a pure Perovskite ferroelectric SBN occurred when the powder precursor was heat-treated in air at temperatures higher than 650°C. A fluorite SBN formed in the 500–600°C range, which appeared to act as an intermediate phase prior to the formation of the Perovskite SBN. The environmentally beneficial aspect of the present aqueous solution route was briefly discussed.

Effect of Cr2O3 in the varistor behaviour of TiO2

Laboratorio Interdisciplinar de Eletroquimica e Cerâmica Departamento de Quimica UFSCar, C.P. 676, 13565-905 Sao Carlos, SP

Low temperature synthesis of lithium niobate powders based on water-soluble niobium malato complexes

Abstract Pure lithium niobate (LN) powders were prepared by a wet-chemical method. Hydrated niobium oxide was dissolved in a hot aqueous solution of oxalic acid, followed by the precipitation of niobic acid by the addition of ammonia solution until pH=11. Niobic acid precipitated was dissolved in an aqueous solution of dl -malic acid. A small amount of the Nb–malic complex synthesized was isolated and characterized by thermogravimetry (TG) and infrared (IR) spectroscopy, and the molecular composition of the complex was determined as H[Nb 2 O(H 3 C 4 O 5 ) 3 ]. The exact content of niobium in the stable solution of Nb–malic solution was determined by gravimetric analysis. Stoichiometric amount of lithium carbonate was added into Nb–malic solution. After the solvent elimination, the remaining solid powder was calcined at 350 °C, ground and calcined over a temperature range from 300 to 900 °C. Calcined powders were characterized by X-ray diffraction (XRD) and Raman spectroscopy. Crystalline LN phase was identified at 500 °C/2 h, although the total elimination of the inorganic carbon occurred only at 650 °C/2 h.

Phase Transformation in Titania Nanocrystals by the Oriented Attachment Mechanism: The Role of the pH Value

The oriented attachment (OA) mechanism has been investigated as an important process in the formation of anisotropic nanostructures such as depicted. The results showed that the control of a desired phase in this system may be attained by the control of OA mechanism through pH value, obtaining several morphologies.A new synthetic method for TiO(2) nanocrystals starting from metallic Ti and hydrogen peroxide was developed, in order to obtain minimal interferences to evaluate phase transformation in the system. The results revealed that the crystal morphology appeared to be dictated by the pH value, which shows a strong dependence on the surface energy. The involvement of the oriented attachment (OA) mechanism is important to modify the morphology and, hence, the distribution of the surface energy and confirmed that the mechanism can accelerate certain phase transitions, albeit pH dependence in terms of how the mechanism affects the final particle morphology and direction of crystalline growth. The importance of the mechanism was also apparent in extremely basic conditions, which indicates a possible correlation with the formation of hydrogen titanate nanostructures.

The effect of silver nanoparticles and nystatin on mixed biofilms of Candida glabrata and Candida albicans on acrylic

The aim of this study was to compare biofilm formation by Candida glabrata and Candida albicans on acrylic, either individually or when combined (single and dual species) and then examine the antimicrobial effects of silver nanoparticles and nystatin on these biofilms. Candidal adhesion and biofilm assays were performed on acrylic surface in the presence of artificial saliva (AS) for 2 h and 48 h, respectively. Candida glabrata and C. albicans adherence was determined by the number of colony forming units (CFUs) recovered from the biofilms on CHROMagar(®) Candida. In addition, crystal violet (CV) staining was used as an indicator of biofilm biomass and to quantify biofilm formation ability. Pre-formed biofilms were treated either with silver nanoparticles or nystatin and the effect of these agents on the biofilms was evaluated after 24 h. Results showed that both species adhered to and formed biofilms on acrylic surfaces. A significantly (P < 0.05) higher number of CFUs was evident in C. glabrata biofilms compared with those formed by C. albicans. Comparing single and dual species biofilms, equivalent CFU numbers were evident for the individual species. Both silver nanoparticles and nystatin reduced biofilm biomass and the CFUs of single and dual species biofilms (P < 0.05). Silver nanoparticles had a significantly (P < 0.05) greater effect on reducing C. glabrata biofilm biomass compared with C. albicans. Similarly, nystatin was more effective in reducing the number of CFUs of dual species biofilms compared with those of single species (P < 0.05). In summary, C. glabrata and C. albicans can co-exist in biofilms without apparent antagonism, and both silver nanoparticles and nystatin exhibit inhibitory effects on biofilms of these species.

Antifungal activity of silver nanoparticles in combination with nystatin and chlorhexidine digluconate against Candida albicans and Candida glabrata biofilms.

Although silver nanoparticles (SN) have been investigated as an alternative to conventional antifungal drugs in the control of Candida‐associated denture stomatitis, the antifungal activity of SN in combination with antifungal drugs against Candida biofilms remains unknown. Therefore, the aim of this study was to evaluate the antifungal efficacy of SN in combination with nystatin (NYT) or chlorhexidine digluconate (CHG) against Candida albicans and Candida glabrata biofilms. The drugs alone or combined with SN were applied on mature Candida biofilms (48 h), and after 24 h of treatment their antibiofilm activities were assessed by total biomass quantification (by crystal violet staining) and colony forming units enumeration. The structure of Candida biofilms was analysed by scanning electron microscopy (SEM) images. The data indicated that SN combined with either NYT or CHG demonstrated synergistic antibiofilm activity, and this activity was dependent on the species and on the drug concentrations used. SEM images showed that some drug combinations were able to disrupt Candida biofilms. The results of this study suggest that the combination of SN with NYT or CHG may have clinical implications in the treatment of denture stomatitis. However, further studies are needed before recommending the use of these drugs safely in clinical situations.

Synthesis and photocatalytic properties of bismuth titanate with different structures via oxidant peroxo method (OPM).

Bismuth titanate (Bi4Ti3O12 and Bi12TiO20) powders were synthesized by the Oxidant Peroxide Method (OPM), and the effect of temperatures on physical and chemical properties of particles was investigated. The results showed that the morphology and average particle size of materials can be successfully controlled by adjusting the temperature. The samples after calcination were characterized by X-ray diffractometry, transmission electron microscopy, diffuse reflectance spectroscopy, Raman spectroscopy, and BET isotherms. The photocatalytic activity of materials was also evaluated by studying the degradation of 10ppm aqueous rhodamine B dye under ultraviolet radiation.

Synthesis of Ultra-Fine Columbite Powder MgNb2O6 by the Polymerized Complex Method

Pure MgNb2O6 powders with high specific surface area and high crystallinity have been successfully synthesized by the “Polymerized Complex (PC) Method”. A solution of water, citric acid, ethylene glycol and niobium and magnesium ions, was polymerized at 130°C by the water elimination and was calcined at 400°C for 2 h. The precursor formed was calcined at temperatures from 700°C to 1000°C in air to obtain the columbite phase. Thermal analysis, Raman spectroscopy, x-ray diffraction, adsorption/desorption hysteresis and scanning electron microscopy were used to investigate the polymer decomposition and the columbite phase evolution. No evidence for phase separation of crystalline MgCO3 and Nb2O5 in Raman spectra and x-ray diffraction pattern as distinct intermediates were found, and the MgNb2O6 probably is formed through a single-step decomposition of oxycarbonate intermediate, as other double oxide synthesized by the PC Method, as indicated by the thermal decomposition of the precursor.