Marcelo Martins Seckler

Silver Nanoparticles: Therapeutical Uses, Toxicity, and Safety Issues

The promises of nanotechnology have been realized to deliver the greatest scientific and technological advances in several areas. The biocidal activity of Metal nanoparticles in general and silver nanoparticles (AgNPs) depends on several morphological and physicochemical characteristics of the particles. Many of the interactions of the AgNPs with the human body are still poorly understood; consequently, the most desirable characteristics for the AgNPs are not yet well established. Therefore, the development of nanoparticles with well-controlled morphological and physicochemical features for application in human body is still an active area of interdisciplinary research. Effects of the development of technology of nanostructured compounds seem to be so large and comprehensive that probably it will impact on all fields of science and technology. However, mechanisms of safety control in application, utilization, responsiveness, and disposal accumulation still need to be further studied in-depth to ensure that the advances provided by nanotechnology are real and liable to provide solid and consistent progress. This review aims to discuss AgNPs applied in biomedicine and as promising field for insertion and development of new compounds related to medical and pharmacy technology. The review also addresses drug delivery, toxicity issues, and the safety rules concerning biomedical applications of silver nanoparticles.

Calcium phosphate precipitation in a fluidized bed in relation to process conditions: A black box approach

The precipitation features of calcium phosphate in a fluidized bed reactor in the concentration range between 5 and 100 mg P 1−1 were studied, and the conditions for optimum phosphate removal efficiency were established. The supply of calcium ions should be such that a Ca/P molar ratio of 3 at the inlet of the reactor is achieved. If the water to be treated does not contain magnesium or carbonate ions, the supply of base should suffice to promote a conversion of 50–65% of the incoming phosphate to the solid phase. In the presence of carbonate and magnesium ions, the base supply should provide a conversion of 80–95%. Magnesium and carbonate ions did not have a detrimental effect on the phosphate removal efficiency for inlet concentrations of up to 4.8 × 10−3 (Mg/P < 2 mol mol−1) and 1.8 × 10−3 kmol m−3, respectively. The feasibility of a process based on the precipitation of magnesium phosphate instead of calcium phosphate was demonstrated for waters with a low calcium content (Ca/P < 0.8 mol mol−1). Finally a method is presented to select process conditions where co-precipitation of unwanted phases can be avoided.

Phosphate removal in a fluidized bed—II. Process optimization

The aggregation of fine primarily formed calcium phosphate particles with sand grains in a fluidized bed for phosphate removal was studied experimentally by means of a set-up which isolated aggregation from other processes during calcium phosphate precipitation, as well as through experiments under normal operation of the fluidized bed. The net aggregation process was described by means of a mathematical model which takes into account two competing mechanisms: orthokinetic aggregation and breakage. The net aggregation process was found to account for ∼ 60% of the phosphate removed by the fluidized bed. It was found that the orthokinetic aggregation can be improved by spreading the supersaturation more evenly throughout the reactor, and breakage can be diminished by a low energy dissipation rate in the bed. Optimization of the phosphate removal efficiency was therefore achieved by selecting sand grains of small sizes (0.1–0.3 mm) and a low superficial velocity (7·10−3 m/s), and by spreading the addition of the NaOH solution (reactant) over two dosage points. Under these conditions the phosphate removal efficiency was ∼ 80%.

Phosphate removal in a fluidized bed—I. Identification of physical processes

The main processes concerning the precipitation of calcium phosphate in a fluidized bed were studied. Primary nucleation and molecular growth occur at the bottom of the bed, where the incoming phosphate is mixed with the reactants, producing fine particles which partly aggregate with the grains of the bed and further leave the reactor with the liquid effluent. This aggregation seems to be the most important process for phosphate removal, while molecular growth of the grains seems to be of secondary importance.

INDUSTRIAL CRYSTALLIZATION AND PRECIPITATION FROM SOLUTIONS: STATE OF THE TECHNIQUE

Crystallization and precipitation from solutions are responsible for 70% of all solid materials produced by the chemical industry. Competing with distillation as a separation and purification technique, their use is widespread. They operate at low temperatures with low energy consumption and yield with high purifications in one single step. Operational conditions largely determine product quality in terms of purity, filterability, flowability and reactivity. Producing a material with the desired quality often requires a sound knowledge of the elementary steps involved in the process: creation of supersaturation, nucleation, crystal growth, aggregation and other secondary processes. Mathematical models coupling these elementary processes to all particles in a crystallizer have been developed to design and optimize crystallizer operation. For precipitation, the spatial distribution of reactants and particles in the reactor is important; thus the tools of computational fluid dynamics are becoming increasingly important. For crystallization of organic chemicals, where incorporation of impurities and crystal shape are critical, molecular modeling has recently appeared as a useful tool. These theoretical developments must be coupled to experimental data specific to each material. Theories and experimental techniques of industrial crystallization and precipitation from solutions are reviewed, and recent developments are highlighted.

Antimicrobial effectiveness of silver nanoparticles co-stabilized by the bioactive copolymer pluronic F68

BackgroundSilver nanoparticles (AgNps) have attracted much interest in biomedical engineering, since they have excellent antimicrobial properties. Therefore, AgNps have often been considered for incorporation into medical products for skin pathologies to reduce the risk of contamination. This study aims at evaluating the antimicrobial effectiveness of AgNps stabilized by pluronic™ F68 associated with other polymers such as polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP).MethodsAgNps antimicrobial activity was evaluated using the minimum inhibitory concentration (MIC) method. The action spectrum was evaluated for different polymers associated with pluronic™ F68 against the gram negative bacteria P. aeuroginosa and E. coli and the gram positive bacteria S. Aureus.ResultsAgNps stabilized with PVP or PVA and co-stabilized with pluronic™ F68 are effective against E. coli and P. aeruginosa microorganisms, with MIC values as low as 0.78% of the concentration of the original AgNps dispersion. The antimicrobial action against S. aureus is poor, with MIC values not lower than 25%.ConclusionsAgNps stabilized by different polymeric systems have shown improved antimicrobial activity against gram-negative microorganisms in comparison to unstabilized AgNps. Co-stabilization with the bioactive copolymer pluronic™ F68 has further enhanced the antimicrobial effectiveness against both microorganisms. A poor effectiveness has been found against the gram-positive S. aureus microorganism. Future assays are being delineated targeting possible therapeutic applications.

Evaluation of the Performance of a Newly Developed Eutectic Freeze Crystallizer: Scraped Cooled Wall CrystalIizer

Eutectic freeze crystallization (EFC) separates aqueous inorganic solutions into pure water and pure salt. By operating at the eutectic point, ice and salt can be formed simultaneously as two separate phases. The scraped cooled wall crystallizer (SCWC), specially developed for eutectic operation, is introduced. It features cooling through an outer wall combined with an internal cooling cylinder. Experiments were executed in a 1151 model SCWC using a ternary aqueous system of KN0 3 –HN0 3 . The SCWC is equipped with temperature sensors measuring bulk temperature and the temperatures of the coolant entering and exiting the cooling walls. The total heat flux from coolant to bulk equals 490-585 W m −2 K −1 at a temperature difference between cooling wall and bulk of 5–6K. At this heat flux the production capacity equals 3.8 x 10 −4 kg m −2 K −1 s −1 for ice and 3.1 x 10 −5 kgm −2 K −1 s −1 for salt. The KN0 3 crystals produced are reasonably well faceted with average size of 80–230 μm. Both ice and salt crystals are easily filtered. Impurities in the ice crystals drop below 50ppm K+-ions after three washings. Ice solid content measurements indicated that 0.01 wt% of the ice slurry consisted of entrained salt crystals. Washed salt samples contained less than 5 ppm of ionic impurities while impurity levels in the feed ranged from 50 to 500 ppm.

Dynamic modeling and simulation of eutectic freeze crystallization

Abstract A computer-based dynamic model of an eutectic freeze crystallizer comprised of coupled kinetics, population, mass, and energy balances has been developed to simulate its transient behaviour. The model assumed an MSMPR crystallizer and was used to simulate the transient responses of crystal size distribution of salt and ice during the start-up of the crystallizer. The temperature and the solute concentration inside the crystallizer achieved constant values after two residence times, whereas the steady state of the crystal size distributions were reached after ten residence times. A coupled effect of the simultaneous crystallization of salt and ice was clearly visible when the high mass production rate of ice induced the occurrence of a second peak of the supersaturation of salt.

Recrystallization of calcium sulfate in phosphoric acid solutions; batchwise operation

A model is presented for the solvent mediated batchwise recrystallization of hemihydrate into dehydrate. The model takes into account the rates of dissolution of hemihydrate and of growth of gypsum. These rates result from the driving forces (under- and supersaturation) that are influenced by temperature and acid concentrations, and from the rate constants, which are mainly affected by impurities. Secondary nucleation can be neglected with respect to the observed recrystallization rates. The presented model can also be applied more generally.

Diesel exhaust particulates affect cell signaling, mucin profiles, and apoptosis in trachea explants of Balb/C mice

Particulate matter from diesel exhaust (DEP) has toxic properties and can activate intracellular signaling pathways and induce metabolic changes. This study was conducted to evaluate the activation of extracellular signal‐regulated kinase (ERK) and c‐Jun N‐terminal kinase (JNK) and to analyze the mucin profile (acid (AB+), neutral (PAS+), or mixed (AB/PAS+) mucus) and vacuolization (V) of tracheal explants after treatment with 50 or 100 μg/mL DEP for 30 or 60 min. Western blot analyses showed small increases in ERK1/2 and JNK phosphorylation after 30 min of 100 μg/mL DEP treatment compared with the control. An increase in JNK phosphorylation was observed after 60 min of treatment with 50 μg/mL DEP compared with the control. We did not observe any change in the level of ERK1/2 phosphorylation after treatment with 50 μg/mL DEP. Other groups of tracheas were subjected to histological sectioning and stained with periodic acid‐Schiff (PAS) reagent and Alcian Blue (AB). The stained tissue sections were then subjected to morphometric analysis. The results obtained were compared using ANOVA. Treatment with 50 μg/mL DEP for 30 min or 60 min showed a significant increase (p < 0.001) in the amount of acid mucus, a reduction in neutral mucus, a significant reduction in mixed mucus, and greater vacuolization. Our results suggest that compounds found in DEPs are able to activate acid mucus production and enhance vacuolization and cell signaling pathways, which can lead to airway diseases.