Optomechanical Processing of Silver Colloids: New Generation of Nanoparticle-Polymer Composites with Bactericidal Effect.

The properties of materials at the nanoscale open up new methodologies for engineering prospective materials usable in high-end applications. The preparation of composite materials with a high content of an active component on their surface is one of the current challenges of materials engineering. This concept significantly increases the efficiency of heterogeneous processes moderated by the active component, typically in biological applications, catalysis, or drug delivery. Here we introduce a general approach, based on laser-induced optomechanical processing of silver colloids, for the preparation of polymer surfaces highly enriched with silver nanoparticles (AgNPs). As a result, the AgNPs are firmly immobilized in a thin surface layer without the use of any other chemical mediators. We have shown that our approach is applicable to a broad spectrum of polymer foils, regardless of whether they absorb laser light or not. However, if the laser radiation is absorbed, it is possible to transform smooth surface morphology of the polymer into a roughened one with a higher specific surface area. Analyses of the release of silver from the polymer surface together with antibacterial tests suggested that these materials could be suitable candidates in the fight against nosocomial infections and could inhibit the formation of biofilms with a long-term effect.

Optimization of aqueous two-phase systems for the production of 6-aminopenicillanic acid in integrated microfluidic reactors-separators.

Aqueous two-phase systems (ATPSs) were screened for the production of 6-aminopenicillanic acid (6-APA) catalyzed by penicillin acylase, followed by the extractive separation of 6-APA from the reaction mixture. The key point of this study was to find an ATPS exhibiting a large difference in the partition coefficients of the biocatalyst and reaction products. Several ATPSs based on polyethylene glycol (PEG)/phosphate, PEG/citrate, and PEG/dextran were tested. We found that an ATPS consisting of 15 wt% of PEG 4000, 10 wt% of phosphates, 75 wt% of water (pH value 8.0 after dissolution) provided optimal separation of 6-APA from the enzyme. While the 6-APA was mainly found in the top PEG phase, the free enzyme favored the bottom salt-rich phase. This ATPS also fulfils other important requirements: (i) high buffering capacity, reducing an undesirable pH decrease due to the dissociation of phenylacetic acid (the side product of the reaction), (ii) a relatively low cost of the ATPS components, (iii) the possibility of electrophoretic transport of fine droplets as well as the reaction products for both the acceleration of phase separation and the enhancement of 6-APA concentration in the product stream. Extraction experiments in microcapillary and batch systems showed that the transport of 6-APA formed in the salt-rich phase to the corresponding PEG phase could occur within 30 s. The experimental results described form a base of knowledge for the development of continuously operating integrated microfluidic reactors-separators driven by an electric field for the efficient production of 6-APA.

Immobilization of Irpex lacteus to liquid-core alginate beads and their application to degradation of pollutants.

White rot fungi (WRF) are applicable to biodegradation of recalcitrant pollutants. However, excessive biomass growth typical for WRF cultivation can hinder their large scale applications. Therefore, immobilization of Irpex lacteus to liquid-core alginate beads restricting excessive mycelium growth and simultaneously keeping high degradation rate of pollutants was tested. Effective diffusivities of dyes to the beads varied from (2.98 ± 0.69) × 10-10 to (10.27 ± 2.60) × 10-10 m2/s. Remazol Brilliant Blue R (RBBR), Reactive Orange 16 (RO16), and Naphthol Blue Black (NBB) were used as model dyes. The immobilized fungus decolorized model dyes when applied both in microwell plates and in fluidized bed reactors. Using the microwell plates, the apparent reaction rate constants ranged from (2.06 ± 0.11) × 10-2 to (11.06 ± 0.27) × 10-2 1/h, depending on the dye used and its initial concentration. High initial concentrations negatively affected the dye decolorization rate. No fungal growth outside the beads was observed in fluidized bed reactors and thus no operational problems linked to an excessive biomass growth occurred. When RBBR was decolorized in subsequent batches in the fluidized bed reactor, the apparent reaction rate constant increased from (11.63 ± 0.35) × 10-2 to (29.26 ± 7.19) × 10-2 1/h.

Macro-instability: a chaotic flow component in stirred tanks.

Chaotic features of the macro-instability (MI) of flow patterns in stirred tanks are studied in this paper. Datasets obtained by measuring the axial component of the fluid velocity and the tangential force affecting the baffles are used. Two geometrically identical, flat-bottomed cylindrical mixing tanks (diameter of 0.3m) stirred with either pitched blade turbine impellers or Rushton turbine impeller are used in the experiments, and water and aqueous glycerol solutions are used as the working liquids. First, the presence of the MI component in the data is examined by spectral analysis. Then, the MI components are identified in the data using the proper orthogonal decomposition (POD) technique. The attractors of the macro-instability are reconstructed using either the POD eigenmodes or a method of delays and finally the attractor invariants are evaluated. The dependence of the correlation dimension and maximum Lyapunov exponent on the vessel operational conditions is determined together with their distribution within the tank. No significant spatial variability of the correlation dimension value is observed. Its value is strongly influenced by impeller speed and by the vessel-impeller geometry. More profound spatial distribution is displayed by the maximum Lyapunov exponent taking distinctly positive values. These two invariants, therefore, can be used to locate distinctive regions with qualitatively different MI dynamics within the stirred tank.

Continuous penicillin G hydrolysis in an electro-membrane reactor with immobilized penicillin G acylase.

Penicillin G (2%, w/v in phosphate buffer, pH 8) was hydrolysed in a flow-through, miniature electro-membrane reactor with the penicillin G acylase immobilized in 5% (w/v) polyacrylamide (diam. 10 mm, thickness 2.6 mm, enzyme activity 24 U ml(-1)). The conversion of penicillin G increased from 0.15 to almost 0.5 when the electric current applied to the reactor was changed from -600 to +600 A/m2 with a substrate residency of 1 h.

Chaotic patterns in a coupled oscillator-excitator biochemical cell system.

In this paper we examine dynamical modes resulting from diffusion-like interaction of two model biochemical cells. Kinetics in each of the cells is given by the ICC model of calcium ions in the cytosol. Constraints for one of the cells are set so that it is excitable. One of the constraints in the other cell - a fraction of activated cell surface receptors-is varied so that the dynamics in the cell is either excitable or oscillatory or a stable focus. The cells are interacting via mass transfer and dynamics of the coupled system are studied as two parameters are varied-the fraction of activated receptors and the coupling strength. We find that (i) the excitator-excitator interaction does not lead to oscillatory patterns, (ii) the oscillator-excitator interaction leads to alternating phase-locked periodic and quasiperiodic regimes, well known from oscillator-oscillator interactions; torus breaking bifurcation generates chaos when the coupling strength is in an intermediate range, (iii) the focus-excitator interaction generates compound oscillations arranged as period adding sequences alternating with chaotic windows; the transition to chaos is accompanied by period doublings and folding of branches of periodic orbits and is associated with a Shilnikov homoclinic orbit. The nature of spontaneous self-organized oscillations in the focus-excitator range is discussed. (c) 1999 American Institute of Physics.