Self‐Defensive Biomaterial Coating Against Bacteria and Yeasts: Polysaccharide Multilayer Film with Embedded Antimicrobial Peptide

Prevention of pathogen colonization of medical implants is a major medical and financial issue since infection by microorganisms constitutes one of the most serious complications after surgery or critical care. Immobilization of antimicrobial molecules on biomaterials surfaces is an efficient approach to prevent biofilm formation. Herein, the first self‐defensive coating against both bacteria and yeasts is reported, where the release of the antimicrobial peptide is triggered by enzymatic degradation of the film due to the pathogens themselves. Biocompatible and biodegradable polysaccharide multilayer films based on functionalized hyaluronic acid by cateslytin (CTL), an endogenous host‐defensive antimicrobial peptide, and chitosan (HA‐CTL‐C/CHI) are deposited on a planar surface with the aim of designing both antibacterial and antifungal coating. After 24 h of incubation, HA‐CTL‐C/CHI films fully inhibit the development of Gram‐positive Staphylococcus aureus bacteria and Candida albicans yeasts, which are common and virulent pathogens agents encountered in care‐associated diseases. Hyaluronidase, secreted by the pathogens, leads to the film degradation and the antimicrobial action of the peptide. Furthermore, the limited fibroblasts adhesion, without cytotoxicity, on HA‐CTL‐C/CHI films highlights a medically relevant application to prevent infections on catheters or tracheal tubes where fibrous tissue encapsulation is undesirable.     

Mayall's life-size portrait of George Peabody

Abstract

The miniature painter's occupation is nearly gone, and we may perhaps see the second-rate portrait painter also superseded, and the same negative made to print pictures for the walls of town-hall or mansion, or for the album in the lady's boudoir.     

Daguerreotype Portraiture

Abstract

Facing the Light is a major national exhibition of 110 daguerreotype portraits gathered from 35 sources. In his introduction to this catalogue for the exhibition, Pfister outlines his criteria for selection in the National Portrait Gallery's show. For consideration, the works had to be ‘unmistakably identified portraits of nationally prominent individuals … [whose] inclusion was first determined by the existence of a striking example of the daguerrean [sic] art’. This respect for the medium, as well as for the likenesses represented, makes the book a happy blend that should appeal to a broad audience. It is fitting that a national exhibition sponsored in part by the government and in part by the public-minded Polaroid Corporation should have set itself this task.     

Herschel,Talbot and Photography: Spring 1831 and Spring 1839

Abstract

The rich, productive, and enthusiastic interaction between Henry Talbot and John Herschel is a fascinating microcosm of early photographic research. An isolated experiment, shared by them in 1831, is a typical example of the tantalizing near-misses that pervade the chronicles of the pre-history of photography. Their correspondence in early 1839, before Herschel saw Daguerre's then superior productions, is a window for us today to learn from the initial thoughts of the excited pioneers. We face contemporary reports of discovery and hope, unedited and unrefined by the influence of time and later events.     

Magnetisation effects of multicore magnetite nanoparticles crystallised from a silicate glass

Magnetic multicore nanoparticles were produced by crystallisation of a glass with the composition Na₂O·Al₂O₃·B₂O₃·SiO₂·Fe₂O₃. During cooling of the melt, in a first step, phase separation occurred and droplets enriched in boron and iron oxide were formed. These droplets crystallised spontaneously during cooling. The phase-separated droplets had sizes in the range from 200 to 800 nm. Inside the droplets, magnetite crystals with a mean size of 33 nm occurred. Magnetometer measurements showed the occurrence of a small hysteresis which indicates predominantly superparamagnetic behaviour of the magnetite crystals. The magnetic domains of the phase-separated droplets were studied by magnetic force microscopy. In this article, a glass which is exposed to a magnetic field shows droplet-shape phase separations where the single-domain magnetite crystals do not have a preferred orientation of the magnetic dipoles. By contrast, the whole droplet shows one magnetic dipole parallel to the external field if the glass is exposed to a magnetic field during measurement.     

Tomography measurements of gas holdup in rotating foam reactors with Newtonian, non-Newtonian and foaming liquids

Rotating solid foam reactors have already proven to show high mass transfer rates and to be a potential alternative to slurry reactors. The rotation of a foam block stirrer results in a high mass transfer and in the development of different reactor sections showing specific hydrodynamics and gas holdup distributions. In order to optimize the reactor system the hydrodynamics in a lab scale reactor are studied using γ-ray tomography, a powerful method to measure the gas holdup in three-phase reactors. The influence of liquid properties, such as viscosity and surface tension, and the rotational speed on the gas/liquid distribution in the different reactor sections is investigated. Especially the viscosity has a strong effect on the entrapment of gas bubbles in the foam block structure, while the surface tension is the dominant parameter in the outer reactor section. The influence of these parameters on the inset of foaming and the collapse of the gas/liquid dispersion is investigated. Conclusions on the mass transfer performance are drawn and recommendations for further optimizations of the reactor design and the operational conditions depending on the liquid properties are developed.     

Hydrodynamical particle containment in a rotor‐stator spinning disk device

A novel type of rotor‐stator spinning disk device is proposed which allows for the entrapment of solid particles solely by hydrodynamic means. In this new configuration, the solid rotating disk is replaced with two conjoined rotors with a variable gap spacing. Liquid is fed through the top stator and can flow out again through the rotor‐rotor interior and the hollow rotation axis. Moreover, the volume between the two rotors is optionally filled with a highly porous reticulated carbon foam. It was found that particle containment was strongly improved by the presence of this reticulated foam as it hinders the buildup of centripetal boundary layer flow near the disks in the interior of the rotor‐rotor assembly. These centripetal boundary layers drag along particles resulting in a loss of containment. Experiments utilizing glass beads showed that particles with a diameter down to 17.8 µm can be completely entrapped when a carbon foam is placed between the two conjoined disks at rotor speeds up to the maximum investigated value of 178 rad s^?1. Additionally, the rotor‐rotor gap did not have an effect on the particle entrapment level when the reticulated carbon foam was omitted and can be ascribed to the build‐up of boundary layers, which is independent of rotor‐rotor distance. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3656–3665, 2015     

Optimal placement of probes for dynamic pressure measurements in large-scale fluidized beds

Pressure data sampled at sufficiently high frequency (typically 20 Hz or higher) can yield much information about the hydrodynamic state of a fluidized bed. Since part of the pressure waves travelling through large (industrial) fluidized beds is only detectable in a limited area of the bed, pressure measurements need to be performed at several positions to cover the whole bed. We examine these local pressure waves (caused by, e.g., passing bubbles or coalescing bubbles) in a 0.80 m i.d. bubbling fluidized bed of Geldart B particles. Experiments and simulations are performed to determine the intensity decrease as local pressure waves propagate from their origin. A new spectral method is applied to determine the degree of coherence for pressure signals measured at two different positions in a fluidized bed. For a superficial gas velocity of 5u_mf, local pressure waves can be detected up to a radial distance of about 0.5 m from their origin; this distance is somewhat lower for lower gas velocities. This means that the radial spacing of pressure probes should not exceed 1 m. For large diameter beds with a bed height below 1.5 m, a set of probes at a single level and at several radial positions is sufficient to observe or monitor the dynamic state of the complete bed; the probes should preferably be placed at a height of 30% to 40% of the total bed height.     

Convective condensation in a stator–rotor–stator spinning disc reactor

Centrifugal intensification of condensation heat transfer in the rotor–stator cavities of a stator–rotor–stator spinning disc reactor (srs‐SDR) is studied, as a function of rotational velocity ω, volumetric throughflow rate , and average temperature driving force . For the current range of ω, heat transfer from the vapor bubbles to the condensate liquid is limiting, due to a relatively low gas–liquid interfacial area a_GL. For rad s^?1, a strong increase of a_GL, results in increasing the reactor‐average condensation heat transfer coefficient h_c from 1600 to 5600 W m^?2 K^?1, for condensation of pure dichloromethane vapor. Condensation heat transfer in the srs‐SDR is enhanced by rotation, independent of the vapor velocity. The intensified condensation comes at the cost of relatively high energy dissipation rates, indicating condensation in the srs‐SDR is more suited as a means to supply heat (e.g. in an intensified reactor‐heat exchanger), rather than for bulk cooling purposes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3784–3796, 2016