Biofilm formation by bacteria isolated from retrieved failed prosthetic hip implants in an in vitro model of hip arthroplasty antibiotic prophylaxis

Bacterial infection primarily with Staphylococcus spp. and Propionibacterium acnes remains a significant complication following total hip replacement. In this in vitro study, we investigated the efficacy of gentamicin loading of bone cement and pre- and postoperative administration of cefuroxime in the prevention of biofilm formation by clinical isolates. High and low initial inocula, representative of the number of bacteria that may be present at the operative site as a result of overt infection and skin contamination, respectively, were used. When a high initial inoculum was used, gentamicin loading of the cement did not prevent biofilm formation by the 10 Staphylococcus spp. and the 10 P. acnes isolates tested. Similarly, the use of cefuroxime in the fluid phase with gentamicin-loaded cement did not prevent biofilm formation by four Staphylococcus spp. and four P. acnes isolates tested. However, when a low bacterial inoculum was used, a combination of both gentamicin-loaded cement and cefuroxime prevented biofilm formation by these eight isolates. Our results indicate that this antibiotic combination may protect against infection after intra-operative challenge with bacteria present in low numbers as a result of contamination from the skin but would not protect against bacteria present in high numbers as a result of overt infection of an existing implant.

Current-induced transition in atomic-sized contacts of metallic alloys

We have measured conductance histograms of atomic point contacts made from the noble-transition-metal alloys CuNi, AgPd, and AuPt for a concentration ratio of 1:1. For all alloys these histograms at low-bias voltage (below 300 mV) resemble those of the noble metals, whereas at high bias (above 300 mV) they resemble those of the transition metals. We interpret this effect as a change in the composition of the point contact with bias voltage. We discuss possible explanations in terms of electromigration and differential diffusion induced by current heating.

Monte Carlo simulation of properties of monolayers and metal islands adsorbed on metallic (111) surfaces

To obtain the surface stress changes due to the adsorption of metal monolayers onto metallic surfaces, a new model derived from thermodynamic considerations is presented. Such a model is based on continuum Monte Carlo simulations with embedded atom method potentials in the canonical ensemble, and it is extended to consider the behavior on different islands adsorbed onto (111) substrate surfaces. Homoepitaxial and heteroepitaxial systems are studied. Pseudomorphic growth is not observed for small metal islands with considerable positive misfit with the substrate. Instead, the islands become compressed upon increase of their size. A simple model is proposed to interpolate between the misfits of atoms in small islands and the pseudomorphic behavior of the monolayer.

Auditory sensory memory and working memory processes in children with normal hearing and cochlear implants.

There can be wide variation in the level of oral/aural language ability that prelingually hearing-impaired children develop after cochlear implantation. Automatic perceptual processing mechanisms have come under increasing scrutiny in attempts to explain this variation. Using mismatch negativity methods, this study explored associations between auditory sensory memory mechanisms and verbal working memory function in children with cochlear implants and a group of hearing controls of similar age. Whilst clear relationships were observed in the hearing children between mismatch activation and working memory measures, this association appeared to be disrupted in the implant children. These findings would fit with the proposal that early auditory deprivation and a degraded auditory signal can cause changes in the processes underpinning the development of oral/aural language skills in prelingually hearing-impaired children with cochlear implants and thus alter their developmental trajectory

Physicochemical characterization of bioactive polyacrylic acid organogels as potential antimicrobial implants for the buccal cavity

This study describes the formulation and physicochemical characterization of poly(acrylic acid) (PAA) organogels, designed as bioactive implants for improved treatment of infectious diseases of the oral cavity. Organogels were formulated containing a range of concentrations of PAA (3-10% w/w) and metronidazole (2 or 5% w/w, representing a model antimicrobial agent) in different nonaqueous solvents, namely, glycerol (Gly), polyethylene glycol (PEG 400), or propylene glycol (PG). Characterization of the organogels was performed using flow rheometry, compressional analysis, oscillatory rheometry, in vitro mucoadhesion, moisture uptake, and drug release, methods that provide information pertaining to the nonclinical and clinical use of these systems. Increasing the concentration of PAA significantly increased the consistency, compressibility, storage modulus, loss modulus, dynamic viscosity, mucoadhesion, and the rate of drug release. These observations may be accredited to enhanced molecular polymer entanglement. In addition, the choice of solvent directly affected the physicochemical parameters of the organogels, with noticeable differences observed between the three solvents examined. These differences were accredited to the nature of the interaction of PAA with each solvent and, importantly, the density of the resultant physical cross-links. Good correlation was observed between the viscoelastic properties and drug release, with the exception of glycerol-based formulations containing 5 and 10% w/w PAA. This disparity was due to excessive swelling during the dissolution analysis. Ideally, formulations should exhibit controlled drug release, high viscoelasticity, and mucoadhesion, but should flow under minimal stresses. Based on these criteria, PEG 400-based organogels composed of 5% or 10% w/w PAA exhibited suitable physicochemical properties and are suggested to be a potentially interesting strategy for use as bioactive implants designed for use in the oral cavity. © 2008 American Chemical Society.

Theoretical analysis on microwave heating of oil–water emulsions supported on ceramic, metallic or composite plates

A detailed theoretical analysis has been carried out to study efficient heating due to microwaves for one-dimensional (1D) oil–water emulsion samples placed on various ceramic, metallic (reflective) and ceramic–metallic composite supports. Two typical emulsion systems are considered such as oil-in-water (o/w) and water-in-oil (w/o). A preliminary study has been carried out via average power vs emulsion thickness diagram to estimate microwave power absorption within emulsion samples for various cases. The maxima in average power, also termed as ‘resonances’, are observed for specific emulsion thicknesses and the two consecutive resonances of significant magnitudes are termed as R1 and R2 modes. For both o/w and w/o emulsions, it is observed that microwave power absorption is enhanced in presence of metallic and composite supports during both R1 and R2 modes. The efficient heating strategies characterized by ‘large heating rates’ with ‘minimal thermal runaway’ i.e. uniform temperature distributions within the sample have been assessed for each type of emulsion. Based on the detailed spatial distributions of power and temperature for various cases, SiC-metallic composite support may be recommended as an optimal heating strategy for o/w samples with higher oil fractions (0.45) whereas metallic and Alumina-metallic composite supports may be favored for samples with smaller oil fractions (=0.3) during R1 mode. For w/o samples, SiC-metallic composite support may be suitable heating strategy for all ranges of water fractions during R1 mode. During R2 mode, metallic and Alumina-metallic composite supports are favored for both o/w and w/o emulsion samples. Current study recommends the efficient way to use microwaves in a single mode waveguide and the heating strategy can be suitably extended for heating of any other emulsions for which dielectric properties are easily measurable or available in the literature.

Injection of metallic elements into an electron-beam ion trap using a Knudsen cell

A method of injecting metallic elements into an electron-beam ion trap (EBIT) is described. The method is advantageous over the conventional coaxial and pulsed injection methods in two ways: (a) complicated switching of injection and extraction beams can be avoided when extracting beams of highly charged ions from the EBIT and (b) a beam of stable intensity can be achieved. This method may be applicable to any metallic elements or metallic compounds that have vapor pressures of similar to 0.1 Pa at a temperature lower than 1900 degrees C. We have employed this method for the extraction of highly charged ions of Bi, Er, Fe, and Ho. (c) 2006 American Institute of Physics.

Tailoring the AMC and EBG characteristics of periodic metallic arrays printed on grounded dielectric substrate

The artificial magnetic conductor (AMC) and electromagnetic band gap (EBG) characteristics of planar periodic metallic arrays printed on grounded dielectric substrate are investigated. The currents induced on the arrays are presented for the first time and their study reveals two distinct resonance phenomena associated with these surfaces. A new technique is presented to tailor the spectral position of the AMC operation and the EBG. Square patch arrays with fixed element size and variable periodicities are employed as working examples to demonstrate the dependence of the spectral AMC and EBG characteristics on array parameters. It is revealed that as the array periodicity is increased, the AMC frequency is increased, while the EBG frequency is reduced. This is shown to occur due to the different nature of the resonance phenomena and the associated underlying physical mechanisms that produce the two effects. The effect of substrate thickness is also investigated. Full wave method of moments (MoM) has been employed for the derivation of the reflection characteristics, the currents and the dispersion relations. A uniplanar array with simultaneous AMC and EBG operation is demonstrated theoretically and experimentally.