Biological efficacy of electroless-deposited silver on plasma activated polyurethane

Silver coating of catheters has been shown to have inhibitory effects on bacterial growth and adhesion to catheter surfaces. In this study, plasma-modification was used to enhance the adhesion of an electroless silver coating on polyurethane. Both the antibacterial and antiadhesive properties of these coatings were investigated. Bacterial growth was inhibited in cultures exposed to silver-treated polyurethane compared to unmodified polyurethane. Higher growth inhibition was observed for polyurethane surfaces with lower silver coverage. Bacterial adhesion was completely inhibited on all silver-coated surfaces.

Modelling and fixed bed column adsorption of Cr(VI) onto orthophosphoric acid-activated lignin

The advantage of using an available and abundant residual biomass, such as lignin, as a raw material for activated carbons is that it provides additional economical interest to the technical studies. In the current investigation, a more complete understanding of adsorption of Cr(VI) from aqueous systems onto H PO -acid activated lignin has been achieved via microcolumns, which were operated under various process conditions. The practice of using microcolumn is appropriate for defining the adsorption parameters and for screening a large number of potential adsorbents. The effects of solution pH (2-8), initial metal ion concentration (0.483-1.981 mmol·L ), flow rate (1.0-3.1 cm ·min ), ionic strength (0.01-0.30 mmol·L ) and adsorbent mass (0.11-0.465 g) on Cr(VI) adsorption were studied by assessing the microcolumn breakthrough curve. The microcolumn data were fitted by the Thomas model, the modified Dose model and the BDST model. As expected, the adsorption capacity increased with initial Cr(VI) concentration. High linear flow rates, pH values and ionic strength led to early breakthrough of Cr(VI). The model constants obtained in this study can be used for the design of pilot scale adsorption process. © 2012 Chemical Industry and Engineering Society of China (CIESC) and Chemical Industry Press (CIP).

Optimisation of rheological parameters and mechanical properties of superplasticised cement grouts containing metakaolin and viscosity modifying admixture

The objective of this research was to optimise the rheological parameters, hardened properties, and setting times of cement grouts containing metakaolin (MTK), viscosity-modifying agent (VMA) and superplasticiser (SP). All mixes were made with water-to-binder ratio (W/B) of 0.40. The replacement of cement by MTK was varied from 6% to 20% (by mass), and dosages of SP and VMA were varied from 0.3% to 1.4%, and 0.01% and 0.06% (by mass of binder), respectively. Increased SP led to an increase in fluidity, reduction in flow time, plate cohesion, rheological parameters, and an increase in the setting times. Increased VMA demonstrated a reduction in fluidity, an increase in Marsh cone time, plate cohesion, yield stress, and plastic viscosity. Results indicate that the use of MTK increased yield stress, plastic viscosity, cohesion plate, and flow time due to the higher surface area associated with an increase in the water demand. MTK reduced mini-slump and setting times, and improved compressive strength.

Transient Ca2+-activated Cl-currents with endothelin in isolated arteriolar smooth muscle cells of the choroid

To characterize the effects of endothelin (ET)-1 on the Ca2+-activated Cl- conductance of choroidal arteriolar smooth muscle.

Diabetes downregulates large-conductance Ca2+-activated potassium beta 1 channel subunit in retinal arteriolar smooth muscle

Retinal vasoconstriction and reduced retinal blood flow precede the onset of diabetic retinopathy. The pathophysiological mechanisms that underlie increased retinal arteriolar tone during diabetes remain unclear. Normally, local Ca(2+) release events (Ca(2+)-sparks), trigger the activation of large-conductance Ca(2+)-activated K(+)(BK)-channels which hyperpolarize and relax vascular smooth muscle cells, thereby causing vasodilatation. In the present study, we examined BK channel function in retinal vascular smooth muscle cells from streptozotocin-induced diabetic rats. The BK channel inhibitor, Penitrem A, constricted nondiabetic retinal arterioles (pressurized to 70mmHg) by 28%. The BK current evoked by caffeine was dramatically reduced in retinal arterioles from diabetic animals even though caffeine-evoked [Ca(2+)](i) release was unaffected. Spontaneous BK currents were smaller in diabetic cells, but the amplitude of Ca(2+)-sparks was larger. The amplitudes of BK currents elicited by depolarizing voltage steps were similar in control and diabetic arterioles and mRNA expression of the pore-forming BKalpha subunit was unchanged. The Ca(2+)-sensitivity of single BK channels from diabetic retinal vascular smooth muscle cells was markedly reduced. The BKbeta1 subunit confers Ca(2+)-sensitivity to BK channel complexes and both transcript and protein levels for BKbeta1 were appreciably lower in diabetic retinal arterioles. The mean open times and the sensitivity of BK channels to tamoxifen were decreased in diabetic cells, consistent with a downregulation of BKbeta1 subunits. The potency of blockade by Pen A was lower for BK channels from diabetic animals. Thus, changes in the molecular composition of BK channels could account for retinal hypoperfusion in early diabetes, an idea having wider implications for the pathogenesis of diabetic hypertension.

Characterising cement-superplasticiser interaction using zeta potential measurements

The zeta potential generated at the interface between cement particle surfaces adsorbed with superplasticisers have been studied using electroacoustic technique, which is capable of measuring zeta potential at high concentrated suspensions. The study has been undertaken to examine the differences in the magnitude of the zeta potential for ordinary Portland cement (OPC) and Portland pozzolanic (fly ash) cement (PPC) pastes along with the differential impacts of different types of superplasticisers on both the varieties of cement pastes. In the latter context, the effects of three different types of superplasticisers namely Ligno Sulphonate (LS), Sulphonated Melamine Formaldehyde (SMF) and Sulphonated Naphthalene Formaldehyde (SNF) have been specifically studied. The results show that the cement pastes with PPC shows better dispersion when compared with the OPC. The paper also endeavors to unfold the relationship and significance of cement interaction with three different superplasticisers.

The unexpected discovery of a novel low-oxygen-activated locus for the anoxic persistence of Burkholderia cenocepacia

Burkholderia cenocepacia is a Gram-negative aerobic bacterium that belongs to a group of opportunistic pathogens displaying diverse environmental and pathogenic lifestyles. B. cenocepacia is known for its ability to cause lung infections in people with cystic fibrosis and it possesses a large 8?Mb multireplicon genome encoding a wide array of pathogenicity and fitness genes. Transcriptomic profiling across nine growth conditions was performed to identify the global gene expression changes made when B. cenocepacia changes niches from an environmental lifestyle to infection. In comparison to exponential growth, the results demonstrated that B. cenocepacia changes expression of over one-quarter of its genome during conditions of growth arrest, stationary phase and surprisingly, under reduced oxygen concentrations (6% instead of 20.9% normal atmospheric conditions). Multiple virulence factors are upregulated during these growth arrest conditions. A unique discovery from the comparative expression analysis was the identification of a distinct, co-regulated 50-gene cluster that was significantly upregulated during growth under low oxygen conditions. This gene cluster was designated the low-oxygen-activated (lxa) locus and encodes six universal stress proteins and proteins predicted to be involved in metabolism, transport, electron transfer and regulation. Deletion of the lxa locus resulted in B. cenocepacia mutants with aerobic growth deficiencies in minimal medium and compromised viability after prolonged incubation in the absence of oxygen. In summary, transcriptomic profiling of B. cenocepacia revealed an unexpected ability of aerobic Burkholderia to persist in the absence of oxygen and identified the novel lxa locus as key determinant of this important ecophysiological trait.

Development of a bovine collagen-apatitic calcium phosphate cement for potential fracture treatment through vertebroplasty

The aim of this study was to examine the potential of incorporating bovine fibres as a means of reinforcing a typically brittle apatite calcium phosphate cement for vertebroplasty. Type I collagen derived from bovine Achilles tendon was ground cryogenically to produce an average fibre length of 0.96 ± 0.55 mm and manually mixed into the powder phase of an apatite-based cement at 1, 3 or 5 wt.%. Fibre addition of up to 5 wt.% had a significant effect (P = 0.001) on the fracture toughness, which was increased by 172%. Adding =1 wt.% bovine collagen fibres did not compromise the compressive properties significantly, however, a decrease of 39-53% was demonstrated at =3 wt.% fibre loading. Adding bovine collagen to the calcium phosphate cement reduced the initial and final setting times to satisfy the clinical requirements stated for vertebroplasty. The cement viscosity increased in a linear manner (R = 0.975) with increased loading of collagen fibres, such that the injectability was found to be reduced by 83% at 5 wt.% collagen loading. This study suggests for the first time the potential application of a collagen-reinforced calcium phosphate cement as a viable option in the treatment of vertebral fractures, however, issues surrounding efficacious cement delivery need to be addressed. © 2012 Acta Materialia Inc.

Development of calcium phosphate cement for the augmentation of traumatically fractured porcine specimens using vertebroplasty

The study aim was to develop and apply an experimental technique to determine the biomechanical effect of polymethylmethacrylate (PMMA) and calcium phosphate (CaP) cement on the stiffness and strength of augmented vertebrae following traumatic fracture. Twelve burst type fractures were generated in porcine three-vertebra segments. The specimens were randomly split into two groups (n=6), imaged using microCT and tested under axial loading. The two groups of fractured specimens underwent a vertebroplasty procedure, one group was augmented with CaP cement designed and developed at Queen's University Belfast. The other group was augmented with PMMA cement (WHW Plastics, Hull, UK). The specimens were imaged and re-tested . An intact single vertebra specimen group (n=12) was also imaged and tested under axial loading. A significant decrease (p<0.01) was found between the stiffness of the fractured and intact groups, demonstrating that the fractures generated were sufficiently severe, to adversely affect mechanical behaviour. Significant increase (p<0.01) in failure load was found for the specimen group augmented with the PMMA cement compared to the pre-augmentation group, conversely, no significant increase (p<0.01) was found in the failure load of the specimens augmented with CaP cement, this is attributed to the significantly (p<0.05) lower volume of CaP cement that was successfully injected into the fracture, compared to the PMMA cement. The effect of the percentage of cement fracture fill, cement modulus on the specimen stiffness and ultimate failure load could be investigated further by using the methods developed within this study to test a more injectable CaP cement.