1,720,973 research outputs found
Cleaning up marine antifouling
No full textAn overview of marine fouling and past and future strategies for reducing it
A marine biofilm flow cell for in situ determination of drag and biofilm structure
No full textIt is not straightforward to link biofilm parameters to frictional drag, because of the heterogeneous distribution and viscoelasticity of the produced matrix. Here we present the design and calibration of a flow cell in which marine biofilms can be cultured under flow and then assessed for drag, structural and mechanical properties. The flow cell test section comprised a rectangular channel constructed by sandwiching together rigid PVC panels and side panels of clear acrylic, which allow natural light to enter. The Fanning friction factor (Cf) of the flow cell was found by measuring the pressure drop (ΔP) at various flow velocities (u). Flow cell calibration was carried out using a clean inert marine coating, and various roughness grades of sandpaper sheets to find Cf for each rigid roughness. ΔP was proportional to u2, indicating flow was turbulent (R2 = 0.99). The top panel of the flow cell can be substituted with a clear acrylic lid to allow simultaneous measurement of Cf and biofilm physico-mechanical properties by optical coherence tomography (OCT). Here, we demonstrated that the flow cell can be used to image microbial fouling using OCT. Future experiments will assess physico-mechanical and drag properties of marine fouling biofilms under flow
A marine biofilm flow cell for in situ determination of drag, structure and viscoelastic properties
No full textIt is not straightforward to link biofilm parameters to frictional drag, likely because of the heterogeneous nature of slime. Here we present the design and calibration of a pragmatic, small scale flow-cell in which biofilms can either be cultured under flow or grown statically and then assessed under flow for drag and other properties. The flow cell test section comprised a rectangular channel (870x10x55mm) constructed by sandwiching together rigid opaque PVC panels and side panels of clear acrylic, which allow natural light to enter. A maze-like entry section evened out the inlet flow. Seawater flow rate through the channel was monitored by an in-line digital flowmeter, and pressure drop (ΔP) along the test section was measured using a differential pressure sensor. The friction coefficient (Cf) of the flow cell was found by measuring the ΔP at various flow velocities (u) over the entire pump range (maximum Re ~22,000). Flow cell calibration was carried out using a clean inert marine coating, and various roughness grades (P40, P80 and P120) of waterproof sandpaper sheets, fixed to the wide faces of the channel, to find Cf for each rigid roughness. ΔP was proportional to u2, indicating flow was turbulent in this region (R = 99%). When fouled panels are used as the channel floor and a clear acrylic panel as the ceiling, the flow cell allows for simultaneous measurement of Cf of the lower surface and biofilm physico-mechanical properties (e.g. thickness, roughness, viscoelasticity) by optical coherence tomography (OCT) imaging, which generates depth profiles of translucent samples. Changes to biofilm physico-mechanical properties during flow loading/unloading cycles, determined by image analysis, can be compared to simultaneously collected ΔP measurements scaled to a one-sided sandpaper Cf calibration. Future experiments will assess physico-mechanical and drag properties of marine fouling biofilms in flow using ΔP and OCT
A marine biofilm flow-cell for screening antifouling marine coatings using optical coherence tomography
No full textA novel fouling marine flow-cell was designed and fitted with a top clear 5 mm thick plastic lid to allow real time imaging of the biofilm using optical coherence tomography (OCT). The OCT was used to analyse biofilm removal and mechanical properties during shear-stress experiments. The OCT measures intensity depth profiles from translucent samples such as biofilms. Consecutive scans provide a cross-sectional view of the biofilm structure which are then combined to give volumetric representations. The scanning speed of the OCT reached up to 30,000 scans/s and covers a field of view of 9x9 mm2. The bottom plate of the flow-cell was machined to allow the insertion of fouled microscope slides (25 x 55 x 1 mm). Marine biofilms were grown on spray coated (inert coating) slides in seawater for up to 2 years to test mechanical properties (triplicates). Marine biofilms were grown dynamically on 6 different antifouling coatings (A, B, C, D, E, F) for 8 weeks to test biofilm removal (duplicates). Marine biofilms were also grown statically and dynamically on an antifouling coating G to assess biofilm removal. Biofilm mechanical behaviour and removal were assessed by increasing (load cycle) or decreasing (unload cycle) the flow velocity (and therefore shear stress) in a stepwise manner over the entire pump range. Each step interval lasted 30 s except at the highest flow which was held for 5 min before starting the unloading cycle. The OCT was set to measure 10 xz-cross sections along the flow for each velocity step. 3D C-scans were also acquired before the loading cycle and at the end of the unloading cycle. The OCT images were analysed using ImageJ and Matlab. The angle of deformation of individual biofilm clusters were measured for each shear stress to obtain a stress/strain curve. Stress/strain curves showed classic viscoelastic biofilm behaviour. From the initial linear region of the load cycle the shear modulus (G) was estimated to be G = 46.2 ±5.43 Pa (n = 3). The biofilm also showed a residual strain εR = 0.28± 0.01 (n = 2). The % cross-sectional area removed (%A) as a function of the shear stress was measured from the OCT images for each antifouled slide. The %A value increases exponentially for all the antifouling coatings until a shear stress of ~25 Pa, when it reached a plateau. Considering a shear stress of 15 Pa, %A of coating C (A% = 75%) was significantly higher than the value of the other coatings showing best performance. The %A of the biofilm grown on coating G statically (A% = 68%) was lower than the value of the biofilm grown dynamically (A% = 82%). These results show that the marine biofilm flow-cell combined with OCT can be used to assess mechanical properties of marine biofilms and detect differences (in terms of removal) in biofilms grown on different coatings. Future testing will focus on assessing how mechanical properties of biofilms interact with their physical properties (roughness, thickness, extent) to produce drag
Rheometry for rapid screening of drag-reducing marine coatings
No full textUse of a sensitive controlled stress rheometer allows the rapid bench-top measurement of small changes in hydrodynamic drag due to mild biofouling such as slime coverage
Biofilm inhibition by novel natural product- and biocide-containing coatings using high-throughput screening
Full text linkThe use of natural products (NPs) as possible alternative biocidal compounds for use in antifouling coatings has been the focus of research over the past decades. Despite the importance of this field, the efficacy of a given NP against biofilm (mainly bacteria and diatoms) formation is tested with the NP being in solution, while almost no studies test the effect of an NP once incorporated into a coating system. The development of a novel bioassay to assess the activity of NP-containing and biocide-containing coatings against marine biofilm formation has been achieved using a high-throughput microplate reader and highly sensitive confocal laser scanning microscopy (CLSM), as well as nucleic acid staining. Juglone, an isolated NP that has previously shown efficacy against bacterial attachment, was incorporated into a simple coating matrix. Biofilm formation over 48 h was assessed and compared against coatings containing the NP and the commonly used booster biocide, cuprous oxide. Leaching of the NP from the coating was quantified at two time points, 24 h and 48 h, showing evidence of both juglone and cuprous oxide being released. Results from the microplate reader showed that the NP coatings exhibited antifouling efficacy, significantly inhibiting biofilm formation when compared to the control coatings, while NP coatings and the cuprous oxide coatings performed equally well. CLSM results and COMSTAT analysis on biofilm 3D morphology showed comparable results when the NP coatings were tested against the controls, with higher biofilm biovolume and maximum thickness being found on the controls. This new method proved to be repeatable and insightful and we believe it is applicable in antifouling and other numerous applications where interactions between biofilm formation and surfaces is of interest
Anti-biofilm performance of three natural products against initial bacterial attachment
No full textAbstract: Marine bacteria contribute significantly towards the fouling consortium, both directly (modern foul release coatings fail to prevent “slime” attachment) and indirectly (biofilms often excrete chemical cues that attract macrofouling settlement). This study assessed the natural product anti-biofilm performance of an extract of the seaweed, Chondrus crispus, and two isolated compounds from terrestrial sources, (+)-usnic acid and juglone, against two marine biofilm forming bacteria, Cobetia marina and Marinobacter hydrocarbonoclasticus. Bioassays were developed using quantitative imaging and fluorescent labelling to test the natural products over a range of concentrations against initial bacterial attachment. All natural products affected bacterial attachment; however, juglone demonstrated the best anti-biofilm performance against both bacterial species at a concentration range between 5–20 ppm. In addition, for the first time, a dose-dependent inhibition (hormetic) response was observed for natural products against marine biofilm forming bacteria
Dataset for Bubbles vs biofilms: a novel method for the removal of marine biofilms attached on antifouling coatings using an ultrasonically activated water stream
No full textDataset to support:
Salta, M. et al (2016) Bubbles vs biofilms: a novel method for the removal of marine biofilms attached on antifouling coatings using an ultrasonically activated water stream. Surface Topography: Metrology and Properties.</span
Miniaturized rotating disc rheometer test for rapid screening of drag reducing marine coatings
Full text linkFrictional drag from the submerged hull surface of a ship is a major component of the resistance experienced when moving through water. Techniques for measuring frictional drag on test surfaces include towing tanks, flow tunnels and rotating discs. These large-scale methods present practical difficulties that hinder their widespread adoption and they are not conducive to rapid throughput. In this study a miniaturized benchtop rotating disc method is described that uses test discs 25 mm in diameter. A highly sensitive analytical rheometer is used to measure the torque acting on the discs rotating in water. Frictional resistance changes are estimated by comparing momentum coefficients. Model rough surfaces were prepared by attaching different grades of sandpaper to the disc surface. Discs with experimental antifouling coatings applied were exposed in the marine environment for the accumulation of microbial fouling, and the rotor was capable of detecting the increased drag due to biofilm formation. The drag due to biofilm was related to an equivalent sand roughness
Understanding the effects of tooth brushing using an abrasive dentifrice on the wear of enamel
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