1,721,028 research outputs found
Interfacial instability generation in dental biofilms by high-velocity fluid flow for biofilm removal and antimicrobial delivery
No full textOral biofilms play an important role in the development and the persistence of caries, gingivitis and periodontitis. The addition of antimicrobials to toothpastes and mouthwashes combined with biofilm mechanical disruption through dental cleaning devices is the most common way to control oral diseases. However, biofilms’ complicated structure increases their resistance to antiplaque and/or antimicrobials by limiting the diffusion of dentifrices into and inside the biofilm. Studies showed that fluid-dynamic activity generated by power toothbrushes can enhance mass transfer inside the remaining biofilm compared to simple diffusional transport. Microsprays have the advantage in that they are low volume but also have an air/water interface which facilitates biofilm removal. The role of the hydrodynamics in the enhancement of dentifrices inside the biofilm has become a topic of interest since it has been shown that mechanical perturbation caused by fluid-dynamic activity can significantly weaken biofilm structure.Here we showed that high-velocity microsprays enhance microparticles penetration and Chlorhexidine and Cetylpyridinium chloride antimicrobial activity inside Streptococcus mutans dental biofilms through the generation of hydrodynamic deformations. Using highspeed camera videography, we documented S. mutans biofilm extremely transient fluid behavior and the generation of ripple-like structures at the biofilm/fluid interface when exposed to water microsprays. Mathematical modelling demonstrated that ripples were Kelvin Helmotz Instabilities suggesting the development of fluid-like turbulent mixing in biofilms. Shear stresses generated at the biofilm/burst interface might have enhanced beads and antimicrobials delivery inside the remaining biofilm by combining forced advection into the biofilm matrix with the mixing of the biofilm itself. This project provided further insight into the mechanical behaviour of biofilms as complex liquids and how high-shear fluid-biofilm interaction can be induced to modulate biofilm survival and tolerance
Fluid-driven Interfacial instabilities and turbulence in bacterial biofilms
No full textBiofilms are thin layers of bacteria embedded within a slime matrix that live on surfaces. They are ubiquitous in nature and responsible for many medical and dental infections, industrial fouling and are also evident in ancient fossils. A biofilm structure is shaped by growth, detachment and response to mechanical forces acting on them. The main contribution to biofilm versatility in response to physical forces is the matrix that provides a platform for the bacteria to grow. The interaction between biofilm structure and hydrodynamics remains a fundamental question concerning biofilm dynamics. Here we document the appearance of ripples and wrinkles in biofilms grown from three species of bacteria when subjected to rapid high-velocity fluid flows. Theoretical treatment of the process as a Kelvin-Helmholtz instability indicates that the rippling process was primarily due to physics rather than chemistry or biology. The analysis also predicted a strong dependence of the instability formation on biofilm viscosity explaining the different surface corrugations observed. Turbulence through Kelvin-Helmholtz instabilities occurring at the interface demonstrated that the biofilm flows like a viscous liquid under high flow velocities applied within milliseconds. Biofilm fluid-like behavior may have important implications for our understanding of how fluid flow influences biofilm biology since turbulence will likely disrupt metabolite and signal gradients as well as community stratification. </span
Streptococcus mutans biofilm transient viscoealstic fluid behaviour during high-velocity microsprays
No full textUsing high-speed imaging we assessed Streptococcus mutans biofilm-fluid interactions during exposure to a 60-ms microspray burst with a maximum exit velocity of 51 m/sec. S. mutans UA159 biofilms were grown for 72 h on 10 mm-length glass slides pre-conditioned with porcine gastric mucin. Biofilm stiffness was measured by performing uniaxial-compression tests. We developed an in-vitro interproximal model which allowed the parallel insertion of two biofilm-colonized slides separated by a distance of 1 mm and enabled high-speed imaging of the removal process at the surface. S. mutans biofilms were exposed to either a water microspray or an air-only microburst. High-speed videos provided further insight into the mechanical behaviour of biofilms as complex liquids and into high-shear fluid-biofilm interaction. We documented biofilms extremely transient fluid behaviour when exposed to the high-velocity microsprays. The presence of time-dependent recoil and residual deformation confirmed the pivotal role of viscoelasticity in biofilm removal. The air-only microburst was effective enough to remove some of the biofilm but created a smaller clearance zone underlying the importance of water and the air-water interface of drops moving over the solid surface in the removal process. Confocal and COMSTAT analysis showed the high-velocity water microspray caused up to a 99.9 % reduction in biofilm thickness, biomass and area coverage, within the impact area.</span
High-velocity microsprays enhance antimicrobial activity in S. mutans biofilms
No full textStreptococcus mutans in dental plaque biofilms play a role in caries development. The biofilm complex structure enhances the resistance to antimicrobial agents by limiting the transport of active agents inside the biofilm. We assessed the ability of high-velocity water microsprays to enhance delivery of antimicrobials into 3-days old S. mutans biofilms. Biofilms were exposed to a 90° or 30° impact, firstly using a 1-µm tracer beads solution (109 beads/mL) and secondly, a 0.2% Chlorhexidine (CHX) or 0.085% Cetylpyridinium chloride (CPC) solution. For comparison, a 30 sec diffusive transport and simulated mouthwash were also performed. Confocal microscopy was used to determine number and relative bead penetration depth (PD) into the biofilm. Instead, the antimicrobial’s depth of killing (KD) was calculated from the resultant zone of killing detected by live/dead viability staining. We firstly demonstrated that the microspray was able to deliver significantly more microbeads deeper in the biofilm compared to a simple 30-sec diffusion assay and simulated mouthwashing. Next our experiments revealed that the microspray yielded better antimicrobial penetration evidenced by a deeper killing inside the biofilm and a wider killing zone around the zone of clearance than a diffusion transport with the same antimicrobials. Interestingly the 30° impact in the distal position delivered approximately 16 times more microbeads and yielded approximately 15% more bacteria killing (for both CHX and CPC) than the 90o impact. These data suggest that high-velocity water microsprays can be used as an effective mechanism to deliver micro-particles and antimicrobials inside S. mutans biofilms. High shear stresses generated at the biofilm/burst interface might have enhanced beads and antimicrobials delivery inside the remaining biofilm by combining forced advection into the biofilm matrix and physical restructuring of the biofilm itself. Further, the impact angle has potential to be optimized both for biofilm removal and active agents’ delivery inside biofilm in those protected areas where some biofilm might remain. </span
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
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
