Surface properties influence marine biofilm rheology, with implications for ship drag

Marine biofilms on ship hulls increase frictional drag, which has economic and environmental consequences. It is hypothesised that biofilm mechanics, such as viscoelasticity, play a critical role in biofilm-associated drag, yet is a poorly studied area. The current study aimed to rheologically characterise ship-relevant marine biofilms. To combat marine biofilms on ship hulls, fouling-control coatings are often applied; therefore, the effect of different surfaces on marine biofilm mechanics was also investigated. Three surfaces were tested: a non-biocidal, chemically inert foul-release coating (FRC), an inert primer (ACP) and inert PVC. Physical properties of biofilms were explored using Optical Coherence Tomography (OCT) and a parallel-plate rheometer was used for rheological testing. Image analysis revealed differences in the thickness, roughness, and percent coverage between the different biofilms. Rheological testing showed that marine biofilms, grown on FRC and ACP acted as viscoelastic materials, although there were differences. FRC biofilms had a lower shear modulus, a higher viscosity, and a higher yield stress than the ACP biofilms, suggesting that the FRC biofilms were more readily deformable but potentially more robust. The results confirmed that surface treatment influences the structural and mechanical properties of ship-relevant marine biofilms, which could have implications for drag. A better understanding of how different surface treatments affect marine biofilm rheology is required to improve our knowledge on biofilm fluid-structure interactions and to better inform the coating industry of strategies to control biofilm formation and reduce drag.

Monitoring Aerobic Marine Bacterial Biofilms on Gold Electrode Surfaces and the Influence of Nitric Oxide Attachment Control

Detection of aerobic marine bacterial biofilms using electrochemical impedance spectroscopy has been done to monitor the interfacial response of Pseudoalteromonas sp. NCIMB 2021 attachment and growth in order to identify characteristic events on a 0.2 mm diameter gold electrode surface. Uniquely, the applicability of surface charge density has been proven to be valuable in determining biofilm attachment and cell enumeration over a 72 h duration on a gold surface within a modified continuous culture flow cell (a controlled low laminar flow regime with Reynolds number ≈ 1). In addition, biofilm dispersal has been evaluated using 500 nM sodium nitroprusside, a nitric oxide donor (nitric oxide is important for the regulation of several diverse biological processes). Ex situ confocal microscopy studies have been performed to confirm biofilm coverage and morphology, plus the determination and quantification of the nitric oxide biofilm dispersal effects. Overall, the capability of the sensor to electrochemically detect the presence of initial bacterial biofilm formation and extent has been established and shown to have potential for real-time biofilm monitoring.

Electrochemical Sensing and Characterization of Aerobic Marine Bacterial Biofilms on Gold Electrode Surfaces

Reliable and accurate in situ sensors capable of detecting and quantifying troublesome marine biofilms on metallic surfaces are increasingly necessary. A 0.2 mm diameter gold electrochemical sensor was fully characterized using cyclic voltammetry in abiotic and biotic artificial seawater media within a continuous culture flow cell to detect the growth and development of an aerobic Pseudoalteromonas sp. biofilm. Deconvolution of the abiotic and biotic responses enable the constituent extracellular electron transfer and biofilm responses to be resolved. Differentiation of enhanced oxygen reduction kinetics within the aerobic bacterial biofilm is linked to enzyme and redox mediator activities.

A rapid benchtop method to assess biofilm on marine fouling control coatings

A rapid benchtop method to measure the torque associated with minidiscs rotating in water using a sensitive analytical rheometer has been used to monitor the drag caused by marine fouling on coated discs. The method was calibrated using sandpaper surfaces of known roughness. Minidiscs coated with commercial fouling control coatings, plus an inactive control, were exposed in an estuarine harbour. After 176 days the drag on the fouling control-coated discs, expressed as a moment coefficient, was between 73% and 90% less than the drag on the control coating. The method has potential use as a screen for novel antifouling and drag reducing coatings and surfaces. Roughness functions derived using Granville's indirect similarity law are similar to patterns found in the general hydrodynamics literature, and so rotational minidisc results can be considered with reference to other fouling drag datasets.Supplemental data for this article is available online at https://doi.org/10.1080/08927014.2021.1929937 .

Biofilm Inhibition by Novel Natural Product- and Biocide-Containing Coatings Using High-Throughput Screening

The 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.

An experimental and computational study of the hydrodynamics of high-velocity water microdrops for interproximal tooth cleaning

The flow field and local hydrodynamics of high-velocity water microdrops impacting the interproximal (IP) space of typodont teeth were studied experimentally and computationally. Fourteen-day old Streptococcus mutans biofilms in the IP space were treated by a prototype AirFloss delivering 115 µL of water at a maximum exit-velocity of 60 ms(-1) in a 33-ms burst. Using high-speed imaging, footage was generated showing the details of the burst, and demonstrating the removal mechanism of the biofilms. Footage was also generated to characterize the viscoelastic behavior of the biofilms when impacted by an air-only burst, which was compared to the water burst. Image analysis demonstrated the importance of fluid forces on the removal pattern of interdental biofilms. X-ray micro-Computed Tomography (µ-CT) was used to obtain 3D images of the typodont and the IP spaces. Computational Fluid Dynamics (CFD) simulations were performed to study the effect of changing the nozzle position and design on the hydrodynamics within the IP space. Results confirmed our previous data regarding the wall shear stress generated by high-velocity water drops which dictated the efficacy of biofilm detachment. Finally, we showed how CFD models could be used to optimize water drop or burst design towards a more effective biofilm removal performance.

Life under flow: A novel microfluidic device for the assessment of anti-biofilm technologies

In the current study, we have developed and fabricated a novel lab-on-a-chip device for the investigation of biofilm responses, such as attachment kinetics and initial biofilm formation, to different hydrodynamic conditions. The microfluidic flow channels are designed using computational fluid dynamic simulations so as to have a pre-defined, homogeneous wall shear stress in the channels, ranging from 0.03 to 4.30 Pa, which are relevant to in-service conditions on a ship hull, as well as other man-made marine platforms. Temporal variations of biofilm formation in the microfluidic device were assessed using time-lapse microscopy, nucleic acid staining, and confocal laser scanning microscopy (CLSM). Differences in attachment kinetics were observed with increasing shear stress, i.e., with increasing shear stress there appeared to be a delay in bacterial attachment, i.e., at 55, 120, 150, and 155 min for 0.03, 0.60, 2.15, and 4.30 Pa, respectively. CLSM confirmed marked variations in colony architecture, i.e.,: (i) lower shear stresses resulted in biofilms with distinctive morphologies mainly characterised by mushroom-like structures, interstitial channels, and internal voids, and (ii) for the higher shear stresses compact clusters with large interspaces between them were formed. The key advantage of the developed microfluidic device is the combination of three architectural features in one device, i.e., an open-system design, channel replication, and multiple fully developed shear stresses.

Anti-biofilm performance of three natural products against initial bacterial attachment

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.

Characterisation of Crevice and Pit Solution Chemistries Using Capillary Electrophoresis with Contactless Conductivity Detector

The ability to predict structural degradation in-service is often limited by a lack of understanding of the evolving chemical species occurring within a range of different microenvironments associated with corrosion sites. Capillary electrophoresis (CE) is capable of analysing nanolitre solution volumes with widely disparate concentrations of ionic species, thereby producing accurate and reliable results for the analysis of the chemical compositions found within microenvironment corrosion solutions, such as those found at crevice and pit corrosion sites. In this study, CE with contactless conductivity detection (CCD) has been used to characterize pitting and crevice corrosion solution chemistries for the first time. By using the capillary electrophoresis with contactless conductivity detection (CE-CCD) system, direct and simultaneous detection of seven metal cations (Cu²⁺, Ni²⁺, Fe³⁺, Fe²⁺, Cr³⁺, Mn²⁺, and Al³⁺) and chloride anions was achieved with a buffer solution of 10 mM 2,6-pyridinedicarboxylic acid and 0.5 mM cetyltrimethylammonium hydroxide at pH 4 using a pre-column complexation method. The detection limits obtained for the metal cations and chloride anions were 100 and 10 ppb, respectively. The CE-CCD methodology has been demonstrated to be a versatile technique capable of speciation and quantifying the ionic species generated within artificial pit (a pencil electrode) and crevice corrosion geometries for carbon steels and nickel-aluminium bronze, thus allowing the evolution of the solution chemistry to be assessed with time and the identification of the key corrosion analyte targets for structural health monitoring.

Pseudotumour formation due to tribocorrosion at the taper interface of large diameter metal on polymer modular total hip replacements

We present an in-depth failure analysis of two large diameter bearing metal-on-polymer (MoP) modular total hip replacements, which have required revision surgery due to pseudotumour formation. The failure analysis showed a discrete pattern of material loss from the distal end of the head taper/stem trunnion interface. We postulate that the use of a proximal contacting taper design had provided insufficient mechanical locking between the head and the stem, enabling the head to toggle on the trunnion. In addition, the difference in angle between the taper and the trunnion formed a crevice between the two components. Through a combination of crevice environment, mechanically assisted corrosion, mechanical wear and erosion; debris and metal-ions have been released resulting in the adverse local tissue reactions (ALTR).

Marine biofilms on artificial surfaces: structure and dynamics

The search for new antifouling (AF) coatings that are environmentally benign has led to renewed interest in the ways that micro-organisms colonize substrates in the marine environment. This review covers recently published research on the global species composition and dynamics of marine biofilms, consisting mainly of bacteria and diatoms found on man-made surfaces including AF coatings. Marine biofilms directly interact with larger organisms (macrofoulers) during colonization processes; hence, recent literature on understanding the basis of the biofilm/macrofouling interactions is essential and will also be reviewed here. Overall, differences have been identified in species composition between biofilm and planktonic forms for both diatoms and bacteria at various exposure sites. In most studies, the underlying biofilm was found to induce larval and spore settlement of macrofoulers; however, issues such as reproducibility, differences in exposure sites and biofilm composition (natural multispecies vs. monospecific species) may influence the outcomes.

A review of experimental techniques to produce a nacre-like structure

The performance of man-made materials can be improved by exploring new structures inspired by the architecture of biological materials. Natural materials, such as nacre (mother-of-pearl), can have outstanding mechanical properties due to their complicated architecture and hierarchical structure at the nano-, micro- and meso-levels which have evolved over millions of years. This review describes the numerous experimental methods explored to date to produce composites with structures and mechanical properties similar to those of natural nacre. The materials produced have sizes ranging from nanometres to centimetres, processing times varying from a few minutes to several months and a different range of mechanical properties that render them suitable for various applications. For the first time, these techniques have been divided into those producing bulk materials, coatings and free-standing films. This is due to the fact that the material's application strongly depends on its dimensions and different results have been reported by applying the same technique to produce materials with different sizes. The limitations and capabilities of these methodologies have been also described.

Fluorescence microscopy techniques for quantitative evaluation of organic biocide distribution in antifouling paint coatings: application to model antifouling coatings

A test matrix of antifouling (AF) coatings including pMMA, an erodible binder and a novel trityl copolymer incorporating Cu₂O and a furan derivative (FD) natural product, were subjected to pontoon immersion and accelerated rotor tests. Fluorescence and optical microscopy techniques were applied to these coatings for quantification of organic biocide and pigment distribution. Total leaching of the biocide from the novel copolymer binder was observed within 6 months of rotor immersion, compared to 35% from the pMMA coating. In pontoon immersions, 61% of the additive was lost from the pMMA coating, and 53% from the erodible binder. Profiles of FD content in the binders revealed an accelerated loss of additive from the surface of the CDP resulting from rosin degradation, compared to even depletion from pMMA. In all samples, release of the biocide was inhibited beyond the Cu₂O front, corresponding to the leached layer in samples where Cu₂O release occurred.

Electrochemical sensing of aerobic marine bacterial biofilms and the influence of nitric oxide attachment control

Suitable in situ techniques capable of sensing for the presence of a biofilm on metallic surfaces are becoming increasingly necessary, especially in order to maintain seawater pipe system performance. This study has investigated the detection of aerobic marine bacterial biofilms using electrochemical impedance spectroscopy by monitoring the interfacial response of Pseudoalteromonas sp. NCIMB 2021 attachment and growth in order to identify characteristic events on a 0.2 mm diameter gold electrode surface. Uniquely, the applicability of surface charge density has been proven to be valuable in determining biofilm attachment and cell enumeration over 72 h duration on a gold surface within a modified continuous culture flow cel(lsa controlled low laminar flow regime with a Reynolds number ≈ 1).In addition, the potential for biofilm disruption has been evaluated using 500 nM of the nitric oxide (NO) donor sodium nitroprusside (NO is important for the regulation of a number of diverse biological processes). Ex situ confocal microscopy studies were performed to confirm biofilm coverage and morphology, plus the determination and quantification of the NO biofilm dispersal effects. Overall, the capability of the sensor to electrochemically detect the presence of initial bacterial biofilm formation and extent has been established and shown to have potential for real-time biofilm monitoring.

Designing biomimetic antifouling surfaces

Marine biofouling is the accumulation of biological material on underwater surfaces, which has plagued both commercial and naval fleets. Biomimetic approaches may well provide new insights into designing and developing alternative, non-toxic, surface-active antifouling (AF) technologies. In the marine environment, all submerged surfaces are affected by the attachment of fouling organisms, such as bacteria, diatoms, algae and invertebrates, causing increased hydrodynamic drag, resulting in increased fuel consumption, and decreased speed and operational range. There are also additional expenses of dry-docking, together with increased fuel costs and corrosion, which are all important economic factors that demand the prevention of biofouling. Past solutions to AF have generally used toxic paints or coatings that have had a detrimental effect on marine life worldwide. The prohibited use of these antifoulants has led to the search for biologically inspired AF strategies. This review will explore the natural and biomimetic AF surface strategies for marine systems.

Unusual presentations of pleomorphic adenoma and adenoid cystic carcinoma of the lacrimal gland

PURPOSE

To report two atypical cases of pleomorphic adenoma and adenoid cystic tumours of the lacrimal gland.

METHODS

Two case reports are presented. The first is of a 65-year-old female with a long history of right hypoglobus with sudden recent worsening. Computed tomography (CT) showed a round, well-defined lesion in the fossa for the lacrimal gland with an anterior hypodense extension suggestive of possible malignancy in a pleomorphic adenoma. The tumour in the second case, a 35-year-old male, was diagnosed after presentation following a relatively minor periorbital injury. The smooth rounded mass on CT scan was suggestive of a benign lacrimal gland tumour.

RESULTS

The lesion in case 1 was excised with a diagnosis of haemorrhage within a pleomorphic adenoma. The lesion in case 2 was excised with a diagnosis of adenoid cystic carcinoma of the lacrimal gland with pseudocapsule.

CONCLUSIONS

Haemorrhagic cyst developing beneath the pseudocapsule of a pleomorphic adenoma should be considered in the differential diagnosis of secondary development of malignancy in a pleomorphic adenoma. Adenoid cystic tumours of the lacrimal gland can present with a pseudocapsule.

Self-focused and somatic attention in patients with tinnitus

Self-focused and somatic attention were examined in a sample of 51 patients with tinnitus using the Self-Focus Sentence Completion Test, Private Self-Consciousness Subscale of the Self-Consciousness Scale, Modified Somatic Perception Questionnaire, and the Somatization Subscale of the Symptoms Checklist-90-Revised. Two subgroups of patients emerged following a cluster analysis of the attentional tasks. One group scored lower on both self-attention and somatic attention measures ("low self-attenders"), whereas a second group was more internally directed and scored higher on the attention measures ("high self-attenders"). Between-group comparisons showed that the high self-attenders were, on average, more depressed, had greater emotional distress due to tinnitus, and had greater perceived tinnitus handicap. In contrast, no differences were observed for pitch and loudness measures using either psychophysical or rating scale techniques. Results of this investigation support the belief that attentional mechanisms play an important role in patients' perception of tinnitus and should be considered when planning management strategies.

Electrophysiological indices of selective auditory attention in subjects with and without tinnitus

The present investigation was conducted in an attempt to determine whether selective auditory attention abilities differed between normal subjects and subjects with bothersome tinnitus. Subjects were 37 adults with tinnitus and high-frequency hearing loss (not affecting thresholds at 500 and 1000 Hz) and 15 subjects who were audiometrically and otologically normal. Results suggested that an electrophysiological index of early selective auditory attention (i.e., the negative difference wave, Nd) was of greater magnitude in tinnitus patients. Also, the cortical NI component occurred significantly later in the presence of selective attention in tinnitus subjects only. Results of this investigation may support the view that early selective auditory attention in subjects with bothersome tinnitus differs from that of normal subjects.

Retest stability of the tinnitus handicap questionnaire

The test-retest stability of the Tinnitus Handicap Questionnaire was assessed for a sample of 32 tinnitus patients. The questionnaire is a self-report measure that quantifies the physical, emotional, and social consequences of tinnitus (factor 1), the interfering effects of tinnitus on the hearing ability of the patient (factor 2), and the patients' view of tinnitus (factor 3). Retest stability estimates were obtained in order to determine the applicability of using the questionnaire as an outcome measure following tinnitus management. High test-retest correlations emerged for factors 1 and 2, whereas factor 3 yielded inadequate retest reliability. Therefore, it is recommended that only factors 1 and 2 be used for documenting changes in self-perceived tinnitus handicap following medical, surgical, or rehabilitative intervention.

Relationships among psychoacoustic judgments, speech understanding ability and self-perceived handicap in tinnitus subjects

Tinnitus is often a disturbing symptom which affects 6-20% of the population. Relationships among tinnitus pitch and loudness judgments, audiometric speech understanding measures and self-perceived handicap were evaluated in a sample of subjects with tinnitus and hearing loss (THL). Data obtained from the THL sample on the audiometric speech measures were compared to the performance of an age-matched hearing loss only (HL) group. Both groups had normal hearing through 1 kHz with a sloping configuration of < or = 20 dB/octave between 2-12 kHz. The THL subjects performed more poorly on the low predictability items of the Speech Perception in Noise Test, suggesting that tinnitus may interfere with the perception of speech signals having reduced linguistic redundancy. The THL subjects rated their tinnitus as annoying at relatively low sensation levels using the pitch-match frequency as the reference tone. Further, significant relationships were found between loudness judgment measures and self-rated annoyance. No predictable relationships were observed between the audiometric speech measures and perceived handicap using the Tinnitus Handicap Questionnaire. These findings support the use of self-report measures in tinnitus patients in that audiometric speech tests alone may be insufficient in describing an individual's reaction to his/her communication breakdowns.

False negative auditory brainstem response findings in vestibular schwannoma: case reports

The false negative rate of the auditory brainstem response (ABR) for the detection of vestibular schwannoma (VS; acoustic neuroma) has been reported to range from 2 to 9 percent. The introduction of magnetic resonance with gadolinium contrast (Gd MRI) may be expected to raise the false negative rate, because smaller tumors can now be detected. We present two cases that illustrate some of the complex issues raised by the detection of small asymptomatic VS by Gd MRI that were missed by ABR. The role of ABR testing in the diagnosis and management of VS remains well established and will continue to evolve.

The influence of hearing aid cost on perceived benefit in older adults

Self-report hearing handicap scales are gaining widespread acceptance among clinicians as a technique for quantifying hearing aid benefit. Both auditory and nonauditory (e.g., personality, health, motivation) factors contribute to an individual's response to hearing loss and ultimately to perceived hearing aid benefit. Among the recognized extra-audiological variables, financial concerns may influence a hearing aid user's expectations regarding hearing aid benefit. The present study compared self-perceived benefit in 26 insured and 26 uninsured new hearing aid wearers using the Hearing Handicap Inventory for the Elderly (HHIE). HHIE scores at 3 weeks and 6 mo postfitting were equivalent between groups. The findings suggest that the HHIE may be used as an index of hearing aid benefit without concern that the source of funds required to purchase amplification may act as an uncontrolled variable.

Influence of menopause on the auditory brainstem response

Auditory brainstem response (ABR) wave latency, interpeak interval and amplitude as a function of intensity were measured in 40 subjects divided into equal groups of postmenopausal females, age-matched males and young adults of both sexes. The results illustrate that age and gender play a significant role in ABR wave latency and amplitude. A larger age effect occurred for the female subjects. While this does not dispute an anatomical explanation for the gender effect in ABR, hormonal changes accompanying menopause may also account for some of the gender differences noted in ABR.