Undamaged Surface Research Articles

Quantifying the surface damage of involute gear flanks independent of the gear datum axis

Abstract Surface damage on involute gear tooth flanks can develop during the operation of a gearbox and affects their life, durability and efficiency. Understanding the extent and severity of this damage is critical, especially in long life applications such as wind turbines where gearboxes are a critical component that incur high down time and costs for replacement. Accessing gears in service is difficult and relating gear form measurements to the gear datum is often impossible without its removal. Additionally, damage measurements are typically not areal, which can miss the most severe areas, or require lengthy measurement times. This paper describes a method for characterising and quantifying localised damage relative to the undamaged tooth surface independent of the gear datum axis, and provides a method to estimate the damage location using involute co-ordinates. By taking soft replicas of the gear flank and measuring them with optical methods, the damage is characterised. This method allows for the areal evaluation of damage that relates to involute coordinates, which can be combined with nominal data or measurements after manufacture to create data sets for simulation in tooth contact analysis models, used to train condition monitoring models or for improved maintenance programming to improve reliability and reduce costly downtime.

Study of Prefabricated Crack Propagation on Monocrystalline Silicon Surfaces for Grinding Damage Analysis.

Crack generation and propagation are critical aspects of grinding processes for hard and brittle materials. Despite extensive research, the impact of residual cracks from coarse grinding on the cracks generated during fine grinding remains unexplored. This study aims to bridge this gap by examining the propagation law of existing cracks under indentation using the extended finite element method. The results reveal that prefabricated cracks with depths less than the crack depth produced on an undamaged surface tend to extend further without surpassing the latter. Conversely, deeper prefabricated cracks do not exhibit significant expansion. A novel method combining indentation and prefabricated cracks with fracture strength tests is proposed to determine crack propagation. Silicon wafers with varying damaged surfaces are analyzed, and changes in fracture strength, measured by the ball-on-ring method, are utilized to determine crack propagation. The experimental results confirm the proposed crack evolution law, validated by damage assessments across different grinding processes, which is suitable for crack damage. The findings demonstrate that residual cracks from coarse grinding are negligible in predicting the maximum crack depth during fine grinding. This research provides a crucial foundation for optimizing the wafer thinning process in 3D stacked chip manufacturing, establishing that changes in fracture strength are a reliable indicator of crack propagation feasibility.

Modeling of surface evolution in plasma etching for SiC microgroove fabrication

Monocrystalline silicon carbide (SiC) has attracted attention for applications in devices operating in harsh environments due to its excellent physicochemical properties. However, it is difficult to obtain extremely small-feature sizes with undamaged surfaces due to its extremely high hardness. Herein, a novel method to fabricate SiC microgrooves is proposed that combines molding with inductively coupled plasma (ICP) etching process. First, a Ni–P microgroove master mold was fabricated by ultraprecision cutting and replicated on a polydimethylsiloxane (PDMS) surface, which was then used as the microgroove mold for hot embossing. Then, the patterned mask fabricated by hot embossing was transferred to the SiC substrate by ICP etching. To obtain customized microgrooves, an interface-evolution model based on angular dependence theory was established. A numerical method based on a string algorithm approach is developed for interface-evolution simulations. During ICP etching, the characteristic size d of homogeneous materials and the sidewall angle in heterogeneous materials varied with the sidewall angle of the SU-8 mask due to the angular dependence of etch rate. Finally, seven sets of microgrooves were machined on SU-8 to study the interface-evolution process. Variations in the characteristic size Δd and sidewall angle θ for each unit in homogeneous material, as well as the variations in sidewall angle before and after etching in heterogeneous materials are described. The high accuracy of the proposed interface-evolution model was experimentally validated.

Current Knowledge of Enterococcal Endocarditis: A Disease Lurking in Plain Sight of Health Providers.

Enterococcus faecalis is a bacterial pathogen that can cause opportunistic infections. Studies indicate that initial biofilm formation plays a crucial regulatory role in these infections, as well as in colonising and maintaining the gastrointestinal tract as a commensal member of the microbiome of most land animals. It has long been thought that vegetation of endocarditis resulting from bacterial attachment to the endocardial endothelium requires some pre-existing tissue damage, and in animal models of experimental endocarditis, mechanical valve damage is typically induced by cardiac catheterisation preceding infection. This section reviews historical and contemporary animal model studies that demonstrate the ability of E. faecalis to colonise the undamaged endovascular endothelial surface directly and produce robust microcolony biofilms encapsulated within a bacterially derived extracellular matrix. This report reviews both previous and current animal model studies demonstrating the resilient capacity of E. faecalis to colonise the undamaged endovascular endothelial surface directly and produce robust microcolony biofilms encapsulated in a bacterially derived extracellular matrix. The article also considers the morphological similarities when these biofilms develop on different host sites, such as when E. faecalis colonises the gastrointestinal epithelium as a commensal member of the common vertebrate microbiome, lurking in plain sight and transmitting systemic infection. These phenotypes may enable the organism to survive as an unrecognised infection in asymptomatic subjects, providing an infectious resource for subsequent clinical process of endocarditis.

Effect of Different Chemical Solvents on Bond Strength of Orthodontic Brackets: An In Vitro Study.

The purpose of the present study was to evaluate the impact of various chemical solvents on bond strength of orthodontic brackets. One hundred healthy human premolars with undamaged buccal surfaces that were extracted for orthodontic purposes were gathered. Using 37% orthophosphoric acid, primer, and Transbond XT adhesive, ceramic 0.018" × 0.022" slot orthodontic brackets were adhered to the tooth surface. Following thermocycling, all samples were divided into four groups, with 25 samples in each group: group I: control; group II: application of ethanol; group III: application of acetone; and group IV: application of dimethyl sulfoxide (DMSO). Following the debonding tests, a double-ocular stereomicroscope was used to inspect the tooth surfaces. Additionally, adhesive remnant index (ARI) values were evaluated at 40× magnification. Data were recorded and statistically analyzed. The bond strength was lesser in acetone applied group (16.18 ± 3.64) followed by DMSO applied group (22.08 ± 2.86), ethanol applied group (24.36 ± 4.02), and control group (27.14 ± 3.68). There was a highly significant difference found between the chemical solvents group. The ARI score 3 was present in control (12%), ethanol (8%), and DMSO (4%), and it was absent in acetone applied group. The ARI score 0 was more in acetone applied group (24%). The present study concluded that the reduced debonding force was found with the application of acetone solvent followed by DMSO, ethanol, and control groups. Applying acetone can be a substitute technique to help with ceramic bracket debonding. Orthodontic bracket debonding cannot occur without shear bond strength (SBS). The need for an ideal debonding technique for ceramic brackets without negative consequences arises from the risk of enamel damage that frequently follows the process. Acetone treatment prior to ceramic bracket debonding could be an alternate clinical technique to preventing enamel damage and facilitating debonding. How to cite this article: Bhushan R, Singh S, Sam G, et al. Effect of Different Chemical Solvents on Bond Strength of Orthodontic Brackets: An In Vitro Study. J Contemp Dent Pract 2023;24(12):940-943.

Xerophilic fungi contaminating historically valuable easel paintings from Slovenia.

Historically valuable canvas paintings are often exposed to conditions enabling microbial deterioration. Painting materials, mainly of organic origin, in combination with high humidity and other environmental conditions, favor microbial metabolism and growth. These preconditions are often present during exhibitions or storage in old buildings, such as churches and castles, and also in museum storage depositories. The accumulated dust serves as an inoculum for both indoor and outdoor fungi. In our study, we present the results on cultivable fungi isolated from 24 canvas paintings, mainly exhibited in Slovenian sacral buildings, dating from the 16th to 21st centuries. Fungi were isolated from the front and back of damaged and undamaged surfaces of the paintings using culture media with high- and low-water activity. A total of 465 isolates were identified using current taxonomic DNA markers and assigned to 37 genera and 98 species. The most abundant genus was Aspergillus, represented by 32 species, of which 9 xerophilic species are for the first time mentioned in contaminated paintings. In addition to the most abundant xerophilic A. vitricola, A. destruens, A. tardicrescens, and A. magnivesiculatus, xerophilic Wallemia muriae and W. canadensis, xerotolerant Penicillium chrysogenum, P. brevicompactum, P. corylophilum, and xerotolerant Cladosporium species were most frequent. When machine learning methods were used to predict the relationship between fungal contamination, damage to the painting, and the type of material present, proteins were identified as one of the most important factors and cracked paint was identified as a hotspot for fungal growth. Aspergillus species colonize paintings regardless of materials, while Wallemia spp. can be associated with animal fat. Culture media with low-water activity are suggested in such inventories to isolate and obtain an overview of fungi that are actively contaminating paintings stored indoors at low relative humidity.

Research on the Preparation and Application of Fixed-Abrasive Tools Based on Solid-Phase Reactions for Sapphire Wafer Lapping and Polishing.

Single-crystal sapphire specimen (α-Al2O3) have been widely applied in the semiconductor industry, microelectronics, and so on. In order to shorten the production time and improve the processing efficiency of sapphire processing, an integrated fixed-abrasive tool (FAT) based on solid-phase reactions is proposed in this article. The optimal FAT composition is determined using a preliminary experiment and orthogonal experiments. The mass fraction of the abrasives is chosen as 55 wt%, and the mass ratio of SiO2/Cr2O3 is 2. Surface roughness Ra decreased from 580.4 ± 52.7 nm to 8.1 ± 0.7 nm after 150 min, and the average material removal rate was 14.3 ± 1.2 nm/min using the prepared FAT. Furthermore, FAT processing combined with chemical mechanical polishing (CMP) was shortened by 1.5 h compared to the traditional sapphire production process in obtaining undamaged sapphire surfaces with a roughness of Ra < 0.4 nm, which may have the potential to take the place of the fine lapping and rough polishing process.

Study Comparing the Shear Bond Forte of Ceramics with Metal Reinforcement to Unreinforced Ceramic Brackets

Background: In an effort to address the growing need for more aesthetic appliances, ceramic brackets were introduced into orthodontics. The need for more aesthetic and less obvious appliances has risen as a result of adult orthodontic therapy. Aim: To assess the shear bond strength of the Clarity and Transcend 6000 brackets as well as the bracket breakdown mechanism while utilising shear force with Schimadzu testing equipment, information from this study will be useful for orthodontic participants as well as practitioners. Methodology: This comparative study was conducted at Orthodontic Department, Bacha Khan College of Dentistry, Mardan from 1st July 2021 to 31st December 2022. A total of 150 brackets (75 reinforced ceramic brackets and 75 conventional ceramic brackets in each cluster) were enrolled. The first premolar teeth that had been pulled in their entirety for orthodontic treatment were chosen to be bonded. Only the first maxillary premolar teeth with undamaged surfaces that had recently been removed and preserved were used. Premolars that had broken down or decayed were eliminated. Result: There was no statistically significant difference amongst the two brackets evaluated, according to an independent t-test associating the clarity and transcends 6000 ceramic brackets. Conclusion: The differences in adhesive remnant index ratings and shear bond forte between the Transcend 6000 ceramic and Clarity were negligible. Key words: Adhesive remnant index (ARI), De-bonding, Shear bond strength

Simulation and experimental research on magnetorheological finishing under dynamic pressure with a gap-varying

Magnetorheological finishing (MRF) is a novel machining method used to obtain ultra-smooth and even surfaces. To improve the material removal rate (MRR) while attaining smooth and undamaged surfaces, an MRF method with a varying machining gap between the polishing disks and workpieces is proposed to increase the polishing efficiency and improve the surface quality. According to the computational fluid dynamics (CFD) method, the behaviors of MRF fluids under the effect of magnetic fields are measured using a rheometer. Furthermore, a simulation model for fluids based on the gap-varying MRF is established to evaluate the influence of the varying machining gap on the behaviors of the flow field of MRF fluids. The results show that the flow field formed during gap-varying MRF presents a periodic dynamic change and formation of turbulence. Both the fluid pressure and velocity on the workpiece surface show a periodic change and the maximum fluid velocity on the workpiece surface in the x-direction is much greater than that in the z-direction; the transverse shear velocity contributes to the material removal and abrasive update. Under the same polishing time and rotational speed, the surface roughness is reduced from Ra 6.36 nm to Ra 0.155 nm after MRF without varying gaps for 5 h; in contrast, the surface roughness decreases from Ra 6.44 nm to Ra 0.104 nm after MRF with a varying gap, attaining an atomic step-structure. Properly increasing the frequency and amplitude of gap variations is conducive to achieving a better polishing effect. By conducting real-time force measurement and establishing a material removal function, it is shown that the simulation results match the test results. MRF with a varying gap can increase the polishing efficiency and surface quality by changing the behaviors of the flow field.

Performance of resin–cement composite clad modified vitrified beads

In this study, organic–inorganic composite modified vitrified beads were prepared with a water-based acrylic resin and cement as modifiers. The effects of the modified cladding on the performance of the vitrified beads were investigated by varying the amount of emulsion and the volume of the spray. The volume of the vitrified beads to be modified was maintained at 100 cm3 and the total amount of cement was maintained at 5.0 g. The results showed that, when the amount of emulsion is 3.0 mL and the volume of the spray is 15.0 mL, the bulk density of the vitrified beads increases by 28.5 kg/m3, the volume water absorption decreases from 39.7% to 3.5%, and the cylinder compressive strength increases by 218.0 kPa. Moreover, the thermal conductivity increases by only 0.0033 W/(m‧K), the degree of bonding is relatively low, and the comprehensive performance is optimal. On the surface of the modified vitrified beads, some of the cement seals the open hole, and the rest of it adheres to the undamaged surface, which is conducive to the improvement of the strength of the material. On the one hand, the resin can fill the pores of cement, and form a staggered organic–inorganic network with cement. Meanwhile, it forms an organic film on the surface of the cement and the glazed layer to play a hydrophobic and strengthening role. On the other hand, it acts as a binder between the cement and the glazed layer to reduce the shedding of cement in the process of material use.

A Recurrent Adaptive Network: Balanced Learning for Road Crack Segmentation with High-Resolution Images

Road crack segmentation based on high-resolution images is an important task in road service maintenance. The undamaged road surface area is much larger than the damaged area on a highway. This imbalanced situation yields poor road crack segmentation performance for convolutional neural networks. In this paper, we first evaluate the mainstream convolutional neural network structure in the road crack segmentation task. Second, inspired by the second law of thermodynamics, an improved method called a recurrent adaptive network for a pixelwise road crack segmentation task is proposed to solve the extreme imbalance between positive and negative samples. We achieved a flow between precision and recall, similar to the conduction of temperature repetition. During the training process, the recurrent adaptive network (1) dynamically evaluates the degree of imbalance, (2) determines the positive and negative sampling rates, and (3) adjusts the loss weights of positive and negative features. By following these steps, we established a channel between precision and recall and kept them balanced as they flow to each other. A dataset of high-resolution road crack images with annotations (named HRRC) was built from a real road inspection scene. The images in HRRC were collected on a mobile vehicle measurement platform by high-resolution industrial cameras and were carefully labeled at the pixel level. Therefore, this dataset has sufficient data complexity to objectively evaluate the real performance of convolutional neural networks in highway patrol scenes. Our main contribution is a new method of solving the data imbalance problem, and the method of guiding model training by analyzing precision and recall is experimentally demonstrated to be effective. The recurrent adaptive network achieves state-of-the-art performance on this dataset.

Experimental Analysis of Ductile Cutting Regime in Face Milling of Sintered Silicon Carbide.

In this study, sintered silicon carbide is machined on a high-precision milling machine with a high-speed spindle, closed-loop linear drives and friction-free micro gap hydrostatics. A series of experiments was undertaken varying the relevant process parameters such as feedrate, cutting speed and chip thickness. For this, the milled surfaces are characterized in a process via an acoustic emission sensor. The milled surfaces were analyzed via confocal laser scanning microscopy and the ISO 25178 areal surface quality parameters such as Sa, Sq and Smr are determined. Moreover, scanning electron microscopy was used to qualitatively characterize the surfaces, but also to identify sub-surface damages such as grooves, breakouts and pitting. Raman laser spectroscopy is used to identify possible amorphization and changes to crystal structure. We used grazing incidence XRD to analyze the crystallographic structure and scanning acoustic microscopy to analyze sub-surface damages. A polycrystalline diamond tool was able to produce superior surfaces compared to diamond grinding with an areal surface roughness Sa of below 100 nm in a very competitive time frame. The finished surface exhibits a high gloss and reflectance. It can be seen that chip thickness and cutting speed have a major influence on the resulting surface quality. The undamaged surface in combination with a small median chip thickness is indicative of a ductile cutting regime.

A metagenomic analysis of the bacterial microbiome of limestone, and the role of associated biofilms in the biodeterioration of heritage stone surfaces

There is growing concern surrounding the aesthetic and physical effects of microbial biofilms on heritage buildings and monuments. Carboniferous stones, such as limestone and marble, are soluble in weak acid solutions and therefore particularly vulnerable to biocorrosion. This paper aims to determine the differences and commonalities between the microbiome of physically damaged and undamaged Lincolnshire limestone, an area of research which has not been previously studied. A lack of information about the core microbiome has resulted in conflicting claims in the literature regarding the biodeteriorative potential of many microorganisms. To address this, we used metagenomics alongside traditional microbiological techniques to produce an in-depth analysis of differences between the bacterial microbiomes found on deteriorated and undamaged external limestone surfaces. We demonstrate there is a core microbiome on Lincolnshire limestone present on both damaged and undamaged surfaces. In addition to the core microbiome, significant differences were found between species isolated from undamaged compared to damaged surfaces. Isolated species were characterised for biofilm formation and biodeteriorative processes, resulting in the association of species with biodeterioration that had not been previously described. Additionally, we have identified a previously undescribed method of biofilm-associated biomechanical damage. This research adds significant new understanding to the field, aiding decision making in conservation of stone surfaces.

Simulating the diffusion of hydrogen in amorphous silicates: A ‘jumping’ migration process and its implications for solar wind implanted lunar volatiles

We use molecular dynamics (MD) simulations to better explain the movement of atomic hydrogen in amorphous silica and quantify the planetary science implications of these findings. Previous MD simulations had a large range of predicted values and did not agree well with experiment. Our simulations sample atomic motion for a longer duration and consider a wider range of temperatures than previous simulations. In contrast to constant atomic motion, the hydrogen atoms were shown to undergo random intermittent jumps from one oxygen atom to another, the number of which increase with temperature. Predicted diffusion coefficients had a better agreement to experimental values than previous MD simulations, suggesting the importance of longer simulation durations for better statistics. The low activation energy and jumps observed at lunar temperatures do not support the theory of diurnal variations in OH content for an undamaged amorphous silica surface. Instead, we conclude that energetic solar wind impacts can induce two competing atomic hydrogen motion processes in the exposed surface: A prompt effect that induces jumps in the temperature spike volume, but also a long-term effect of damage in the structure that traps atomic hydrogen. We then use SDTrimSP to quantify the damage created during exposure and MD to demonstrate the H retention and trapping near these defects. Damage was shown to be dependent on impact energy, with defects easily retaining implanted hydrogen. MD results like those presented herein on unweathered surfaces are therefore most relevant to magnetic anomalies. As a result, we demonstrate the importance of lunar volatile models to account for the damage state of the substrate when modelling hydrogen diffusion, retention, and subsequent OH/water production.

Novel Natural Surfactant-Based Fatty Acids and Their Corrosion-Inhibitive Characteristics for Carbon Steel-Induced Sweet Corrosion: Detailed Practical and Computational Explorations

Steel alloys are significant industrial substances, but they generally suffer severe corrosion under harsh conditions. Using inhibitors is an efficacious method to impede corrosion. So, in this study, two novel natural surfactants based on soybean oil have been synthesized by a facile route, namely, 1-(bis(2-hydroxyethyl)amino)-1-oxooctadecan-9-yl sulfate 2-hydroxyethan-1-aminium (CSM) and–N-(C2H4-OH)2; 1-(bis(2-hydroxyethyl)amino)-1-oxooctadecan-9-yl sulfate bis(2-hydroxyethyl)aminium (CSD), and their chemical structures were elucidated by physical–chemical approaches, Fourier transform infrared (FT-IR) spectroscopy, and surface activity measurements. The inhibitive effect of natural surfactants (CSM and CSD) on the C-steel corrosion in CO2-saturated 3.5% NaCl has been estimated in this investigation by electrochemical and surface analyses including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), linear polarization resistance (LPR) corrosion rate, X-ray photoelectron spectroscopy (XPS), and field-emission scanning electron microscope/energy-dispersive X-ray spectroscopy (FESEM/EDX) approaches. The EIS study reveals the value ofRpaugmented to an increase of 913.5 Ω cm2with a protection capacity of 96.1% at 150 ppm (CSD). The outcomes of PDP suggested that CSM and CSD are mixed-type inhibitors. XPS and FESEM/EDX analyses determined the protective film formation on a metal interface having undamaged surface morphology and more homogeneities in the occurrence of the surfactant. Moreover, the adsorption of natural surfactants on the metal substrate takes place based on the model of Langmuir isotherm. Density functional theory (DFT) calculations and Monte Carlo (MC) simulations were selected for attaining basic atomic/electronic-scale details about the prepared surfactants, which support the practical findings. This study is intended to investigate the protection of C-steel using sweet service conditions with green extract surfactants.

Femtosecond laser processing and field emission properties of the FEAs on single crystal GdB6 (100) surface

The single crystal GdB6 were prepared by optical zone melting method. Moreover, using the femtosecond laser micromachining technology processed the field-emission tip arrays (FEAs) on the (100) surface of single crystal GdB6. The single crystal quality, field emission of the FEAs, as well as the electronic structure of single crystal GdB6 are systematically characterized. The quality of single crystal is good. The curvature radius of the produced FEAs with uniform morphology and undamaged crystal surface structure are about 0.5 μm. The FEAs showed good field emission performance, which the turn-on electric field of the FEAs is 2.6 V/μm with a field emission current of 0.46 A/cm2 at 7.3 V/μm and the emission current has high stability. The calculation electronic structure of GdB6 show that the 5d electron of Gd determines the electronic state of excellent emission performance. The high electric field will greatly decrease the surface barrier and work function of GdB6, according with the field emission theory.

Evaluation of quantitative light-induced fluorescence to assess lesion depth in cavitated and non-cavitated root caries lesions – An in vitro study

BackgroundThis in vitro study aimed to assess carious lesions on root surfaces using quantitative light-induced fluorescence (QLF) and to compare the readings with axial lesion depth on µCT. MethodsThe root surfaces of 107 extracted human teeth were included after visual-tactile inspection. For further analysis, the following parameters were assessed: clinical findings (non-cavitated: leathery or hard, cavitated), QLF- (QLF-D Biluminator 2+), and µCT-images (Bruker Skyscan 1172). The shape of the undamaged tooth surface of the cavitated lesions was virtually re-constructed during µCT analysis. Clinical surface texture,% fluorescence loss, and lesion depth (µCT) were determined. Statistical analysis: chi²-test, Spearman-Rho test, regression analysis. Results∆F was significantly lower in non-cavitated leathery (-50.37 ± 15.10) and cavitated (-61.23 ± 9.92) compared to non-cavitated surfaces with a hard texture (-17.04 ± 16.10, p < 0.01). For non-cavitated surfaces, a negative correlation was observed between ∆F and lesion depth in µCT images regardless of texture (-0.748, p < 0.01). Regression analysis revealed that ∆F predicted lesion depth in µCT for non-cavitated surfaces (β: 0.703, CI95: 0.67–-0.43, p < 0.01). ConclusionThe percentage of fluorescence loss (∆F) in QLF predicted lesion depth of non-cavitated demineralized root surfaces. Therefore, QLF can be recommended for estimating the lesion depth of carious root lesions and seems to expand the possibilities of follow-up and lesion monitoring, especially for non-cavitated surfaces.

Cascaded Ni hard mask to create chlorine-based ICP dry etched deep mesas for high-power devices

A highly selective cascaded Ni hard mask without stress and film damage issues suitable for the formation of deep vertical mesas for high-power devices is presented. A Cl2/BCl3/Ar inductively coupled plasma dry etch was used to investigate the effect of photoresist, and patterned Ni hard masks applied via four different methods on the etch rate of GaN, and mask selectivity. Strain in the e-beam only deposited Ni films produced low yield due to poor adhesion. Electroplated Ni showed rough mask morphology. Sputtered Ni left damage/chemically reacted layers on the GaN under the mask. A cascaded 50 nm e-beam evaporated Ni followed by 2 µm of sputtered Ni mask method improved the yield to 100%, achieved high selectivity and retained an undamaged GaN surface morphology. The cascaded Ni hard mask successfully achieved GaN mesas up to 13 µm. The dry etching rates of the photoresist, GaN and Ni masks were 250, 275 and 13 nm min−1, respectively giving an etch selectivity of the GaN/Ni hard mask of ∼20, much higher than the etch selectivity of 1.1 for the photoresist. Furthermore, yield of the cascaded Ni hard mask was 100% making it suitable for commercial high-power electronics.

Enterococcus faecalis colonizes and forms persistent biofilm microcolonies on undamaged endothelial surfaces in a rabbit endovascular infection model.

ABSTRACTInfectious endocarditis (IE) is an uncommon disease with significant morbidity and mortality. The pathogenesis of IE has historically been described as a cascade of host-specific events beginning with endothelial damage and thrombus formation and followed by bacterial colonization of the nascent thrombus. Enterococcus faecalis is a Gram-positive commensal bacterial member of the gastrointestinal tract microbiota in most terrestrial animals and a leading cause of opportunistic biofilm-associated infections, including endocarditis. Here, we provide evidence that E. faecalis can colonize the endocardial surface without pre-existing damage and in the absence of thrombus formation in a rabbit endovascular infection model. Using previously described light and scanning electron microscopy techniques, we show that inoculation of a well-characterized E. faecalis lab strain in the marginal ear vein of New Zealand White rabbits resulted in rapid colonization of the endocardium throughout the heart within 4 days of administration. Unexpectedly, ultrastructural imaging revealed that the microcolonies were firmly attached directly to the endocardium in areas without morphological evidence of gross tissue damage. Further, the attached bacterial aggregates were not associated with significant cellular components of coagulation or host extracellular matrix damage repair (i.e. platelets). These results suggest that the canonical model of mechanical surface damage as a prerequisite for bacterial attachment to host sub-endothelial components is not required. Furthermore, these findings are consistent with a model of initial establishment of stable, endocarditis-associated E. faecalis biofilm microcolonies that may provide a reservoir for the eventual valvular infection characteristic of clinical endocarditis. The similarities between the E. faecalis colonization and biofilm morphologies seen in this rabbit endovascular infection model and our previously published murine gastrointestinal colonization model indicate that biofilm production and common host cell attachment factors are conserved in disparate mammalian hosts under both commensal and pathogenic contexts.

Enterococcal Endocarditis: Hiding in Plain Sight.

Enterococcus faecalis is a major opportunistic bacterial pathogen of increasing clinical relevance. A substantial body of experimental evidence suggests that early biofilm formation plays a critical role in these infections, as well as in colonization and persistence in the GI tract as a commensal member of the microbiome in most terrestrial animals. Animal models of experimental endocarditis generally involve inducing mechanical valve damage by cardiac catheterization prior to infection, and it has long been presumed that endocarditis vegetation formation resulting from bacterial attachment to the endocardial endothelium requires some pre-existing tissue damage. Here we review both historical and contemporary animal model studies demonstrating the robust ability of E. faecalis to directly attach and form stable microcolony biofilms encased within a bacterially-derived extracellular matrix on the undamaged endovascular endothelial surface. We also discuss the morphological similarities when these biofilms form on other host tissues, including when E. faecalis colonizes the GI epithelium as a commensal member of the normal vertebrate microbiome - hiding in plain sight where it can serve as a source for systemic infection via translocation. We propose that these phenotypes may allow the organism to persist as an undetected infection in asymptomatic individuals and thus provide an infectious reservoir for later clinical endocarditis.