Nanoscale Adhesion Forces Research Articles

Effect of UV Light Exposure Duration on the Removal of Exfoliation Agent Residues in Two-Dimensional Perovskite Nanosheets: An AFM Study.

Accurate determination of dielectric properties and surface characteristics of two-dimensional (2D) perovskite nanosheets, produced by chemical exfoliation of layered perovskites, is often hindered by exfoliation agent residues such as tetrabutylammonium (TBA). This study investigates the effect of ultraviolet (UV) light exposure duration on the removal of TBA residues from 2D Ca2NaNb4O13- nanosheets deposited on silicon substrates via Langmuir-Blodgett method using atomic force microscopy (AFM). Nanoscale adhesion forces between silicon AFM tips and nanofilms exposed to UV light for 3, 12, 18, and 24 hours were measured. Nanofilms exposed to UV for 12 hours showed significant heterogeneity in adhesion forces compared to control nanofilms not exposed to UV. This heterogeneity improved after 18 hours and reached maximum homogeneity at 24 hours. A noticeable decrease in adhesion forces indicated a reduction in TBA residues after 18 hours, with further reduction observed at 24 hours. The most probable adhesion forces for control nanofilms and those exposed to UV for 3 and 12 hours were 1.6-fold and 2.0-fold higher, respectively, compared to nanofilms exposed to UV for 18 and 24 hours. Similarly, surface roughness peaked at 12 hours and then decreased with longer exposure, resulting in a smoother surface at 24 hours.

Understanding the nanoscale adhesion forces between the fungal pathogen Candida albicans and antimicrobial zinc-based layered double hydroxides using single-cell and single-particle force spectroscopy.

Antifungal resistance has become a very serious concern, and Candida albicans is considered one of the most opportunistic fungal pathogens responsible for several human infections. In this context, the use of new antifungal agents such as zinc-based layered double hydroxides to fight such fungal pathogens is considered one possible means to help limit the problem of antifungal resistance. In this study, we show that ZnAl LDH nanoparticles exhibit remarkable antifungal properties against C. albicans and cause serious cell wall damage, as revealed by growth tests and atomic force microscopy (AFM) imaging. To further link the antifungal activity of ZnAl LDHs to their adhesive behaviors toward C. albicans cells, AFM-based single-cell spectroscopy and single-particle force spectroscopy were used to probe the nanoscale adhesive interactions. The force spectroscopy analysis revealed that antimicrobial ZnAl LDHs exhibit specific surface interactions with C. albicans cells, demonstrating remarkable force magnitudes and adhesion frequencies in comparison with non-antifungal negative controls, e.g., Al-coated substrates and MgAl LDHs, which showed limited interactions with C. albicans cells. Force signatures suggest that such adhesive interactions may be attributed to the presence of agglutinin-like sequence (Als) adhesive proteins at the cell wall surface of C. albicans cells. Our findings propose the presence of a strong correlation between the antifungal effect provided by ZnAl LDHs and their nanoscale adhesive interactions with C. albicans cells at both the single-cell and single-particle levels. Therefore, ZnAl LDHs could interact with C. albicans fungal pathogens by specific adhesive interactions through which they adhere to fungal cells, leading to their damage and subsequent growth inhibition.

In Situ Probing of the Intrinsic Adhesion Strength of Single Anaerobic Microbial Cells.

Probing the single-cell mechanobiology in situ is imperative for microbial processes in the medical, industrial, and agricultural realms, but it remains a challenge. Herein, we present a single-cell force microscopy method that can be used to measure microbial adhesion strength under anaerobic conditions in situ. This method integrates atomic force microscopy with an anaerobic liquid cell and inverted fluorescence microscopy. We obtained the nanomechanical measurements of the single anaerobic bacterium Ethanoligenens harbinense YUAN-3 and the methanogenic archaeon Methanosarcina acetivorans C2A and their nanoscale adhesion forces in the presence of sulfoxaflor, a successor of neonicotinoid pesticides. This study presents a new tool for in situ single-cell force measurements of various anoxic and anaerobic species and provides new perspectives for evaluating the potential environmental risk of neonicotinoid applications in ecosystems.

Glucosyltransferase-modulated Streptococcus mutans adhesion to different surfaces involved in biofilm formation by atomic force microscopy.

Biofilm on dental restorative materials is an important determinant in the etiology of secondary caries development. Formation of biofilm involves adhesion of bacteria onto substrate, bacterial cell, and biofilm surfaces. Glucosyltransferase B and C (GtfB and GtfC) are essential factors for regulation of Streptococcus mutans biofilm formation, but the mechanisms involving different kinds of bacterial adhesion still lack detailed description. In this study, nanoscale adhesion force measurement was performed using atomic force microscopy. Bacteria-coated cantilevers were used to probe S. mutans adhesion to substrates, bacterial cells, and early biofilms. Two representative dental materials, glass ionomer cement (GIC) and composite resin, served as substrates. It was found that deletion of gtfB and gtfC genes both reduced adhesion forces of S. mutans toward substrate and bacterial cell surfaces (P < 0.05). Notably, reduction of the gtfB gene remarkably decreased bacterial adhesion to biofilm surfaces (P < 0.05), while gtfC showed no obvious effect during this stage. Biofilms cultured on GIG further decreased cell-biofilm adhesion, compared with those on resin (P < 0.05). Confocal fluorescence images and scanning electron microscopy images showed that deletion of gtfB lead to reduced microcolony formation and less production of exopolysaccharides (EPSs) in the biofilm, and after bacterial culturing on GIC, the EPS content was further decreased. Our findings suggest that EPSs mainly mediate bacterial adhesion to early biofilm surface. Deletion of gtfB and coculture with GIC could significantly reduce the cell-biofilm adhesion, which is probably through decreasing of EPS production. gtfB exerts a critical role in the bacterial adhesion for the whole process of biofilm development, while gtfC possibly works only in the early stages.

(Invited) Area-Selective Atomic Layer Deposition for Interconnect Applications

As the semiconductor industry is approaching the 5nm node technology, conventional patterning schemes cannot meet the ever-increasing requirements for alignment imposed by device miniaturization. Area-Selective Deposition (ASD) can potentially alleviate such manufacturing challenges by enabling bottom-up material deposition. The most used and successful approach to achieve ASD envisage a combination of Atomic Layer Deposition (ALD) and surface passivation, such as, self-assembled monolayer (SAM).Among the potential applications, dielectric on dielectric (DoD) ASD emerged as one of the most important for multilayer nano interconnects (e.g.: enabling fully self-aligned vias). In this context, along with the difficulties encountered in preserving a confined material growth, the challenges extend to the fact that the deposited dielectric must exhibit well-defined properties, such as low-dielectric constant. Indeed, the integration an interconnect dielectric deposition process in an ASD scheme is arduous. Vapor-phase deposition of SiO2-like materials typically requires high process temperature as well as strong oxidants or O2-plasma. These are not compatible with the organic passivation films exploited to create well-distinguished local surface chemistries, which is essential to enable selective-material deposition.In this talk, 1-octadecanethiol (ODT) well-known selective chemisorption on Cu over SiO2 is exploited to achieve AS-DoD deposition and understand the surface-driven mechanism that enables a selective material growth. In addition, the proposed ASD scheme in combination with nanoscale adhesion force characterization is used to tackle a critical lack in ASD metrology: monitoring the passivation film directly on patterned substrate. Finally, the challenges and results obtained as an ODT-compatible dielectric deposition process for interconnect applications are discussed in this talk.ASD enabled by metal passivation for Hf3N4, Hf-Silicate, Al2O3, and Al-silicate ALD are explored and presented on Cu/SiO2 patterned substrates, with critical dimension as low as 10nm.

Nanoscale adhesion forces of glucosyltransferase B and C genes regulated Streptococcal mutans probed by AFM.

Glucosyltransferases (Gtfs), represented by GtfB and GtfC, are important virulence factors of Streptococcus mutans and the major etiologic pathogens of tooth decay. However, the individual roles of gtfB and gtfC in the initial attachment of S. mutans are not known. We used atomic force microscopy to explore the contribution of gtfB and gtfC, as well as enamel-surface roughness, on the initial attachment of S. mutans. Adhesion forces of four S. mutans strains (wild-type, ΔgtfB, ΔgtfC, and ΔgtfBC), onto etched enamel surfaces, were determined. Force curves showed that, with increasing etching time from 0 to 10s, the forces of all strains increased accordingly with acid-exposure time, the adhesion forces of wild-type strains were significantly greater than those of mutant strains (p<.05), and the forces of the three mutants were similar (p<.05). When the etching time was increased from 10 to 30s, difference in force between 20 and 30s was not observed, and adhesion forces among ΔgtfB, ΔgtfC, and wild-type strains were not significantly different when the etching time was >20s (p>.05). These data suggest that the roughness and morphology of enamel surfaces may have a significant influence upon the initial attachment of bacteria, and that gtfB and gtfC are essential for the adhesion activity of bacteria. Furthermore, gtfB seems to be more important than gtfC for bacterial-biofilm formation, and gtfB inactivation is an effective strategy to inhibit the virulence of cariogenic biofilms.

Effects of Rediset on the adhesion, stripping, thermal and surface morphologies of PG76 binder

Apart from lowering the production and application temperature, Warm Mix Asphalt (WMA) additive has the potential to enhance the adhesion property of the base binders. Surface free energy (SFE) from contact angles was determined by sessile drop device (SDD) to find out the work of adhesion of WMA additive-modified binders. It is shown that addition of WMA additive at different weight percentage would initiate dissimilar implications on surface properties. Test data are compared with the nanoscale adhesion force of WMA additive-PG76 using atomic force microscopy (AFM). The connection between the contact angle analysis with the topography was also investigated; SFE and AFM results exhibit some agreement in findings. The WMA additive had improved the adhesion characteristics of warm mix additive-modified binders. In addition to that, adhesion and stripping behaviour of the blends were also observed via the Boiling Water test. The test demonstrated that the adhesive characteristics of the blending are at its best and the results inclined to the conclusion that the WMA additive had effect on the adhesion and stripping behaviour. The thermogravimetry analysis (TGA) was carried out to observe the thermal behaviour of the samples. It is found that the thermal decomposition of these blends takes place at temperature between 300 and 500 °C. Together, all the findings are in agreement that the addition of Rediset into PG76 could benefit for the WMA application.

Prediction and sensitivity analysis of CNTs-modified asphalt’s adhesion force using a radial basis neural network model

The expected longer service life of modified asphalt can be jeopardized by different environmental factors, such as moisture, oxidation, etc. which affect the desired properties by altering the adhesive property. An insight into knowledge of the adhesive property of the asphalt can help in providing more durable asphalt pavement. The study attempted to develop different models of adhesive properties of polymers and carbon nanotubes (CNTs) modified asphalt binders. The polymer-CNT modified asphalt is processed to prepare different types of samples, by simulating the damage due to moisture and oxidization, following the corresponding standard method. An Atomic Force Microscopy (AFM) was employed to assess the nanoscale adhesion force of the tested samples following the existing functional group in asphalt. Finally, the study has developed Radial Basis Function Neural Network (RBFNN) as a function of different parameters including; asphalt chemistry (i.e. AFM tip type and constant), type and percentages of polymers and CNTs and different environmental exposures (oxidation, moisture, etc.) to predict the nano adhesion force of asphalt. It is observed that the adhesive property of the Styrene–Butadiene modified asphalt is more consistent compared to the Styrene–Butadiene–Styrene modified asphalt, while the presence of Single-Wall Nanotubes (SWNT) is observed to affect the adhesive properties of asphalt significantly as compared to Multi-Wall Nanotubes (MWNT). The higher accuracy level of RBFNN model also indicates that the functional group (tip-type) adding with the percentages and types of polymers and CNTs significantly affect the adhesive properties of asphalt.

The Effects of β-Lactam Antibiotics on Surface Modifications of Multidrug-Resistant Escherichia coli: A Multiscale Approach.

Possible multidrug-resistant (MDR) mechanisms of four resistant strains of Escherichia coli to a model β-lactam, ampicillin, were investigated using contact angle measurements of wettability, crystal violet assays of permeability, biofilm formation, fluorescence imaging, and nanoscale analyses of dimensions, adherence, and roughness. Upon exposure to ampicillin, one of the resistant strains, E. coli A5, changed its phenotype from elliptical to spherical, maintained its roughness and biofilm formation abilities, decreased its length and surface area, maintained its cell wall integrity, increased its hydrophobicity, and decreased its nanoscale adhesion to a model surface of silicon nitride. Such modifications are suggested to allow these cells to conserve energy during metabolic dormancy. In comparison, resistant strains E. coli D4, A9, and H5 elongated their cells, increased their roughness, increased their nanoscale adhesion forces, became more hydrophilic, and increased their biofilm formation upon exposure to ampicillin. These results suggest that these strains resisted ampicillin through biofilm formation that possibly introduces diffusion limitations to antibiotics. Investigations of how MDR bacterial cells modify their surfaces in response to antibiotics can guide research efforts aimed at designing more effective antibiotics and new treatment strategies for MDR bacterial infections.

Adhesion properties of warm-modified bituminous binders (WMBBs) determined using pull-off tests and atomic force microscopy

The aggregate-binder bond is one of the main factors that affect the durability of asphalt mixtures. This can be investigated based on the energy required to fracture the adhesive bond between binder and aggregate. In this study, the effects of Sasobit, Rediset WMX and Rediset LQ on the adhesive bond strength of an aggregate-binder system is investigated using the pull-off test. Test data are compared with the nano-scale adhesion force determined using atomic force microscopy (AFM) using the PeakForce Quantitative Nanomechanical Mapping (PFQNM) method. The impact of warm mix additives, test temperature and binder grade on the practical work of fracture was investigated. It was found that Sasobit, Rediset WMX and Rediset LQ increased the practical work of fracture by 170%, 100% and 143%, respectively, for the aggregate-binder system produced using 40/60 Pen binder, and 70%, 25% and 50%, respectively, for the system produced using 100/150 Pen binder. The contribution of warm mix additives in improving the practical work of fracture has been linked to the adhesion force determined using AFM. AFM offers great advantage in characterising the nano-scale properties which were shown to include co-localisation of nano-topography with adhesion, ease of sample preparation and reduction in experimental time relative to the direct tension pull-off test.

Spatially resolved organic coating on clay minerals in bitumen froth revealed by atomic force microscopy adhesion mapping

Mineral solids in oil sands are often coated with organic matter. These organically-modified mineral solids hinder bitumen aeration and stabilize water-in-oil emulsions, leading to low bitumen recovery and poor bitumen product quality. The study of these organic coating on the fine solids has been elusive due to the nanometer length scale and the unsuitability of sampling in high vacuum sample chambers. In the present work, we report the first attempt of using PeakForce Quantitative Nanomechanical Mapping (QNM) Atomic Force Microscopy (AFM) to study the organic matter adsorption on fine mineral solids extracted from bitumen froth. Taking advantage of the simultaneous nano-scale resolution topographic imaging and adhesion force mapping enabled by PeakForce QNM-AFM, the mineral and organic components in the bitumen froth fine solids were clearly distinguished due to their variations in shapes and mechanical properties. The inhomogeneous spatial distribution of adhesion force on surfaces of platy particles indicated the existence of organic patches on clay minerals. The area percentage of surface organic matter coverage on the clay basal faces was calculated to be 17±6%, and the average thickness of the organic coating was estimated to be 1.4nm based on the adhesion force maps. The organic matter associated with the mineral solids, which cannot be washed off by toluene, was different from asphaltenes in terms of mechanical properties. More specifically, the irreversibly-adsorbed organic matter on clay minerals was found to be softer than the asphaltene fraction of oil sands bitumen.

Nanoscale adhesion forces between the fungal pathogen Candida albicans and macrophages.

The development of fungal infections is tightly controlled by the interaction of fungal pathogens with host immune cells. While the recognition of specific fungal cell wall components by immune receptors has been widely investigated, the molecular forces involved are not known. In this Communication, we show the ability of single-cell force spectroscopy to quantify the specific adhesion forces between the fungal pathogen Candida albicans and macrophages. The Candida-macrophage adhesion force is strong, up to ∼3000 pN, and corresponds to multiple cumulative bonds between lectin receptors expressed on the macrophage membrane and mannan carbohydrates on the fungal cell surface. Adhesion force signatures show constant force plateaus, up to >100 μm long, reflecting the extraction of elongated tethers from the macrophage membrane, a phenomenon which may increase the duration of intercellular adhesion. Adhesion strengthens with time, suggesting that the macrophage membrane engulfs the pathogen quickly after initial contact, leading to its internalization. The force nanoscopy method developed here holds great promise for understanding and controlling the early stages of microbe-immune interactions.

Heterogeneity and Specificity of Nanoscale Adhesion Forces Measured between Self-Assembled Monolayers and Lignocellulosic Substrates: A Chemical Force Microscopy Study.

Lack of fundamental understanding of cellulase interactions with different plant cell wall components during cellulose saccharification hinders progress toward achieving an economic production of biofuels from renewable plant biomass. Here, chemical force microscopy (CFM) was utilized to quantify the interactions between two surfaces that model either hydrophilic or hydrophobic functional groups of cellulases and a set of lignocellulosic substrates prepared through Kraft, sulfite, or organosolv pulping with defined chemical composition. The measured forces were then decoupled into specific and nonspecific components using the Poisson statistical approach. Heterogeneities in the distributions of forces as a function of the pretreatment method were mapped. Our results showed that hydrophobic domains and chemical moieties involved in hydrogen bonding and polar interactions were homogeneously distributed on all substrates but with distribution densities that varied with the type of the pretreatment method used to prepare substrates. In addition, we showed that increasing surface lignin coverage increased the heterogeneity of the substrates. When forces were decoupled, our results indicated that xylan reduced the strength of hydrogen bonding between the hydrophilic model surface and substrates. Permanent dipole-dipole interactions dominated the adhesion of the hydrophilic model surface to lignosulfonates, whereas hydrophobic interactions facilitated the adhesion of the hydrophobic model surface to Kraft lignin. We further showed that the structure of lignin determines the type of forces that dominate lignocellulosic interactions with other surfaces. Our findings suggest that nonproductive binding of cellulases to lignocellulosic biomass can be reduced by altering the hydrophobicity and/or chemical moieties involved in the polar interactions and by utilizing organosolv as a pretreatment method.

Effect of enamel morphology on nanoscale adhesion forces of streptococcal bacteria : An AFM study.

We explore the influence of enamel surface morphology on nanoscale bacterial adhesion forces. Three dimensional morphology characteristics of enamel slices, which were treated with phosphoric acid (for 0 s, 5 s, 10 s, 20 s, and 30 s), were acquired. Adhesion forces of three initial colonizers (Streptococcus oralis, Streptococcus sanguinis, and Streptococcus mitis) and two cariogenic bacterial strains (Streptococcus mutans and Streptococcus sobrinus) with etched enamel surfaces were determined. Comparison of the forces was made by using bacterial probe method under atomic force microscope (AFM) in adhesion buffer. The results showed that enamel morphology was significantly altered by etching treatment. The roughness, peak-to-valley height, and valley-to-valley width of the depth profile, surface area, and volume increased linearly with acid exposure time, and reached the maximum at 30s, respectively. The adhesion forces of different strains increased accordingly with etching time. Adhesion forces of S. oralis, S. mitis, S. mutans, and S. sobrinus reached the maximum values of 0.81 nN, 0.84 nN, 0.73 nN, and 0.64 nN with enamel treated for 20s, respectively, whereas that of S. sanguinis at 10s (1.28nN), and dropped on coarser enamel surfaces. In conclusion, enamel micro-scale morphology may significantly alter the direct adhesion forces of bacteria. And there may be a threshold roughness for bacterial adhesion on enamel surface.

Influence of atomic force microscope (AFM) probe shape on adhesion force measured in humidity environment

In micro-manipulation, the adhesion force has very important influence on behaviors of micro-objects. Here, a theoretical study on the effects of humidity on the adhesion force is presented between atomic force microscope (AFM) tips and substrate. The analysis shows that the precise tip geometry plays a critical role on humidity dependence of the adhesion force, which is the dominant factor in manipulating micro-objects in AFM experiments. For a blunt (paraboloid) tip, the adhesion force versus humidity curves tends to the apparent contrast (peak-to-valley corrugation) with a broad range. This paper demonstrates that the abrupt change of the adhesion force has high correlation with probe curvatures, which is mediated by coordinates of solid-liquid-vapor contact lines (triple point) on the probe profiles. The study provides insights for further understanding nanoscale adhesion forces and the way to choose probe shapes in manipulating micro-objects in AFM experiments.

Nanoscale Adhesion Forces between Enamel Pellicle Proteins and Hydroxyapatite

The acquired enamel pellicle (AEP) is important for minimizing the abrasion caused by parafunctional conditions as they occur, for instance, during bruxism. It is a remarkable feature of the AEP that a protein/peptide film can provide enough protection in normofunction to prevent teeth from abrasion and wear. Despite its obvious critical role in the protection of tooth surfaces, the essential adhesion features of AEP proteins on the enamel surface are poorly characterized. The objective of this study was to measure the adhesion force between histatin 5, a primary AEP component, and hydroxyapatite (HA) surfaces. Both biotinylated histatin 5 and biotinylated human serum albumin were allowed to adsorb to streptavidin-coated silica microspheres attached to atomic force microscope (AFM) cantilevers. A multimode AFM with a Nanoscope IIIa controller was used to measure the adhesion force between protein-functionalized silica microspheres attached to cantilever tips and the HA surface. The imaging was performed in tapping mode with a Si3N4 AFM cantilever, while the adhesion forces were measured in AFM contact mode. A collection of force-distance curves (~3,000/replicate) was obtained to generate histograms from which the adhesion forces between histatin 5 or albumin and the HA surface were measured. We found that histatin 5 exhibited stronger adhesion forces (90% >1.830 nN) to the HA surface than did albumin (90% > 0.282 nN). This study presents an objective approach to adhesion force measurements between histatin 5 and HA, and provides the experimental basis for measuring the same parameters for other AEP constituents. Such knowledge will help in the design of synthetic proteins and peptides with preventive and therapeutic benefits for tooth enamel.

AFM studied the effect of celastrol on β1 integrin-mediated HUVEC adhesion and migration

Integrin-mediated human umbilical vein endothelial cells (HUVECs) adhesion to the extracellular matrix plays a fundamental role in tumor-induced angiogenesis. Celastrol, a traditional Chinese medicine plant, has possessed anticancer and suppressed angiogenesis activities. Here, the mechanism underling the antiangiogenesis capacity of celastrol was investigated by exploring the effect of celastrol on β1(CD29) integrin-mediated cell adhesion and migration. Flow cytometry results showed that the HUVECs highly expressed CD29 and cell adhesion assay indicated that celastrol specifically inhibited the adhesion of HUVECs to fibronectin (FN) without affecting nonspecific adhesion to poly-L-lysine (PLL). After cell FN adhesion being inhibited, the cell surface nanoscale structure and adhesion force were detected by atomic force microscope (AFM). High-resolution imaging revealed that cell morphology and ultrastructure changed a lot after being treated with celastrol. The membrane average roughness (Ra) and the major forces were decreased from 31.34 ± 4.56 nm, 519.60 ± 82.86 pN of 0 μg/ml celastrol to 18.47 ± 6.53 nm, 417.79 ± 53.35 pN of 4.0 μg/ml celastrol, 10.54 ± 2.85 nm, 258.95 ± 38.98 pN of 8.0 μg/ml celastrol, respectively. Accompanying with the decrease of adhesion force, the actin cytoskeleton in the cells was obviously disturbed by the celastrol. All of these changes influenced the migration of HUVECs from the wound-healing migration assay. Taken together, our results suggest that celastrol can be as an inhibitor of HUVEC adhesion to FN. This work provides a novel approach to inhibition of tumor angiogenesis and tumor growth.

Ethanol-wet bonding may improve root dentine bonding performance of hydrophobic adhesive

ObjectivesThe current study aimed to assess ethanol-wet dentine surfaces by atomic force microscopy (AFM), and to evaluate the efficacy of ethanol-wet bonding on root dentine by determining the shear bond strength (SBS) and interfacial nanoleakage expression. MethodsFlat dentine slices from human premolar roots were randomly grouped into five. All specimens were acid-etched, rinsed, and left moist. They were then treated with 100% ethanol for 0s (control group), 20s (Group 1), 60s (Group 2), three 60s periods (Group 3), or stepwise ethanol application (Group 4). After treatment, each group was bonded either with Adper™ Scotchbond™ Multi-Purpose (Scotchbond) or experimental hydrophobic adhesive. Nano-scale adhesion forces (Fad) were probed by AFM and analysed using one-way ANOVA. The SBS results were analysed using two-way ANOVA. Tukey's test was employed for multiple comparisons. ResultsEthanol-wet protocols significantly decreased the value of Fad (p<0.001). When bonded with Scotchbond, ethanol treatment did not affect the bond strength (p>0.05), but decreased the interfacial nanoleakage. The SBS values of the groups bonded with hydrophobic adhesive varied with different ethanol-wet protocols (p<0.05). Decreased nanoleakage was manifested in all experimental groups, except Group 1. Compared with the classical water-wet bonding with Scotchbond in the control group, Group 4 bonded with hydrophobic adhesive exhibited a significantly higher bond strength (p<0.05). ConclusionsEthanol-wet bonding using a stepwise ethanol application protocol may have potential benefits in the root dentine bonding of hydrophobic adhesive.

Thiol-ene “click” networks from amphiphilic fluoropolymers: full synthesis and characterization of a benchmark anti-biofouling surface

The synthesis of heterogeneous, amphiphilic crosslinked networks from photo-initiated thiol-ene chemistry and full characterization of the physicochemical, anti-biofouling, mechanical, and thermal properties of this system are reported. Although interest in coatings that present heterogeneous surface features is increasing, anti-biofouling performance is typically compared to homogeneous biocidal- or non-toxic polydimethylsiloxane-based paints, for the advancement of commercial and novel systems, which leaves a need for a benchmark to compare highly complex, heterogeneous composites with similar complexities. This system has been generated and rigorously analyzed to understand how microscopic and nanoscopic disorder, resistance to protein adsorption and surface mechanical properties can be fine-tuned and optimized through oligomer selection, blend ratios and process conditions. Solution-state studies of individual and blended constituents probed the relative fluorescence intensities based on concentration and neighboring species that were used to identify microscopic disorder on the surface. Incubation of a fluorescently labelled protein on the benchmark surface showed 42% and 72% less adsorption than on model surfaces that largely expressed a single component. The extent of reaction and the identification of unconsumed functionalities were found through infrared spectroscopy. The benchmark surface had a Young's modulus of approximately 0.5 GPa, 7 to 35 times higher than model surfaces, with 50 times the variation in modulus. Nanoscale surface adhesion force variation and bulk wettability and bulk thermal stability are also reported. This study provides an extensive list of metrics to be used for the development of complex, heterogeneous, anti-biofouling coatings, appropriate to both surface optimization and mechanical tunability, for implementation in real-world applications.

Protein adhesion regulated by the nanoscale surface conformation

Protein adhesion and adsorption behaviors vary in response to variations in surface wettability; however, few reports have examined the dependence of such behaviors on variations in the surface molecular conformations. This study examines the degree to which molecular disorder at the surface of a surface-modified hydrocarbon chain monolayer regulates protein adhesion. Octadecyltrichlorosilane (OTS) molecules were deposited onto silicon wafers at two temperatures, 5 °C or 55 °C, to prepare two OTS surfaces with different degrees of molecular disorder. Atomic force microscopy (AFM) was used to evaluate the nanoscale adhesion force between proteins and the two types of OTS monolayers during a short contact time (<1 s). Bovine serum albumin (BSA) and human fibrinogen (HF) adhered more strongly to the disordered than to the ordered OTS monolayer. The adhesion strength at longer contact times (30 s–90 min) was evaluated by investigating the resistance of proteins on the OTS monolayer to detachment by washing. The magnitude of the resistance could be predicted from the topologies of the monolayers, as determined by AFM, after the adsorption of proteins and the subsequent washing experiments. After a 90 min adsorption period, BSA displayed a higher resistance to detachment from the disordered OTS monolayer than from the ordered OTS monolayer. HF displayed a higher resistance to detachment from the disordered OTS monolayer for only very short adsorption times of less than 1 min. The results suggest that the proteins altered their adhesion onto monolayers with different OTS conformations and that different adsorption times were required for each protein to present the different degrees of adhesion.