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In orthopedic surgery, metals are preferred to support or treat damaged bones due to their high mechanical strength. However, the necessity for a second surgery for implant removal after healing creates problems. Therefore, biodegradable metals, especially magnesium (Mg), gained importance, although their extreme susceptibility to galvanic corrosion limits their applications. The focus of this study was to control the corrosion of Mg and enhance its biocompatibility. For this purpose, surfaces of magnesium-calcium (MgCa1) alloys were modified with calcium phosphate (CaP) or CaP doped with zinc (Zn) or gallium (Ga) via MgCa1 microarc oxidation. The effects of surface modifications on physical, chemical, and mechanical properties and corrosion resistance of the alloys were studied using surface profilometry, goniometry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), nanoindentation, and electrochemical impedance spectroscopy (EIS). The coating thickness was about 5-8 mu m, with grain sizes of 43.1 nm for CaP coating and 28.2 and 58.1 nm for Zn- and Ga-doped coatings, respectively. According to EIS measurements, the capacitive response (Y-c) decreased from 11.29 to 8.72 and 0.15 Omega(-1) cm(-2) s(n) upon doping with Zn and Ga, respectively. The E-corr value, which was -1933 mV for CaP-coated samples, was found significantly electropositive at -275 mV for Ga-doped ones. All samples were cytocompatible according to indirect tests. In vitro culture with Saos-2 cells led to changes in the surface compositions of the alloys. The numbers of cells attached to the Zn-doped (2.6 x 10(4) cells/cm(2)) and Ga-doped (6.3 x 10(4) cells/cm(2)) coatings were higher than that on the surface of the undoped coating (1.0 x 10(3) cells/cm(2)). Decreased corrosivity and enhanced cell affinity of the modified MgCa alloys (CaP coated and Zn and Ga doped, with Ga-doped ones having the greatest positive effect) make them novel and promising candidates as biodegradable metallic implant materials for the treatment of bone damages and other orthopedic applications.

Wax is an important factor that affects the durability of asphalt binder. In order to understand the molecular weight distribution and branching of wax on the moisture sensitivity of asphalt binder, pure wax-doped asphalt binders are prepared and the performance of model asphalt binders are evaluated by surface free-energy (SFE) and binder bond strength (BBS) tests. In addition, asphaltene is regarded as an additive in this study. The results show that the addition of eicosane, triacontane, squalane and asphaltene can reduce the moisture sensitivity of asphalt, but not necessarily improve its moisture-induced damage resistance. The physical hardening effect of high-wax asphalt and its model asphalt is stronger than that of the corresponding low-wax asphalt and its model asphalt, and its moisture sensitivity is weaker than that of the low-wax asphalt. For all the model asphalts, there is a good correlation between the cohesion work, cohesion POTS (pull-off tensile strength), POTS ratio (the BBS moisture sensitivity index) and ER (the SFE moisture sensitivity index). When using the BBS test to characterize the moisture sensitivity of high-wax asphalt, it is recommended to leave the sample for some time until it is physically hardened and stable.

Studies on carbon fiber (CF)/poly(ether ether ketone) (PEEK) fiber hybrid textiles were initiated several decades ago because their flexibility and conformability make them a promising alternative to traditional prepregs. The adhesion between the CFs and PEEK is mostly controlled by their inherent surface properties and mutual wettability. However, details of these properties remain largely unknown, especially those of PEEK. Therefore, to determine the surface and interfacial properties of these fibers, we performed a comprehensive study and characterized their surface topography (atomic force microscopy, scanning electron microscopy), surface chemistry [X-ray photoelectron spectrometry (XPS), acid-base titration], surface energies (wetting tests, acid-base approach), and interfacial mechanical properties [droplet test, interfacial shear strength (IFSS)]. These experiments were complemented by a theoretical approach to the prediction of the surface energy components (parachor) and contact angles of PEEK. We found good agreement between the results obtained by XPS and wetting tests (base-to-acid surface energy component ratio), as well as between the predicted and measured surface energy and contact angles. The results highlight the consistency and reliability of the proposed methodology. We found that both CFs and PEEK fibers appear to be smooth at the nanoscale and have large dispersive and basic surface energy components. The IFSS of CF/PEEK is significantly higher (44.87 ± 5.76 MPa) compared to that of other thermoplastic systems. The findings not only demonstrate the potential of CF/PEEK hybrid textiles but also emphasize the need to further increase the compatibility between CFs and PEEK fibers by increasing the acidic component of CF surfaces. Surface treatments and the design of a suitable sizing are potential methods to achieve this objective in future studies. ispartof: ACS APPLIED MATERIALS & INTERFACES vol:11 issue:34 pages:31520-31531 ispartof: location:United States status: published

The optimal mechanical properties render magnesium widely used in industrial and biomedical applications. However, magnesium is highly reactive and unstable in aqueous solutions, which can be modulated to increase stability of reactive metals that include the use of alloys or by altering the surface with coatings. Plasma electrolytic oxidation is an efficient and tuneable method to apply a surface coating. By varying the plasma electrolytic oxidation parameters voltage, current density, time and (additives in the) electrolytic solution, the morphology, composition and surface energy of surface coatings are set. In the present study, we evaluated the influence on surface coatings of two solute additives, i.e. hexamethylenetetramine and mannitol, to base solutes silicate and potassium hydroxide. Results from in vitro studies in NaCl demonstrated an improvement in the corrosion resistance. In addition, coatings were obtained by a two-step anodization procedure, firstly anodizing in an electrolyte solution containing sodium fluoride and secondly in an electrolyte solution with hexamethylenetetramine and mannitol, respectively. Results showed that the first layer acts as a protective layer which improves the corrosion resistance in comparison with the samples with a single anodizing step. In conclusion, these coatings are promising candidates to be used in biomedical applications in particular because the components are non-toxic for the body and the rate of degradation of the surface coating is lower than that of pure magnesium.

Calcium phosphate (CaP)-based ceramics are the most widely applied synthetic biomaterials for repair and regeneration of damaged and diseased bone. CaP bioactivity is regulated by a set of largely intertwined physicochemical and structural properties, such as the surface microstructure, surface energy, porosity, chemical composition, crystallinity and stiffness. Unravelling the role of each individual property in the interaction between the biomaterial and the biological system is a prerequisite for evolving from a trial-and-error approach to a design-driven approach in the development of new functional biomaterials. This progress report critically reviews various strategies developed to decouple the roles of the individual material properties in the biological performance of CaP ceramics. It furthermore emphasizes on the importance of a comprehensive and adequate material characterization that is needed to enhance our knowledge of the property-function relationship of biomaterials used in bone regeneration, and in regenerative medicine in general.

Tribological experiments on phenol-formaldehyde composite reinforced with polytetrafluoroethylene (PTFE) and glass fibers were performed against 100Cr6 steel and TiC/a-C:H thin film-coated 100Cr6 steel. In both cases, the coefficient of friction increases with increasing sliding distance until a steady-state value is reached. Although the steady-state values of the coefficient of friction are very close and ultralow, the wear rate of the PTFE composite liner at a long sliding distance (1,000 m) is reduced when the steel ball is coated with the TiC/a-C:H coating. This behavior is mainly attributed to the smoother surface after long sliding and the improved wear resistance of TiC/a-C:H coating. PTFE transfer films are evident on the surfaces of the hard counterparts. The average thickness of the transfer film on TiC/a-C:H-coated surfaces is about 3.8 nm. On the surface of uncoated steel ball, a continuous but non-uniform transfer film of around 13.9 nm average thickness was found.

International audience; BACKGROUND: Starch and whey protein isolate and their mixtures were used for making edible films. Moisture sorption isotherms, water vapour permeability, sorption of aroma compounds, microstructure, water contact angle and surface properties were investigated.RESULTS: With increasing protein content, the microstructure changes became more homogeneous. The water vapour permeability increases with both the humidity gradient and the starch content. For all films, the hygroscopicity increases with starch content. Surface properties change according to the starch/whey protein ratio and are mainly related to the polar component of the surface tension. Films composed of 80% starch and 20% whey proteins have more hydrophobic surfaces than the other films due to specific interactions.CONCLUSIONS: The effect of carbohydrate/protein ratio significantly influences the microstructure, the surface wettability and the barrier properties of wheat starch-whey protein blend films. (C) 2016 Society of Chemical Industry

International audience; Understanding the mechanism of the bacterial cell adhesion to solid surfaces is of great medical and industrial importance. Bacterial adhesion to inert surfaces, such as a catheter, and other indwelling devices can form biofilm, consequently cause severe morbidity and often fatal infections. Initial bacterial adhesion to the material surfaces is a complicated process that is affected by various physicochemical properties of both bacterial cells and substratum surfaces. The surface properties of the cells were characterized by the sessile drop technique. Moreover, the interfacial free energy of Staphylococcus aureus adhesion to the supporting materials was determined. The results showed that S. aureus examined at different pH levels could be considered hydrophilic. We noted hat the electron-donor character of S. aureus was important at intermediate pH (pH 5, pH 7, and pH 9) and it decreased at both limits acidic and basic conditions. In addition, the adhesion of Staphylococcus aureus ATCC 25923 to the hydrophilic glass and hydrophobic indium tin oxide (ITO)-coated glass surfaces at different pH values (2, 3, 5, 7, 9 and 11) was investigated using atomic force microscopy (AFM) and image analysis was assessed with the Mathlab(A (R)) program. The data analysis showed that cells (number of adhering cells to glass and ITO-coated glass surface) adhered strongly at acidic pH and weakly at alkaline pH. Also, S. aureus has the ability to attach to both hydrophobic and hydrophilic surfaces, but the adhesion was higher on hydrophobic surface.

Biomaterials for the restoration of oral function are prone to biofilm formation, affecting oral health. Oral bacteria adhere to hydrophobic and hydrophilic surfaces, but due to fluctuating shear, little biofilm accumulates on hydrophobic surfaces in vivo. More biofilm accumulates on rough than on smooth surfaces. Oral biofilms mostly consist of multiple bacterial strains, but Candida species are found on acrylic dentures. Biofilms on gold and amalgam in vivo are thick and fully covering, but barely viable. Biofilms on ceramics are thin and highly viable. Biofilms on composites and glass-ionomer cements cause surface deterioration, which enhances biofilm formation again. Residual monomer release from composites influences biofilm growth in vitro, but effects in vivo are less pronounced, probably due to the large volume of saliva into which compounds are released and its continuous refreshment. Similarly, conflicting results have been reported on effects of fluoride release from glass-ionomer cements. Finally, biomaterial-associated infection of implants and devices elsewhere in the body is compared with oral biofilm formation. Biomaterial modifications to discourage biofilm formation on implants and devices are critically discussed for possible applications in dentistry. It is concluded that, for dental applications, antimicrobial coatings killing bacteria upon contact are more promising than antimicrobial-releasing coatings.

Biomaterials for the restoration of oral function are prone to biofilm formation, affecting oral health. Oral bacteria adhere to hydrophobic and hydrophilic surfaces, but due to fluctuating shear, little biofilm accumulates on hydrophobic surfaces in vivo. More biofilm accumulates on rough than on smooth surfaces. Oral biofilms mostly consist of multiple bacterial strains, but Candida species are found on acrylic dentures. Biofilms on gold and amalgam in vivo are thick and fully covering, but barely viable. Biofilms on ceramics are thin and highly viable. Biofilms on composites and glass-ionomer cements cause surface deterioration, which enhances biofilm formation again. Residual monomer release from composites influences biofilm growth in vitro, but effects in vivo are less pronounced, probably due to the large volume of saliva into which compounds are released and its continuous refreshment. Similarly, conflicting results have been reported on effects of fluoride release from glass-ionomer cements. Finally, biomaterial-associated infection of implants and devices elsewhere in the body is compared with oral biofilm formation. Biomaterial modifications to discourage biofilm formation on implants and devices are critically discussed for possible applications in dentistry. It is concluded that, for dental applications, antimicrobial coatings killing bacteria upon contact are more promising than antimicrobial-releasing coatings.

High pressure laminates (HPLs) are attractive, resistant to environmental effects and good cost-benefit decorative surface composite materials whose properties can be tailored to meet specific market demands. In this study, the substantial improvement of dirt repellence of HPLs with simultaneous enhancement of its abrasion resistance was achieved for the first time by incorporating nonafluorohexyl polyhedral oligomeric silsesquioxane (FH-POSS) nanoparticles (up to 1% w/w) into a melamine formaldehyde (MF) resin matrix used to impregnate decorative and overlay papers required for HPLs production. FH-POSS particles were synthesized and thoroughly characterized by C-13 and Si-29 solid state nuclear magnetic resonance (NMR) spectroscopy, and by X-ray diffraction (XRD) analysis. Fluoroalkyl moieties in FH-POSS afforded increased hydrophobicity to HPLs thus providing improved surface clean ability, whereas abrasion resistance was improved due to the robust silica core of the POSS particles. Hydrophobicity of HPLs doped with FH-POSS increased with time, after resin curing, and this was attributed to migration of FH-POSS nanoparticles to the composite surface. (C) 2016 Elsevier B.V. All rights reserved.

Introduction Recently, we introduced a new deposition method, based on Ion Plating Plasma Assisted technology, to coat titanium implants with a thin but hard nanostructured layer composed of titanium carbide and titanium oxides, clustered around graphitic carbon. The nanostructured layer has a double effect: protects the bulk titanium against the harsh conditions of biological tissues and in the same time has a stimulating action on osteoblasts. Results The aim of this work is to describe the biological effects of this layer on osteoblasts cultured in vitro. We demonstrate that the nanostructured layer causes an overexpression of many early genes correlated to proteins involved in bone turnover and an increase in the number of surface receptors for alpha 3 beta 1 integrin, talin, paxillin. Analyses at single-cell level, by scanning electron microscopy, atomic force microscopy, and single cell force spectroscopy, show how the proliferation, adhesion and spreading of cells cultured on coated titanium samples are higher than on uncoated titanium ones. Finally, the chemistry of the layer induces a better formation of blood clots and a higher number of adhered platelets, compared to the uncoated cases, and these are useful features to improve the speed of implant osseointegration. Conclusion In summary, the nanostructured TiC film, due to its physical and chemical properties, can be used to protect the implants and to improve their acceptance by the bone.

In this report, we evaluate the impact of a systematic change to the extracellular environment on cell morphology and functionality by combining the inherent properties of biocompatible polymers such as polydimethylsiloxane and polycaprolactone with a specific surface response. By microstructuring pillars and pits on the substrates, varying spacing and height of the structures, we investigate the role of topography in fibroblast cell adhesion and viability. The change of wetting behaviour was tailored and evaluated in terms of contact angle measurements. It was shown that the range of micro-scale physical cues at the interface between the cells and the surrounding environment affects cell shape and migrations, indicating a tendency to respond differently to higher features of the micro-scale. We found that surface topography seems dominant over material wettability, fibroblasts responded to variations in topography by altering morphology and migrating along the direction of spacing among the features biased by the height of structures and not by the material. It is therefore possible to selectively influence either cell adhesion or morphology by choosing adequate topography of the surface. This work can impact in the design of biomaterials and can be applied to implanted biomedical devices, tissue engineering scaffolds and lab on chip devices.

Objectives: The ability of three oral bacteria to adhere to hydrophobic amalgam (water contact angle 60 degrees) and hydrophobic resin composites (Prisma-AP.H 56 degrees, Herculite XRV 82 degrees and Z100 89 degrees) was compared using an in vitro assay.Methods and results: Following preincubation of the materials with human saliva, X-ray photoelectron spectroscopy showed the surfaces to adsorb carbon and nitrogen-containing compounds in a conditioning film that appeared to block the detection of Na and others in 2100 resin, Hg and Ag in amalgam, Si and Zn in Prisma AP.H resin and Ag and Na in Herculite resin. The precoating of the substrata by a proteinaceous conditioning film led to decreased binding of viable cells of Streptococcus sanguis CH3, Streptococcus salivarius HE and Actinomyces viscosus WG as compared with the adhesion to bare composites. With and without salivary coating, there was a correlation between increased bacterial hydrophobicity and increased retention on the substrata. However, there was no statistical difference in binding to the amalgam compared with the resin composites. In vitro studies showed that the bacteria autoaggregated in the presence of saliva.Conclusion: The results indicate the potential ability of normal oral flora to colonize resin composite.

Acid-base properties of wide range of polymers and adhesion systems based on polymers, polymer composites and metals were investigated. Composite materials based on high and low density polyethylenes, ethylene copolymers, other carbochain and heterochain polymers, synthetic rubber and their based on composites, epoxy composites, cured with a wide range of curing agents were used as adhesives. By using the contact angle of test liquids the values of the dispersion, acid-base, acid and base components of the surface free energy were calculated and the acidity parameter was estimated by means of van Oss-Chaudhury-Good and E. Berger methods respectively. Effect of composition on acidity and basicity of polymer composites was shown, and also addressed modification in order of adhesion enhancement was studied. Above mentioned parameters were also obtained for a range of metal surfaces, used in adhesion technology. Adhesion properties dependence on reduced acidity parameter, corresponding to absolute difference in acidity parameters of adhesive and adherend, was shown and its mathematical function was suggested. It was shown that acidity parameter estimated using E.Berger method gives an opportunity to forecast adhesion interaction in designing of certain coating systems and other adhesion compounds and that it is a good method to estimate adhesion properties of polymer composite-metal compounds.

International audience; Hybrid organic-inorganic titanate-silicate thin films were deposited on silicium wafer via a sol-gel route. Hybrid sols were formulated by mixing an inorganic titanium alkoxide solution with solutions of hybrid organic-inorganic silicon alkoxides partially substituted with non-hydrolysable alkyl chains. Three organo-silicate precursors were used to introduce methyl, octyl. or hexadecyl chains in the oxide network. Physico-chemical and morphological properties of derived hybrid films have been studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and atomic force microscopy. Contact angle measurements have also been performed to assess the water and mineral oil wettability of hybrid films. Wettability properties of these films are discussed with respect to physico-chemical and morphological features. It is shown that increasing the fraction and length of alkyl chains in the oxide network conjointly increases water and oil contact angles measured on such hybrid films. (C) 2009 Elsevier B.V. All rights reserved.

Acinetobacter calcoaceticus RAG-1 and MR-48 1, two standard strains used in microbial adhesion to hydrocarbons (MATH), were characterized by contact angles, pH-dependent zeta potentials, elemental surface composition by X-ray photoelectron spectroscopy (XPS), and molecular composition by infrared spectroscopy (IR). Negatively stained (methylamine tungstate) and ruthenium red-stained cells were studied by transmission electron microscopy to reveal the absence or presence of surface appendages. Despite the fact that A. calcoacetius RAG-1 is known to be extremely hydrophobic in MATH, whereas MR-481 is a completely non-hydrophobic mutant, neither XPS nor IR indicated a significant difference in chemical composition of the cell surfaces. Contact angles with polar liquids, water and formamide, were considerably higher on RAG-1 than on MR-481, in accordance with their relative hydrophobicities as measured by MATH. However, no significant differences in contact angles were observed between the two strains with apolar liquids like diiodomethane, alpha-bromonaphthalene, and hexadecane. Fibrous extensions on RAG-1, observed after ruthenium red staining, were absent on the non-hydrophobic mutant MR-481. Tentatively, these extensions could be held responsible for the hydrophobicity of A. calcoaceticus RAG-1.

This study examined bacterial adhesion to a new multi-component cross-linked poly(ethylene glycol)-based polymer coating that can be applied by spin-coating or spraying onto diverse biomaterials. Adhesion of five clinically isolated bacterial strains involved in biomaterial-centered infections were studied in a parallel-plate flow chamber at different shear rates and after exposure of the coating to different physiological fluids. The new chemistry inhibits non-specific biomolecular and cell binding interactions. Relative to glass, the coating reduced adhesion of all strains used in this study by more than 80%, with the exception of Escherichia coli O2K2. Reductions in adhesion of Staphylococcus epidermidis 3399 persisted beyond 168 h exposure of the coatings to phosphate buffered saline or urine, but not after exposure to protein-rich fluids as saliva and blood plasma, despite evidence from X-ray photoelectron spectroscopy that the coating integrity was not affected by exposure to these fluids. We conclude that this new coating chemistry provides beneficial properties to prevent or hinder bacterial adhesion and colonization in applications where low protein-conditions prevail. (c) 2007 Elsevier Ltd. All rights reserved.

Aim: The purpose of the present study was to investigate in periodontitis patients the relationship between the number of bacteria in the saliva and the amount of de novo plaque formation before and after treatment.Methods: At baseline, before any treatment was provided, patients rinsed with 10 ml sterile saline. After professional tooth cleaning the patients were instructed to abolish all tooth cleaning procedures for the subsequent 24 h. After this period, the rinsing procedure was repeated and the amount of de novo plaque was assessed. Three months after the initial periodontal therapy was completed the experiment was repeated. The microbiological evaluation of the rinsing samples was carried out by means of phase contrast microscopy and anaerobic culturing.Results: After treatment the amount of de novo plaque was less compared to before treatment, 0.40 and 0.65 respectively. Both before and after treatment more de novo plaque was present at sites with inflammation than at healthy sites. In order to evaluate the contribution of the numbers of salivary bacteria to the amount of de novo plaque formation an analysis was carried out for healthy sites. This analysis included only healthy sites as determined before treatment and the same sites after treatment. The results showed a significant reduction in the de novo plaque formation after treatment (0.49 before and 0.22 after treatment). Phase contrast microscopic evaluation showed that the number of bacteria in the rinsing samples after treatment was less than before treatment. After treatment also a reduction was found in the prevalence of Prevotella intermedia, Tannerella forsythensis and Peptostreptococcus micros in the rinsing samples.Conclusion: The present study confirms the observation in the literature that the periodontal condition is of major importance in the rate of de novo plaque formation. In addition, the results suggest that the number of bacteria in the saliva may play a role.

This study was undertaken to evaluate the effects of reclaimed asphalt pavement (RAP) on moisture-induced damage potential of asphalt mixes using two different approaches: (i) micro-structural analysis of aggregate-asphalt bonding based on the surface free energy (SFE), and (ii) mechanical testing of asphalt mixes using retained indirect tensile strength ratio (TSR) and Hamburg wheel tracking (HWT). This study involved two phases. In the first phase, the SFE (non-polar, acidic and basic) components of a virgin performance grade (PG) 64-22 binder mixed with 0, 25, and 40% of simulated RAP binder and aggregates (limestone, rhyolite, RAP extracted aggregate) were measured using a dynamic contact angle (DCA) device and a universal sorption device (USD), respectively. Thereafter, composite work of adhesion and composite work of debonding, and composite energy ratios for each combination of asphalt binder and aggregates were determined to assess the moisture-induced damage potential of the mixes containing different percentages of RAP (0, 25, and 40%). In the second phase, the TSR and HWT tests were conducted on asphalt mixes containing different percentages of RAP (0, 25, and 40%) to evaluate their moisture-induced damage potential. Both the methods showed that the moistureinduced damage potential decreased with increasing amount of RAP in asphalt mixes. A strong correlation was found to exist between the moisture-induced damage potential predicted using the micro-structural method and laboratory performance tests. It was found that the micro-structural energy approach, as a mechanistic framework, can be successfully used as an indicator of moisture-induced damage potential of the asphalt mixes. It is expected that the present study would be helpful in understanding the moisture-induced damage potential of flexible pavements containing RAP.

Acid-base interactions play an important role in adhesion, including microbial adhesion to surfaces. Qualitatively acid-base interactions in microbial adhesion can be demonstrated by comparing adhesion to hexadecane (a negatively charged interface in aqueous solutions, unable to exert acid-base interactions) and chloroform (able to exert acid-base interactions) from aqueous suspensions of microorganisms. For 31 different microbial strains (4 Escherichia coli, 4 Enterococcus faecalis, 4 lactobacilli, 10 staphylococci, 9 streptococci) in low and high ionic strength potassium phosphate buffers, adhesion to chloroform was initially faster and in a stationary end-point more extensive than to hexadecane, due to acid-base interactions additionally operative from chloroform. However, a quantitative surface thermodynamical analysis of acid-base interactions based on water, formamide, methylene iodide and a-bromonaphthalene contact angles failed to explain the adhesion data obtained at low ionic strength, likely because of interference of electrostatic interactions. A weak relationship between initial removal rates and the acid-base interfacial free energy of adhesion was observed for the high ionic strength data, provided the analysis was confined to strains with an absolute zeta potential less than 15 mV. Similarly, a weak relationship was obtained between the Gibbs free energy of partitioning, calculated from the stationary end-point adhesion of the strains, and the acid-base interfacial free energy of adhesion. It is concluded that acid-base interactions play a definitive role in microbial adhesion, but the extent to which thermodynamically determined acid-base interactions eventually become operative in microbial adhesion may vary from strain to strain due to the presence of structural appendages and chemical heterogeneities on microbial cell surfaces.

Acid-base interactions play an important role in adhesion, including microbial adhesion to surfaces. Qualitatively acid-base interactions in microbial adhesion can be demonstrated by comparing adhesion to hexadecane (a negatively charged interface in aqueous solutions, unable to exert acid-base interactions) and chloroform (able to exert acid-base interactions) from aqueous suspensions of microorganisms. For 31 different microbial strains (4 Escherichia coli, 4 Enterococcus faecalis, 4 lactobacilli, 10 staphylococci, 9 streptococci) in low and high ionic strength potassium phosphate buffers, adhesion to chloroform was initially faster and in a stationary end-point more extensive than to hexadecane, due to acid-base interactions additionally operative from chloroform. However, a quantitative surface thermodynamical analysis of acid-base interactions based on water, formamide, methylene iodide and a-bromonaphthalene contact angles failed to explain the adhesion data obtained at low ionic strength, likely because of interference of electrostatic interactions. A weak relationship between initial removal rates and the acid-base interfacial free energy of adhesion was observed for the high ionic strength data, provided the analysis was confined to strains with an absolute zeta potential less than 15 mV. Similarly, a weak relationship was obtained between the Gibbs free energy of partitioning, calculated from the stationary end-point adhesion of the strains, and the acid-base interfacial free energy of adhesion. It is concluded that acid-base interactions play a definitive role in microbial adhesion, but the extent to which thermodynamically determined acid-base interactions eventually become operative in microbial adhesion may vary from strain to strain due to the presence of structural appendages and chemical heterogeneities on microbial cell surfaces.

Acid-base interactions play an important role in adhesion, including microbial adhesion to surfaces. Qualitatively acid-base interactions in microbial adhesion can be demonstrated by comparing adhesion to hexadecane (a negatively charged interface in aqueous solutions, unable to exert acid-base interactions) and chloroform (able to exert acid-base interactions) from aqueous suspensions of microorganisms. For 31 different microbial strains (4 Escherichia coli, 4 Enterococcus faecalis, 4 lactobacilli, 10 staphylococci, 9 streptococci) in low and high ionic strength potassium phosphate buffers, adhesion to chloroform was initially faster and in a stationary end-point more extensive than to hexadecane, due to acid-base interactions additionally operative from chloroform. However, a quantitative surface thermodynamical analysis of acid-base interactions based on water, formamide, methylene iodide and a-bromonaphthalene contact angles failed to explain the adhesion data obtained at low ionic strength, likely because of interference of electrostatic interactions. A weak relationship between initial removal rates and the acid-base interfacial free energy of adhesion was observed for the high ionic strength data, provided the analysis was confined to strains with an absolute zeta potential less than 15 mV. Similarly, a weak relationship was obtained between the Gibbs free energy of partitioning, calculated from the stationary end-point adhesion of the strains, and the acid-base interfacial free energy of adhesion. It is concluded that acid-base interactions play a definitive role in microbial adhesion, but the extent to which thermodynamically determined acid-base interactions eventually become operative in microbial adhesion may vary from strain to strain due to the presence of structural appendages and chemical heterogeneities on microbial cell surfaces.

This study used a mechanistic framework (i.e., surface free energy) to evaluate the moisture susceptibility of warm mix asphalt (WMA) with three different WMA additives, namely, Sasobit, Advera, and Evotherm. The surface free energy (SFE) components of modified PG64-22 asphalt binder with different percentages of WMA additives and selected aggregates were measured in the laboratory. The wettability, the work of adhesion, the work of debonding, and energy ratios were estimated in order to assess the moisture-induced damage potential of combinations of modified asphalt binders and different aggregates. The results indicate that Sasobit and Advera are able to reduce the moisture susceptibility potential of the mixes, but their use is not recommended with highly acidic aggregates such as granite. Evotherm resulted in the highest increases in wettability, total surface free energy, and increased work of adhesion and a reduction in the work of debonding, resulting in a better possible aggregate coating with asphalt binder and lower moisture susceptibility with all types of tested aggregates relative to those of other WMA additives. Furthermore, tensile strength ratio (TSR) tests were conducted on Advera and Evotherm-modified and neat (unmodified) asphalt mixes, and the results were compared with those from the SFE test. It was found that the SFE approach is a better indicator of moisture susceptibility than the traditional TSR test. The findings of the present study would help the highway engineers and agencies to better understand the moisture damage potential of flexible pavements constructed with WMA technologies.

Objectives: The ability of three oral bacteria to adhere to hydrophobic amalgam (water contact angle 60 degrees) and hydrophobic resin composites (Prisma-AP.H 56 degrees, Herculite XRV 82 degrees and Z100 89 degrees) was compared using an in vitro assay. Methods and results: Following preincubation of the materials with human saliva, X-ray photoelectron spectroscopy showed the surfaces to adsorb carbon and nitrogen-containing compounds in a conditioning film that appeared to block the detection of Na and others in 2100 resin, Hg and Ag in amalgam, Si and Zn in Prisma AP.H resin and Ag and Na in Herculite resin. The precoating of the substrata by a proteinaceous conditioning film led to decreased binding of viable cells of Streptococcus sanguis CH3, Streptococcus salivarius HE and Actinomyces viscosus WG as compared with the adhesion to bare composites. With and without salivary coating, there was a correlation between increased bacterial hydrophobicity and increased retention on the substrata. However, there was no statistical difference in binding to the amalgam compared with the resin composites. In vitro studies showed that the bacteria autoaggregated in the presence of saliva. Conclusion: The results indicate the potential ability of normal oral flora to colonize resin composite.

Acinetobacter calcoaceticus RAG-1 and MR-48 1, two standard strains used in microbial adhesion to hydrocarbons (MATH), were characterized by contact angles, pH-dependent zeta potentials, elemental surface composition by X-ray photoelectron spectroscopy (XPS), and molecular composition by infrared spectroscopy (IR). Negatively stained (methylamine tungstate) and ruthenium red-stained cells were studied by transmission electron microscopy to reveal the absence or presence of surface appendages. Despite the fact that A. calcoacetius RAG-1 is known to be extremely hydrophobic in MATH, whereas MR-481 is a completely non-hydrophobic mutant, neither XPS nor IR indicated a significant difference in chemical composition of the cell surfaces. Contact angles with polar liquids, water and formamide, were considerably higher on RAG-1 than on MR-481, in accordance with their relative hydrophobicities as measured by MATH. However, no significant differences in contact angles were observed between the two strains with apolar liquids like diiodomethane, alpha-bromonaphthalene, and hexadecane. Fibrous extensions on RAG-1, observed after ruthenium red staining, were absent on the non-hydrophobic mutant MR-481. Tentatively, these extensions could be held responsible for the hydrophobicity of A. calcoaceticus RAG-1.