Adsorption of aminefluorides onto glass and the determination of surface free energy, zeta potential and adsorbed layer thickness

Aminefluorides are known to affect bacterial adhesion to enamel. In order to obtain information on the structure of adsorbed aminefluoride coatings, dihydroaminefluoride (AmF 297) and oleylaminefluoride (AmF 335) were adsorbed onto glass from solutions with concentrations up to 10 mM. Surface tensions of the solutions were measured at 25°C. After coating the glass surfaces, surface free energies, zeta potentials and adsorbed layer thicknesses were determined from contact angles, electrophoresis and ellipsometry, respectively. Surface free energies decreased after coating with both types of aminefluoride from 109 to _ 45 mJ m-*. Coating with only high concentrations (> 5 mA4) of AmF 297 again resulted in surface free energies above 100 mJ m-‘. Zeta potentials, originally - 45 mV, became positive after coating with both types of aminefluoride (approximately + 5 mV). Coating with only AmF 297 at concentrations above 5 mM gave zeta potentials of + 20 mV. Adsorbed layer thicknesses were in the monolayer range, though AmF 297 on its own clearly formed thicker layers at higher concentrations. Both surfactants showed a tendency to form micelles in solution at concentrations higher than 1 n&f. The results indicate that both aminefluorides adsorb with the positively charged, polar group towards the glass, but only AmF 297 can form double layers at higher concentrations. The second layer, however, adsorbs with the positively charged polar groups towards the solution and is bound to the first layer by relatively weak forces between the hydrocarbon chains. Gentle rinsing with distilled water is sufficient to remove the double layers. This paper shows how a combination of surface techniques can yield a detailed picture of the structure and orientation of adsorbed layers on solid substrata

Spreading pressures of water and n-propanol on polymer surfaces

Spreading pressures of water and n-propanol on polytetrafluoroethylene (PTFE), polystyrene (PS), polymethylmethacrylate (PMMA), polycarbonate (PC), and glass are determined from ellipsometrically measured adsorption isotherms by graphical integration, yielding for water 9, 37, 26, 33, and 141 erg · cm−2 on PTFE, PS, PMMA, PC, and glass, respectively, while for n-propanol 5, 38, 26, 23, and 37 erg · cm−2, respectively. The spreading pressures for water as well as n-propanol are comparable to values previously obtained from contact angle data with water, water/n-propanol mixtures and α-bromonaphthalene using the geometric mean equation. This method yielded spreading pressures of 9, 14, 30, 27, and 70 erg · cm−2 for PTFE, PS, PMMA, PC, and glass, respectively. The numerical correspondence between the spreading pressures for water and n-propanol determined ellipsometrically with the values derived from contact angles indicates the necessity as well as the validity of taking the spreading pressures of water/n-propanol mixtures into account as a constant, if surface free energies of high energy substrata are approximated by contact angle measurements

Adsorption of aminefluorides on human enamel

Changes in surface characteristics of ground and polished human enamel after adsorption of two types of aminefluorides (AmF 297 and AmF 335) have been studied. After adsorption of aminefluorides from solutions with concentrations up to 10 mM for 2 min followed by rinsing of the surface with distilled water, contact angle measurements were carried out to yield surface free energies and ellipsometry was performed to yield the adsorbed layer thickness. In a separate experiment on powdered enamel, set up in an analogous way, zeta potential changes after adsorption of aminefluorides were determined in a 10 mM potassium phosphate buffer at pH 7·0. Surface free energies decreased from 88 erg·cm−2 to 52 erg·cm−2 and 35 erg·cm−1 after adsorption of AmF 297 and AmF 335 respectively at c = 1 mM. Increasing the aminefluoride concentration in solution did not affect the values obtained. Zeta potentials, originally −36 mV, became positive after adsorption, while ellipsometry indicated the buildup of adsorbed layers with a thickness between 3 run and 12 nm. All three types of experiments indicated that both AmF 297 and AmF 335 form an adsorbed monolayer on ground and polished enamel at a concentration of 1 mM. Negligible additional adsorption takes place at higher concentrations under the present experimental circumstances. In vivo, adsorbed aminefluoride layers will be rapidly covered by adsorbed protein layers, shielding both the adsorbed aminefluoride layer as well as its physicochemical characteristics. This effect has been studied in vivo by measuring surface free energy changes of ground and polished enamel, with AmF 297 and AmF 335 adsorbed at c = 2·5 mM as a function of the time, these samples were carried by test persons in partial dentures. On both types of AmF-coated enamel the surface free energies increased within 30 min to values approaching the one obtained previously for pellicle-coated ground and polished enamel (110 ± 9 erg·cm−2)

Staphylococcus aureus-Fibronectin Interactions with and without Fibronectin-Binding Proteins and Their Role in Adhesion and Desorption

Adhesion and residence-time-dependent desorption of two Staphylococcus aureus strains with and without fibronectin (Fn) binding proteins (FnBPs) on Fn-coated glass were compared under flow conditions. To obtain a better understanding of the role of Fn-FnBP binding, the adsorption enthalpies of Fn with staphylococcal cell surfaces were determined using isothermal titration calorimetry (ITC). Interaction forces between staphylococci and Fn coatings were measured using atomic force microscopy (AFM). The strain with FnBPs adhered faster and initially stronger to an Fn coating than the strain without FnBPs, and its Fn adsorption enthalpies were higher. The initial desorption was high for both strains but decreased substantially within 2 s. These time scales of staphylococcal bond ageing were confirmed by AFM adhesion force measurement. After exposure of either Fn coating or staphylococcal cell surfaces to bovine serum albumin (BSA), the adhesion of both strains to Fn coatings was reduced, suggesting that BSA suppresses not only nonspecific but also specific Fn-FnBP interactions. Adhesion forces and adsorption enthalpies were only slightly affected by BSA adsorption. This implies that under the mild contact conditions of convective diffusion in a flow chamber, adsorbed BSA prevents specific interactions but does allow forced Fn-FnBP binding during AFM or stirring in ITC. The bond strength energies calculated from retraction force-distance curves from AFM were orders of magnitude higher than those calculated from desorption data, confirming that a penetrating Fn-coated AFM tip probes multiple adhesins in the outermost cell surface that remain hidden during mild landing of an organism on an Fn-coated substratum, like that during convective diffusional flow

Evaluation of adhesion forces of Staphylococcus aureus along the length of Candida albicans hyphae

Background Candida albicans is a human fungal pathogen, able to cause both superficial and serious, systemic diseases and is able to switch from yeast cells to long, tube-like hyphae, depending on the prevailing environmental conditions. Both morphological forms of C. albicans are found in infected tissue, often in combination with Staphylococcus aureus. Although bacterial adhesion to the different morphologies of C. albicans has been amply studied, possible differences in staphylococcal adhesion forces along the length of C. albicans hyphae have never been determined. In this study, we aim to verify the hypothesis that the forces mediating S. aureus NCTC8325-4GFP adhesion to hyphae vary along the length of C. albicans SC5314 and MB1 hyphae, as compared with adhesion to yeast cells. Results C. albicans hyphae were virtually divided into a "tip" (the growing and therefore youngest part of the hyphae), a "middle" and a so-called "head" region (the yeast cell from which germination started). Adhesion forces between S. aureus NCTC8325-4GFP and the different regions of C. albicans SC5314 hyphae were measured using atomic force microscopy. Strong adhesion forces were found at the tip and middle regions of C. albicans hyphae (−4.1 nN and −4.0 nN, respectively), while much smaller adhesion forces were measured at the head region (−0.3 nN). Adhesion forces exerted by the head region were comparable with the forces arising from budding yeast cells (−0.5 nN). A similar regional dependence of the staphylococcal adhesion forces was found for the clinical isolate involved in this study, C. albicans MB1. Conclusions This is the first time that differences in adhesion forces between S. aureus and different regions of C. albicans hyphae have been demonstrated on a quantitative basis, supporting the view that the head region is different from the remainder of the hyphae. Notably it can be concluded that the properties of the hyphal head region are similar to those of budding yeast cells. These novel findings provide new insights in the intricate interkingdom interaction between C. albicans and S. aureus

Inhibition of adhesion of yeasts and bacteria by poly(ethylene oxide-)brushes on glass in a parallel plate flow chamber

Poly(ethylene oxide) (PEO)-brushes are generally recognized as protein-repellent surfaces, and although a role in discouraging microbial adhesion has been established for some strains and species, no study exists on the effects of PEO-brushes on a large variety of bacterial and yeast strains. In this paper, a PEO-brush has been covalently attached to glass and silica by reaction in a polymer melt. Subsequently, the presence of a PEO-brush was demonstrated using contact angle measurements, X-ray photoelectron spectroscopy and ellipsometry. For five bacterial (Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus salivarius, Escherichia coli and Pseudomonas aeruginosa) and two yeast strains (Candida albicans and Candida tropicalis), adhesion to PEO-brushes was compared with adhesion to bare glass in a parallel plate flow chamber. The initial deposition rates of Sta. epidermidis, Sta. aureus and Str. salivarius to glass were relatively high, between 2400 and 2600 cm-2 s-1, while E. coli and P. aeruginosa deposited much more slowly. The initial deposition rates of the yeasts to glass were 144 and 444 cm-2 s-1 for C. albicans GB 1/2 and C. tropicalis GB 9/9, respectively. Coating of the glass surface with a PEO-brush yielded more than 98 % reduction in bacterial adhesion, although for the more hydrophobic P. aeruginosa a smaller reduction was observed. For both yeast species adhesion suppression was less effective than for the bacteria and here too the more hydrophobic C. tropicalis showed less reduction than the more hydrophilic C. albicans. The PEO-brush had a thickness of 22 nm in water, as inferred from ellipsometry. Assuming that on bare glass the adhered micro-organisms are positioned only a few nanometers away from the surface and that the brush keeps them at a distance of 22 nm, it is calculated that the brush yields a sevenfold attenuation of the Lifshitz–Van der Waals attraction to the surface between the micro-organisms and the surface. Decreased Lifshitz–van der Waals attraction may be responsible for the suppression of the microbial adhesion observed

The use of positively charged or low surface free energy coatings versus polymer brushes in controlling biofilm formation

Biofilm formation on biomaterials implant surfaces and subsequent infectious complications are a frequent reason for failure of many biomedical devices, such as total hip arthroplasties, vascular catheters and urinary catheters. The development of a biofilm is initiated by the formation of a conditioning film of adsorbed macromolecules, such as proteins, followed by adhesion of microorganisms, where after they grow and anchor through secretion of extracellular polymeric substances. Adhesion of microorganisms is influenced by the physico-chemical properties of the biomaterial surface. Positively charged materials stimulate bacterial adhesion, but prevent growth of adhering bacteria. The use of low surface free energy materials did not always reduce in vitro adhesion of bacteria, but has been found beneficial in in vivo applications where fluctuating shear forces prevail, like on intra-oral devices and urine catheters. Polymer brushes have shown a very high reduction in in vitro adhesion of a great variety of microorganisms. However, for clinical application, the long term stability of polymer brushes is still a limiting factor. Further effort is therefore required to enhance the stability of polymer brushes on biomaterial implant surfaces to facilitate clinical use of these promising coating

The influence of ionic strength on the adhesive bond stiffness of oral streptococci possessing different surface appendages as probed using AFM and QCM-D

Bacterial adhesion to surfaces poses threats to human-health, not always associated with adhering organisms, but often with their detachment causing contamination elsewhere. Bacterial adhesion mechanisms may not be valid for their detachment, known to proceed according to a visco-elastic mechanism. Here we aimed to investigate influences of ionic strength on the adhesive bond stiffness of two spherically shaped Streptococcus salivarius strains with different lengths of fibrillar surface appendages. The response of a Quartz-Crystal-Microbalance-with-Dissipation (QCM-D) upon streptococcal adhesion and changes in the ionic strength of the surrounding fluid indicated that the bond stiffness of S. salivarius HB7, possessing a dense layer of 91 nm long fibrils, was unaffected by ionic strength. Atomic-force-microscopic (AFM) imaging in PeakForce-QNM mode showed a small decrease in bond stiffness from 1200 to 880 kPa upon decreasing ionic strength from 57 to 5.7 mM, while Total-Internal-Reflection-Microscopy suggested a complete collapse of fibrils. S. salivarius HBV51, possessing a less dense layer of shorter (63 nm) fibrils, demonstrated a strong decrease in bond stiffness both from QCM-D and AFM upon decreasing the ionic strength, and a partial collapse of fibrils. Probably, the more hydrophobic and less negatively charged long fibrils on S. salivarius HB7 collapse side-on to the cell surface, while the more hydrophilic and negatively charged fibrils of S. salivarius HBV51 remain partially stretched. In summary, we demonstrate how a combination of different methods can yield a description of the structural changes occurring in the interfacial region between adhering, fibrillated streptococci and a substratum surface upon changing the ionic strengt

Relations between macroscopic and microscopic adhesion of Streptococcus mitis strains to surfaces

Application of physico-chemical models to describe bacterial adhesion to surfaces has hitherto only been partly successful due to the structural and chemical heterogeneities of bacterial surfaces, which remain largely unaccounted for in macroscopic physico-chemical characterizations of the cell surfaces. In this study, the authors attempted to correlate microscopic adhesion of a collection of nine Streptococcus mitis strains to the negatively charged, hydrophilic silicon nitride tip of an atomic force microscope (AFM) with macroscopic adhesion of the strains to a negatively charged, hydrophilic glass in a parallel-plate flow chamber. The repulsive force probed by AFM upon approach of the tip to a bacterial cell surface ranged from 1·7 to 7·7 nN depending on the strain considered and was found to correspond to an activation barrier, governing initial, macroscopic adhesion of the organisms to the glass surface. Moreover, maximum distances at which attractive forces were probed by the AFM upon retraction of the tip (120 to 1186 nm) were related to the area blocked by an adhering bacterium, i.e. the distance kept between adhering bacteria. Bacterial desorption could not be related to adhesive forces as probed by the AFM, possibly due to the distinct nature of the desorption process occurring in the parallel-plate flow chamber and the forced detachment in AFM