Electrical activity of cellobiose dehydrogenase adsorbed on thiols: Influence of charge and hydrophobicity.

The interface between protein and material surface is of great research interest in applications varying from implants, tissue engineering to bioelectronics. Maintaining functionality of bioelements depends greatly on the immobilization process. In the present study direct electron transfer of cellobiose dehydrogenase from Humicola insolens (HiCDH), adsorbed on four different self-assembled monolayers (SAMs) formed by 5-6 chain length carbon thiols varying in terminal group structure was investigated. By using a combination of quartz crystal microbalance with dissipation, ellipsometry and electrochemistry the formation and function of the HiCDH film was studied. It was found that the presence of charged pyridinium groups was needed to successfully establish direct electron contact between the enzyme and electrode. SAMs formed from hydrophilic charged thiols achieved nearly two times higher current densities compared to hydrophobic charged thiols. Additionally, the results also indicated proportionality between HiCDH catalytic constant and water content of the enzyme film. Enzyme films on charged pyridine thiols had smaller variations in water content and viscoelastic properties than films adsorbed on the more hydrophobic thiols. This work highlights several perspectives on the underlying factors affecting performance of immobilized HiCDH.

Strategies for a direct characterization of phosphoproteins on hydroxyapatite surfaces.

We show in this work how systems formed by phosphoproteins on calcium phosphate surfaces can be directly characterized, in real time, in liquid medium, without the need for elution or labeling. Specifically, we show how this is possible by applying three different techniques: ellipsometry, quartz crystal microbalance with dissipation, and atomic force microscopy-based friction force spectroscopy. We apply these techniques to study two different model systems, i.e. those formed upon the adsorption of two model phosphoproteins (κ- and ß-casein) on hydroxyapatite (HA) surfaces. Information on the kinetics of adsorption, surface excess, viscoelasticity, water content, thickness of the layers, and protein-surface interaction is provided. Results indicate that both phosphoproteins form homogeneous elastic highly hydrated monolayers on the HA surfaces, the strength of ß-casein layers being higher by approximately a factor of 4. Based on the experimental results, models for the conformation of κ- and ß-casein molecules adsorbed on HA surfaces are proposed.

Performance of enzymatic fuel cell in cell culture.

Here we present the very first study of an enzymatic fuel cell (EFC) in a cell culture. An EFC with Corynascus thermophilus cellobiose dehydrogenase (CDH) based bioanode and Myrothecium verrucaria bilirubin oxidase (BOx) based biocathode was constructed at the bottom of a medusa cell culture plate. The constructed EFC had a power density of up to 25 µW cm(-2) at 0.5 V potential in simple buffer solution and in cell culturing medium. L929 murine fibroblast cells were seeded on top of the EFC and possible effects of the EFC on the cells and vice versa were studied. It was shown that on average the power of the EFC drops by about 70% under a nearly confluent layer of cells. The EFC appeared to have a toxic effect on the L929 cell line. It was concluded that the bioanode, consisting of CDH, produced hydrogen peroxide at toxic concentrations. However, the toxic effect was circumvented by co-immobilizing catalase on the bioanode.

Nanowear of salivary films vs. substratum wettability.

The pellicle serves as a multifunctional protective layer, providing, e.g., lubrication and remineralization and also acting as a diffusion barrier. In addition, since the formation of the pellicle precedes the adhesion of micro-organisms, it is also important as a conditioning film. We present a novel approach to study the influence of the water wettability of solid surfaces on the strength of adsorbed salivary films. It is based on studying the wear resistance of the films with an atomic force microscope operated in the friction force spectroscopy mode. This methodology provides the strength of the films in terms of the forces needed for breaking and removing them. Our results indicate that these forces are highly dependent on the water wettability of the underlying substrata, decreasing with increasing hydrophobicity. Thus, this study provides valuable information for the design of materials exposed in the oral cavity, i.e., materials that will minimize plaque formation and be easy to clean.

Ellipsometric characterization of ethylene oxide-butylene oxide diblock copolymer adsorption at the air-water interface.

Ellipsometry was used to determine the adsorbed layer thickness (d) and the surface excess (adsorbed amount, Gamma) of a nonionic diblock copolymer, E(106)B(16), of poly(ethylene oxide) (E) and poly(butylene oxide) (B) at the air-water interface. The results were obtained (i) by the conventional ellipsometric evaluation procedure using the change of both ellipsometric angles Psi and Delta and (ii) by using the change of Delta only and assuming values of the layer thickness. It was demonstrated that the calculated surface excesses from the different methods were in close agreement, independent of the evaluation procedure, with a plateau adsorption of about 2.5 mg/m(2) (400 A(2)/molecule). Furthermore, the amount of E(106)B(16) adsorbed at the air-water interface was found to be almost identical to that adsorbed from aqueous solution onto a hydrophobic solid surface. In addition, the possibility to use combined measurements with H(2)O or D(2)O as substrates to calculate values of d and Gamma was investigated and discussed. We also briefly discuss within which limits the Gibbs equation can be used to determine the surface excess of polydisperse block copolymers.

Characterization of the binding of delmopinol to salivary precipitates.

The aim of this study was to quantify the amount of delmopinol recovered in different molecular weight ranges of salivary proteins in the supernatant and pellet of delmopinol-saliva mixes. Unstimulated whole saliva was collected from 5 subjects and mixed with radiolabeled delmopinol to obtain a final drug concentration of 9.7 mM. The salivary-delmopinol solutions were incubated and then centrifuged. The resulting pellets and supernatants were studied in an electrophoresis assay. Each individual sample was run in three different electrophoretic gel lanes. The first lane was stained with silver dyes; the second lane was used for electrophoretic blotting and autoradiography; the third lane was cut in standard slices that were dissolved and analyzed with scintillation counting. The scintillation results demonstrated that higher radioactivity levels were detected at high molecular weight ranges (700-600 kDa). Furthermore, pellet samples were found to contain the highest amounts of delmopinol. The autoradiography results confirmed that delmopinol was bound to proteins of high molecular weight (700-600 kDa).

Proteolytic degradation of oral biofilms in vitro and in vivo: potential of proteases originating from Euphausia superba for plaque control.

This paper deals with enzymatic removal of dental plaque, in vitro as well as in vivo, using proteases from the Antarctic krill shrimp (Euphausia superba), referred to as Krillase. Krillase exhibits both endo- and exopeptidase activity but has no microbicidal effect. In model systems with pure cultures of oral microorganisms. Krillase demonstrated inhibition of microbial adhesion to saliva-coated hydroxyapatite. Furthermore, a protocol for the growth of reproducible in vitro plaque films has been developed, and effects of Krillase on the plaque film were investigated by means of scanning electron microscopy (SEM). The results showed that Krillase efficiently released microorganisms from plaque in vitro, the effect being dependent on the enzymatic activity. The surface energy of the substratum had a minor influence on the formation and removal of plaque in vitro. Ellipsometric studies on the formation and enzymatic removal of a salivary pellicle indicated that the enzymatic effect on plaque may partly depend on degradation of the salivary pellicle. Krillase was also able to remove plaque accumulated on dentures in vivo. Our results demonstrate the potential of Krillase for plaque control, and that these enzymes are worthy of further investigations including clinical studies and work to find a suitable vehicle.

Interactions between Local Anaesthetic Agents and Poly(N-isopropyl acrylamide) through Phase Behavior, Surface Tension, and Adsorption Measurement.

The interaction between the local anaesthetic agents prilocaine and lidocaine, on one hand, and poly(N-isopropyl acrylamide) (pNIPAM), on the other, is investigated through studies of the polymer phase behavior and through surface tension and adsorption measurements. In particular, the cloud points (CP) for pNIPAM in the presence of lidocaine and prilocaine under different conditions were compared to the effects of electrolytes and alcohols. It was found that the electrolytes affect the CP of pNIPAM in a lyotropic manner, whereas alcohols depress the CP of pNIPAM in an alkyl chain length dependent way; i.e., the longer the chain, the larger the decrease in CP. Lidocaine and prilocaine affect the CP of pNIPAM in a pH-dependent manner. Below the pK(a) of lidocaine and prilocaine, these cosolutes do not substantially affect the CP in the concentration range investigated, but rather behave analogous to simpler electrolytes. Above the pK(a), on the other hand, they strongly depress the CP already at low concentrations. In parallel, at low pH, the surface tension reduction due to lidocaine or prilocaine is marginal, whereas at high pH the surface tension is reduced considerably. Thus, the poor solubility of prilocaine and lidocaine at high pH causes these to become more surface active and simultaneously interact in a more pronounced way with pNIPAM. Furthermore, it was found from ellipsometry that an adsorbed pNIPAM layer contracts when lidocaine is added, presumably due to a lidocaine-pNIPAM interaction similar to that causing pNIPAM to phase separate. Analogous to this, it was demonstrated that an adsorbed pNIPAM layer shrinks and swells reversibly when the temperature is cycled above and beneath the CP. Copyright 2001 Academic Press.

Film-forming properties and viscosities of saliva substitutes and human whole saliva.

Hypo-salivation, related to medical remedies, is an increasing clinical problem. Studies report a weak correlation between subjective mouth dryness and objective sialometry. This indicates that both quantity and quality of saliva are important for the surface-associated functions of saliva, such as lubrication and hydration, to be expressed. Film-forming properties and viscosities of three saliva substitutes were compared to human saliva. Adsorption to surfaces was measured by ellipsometry, infrared spectroscopy and drop-volume technique. Viscosity measurements were carried out using an oscillating rheometer. Saliva, with the lowest viscosity value and the highest protein content, presented superior film retention on both hydrophilic and hydrophobic surfaces. The carboxymethylcellulose-based MAS 84 showed intermediate values of viscosity, poorest ability to reduce surface tension, and negligible film-forming capacity. The porcine mucin-based Saliva Orthana showed about twice the viscosity of saliva and film-forming capability on preferably hydrophobic substrates. Salinum, a linseed extract, possessed the highest viscosity value and an initial surface tension close to that of saliva. The film retention on hydrophilic surfaces was not as effective as for saliva. The results indicate that the film-forming capacity of saliva substitutes is a property also to be considered in the exploration of clinically effective artificial salivas.

Bioadhesion--a phenomenon with multiple dimensions.

This paper reviews some relevant citations regarding the non-specific forces that must be considered in oral bioadhesive events. These range from forces related to restorative dentistry to those related to prevention and molecular biology. Types of interactions discussed are: 1. Van der Waal's forces; 2. electrostatic double-layer forces; 3. solvent-dependent interactions; 4. hydrogen bonding; 5. hydrophobic interactions; 6. hydration forces; 7. steric forces; and 8. covalent bonds. Examples are given of the various types of interaction that occur at different surface separation (< or =400 A) between adsorbed films of a pure salivary protein fraction (PRP1).

The content of delmopinol and characterization of the molecular weight pattern of salivary protein precipitates.

The aims of this investigation were: a) To quantify the amount of radiolabelled delmopinol in precipitates formed in a mixture of saliva and delmopinol at two concentrations, b) To analyze the precipitates by polyacrylamide gel electrophoresis. Unstimulated whole saliva was collected from 5 individuals and the samples were clarified by centrifugation. In a first series of experiments radiolabelled delmopinol hydrochloride at the final concentrations of 1.6 mM and 6.4 mM was incubated with the saliva samples and centrifuged. The supernatants and the pellets were immediately transferred to scintillation vials and radiolabelled delmopinol was detected by using scintillation counting. In a second series of experiments, similar saliva-delmopinol mixtures were centrifuged and the supernatants and pellets were prepared for electrophoresis. Videodensitometry was used to quantify the relative density of stained protein in the pellet samples within four ranges of molecular weight (10-21.5, 21.5-26, 26-45, 45-300 kDa). The results of this study showed that the amounts of labeled delmopinol found in the precipitates were higher at 6.4 mM delmopinol than at 1.6 mM. The amount of salivary protein precipitated by delmopinol was found to depend on delmopinol concentration as well as salivary composition. Delmopinol interactions to salivary proteins could influence protein availability on oral cavity surfaces.

Delmopinol hydrochloride- and chlorhexidine digluconate-induced precipitation of salivary proteins of different molecular weights.

Gel electrophoresis was used to analyze precipitates formed of delmopinol hydrochloride or chlorhexidine digluconate mixed with unstimulated whole saliva samples from five test subjects. Final concentrations of delmopinol (6.4 mM) or chlorhexidine (6.4 mM, 2.2 mM) mixed with whole saliva were incubated for 10 min at 37 degrees C. The precipitates were pelleted by centrifugation and resuspended to a similar protein density. The protein patterns in the pellets were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, using 12.3% gels. The amount of pellet protein was determined by densitometry in four molecular weight ranges (10-21.5, 21.5-26, 26-45, and 45-300). The results indicated that high molecular weight (45-300) proteins dominated in the precipitate and that 2.2 mM chlorlhexidine precipitated more salivary protein than 6.4 mM. At equimolar concentration (6.4 mM) delmopinol precipitated more high molecular weight salivary proteins than chlorhexidine.

Time-dependent interfacial tension of whole saliva and saliva-bacteria mixes.

Using a tensiometer in accordance with the drop volume principle, the surface tension decrease with time was determined for whole and for 2%, 10%, and 50% aqueous solutions of saliva from one healthy donor. The reduction of surface tension with time was also measured for 10% and 20% saliva solutions with added samples of Streptococcus salivarius KRF2, S. sanguis KRF3, and Actinomyces naeslundii 2t-55. The results show that 1) there is a time dependence of the surface tension reduction of both whole saliva and diluted saliva, 2) an increase of the concentration of whole saliva in salivary solutions gives rise to larger and more rapid surface tension reduction, 3) the proteinaceous components of saliva appear to have a dominant contribution on surface tension in whole saliva and diluted saliva, and 4) the surface-active proteinaceous components in saliva have the ability to dominate the air-saliva interface also in the presence of high concentrations of salivary bacteria.

Adsorption during Heat Treatment Related to the Thermal Unfolding/Aggregation of beta-Lactoglobulins A and B

Adsorption onto chromium surfaces during heat treatment (65-68°C) of beta-lactoglobulin A and B in phosphate buffer, pH 6.88, was investigated by in situ ellipsometry. Thermal unfolding and in situ heat-induced aggregation under the same conditions were studied by differential scanning calorimetry and dynamic light scattering, respectively. A lag phase was observed for buildup of the thickness of the adsorbed layer of beta-lactoglobulin A and B at 68°C. The lag period was found to increase with decreasing temperature. The difference in adsorption rate between the variants was found to be in agreement with the aggregation difference in solution, that is, the A variant aggregated more rapidly after a somewhat slower beginning. These results could be related to a difference in the thermal unfolding behavior. By applying a non-two state model the second of two transitions was suggested to involve the activation of the free sulfydryl group. The results indicated that fouling proceeds via attachment of aggregates with an activated free sulfydryl group through an interchange reaction with a disulfide bond in the adsorbed protein layer.

The binding of delmopinol and chlorhexidine to Streptococcus mutans and Actinobacillus actinomycetemcomitans strains with varying degrees of surface hydrophobicity.

This study evaluated the binding of chlorhexidine and the new surface-active anti-plaque agent delmopinol hydrochloride to Streptococcus mutans and Actinobacillus actinomycetemcomitans cells with various cell surface hydrophobicities. The influence of saliva concentration on the binding of these compounds was also investigated. The radiolabeled compounds were incubated with bacteria and the cells were recovered using a centrifugal filtering technique. Delmopinol had higher binding to the hydrophilic variant strains than to the hydrophobic parent strains; chlorhexidine had higher binding to hydrophobic than to hydrophilic A. actinomycetemcomitans strains and higher binding to hydrophilic than to hydrophobic S. mutans strains. The presence of salivary films decreased the binding of both compounds. Both delmopinol and chlorhexidine had stronger affinity to A. actinomycetemcomitans cells than to S. mutans cells. At equimolar concentrations, delmopinol had a lower binding to all strains tested than chlorhexidine. The high reversibility of the delmopinol binding might be related to a higher diffusion rate and solubility compared with that of chlorhexidine. The amphiphilicity of both molecules is an important feature in their retention to S. mutans and A. actinomycetemcomitans strains of varying hydrophobicities and could play an important role in the substantivity of delmopinol or chlorhexidine in the oral cavity.

Reflectometry: a new method for quantitative determinations of intraoral film formation.

A simple optical method--reflectometry--is described to determine the thickness and mass of salivary films formed on solid surfaces at oral exposure. Reflectometry is based on the fact that p-polarized light is reflected with minimum intensity at an interface when the angle of incidence equals the so-called pseudo-Brewster angle. Hydrophilic and hydrophobized silica surfaces were used as substrates and the reflectometer was calibrated against a null ellipsometer. A linear relation was found between the square of the ellipsometrically measured thickness of silicon oxides on silicon substrates and the reflectometrically registered intensity of the reflected light at these surfaces. Thirty volunteers participated in the study of the thickness of films formed on the test substrates at oral exposure. The test silica surfaces were positioned in the vestibular sulcus of each test subject for periods of 1, 5, 15, 30, 60, and 120 min. The results show that films formed on hydrophobic surfaces leveled-off to a thickness value of 140 A after 60 min. Films formed on hydrophilic surfaces, however, reached a plateau value of approximately 100 A after only 300 min. Reflectometry seems to be an accurate and valid, yet inexpensive and quick method for quantitative investigations and thickness measurements of early salivary pellicles in large subject groups.

An in vitro study of salivary film formation at solid/liquid interfaces.

The aim of this study was to use the technique of in situ null ellipsometry to study some aspects of salivary film formation at solid/liquid interfaces. Experiments were performed in a fused quartz cell, and hydrophilic plasma cleaned silica and methylated hydrophobic silica surfaces were used as substrates. Samples of unstimulated whole saliva were allowed to adsorb on the test surfaces for 30 min. After the adsorption period, rinsing was performed for 5 min. Recordings were continued for another 30 min, and then new saliva samples were added in the cell. The results showed that statistically significant higher amounts were adsorbed on the hydrophobic than on the hydrophilic surfaces. The adsorbed films on both types of tested substrates consisted of loosely associated parts which were removed after rinsing and of more tightly adsorbed fractions. A significantly larger fraction was desorbed from the films adsorbed on the hydrophobic than on the hydrophilic surfaces. When saliva was introduced again in the cell, it was shown that the amounts adsorbed attained the values obtained before the rinsings. Increase in the concentration of saliva in the cell without previous rinsing did not cause any further increase in the mass of the adsorbed film.

Interactions of chlorhexidine with salivary films adsorbed at solid/liquid and air/liquid interfaces.

Chlorhexidine is a cationic compound which has been shown to bind to salivary proteins and enamel through electrostatic interactions. The aims of this study were to investigate the interaction of chlorhexidine molecules with salivary films adsorbed on solid surfaces with varying physico-chemical characteristics and to investigate the effect of different concentrations of chlorhexidine on the surface tension of saliva. The interactions between 0.2% chlorhexidine digluconate with films adsorbed from whole saliva were monitored by a Rudolph Thin-film ellipsometer equipped with a He-Ne laser (632.8 nm). The films were adsorbed on hydrophilic silica surfaces which were plasma cleaned or on methylated hydrophobic surfaces. Experiments of chlorhexidine adsorption on bare surfaces were also performed. The surface tension of mixtures of whole saliva with various concentrations of (0.1%, 0.2%, 1%) chlorhexidine was monitored with a tensiometer. The results show that chlorhexidine adsorbs on both types of studied substrates. Addition of the substance followed by rinsing caused a partial desorption of the adsorbed pellicles. Furthermore, at all studied concentrations chlorhexidine reduced the interfacial tension. There are indications that the amphiphilic characteristics of the molecule play an important role in the retention of the substance in the oral cavity.

In vitro interactions of delmopinol hydrochloride with salivary films adsorbed at solid/liquid interfaces.

Delmopinol hydrochloride is a highly surface active substance which has been shown to reduce the amount of plaque in vitro and in vivo and the level of gingivitis in vivo. Ellipsometry was used to evaluate the effect of delmopinol on films formed from whole, parotid and sublingual/submandibular saliva on solid surfaces. Hydrophilic plasma cleaned silica and methylated hydrophobic substrates were used. The adsorption processes of the salivary proteins and their interactions with delmopinol were monitored in situ with a Rudolph thin-film ellipsometer. The adsorption of delmopinol on bare substrates with out previous salivary adsorption was also investigated and the results indicate that delmopinol molecules were adsorbed on both hydrophilic and hydrophobic surfaces. When delmopinol interacted with the films formed from the different types of saliva an initial increase in the adsorbed amounts was observed in the majority of the cases indicating binding to the salivary pellicles and/or substrate surface. The noted increases were largest for the films adsorbed from whole and sublingual/submandibular saliva. After rinsing in the system, partial desorption of the salivary films took place. It is thus indicated that delmopinol binds to salivary proteins within the pellicles and alters the cohesive and adhesive properties of these films.

Adsorption of whole saliva onto hydrophilic and hydrophobic solid surfaces: influence of concentration, ionic strength and pH.

The influence of the concentration of salivary proteinaceous material from solutions of whole saliva on the kinetics of in vitro pellicle formation were studied together with the effects of ionic strength, pH and certain substrate characteristics. The pellicle formation was monitored by an automated Rudolph ellipsometer, equipped with a He-Ne laser (wavelength 632.8 nm). The substrates compared in the study were hydrophilic negatively charged silica surfaces and hydrophobic methylated silica surfaces. The results show that the adsorption of salivary proteins is a very rapid process on both types of surfaces. Part of the formed biofilm, however, desorbed upon rinsing, indicating that the proteinaceous material was adsorbed with varying binding strengths. Larger adsorbed amounts were recorded on hydrophobic than on hydrophilic surfaces. Increase of ionic strength caused larger amounts to be adsorbed on both types of surfaces but change of pH did not affect the adsorption on either of the studied surfaces. Ellipsometry was found to be a suitable technique to monitor the adsorption of salivary proteins at solid/liquid interfaces.