Koji Kawasaki

Measurements of the Wettability of Protein–Covered Hydroxyapatite Surfaces

We developed a new method (dropping time method, DTM) to investigate the wettability of a surface of a protein layer adsorbed on glass plates in aqueous solution. However, the previous setup of DTM can only be utilized for optically transparent materials. In this study, we have extended the method to optically nontransparent materials such as hydroxyapatite plates. DTM is based on measuring the dropping time of a liquid film along a protein–covered surface when this surface is instantaneously vertically removed from the protein solution. The intensity of the reflected light beam depends on the presence of a liquid film on the surface. This allows to estimate the movement of the liquid film along the sorbent surface. Thus, the extended DTM can be used for determining the wettability of optically nontransparent solid plates. The adsorption behavior of four proteins (albumin, lysozyme, β–lactoglobulin, ovalbumin) on a hydrophobic hydroxyapatite plate in water was studied by this method. When adsorbed from a protein solution of high concentration, the surfaces of adsorbed proteins, except ovalbumin, were fairly hydrophilic; this hydrophilicity was already attained at the initial stage of the adsorption process. The surface of ovalbumin on hydroxyapatite was more hydrophobic than those of the other proteins, and the hydrophilicity increased with the protein adsorption process. At low protein concentration, the hydrophilicity increased in the course of the adsorption process. The change in hydrophilicity with time depends on the kind of protein. Hen’s egg lysozyme is more hydrophilic and the time to reach saturation is shorter than for the other proteins. The processes of increasing hydrophilicity of the surface of human serum albumin, β–lactoglobulin and ovalbumin are similar. However, for β–lactoglobulin hydrophobicity at adsorption saturation is stronger than for human serum albumin and ovalbumin. Thus, using DTM it is shown that the hydrophilicity of the surface of adsorbed protein on hydroxyapatite depends strongly on the kind of protein.

Characterization of the surface of protein-adsorbed dental materials by wetting and streaming potential measurements

Abstract In this study we have elucidated the water-wettability and the electrokinetic surface potential of protein-covered dental materials. The proteins used here as typical proteins were human serum albumin and lysozyme from hens egg. The wettability (hydrophobicity/hydrophilicity) and the surface potential may dominate bacterial adhesion on the tooth materials and hence influence their biological activity. The artificial tooth materials we investigated were platinum–gold alloy, porcelain and dental resin. Hydroxyapatite was chosen as a reference reflecting natural tooth surface. The wetting was measured by the dropping time method of a thin liquid film along the surface of a protein-covered solid plate sample. The zeta potential was derived from the streaming potential invoked by flowing an electrolyte solution between two parallel sample plates. A variety of surface properties have been found for different combinations of protein and dental material.

Wetting of protein-adsorbed solid surfaces studied by a dynamic method

Abstract The water wetting of an adsorbed protein layer on a solid surface immersed in an aqueous solution is an important property with respect to possible subsequent adsorption or adhesion of other (biological) components on that layer. In this paper we describe a novel method to determine the wetting of adsorbed protein layers. This method, the dropping time method (DTM), overcomes some drawbacks of more conventional techniques such as the sessile drop method, etc., where the protein molecules adsorbed on the solid surface from the bulk solution may change their conformation when the surface is dried in air. DTM is based on measuring the dropping time of a film of liquid along a protein-covered surface when this surface is instantaneously vertically removed from the protein solution. It is thus shown by DTM that the wetting of an adsorbed protein layer behaves very dynamically. It depends strongly on the protein concentration in solution and, even more so, on the incubation time of the sorbent surface in the protein solution. In particular for hydrophilic sorbent surfaces the wetting of the protein layers is extremely dynamic, showing a transient drop in wetting as protein adsorption proceeds. Comparison of these results with those obtained with the conventional sessile drop method, where the protein layer has to be dried before applying the water droplet, indicates that after drying the protein layer is much more hydrophobic and less dynamic.

Effects of ion-releasing tooth-coating material on demineralization of bovine tooth enamel.

We compared the effect of a novel ion-releasing tooth-coating material that contained S-PRG (surface-reaction type prereacted glass-ionomer) filler to that of non-S-PRG filler and nail varnish on the demineralization of bovine enamel subsurface lesions. The demineralization process of bovine enamel was examined using quantitative light-induced fluorescence (QLF) and electron probe microanalyzer (EPMA) measurement. Ion concentrations in demineralizing solution were measured using inductively coupled plasma atomic (ICP) emission spectrometry and an ion electrode. The nail varnish group and the non-S-PRG filler group showed linear demineralization. Although the nail varnish group and the non-S-PRG filler group showed linear demineralization, the S-PRG filler group did not. Further, plane-scanning by EPMA analysis in the S-PRG filler group showed no changes in Ca ion distribution, and F ions showed peak levels on the surface of enamel specimens. Most ions in the demineralizing solution were present at higher concentrations in the S-PRG filler group than in the other two groups. In conclusion, only the S-PRG filler-containing tooth-coating material released ions and inhibited demineralization around the coating.

Protein adsorption at polymer-grafted surfaces: Comparison between a mixture of saliva proteins and some well-defined model proteins

Grafting a dense layer of soluble polymers onto a surface is a well-established method for controlling protein adsorption. In the present study, polyethylene oxide (PEO) layers of three different grafting densities were prepared, i.e. 10 – 15 nm2, 5.5 nm2 and 4 nm2 per polymer chain, respectively. The adsorption of different proteins on the PEO grafted surfaces was measured in real time by reflectometry. Furthermore, the change of the zeta-potential of such surfaces resulting from adsorption of the proteins was determined using the streaming potential method. Both the protein adsorption and the zeta-potential were monitored for 1 h after exposure of the protein solution to the surface. The adsorption pattern for a mixture of saliva proteins was compared to those observed for a number of well-defined model-proteins (lysozyme, human serum albumin, β-lactoglobulin and ovalbumin). The results of the adsorption kinetics and streaming potential measurements indicate that the effect of the PEO layer on protein adsorption primarily depends on the size and the charge of the protein molecules. The saliva proteins are strongly blocked for adsorption, whereas the change in the zeta-potential is larger than for the other proteins (except lysozyme). It is concluded that positively charged protein molecules, having dimensions larger than those of lysozyme, are involved in the initial stage of adsorption from saliva onto a negatively charged surface.