Measurements of the Wettability of Protein–Covered Hydroxyapatite Surfaces

Abstract

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.

Protein adsorption on titanium surfaces and their effect on osteoblast attachment

“…5,6 The amphoteric characteristics of titanium oxide that resulted from surface hydroxyl groups were reported to change its surface zeta potential as a result of the change in pH. 17,24,25 Surface analyses from our group using X-ray photoelectron spectroscopy indicated a 5.8 eV peak separation between the Ti 2p 1/2 and Ti 2p 3/2 peaks for the Ti surfaces and the TiO 2 single crystal standard. 26 In concurrence with other investigators, this peak separation and peak position indicated the presence of TiO 2 , with an oxidation state of 4ϩ.…”

Enamel Erosion in Dietary Acids: Inhibition by Food Proteins in vitro

“…It is possible that the mechanism of action is adsorption to the enamel and/or to the pellicle proteins. Certainly both casein and ovalbumin bind to hydroxyapatite: both contain phosphoserine sequences, which are known to be important in the binding of casein to hydroxyapatite [Reynolds et al, 1982;Kawasaki et al, 1999;Huq et al, 2000]. There is also evidence that related proteins can bind with salivary proteins; the casein-derived molecules caseinoglycomacropeptide and caseinophosphopeptide incorporate into the salivary pellicle as does whole casein.…”

“…apatite dissolution in simple acid solutions in vitro Hemingway et al, 2008], and this is thought to be due to adsorption of protein to the hydroxyapatite surface since both proteins are known to adsorb to hydroxyapatite [Reynolds and Wong, 1983;Kawasaki et al, 1999]. However, these studies used compressed hydroxyapatite as the dissolving substrate, instead of natural tissue.…”

In vitro evaluation of the erosive potential of viscosity-modified soft acidic drinks on enamel

“…It has been also shown that the addition of food proteins (casein and ovalbumin) reduced enamel erosion [6], probably due to adsorption of protein to the hydroxyapatite surface [7]. The proteins might form a semi-permeable barrier, hindering transport of protons towards the hydroxyapatite crystal surface and/or calcium and phosphate ions away from the surface [8].…”