1991 Volume 54 Issue 4 Pages 333-346
We studied electrochemically the effect of stannous fluoride (SnF2) on the adsorption of protein to synthetic hydroxyapatite (HAp). Fifty milligram samples of HAp were immersed in 25ml of SnF2 solution adjusted to fluoride concentrations to 100, 1,000 and 9,000ppm. The surface characterization of SnF2-treated HAp was investigated by measuring the zeta potential in 1mM KNO3 and 1/30 M phosphate buffer at pH7.0, and by measuring the contact angle using the sessile drop method. The zeta potential of SnF2-treated HAp decreased significantly compared with that of untreated HAp, although there were no statistically significant differences for different concentrations of fluoride. Dental enamel treated with SnF2 was found to be more hydrophobic than untreated HAp.
The adsorption of human serum albumin (HSA, pI=4.7), chicken egg conalbumin (CA, pI=6.8) and salmon protamine (PR, pI=11.0) to the SnF2-treated HAp was determined by placing the HAp in each of the protein solutions for one hour at room temperature. The zeta potentials of the protein solutions were measured by micro-electrophoresis (Pen-Kem, Co., Lazer Zee, Model 501) and the values obtained were analyzed by the formula of Miyake, et al. The zeta potentials decreased dramatically even for the lowest protein concentrations. The correlation between 1/Δζ and 1/C showed good linearity. Thus, the adsorption of protein to SnF2-treated HAp conformed to the monolayer model of Langmuir. The component of protein in the zeta potential was close to that of untreated HAp for HSA and PR. However, for CA the component of protein in the zeta potential for treated HAp was smaller than for untreated HAp. It is suggested that the adsorption of protein to SnF2-treated HAp depends on the conformation of protein adsorbed and the interaction of surface net charge and hydrophobicity between the sorbent and protein.
