Interfacial-Electrochemical Study on the Adsorption of Protein to Fluoride-Treated Synthetic Hydroxyapatite

Abstract

We studied electrochemically the adsorption of protein to synthetic hydroxyapatite (HAp) treated with sodium fluoride (NaF) and acidulated fluoride phosphate (APF). The fluoride concentrations of NaF and APF were adjusted to 0.01%, 0.1%, and 0.9%. The protein solutions used were human serum albumin (HSA, pI=4.7), chicken egg conalbumin (CA, pI=6.8) and salmon protamine (PR, pI=11.0) in 1/30 M phosphate buffer at pH7.0. The protein concentrations were set at the five levels of 20%, 40%, 60%, 80% and 100% the concentration necessary to achieve saturated adsorption of the protein to the HAp. The fluoride was applied by immersing 50 mg of HAp in 25 ml of each of the fluoride solutions for four minutes. The adsorption of protein to the fluoride-treated HAp was determined by placing the HAp in protein solutions for one hour at room temperature.
The zeta potential of the fluoride-treated HAp in the protein solutions was measured by micro-electrophoresis (Pen-Kem Co., Lazer Zee Model 501), and the value obtained was analyzed by the formula of Miyake, et al. The zeta potentials of NaF-treated HAp were the same as these of untreated HAp in the several proteins. The adsorption coverage and free energy of adsorption of HAp treated with APF was lower than that of the other HAp. The adsorption of protein to HAp was affected to prevent by APF treatment. These results suggest that the adsorption of protein to fluoride-treated HAp was a monolayer model of Langmuir, and was dependent on the interaction between the protein and the surface charge structure on the HAp which had been treated with application of NaF and APF.