Factors affecting the Adsorption of Chlorhexidine Gluconate by Hydroxyapatite

Abstract

In order to assess the suitability of chlorhexidine for dental use, we investigated the effects of various factors such as temperature, pH, inorganic ions (F^-, Ca²⁺, Sr²⁺, Na⁺) and polymers (mucin, bovine serum albumin, polyvinylpyrrolidone) on the adsorption of chlorhexidine gluconate (CHG) from aqueous solution by hydroxyapatite (HAP). The adsorption isotherms were of Langmuir type at low equilibrium concentration. The amount adsorbed was of the order of 10^-7 mol/g, and was a little higher at 10°than at 37°. With the addition of inorganic ions such as Ca²⁺, Sr²⁺ and Na⁺, the amount of CHG adsorbed decreased. These results indicated that the adsorption involves electrostatic forces, and is a physical adsorption. Fluoride had an interesting effect on the adsorption. When the concentration of F^- was low (0.01 M), the amount adsorbed was higher, while when the concentration was high (0.1 and 0.25 M), the amount adsorbed was lower. This phenomenon might be a result of the formation of CaF₂ on the surface of HAP. Polymers such as mucin and bovine serum albumin increased the adsorption of CHG by HAP. This might be due to the strong binding of CHG with these polymers. On the other hand, polyvinylpyrrolidone had no significant effect on the adsorption.