Surface adhesion of $TiO_2$ -encapsulated microparticles on hydroxyapatite surface

Abstract

The microcapsules for hard-surface adhesion prepared by spray drying and surface coating method were investigated by particle surface properties and adhesion properties on hydroxyapatite and model teeth. $TiO_2$ particles were encapsulated with Eudragit, chitosan and poly(L-lysine) were selected as positively charged coating materials, since the hard surface models were negatively charged, while since hydroxyapatite has calcium ions, alginate that cross-links with calcium ions was selected. The characteristics of microparticles were determined with SEM image and zeta-potentials. The particle size distribution of microparticles prepared by spray-drying method was 0.5~9μm and the shape of microparticles was sphere distorted during the spray drying. The zeta-potentials of $TiO_2$ and hydroxyapatite were negative, -13 mV and -18mV respectively, while microparticles of positively charged polymers were positive. The hard surface adhesive properties on real and model teeth surface were confirmed with NMR, SEM SEM-EDAX and whitening test. NMR measurements showed the characteristic peaks of each polymer confirming the existence of microcapsule on the teeth surface. The SEM image showed the conditions of teeth surface states directly and SEM-EDAX showed the chemical identities of surface materials. Whitening test was carried out on the model teeth surface when brushing or shaking the samples. Microparticles surface coated with cationic polymers have greater whiteness index than those of microcapsules, except chitosan because of polymer``s own color. In tooth paste the degree of whiteness increased when compared with those of whitening materials-free samples in spite of non-uniform adhesion in SEM images. Therefore, it is concluded that the $TiO_2$ particles --encapsulated with charged polymers can adhere on the surface of hydroxyapatite and maintain the whitening effect in a prolonged period of brushing.