Calcium Phosphate−Gelatin Nanocomposites : Bulk Preparation (Shape- and Phase-Control), Characterization, and Application as Dentine Repair Material

Abstract

Nanocomposites consisting of gelatin and hydroxyapatite as well as of gelatin and mixtures of hydroxyapatite and different amounts of octacalcium phosphate were prepared as bulk-materials. The composites were precipitated from aqueous solutions of CaCl2·2H2O and (NH4)2(HPO4), respectively, with varying amounts of gelatin at 25 °C and pH 7. The influence of prestructuring effects of calcium and phosphate ions, respectively, on gelatin and by this on the precipitated materials was investigated in detail. X-ray-diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS), and high-resolution transmission electron microscopy (HR-TEM) revealed that the prestructuring components as well as the total amount of gelatin involved in the reactions have a substantial influence on the composition and shape of the nanocomposites formed. In the case of CaCl2·2H2O used as the prestructuring agent for gelatin, hydroxyapatite is the inorganic phase obtained, independent of the initial amount of gelatin. By the prestructuring of gelatin with (NH4)2(HPO4), a strong dependency of the reaction products on the amount of gelatin was observed. Low gelatin quantities favor the formation of hydroxyapatite, whereas high gelatin concentrations lead to the formation of octacalcium phosphate. Moreover, the morphology of the composites changes gradually. Samples prepared by means of the Ca-prestructuring (CPS) reaction consist of small plate-like particles (∼50 nm × 33 nm). When the PO4-prestructuring (PPS) reaction is used, the particle size is highly influenced by the amount of gelatin. Lower gelatin concentrations lead to small, plate-like particles (∼60 nm × 35 nm), while higher gelatin concentrations cause the development of large foils (∼730 nm × 410 nm). The thickness of the composite particles varies from 2 to 13 nm as determined by means of electron holography. The calcium phosphate−gelatin nanocomposites obtained by the precipitation reactions were investigated for use as dentine repair materials with a special focus on the closing of open tubuli of sensitive tooth necks.