Síntese e caracterização de hidroxiapatita nanoestruturada produzida pelo método sol-gel usando água de coco para aplicações biomédicas

Abstract

Calcium phosphate-based ceramics are significant materials that are in study due to the wide biomedical application (orthopedic, bone defect healing, etc.). Among the phosphates, Hydroxyapatite (HAP) with chemical formula Ca10(PO4)6(OH)2 and hexagonal structure (P63/m space group), presents strong structural similarities with mineral constituents of human bones and teeth. Thanks to its excellent biocompatibility, osteointegration properties, HAP has received a great attention. Many methods are used for the HAP synthesis and the choice of a particular method and the synthesis parameters influenced the final morphological and structural characteristics of the final material. This work aims the investigation of the efficiency of a new route, proteic sol-gel method, that employs green coconut water as the main solvent for the precursor salts, instead of conventional metal alkoxides. The influence of the pH of the precursor solution and the temperatures of thermal treatment (600° to 900°C) were investigated. The reaction happened through the mixture of a solution containing Ca(NO3)2.4H2O (tetrahydrate calcium nitrate) in the solution of (NH4)2HPO4 (dibasic ammonium phosphate). The pH was controlled by addition of ammonium hydroxide (NH4OH). The sample characterizations were made by X-Ray powder Diffraction (XRD), Energy Dispersion X-ray Spectroscopy (EDXRF), Fourier Transformed Infrared spectroscopy (FT-IR), Raman Spectroscopy, Optical Absorption (OA) by Diffuse Reflectance and Scanning Electron Microscopy (SEM). XRD results showed that the pH of the precursor solution and the temperature of the thermal treatment influenced the HAP formation and slight differences in the relative intensity of main HAP peaks were observed, indicating the presence of carbonate ions as impurity. The crystallite size and the crystallinity degree of the studied samples grew as the temperature increased. EDXRF results show the elemental composition of samples, confirming the presence of contaminants, being K the main one, with mean concentration of 6%. The FT-IR spectrums confirmed the presence of the vibrational modes characteristic of the functional groups associated with the HAP and also the presence of carbonate group. Raman spectra show that both temperature and production method influence the Raman active modes of HAP. Optical studies using Optical Absorption (OA) show the absorption bands related to possible intrinsic defects in the hydroxyapatite. SEM images showed that HAP particle sizes are in the nanometric range, with dimensions under 100 nm, and there is a variation of the shape of the particles with different pHs.