Synthesis of hydroxyapatite (HAp) and microwave assisted TiO2-HAp composite coating on Commercially pure (CP)-Titanium for biomedical applications

Abstract

Hydroxyapatite (HAp) is an important bioceramic material widely used for many biomedical applications owing to its similarity to the inorganic composition of bone. Hydroxyapatite was synthesized by using wet precipitation method using calcium nitrate and diammonium hydrogen phosphate as a precursor. To maintain a constant pH, ammonium hydroxide solution was used. After synthesis, HAp samples were calcined at 850 °C and 1200 °C, for 2 hours, and allowed to cool at room temperature. The synthesized HAp and calcined HAp samples were characterized by X-ray diffraction (XRD), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscope (SEM), and transmission electron microscopy (TEM). Zeta potential test was performed and its values were found to be between -14.7 mV and -15.7 mV. The result inferred that hydroxyapatite particles would get precipitated in a short span of time and, not stable in colloidal solution. Dynamic light scattering (DLS) was also used to determine particle size distribution. The z-average diameter of particles was found to range from 400 nm to 457 nm. Transmission electron microscopy (TEM) result confirmed that calcined
HAp (1200°C) has the largest particle size and synthesized HAp has the smallest particle size. After synthesis of HAp, microwave (MW) has been used as a substitutive method for HAp-based composite coatings on commercially pure (CP) titanium substrate. This is performed to enhance the bioactivity which is an important property for biomedical implants. The coating was made by microwave processing of CP-Ti packed in HAp at moderately higher microwave power. The composition of coating demonstrates TiO2 as a major phase (which was formed due to oxidation) along with HAp as a minor phase. Synthesized HAp and calcined (850 °C) HAp coating on CP-Ti were performed and characterized. The XRD and SEM results confirmed the presence of TiO2 and HAp on the CP-Ti specimens. The coated samples showed improved mechanical and biological performances. Microhardness of CP-Ti specimens increased after microwave processing, as the microhardness values of uncoated, synthesized HAp coated, and calcined (at 850 °C) HAp coated CP-Ti samples are 172.64 HV, 192.1 HV, and 192.45 HV respectively.
Hence the studied showed that TiO2-HAp coated CP-Ti specimens has significant potential in a biomedical application with improved bioactive properties.