Microwave Assisted Synthesis of Hydroxyapatite Reinforced with Carbon Nanotubes for Load Bearing Orthopedic Application

Abstract

In this work bioactive hydroxyapatite Ca10(PO4)6(OH)2 was synthesized which is chemically and structurally similar to mineral phase of natural bone and it can also form direct chemical bonds with the hard tissues of the body. Microwaves were used to assist in the synthesis in order to augment the reaction rate and institute energy saving. Ceramic powder was synthesized in presence of microwaves both by wet precipitation and solid state reaction. Exposure time and microwave power were varied to investigate their effect on the stoichiometry and crystallinity and thermal stability of product powder. Wet precipitation was carried out by refluxing the solution of precursors under microwave radiation. Hydroxyapatite (HA) produced in this manner is weak in strength and toughness and is only used in non load bearing orthopedic applications; main focus of this research was to improve the strength and toughness of hydroxyapatite by reinforcing it with multiwall carbon nanotubes without affecting its bioactivity. Carbon nanotubes (CNTs) were acid treated in microwaves to functionalize them by attaching carboxyl groups. In situ synthesis of Hydroxyapatite in CNTs was performed by wet precipitation. XRD shows the phase purity and crystallinity, FTIR spectroscopy indicates the fucntionalization of CNTs and SEM analysis depicts the nanomorphology of powder.Thermal endurance of synthesized hydroxyapatite and composite was investigated by TGA, which showed that CNTs retained at higher temperature in Nitrogen environment while they get oxidized in air at that temperature range. Vicker hardness tests performed shows that hardness of composite is higher than pure HA and its value increases with the increase in CNT contents and it was also observed that hardness increases initially with sintering time then declines due to excessive grain growth.