Preparation And Property Characterizations Of Hydroxyapatite/Pure Metal (Ti, Fe, Mn)Biocomposites

As a kind of ideal bone graft substitute material, hydroxyapatite (HAp) has been received widespread concerns, since the major inorganic composition of HAp is quite similar to that of human hard tissues, However, due to its limited bioactivity and poor mechanical properties, the practical applications of HAp in medicine are still greatly restricted. In view of this, in the present work, the HAp/Ti, HAp/Fe and HAp/Mn biocomposites were synthesized by sintering the powders of HAp mixed directly with pure metals like Ti, Fe and Mn, respectively, with the purpose of improving the bioactivity and mechanical properties of pure HAp. The phase compositions and properties of those synthesized biocomposites were systematically characterized by means of X-ray diffraction (XRD) analyses, in vitro bioactivity assessments, mechanical compressive tests and etc.HAp/Ti biocomposites containing different volumes of Ti (30,50and70vol.%) were prepared by cold pressing the mixed powders of HAp and Ti, and subsequently subject to vacuum sintering at1000℃. It is found that the addition of Ti within a certain volume fraction can effectively reduce the decomposition temperature of HAp, promoting its decomposition. With increasing the amount of Ti, the degree of HAp decomposition becomes firstly increased (as vol.%Ti≤50%), and then decreased (as vol.%Ti=50%). For the HAp-50vol.%Ti composite, the decomposition of HAp is the most remarkable under the action of Ti, and the major phase compositions of the sintered composite sample consist of Ca4O(PO4)2, CaO, TiP and Ti. The in vitro bioactivity assessments show that all the HAp/Ti biocomposites exhibit bioactivity, to a certain extent, particularly for the case of the HAp-50vol.%Ti biocomposite. For example, the ball-like apatite sediments have already appeared on the surface of the HAp-50vol.%Ti sample after it was soaked in the stimulated body fluid (SBF) solution just for24hrs. As the soaking time is increased up to168hrs, the formed bone-like apatite layer becomes more condensed. The deposition of apatite layer is influenced by the product of HAp decomposition, which could provide a lot of Ca2+and P5+, as well as by the Ti-OH groups induced with the reaction of Ti and SBF solution, which provide effective locations for the nucleation of apatite. The uniaxial compression tests show that the ultimate compressive strength of HAp/Ti composites is closely related to the soaking period of time for the material in SBF solution, For the HAp-50vol.%Ti biocomposite, the compressive strength increases firstly and then decreases with the change of soaking time, while the compressive strength of HAp-70vol.%Ti becomes decreased gradually with increasing soaking time.The same method was employed to prepare the HAp-50vol.%reduced Fe, HAp-50vol.%pure Fe and HAp-50vol.%Mn composites. XRD analyses on the sintered samples demonstrate that the reduced Fe, pure Fe and Mn could all promote the HAp decomposition. The major phase compositions of the sintered HAp-50vol.%reduced Fe composite sample consist of Ca10(PO4)6(OH)2, Fe, CaO and Fe2O3, and for the HAp-50vol.%pure Fe sample, Ca8.86(PO4)2(H2O)2and Fe, while the major phase compositions of HAp-50vol.%Mn composite sample are Ca2Mn(PO4)2(H2O)2, Mn2P and MnO. The in vitro bioactivity assessments indicate that all of them present bioactivity, to a certain extent. HAp-50vol.%reduced Fe composites possess somewhat better in vitro bioactivity if compared with HAp-50vol.%pure Fe composites, just judging from the situations of deposited apatite layer. The uniaxial compression tests demonstrate that, after both HAp-50vol.%reduced Fe composites and HAp-50vol.%pure Fe composites were immersed in the SBF solution for different periods of time, their compressive strength becomes increased firstly and then decreased. and the maximum compressive strength are, respectively,73.5MPa and104.2MPa, as the soaking time is reached to120hrs. However, for the HAp-50vol.%Mn composite, its compressive strength all keeps at the level of120MPa after immersing in the SBF solution for different times, which is somewhat higher than that (～100MPa) of sintered sample, and also higher than the relevant values of the HAp/Ti biocomposites.