Study On The Fabrication And Properties Of Carbon Nanotubes Reinforced Hydroxyapatite Composites

Hydroxyapatite?HA?has attracted worldwide attention as an ideal hard tissue implant material due to its excellent biocompatibility,osteoconductivity and bioactivity.However,pure HA is characterized by poor mechanical performance and low reliability,especially the high brittleness.These intrinsic mechanical defects hinder its direct clinical applications under load-bearing conditions.Since the discovery of carbon nanotubes?CNTs?by Iijima,CNTs have proven to be regarded as ideal reinforcement materials in composites.CNTs can significantly improve the mechanical and physical properties of the matrix material in composites;the improved properties can be attributed to the extraordinary strength and toughness,and their excellent electrical,thermal and magnetic properties.Thus,some researchers have explored CNTs reinforced HA composite,and the CNTs in the matrix is expected to display well reinforcement efficiency in the extraordinary strength and toughness.Unfortunately,to date the properties of the CNTs/HA composite has not yet made great breakthrough,particularly in the mechanical properties and biocompatibility.Thus,there is great significance to investigate the fabrication process and properties of the CNTs/HA composite further.In order to improve the mechanical properties and biocompatibility of the CNTs/HA composite,a double in-situ synthesis process for the CNTs/HA composite was designed and realized.The processes to synthesize CNTs/HA in-situ composite powders by chemical vapor deposition?CVD?and further synthesize hydroxyapatite-encapsulated carbon nanotubes?CNTs@HA?composite powders by a sol-gel method were studied in this paper.The mechanical properties and biocompatibility of the CNTs/HA composites fabricated by the powder metallurgy method were investigated.The study on the CNTs/HA in-situ composite powders synthesized by CVD method showed that,under the conditions that Fe is applied as catalyst,the synthesized time is 1h at700^oC,and the ratio of Ar to C₂H₂ is 7:1,CNTs synthesized within the HA matrix display a high degree of graphitization and homogeneous dispersion.And the molecular-level mixture was obtained between the CNTs and HA nanoparticles.Based on this,the study on the synthesized CNTs@HA in-situ composite powders indicated that,a thin layer of HA was deposited in-situ onto the surface of the as-grown CNTs by a sol-gel method.Meanwhile,by controlling the amount of as-grown CNTs/HA composite powders during the sol-gel process,the morphology and structure of the formed HA layer can be adjusted.The thickness of the formed HA layer on the surface of the CNTs decreases when the content of CNTs/HA composite powders increases in the modified system.The CNTs/HA bulk composite was prepared by the powder metallurgy method?cold pressing and sintering?using the double in-situ synthesized CNTs@HA composite powders as raw materials.The tests of mechanical properties show that the flexural strength of the double in-situ synthesized CNTs/HA composite is prior to that of pure HA and the commercial and in-situ synthesized CNTs/HA composites under the same content of CNTs.With the addition of 3wt.%CNTs,the flexural strength of the three kinds of composites reachs the maximum.The results of vitro cell toxicity culture tests show that the pure HA and the double in-situ synthesized CNTs/HA composite have no obvious cytotoxicity and exhibit good biocompatibility.