Preparation And Characterization Of The HA/MWNTs And HA/TiO₂ Nanotubes Composite Biomaterials

Hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂,HA) is the main inorganic component in natural bone and tooth.The synthetic form of HA has good biocompatibility and bioactivity,unfortunately,its mechanical properties including brittleness,low strength, flexural strength and fracture toughness all are lower than that of natural bone,which inhibits its clinical applications.Conducting HA coatings on biomedical titanium have been widely used for human hard tissue substitute materials,based on a combination of good mechanical properties of titanium and the excellent biological properties of HA.However,mismatch of the coefficient of thermal expansion of HA and Ti substrate may cause a residual stress,which reduced the bonding between the coating and substrate,and result in a failure of implantation in clinical application.TiO₂ nanotubes have good biological activity,corrosion resistance and wear resistance, therefore,the development of HA/TiO₂ nanotube composite reinforcements has an important clinical value,for improving toughening and strengthening the mechanical properties of HA coating.Calcium phosphate cement(CPC) is an important hard-tissue repair material,it has been widely applied in clinical practices.How to further improve the mechanical properties of CPC to resolve its mechanical problems, such as compressive strength and low bending strength,it still faces significant challenges.It is expected that the development of CPC/CNTs composite materials may be helpful to obtain fiber reinforced materials with excellent mechanical properties according to the unique mechanical properties of carbon nanotubes(CNTs), in which,the most concerned issue is the toxity and biosafety of the CPC/CNTs composites in medical application.In response to these key issues,in this thesis we prepared HA/TiO₂ nanotubes and HA /MWNTs composite reinforcements by hydrothermal reaction,in order to obtain hard tissue replacement materials and bone cement hard tissue repair materials with excellent mechanical properties.The main findings and progress are as follows: 1.The TiO₂ nanotubes powders with the diameter of 8-10 nm and the length of few microns were successfully prepared through hydrothermal synthesis,by using P-25 as raw materials,maintained solid-liquid ratio 1.5 g/140 mL,in 10 mol/L of NaOH solution for 48 h;2.The electrophoretic deposition method had been developed firstly to prepare a composite coating of HA/TiO₂ nanotubes,after calcined treatment 2 h at 700℃,the shear stress between prepared HA/TiO₂ composite coating and substrate titanium reached 32.97±2MPa(generally the shear stress between the HA coating and substrate is 19.82±3MPa),which closely to the bearing strength of human bones(35MPa).The load scratch test results showed that the binding increase by 2.3 times compared to the binding between the composite coating and Ti substrate to pure HA coating and Ti substrate.The effect of calcination temperature on the binding between the electrophoretic deposition coating and substrate was studied.It is revealed that it can effectively improve toughening and strengthening of the coatings when the calcination temperature is at 700℃;3.The chemical co-precipitation and hydrothermal post-processing were combined to achieve the preparation of HA/MWNTs composite in scale.It is revealed that the MWNTs are well coated with a dense nano-HA particles when the content of MWNTs is about 15%(by mass).After being calcinated at 700℃,the bonding between HA and MWNTs is further strengthened,a more dense and uniform HA film is obtained on the surface of MWNTs;4.The in vitro cell culture demonstrates that the prepared HA/MWNTs nano-composites with 15%(by mass) of MWNTs exhibit with no significant toxicity and show a good biocompatibility.