Study On Calcium Phosphorus Bioactive Coatings Prepared On C/C Composites By Hydrothermal Electrodeposition/Hydrothermal Method

C/C composites have been highlighted as promising artificial materials in orthopedics owing to their unique properties,such as low density,excellent biocompatibility,and high strength,toughness and corrosion resistance.In particular,they show the elastic modulus varying in the range of 5-80 GPa,very close to that of cortical bones,which may help to avoid stress shielding and sequential bone absorption.However,C/C composites are unable to form a chemical bond with host bones due to the lack of bioactivity.Thus,a bioactive hydroxyapatite(HA)coating should be applied onto the C/C composites to improve the integration of C/C implants with adjacent bones.Electrocrystallization is thought to be a convenient and effective technique for fabricating HA coatings on C/C composites.This unique method exhibited some advantages over alternative processes as follows: good flexibility and economy,the ability to form porous or complex shapes and the easiness to control coating composition and structure.However,direct deposition of hydroxyapatite(HA)coatings on carbon/carbon(C/C)composites through hydrothermal electrochemical deposition(HED)were limited by the poor bonding strength.To overcome this problem,HA coatings with high bonding strength were successfully prepared on C/C composites by two-step method using the combination of hydrothermal electrochemical deposition and post-hydrothermal method.The main research contents were as follows:(1)CaHPO4(monetite)coating was firstly deposited on C/C using HED,and then converted into HA coating in an alkaline solution by post-hydrothermal treatment.Effects of post-treatment temperatures on the chemical composition,structure,and bonding strength of the coatings were investigated.The results showed that monetite had a compact microstructure and could react with the solution to produce a well-crystallized HA.The post-treatment temperature possessed a remarkable influence on the composition and characteristic of HA coating.The diameter of rod-like crystals,the Si contents and the adhesive strength of the HA coatings were all increased when the post-hydrothermal temperature was changed from 110℃ to 140℃,and then decreased at 155℃.140℃ is determined to the optimal treatment temperature,at which the HA coating reached the highest critical load of 24.02 N,corresponding to the shear strength of 82.83 MPa.The bioactivity of the HA coating on C/C increased with the increasing post-treatment temperature.(2)In order to improve the mechanical properties of HA coating,we prepared a SiO2/HA composite coating and researched the morphology,microstructure,in-virto bioactivity and biocompatibility of it.Scratch and nano-indentation tests showed that this SiO2/HA composite coating presented an adhesive strength of a critical load of 31.63 N,and its modulus and hardness were 58.3 GPa and 2.93 GPa.In-vitro bioactivity and cell biocompatibility tests showed that the SiO2/HA coating could induce apatite growth and had superior abilities of cell attachment and cell proliferation to naked C/C and the HA coating.(3)The CaHPO4 preparation was simplified through the direct addition of H2O2 into the electrolyte,omitting the pre-treatment procedure of C/C.After the CaHPO4 coating was converted to a HA coating,the HA coating could arrive at a critical load of 29 N,nearly twice as high as the HA coating on the directly treated C/C by H2O2 instead of the H2O2 addition to the electrolyte.And the HA coating had a better bioactivity and cell biocompatibility than that without the H2O2 addition.