Carbon Nanotubes Reinforced CaP Bioactive Composite Coating

Calcium phosphate(CaP)coated carbon/carbon(C/C)composites have good biological activity,high mechanical properties,and excellent biocompatibility,which make them to be potential medical bone implant material.The weak adhesion between CaP and C/C composite substrates and the poor biological stability restrict their application in clinical medicine.In order to achieve improved biological stability and adhesion strength between CaP and C/C composite substrates,the pulse effect and different deposition process were employed to achieve pleomorphic CaP coatings.CaP based coatings reinforced by the well-dispersion CNTs were prepared by combination of electrophoretic deposition,chemical vapor deposition(CVD),pulsed electrochemical deposition and biominerazation.The phase composition and microstructure of CNTs reinforced CaP coatings were analysed;the adhesion strength,bioactivity and electrochenmical stability were investigated;the reninforcement mechanisms of CNTs were researched.Mg and Sr were introduced into the CaP coatings to obtain Mg and Sr codoped CaP coatings,the microstructure and bioactivity of coatings were analysed;the co-doped mechanism of Mg and Sr was researched.The main contents and coclusions are listed as follows:Study on the morohologies control of the CaP coatings.The pulse duty ratio,deposition voltage,deposition temperature and electrolyte concentration were adjusted to obtain nanoscale needle,phosphor shaped,flower shaped,spherical and belt shaped HA coatings,microscale plant shaped and block shaped DCPD coatings.The microstructures and components were investigated.The results show that the deposition efficiency of the coatings is increased after the introduction of the pulse effect,and the coatings is more uniform,compact and smooth.The increasing deposition voltage can achieve the CaP coatings with nanoscale belt shaped to flower shaped to spherical structures;The increasing deposition temperature can achieve the CaP coatings with nanoscale phosphor shaped to spherical to belt shaped structures;The increasing concentration of electrolyte can achieve the transformation from nanoscale belt shaped HA to microscale plant shaped DCPD to microscale block shaped DCPD coating.Study on the bioactivity and adhesion strength of CaP coatings with C/C composite substrates.The bioacitivities of HA coatings with different morphological are as follows:spherical HA>phosphor shaped HA>belt shaped HA>flower shaped HA>needle shaped HA;The adhesion strengthes of HA coatings with different morphologies are shown as follows:needle shaped HA>spherical HA>flower shaped HA>belt shaped HA>phosphorus shaped HA.Electrophoretic deposition and combination electrophoresis and pulsed electrochemical deposition were applied to prepare CNTs reinforced CaP composite coatings.After the carboxylated CNTs integrated with CaP,the composite was deposited by synchronous electrophoretic deposition,which successfully achieved the CNTs reinforced CaP(CNTs/CaP)composite coating.Results showed that,the shortage was that the content and dispersion of CNTs in the CaP coating was difficult to control.Firstly,a 3D porous layer of CNTs was performed on C/C compostite substrates by electrophoretic deposition.Secondly,the pulsed electrochemical deposition was applied to infiltrate the porous preform with the CaP.Results show that,the content of CNTs in the CaP coatings can be controlled accurately by this method.The only crystalline phase HA adhered or coated with CNTs,which achieves the uniform dispersion of CNTs in HA coatings and improves the easy entangling of CNTs.Introducing 0.2wt%of CNTs in HA coatings,the adhesion strength was increased by 41%.The network structure of CNTs,the good interface binding of HA and CNTs and mechanical bonding between CNTs and C/C composite substrate can realize the effective transferof external load to CNTs.Moreover,the pullout and bridging mechanism of CNTs in HA coatings are the key to improve the adhesion strength of HA coatings.Combination of CVD and pulsed electrochenmical deposition methods or biomineralization were employed to prepared CNTs reinforced CaP composite coatings.After a porous layer of CNTs were deposited on C/C composite by CVD,these materials were used as substrates for synthesing CaP coating by pulsed electrochemical deposition or biomineralization.Results showed that,the in-situ CNTs were with free growth orientation and the CaP grains grown on the surface of CNTs,which achieved a dense structure and good bonding of CNTs/CaP;The CaP and Fe catalyst were obtained by pulsed electrochemical deposition,followed by the in situ ICVD synthesis of CNT.Results showed that,CNTs was inserted into HA coating,which formed a good interfacial bonding between them;CaP coated CNTs with a good interface bonding between them,which achieved the improving dispersion of CNTs in CaP and enchancing adhesion strength.The adhesion strength of CNTs/CaP composite coatings by introducting CNTs in CaP coatings were improved by 73%.The reinforcement mechanisms of CNTs including CNTs pull-out,bridging,good interface bonding between CNTs and CaP,a direct chemical combination CNTs and C/C composite substrates played an extremely important role in the enhancing and toughening effect.Study on the bioactivity of CNTs/CaP composite coating in vitro.The bioactivity activity of the coating was evaluated by immersing the SBF solution with different days.The morphologies,the molar ratio of Ca to P and weight change of coatings were analysied to be the standards.Results showed that,after introducing of CNTs,the bioacitivity of composite coatings were not decreased.Study on Mg and Sr co-doped CaP coating.Mg and Sr co-doped DCPD and HA coatings were prepared by pulsed electrochemical deposition.Results showed that,the existence of Mg and Sr elements prolonged the dissolution duration and decreased the nucleation rate of bone-like apatite;Mg was prior to Sr replacing Ca of HA when they coexisted in the electrolyte;Mg element preferred to replace Ca of HA with Ca_?position,Sr element preferred to replace the Ca of HA with Ca_?position in the structure and the replace position of Mg and Sr did not change with the content of elements.