| Carbon/carbon(C/C)composites have good corrosion resistance and biocompatibility.Their elastic modulus is similar to that of human bone.When used as a biomedical material,it can effectively avoid stress shielding effects and bone resorption,which endows them alternative materials for repairing hard bone.However,as a kind of carbon material,C/C composite materials are still inert in nature and lack a necessary biological activity,leading their difficulty in establishing efficient chemical bonding and tissue connection with human bones.There is also a hidden danger of "dark skin effect” about C/C composites.To deal with these issues,the bioactive hydroxyapatite(HA)coatings were prepared on the surface of C/C composites,which can form chemical bonds with soft and hard tissues,and in the meantime prevent carbon particles from abrading and releasing,effectively improving biological activity and the clinical applicability of C/C composites.Ultrasonic hydrothermal electrodeposition/hydrothermal method is a new method for preparing HA-C/C composite materials.This method is simple and controllable,suitable for complex substrates.The resultant coating is could be dense and uniform,and also provides a highly adhesion of HA on C/C.However,natural bone apatite is generally doped with ions,such as sodium,strontium,fluorine,and carbonate.These trace elements play an important role in adjusting the structure and performance of HA.Among them,the content of sodium in bone apatite ranks third,which affects the mechanical and biological properties of bone apatite.Therefore,it is considered to conduct research on doping sodium ions into HA lattice with aid of the ultrasonic hydrothermal deposition/hydrothermal processes,and strive to further improve the bonding strength between HA coating and C / C substrate,and simultaneously enhance the osteoinductive biological activity of this composite material.In this paper,a high-strength HA coating was successfully prepared on the surface of C/C composites by ultrasonic hydrothermal electrodeposition/hydrothermal method.Then,the HA coating was further converted into sodium-doped HA coating by a secondary hydrothermal method using Na OH solution.The main research contents are as follows:Firstly,a precursor calcium phosphate coating was prepared on the C/C surface by ultrasonic hydrothermal electrochemical deposition method,and then hydrothermally converted into an HA coating by ammonia solution.The effects of different deposition temperatures on the composition,morphology,bonding strength and biological activity of the coating were explored.The results show that the deposition temperature mainly affects the composition of the precursor,At 80 ?and90 ?,the prepared precursor coatings were composed of Monetite phase and a small amount of Brushite phase,and at 100 ?,and 110 ?,the coatings consist of single-phase Monetite.Except for the loose arrangement of the coating at 80 ?,the coatings prepared at other temperatures are dense and uniform,and the bonding strength of the coating on the substrate shows a tendency of increasing first and then decreasing with the increase in the deposition temperature.At 90 ?,the as-converted HA coating reached the maximum critical load of 34.46 N.In addition,the other HA coatings showed no significant difference in vitro induction activityIn order to further improve the mechanical properties and biological activity of HA-C/C,we prepared a sodium-doped Na-HA-C/C coating,and the effects of different Na OH hydrothermal temperatures and different Na OH hydrothermal concentrations on the morphology,mechanical properties and in vitro biological activity of the coatings were investigated.The results show that with the increase in Na OH hydrothermal temperature,the bonding strength and the Vickers hardness of the coating gradually increase.During hydrothermal treatment at 155 ?,the critical load of the HA coating was 43.16 N,and the Vickers hardness was 212.5 HV,which were 25.2% and 46.5% higher than those without sodium,respectively.The increment of bone-like apatiteis at seventh day was 2.56 times that of untreated HA.When studying the effect of different hydrothermal concentrations,it was found that the bonding strength,the Vickers hardness and modulus of the coating showed a tendency in decreasing first and then increasing with the increase of the hydrothermal concentration.When the Na OH is 10 M,the critical load of the coating can reach42.68 N,which is 23.9% higher than that without sodium,and its hardness and elastic modulus are the largest 5.5 GPa and 9.22 GPa,respectively.In addition,the HA coating has the lower corrosion current density and the largest amount of bone apatite induction,which indicates that the coating has good corrosion resistance and excellent in-vitro osteoinductive activity.In generally,compared with the non-sodium doped HA coating,the proper introduction of sodium into HA can effectively improve the hardness,elastic modulus,bonding strength,corrosion resistance and in vitro osteoinductive activity of the HA coating.Among them,the higher Na OH hydrothermal temperature(155 ?)and hydrothermal concentration(10 M)are conducive to increase of the diffusion of sodium in HA,and promote the mechanical properties and biological activity. |
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