Research On Preparation Of C-Si-Al₂O₃-nHA Composite Coatings On CF Surface And CF Reinforcing Hydroxyapatite Composites

Carbon fiber?CF?reinforced hydroxyapatite?HA?composites?CF/HA?have broad clinical application prospects in the field of bone tissue repair.However,CF can produce oxidative damage due to the lower oxidation resistance of CF and the dehydroxylation of HA matrix during preparation process of CF/HA.In addition,there are significant differences in thermal expansion coefficient and surface chemistry property between CF and HA.These seriously weaken the interface bonding strength between CF and HA matrix.The toughning effect of CF on HA and the biomechanical properties of composites have not reached the theoretical level,which limits its clinical application in human load-bearing area.In order to solve the above problems,a multi-functional C-Si-Al₂O₃-nHA composite coating was fabricated on the CF surface.The coating is capable of sintering protection for CF and matching the thermal expansion coefficient of CF to HA matrix.CF/C-Si-Al₂O₃-nHA/HA biocomposites were prepared by a process of pressureless and hot-pressing sintering.At the same time,the toughness mechanism of C-Si-Al₂O₃-CF to HA matrix was investigated.The main research contents are listed as follows:?1?A porous Al₂O₃ was prepared by anodic oxidation.The effects of oxidation process on its microstructure,surface wettability and roughness were investigated.It was shown that the uniformity of pore distribution,surface wettability and roughness of Al₂O₃ increased remarkably with the increase of current density and time.At a current density of 7 mA/cm² and oxidation time of4 h,Al₂O₃ exhibited uniform pores and good surface wettability.Then,the bioactive HA coating was deposited on the surface of porous Al₂O₃ by hydrothermal synthesis.With the increasing of hydrothermal temperature and time,the nano sheet-like HA crystal transformed into nanorod-like structure.Furthermore,the bonding strength between HA coating and porous Al₂O₃increased gradually.At the hydrothermal temperature of 180°C and time of 24h,the length of nanorod-like HA crystal ranged from 5?m to 10?m,witn the diameter from 80 nm to 100 nm,respectively.The bonding strength of HA coating to Al₂O₃ substrate reached 18.3±2.4 MPa.Meanwhile,SBF soaking experiments showed that HA-coated Al₂O₃ had good biological activity by inducing the formation of bone-like apatite layer in vitro.?2?A precursor gradient C-Si-Al coating was deposited on the surface of modified CF by magnetron sputtering.The microstructure and thickness of the coating prepared under different sputtering powers were investigated.The effect of C-Si-Al coating on the mechanical properties of CF was explored.At sputtering power of 150 W,a uniform and dense C-Si-Al coating with a thickness of about 800 nm was deposited on the surface of CF.The C-Si-Al-CF maintained the excellent mechanical properties of CF with an average tensile strength of 3.14±0.31 GPa.The conversion of Al coating to Al₂O₃ coating was achieved by anodic oxidation and vacuum heat treatment.At the current density of 7 mA/cm² and the oxidation of was 20 min,A Al₂O₃ coating with uniform in thickness and grain size was achieved.The surface morphology of the coating was similar to that of porous honeycomb.Isothermal oxidation and thermal shock resistance experiments presented that C-Si-Al₂O₃-CF had excellent oxidation and thermal shock resistance in high temperature environment.In addition,bioactive nHA coating was prepared on the surface of C-Si-Al₂O₃-CF by electrochemical deposition.The results showed that with the increase of deposition time,the morphology of nHA coating changed in order of needle-like,flake-like and rod-like.The thickness and density of nHA coatings increased gradually.?3?The CF/C-Si-Al₂O₃-nHA/HA composites were prepared by pressureless and hot-pressing sintering.The effects of composite coating,sintering process on microstructure and mechanical properties of the composites were studied.It was observed that there were no oxidation pits on CF surface during CF/C-Si-Al₂O₃-nHA/HA prepared by pressureless sintering.CF was closely bonded to HA matrix.Moreover,compared to CF/HA composites,the flexural strength,elasticity modulus and fracture toughness of CF/C-Si-Al₂O₃-nHA/HA were increased by 20.78%,4.37%and 24.80%,respectively.The composites prepared by hot-pressing sintering represented more excellent mechanical properties,as its flexural strength,elasticity modulus were 93.16±3.73MPa?2.84±0.30GPa,with a fracture toughness of 2.11±0.07MPa·m^1/2and brittleness index of 2.40±0.07.The flexural strength and fracture toughness can be satisfied with human compact bone.The C-Si-Al₂O₃-nHA-CF reinforcement and CF/C-Si-Al₂O₃-nHA/HA biocomposites have excellent biomechanical compatibility.It lays a theoretical foundation for expanding the clinical application of CF/HA biocomposites in human load-bearing bone and has promising application in the field of bone defect repair as biomedical materials.