Preparation And Properties Of HA/β-TCP Scaffolds With Unidirectional Pore Structure

Biphasic calcium phosphate bioceramics(BCP)is a kind of bone repair materials composed of hydroxyapatite(HA)andβ-tricalcium phosphate(β-TCP)in different proportions,having excellent biocompatibility,biological activity osteo-conductive and osteoinductive properties.The preparation of porous HA/β-TCP biphasic scaffolds with high porosity,high interconnection rate and high compressive strength has become an important field in the research of bone scaffold materials.In this study,calcium deficiency HA whiskers were used as the main raw materials,and HA/β-TCP biphasic calcium phosphate bioceramics were formed in situ according to the behaviour of the phase transformation at high temperature.The BCP scaffolds with controlled directional pore structure was prepared here by a vacuum freeze-drying technology,which could provide a good basis and theoretical basis to overcome the problem between the high porosity,low connectivity and low mechanical properties for the traditional bioceramic scaffold materials,also to the preparation of the self-reinforced preparation of bone scaffolds.In this paper,HA whiskers and HA powders were prepared by hydrothermalmethod and homogeneous co-precipitation.The water was used as a pore-forming agent,and the calcium-deficient HA whiskers were used as the base materials.the aqueous slurry was prepared by mixing HA whishers and HA powders,together with bioglass,dispersant,binder and coagulating modifier.The HA/β-TCP biphasic ceramic adding material with a porosity of 82.84%,a compressive strength of about0.79 MPa and a large number of interconnected macroscopic columnar structures were obtained when the initial freezing temperature was-16 ~oC,the freezing rate was1 ~oC/min,the freezing temperature was-50 ~oC,the firing temperature was 950 ~oC,the firing time was 30 min.It was found that sodium polyacrylate could greatly improve the dispersion performance of the whiskers and their suspension stability due to the electrostatic repulsion and steric hindrance effect caused by the reaction of sodium polyacrylate with the HA slurry,furthermore showing a good pore formation performance.Sodium carboxymethyl cellulose has little effect on the viscosity of the slurry,which can improve the suspension stability of the slurry and show a good pore formation behaviour.Ethanol could reduce the freezing point of HA slurry,decreasing the number of ice nucleation nucleation and accelerating the growth of ice crystals,effectively improving the pore size and porosity of the scaffold materials.The calcination systems mainly affected the phase composition,physical and mechanical properties of the materials.It was found that the pore size of the scaffolds decreased with the increase of firing temperature and duaration time,the porosity decreased and the compressive strength increased.When the calcination temperature was 800°C and duration time was 30 min,HA began to tranceform toβ-TCP.When the temperature was higher than 850°C,the transformation of HA intoβ-TCP was acccerlaerated.The addition of bioglass in the selected HA slurry system not only affected the compressive strength and shrinkage of scaffold materials,but also promoted the transformation of HA toβ-TCP.Its appropriate dosage should be less than 25%.The addition of Mg and Zn could also promote the transition from HA toβ-TCP when using Mg and Zn doped whiskers to prepare the scallfods.The morphology,pore structure and phase composition of the obtained scaffolds were analyzed by XRD,FTIR and SEM.It was found that the preparation conditions of high porosity,high interconnection rate and suitable compressive strength were as follows:Sodium polyacrylate sodium content of 0.075%,sodium carboxymethyl cellulose 0.5%,ethanol 6%,bio-glass 25%,the initial freezing temperature of-16 ~oC,freezing rate of 1 ~oC/min,the freezing temperature of-50 ~oC,the firing temperature of850~950 ~oC,the firing time of 30~60 minutes.