Fabrication And Property Of Hydroxyapatite And Its Composites Used In Bone Tissue Engineering

According to the structure and characteristics of natural bone,porous hydroxyapatite(HA)biomaterial used in bone tissue engineering was prepared. Hydroxyapatite/poly lactic-co-glycolic acid(HA/PLGA)and PLGA-HA-TiO₂ composites were prepared by gel-casting and cold pressing-solidifying,respectively. Results are shown as follows:1.The hole size and connectivity of porous HA ceramic prepared by adding sole PVB are small and bad.This structure will be difficult to be casted by PLGA gel.2.Relative density of HA are affected by sintering processing.The appropriate sintering condition of porous HA is at 1200℃for 4 h.And the main phase of the bulk is HA after sintering.While the volume fraction of(NH₄)₂CO₃ increases,the compressing strength and modulus of elasticity of HA decrease.Containing 10vol.%PVB,15vol.%(NH₄)₂CO₃ and 25vol.%NH₄HCO₃,the material has preferable structure with good hole connectivity and distribution.Its big hole size is over 100μm and the small hole size is in the range from 5μm to 50μm,which is favorable for cell and tissue growing and alimentation transporting.The porosity and compressing strength of HA reached 50.3%and 4.44 MPa,respectively. Modulus of elasticity of HA is near to that of natural bone.3.The influences of concentration,time,temperature and PH value on the viscosity of the PLGA sol are rather obvious.When the concentration of PLGA is under 50g/L, the viscosity of the sol changes a little with time and temperature(＜50℃),but it increases quickly above 50℃.For the concentration of PLGA over 50g/L,the viscosity of the sol falls with time prolonging and temperature increasing(＜40℃), but it rises rapidly when the temperature is over 40℃.The higher the PH value is, the bigger viscosity of the sol is.4.Modulus of elasticity of the HA/PLGA composites prepared by gel-casting approaches that of natural bone.This indicates that the composite may be used in the bone tissue replacing and grafting in the future.The viscosity of the sol increases with the increase of the concentration of PLGA.It is appropriate for the viscosity of the sol with 25.SmPa·S to fill in the holes of HA.In the acidic condition,the sol is easy to fill in the holes with the decrease of the PH value. However,when PH value is lower than 4.289,the filling effect is bad.5.PLGA-HA-TiO₂ composites were successfully prepared by cold pressing and solidifying.The solidification temperature of PLGA increases with the addition of HA or TiO₂.The composites with appropriate contents of 25 wt.%HA and 2.5 wt.%TiO₂ have excellent strength accompanied with good plasticity.HA content less than 50wt.%hasn't any effect on the degradation rate of the composite in SBF, otherwise its degradation rate will be accelerated.Apatite is formed on the surface of PLGA-HA composites immersed in SBF,which shows the composites have good bioactivity in vitro.