Hydrothermal Synthesis And Degradation Study Of COB Made Of β-TCP/α-CSH

Background and ObjectiveThe characteristics of Self-setting and promoting of degradation and osteogeneration are the hot topics of the study of inorganic bone substitute materials.Porousβ- tricalcium phosphate(β-TCP) attained from market at present has better rate of osteogeneration,but its degradation is slow. Furthermore,it can not be self-setting and has not native porous structure of cancellous bone.Alpha calcium sulphate hemihydrate(α-CSH) can be self-seting, but its degradation is too quick.Combined bone graft(COB) can reserve the merits and overcome the deficients of the homogenous material.Therfore,we combinateβ-TCP andα-CSH to synthesize one COB granules,which have native porous structure of cancellous bone,characteristics of self-setting,and defferent degradation rate depended on the ratio of the two materials.This work attempts to develop a new type of COB granules made ofβ-TCP andα-CSH.The synthesis and subsequent deposition ofα-CSH on the inner surface of the pores of theβ-TCP was accomplished by the hydrothermal synthesis method.The degradation mechanism of the COB was investigated via both in vitro and vivo experiments. The obtained understanding was used to manipulate the processing parameters for synthesizing theβ-TCP/α-CSH composites.The ideal effect of bone defect repair was achieved through matching the degradation rate of the implanted bone substitute materials with that of the new bone growth.Materials and Methods1.The healthy bovine femurs was used as materials of makingβ-TCP granules.In order to explore the dynamic law of the transforming from hydroxyapatite(HA) toβ-TCP,the influence to transformation effects of the soaking the primary sintered bone with different concentration of amine phosphate dihydrogen or of different technologies to sinter the bovine cancellous bone were detected by X-ray diffraction(XRD) and scanning electron microscope(SEM).2.Theα-CSH is hydrothermal synthesized from calcium sulphate dehydrate (CSD) powder in a hydrothermal kettle under the special temperature and pressure, adding different ratio of aluminium sulfate and sodium citrate as a combined meta-crystal agent respectively.The composition ofα-CSH were detected by XRD, the crystal structures and particle size were observed by SEM,the influence factors and action mechanisms of the crystal structures and particle size were also analyzed.3.Observing the contribution of different technological parameters to growing up and distribution modes of the out of phase nucleation,thatα-CSH crystallize on the surface ofβ-TCP granules and controlling the poroity COB.XRD was used to detect the composition of the defferent COB,and SEM was used to observe the structure of the defferent COB.Porosity of the different COB were measured by press- mercury meter.4.Testing the setting time,setting strength in vitro after setting of the COB1 (β-TCP/α-CSH=70/30),COB2(β-TCP/α-CSH=50/50) and COB3(β-TCP/α-CSH= 30/70) at proper ratio of solid and liquid,and testing the composition of phases after setting with XRD,and observing the change of these COB section after setting with SEM.5.Prerare COB1,COB2 or COB3 into circular cylinder of 12mm high and 8mm dimeter,and put the cylinder into simulated body fluid to observe the change of the PH of the solution,strength and degradation ratio of the cylinder in vitro.6.Rabbits' bilateral distal femur were made each one bone defects(10×5mm), which was 4mm distance from the articular facet of distal femur.The defects were filled withα-CSH,β-TCP,COB1,COB2 or COB3 respectively,and the control was not filled any materials.Specimens of distal femoral were retrieved at 4,8,12 and 16 weeks after operation.The degradation and osteogeneration of the implant materials were observed and measured using X-ray,molybdenum target films, micro-CT,histology or histomorphometry respectively.The mechanism and infiuencial factors of degradation and osteogeneration of the implant materials were analyzed.Results and Conclusion1.High purity ofβ-TCP can be made by suitable sintering bovine cancellous bone two times.Combined bone graft can be synchronously hydrothermal synthesized by using CSD powder andβ-TCP granules.Reshaping the pore of theβ-TCP granules were carried out simultaneously when theα-CSH was synthesized synchronously on the surface of theβ-TCE Therefore,the pore structures of the COB can be controlled.It has yet been reported in literatures up to now.2.the COB granules have inter-connective micro-pore and maropore structures of native cancellous bone,and the porosity is about 50%.3.The COB has good performance of self-setting in situ,the strength of setting is near to cancellous bone which can meet the need of repairing the defect in the location of non-weight loading.4.The experiments in vivo and vitro shows that the ratio of degradation of COB is between theα-CSH andβ-TCE the degredation rate can be regulated by adjusting the composition ratio of theα-CSH andβ-TCE The COB2(β-TCP/α-CSH = 50/50 ) is the best materials of the three COB.5.The bone formation of combined bone graft is evident in the contained bone defect,and the ability of bone formation is better thanα-CSH andβ-TCP.6.The COB can attain ideal repair of bone defect because its degradation rate is match with the new bone formation rate in bone defect and it can be totally replaced by new bone ultimately.