The Fabrication And Characterization Of Biomedical (HA+β-TCP)/Mg-Ca Composite

Magnesium alloy and calcium phosphate-based bioceramics （HA、β-TCP） are ideal bonetissue substitutes. But the application for bone regeneration of them is limited because of fastdegradation rate of magnesium alloy and lower strength and ductibility of HA+β-TCP. thispaper is to construct composite system of Mg-1Ca（after abbreviated as Mg-Ca） andHA+β-TCP with combining advantages of both Magnesium alloy and porous bioceramics, inorder to provide with instructional principles and experimental basis for the design anddevelopment of new biomedical bone tissue engineering materials.Firstly, the β-TCP and HA powder used in this experiment were synthesized by wetchemical precipitation menthod. Porous bioceramics （β-TCP、35HA+β-TCP、60HA+β-TCP、85HA+β-TCP and HA） were fabricated using polymeric sponge. Secondly, Mg-Ca andporous ceramics composite system（β-TCP/Mg-Ca、（35HA+β-TCP）/Mg-Ca、（60HA+β-TCP）/Mg-Ca、（85HA+β-TCP）/Mg-Ca、HA/Mg-Ca）were prepared by suctioncasting technique. The phase，microstructure，mechanical properties and corrosion behaviorsof powder of β-TCP and HA、porous ceramics as well as the composite have been evaluatedby means of SEM，XRD，TEM、mechanical testing and immersion test in vitro, etc.The results of the study have indicated：the phase of β-TCP and HA after sintering wassingle and the dispersibility of the HA powder was greater than that of β-TCP. Polyurethanefoam、dispersing agent combined with binder have been completely broken down and thephase transformation of the β-TCP and HA was no existence in the whole process of thesintering. The strucutre of porous ceramic was three-dimensional open pores and the porosityof that was above90%. The ultimate compression strength of the porous β-TCP、35HA+β-TCP、60HA+β-TCP in combination with85HA+β-TCP was approximately0.05MPa，but that of the HA was about0.08MPa. With increasing immersion time，the Ca2+and P concentration in SBF gradually declined. There was a kind of new phase-HA appearedafter immering10d and20d of β-TCP. The prominent degradation of the porous HA+β-TCPscaffold was not observed by SEM.The major phases of the Mg-Ca alloy and the composite were Mg and Mg2Ca as well as Mg、Mg2Ca、β-TCP and HA, respectively. The ultimate compression strength of the Mg-Caalloy was about240MPa. The ultimate compressive strength of the β-TCP/Mg-Ca、（35HA+β-TCP）/Mg-Ca、（60HA+β-TCP）/Mg-Ca、（85HA+β-TCP）/Mg-Ca in combinationwith HA/Mg-Ca composite were107±13MPa、130±17MPa、79±22MPa、97±23MPa and68±25MPa, respectively. It concluded by comparing to these results of the compressivestrength that: the compressive strength of the composite was much more inferior than that ofthr matrix while composited between Magnesium alloy and porous ceramic，however， whichwas greater than that of the porous ceramic. The corrosion potential of the Mg-Ca alloy wasthe most negative （-1.89V）. Meanwhile, compared with five kinds of the composite, thecorrosion current of Mg-Ca alloy was the most highest, which indicated that the resitance tocorrosion of the composite was greater than that of the matrix. The improved corrosionproperty of the composite is possibly attributed to multiple-phase and protective corrosionproducts on the surface of the composite. After immering10and20days, the corrosionproduct of the Mg-Ca alloy mainly included Mg（OH）₂. But Mg（OH）₂、Ca₂（PO₄）₃incombination with HA were the main corrosion products of the composite. Additionally, in theentire process of the immering, the magnesium alloy was gradually degraded and porousscaffold was still observed using the SEM when the corrosion products on the surface of thecomposite were rinsed by CrO3. The porous scaffold is benifical to the proliferation anddifferentiation of the cells.