B-type carbonate apatite (CO3Ap) block may be an ideal artificial bone substitute because it is closer in chemical composition to bone mineral. In the present study, the feasibility to fabricate CO3Ap blocks was investigated using compositional transformation, which was based on the dissolution-precipitation reaction of a gypsum-calcite composite with freemolding behavior. For the compositional change, or phosphorization, gypsum-calcite composites of varying CaCO3 contents were immersed in 1 mol/L (NH4)3PO4 aqueous solution at 100°C for 24 hours. No macroscopic changes were found after the treatment, whereas microscopic change was observed at SEM level. X-ray diffraction, Fourier transform infrared spectroscopy and CHN analysis indicated that the composites were B-type CO3Ap containing approximately 6 -7 wt% of CO3, a value similar to that of biological bone apatite. Diametral tensile strength of the CO3Ap block was approximately 1-3 MPa. Based on the results obtained, it was therefore concluded that gypsum-calcite was a good candidate for the fabrication of CO3Ap blocks, coupled with the advantage that the composite can be molded to any shape by virtue of the setting property of gypsum.
Authors' Contribution QJ and SBR conceived and designed the study and wrote the article. QJ and MI collected the specimens and identified them. SBR and SU made the altitude maps. MA, FZ and QZ helped in acquisition of data and edited the manuscript
Silicon-substituted hydroxyapatite (Si-HAP) foam may be an ideal bone substitute since Si-HAP has stimulating effect for bone formation and the foam morphology provides interconnected macro porous structure which is ideal for bone formation. However, lower temperature was reported to be required for the fabrication of pure Si-HAP whereas higher temperature was required for the fabrication of HAP foam. In the present investigation, three calcium silicate compounds (CaSiO 3 , wollastonite; Ca 2 SiO 4 , belite; Ca 3 SiO 5 , alite) were evaluated for their feasibility as a silicon source for the fabrication of Si-HAP foam. Sintering temperature at 1300°C resulted in a very weak HAP foam, whereas sintering at 1400°C resulted in HAP foam with improved compressive strength up to approximately 9 kPa. XRD analysis showed the appearance of a secondary phase, a-tricalcium phosphate, when wollastonite was used as the silicon source. In contrast, pure Si-HAP phase was obtained when belite or alite was used as the silicon source. The porosities of the Si-HAP foams were approximately 95 regardless of composition of the foam. We therefore concluded that Si-HAP foam with fully interconnecting pores could be fabricated when belite or alite was used as the silicon source. Further evaluation is expected based on this initial finding.
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