Investigated in this study are the changes in structure and properties of a tetracalcium phosphate/dicalcium phosphate anhydrous/calcium sulfate hemihydrate (TTCP/DCPA/CSH) cement immersed in Hanks' solution. Experimental results show that the phase transition involving the hydration of CSH and formation of calcium sulfate dihydrate (CSD) continues up to 7 d of immersion. The phase transition from TTCP/ DCPA to hydroxyapatite (HA) is substantially completed after 14 d; after that, both CSH and CSD phase largely diminished, whereas HA becomes and remains to be the only dominant phase throughout 42 d of immersion. A maximum compressive strength is reached; after that, the cement gradually decreases in strength. After 42 d, its CS value is down to 8 MPa. The long-term pH value of the Hanks' solution wherein the cement is immersed remains in the range between 5.4 and 7.0. The cytotoxicity test reveals that the viability value of the cells incubated with conditioned medium of cement extraction is 85% that of Al 2 O 3 control and 84% that of blank medium for an extraction ratio of 0.2; and 90% that of Al 2 O 3 control and 93% that of blank medium for an extraction ratio of 0.1.
This research was devoted to the investigation of changes in structure and properties of a calcium sulfate hemihydrates (CSH) cement immersed in Hanks' solution for different periods of time. XRD patterns indicated a quick phase change (a hydration process) of CSH into calcium sulfate dihydrate (CSD) after the cement powder was mixed with the setting solution. After the hardened cement was immersed in Hanks' solution for 1 d, CSD became the dominant phase. The long-term (up to 30 d) pH value of the Hanks' solution wherein the cement was immersed remained in the range of 67. The hardened cement gradually lost its weight and increased its porosity level with immersion time. When immersed for 1 d, the average compressive strength (CS) value of the cement reached its maximum value. After 30 d, the compressive strength (CS) value of the cement still remained >25 MPa. SEM showed that, after being immersed for 30 d, numerous large, faceted CSD crystals were observed throughout the sample. Cytotoxicity test indicated that the present cement is a biocompatible implant material.
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