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The purpose of the present study was to investigate the ␥-radiation effect on the structure and properties of the single-phase tetracalcium phosphate (TTCP) powder and its derived calcium phosphate cement (CPC). Experimental results show that low-dosed (0 -30 kGy) CPC has a setting time of 10 -12 min, while high-dosed (40 -120 kGy) CPC has a setting time of 8 -10 min. The low dose ␥-radiation does not significantly change porosity volume fraction or compressive strength of the CPC. The pH values of all CPC samples fell in a relatively narrow band, with a band width of 8.5-9.1 (in terms of pH value). With a dose of 10 or 20 kGy ␥-radiation, the TTCP-apatite conversion ratio does not change much. With 30 kGy the conversion ratio significantly increases and reaches a maximum value. With further increases in dose, the conversion ratio quickly declines. With increasing ␥-ray dose, the CPC morphology becomes more porous/loose and apatite particles become larger in size. When exposed to a high dose (120 kGy) of ␥-radiation, TTCP structure is radiation-damaged, and ␥-ray-induced formation of apatite is confirmed by transmission electron microscopic/selected-area diffraction/lattice imaging analyses.

A pre-hardened, TTCP-derived CPC was immersed in Hanks' solution as well as subcutaneously implanted into abdomen of rats. The implant-soft tissue interfacial morphology was examined and properties of the CPC were evaluated and compared under in vitro and in vivo conditions. The results indicate that the surface of immersed samples appeared rougher and more porous than that of implanted samples and was covered with a layer of fine apatite crystals. The CPC samples implanted for 4 weeks or longer were surrounded by a layer of fibrous tissue, which was further surrounded by a soft tissue capsule comprising numerous fat cells. The soft tissue capsule had a non-uniform distribution in thickness, which increased most significantly between 4 weeks and 12 weeks after implantation. None of polymorphic cells, osteoblast cells or bone cells adjacent to the implant were observed. The majority of original TTCP powder was transformed into apatite after 1 day of either immersion in Hanks' solution or implantation. The average porosity values of samples immersed in Hanks' solution for 4 weeks or longer were significantly larger than those immersed for 1 day or 1 week. The porosity values of samples implanted for different times were not significantly different. The DTS values of Hanks' solution-immersed samples largely decreased after a few weeks of immersion. The implanted samples maintained their strengths throughout the study.

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