Immersion-induced changes in structure and properties of a calcium sulfate cement

This research was devoted to the investigation of changes in structure and properties of a calcium sulfate hemihydrates (CSH) cement immersed in Hank' 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 Hank' solution for 1 d, CSD became the dominant phase. The long-term (up to 30 d) pH value of the Hank' 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.