To investigate the effect of basic calcium carbonate on the physical and chemical properties of medical grade calcium sulfate, and to provide a theoretical basis for the preparation of injectable calcium sulfate bone cement with suitable for pH.

According to the mass ratio of CaCO₃ in calcium sulfate complex, they were divided into 5 groups: 0%, 5%, 10%, 20% and 30%. The powder of bone cement was prepared by fully mixing different contents and surgical grade calcium sulfate. Methylcellulose solution with a concentration of 3% was used as the liquid agent of bone cement. According to the liquid-solid ratio of 0.4∶1, the powder and liquid of the bone cement are mixed and stirred evenly to form a slurry. According to different molds, the initial setting time, final setting time, compressive strength, in vitro degradation rate and pH value of CaCO₃/ calcium sulfate composite were measured and recorded.

The initial setting time and final setting time of calcium sulfate were (4.96±0.20) min and (5.83±0.12) min, respectively. With the increase of CaCO₃ content, the initial setting time and final setting time increased first and then decreased (F=25.428, P<0.001; F=30.780, P<0.001). When the content was 10%, the initial setting time and final setting time were the longest (13.17±1.87 and 14.22±2.00). The compressive strength of pure calcium sulfate is (23.33±6.35) MPa. With the increase of CaCO₃ content, the compressive strength first increases and then decreases. When the content is 20%, the maximum compressive strength is (27.33±5.86) MPa; However, there was no significant difference in the effect of CaCO₃ on the compressive strength of calcium sulfate (F=1.272, P=0.344). The degradation process of pure calcium sulfate was in acidic environment (pH=5.32), and different content of calcium carbonate could increase the pH value; When the content was 10%, the pH tended to balance (pH=6.67).

Calcium carbonate can change the physical and chemical properties of calcium sulfate bone cement. When the concentration is 10%, it can provide the best setting time and enough time for the operator; And does not affect the compressive strength of calcium sulfate after solidification; In addition, when the concentration is 10%, the pH in the process of degradation in vivo is also conducive to promote the formation of new bone. However, when the concentration is more than 10%, the degradation time is short, and other modifiers still need to be added.