Abstract
The effect of particle size on in vivo and in vitro Zn release of ZnTCP was investigated for the purpose of understanding Zn release behavior from a sustained‐release device. The tricalcium phosphate powders (Ca2.7Zn0.3(PO4)2), with particle size of 7.5 and 553 μm (S‐ZnTCP and L‐ZnTCP), including a 10 mol% of Zn (6.17 w/w%), as new sustained‐release preparations, were synthesized by heating, after then ground and sieved using 38 and 300 μm screens. The different powder samples were characterized by the X‐ray powder diffractometry and scanning electron microscopy. The release rates from Zn‐TCP powders (10 mg) were measured in 10 ml of simulated body fluid (SBF) containing 10 mg/100 ml Ca2+(SBF/H), SBF containing 5 mg/100 ml Ca2+ (SBF/L) or SBF without Ca2+ (SBF/‐) at 37.0°C. The in vitro Zn release profiles for the smallest and the largest particles size of ZnTCP powders (L‐ZnTCP and S‐ZnTCP) at various Ca concentrations in SBF were significantly higher in SBF/‐ and SBF/L than in SBF/H. The Zn release rate from ZnTCP with different particle sizes were found to be inversely proportional to the concentration of calcium in SBF. After injection of a ZnTCP suspension containing 30 mg of S‐ZnTCP powder on the backs of the rats, the plasma Zn level increased rapidly, reaching a concentration range of around 2 μg/ml. The area under the curve values of the plasma Zn concentration (Zn‐AUC) over 6 days post injection of S‐ZnTCP and L‐ZnTCP were significantly higher than that of the control experiment. After the injection of S‐ZnTCP and L‐ZnTCP suspension, the plasma alkaline phosphatase activity (AIP) levels increased to more than 300 IU/l. In contrast, the AIP for the control decreased after 2 days. The area under the curve of the AIP (AIP‐AUC) for 6 days of S‐ZnTCP was significantly higher than that of other groups.