Evaluation of daidzein-loaded chitosan microspheres in vivo after intramuscular injection in rats.

Daidzein-loaded chitosan microspheres were prepared by emulsification/chemical-crosslinking technique. The dialysis bag method determined the release of daidzein from the microspheres. It demonstrated that the accumulative release curve in vitro was fit for the zero-order release equation and had good correlation with the absorptive fraction in vivo, suggesting the dialysis bag method evaluated the release of the microspheres well. The release of chitosan determined by the ninhydrin assay in vitro was very slow, less than 3 percent at 35 day. The pathological section by hematoxylin-eosin staining found the good biocompatibility of the prepared microspheres in the injective site. Combining the degradation photos by scanning electron microscopy with the plasma concentration-time data, it was speculated that the drug on the surface of the microspheres firstly released, then the major of drug near the surface and the inner of the microspheres released by diffusion through the shallow cavities and crack, lastly the drug released rapidly and completely being companied with the beginning of polymer degradation.