Then,the activity L929 fibroblasts were cultured on each test sample and determined after two, four and six days. 20 l/well of MTT solution (5 mg/ml in phosphate buffered saline (PBS)) was added in each well and the plate was incubated at 37 ◦C to allow the formation of formazan crystals. After 4 h the dimethylsulfoxide (1.5 ml/well) was added to all wells after aspirating the culture medium and mixed thoroughly to dissolve the dark blue crystals at room temperature. Ten minutes later, the optical density (OD) at 492 nm was measured with a microplate reader (Model550, Bio Rad Corp.USA).