76 the membrane and inside of cell. We infer that the nano- particles or their aggregates are absorbed on the membrane due to their small size effect, and incorporated by endo- cytosis vesicles through the deformation of the membrane, and then dispersed in cytoplasm of SMC. We can observe that the particles are swallowed by lysosome in cytoplasm from Fig. 7b and c. However, the fate of MNPs during cellular degradation is a key and unknown question. TNF-a Level Tumor necrosis factor a is a polypeptide cytokine that promotes antitumor and immune responses [33], also called pro-inﬂammatory cytokine. For SMC, TNF-a is released from cells when the cells are damaged, and then the free TNF-a will promote the inﬂammatory damage of cells inversely. The supernate of SMC incubated with DMSA- MNPs under the same experiment conditions was collected and mixed. Then, the TNF-a was assayed by ELISA. The results were shown in Fig. 8 The level of TNF-a is normal compared with control, which means that DMSA-MNPs did not elicit the production of the pro-inﬂammatory cytokine TNF-a. Therefore, DMSA-MNPs cannot lead to SMC inﬂammatory damage in vitro. The other two types of MNPs show the same results (the data not shown). In Nanoscale Res Lett (2009) 4:70–77 conclusion, the three types of MNPs display the biocom- patibility with SMC. Using our chosen endpoints, SMC do not damaged by the MNPs. SMC Viability/Cytotoxicity Studies The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra- zolium bromide) assay is a simple nonradioactive colori- metric assay to measure cell cytotoxicity, proliferation, or viability [34]. The active SMC is able to convert this dye into a water-insoluble dark-blue formazan by reductive cleavage of the tetrazolium ring [35]. Formazan crystals, then, was dissolved in acidiﬁcation isopropanol by mea- suring the absorbance of the solution at 570 nm, and the resultant value is related to the number of living cells. The viability of SMC is apparently decreased with the increasing of the concentration and incubation time of DMSA-MNPs compared with the control, as shown in Fig. 9a and b. The data were analyzed by statistical method and the result indicates there is statistical difference when the concentration of magnetic nanoparticles is more than 0.1 mg/mL (p \ 0.05). Here, the viability means the activity, the cytotoxicity and the number of SMC. The decrease of viability may be resulted from the damage, proliferation inhibition of SMC by DMSA-MNPs. Fig. 9 The viability of SMC incubated with MNPs. All values are expressed as the mean ± (SD) of three experiments, each performed in octuple. Control columns mean that SMC was incubated with only DMEM. a SMC was incubated with DMEM containing the indicated concentration of DMSA-MNPs for 24 h. b SMC was incubated with DMEM containing 0.1 mg/ mL DMSA-MNPs for the indicated incubation time. c SMC was incubated with DMEM containing 0.1 mg/mL indicated MNPs for 24 h 123