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ePaper created 2017-03-17, 12:41:55 | version 1.38.0
| research Occurance of black spots in DPSC cells Occurance of black spots in CHO cells mW Total of irradiated cells Cells with spots mW Total of irradiated cells Cells with spots 16 18 20 26 10 10 69 72 0 0 1 21 16 18 20 26 Table 1 10 10 69 72 0 0 0 11 Table 2 Life-/Dead-Test First, the DPSC cells were irradiated with different power parameters (4 mW, 12 mW, 16 mW, 20 mW and 32 mW). The irradiated cells were marked, incubated after 5.5 hours with the Life-/Dead-Kit and after 1 hour of incubation tested concerning their fluores- cence behaviour. At an irradiation of 20 mW, 64 of 69 DPSC cells revealed a green cytoplasm fluoresence, Figs. 3a–f: Verification of the laser-induced formation of ROS. Fig. 3a Fig. 3b Fig. 3c Fig. 3d Fig. 3e Fig. 3f 20 laser 1 2017 while a red fluorescence was observed in 5 DPSC cells (Tab. 3). This corresponds to a damage of 7%. When the power was raised to 26 mW, already 35 % were subjected to a lethal effect. However all of the CHO cells tolerated a power of 20 mW, with 15 % of them dying at 36 mW (Tab. 4 and Fig. 2). The comparison with experiments of shorter pulse widths, at which already 73 % of the DPSC cells were damaged at a power of 20 mW, shows that the longer pulse width of 700 fs is better tolerated by the cells. Verification of the laser-induced formation of ROS (reactive oxygen species) The irradiation showed that no detectable DHF sig- nals occurred at average power lower than 35 mW. As can be seen from Figure 3 (upper part of a and b) ROS signals were detected at a higher power of 37 mW in both upper irradiated cells. Weak fluoresence signals occurred in the lower non-irradiated cell too. However, this cell was linked to the irradiated cells via membrane contacts. If the power is only insignificantly increased, its effects become more pronounced. In Figure 3c the irradiated cells show a significantly higher intensity. This effect is also confirmed by the considerable fluo- rescence of the irradiated cell (Fig. 3f). Thus, destruc- tive oxygen radicals are formed during irradiation of a pulse duration of 700 fs. In comparison to the 170 fs experiments, a significantly higher average power is necessary to achieve detectable ROS formation. Conclusions DPSC are less sensitive to irradiation with femtosec- ond NIR laser at a pulse width of 700 fs under the de- scribed irradiation conditions than to shorter pulse width of 170 fs. At average power parameters of 20 mW, up to 10 % of the cells were subjected to lethal effects within six hours after irradiation. At an average power of 26 mW, still two thirds of the cells survived. At the shorter pulse width all cells would be subjected to a lethal effect. The observed lesser sensitivity at higher pulse widths and constant pulse energy corresponds to the results of earlier studies on Chinese hamster ovary