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ePaper created 2017-11-24, 11:00:53 | version 1.38.0
photodamage of pulpa cells research | Lethality of DPSC cells Lethality of CHO cells mW Total of irradiated cells vital lethal % lethal mW Total of irradiated cells vital lethal % lethal 16 18 20 26 10 10 69 72 10 10 64 47 0 0 5 0 0 7 25 35 Table 3 16 18 20 26 10 10 69 72 10 10 68 65 0 0 0 0 0 0 11 14,5 Table 4 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. As in comparison an increase of the pulse width by factor F = 700 fs / 170 fs = 4 exists, it follows that a power increase by factor S = 1.7 to 2 should be neces- sary in order to achieve the same destructive effect. 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 cells (CHO) at an irradiation wavelength of 780 nm.3 In these earlier studies, it was concluded that the damage is subject to a two-photon effect, for which a damage effect E can be expected according to the formula E ~ P² / with P: average laser power and : pulse width. This relation cannot be confirmed exactly basing on the presented data, but a factor S > 1.25 can be as- sumed, as already 7 % of the DPSC cells died at an average power of 16 mW and a pulse duration of 170 fs, but 20 mW at 700 fs were necessary to achieve the same effect. DPSC cells react slightly more sensitive at a pulse width of 700 fs than CHO cells. At an exposure of 26 mW laser power only 15 % of the CHO cells were damaged in comparison to 35 % of the DPSC cells. The detected ROS formation indicates a photochemi- cal damage process._ Editorial note: A list of references is available from the publisher. contact Prof. Dr Karsten König Saarland University Campus A5.1, Room 2.35 66123 Saarbrücken Germany Tel.: +49 681 3023451 k.koenig@blt.uni-saarland.de Dr Anton Kasenbacher Obere Hammerstr. 5 83278 Traunstein Germany Tel.: +49 861 4692 a.k@ts-net.de roots 4 2017 13