| Summary: | 碩士 === 國立成功大學 === 醫學工程研究所 === 87 === Investigation of characteristic of cellular responses to the temperature factor is important in the field of medicine and biotechnology. In general, temperature factors are significant for both cryosurgery and cryo-preservation. Cryosurgery aims to destroy tumor as much as possible and to reduce normal tissue injury. Investigation of temperature in the influence of live or death for the cells will lead to better clinical application. Such kind of in vivo study is difficult to interpret due to indirect effect from vascular changes and complexity of temperature distribution. We established two in vitro study systems, a simulated system for thermal process in cryosurgery and uniform temperature system, to evaluate temperature factors related to determine biological effects. The results were described as follows :
(1) Efficiency of freezing devices and accuracy of estimations : The cooling power of cryoprobe cooled to -190℃ within four minutes. Temperature changes on any positions of interpolated area were estimated accurately by raw data obtained from 16 array thermocouples, image processing of cell death boundary and cubic spline interpolation. The differences between measured and estimated temperature were within 2℃ and the correlation coefficient were above 0.99. Estimated temperature was usually reliable in both level and tilted environment. An uniform temperature device froze and thawed cells identically every moment by excellent characteristic of thermal conductivity of aluminum and thin medium. We would adjust conditions for analysis of biological effects.
(2) Relation among biological effects and the temperature factors : The thermal history could be defined by the coldest temperature (T) and freezing rate (S). The coldest temperature caused major cell-killing effect on mouse bladder tumor, however, as the freezing rate dropped, the coldest temperature also dropped. The relation between the two factors could be approximated as T = -10.9 - 6.6 / S. An uniform system was designed to study relation between two temperature factors and percentage of cell survival (P). These three variables were analyzed by using multiple regression, and a optimal plane, P = 3.1 T + 19.3 / S + 87.4, was obtained (p < 0.05). The responses of cells in different cooling devices were very alike at 50% cell survival. Cell viability was influenced by the coldest temperature and freezing rate, and these two factors interact, to determine live or death for the cells.
The two systems may be useful to assess biological effects. An interaction of temperature factors in determining cell death was found, which may be useful in cryobiological studies.
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