Laser-triggered releasing of fluorescein from thermosensible liposomes: a new method for quantification of laser-induced photocoagulation

The objective of this in-vivo study was to assess the possible use of temperature sensitive liposomes in an established model such as liver as a new approach to monitor the temperature induced by a laser. Temperature sensitive liposomes (DSPC: distearoylphosphatidylcholine) loaded with carboxyfluorescein were prepared by the Bancham procedure. These liposomes (1 ml solution) were injected into adult male wistar rats. Two hours later, the liver was exposed and irradiated with a 100 W Nd:YAG laser using pulses lasting from 100 ms to 260 ms. Simultaneously, the surface temperature was recorded with a thermographic camera. The fluorescence emission was measured with a fluorescent imaging system. The results show that the dye is released in response to laser energy. The amount of the drug release increases linearly with increasing temperature in the range 45 degree(s)C - 60 degree(s)C. Moreover, the release occurs in a short period of time upon brief exposure to its phase transition temperature. The temperature range could be modified and adapted by using different liposomes formulation, for example DPPC (dipalmitoylphosphatidylcholine) for lower temperature (35 - 45 degree(s)C) or DSPE (distearoylphosphatidylethanolamine) for higher temperature (65 - 75 degree(s)C).