A potential method for local drug and dye delivery in the ocular vasculature

We propose a new drug and dye delivery system that would allow repeated release of substances in the ocular vasculature by an externally controlled mechanism. The substances are encapsulated in heat-sensitive liposomes, which are lysed by locally applying a heat pulse produced by an argon laser. The system was tested by investigating the release of carboxyfluorescein encapsulated in the liposomes. The liposome suspension was incubated at 37 degrees or 38.5 degrees C and irradiated at different powers and pulse durations. The amount of dye released was monitored by fluorophotometry and compared with the concentration obtained when the liposomes were lysed at their transition temperature of 41 degrees C. The results showed that 85% of the encapsulated substance can be released. Moreover, a dramatic contrast was observed between the fluorescence before and after the lysis. Presently the energy density is higher than but close to the maximal permissible exposure for humans. The release mechanism with the short laser pulse appeared to be similar to that present when liposomes were heated slowly.