Upper critical solution temperature behavior of cinnamic acid and polyethyleneimine mixture and its effect on temperature-dependent release of liposome

초록

The mixture of polyethyleneimine (PEI) and cinnamic acid (CA) in HEPES buffer (pH 7.0) exhibited an upper critical solution temperature in the temperature range of 20-50 degrees C. CA would be electrostatically conjugated with PEI and the PEI-CA conjugate is thought to act as a thermo-sensitive polymer. On the optical microscope image of PEI/CA mixture, microparticles were found at 25 degrees C, disappeared when heated to 50 degrees C, and formed again upon cooling to 25 degrees C. PEI-CA conjugate was immobilized on the surface of egg phosphatidylcholine (EPC) liposome by adding PEI to the suspension of liposome incorporating CA. The size and the zeta potential of the liposome markedly increased by cooling the liposomal suspension from 50 degrees C to 20 degrees C. This could be ascribed to the cooling-induced self-assembling property of PEI-CA conjugate. The release profile of Rhodamine B base from liposome incorporating CA with PEI was investigated while the liposome suspension of 50 degrees C was exposed to the release medium of 20 degrees C, 30 degrees C, 40 degrees C and 50 degrees C. The release degree was higher at a lower temperature. When exposed to a lower temperature (20 degrees C, 30 degrees C, 40 degrees C), PEI-CA could be self-assembled and change its configuration on the surface of liposome, promoting the release from the liposome. (C) 2015 Elsevier B.V. All rights reserved.

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